Mars Exploration Rovers Update: NASA Approves Extended Missions Spirit & Opportunity Receive Upgrades
Posted by A.J.S. Rayl
09-04-2004 12:00 CDT
As the Mars Exploration Rovers achieved new milestones on the Red Planet this week, NASA approved a plan to extend the missions for both Spirit and Opportunity to mid-September.
"The project submitted a very compelling proposal to NASA for extending the mission of the two rovers and NASA approved it," announced Firouz Naderi, manager of Mars exploration at the Jet Propulsion Laboratory (JPL), at the weekly news briefing. The five-month extensions will approximately triple the lengths of the missions, added Naderi.
Spirit -- the first of the twin robot explorers -- fulfilled her '90-day warranty' and met all the success criteria set for her prime mission at Gusev Crater by the time she went to 'sleep' last Sunday night. Since Opportunity landed three weeks after Spirit, that rover is not scheduled to complete her prime mission April 26. [Each Martian day, or sol, lasts about 40 minutes longer than an Earth day.]
NASA's approval of the extended missions provides $15 million to cover the costs of operating the rovers through September. That allotment, officials noted, more than doubles the exploration gained for less than a 2% additional investment, providing the rovers remain in working condition. The total cost of the rovers, through their extended missions, is now about $815 million.
Three factors or "constraints on the lifetime" of the rovers played into the decision to extend the missions for five months. Naderi explained:
- One is the amount of energy that can be taken in by the solar array panels, which helps power the rovers. Controllers now estimate that the rovers have lost 20% of their intake ability due to dust accumulation, (although that has yet to be verified). In addition, as the fall season continues on Mars, the Sun will be getting increasingly lower and lower in sky, and "the combination of two will limit the energy intake."
- The second constraint is "the thermal cycle during the night and day" -- the heating required for the rovers' instruments to survive Mars' colder-than-cold nights "will eventually take [their] tolls."
- The third constraint is simple mechanics. The rovers are "very motorized vehicles," and while some of the motors will continue on, others will no doubt "wear out after a while."
During the development of the rovers, however, the various components were each tested to about 270 sols worth of thermal cycle, and the motors were produced to run for 10 million cycles, so even with the constraints considered, Naderi said: "We believe we are 'good to go' in terms of that for about mid-September -- or about 250 sols." The JPL executive tempered that optimism with the words of caution those in the space exploration business know only too well. "While we have all the expectations, we look at this extended mission as purely bonus science -- it's gravy really," Naderi said. "It may go to 250 and well beyond, or, something may happen in June and one or both of the rovers could come to a dead stop."
No one at JPL seems to be anticipating anything but many bright sols ahead for the rovers, even though the washing machine-sized robots are operating under extremely harsh conditions. What if -- like Energizer™ bunnies -- they just keep going and going? "If we have healthy rovers at the end of September, we'll entertain another extended mission," Naderi responded.
Although the lifetimes of Spirit and Opportunity are, right now, unknown, one thing the MER team does know is that a conjunction begins on Mars September 13. That was another factor that played into the choice of a mid-September endpoint for the extended missions. During this conjunction, Mars, the Sun and the Earth all line up, with the Sun between the two planets and effectively blocking communication antennas; therefore, the mission will have to pause for a week to 10 days around that time frame anyway.
As the space agency brass considered the MER team's proposed extension of the rover missions this week, up on Mars both Spirit and Opportunity were meeting "some real critical milestones," reported Jennifer Trosper, Spirit mission manager, at the news briefing. Spirit woke up Monday morning just like she has every morning since landing, and roved seamlessly into her extended mission, making some good tracks to the Columbia Hills. On the other side of the planet, at Meridiani Planum, Opportunity began her journey to Endurance Crater with a fast dash Monday, setting a new driving record for most logged mileage in a day -- 328 feet [100 meters], blowing out Spirit's record of 165 feet [50.2] meters, set just two days before, on the drive that took her odometer past the 600-meter or 1,969-foot goal needed to complete the mission success objectives.
In their first three months on Mars, the rovers have returned remarkable science results that will keep scientists busy for at least a decade. The most dramatic discoveries have been Opportunity's findings of evidence of a shallow salty sea in Meridiani Planum's past. Spirit also found hints of ground water and team is now anxious to get to the Columbia Hills to uncover the clues to the water story at Gusev they believe are hidden there. The reason Gusev was chosen as a landing site was in part because many Mars scientists believe it once featured an ancient lake.
With their extended missions, Spirit and Opportunity now have new goals. For Spirit, the number one objective is to reach the Columbia Hills and find the geological clues to Gusev's water story. Opportunity's main goal is to seek geologic context for the outcrop in the Eagle Crater by examining other outcrops in Endurance Crater, and elsewhere. Other science objectives for both rovers are to continue atmospheric studies at both sites to better refine Mars' seasonal cycle, and to calibrate and validate data from the Mars orbiters -- Odyssey and Mars Global Surveyor (MGS) -- for additional types of rocks and soils examined on the ground.
Beyond science, the rovers also have three new engineering objectives: to traverse more than a kilometer [0.62 mile] to demonstrate their mobility technologies; to characterize solar-array performance over long durations of dust deposition at both landing sites; and to demonstrate long-term operation of two mobile science robots on a distant planet with a human ground team operating on Earth time.
During the past two weeks, the two rover teams at JPL have switched from Mars-clock schedules back to Earth-clock schedules, which officials anticipate will be less stressful and more sustainable over a longer period. "The real challenge is ahead of us -- the issues with Earth time is -- as Mars data comes later and later in the Earth day, you have less time to make changes to your plan that need to get up to rover," Trosper explained. "But we've made templates, and we've made process enhancements. Actually, the time it took us at the beginning of the mission to plan a day was 16 hours and we're down to about 10 hours now, so we've really improved the processes, and we'll work to improve that even more."
Throughout the weekend, science team members will be able to take a much-deserved break as Spirit and Opportunity receive the much talked-about new flight software. In fact, the team began uploading the new software to Spirit on Thursday, and will begin the process on Opportunity Saturday.
The team is uploading new flight software on both vehicles to gain "three capabilities we'd like to have," Trosper said.
- One is the Deep Sleep mode option that they will put on Opportunity to mitigate for the energy loss from the errant heater on the instrument deployment device (IDD);
- A second feature of this new software is an enhanced auto navigation program that will allow the rovers to more efficiently identify and guide themselves around obstacles and hazards, "mostly for the Spirit site, where we have hazards," Trosper noted;
- The third new feature is an add to the software to insure that neither rover ever experience the breakdown in the flash memory system that all but shut Spirit down for a couple of weeks. "There are some changes in the software that would allow a lot of the debugging that we did from the ground to actually happen automatically," said Trosper, "allowing the software to get itself into a stable state."
The process of uploading the software will take four days. "We're not actually changing the software, we're just loading these files," Trosper explained. They won't be using the orbiters to relay the software, but will instead rely on the direct communications link using the rovers' high gain antennas (HGAs). "We have the vehicles set up so that for six hours a day, the high gain antenna, which can get 2000 bits per second, will track the Earth all the way across the Martian sky, and during those six hours we will be uplinking files."
Once the team has verified that all the files are there, then, Trosper continued, "we will actually build the flight software" on the rovers. "That's what we'll do Monday on Spirit, and then Wednesday for Opportunity." Once the software is built and installed, the team will shut down the rovers. "And when we wake back up 15 minutes later, we'll be on the new version of the flight software."
It may seem risky to change anything on two almost perfectly functioning rovers on Mars, but on the MER mission uplinking software has been a "fairly routine" procedure, Trosper noted. "We loaded the entry, descent and landing software on the cruise vehicles as they were flying toward Mars in early December . We loaded the final version of the flight software onboard about a month prior to launch, and the load itself we've done many times. In the same way, that it's risky to change the state of the spacecraft at all, yes, there is risk associated with this. But we're confident that the software will perform all the functions we need it to. We wouldn't put it up there if we didn't think it was going to work."
Although the science team members get to take a bit of break during what is, essentially, a science 'stand down' for the four days each rover will be getting its new flight software, the rovers won't really be standing down at all. "During the stand down -- as the flight software is being uploaded -- on a 'best efforts' basis we'll be doing Mössbauer measurements [of nearby targets] during the day and APXS measurements in the evening of the air," said Ray Arvidson, deputy principal investigator.
The science team is hoping that the measurements of air will provide them with a calibration of instrument 'noise.' "What that will do when we make measurements subsequently, and also look at the data we acquired, is allow us to back out the trace elements, and give us more information about the chemistry than we would have otherwise."
SPIRIT FROM GUSEV CRATER
Sols 90 - 96
When Spirit shut down last Sunday night, the robot field geologist also brought her primary mission of 90 days to an end, resting comfortably, if only for a night, on her laurels. The rover had checked off the final two objectives on April 3 - Sol 89, and April 5 - Sol 91, when she exceeded 600 meters -- 1,969 feet of total drive distance and completed 90 operational days after landing on Mars.
"Spirit had a huge week with the completion of the prime mission on Sunday," Trosper said as she reviewed the rover's journey from egress around an errant airbag last January to uncovering hints of water at Mazatzal last week, providing the narrative 'soundtrack' to a video edited together by some of the MER flight team called 90 Sols in 90 Seconds presented at the news briefing.
Looking back, Trosper said that even when the flash memory-management problem on the rover caused trouble for two weeks, she had confidence Spirit and the operations team could get through the crisis and reach the 90-sol benchmark. "We never felt it was over, but certainly when we were getting absolutely no data from the spacecraft and were trying to figure out what happened, we were worried," she said.
Trosper had been less confident about Spirit's prospects for reaching the criterion of 600 meters by Sol 91, given the challenging terrain of the landing area within Gusev Crater. With but a day to spare, however, Spirit lived up to her name and accomplished that goal, setting a short-lived record for Martian driving, with a single-sol distance of 165 feet [50.2 meters] that pushed her odometer total to 2,024 feet [617 meters]. (Two days later, Opportunity would shatter that record with a 328-foot [100-meter] drive.)
For Spirit, Monday - Sol 91 began much like any other day. She started her work day by taking some remote sensing observations of the sky and ground, as well as navigation camera (NavCam) images of the landscape to the east. Then, the rover completed miniature thermal emission spectrometer (mini-TES) ground surveys and took some pictures of the sky and ground with her panoramic camera (PanCam). After a short nap, Spirit woke to take some pre-drive pictures with her PanCam, including a super-spectral look at an interesting spot just in front of her.
Early that Martian afternoon, Spirit began a 4.4-foot [1.35-meter] drive to get closer to a rock called Route 66. After analyzing the instrument deployment device's (IDD) workspace area with her hazard-avoidance camera (HazCam) images and a stare by mini-TES, the rover made a quick adjustment of 2.6 feet [0.8 meter] to put her in the perfect position to examine Route 66 up close.
Spirit spent the afternoon taking a systematic soil survey with her PanCam, and then a 13-filter image of the Columbia Hills, her ultimate destination. The rover then acquired some mini-TES data of the soil locations.
The robot field geologist awoke on Sol 92, took some early morning PanCam sky and ground images, then turned the camera on the capture and filter magnets. Following a short mid-morning nap, around 12:30 p.m., Mars local solar time, the rover opened the doors of her APXS and took three observations of each magnet. The rover later placed her Mössbauer spectrometer on the capture magnet and began an integration.
That afternoon, Spirit completed her coordinated observations with the thermal emission spectrometer instrument (TES) on the MGS orbiter. The observations involved mini-TES pre-flight, simultaneous, and post-flight sky and ground measurements. Spirit also collected a PanCam opacity observation, an image that should give scientists an idea of how dense the dust is in the local atmosphere.
Shortly after being woken on Wednesday, Spirit heated up her high gain antenna (HGA) in preparation for the new flight software upload to begin on Thursday, then got work on the last day for newly planned science observations before the four-day stand down.
The rover took some calibration measurements and NavCam images of the APXS' placement on the magnet. Around 10:30 a.m., Mars local solar time, Spirit moved her IDD out of the way to take some HazCam pictures of Route 66. The rover then placed her Mössbauer spectrometer on the rock for a four-hour integration. During the integration, the rover captured the memory of her current location with a PanCam mosaic of the vista toward the Columbia Hills, and of her tracks.
After a short nap, Spirit took mini-TES observations of her tracks, and of the new rock targets, Everest and Pisa. Following the completion of her Mössbauer spectrometer integration, Spirit then pulled out her APXS and pointed it up to the sky to acquire air measurements. The IDD will remain in this basic position during the flight software load time period, allowing for long integrations of the Mössbauer spectrometer on Route 66 and the APXS of the air and sky.
On Thursday, rover engineers woke up Spirit and instructed her to perform a sunrise imaging operation, then the MER team began uploading the new flight software. The process will continue, as noted above, through Sunday - Sol 97. Throughout the duration of her software upgrade, the rover will remain parked in front of Route 66.
At the same time, the Mössbauer spectrometer will be integrating on the rock as planned, an official release noted Friday, and the APXS will be taking measurements of the air and sky. Once the process is finished, the team plans to 'reboot' Spirit on Monday April 12 - Sol 98, at which point the rover will be given new life.
In coming sols, Spirit will keep on truckin' to the Columbia Hills, stopping along the way to check out the many light-toned rocks in her path, chasing the water story. "Light-toned rocks are interesting [because] many of us feel they speak to water, in some way shape or form in terms of coating," explained Ray Arvidson. "The interesting point is the light-toned rocks were coated after they were shaped by wind, so this is not a process that goes back billions of years but is a more recent process."
There is, not surprisingly, debate within the team as to when the process might have happened. "For example, and this is speculation -- occasionally the spin axis of Mars will get as high as 45-degrees, and if that's the case, then the equatorial regions can ice over," Arvidson suggested. "So if you have snow and ice at the craters, you have water in contact with the rocks and soils, and you might get a little bit of melt -- kind of intergranular melt -- and that could put the salts, the sulfates that we think make up the light-toned material on the rocks, and it might also explain why all the soils are crusty. All the soils we've looked at with Spirit are cloddy or crusty at the surface, down to a depth of a centimeter or so. Again, it may be associated with a little bit of salt or a little bit of iron oxide that may [have been] mobilized when the conditions were a little bit wetter."
The process of "getting these snowstorms and ice deposits occasionally, quasi-periodically through geologic time," is, Arvidson added, an "interesting" way of having water infiltrate a region, "because the evidence leaves -- when the obliquity comes back to normal, the volatiles go back to the polar regions." This concept is, he stressed, "speculation at this point."
In images that show Spirit's route to the Columbia Hills, the light-toned rocks "tend to be low to the ground and they're everywhere," Arvidson continued. "So this process is ubiquitous across the plains. We'll investigate those [rocks] and we'll investigate the soils and the extent to which they're crusty, and we'll stop and explore new features. But there's a compelling feeling within the team to get on with business and get to those hills."
Answers and clues, they are confident, can be found there. "That should tell us if we are looking at a whole chunk of the ejecta associated with impact when Gusev formed or if we're looking at volcanic rock that's been eroded, or if we're looking at the sedimentary section that we've been searching for to tell us about the marine history of [water] flow history of this place."
OPPORTUNITY FROM MERIDIANI PLANUM
Last weekend, Opportunity completed her study of Bounce Rock with the various instruments on her arm. She spent what time she had left on Sunday checking out soil targets with her MI and Mössbauer spectrometer, and preparing for her 750-meter trip toward Endurance Crater.
To get Opportunity ready for her first big day of roving toward Endurance Crater, the rover team woke up their charge with a classic cruising tune, the Grateful Dead's "Truckin." They then had the rover conduct one more maneuver on Bounce Rock -- which engineers lightheartedly called a 'crush and go' -- which really meant she roved right over it.
There was a reason behind this rover 'madness.' In order to gather more data about the rock's hardness, the intentional drive over Bounce was an attempt to fracture it so the scientists could see what's inside. [All Earth drivers are advised: Do not try this on your home planet.]
While the science team awaited images from the rover's rear HazCam to see if they even left a mark, Opportunity put it into gear and finally took off for good from the rim of her Eagle Crater landing-site. Actually 'took off' might be an understatement of sorts -- the rover cruised for some 328 feet [100 meters] to a target crevice area dubbed Anatolia, shattering the record Spirit had set just two days before when she roved 165 feet [50.2 meters]. It is only the first of what the MER team anticipates will be many long drives across the "parking lot" like surface of the Meridiani Plains.
Anatolia is an area that sits along a winding crack in the plains of Meridiani Planum, defined by deep impressions in the sand sprinkled with Eagle Crater-like rocks. Once she arrived, Opportunity drove around the winding trough in a long dogleg pattern, conducting some remote sensing studies of the crevice along the 164-foot [50-meter] drive to her ultimate position for the sol, at the northeast extreme of Anatolia.
On Thursday - Sol 73, Opportunity excavated a trench and placed the Mössbauer spectrometer on the trenched area, Arvidson informed at the news briefing. The plan now calls for the rover to stay there until the flight software upload is complete. "At Meridiani Planum, Endurance Crater is our long-term objective 750 meters away," he reminded. "On a 'best efforts' basis, we will try to get APXS measurements of the air for calibration, and if we can afford to, some Mössbauer data on the soil. Then, when we come back to operations next week, we'll finish the trench work," he added.
"One of the key observations that we'll have here is the extent to which the morphology, the chemistry, and the mineralogy of this outcrop looks similar to what we've seen at Eagle Crater," Arvidson pointed out. The team will be looking to find out if the chemistry of the outcrop "again speaks to water," and if so, how extensive the water environment might have been.
"Another interesting point is that the trough is probably fractured," Arvidson informed. Not only that, but it's apparently, he said, "a fractured system that's been active, in a relative sense, faster than wind has been able to pile material into it." That, he added, is "wasting this kind of gravity-driven motion of the sediment into the trough that's filled it in." Although they don't know how young the system is or the rate at which it operates . . . it's operating faster than the processes that bring the sediment in, so it's fascinating," he contended.
Despite the desire of some to stay and thoroughly check this trough out, Arvidson reiterated that the strong desire "to do these hundred-meter drives and get to Endurance Crater and what we think is going to be a thick section of sedimentary crop to explore."
If all goes as planned this weekend, the rover team will begin uplinking the new flight software to Opportunity on Saturday - Sol 75, with a 'reboot' scheduled for Wednesday morning.To be continued. . . . next week.