Spirit Updates

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M I S S I O N     M A N A G E R S
	Colette Lohr		Cindy Oda		Richard Morris		Al Herrera

P R E V I O U S    M I S S I O N    M A N A G E R S
	Byron Jones		Mark Adler		Leo Bister		Beth Dewell		Emily Eelkema

	Jeff Favretto		Saina Ghandchi		Andy Mishkin		Art Thompson		Rick Welch

sol 1628-1634, August 01-07, 2008:  Waiting Out the Winter

Spirit's battery levels are slowly edging upward, thanks to a slight decrease in atmospheric dust (Tau) and a gradual increase in sunlight as winter gives way to spring.

Early in the week, Spirit spent two Martian days carrying out contingency plans following a temporary delay in data transmission from Earth. Spirit implemented the so-called "runout" portion of an earlier master sequence on sols 1628 and 1629 (Aug. 1-2, 2008). Subsequent relays of new instructions from Earth on sols 1629 and 1632 (Aug. 2 and Aug. 5, 2008) went off without a hitch.

Spirit remains healthy, with all subsystems performing as expected as of sol 1630 (Aug. 3, 2008).

Sol-by-sol summary

In addition to using the panoramic camera to make daily measurements of dust-related changes in atmospheric clarity, Spirit completed the following activities:

Sol 1628 (Aug. 1, 2008): Spirit implemented the runout portion of the master sequence of commands already on board the rover.

Sol 1629: Upon awakening, Spirit continued to implement the runout portion of the master sequence sent earlier. Spirit then received new instructions directly from Earth via the rover's high-gain antenna.

Sol 1630: Spirit acquired column 13 of the "Bonestell panorama" using all 13 color filters of the panoramic camera. The rover relayed fresh data from Mars at UHF radio frequencies to NASA's Odyssey orbiter to be transmitted to Earth.

Sol 1631: Spirit recharged the batteries.

Sol 1632: Spirit received new instructions from Earth via the rover's high-gain antenna.

Sol 1633: Spirit acquired six freeze frames for a time-lapse movie in search of Martian clouds using the navigation camera. The rover took spot images of the sky for calibration purposes with the panoramic camera and monitored dust on the panoramic-camera mast assembly.

Sol 1634 (Aug. 7, 2008): Spirit transmitted fresh data to Odyssey to be relayed to Earth.

Odometry:

As of sol 1634 (Aug. 7, 2008), Spirit's total odometry remained at 7,528.0 meters (4.7 miles).

sol 1621-1627, July 25-31, 2008:  With Batteries Charged, Spirit is Ready for More Science

Spirit has fully recovered from a recent rundown in battery power. Energy has improved to levels not seen since sol (Martian day) 1604 (July 7, 2008). The hit in battery energy was primarily the result of data transmissions taking place later in the day, when less solar energy was available.

During the past week, rover planners eliminated the late communications sessions. Spirit is not scheduled to have another one until sol 1636 (Aug. 9, 2008). To mitigate the impact that one will have on power, rover planners plan to shorten the duration of data transmission from 20 minutes to only 10 minutes. This will allow sufficient time to get new instructions on board the rover while minimizing battery drain.

A transmitter problem thwarted data transmission on sol 1625 (July 29, 2008). The uplink from Earth was to have loaded activity plans and maintenance instructions for sols 1626, 1627, 1628 and 1629 (July 30-Aug. 2, 2008). The sequences already on board Spirit were designed with built-in contingency plans to handle just such an event. As a result, while Spirit continues the "runout" portion of the earlier master sequence, rover operators will send a new set of commands for sols 1630, 1631 and 1632 (Aug. 3-5, 2008) on sol 1629 (Aug. 2, 2008).

Spirit remains healthy, with all subsystems performing as expected as of sol 1626.

Sol-by-sol summary

In addition to using the panoramic camera to make daily measurements of dust-related changes in visibility, Spirit completed the following activities:

Sol 1621 (July 25, 2008): Spirit recharged the batteries.

Sol 1622: Spirit received instructions from Earth via the rover's high-gain antenna and relayed data to NASA's Odyssey orbiter via the rover's UHF antenna.

Sol 1623: Spirit acquired images of sand formations with the rear hazard-avoidance and navigation cameras. The rover took six, time-lapse, movie frames in search of clouds with the navigation camera, as well as images of the sky (called "sky flats") for calibration purposes.

Sol 1624: Spirit recharged the batteries.

Sol 1625: Spirit took spot images of the sky for calibration purposes with the panoramic camera and acquired movie frames in search of clouds with the navigation camera.

Sol 1626: Spirit completed a horizon survey with the panoramic camera and relayed data to Odyssey for transmission to Earth.

Sol 1627 (July 31, 2008): Spirit recharged the batteries.

Odometry:

As of sol 1626 (July 30, 2008), Spirit's total odometry remained at 7,528.0 meters (4.7 miles).

sol 1615-1620, July 19-24, 2008:  Time to Recharge the Batteries

Spirit is recovering from a recent rundown in battery power. Over the last two weeks, Spirit's battery levels have steadily dropped by about 18 percent. The decrease appears to be a result of transmitting data to Earth later in the day and staying awake longer to accommodate extra science activities.

When Spirit sends transmissions late in the day, there's not enough sunlight left to recharge the batteries. As a consequence, each late uplink has contributed to an energy deficit.

Barring sudden changes in Martian temperature or atmospheric dust levels, engineers expect it may take as long as two weeks to recharge the batteries enough to resume work on the Bonestell panorama and other science activities.

Spirit remains healthy and all subsystems are operating as expected as of Martian day, or sol, 1618 (July 22, 2008).

Sol-by-sol summary

In addition to daily, panoramic-camera measurements of atmospheric opacity caused by dust, Spirit completed the following activities:

Sol 1615 (July 19, 2008): Spirit received new instructions from Earth via the rover's high-gain antenna.

Sol 1616: Spirit monitored dust accumulation on the panoramic-camera mast assembly.

Sol 1617: Spirit recharged the batteries.

Sol 1618: Spirit received instructions from Earth over the rover's high-gain antenna and relayed data to Earth via NASA's Mars Odyssey orbiter.

Sol 1619: Spirit took spot images of the sky for calibration purposes with the panoramic camera and acquired movie frames in search of clouds with the navigation camera.

Sol 1620 (July 24, 2008): Spirit recharged the batteries.

Odometry:

As of sol 1618 (July 22, 2008), Spirit's total odometry remained at 7,528.0 meters (4.7 miles).

sol 1608-1614, July 11-18, 2008:  A Juggling Act

Winter planning for Spirit requires human operators to perform a complex juggling act to maintain overall rover health. They must manage engineering activities, such as receiving science and engineering data from Mars and sending new operation plans from Earth, as well as try to fit in science observations when possible. But they must also give the rover sufficient downtime between these activities to recharge the batteries. In recent months, the team's juggling skills have continued to improve.

Meanwhile, Mars has been helping out with steady temperatures and low levels of atmospheric dust, providing stability when it comes to allocating energy for heating and predicting the amount of sunlight reaching the rover's solar panels to generate electricity. Solar energy has been steady between 225 watt-hours to 230 watt-hours, of which about 65 to 75 watt-hours is required for heating the batteries and the miniature thermal emission spectrometer.

The overall state of charge on the battery has dropped slightly as a result of the timing of engineering and science activities. To restore the state of charge, the rover team will be making adjustments in upcoming plans.

Spirit is healthy and all subsystems are performing as expected as of sol 1610 (July 13, 2008).

Sol-by-sol summary

During the past week, in addition to making daily measurements of atmospheric opacity caused by dust with the panoramic camera, Spirit completed the following activities:

Sol 1608 (July 11, 2008): Spirit received new instructions from Earth via the rover's high-gain antenna.

Sol 1609: Spirit acquired column 17, part 3 of the so-called "Bonestell panorama" using all 13 color filters of the panoramic camera. The rover acquired six, time-lapse, movie frames in search of clouds with the navigation camera.

Sol 1610: Spirit relayed science and engineering data to NASA's Odyssey orbiter for transmission to Earth.

Sol 1611: Spirit received instructions from Earth over the rover's high-gain antenna and sent a timing beep to Earth at X-band frequencies.

Sol 1612: Spirit acquired column 15, part 3 of the full-color Bonestell panorama.

Sol 1613: Spirit recharged the battery.

Sol 1614 (July 18, 2008): Spirit relayed science and engineering data to Odyssey for transmission to Earth.

Odometry:

As of sol 1610 (July 13, 2008), Spirit's total odometry remained at 7,528.0 meters (4.7 miles).

sol 1601-1607, July 04-10, 2008:  Solar Energy Evens Out

A week after the winter solstice, NASA's Mars rover Spirit is experiencing stable solar energy levels of between 225 watt-hours and 230 watt-hours. (One hundred watt-hours is the amount of energy needed to light a 100-watt bulb for one hour). Spirit continues to perform light science activities every three to four Martian days, or sols. Science activities this week included acquiring additional frames of the so-called "Bonestell panorama" of Spirit's overwintering locale.

The rover continues to relay data to NASA's Odyssey orbiter every four sols. The reduced level of activity has allowed Spirit to maintain a healthy battery charge despite the low level of solar energy input.

Spirit is healthy and all subsystems were performing as expected as of the downlink of fresh data from Odyssey on Sol 1606 (July 9, 2008).

Sol-by-sol summary

During the past week, Spirit completed the following activities:

Sol 1601 (July 4, 2008): Spirit assessed atmospheric dust levels based on the darkness of the sky with the panoramic camera.

Sol 1602: Spirit assessed atmospheric dust, monitored the dune field known as "El Dorado," and took spot images of the sky for calibration purposes with the panoramic camera. The rover relayed data to Odyssey for transmission to Earth.

Sol 1603: Spirit recharged the battery and measured atmospheric dust opacity with the panoramic camera.

Sol 1604: Spirit received a new activity plan from Earth via the rover's high-gain antenna and assessed atmospheric dust levels with the panoramic camera.

Sol 1605: Spirit again gauged atmospheric dust levels and also surveyed the horizon with the panoramic camera. The rover acquired Column 16, Part 4 of the Bonestell panorama, using all 13 color filters of the panoramic camera.

Sol 1606: Spirit assessed atmospheric dust with the panoramic camera and sent fresh data to Odyssey for transmision to Earth.

Sol 1607 (July 10, 2008): Spirit recharged the battery and measured atmospheric dust with the panoramic camera.

Odometry:

As of sol 1606 (July 9, 2008), Spirit's total odometry remained at 7,528.0 meters (4.7 miles).

sol 1594-1600, June 27-July 03, 2008:  Biding Time

Spirit continues to ride out the Martian winter by doing minimal activities to conserve power. The rover conducts very light science activities every three to four Martian days, or sols, and relays data to NASA's Odyssey orbiter for transmission to Earth every 4 sols. The rest of the time, Spirit mostly sleeps.

As it has been some time since Spirit's operators were able to synchronize the spacecraft clock to Earth time, they wished to determine how far the spacecraft clock had drifted (how much it had changed over time). Synchronization of the clock is a process that requires a power-intensive, two-way, X-band communications link. When the power situation allowed it, they decided to perform an X-band "beep" (a five-minute, low-gain communication session) to estimate the amount of drift. The transmission of plans to do so on sol 1594 (June 27, 2008) were not detected by the ground station. Engineers hoped to make another attempt on sol 1604 (July 7, 2008).

Spirit is healthy and all subsystems were performing as expected as of the Odyssey downlink on sol 1598 (July 1, 2008). Solar-array energy has been steady within the range of 225 watt-hours to 230 watt-hours (100 watt-hours is the amount of energy needed to light a 100-watt bulb for one hour).

Sol-by-sol summary

During the past week, Spirit completed the following activities:

Sol 1594 (June 27, 2008): Plans called for Spirit to perform a five-minute "beep" at X-band frequencies after relaying data to Earth via the Odyssey orbiter.

Sol 1595: Spirit recharged the battery and measured atmospheric dust opacity, known as Tau, using the panoramic camera.

Sol 1596: Spirit recharged the battery and measured atmospheric dust opacity with the panoramic camera.

Sol 1597: Spirit recharged the battery and measured atmospheric dust opacity with the panoramic camera.

Sol 1598: Spirit received new instructions from Earth via the rover's high-gain, X-band antenna and relayed data to Odyssey at UHF frequencies for transmission of the latest Martian data to Earth. The rover measured atmospheric darkness caused by suspended dust particles with the panoramic camera.

Sol 1599: Spirit conducted light remote sensing.

Sol 1600 (July 3, 2008): Spirit recharged the battery and again measured atmospheric dust with the panoramic camera.

Odometry:

As of sol 1598 (July 1, 2008), Spirit's total odometry remained at 7,528.0 meters (4.7 miles).

sol 1587-1594, June 20-27, 2008:  Here Comes the Sun

With this week's passage of the longest night and shortest day of the year, also known as the winter solstice, Spirit's solar power levels should slowly but steadily increase. The winter solstice occurred on Martian day, or sol, 1591 (June 24, 2008, Pacific time).

In fact, Spirit's solar array energy and battery state of charge have already improved in recent days to the point where rover operators have begun adding some planning features back into the rover's schedule. The first change, adopted as of sol 1592 (June 25, 2008), was to return to a planning schedule covering every 3 or 4 sols. The plans themselves remain quite spartan at this time. In particular, rover operators are still planning to have Spirit relay data to Earth only every 4 sols. To do this, the rover sends data to NASA's Odyssey spacecraft, in orbit above Mars. To save power, engineers are keeping the data relays short in duration. Spirit has begun measuring dust-related atmospheric darkness every sol instead of every other sol.

Because it has been some time since engineers have been able to synchronize the spacecraft clock to Earth time, they decided to determine how much the clock had "drifted" -- that is, changed with time. To do this usually requires a power-intensive, two-way, X-Band communication session. This time, to save energy, they decided to perform an X-band "beep," a five-minute communication session using the rover's low-gain antenna, on sol 1594 (June 27, 2008). Accuracy will not be as good, but they expect to get an estimate of drift that is accurate to within about a minute.

Spirit is healthy and all subsystems are performing as expected as of the Odyssey downlink on sol 1590 (June 23, 2008). Solar array energy has been steady at 230 watt-hours, enough energy to light a 100-watt bulb for 2.5 hours.

Sol-by-sol summary

During the past week, Spirit completed the following activities:

Sol 1587 (June 20, 2008): Spirit recharged the battery.

Sol 1588: Spirit recharged the battery and received new instructions direct from Earth via the rover's high-gain dish antenna. Spirit measured atmospheric dust opacity, known as Tau, with the panoramic camera.

Sol 1589: Spirit recharged the battery.

Sol 1590: Spirit recharged the battery, measured atmospheric opacity caused by dust with the panoramic camera, and relayed data to Odyssey for transmission to Earth.

Sol 1591: Spirit recharged the battery and received a backup relay of commands from Earth via the rover's high-gain antenna.

Sol 1592: Spirit recharged the battery and conducted light remote sensing.

Sol 1593: Spirit recharged the battery.

Sol 1594 (June 27, 2008): Plans called for Spirit to send data to Odyssey for relay to Earth and transmit a five-minute signal to Earth to allow spacecraft operators to estimate drift in the spacecraft clock.

Odometry

As of sol 1586 (June 19, 2008), Spirit's total odometry remained at 7,528.0 meters (4.7 miles).

sol 1580-1586, June 13-19, 2008:  Battery Power on the Rise

Spirit's battery is recharging nicely now that rover planners have reduced the frequency of communications to and from the rover during the darkest days of Martian winter. Most measures of battery health are showing an increase of about 2 amp-hours in the battery state of charge (an amp-hour is equivalent to the amount of charge flowing for one hour from a current of 1 amp). The minimum state of charge has improved from 10.92 amp-hours to 12.97 amp-hours, the maximum from 16.77 amp-hours to 18.17 amp-hours, which is fairly close to the battery's full capacity of 19.5 amp-hours.

Because battery energy increased sufficiently, the team added 12 minutes of remote sensing science to Spirit's to-do list for Sol 1586 (June 19, 2008). Spirit was to monitor atmospheric dust with the panoramic camera as well as dust on the panoramic-camera mast assembly and acquire seven, time-lapse movie frames in search of clouds with the navigation camera. Engineers anticipate that the additional activities will have no significant effect on the battery's state of charge.

Skies remain remarkably clear. Solar array energy is up slightly, averaging 229 watt-hours (100 watt-hours is the amount of energy needed to light a 100-watt bulb for one hour). Atmospheric darkness caused by dust (known as Tau) increased by an insignificant amount, going from an average of 0.193 the previous week to 0.205 this week. The dust factor, the fraction of sunlight hitting the arrays that penetrates the dust layer, also rose insignificantly, from 0.349 to 0.352.

Rover planners are generating new activity plans for Spirit only once a week to minimize uplink time and therefore the length of time the rover must stay awake. Spirit relays data to Earth only every fourth sol to minimize battery usage.

In addition to estimating the amount of scattering and absorption of sunlight by atmospheric dust, Spirit received one transmission of new instructions direct from Earth to the rover's high-gain antenna on Sol 1581 (June 14, 2008). Spirit sent two transmissions of data to Earth via Odyssey on sols 1582 and 1586 (June 15 and June 19, 2008). Data from the sol 1582 downlink showed that the backup uplink on sol 1584 (June 17, 2008) was not needed and the communications link was shortened to save energy.

Spirit remains healthy and all subsystems were performing as expected as of the downlink to Earth via NASA's Odyssey Mars orbiter on sol (Martian day) 1582 (June 15, 2008).

Sol-by-sol summary

During the past week, Spirit completed the following activities:

Sol 1580 (June 13, 2008): Spirit recharged the battery and measured atmospheric opacity caused by dust (Tau) using the panoramic camera.

Sol 1581: Spirit recharged the battery and received new instructions direct from Earth to the rover's high-gain dish antenna.

Sol 1582: Spirit soaked up the sunlight to recharge the battery, assessed atmospheric darkness caused by dust particles with the panoramic camera, and sent data to NASA's Odyssey orbiter for transmission to Earth.

Sol 1583: Spirit recharged the battery.

Sol 1584: Spirit recharged the battery, surveyed atmospheric dust with the panoramic camera, and received new commands from Earth over the rover's high-gain antenna.

Sol 1585: Spirit recharged the battery.

Sol 1586 (June 19, 2008): Plans called for Spirit to recharge the battery, conducted remote sensing, and send data to Odyssey for relay to Earth.

Odometry

As of sol 1578 (June 11, 2008), Spirit's total odometry remained at 7,528.0 meters (4.7 miles).

sol 1574-1579, June 06-12, 2008:  New Tricks for an Old Rover

To conserve energy and protect one of the on-board spectrometers, spacecraft operators have established the first major change to planning for the Mars Exploration Rover mission since the end of the primary mission, which lasted for 90 days in early 2004.

Spirit's scientists have declared that their highest priority for the winter is preserving the miniature thermal emission spectrometer, an instrument that identifies minerals in rocks from a distance. To do this, the rover heats the instrument overnight and into the morning of every sol. These heaters have been running longer as winter temperatures have dropped and are now averaging about 55 watt-hours per sol.

Heating for Spirit's batteries has increased as well and is now averaging 29 watt-hours per sol. Together, the two heaters account for 84 watt-hours or about 37 percent of Spirit's total energy usage. Everything else, including on-board computers and memories, radios, cameras, sensors and actuators, gets by on about 140 watt-hours -- enough energy to run a microwave oven for a scant 7 minutes.

In response, rover operators have further reduced Spirit's activity levels. The rover now transmits data to Odyssey to be relayed to Earth only every fourth sol. Instead of spending 20 minutes each sol using the rover's high-gain antenna to listen for new instructions from Earth, Spirit spends five minutes listening for instructions using the low-gain antenna on all but two sols per week.

Rover operators create new activity plans once a week, on Fridays, that cover seven sols at a time. Because Spirit isn't engaged in activities that require rover operators to have new images or other data for planning, the rover does not have to relay data to Odyssey just before a planning day. Despite changes to multiple procedures and software tools, the transition has been remarkably smooth.

For the time being, Spirit is basically just hanging out, charging the batteries.

Recent Events

Initially, the uplink team deleted virtually all science activities except for tau measurements of atmospheric dust. They then limited transmission of rover data to NASA's Odyssey orbiter, which consumes about 30 watt-hours, to every other sol. Still, the batteries continued to use more energy than they could replenish.

Prior to this change, Spirit received new plans three times a week and listened for new instructions for 20 minutes every sol. The 20-minute, high-gain-antenna communication window was costing the rover a lot of unnecessary awake time. On the other hand, engineers on Earth needed Spirit to be awake for at least 15 minutes every sol. By changing some of the unneeded 20-minute communication windows to shorter, five-minute, low-gain-antenna communication windows, and by having the windows overlap with the required awake time, Spirit's operators have shortened the overall awake time from 39 minutes to 16 minutes and saved another 15 watt-hours per sol.

Engineers have also gotten more strategic about how they communicate with Spirit. They send a new activity plan to Spirit every week (after the Friday planning session). Because Odyssey downlinks happen only every fourth sol, they can't guarantee they'll have a communication from Odyssey showing whether an uplink actually made it to the rover. So they send the same activity plan a second time. If the first uplink is successful, software on the rover automatically changes the second, high-gain communication window to a five-minute, low-gain window, saving 15 watt-hours. When this occurs, the second uplink fails and flight software generates a bunch of warnings, known as event reports. The warnings tell engineers that the plan is on board. If the first uplink fails, the instructions to change the second uplink window don't take place.

Why do engineers do the planning on Fridays? A new schedule of communication opportunities, called a "strategic load," goes into effect every other Friday. Rover operators plan activities on Friday so they can include the strategic load in the uplink.

The new strategy is working. Battery states of charge are up about two amp-hours (an amp-hour is a measure of electrical current flowing for one hour) above the rather scary levels of two weeks ago and other indicators of battery health are similarly improving. Spirit now has some margin of protection against further increases in heating power or unpleasant changes in the Martian environment. One concern is the possibility that thin, water-ice clouds could form overhead during the Martian winter. Such clouds are nearly invisible without image enhancement but they're thick enough to noticeably lower solar array energy. Fortunately, there's been no evidence of water-ice clouds so far.

Turning the Corner

The Martian winter solstice will be on June 25, 2008 (sol 1591). During the winter solstice, the Sun is as low in the sky as it ever gets. From there, it will rise higher each sol until the summer solstice in May 2009. For Spirit, solar power levels are expected to increase in a few weeks. Unlike Earth, where the coldest temperatures arrive 4-6 weeks after the solstice, Martian temperatures will begin to rise again almost immediately -- but slowly, very, very slowly.

With little dust overhead, Spirit is seeing very little additional dust settling out on the rover's solar arrays. The dust factor, a measure of the proportion of sunlight penetrating the coating of dust on the solar arrays, has remained almost unchanged at 0.349 (meaning that 34.9 percent of the sunlight, direct and scattered, that reaches the arrays penetrates the dust layer to generate electricity).

Energy has been steady, averaging about 226 watt-hours each Martian day, or sol, and varying by only a couple of watt-hours (100 watt-hours is the amount of energy needed to light a 100-watt bulb for one hour). This is due in large part to a clear and stable atmosphere.

Tau, a measure of dust in the atmosphere, has ranged from 0.178 to 0.207 and averaged 0.193. As a result, between 81 percent and 84 percent of the sunlight reaching Mars continues down through the atmosphere to Spirit's solar array. (The remaining 16 percent to 19 percent is either scattered or absorbed by dust particles in the atmosphere. The portion of sunlight that's scattered also contributes to Spirit's solar array energy.)

A Tau this low means the skies above Spirit are remarkably clear. Not only that, Tau has decreased by an average of about 0.01 per week over the last month. (Though scattering and absorption are different and not exactly comparable, a clear mountain day on Earth has a Tau of 0.1-0.2.)

Spirit is healthy and all subsystems are performing as expected as of the Odyssey downlink on Sol 1578 (June 11, 2008). The next planned Odyssey downlink will be on Sol 1582 (June 15, 2008).

What Do You Say When You Call Home?

One of the key ways engineers monitor Spirit is through "event records." These are messages generated by the flight software -- basically, the rover's operating system -- telling Earth how Spirit is doing and why. Most modern operating systems store such information in log files; Spirit transmits it over long distances.

Spirit's event records come in five "flavors." Activity event records note that some event has occurred. Command event records log the issuance and success or failure of commands. Warning event records indicate unexpected events. Fault event records indicate more serious problems the flight software must address, usually by disabling further use of some device or capability. Fatal event records indicate problems so severe they invoke the fault protection features of the operating system. At that point, the whole rover is "disabled" and goes into so-called "safe" mode by shutting down all activities while waiting for instructions from home.

Whether such warnings indicate a problem depends on the context. For example, every time a motor stalls (stops turning while still powered), Spirit's flight software generates a warning event record. Sometimes, the stall is intentional. For example, engineers calibrate the position of an actuator by slowly driving it into a mechanical "hardstop" at a known position. When the hardstop is reached, the motor stalls and issues a warning event record. If one of the motors stalls unexpectedly, that same event record could indicate a problem.

It's like easing into a parking space until your wheels hit the parking bumper. The resulting jolt says you are correctly parked. On the other hand, a similar jolt could mean a fender bender, depending on the context.

Spirit's operators are sending two copies of new command sequences and then sending it twice again on a backup uplink one or two sols later. Data relays are so sparse, they don't always know if the first attempt succeeded and want to minimize the risk of not getting a new sequence on board.

Typically, the first attempt is successful and the second is rejected. Flight software generates event records telling engineers that the rover received the files correctly and copied them into the primary and secondary file systems. The software then rejects the same files later because their names conflict with existing files of the same name.

Rover operators don't actually read all the event reports in text form. An identification number encodes the "flavor" of the event report and a time tag called SCLK for "spacecraft clock" translates the time into readable format. Ground software decodes these and a few other parameters and converts them into readable words.

Sol-by-sol summary

Spirit completed the following activities:

Sol 1574 (June 6, 2008): Spirit recharged the batteries, listened to instructions from Earth for five minutes using the low-gain antenna, measured atmospheric opacity caused by dust using the panoramic camera, and relayed data to the Odyssey orbiter as it passed overhead.

Sol 1575: Spirit recharged the batteries and listened to instructions from Earth for 20 minutes using the high-gain antenna.

Sol 1576: Spirit recharged the batteries, listened to instructions from Earth for five minutes using the low-gain antenna, and measured atmospheric opacity caused by dust using the panoramic camera.

Sol 1577: Spirit recharged the batteries and listened to instructions from Earth for five minutes using the low-gain antenna.

Sol 1578: Spirit recharged the batteries, listened to instructions from Earth for five minutes using the low-gain antenna, measured atmospheric opacity caused by dust using the panoramic camera, and relayed data to Odyssey during the overhead pass of the orbiter.

Sol 1579 (June 12, 2008): Spirit recharged the batteries and listened to instructions from Earth for five minutes using the low-gain antenna.

Odometry:

As of sol 1578 (June 11, 2008), Spirit's total odometry remained at 7,528.0 meters (4.7 miles).

sol 1567-1573, May 30-June 5, 2008:  Not Quite Hibernation

To save energy, engineers on Earth are sending new instructions to Spirit once every seven Martian days, or sols, with an additional 10 sols of "runout" instructions in the event of an interruption in communications.

The reason for the reduced workload is that rover engineers are trying to avoid having the state of charge in Spirit's battery go below 8.0 amp-hours (an amp-hour is equivalent to the amount of charge flowing for one hour from a current of 1 amp). By doing so, they hope to avoid a low-power fault condition, during which the rover goes to sleep until it senses that it has enough energy to wake up and communicate with Earth.

Spirit has come close to tripping a low-power fault a couple of times recently, but for the most part, the minimum battery state of charge has hovered around 8.5 amp-hours. Should the battery state of charge drop below that level, engineers would have to consider another course of action, such as further reducing the load or turning off the heater to the miniature thermal emission spectrometer, one of Spirit's scientific instruments.

Rover operators selected Friday as the day for building weekly activity plans for Spirit, because it naturally fits within the two-week cycle of updates to communications "windows" -- opportunities to transmit to and receive data from the rover via NASA's Odyssey spacecraft in orbit above Mars.

Spirit received the first seven-sol plan without a glitch. Preliminary reports indicate power and battery levels remain somewhat steady, but the team will be monitoring those numbers closely.

To further reduce Spirit's workload, engineers could continue to curtail communications via Odyssey as well as direct-from-Earth transmissions to the rover's high-gain antenna. Another approach would be to build activity plans lasting 14 sols, using only one high-gain uplink every two weeks for sending new plans to Spirit (with backups to make sure the rover receives them). Because the high-gain uplinks occur during peak solar power levels on the rover, reducing their frequency would not save as much energy as using fewer Odyssey transmissions.

The other downside is that, while a 14-sol plan would reduce the load on Spirit's battery, it would also result in receiving data less often from the spacecraft. Rover planners could try to listen for direct-to-Earth transmissions indicating potential problems, such as low-power faults or spacecraft clock issues. Still, listening for an indication of trouble does not compare to getting fresh data on a regular basis, making longer planning cycles undesirable.

Spirit is healthy and all subsystems are performing within normal range. Current solar array energy has been around 223 watt-hours per Martian day, or sol (100 watt-hours is the amount of energy needed to light a 100-watt bulb for one hour).

Sol-by-sol summary

During the past week, Spirit completed the following activities:

Sol 1567 (May 30, 2008): Spirit received new commands from Earth and recharged the batteries.

Sol 1568: Spirit measured atmospheric opacity caused by dust (Tau) with the panoramic camera, sent data to NASA's Odyssey orbiter to be relayed to Earth, and recharged the batteries.

Sol 1569: Spirit soaked up the sunlight to recharge the batteries.

Sol 1570 (June 2, 2008): Spirit measured atmospheric opacity caused by dust (Tau) with the panoramic camera, sent data to NASA's Odyssey orbiter to be relayed to Earth, and recharged the batteries.

Sol 1571: Spirit received new commands from Earth and recharged the batteries.

Sol 1572: Spirit measured atmospheric opacity caused by dust (Tau) with the panoramic camera and recharged the batteries.

Sol 1573 (June 5, 2008): Spirit recharged the batteries.

Odometry:

As of sol 1570 (June 2, 2008), Spirit's total odometry remained at 7,528.0 meters (4.7 miles).

sol 1559-1566, May 22-29, 2008:  Energy Levels Reach Record Low

Energy production reached a record low for Spirit this past week. On Sol 1560 (May 23, 2008), solar array input was 220 watt-hours (enough energy to light a 100-watt bulb for two hours and 12 minutes). On sol 1563, Spirit expended the highest amount of energy yet on running heaters to maintain minimum temperatures for batteries (30.6 watt-hours) and the miniature thermal emission spectrometer (54.0 watt-hours). Activity levels on Spirit have been kept low this week to compensate for the reduced energy production.

As was the case last week, Spirit had insufficient energy to transmit data to Earth each day. As a result, the operations team selected which Martian days, or sols, would be used for data downlinks to Earth.

Uplinks of communications from Earth have also been curtailed. Spirit typically has a daily communications window when the rover wakes up and points its High-Gain Antenna toward Earth and listens for new commands. By passing up on some of these uplink opportunities, the rover is able to stay awake for shorter periods of time each sol. Rover operators still have the ability to send new commands if necessary.

Despite low energy levels, Spirit continues to be in good health. The rover continues to conduct atmospheric observations, especially measurements of atmospheric opacity. As explained in last week's report, these Tau measurements of the amount of dust in the atmosphere provide valuable data for science and operations planning because they affect the amount of solar energy that reaches the rover's solar panels.

All subsystems are performing as expected.

Sol-by-sol summary:

In addition to receiving direct-from-Earth instructions over the rover's high-gain antenna, Spirit completed the following activities:

Sol 1559 (May 22, 2008): Spirit received new commands from Earth, measured atmospheric opacity caused by dust (Tau) with the panoramic camera and sent data to NASA's Odyssey orbiter to be relayed to Earth.

Sol 1560: Spirit again measured atmospheric dust with the panoramic camera and recharged the batteries.

Sol 1561: Spirit received new commands from Earth. The rover measured atmospheric darkness caused by dust with the panoramic camera.

Sol 1562: Spirit recharged the batteries.

Sol 1563: Spirit measured atmospheric dust with the panoramic camera and transmitted data to Odyssey.

Sol 1564: Spirit received new commands from Earth.

Sol 1565: Spirit recharged the batteries.

Sol 1566 (May 29, 2008): Spirit measured atmospheric opacity caused by dust with the panoramic camera and sent data to Odyssey to be relayed to Earth.

Odometry:

As of sol 1566 (May 29, 2008), Spirit's total odometry remained at 7,528.0 meters (4.7 miles).

sol 1552-1558, May 15-21, 2008:  Some Data Fly First Class, Others Fly Coach and Standby

Lately, Spirit has begun assigning seating priorities to data traveling to Earth. The highest-priority, critical data are like first-class passengers who get to board first, followed by other critical data, who fly coach. These data are guaranteed a seat because they must be returned to Earth to enable engineers to plan the next round of activities.

Non-critical data are like standby passengers. They get to board only if there's room after all the critical data have been seated.

The reason for the seating arrangement is that Spirit's energy levels are so low that the rover has to miss out on some opportunities to transmit data to NASA's Odyssey orbiter, which relays data from the rover to Earth. Odyssey usually passes overhead twice a day, once in the very early morning and again in the afternoon. Spirit hasn't had enough energy to stay awake for a very-early-morning pass in nearly a year, and now is missing some afternoon passes as well.

Uplinks to Odyssey use more energy than the solar arrays have been able to provide, even during peak output at noon. Because Odyssey overflights occur late in the afternoon, they require even more battery power. By deleting some of the Odyssey passes, Spirit saves energy, though doing so limits the amount and "freshness" of the data.

In addition, not all Odyssey passes are created equal. When Odyssey passes directly overhead, communication is excellent, enabling transmission of a large volume of data. When the orbiter is lower in the sky (nearer the horizon), communication can be harder and data volumes smaller.

Last week, a combination of deleted communication links and low data volumes created a problem. The rover wasn't transmitting Tau measurements of sunlight-blocking dust in the Martian atmosphere. Spirit can go a few days without updating Tau measurements, but the longer engineers on Earth go without an update, the greater their uncertainty about actual conditions on Mars. To improve the timeliness of the data, they assigned a much higher priority to new Tau measurements. Spirit used the new priority on Sol 1555 (May 18, 2008).

Overall, Spirit remains healthy and all subsystems are performing as expected.

Energy production was down slightly during the past week, dropping from the previous week's average of 231 watt-hours to an average of 229 watt-hours (100 watt-hours is the amount of energy needed to light a 100-watt bulb for one hour). Instead of remaining constant, energy declined by a watt-hour or two each Martian day, or sol. By the end of the week, power levels were down to 226 watt-hours.

Spirit has been a bit more active, using a little more battery energy and lowering the battery voltage. The lower voltage explains the lower energy production, because environmental factors such as Tau and the dust factor have remained nearly constant.

Tau, a measurement of the loss of sunlight as it passes through the atmosphere, averaged 0.23 the previous week and 0.24 this past week. The 0.01 change represents random fluctuations and is not significant. In both cases, 79 percent of the sunlight hitting Mars' atmosphere reached Spirit's solar arrays.

Spirit measures Tau by taking pictures of the Sun and calculating its brightness. A bright Sun means a low Tau, a dimmer Sun means a higher Tau. The time of day when Tau is measured makes a difference. A noontime Tau measures sunlight through the minimum depth of atmosphere. A sunset Tau measures sunlight as it travels along a slanting path through a thicker swath of atmosphere. By combining the measurements, the rover cancels out losses of sunlight caused by dust on the camera lens.

Tau measures direct sunlight only. As on Earth, dust both blocks and scatters light, and the scattered light changes direction and makes the whole sky seem to "glow." On Earth, the glow is bluish and causes the sky to appear blue. On Mars, the glow is pinkish. Without scattered light, the sky would look pitch black. Scattered light provides some of the rover's solar energy.

Spirit's other measure of energy loss is the dust factor, or the percentage of sunlight reaching the solar arrays that penetrates the dust to make electricity. The average dust factor dropped from 36 percent to 35 percent during the past week, though this, too, was not statistically significant.

Besides foregoing some of the Odyssey uplinks, Spirit has begun eliminating occasional higher-frequency links, known as X-band windows, as well. A communications window is a specific time interval when either the X-band or UHF radio is to be used to send data. When no communications window is active, the system defaults to using the X-band receiver with the low-gain antenna. Because the X-band receiver is always on when the rover is awake, Spirit doesn't save energy simply by deleting a communcations window but is able to wake up later in the day, reducing overall energy use.

On Sols 1557 and 1558 (May 20-21, 2008), Spirit reset the on-board system of fiber-optic gyroscopes and solid-state accelerometers that help the rover keep track of where and how it moves. Known as the inertial measurement unit, the system measures changes in the rover's orientation (yaw, pitch, and roll) and changes in the rover's location. (Activity plans run from roughly noon of one sol to noon of the next sol.)

Because each measurement has a small error, the sum of the measurements can accumulate a significant error (called "drift"). Normally, engineers correct this error by finding the Sun and comparing its actual position to where it would be if the inertial measurement system measurements were exact. Staying up to do that correction (called a "quick fine attitude") takes more energy than Spirit can spare and isn't necessary. Because Spirit hasn't moved since the last time the rover completed a quick fine attitude, engineers are able to use the values measured at that time.

Sol-by-sol summary:

In addition to receiving direct-from-Earth instructions over the rover's high-gain antenna, Spirit completed the following activities:

Sol 1552 (May 15, 2008): Spirit checked for drift (changes with time) in the miniature thermal emission spectrometer and completed a mini-survey of the sky and ground with the instrument. The rover transmitted data to Odyssey during its afternoon pass.

Sol 1553: In the morning, Spirit acquired column 14, part 1 of the full-color "Bonestell panorama," using all 13 filters of the panoramic camera. Spirit measured atmospheric opacity caused by dust (Tau) with the panoramic camera. The rover checked for drift in the miniature thermal emission spectrometer and completed a mini-survey of the sky and ground with the instrument.

Sol 1554: In the morning, Spirit watched the sky for clouds with the navigation camera and acquired spot images of the sky for calibration purposes with the panoramic camera. Later, the rover measured atmospheric dust with the panoramic camera. Spirit checked for drift in the miniature thermal emission spectrometer and completed a mini-survey of the sky and ground with the instrument.

Sol 1555: In the morning, Spirit surveyed the external calibration target with the miniature thermal emission spectrometer, acquired six movie frames in search of clouds with the navigation camera, measured atmospheric dust with the navigation camera, and watched for dust devils. Spirit completed its first critical-priority Tau measurement of atmospheric dust and relayed data to the Odyssey orbiter.

Sol 1556: Spirit conducted no morning science activities and did not receive X-band radio instructions direct from Earth. The rover spent the day recharging the batteries.

Sol 1557: Spirit measured atmospheric dust opacity with the panoramic camera. The rover checked for drift in the miniature thermal emission spectrometer and completed a mini-survey of the sky and ground with the instrument. Spirit transmitted data to Odyssey in the afternoon.

Sol 1558 (May 21, 2008): First thing in the morning, Spirit reset the inertial measurement unit and scanned the sky for clouds with the navigation camera. Later, the rover measured atmospheric dust opacity. Spirit checked for drift in the miniature thermal emission spectrometer and completed a mini-survey of the sky and ground with the instrument. Plans for the next morning called for Spirit to acquire column 16, part 1 of the full-color Bonestell panorama.

Odometry:

As of sol 1557 (May 20, 2008), Spirit's total odometry remained at 7,528.0 meters (4.7 miles).

sol 1546-1551, May 09-14, 2008:  Rover Hindered by Moon over Madrid

Though Martian skies have been quite clear, the Moon recently prevented Spirit from having a clear view of Earth. Such events are rare, but during the past week, a lunar occultation prevented instructions from Earth from reaching the rover. In fact, they are so rare that the mission has never before had its communications blocked by a lunar occultation. There have been only two lunar occultations since the rover landed, but because they last only about 30 minutes, there is only a slight chance that they might interfere with a 20-minute uplink from Earth. If Spirit is on an energy-saving communications diet, as it is now, interference is even less likely. Spirit will not see another lunar occultatation at least through the end of 2009.

At first, mission planners thought that light rainfall at NASA's Deep Space Network station near Madrid, Spain, might have absorbed the microwaves used to transmit the instructions. But the rain in Spain wasn't enough to stop the uplink. They also wondered if something was amiss at the station or on board the rover but found nothing wrong. Then someone had a brilliant idea: Where was the Moon? Sure enough, the Moon was directly between Spain and Spirit during the failed uplink on sol 1547 (May 10, 2008).

Winter Wattage

Overall, Spirit remains healthy and all subsystems are performing as expected. Power values have remained remarkably steady and energy has averaged 231 watt-hours, varying by only a single watt-hour (100 watt-hours is the amount of energy needed to light a 100-watt bulb for one hour). Tau, a measure of atmospheric opacity, was 0.23 (resulting in 79 percent of direct sunlight passing through the atmosphere). The other 21 percent was either absorbed or scattered. (The scattered portion contributes to power levels but is not part of the tau measurement.)

The dust factor, too, has been steady at 0.36, meaning that only 36 percent of the sunlight that reaches the rover has been penetrating the dust to make electricity. It is this dust that has made life difficult for Spirit.

Mars passed its aphelion -- the farthest point from the Sun in its orbit -- on Sol 1549 (May 12, 2008) at 10:00 a.m. Local Solar Time, which happened to be 5:14 a.m. Pacific Daylight Time. In the southern hemisphere, where Spirit is located, Mars will be at its winter solstice -- the same day as the summer solstice in the red planet's northern hemisphere -- on Sol 1591 (June 24, 2008) at 22:13 LST (10:30 p.m. Pacific Daylight Time). The winter solstice is effectively the "peak" or mid-point of winter, when the Sun is lowest in the northern sky. Weather conditions for Spirit are expected to improve after that time.

Mars Time

Local Solar Time (LST) is like ordinary civil time on Earth. Sixty Mars seconds make a Mars minute, 60 Mars minutes make a Mars hour, and 24 Mars hours make a Mars day, or sol. Because a sol is as long as 24.66 Earth hours, Mars time intervals are 24.66/24 or 1.027 (2.7 percent) longer than corresponding time intervals on Earth. And, as on Earth, Martian time varies depending on location. Instead of universal time (UTC) or Pacific Daylight Time (PDT), Local Solar Time denotes the time at each rover's site. And just as different locations on Earth can be in different time zones, the rovers are in different time zones denoted "LSTA" or "LSTB."

Sequencing Blackout

Because Spirit is a robot, it needs to be told what to do and when to do it. The time-tagged series of commands for each sol's activities is known as a "sequence." Because it's hard to prepare more than three sequences in a single planning session, the rover's operators limit advance planning to no more than three sols at a time.

Shortly before planning Spirit's schedule of activities for sols 1547-1549 (May 10-12, 2008), engineers learned that their normal uplink session for sol 1550 (May 13, 2008) was needed by another mission. Because it was too late to adjust the sequencing plan and they couldn't create a four-sol plan, they decided to let sol 1550 be a "runout sol," during which the rover conducts very limited and standardized activities while awaiting a new set of instructions. If no new sequences arrive, the rover drops into "automode," waking up only for pre-programmed information exchanges, known as communication windows.

Spirit's operators expected the rover to attempt a standard "handover" from the old sequence for Sol 1549 (May 12, 008) to a new sequence for Sol 1550 (May 13, 2008) and then execute another runout for sol 1549 and attempt a handover to the sequence for sol 1551 (May 14, 2008), which by then would be on board the spacecraft.

Things don't always go as expected. The uplink of instructions on Sol 1547 (May 10, 2008) failed and the sequences for sols 1547-1549 did not get on board. Spirit began executing the runout on sol 1546 (May 9, 2008). Because this occurred on a weekend and the rover was safe, rover operators decided to wait until Monday to retransmit the sequences.

Again, things didn't go as expected. As a result of a lot of complexity, the sequences weren't transmitted on Sol 1549, either! All this time, Spirit continued to execute the sol 1546 runout, trying to hand over first to the Sol 1547 sequence, then the Sol 1548 sequence, and finally the Sol 1549 sequence. None were on board. Finally, after the third attempt, the Sol 1546 sequence ran out and Spirit dropped into automode on Sol 1549 at 11:51 LST.

Spirit remained in automode until the Sol 1551 sequence arrived along with a real-time activate command. The activate command started the Sol 1551 sequence and Spirit was resumed normal operations.

Interestingly, rover operators had planned to delete communications with the Odyssey orbiter to save energy. But Spirit didn't receive those instructions and went ahead and sent data to Earth on sols 1547 and 1549 (May 10 and May 12, 2008). Given the low level of activity during runout and automode, power levels were not adversely affected.

Robotic Arm Hibernation

To conserve power, Spirit's operators originally planned to stow the robotic arm in a winter hibernation position on Sol 1547. It turned out the arm would have been too cold to move without heating and team members had concerns about heating the robotic arm. Rover operators postponed the hibernation date to sol 1551 (May 14, 2008), when startup time would be later in the morning and temperatures would be warmer. They transmitted commands to move the arm. Confirmation wnould have to wait until sol 1552 (May 15, 2008).

The arm will remain in hibernation for several months. Members of the science team considered leaving the Mössbauer spectrometer in place on the soil until they realized they wouldn't have enough power to use it. They were also concerned about the possibility that a joint could fail. If that happened, they couldn't drive the following spring. They chose Spirit's winter hibernation position because it preserved the rover's ability to continue driving if the robotic arm "froze" in place, with the alpha-particle X-ray spectrometer in position to acquire atmospheric argon measurements. (Argon is a trace gas in the atmosphere. By measuring it, scientists can infer changes in barometric pressure).

With the arm in hibernation, Spirit will be ready for the worst of winter. The rover will still be active, acquring more frames of the "Bonestell panorama" as well as other images and measurements, but activity levels will decrease as the winter solstice approaches. Engineers think they may be able to support limited science activities every sol or two.

Sol-by-sol summary:

In addition to receiving direct-from-Earth instructions over the rover's high-gain antenna, Spirit completed the following activities:

Sol 1546 (May 9, 2008): Spirit measured atmospheric opacity caused by dust -- known as tau -- with the panoramic camera, checked for drift (changes with time) in the miniature thermal emission spectrometer, and completed a mini-survey of the sky and ground with the spectrometer. Spirit did not relay data to Odyssey.

Sol 1547: In the morning, Spirit acquired column 16, part 2 of the Bonestell panorama, using all 13 filters of the panoramic camera, and monitored dust accumulation on the panoramic-camera mast assembly. The attempted uplink of a new sequence of activities to the rover was unsuccessful, causing Spirit to execute runout activities. The rover relayed data to Odyssey.

Sol 1548: In the morning, Spirit spent 10 minutes measuring atmospheric opacity caused by dust with the panoramic camera and again conducted runout activities, which included sending data to Odyssey and spending 10 minutes the next morning assessing atmospheric dust with the panoramic camera. The rover did not, as planned, acquire thumbnail images of the sky or complete a horizon survey with the panoramic camera.

Sol 1549: Spirit conducted runout activities and dropped into automode.

Sol 1550: Spirit remained in automode. The rover's only activity was the transmission of data to Odyssey.

Sol 1551 (May 14, 2008): Spirit was to move the robotic arm to the winter hibernation position. The rover was not instructed to communicate with Odyssey.

Odometry:

As of sol 1551 (May 14, 2008), Spirit's total odometry remained at 7,528.0 meters (4.7 miles)

sol 1532-1538, Apr 24-30, 2008:  "Catch-22":  Staying Awake vs. Going to Sleep

Spirit's Tau measurements of atmospheric dust have remained steady, but solar array input has dropped a bit to 235 watt-hours per sol. Spirit still has enough energy to squeeze in Mössbauer studies of iron-bearing minerals at a time of year when the rover's handlers expected Spirit to be concerned only with survival. At present, the rover's target of scientific interest is a soil exposure nicknamed after Arthur C. Harmon, a former Tuskegee airman. Spirit conducted 8 more hours of Mössbauer integration, for a total of 12 hours. Scientists hope the rover will be able to collect 36 more hours' worth of data from the same target. Meanwhile, Spirit continued to acquire panoramic-camera images, using all 13 color filters, of the "Bonestell panorama," informally named in honor of famed space artist Chesley Bonestell.

Concerned that cold winter temperatures on Mars might trigger the survival heaters on the rover electronics module, rover planners took the extra precaution of disabling those particular heaters on sol 1533 (April 25, 2008) to conserve power. With the heaters turned off, the rover's handlers must monitor temperatures carefully to make sure the module doesn't get too cold. Besides the survival heaters, the remaining means of keeping the module warm enough during the night is to generate more heat during the day by keeping the rover awake for about one additional hour. Of late, 39 minutes is the shortest possible awake time for conducting minimal activities. Another 20-plus minutes of awake time are needed on days when the rover transmits data to NASA's Odyssey orbiter during its overhead pass. On other sols, rover planners may arbitrarily increase the rover's awake time to 50 minutes or longer to generate enough heat to keep the electronics module alive, even if science activities do not require Spirit to be awake that long.

In summary, the challenge for Spirit's handlers during each planning cycle is to recharge the battery enough to do significant science, then recharge the battery again to transmit data to Odyssey for downlink to Earth. By keeping the rover awake for shorter periods, they conserve energy but generate less thermal inertia (heat) for keeping the rover electronics module alive. The more consecutive sols that go by without transmitting temperature and power updates to Odyssey and from there to Earth, the more Spirit's handlers must rely on margin ("wiggle room") from earlier predictions and keep the rover awake longer to protect the electronics module. As a result, Spirit is caught in a "catch-22" set of tradeoffs among power, heat, communications, and science. This delicate balance will become increasingly more precarious as the rover moves closer to the winter solstice, with its even colder temperatures and lower solar array input.

Sol-by-sol summary:

In addition to measuring atmospheric dust levels with the panoramic camera and receiving direct-from-Earth instructions via the rover's high-gain antenna, Spirit completed the following activities:

Sol 1532 (April 24, 2008): Spirit spent 8 hours acquiring data from Arthur C. Harmon with the Mössbauer spectrometer.

Sol 1533: In the morning, Spirit took spot images of the sky with the panoramic camera for calibration purposes and acquired panoramic-camera images of the dune field known as "El Dorado." The rover recharged the battery, disabled the survival heaters on the rover electronics module, and shortened the "Up_Too_Long" computer sequence to 30 minutes.

Sol 1534: Spirit recharged the battery and relayed data to NASA's Odyssey orbiter for transmission to Earth.

Sol 1535: Spirit recharged the battery.

Sol 1536: Spirit recharged the battery and relayed data to the Odyssey orbiter. The rover checked for drift (changes with time) in the miniature thermal emission spectrometer and surveyed the sky and ground with the instrument. The rover was awake for a total of 61 minutes.

Sol 1537: In the morning, Spirit acquired full-color images, using all 13 filters of the panoramic camera, of column 12, part 2 of the Bonestell panorama. The rover recharged the battery, checked for drift in the miniature thermal emission spectrometer, and surveyed the sky and ground with the miniature thermal emission spectrometer. Spirit was awake for a total of 39 minutes.

Sol 1538 (April 30, 2008): Spirit checked for drift in the miniature thermal emission spectrometer and surveyed the sky and ground with the instrument. After sending data to Odyssey, the rover used the alpha-particle X-ray spectrometer to measure argon gas in the Martian atmosphere. Plans for the next morning called for Spirit to complete work on column 12, part 3 of the Bonestell panorama.

Odometry:

As of sol 1538 (April 30, 2008), Spirit's total odometry remained at 7,528.0 meters (4.7 miles).

sol 1525-1531, Apr 17-23, 2008:  Rover "Spirit" High Despite Low Power Levels

Given the substantial coating of dust on the solar array, Spirit continues to enjoy energy levels that are higher than expected for this time of year, at around 240 watt-hours per sol (enough energy to light two 100-watt bulbs and one 40-watt bulb for one hour).

Spirit continues to make progress on the full-color "Bonestell panorama" of the rover's winter surroundings. Of 27 columns of stacked images needed for a complete mosaic, Spirit has completed work on 11 columns, each comprising three parts. Each Martian day, or sol, Spirit has enough energy to complete one part. Science team members have nicknamed the panorama after Chesley Bonestell (1888-1986), considered the father of modern space art.

Analysis of iron-bearing minerals in a patch of undisturbed soil will require an estimated 24 hours of data collection during the coming week with the Mössbauer spectrometer. The soil target is known informally as "Arthur C. Harmon." Spirit can complete 4 to 8 hours of integration with the spectrometer before needing to recharge the batteries. To conserve power, Spirit is on a communications diet, in which the rover limits data transmissions to Earth to, at most, every other sol.

Spirit is healthy and all systems are operating as expected.

Sol-by-sol summary:

In addition to communication activities that include direct-from-Earth instructions via the rover's high-gain antenna and, power permitting, data relays to Earth via the Odyssey orbiter, Spirit continues to monitor atmospheric dust levels with the panoramic camera, check for drift (changes with time) in the miniature thermal emission spectrometer, and survey the sky and ground with the spectrometer. During the past week, Spirit also completed the following activities:

Sol 1525 (April 17, 2008): Spirit acquired column 10, part 1 of the Bonestell panorama, using all 13 filters of the panoramic camera.

Sol 1526: In the morning, Spirit surveyed the external calibration target with the miniature thermal emission spectrometer and parked the panoramic camera mast assembly with the panoramic camera pointed below the horizon to minimize dust accumulation.

Sol 1527: In the morning, Spirit completed work on column 10, part 2 of the Bonestell panorama, then parked the panoramic camera mast assembly with the panoramic camera pointed below the horizon to minimize dust accumulation. The rover exchanged tools to put the Mössbauer spectrometer in position to study Arthur C. Harmon.

Sol 1528: Spirit spent the morning working on column 10, part 3 of the Bonestell panorama. The rover relayed data to Odyssey for transmission to Earth.

Sol 1529: Spirit acquired column 11, part 1 of the Bonestell panorama and spent 4.5 hours acquiring data from Arthur C. Harmon with the Mössbauer spectrometer.

Sol 1530: In the morning, Spirit monitored dust on the panoramic camera mast assembly and acquired column 11, part 2 of the Bonestell panorama. The rover then completed work on column 11, part 3 of the panorama and relayed data to Odyssey.

Sol 1531: (April 23, 2008): Spirit recharged the battery. The following morning, Spirit was to acquire column 12, part 1 of the Bonestell panorama.

Odometry:

As of sol 1531 (April 23, 2008), Spirit's total odometry remained at 7,528.0 meters (4.7 miles).

sol 1517-1524, Apr 09-16, 2008:  Spirit Still "Sitting Pretty" for This Time of Year

Despite a slight increase in atmospheric opacity caused by dust, Spirit is still enjoying higher-than-expected energy levels for this time of year. Solar array input has been approximately 240 watt-hours per Martian day, or sol (100 watt-hours is the amount of energy needed to light a 100-watt bulb for one hour).

Clear skies have had the unfavorable effect, however, of causing a drop in temperatures at the surface of Mars, increasing the bitter cold experienced by Spirit's rover electronics module. Nighttime temperatures are creeping closer to the point where they will trigger the survival heaters, which draw a large amount of power. A much more desirable strategy is to keep Spirit awake long enough each day to keep the electronics module sufficiently warm with heat from normal operations, providing more time for science observations. "Awake time" vs. heating time is just one of the many trade-offs the team makes each day to keep Spirit going through the Martian winter.

Sol-by-sol summary:

In addition to daily communications that include direct-from-Earth instructions via the rover's high-gain antenna and, as power permits, data relays to Earth via the Odyssey orbiter, Spirit continues to monitor atmospheric dust levels each day with the panoramic camera. In addition, during the past week, Spirit completed the following activities:

Sol 1517 (April 9, 2008): Spirit completed a mini-survey of the sky and ground with the miniature thermal emission spectrometer; acquired column 8, part 3 of the full-color "Bonestell Panorama" using all 13 filters of the panoramic camera; and shot movie frames in search of clouds with the navigation camera.

Sol 1518: Spirit completed a mini-survey of the sky and ground with the miniature thermal emission spectrometer; acquired a 2-by-1-by-1 stack of microscopic images of the rover's solar array; acquired column 9, part 1 of the Bonestell panorama; and took spot images of the sky for calibration purposes with the panoramic camera.

Sol 1519: Spirit surveyed the rover's external calibration target with the miniature thermal emission spectrometer and acquired column 9, part 2 of the Bonestell panorama. To conserve energy, the rover did not relay data to Odyssey.

Sol 1520: Spirit completed a mini-survey of the sky and ground with the miniature thermal emission spectrometer; measured atmospheric opacity caused by dust with the navigation camera (as well as the panoramic camera); and acquired movie frames in search of clouds with the navigation camera. The rover took spot images of the sky and surveyed the horizon with the panoramic camera. Spirit did not relay data to Odyssey.

Sol 1521: Spirit completed a mini-survey of the sky and ground with the miniature thermal emission spectrometer; calibrated the elevation of the miniature thermal emission spectrometer; and acquired column 9, part 3 of the Bonestell panorama.

Sol 1522: Spirit completed a mini-survey of the sky and ground with the miniature thermal emission spectrometer; took thumbnail images of the sky and surveyed the horizon with the panoramic camera; and acquired lossless-compression images of wind-blown deposits next to the rover with the hazard-avoidance cameras. Spirit did not relay data to Odyssesy.

Sol 1523: Spirit recharged the battery and did not relay data to Odyssey.

Sol 1524: (April 16, 2008): Spirit recharged the battery.

Odometry:

As of sol 1524 (April 16, 2008), Spirit's total odometry remained at 7,528.07 meters (4.68 miles).

sol 1511-1516, Apr 03-08, 2008:  Clear Skies at "Home Plate"

Spirit is currently experiencing the clearest skies seen by either of NASA's two Mars Exploration Rovers. On sol 1511 (April 3, 2008), Tau measurements of atmospheric dust hit an all-time low of 0.127. By sol 1516 (April 8, 2008), this measurement had increased slightly to 0.170. The low Tau values have held power levels at around 250 watt-hours (enough energy to light a 100-watt bulb for about 2.5 hours). If Tau were not so cooperative, Spirit would be getting only about 200 watt-hours of energy, compelling the rover's handlers to disable the heaters on the miniature thermal emission spectrometer and take other measures to conserve power.

The engineering team still expects to implement energy-conservation strategies, but not for several weeks. Meanwhile, Spirit continues to make progress on remote-sensing activities, scientific investigations, and the "Bonestell panorama" of the rover's view from the north rim of "Home Plate."

Sol-by-sol summary:

To conserve energy, mission planners have restricted the number of sols on which Spirit receives direct-from-Earth instructions via the rover's high-gain antenna and transmits data to Earth via the Odyssey orbiter. Spirit continues, on a daily basis, to monitor atmospheric dust levels with the panoramic camera and survey the sky and ground with the miniature thermal emission spectrometer. In addition, during the past week, Spirit completed the following activities:

Sol 1511 (April 3, 2008): Spirit took thumbnail images of the sky with the panoramic camera.

Sol 1512: Spirit gathered compositional data from the soil target known as "Arthur C. Harmon" using the alpha-particle X-ray spectrometer. The rover used the panoramic camera to acquire super-resolution images of a target informally named "Arthur C. Clarke."

Sol 1513: Spirit acquired column 7, part 3 of the full-color Bonestell panorama, using all 13 filters of the panoramic camera.

Sol 1514: Spirit pointed the alpha-particle X-ray spectrometer skyward to measure argon gas in the Martian atmosphere and acquired stability images of the rover's 30-degree tilt. The rover transmitted data to Odyssey and spent about 4.5 hours measuring atmospheric argon. Spirit also acquired column 8, part 1 of the Bonestell panorama and took spot images of the sky for calibration purposes with the panoramic camera.

Sol 1515: Spirit surveyed the sky with the panoramic camera and monitored dust on the panoramic camera mast assembly.

Sol 1516: (April 8, 2008): Spirit acquired column 8, part 2 of the Bonestell panorama and surveyed the horizon with the panoramic camera.

Odometry:

As of sol 1516 (April 8, 2008), Spirit's total odometry remained at 7,528.07 meters (almost 4.68 miles).

sol 1504-1510, Mar. 27 - Apr 02, 2008:  Spirit Advances Toward Midwinter

Seasons are about twice as long on Mars as on Earth and are offset relative to Earth because Mars takes about twice as long to complete one orbit around the Sun. At Spirit's location, the fall equinox -- the start of fall, when night and day are equal in length -- arrived Dec. 12, 2007. The winter solstice -- the time of year with the shortest day -- will arrive June 25, 2008.

Solar array energy has varied from 244 watt-hours to 256 watt-hours, averaging 250.4 watt-hours for this period (100 watt-hours is the amount of energy needed to light a 100-watt bulb for one hour). Tau, the measure of atmospheric dust, has averaged 0.16, varying by only a hundredth. The dust factor has been nearly constant at 0.35, meaning 35 percent of the sunlight reaching the arrays penetrates the dust layer to make electricity. A low Tau is good because it means the skies are fairly clear; a low dust factor is bad because it means the solar arrays are coated with a fair amount of dust.

Astronomers use the symbol L(s) -- pronounced L-sub-s -- to denote how far Mars has progressed in its orbit around the Sun. If you imagine looking down at the solar system, with the Sun in the middle and Mars orbiting around it, L(s) gives the location of Mars. By definition, L(s) = 0 degrees when the Sun crosses the Martian equator. This is the first day of Martian spring, the vernal equinox, when night and day are equal in length, in the northern hemisphere. It's also the first day of fall, the autumnal equinox, in the southern hemisphere. At Spirit's location in Mars' southern hemisphere, the season is currently mid- to late fall, and L(s) is about 55 degrees, roughly equivalent to Nov. 17 in Earth's northern hemisphere and May 18 in Earth's southern hemisphere. L(s) will equal 90 degrees at the time of the winter solstice.

Spirit is healthy and all subsystems are performing as expected.

Sol-by-sol summary:

To conserve energy, mission planners have restricted the number of sols on which Spirit receives direct-from-Earth instructions via the rover's high-gain antenna and transmits data to Earth via the Odyssey orbiter. Spirit continues, on a daily basis, to monitor atmospheric dust levels with the panoramic camera, check for drift (changes with time) in the miniature thermal emission spectrometer, and survey the sky and ground with the instrument. In addition, during the past week, Spirit completed the following activities:

Sol 1504 (March 27, 2008): Spirit calibrated the miniature thermal emission spectrometer and acquired a microscopic image of the capture magnet.

Sol 1505: Upon awakening, Spirit took spot images of the sky for calibration purposes with the panoramic camera and acquired column 6, part 1 of the full-color "Bonestell panorama" using all 13 filters of the panoramic camera. The rover also recharged the battery.

Sol 1506: Spirit acquired column 6, part 2 of the Bonestell panorama and monitored dust on the panoramic-camera mast assembly. Spirit looked at the miniature thermal emission spectrometer for calibration purposes, acquired microscopic images of the solar panel, and acquired images of the external magnets, which capture magnetic dust particles, using the panoramic camera.

Sol 1507: Spirit acquired column 6, part 3 of the full-color Bonestell panorama and recharged the battery.

Sol 1508: Spirit acquired column 7, part 1 of the full-color Bonestell panorama and relayed data to Odyssey during the orbiter's afternoon pass overhead.

Sol 1509: Spirit surveyed the sky at high Sun with the panoramic camera and completed a "runout" of previously loaded activities after not being able to receive new instructions from Earth. The rover recharged the battery and relayed data to Odyssey.

Sol 1510: (April 2, 2008): Spirit acquired a 1-by-1-by-3 stack of microscopic images of a soil target known informally as "Arthur_C_Hammon" and placed the alpha-particle X-ray spectrometer on the soil target. Plans for the following morning called for Spirit to acquire column 7, part 2 of the full-color Bonestell panorama.

Odometry:

As of sol 1509 (April 1, 2008), Spirit's total odometry was 7,528 meters (almost 4.7 miles).

sol 1498-1503, Mar. 20-26, 2008:  Spirit Sees Clearest Skies Since Landing on Mars!

Like a calm after the recent Martian dust storms, atmospheric dust above Spirit's overwintering site has reached the lowest levels the rover has seen since arriving on Mars. To be sure, sunblocking dust that has settled on the rover's solar panels and low-angle winter sunlight have combined to reduce Spirit's energy levels. But clear skies mean more sunlight penetrates the atmosphere, making rover planners optimistic that Spirit will have a slim but adequate amount of energy to survive until Martian spring.

Earlier estimates predicted a near-starvation energy diet for Spirit during the darkest days of winter. The coming winter solstice, the peak of Martian winter, will be June 25, 2008. To conserve energy, Spirit may have to disable some heaters and curtail communications and other activities, but is expected to be able to conduct limited scientific investigations.

Solar-array energy during the past week has varied between 244 watt-hours and 254 watt-hours, averaging 249.5 watt-hours for the period (100 watt-hours is the amount of energy needed to light a 100-watt bulb for one hour). Tau, the measure of atmospheric dust, has averaged 0.2, varying by only a few hundredths. The dust factor has been nearly constant at 0.36 (meaning 36 percent of the sunlight reaching the arrays penetrates the dust layer to make electricity). A low Tau is good; a low dust factor is bad.

Because dust is constantly settling out from the Martian atmosphere onto the solar arrays, Tau and the change in the dust factor are related. When Tau is high, the dust factor rapidly decreases as dust from the atmosphere rains onto the arrays. When Tau is low (as it is now), the atmosphere carries less dust and the dust factor decreases more slowly. The clearer atmosphere doesn't affect dust already on the solar arrays, but it does affect the rate at which new dust is added.

The atmosphere above the Spirit site is remarkably clear at present and Tau has been as low as 0.170 -- the lowest seen by Spirit in the entire mission. Not surprisingly, the dust factor has been virtually unchanged.

Spirit also analyzed material on the external capture magnet. Spirit has several magnets of which two, the capture and filter magnets, are mounted at the front of the solar array. The capture magnet is relatively strong, the filter magnet only half as strong.

Viking data from the 1970s showed that Martian dust was slightly magnetic, comprising 1 to 7 percent magnetic material. Spirit's filter and capture magnets winnow the dust for this material. The capture magnet, being stronger, gathers all magnetic materials while the filter magnet retains only the most magnetic particles. Using the alpha-particle X-ray spectrometer, Spirit can determine the chemical composition of the captured particles. The observations will help scientists ascertain whether the magnetic material is uniform or has more than one constituent. The dust composition provides insight into whether the magnetic material is the product of weathering in the presence of water or weathering of dry bedrock.

Spirit continued to scale back the frequency of afternoon communications with the Odyssey orbiter to save energy. Overhead passes by Odyssey happen late in the day when little solar energy is available, requiring the use of significant battery power. By deleting some of the passes, Spirit can conserve energy acquired earlier in the day to provide power for subsequent science observations. The downside is that fewer passes slow the rate at which pictures and other data can be downlinked to Earth.

Spirit continued work on the Bonestell (Bon-ES-tell) panorama, a high-resolution, 360-degree mosaic of images divided into wedges (columns) spanning roughly 5 compass degrees and extending from near the rover to just above the horizon. Each column typically has three or four separate images or "parts." The panorama is named for Chesley Bonestell (1888-1986), considered the "father of modern space art."

Spirit is healthy and all subsystems are performing as expected.

Sol-by-sol summary:

To conserve energy, mission planners have restricted the number of sols on which Spirit receives direct-from-Earth instructions via the rover's high-gain antenna and transmits data to Earth via the Odyssey orbiter. Spirit continues, on a daily basis, to monitor atmospheric dust levels with the panoramic camera, check for drift (changes with time) in the miniature thermal emission spectrometer, and survey the sky and ground with the instrument. In addition, during the past week, Spirit completed the following activities:

Sol 1498 (March 20, 2008): Spirit placed the alpha-particle X-ray spectrometer on the capture magnet, took images with the hazard avoidance cameras, took images with the navigation camera for lossless-compression visual odometry, and relayed data to Odyssey.

Sol 1499: Spirit acquired column 4, part 2 of the full-color Bonestell panorama, using all 13 filters of the panoramic camera.

Sol 1500: Spirit acquired column 4, part 3 of the full-color Bonestell panorama, using all 13 filters of the panoramic camera.

Sol 1501: Spirit acquired column 5, part 1 of the full-color Bonestell panorama and relayed data to Odyssey during the orbiter's afternoon pass.

Sol 1502: Spirit took six movie frames in search of clouds with the navigation camera and acquired column 5, part 2 of the Bonestell panorama. Using the alpha-particle X-ray spectrometer, Spirit acquired data on the elemental composition of magnetic particles on the external capture magnet.

Sol 1503 (March 26, 2008): Spirit acquired column 5, part 3 of the Bonestell panorama and relayed data to Odyssey. Plans for the following morning called for Spirit to acquire super-resolution images of a rock target informally named "Roger_Zelazny" (after the science fiction author) with the panoramic camera.

Odometry:

As of sol 1501 (March 23, 2008), Spirit's total odometry was 7,528.07 meters (4.68 miles).

sol 1491-1497, Mar. 13-19, 2008: Spirit Phones Home to Set Clock

Spirit is feeling the strain of juggling activities on Mars in the face of declining power levels as the winter Sun sinks lower on the horizon. After acquiring compositional data from a rock target informally named "Wendell Pruitt," Spirit had to wait a few sols (Martian days) to have enough energy to conduct atmospheric studies and move the robotic arm out of the way for a panoramic-camera portrait of a rock target known as "Freeman." First, the rover had to make a "phone call" to Earth to correct for drift -- changes in time -- in the spacecraft clock.

When Spirit phones home using a direct-to-Earth, X-band communications link, the rover's transmitter has to be running, which requires a fair amount of energy. During more typical, direct-from-Earth communications, only the rover's receiver has to be on. To set the spacecraft clock, Spirit transmits a data product called a time packet. The time packet is used to synchronize the rover's clock back to Earth time (also known as Universal Time). A previous attempt to relay the time packet was unsuccessful, causing Spirit's clock to be off by as much as a minute and a half.

In addition to resetting the clock, Spirit completed a light schedule of activities on sols 1493-1494 (March 15-16, 2008). By sol 1496 (March 18, 2008), Spirit had generated enough solar power to proceed with measurements of argon gas in the Martian atmosphere and studies of the Freeman rock target. Interspersed with those activities, Spirit continued to work on the "Bonestell panorama" and take panoramic-camera images of a target dubbed "C.S. Lewis." The rover spent sols 1492, 1494, and 1497 (March 14, 16, and 19, 2008) recharging the battery, conducting only minimal science activities, and storing data for later transmission to Earth.

Spirit continued to have difficulty receiving spacecraft commands via the rover's high-gain, X-band, dish antenna as a result of the mast that holds the panoramic and navigation cameras getting in the way and partially obscuring the signal. To help address this challenge, rover planners had Spirit complete a self-assessment to see if the rover could independently recognize an occlusion of the high-gain signal and respond by swiveling the high-gain antenna to a different position. The self-assessment, on sol 1493 (March 15, 2008), was successful. Spirit used the technique prior to an actual uplink session on sol 1496 (March 18, 2008), when the rover's handlers were expecting a particularly severe occlusion. The activity was successful and the uplink did not appear to be impeded in any way. Currently, this activity involves having the rover use a temporary parameter that then goes away when the rover shuts down for a nap. Rover planners are considering making the temporary parameter permanent.

Looking forward, Spirit will go increasingly into "hibernate" mode as the Sun continues to dim. Rover planners predict Spirit will be able to conduct science activities until about late April.

Spirit is healthy and all subsystems are performing as expected. The latest available power readings from sol 1496 (March 18, 2008) showed power at 249 watt-hours (100 watt-hours is the amount of energy needed to light a 100-watt bulb for one hour). Spirit has no plans to move before the next Martian spring and is hard at work accomplishing as much as possible before power levels drop to a point that temporarily precludes use of the scientific instruments on the rover's arm.

Sol-by-sol summary:

To conserve energy, mission planners have restricted the number of sols on which Spirit receives direct-from-Earth instructions via the rover's high-gain antenna and transmits data to Earth via the Odyssey orbiter. Spirit continues, on a daily basis, to monitor atmospheric dust levels with the panoramic camera, check for drift (changes with time) in the miniature thermal emission spectrometer, and survey the sky and ground with the instrument. In addition, during the past week, Spirit completed the following activities:

Sol 1491 (March 13, 2008): After communicating with Odyssey, Spirit studied the elemental composition of "Wendell Pruitt" with the alpha-particle X-ray spectrometer.

Sol 1492: In addition to monitoring atmospheric dust and conducting surveys with the miniature thermal emission spectrometer, Spirit recharged the battery.

Sol 1493: Spirit initiated a direct-to-Earth communications link using the X-band antenna and transmitted a data packet to correct the spacecraft clock.

Sol 1494: In addition to monitoring atmospheric dust and conducting surveys with the miniature thermal emission spectrometer, Spirit recharged the battery.

Sol 1495: In the morning, Spirit acquired column 3, part 1 of the full-color Bonestell panorama, using all 13 filters of the panoramic camera. Spirit positioned the alpha-particle X-ray spectrometer to measure argon gas in the Martian atmosphere. The rover took a single-frame image with the navigation camera. After communicating with Odyssey, Spirit measured argon with the alpha-particle X-ray spectrometer.

Sol 1496: Spirit monitored dust accumulation on the rover mast and acquired column 3, part 3 of the full-color Bonestell panorama. The rover acquired full-color images, using all 13 filters of the panoramic camera, of the Freeman rock target.

Sol 1497 (March 19, 2008): Spirit looked for changes in the "El Dorado" dune field with the panoramic camera and acquired column 4, part 1 of the Bonestell panorama. The rover recharged the battery. The following morning, Spirit was to acquire movie frames in search of clouds with the navigation camera, acquire super-resolution, panoramic-camera images of a target dubbed "C.S. Lewis half," and survey the horizon with the panoramic camera.

Odometry:

As of sol 1496 (March 18, 2008), Spirit's total odometry was 7,528 meters (almost 4.7 miles).

sol 1484-1490, Mar. 6-12, 2008: Spirit Begins Preparing for "Hibernation" Mode

Spirit has reached its final position for the coming Martian winter and has no plans to move before the next Martian spring. During the next few months, the rover will increasingly go into a "hibernate" mode as the sun continues to dim.

Spirit is currently wrapping up a campaign of scientific studies of the rock target known as "Wendell Pruitt," interspersed with remote science observations of targets nicknamed "Lucius Theus" and "Theopolis Johnson." These targets were all named in honor of distinguished members of the "Tuskegee Airmen," the popular name for the 332nd Fighter Group, an all African-American unit of the U.S. Army Air Corps that served in the European Theater during World War II.

Spirit's previous attempt to use the wire brush on the rock abrasion tool on sol (Martian day) 1479 (March 1, 2008) failed to sufficiently brush the surface of Wendell Pruitt. The rover repeated the effort on sol 1484 (March 6, 2008) with greater success. On sol 1486 (March 8, 2008), Spirit acquired a 2-by-2-by-5 stack of stereo microscopic images of Wendell Pruitt. The rover placed the alpha-particle X-ray spectrometer on the target on sol 1489 (March 11, 2008) but postponed data collection with the instrument to conserve power for an operational readiness test in support of the Phoenix mission scheduled for the late morning of sol 1491 (March 13, 2008). At that time, the rover was to send a tone at UHF frequencies directly to the Green Bank radio telescope in West Virginia. The tone was to serve as a beacon; the rover would not be transmitting data.

Spirit continued to take panoramic-camera images for the 360-degree "Bonestell panorama." The rover recharged its battery on sols 1485, 1487, 1488, and 1490 (March 7, 9, 10, and 12, 2008). On recharge days, the rover typically conducts minimal science activity and does not relay Eartbound data to the Odyssey orbiter as it passes overhead.

A complication in Spirit's current circumstances is that the mast holding the panoramic and navigation cameras is partially obscuring the X-band, high-gain antenna that Spirit's handlers use to command the spacecraft from Earth. Engineers have been experimenting with "parking" these instruments in positions that minimize this obscuration.

Spirit is healthy and all subsystems are performing as expected. The latest available power readings from sol 1489 (March 11, 2008) showed power at 254 watt-hours (100 watt-hours is the amount of energy needed to light a 100-watt bulb for one hour).

Sol-by-sol summary:

To conserve energy, mission planners have restricted the number of sols on which Spirit receives direct-from-Earth instructions via the rover's high-gain antenna and transmits data to Earth via the Odyssey orbiter. Spirit continues, on a daily basis, to monitor atmospheric dust levels with the panoramic camera, check for drift (changes with time) in the miniature thermal emission spectrometer, and survey the sky and ground with the instrument. In addition, during the past week, Spirit completed the following activities:

Sol 1484 (March 6, 2008): Spirit brushed the surface of Wendell Pruitt, acquired a single-frame, lossless-compression (high-resolution) image of the area in front of the rover with the navigation camera, and took stereo images with the front hazard avoidance cameras.

Sol 1485: Spirit acquired super-resolution images of half of Lucius Theus and recharged the battery.

Sol 1486: Spirit surveyed the horizon and took spot images of the sky for calibration purposes with the panoramic camera. Spirit monitored dust on the rover mast and acquired a 2-by-2-by-5 stack of stereo microscopic images of Wendell Pruitt. The rover acquired a single-frame, lossless-compression image of the area in front of the rover with the navigation camera as well as stereo images with the front hazard avoidance cameras.

Sol 1487: In the morning, Spirit acquired column 2, part 3 and column 3, part 1 of the full-color Bonestell panorama, using all 13 filters of the panoramic camera, then spent much of the Martian day recharging the battery.

Sol 1488: In the morning, Spirit used the navigation camera to take images of the sky (called "sky flats") for calibration purposes and used the panoramic camera to take super-resolution images of Theopolis Johnson. The rover turned the panoramic camera mast assembly to prepoint the camera, then recharged the batteries.

Sol 1489: Spirit placed the alpha-particle X-ray spectrometer on Wendell Pruitt and, after relaying data to Odyssey, acquired data with the instrument.

Sol 1490 (March 12, 2008): Spirit acquired column 3, part 2 of the Bonestell panorama and recharged the batteries. Plans for the next morning called for Spirit to acquire thumbnail panoramic-camera images of the sky looking starboard (to the rover's right) for calibration purposes.

Odometry:

As of sol 1489 (March 11, 2008), Spirit's total odometry remained at 7,528.07 meters (4.68 miles).

sol 1478-1483, Feb. 29- Mar. 05, 2008: Work Continues on 360-Degree View of Spirit's Winter Perch

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