As Spirit continued her journey to the Columbia Hills in Gusev Crater, Opportunity cruised into her extended mission at Meridiani Planum this week, marking the milestone of the rovers' Martian adventure -- full mission success.
Opportunity finished her 90th Martian day of surface operations Sunday, April 24, roving seamlessly, like Spirit three weeks before her, into the extended phase of her journey on Monday.
For the Mars Exploration Rovers team, everything the two rovers examine, discover, study, and uncover from here on out is a bonus to the data the twin rovers have returned during their first 90 days. Earlier this month, as Spirit passed her primary mission mark, NASA approved funding to extend the operations of both rovers through September.
"With the completion of the prime mission on Opportunity, we have either completed or exceeded all of our surface operation, duration, traverse, payload operation, and science site experimentation [objectives] to have successfully achieved full mission success for the project," announced Opportunity Mission Manager Matt Wallace, at the latest MER news briefing Wednesday at the Jet Propulsion Laboratory (JPL), where the rover's assembly began just two years ago. "Now, both vehicles are in their extended mission, which we hope will be long and just as exciting as the primary mission."
In her first 90-days, Opportunity drove a grand total of more than one-half mile [811.57 meters] and sent home 15.2 gigabits of data, including 12,429 images. The rover -- which was the first to be built and the second to be launched -- logged what is still the longest drive by a rover on Mars in a single sol -- 462 feet [140.99 meters], as well as the second longest, 328 feet [100 meters]. Along the way, the robot field geologist also RATed five different rocks, dug three trenches, and performed a few 'scuffs' as well. Wallace couldn't help but note that Opportunity's accomplishments make for "a rather impressive 3 months on the surface of Mars."
Now, both Spirit and Opportunity are roving forth in pretty good health. Although the rovers have experienced a few burps and hiccups along the way -- the team had to deal with a memory problem that put Spirit out of commission for about a week and a half and still has to deal with the errant heater on Opportunity's instrument deployment device that remains stuck in the 'on' position -- "there are no new engineering issues on either of the vehicles," reported Wallace.
"We built the vehicles with every bit of experience and reliability and quality we could build into them, and it's not unusual for the vehicle problems to show up early in the new environment, either in the space environment or surface environment, and then for things to stabilize," Wallace elaborated. "On the other hand, these are extremely complex vehicles and somewhere along the line, that's something that has to be factored in."
Another reality that must be factored in is the inevitable dust accumulation on the solar arrays, which serve as a primary source of rover power. Eventually, the dust build-up will coat the arrays, blocking them from utilizing the photon power of the Sun. New environmental estimates of the dust accumulation on both Spirit and Opportunity have revealed that the "degradation is a little steeper than we had thought we might be seeing [at this point], based on some earlier data," Wallace said. "We're going to keep a close eye on that and continue to track it and trend it, and see what the implications are down the road, but there is nothing [life-threatening] in the near term. From a health standpoint of the subsystems, the vehicles are both very healthy." And, so far, he added, "things are looking very good."
The rover team members are looking pretty healthy, too -- at least healthier than when they were a few weeks back when they were in the throes of living on Mars time. Wallace and science team members Scott McLennan, of State University of New York, Stony Brook, and Dave Des Marais, of NASA Ames Research Center, all agreed that everyone was happy to be back on terra firma time. "It's a wonderful thing being on Earth time again - you feel like you've returned from someplace -- like Mars -- and you're back home again," Wallace offered. "It is just wonderful to see sunshine come through the windows of our work areas," McLennan added, as he seconded Wallace's emotion.
"There's an interesting dichotomy for people who live here and people who live elsewhere," mused Des Marais. "That is, people who live here have their families and Mars time is really hard on them. Those of us who are from elsewhere were are already from elsewhere and so why not go the rest of the way to Mars?" he explained, drawing chuckles and smiles from those attending the press conference. "Overall, for everybody's physiology, going back to Earth time has helped a lot. We really couldn't have done this at the beginning of the mission, because of all the complexities of operating these rovers right after landing. It took us awhile to get to a smoothness of operation where we could do these compressed schedules. Having achieved that now, we're squeezing everything we can out of these rovers everyday."
The rovers seem to be complying happily, and the new flight software uploaded about three weeks ago is helping to dramatically improve their mobility, as well as expand the options for the MER team to plan explorations. In fact, Spirit and Opportunity have driven farther in April than in the previous three months combined.
As Opportunity closes in today on her major destination, Endurance Crater, the focus for Spirit right now is to log as many miles as possible to beat down the distance to her ultimate target, the Columbia Hills, still about a mile away. "It's quite a schedule to stick to, and the question now is -- how much real good science can we put into these observations as we go across?" said Des Marais.
SPIRIT FROM GUSEV CRATER
Sol 103 - 114
Since leaving Bonneville Crater on Sol 88, Spirit has been making tracks to the Columbia Hills, symbolic now for the names with which they have been unofficially christened by NASA. While the complex itself is named for the space shuttle Columbia, the individual hills are named for Rick Husband, Willie McCool, Michael Anderson, K.C. Chawla, David Brown, Laurel Clark, and Israeli astronaut Ilan Ramon, the seven astronauts who lost their lives when the orbiter broke up on reentry in February 2003.
Evidence from orbital images and data, as well as the size of these hills indicate that these rock layers are much older than the volcanic plain Spirit has been crossing thus far. And, hidden inside those layers, the scientists believe, may be the clues they need to determine the role that water might have played in the history of Gusev Crater.
To date, Spirit has journeyed more than three-fourths of a mile [1.2 kilometers], with another mile or so [1.8 kilometers] to go before she reaches the base of these highlands.
Making an analogy to a train line, Des Marais said that Spirit is, essentially, on an "express route" that includes some whistle-stops along the way. "We have the objective of traversing the plains [of Gusev], because we want to 'get to them thar hills,' but we are also [conducting] some geology as we go along."
During the last week and a half, Spirit has roved from the rock Route 66, which she 'engraved' with a six-position RAT or 'daisy' on Sol 99, to Missoula Crater, where she conducted a good deal of remote sensing. Along this part of the "express route," the rover took pictures with her panorama camera (PanCam) and navigation camera (NavCam), and collected compositional data with her suite of spectrometers -- the Mössbauer spectrometer, alpha particle x-ray spectrometer (APXS), and mini-thermal emission spectrometer (mini-TES) -- and her microscopic imager (MI).
While Spirit will be systematically surveying the soils, rocks and other features on the plain as she continues toward her ultimate destination, the main goal is to get to the Columbia Hills, so the scientists are having to make some fast and hard decisions day-to-day about what they can afford to inspect closely.
"We know that we can't use all of the wonderful instruments on [Spirit's] payload on every day of operation, so we've adopted a sort of cadence," said Des Marais. "We call it a quartet of sols, where every four sols we make sure we have rotated through use of the instruments, but also more importantly, rotated through many of the science objectives, many of the observations we'd like to make. For example, once every four sols, we'll put that arm down on the ground and do a characterization of the soil [where] we happen to stop. At the end of this traverse, we'll have a sense of any trends in the composition of the soil that might have occurred. Likewise, with the camera and the mast, we'll do observations to look around at the geography, how the terrain changes as we get closer to, and further from, the [various] craters."
In addition, since Mars is currently undergoing a seasonal change from summer to fall, the science team is also conducting systematic atmospheric observations at sunrise and at other times during the day, "to track the changes that occur," explained Des Marais. "If we do this to the beat of a set of observations every four sols, by the time we get to the Columbia Hills, we will have made on the order of 10 of these sets of observations, and we'll have a very nice characterization of this terrain -- and, perhaps, make some interesting discoveries along the way."
En route to the Missoula Crater whistle-stop, Spirit spent Monday, April 19 - Sol 104, conducting remote sensing, including taking PanCam images of Mars' moon Phobos as it transited across the Sun, and during the daytime another video search for dust devils. Although the team knows the dust devils occur with some frequency at Gusev, they have not yet caught one on video. "They're out there and they have been observed elsewhere on Mars, but we haven't made any observations of them yet," said Des Marais. "With this traveler's capability we have on Spirit, our dust devil operation can occur once every four sols or so, and part of the secret to catching one of these devils is to make a commitment to a periodic set of observations. Once we do that our chances for catching one will go up."
As Spirit moved in on Missoula, she roved "off of one ejecta blanket and onto another," said Des Marais. Located southeast of Bonneville Crater in the general direction of the Columbia Hills, Missoula Crater is slightly smaller, but is a significantly older crater than Bonneville. "As a result of that, we can see differences that could be attributed to the aging of a crater," he noted, including rocks that "are broken down more."
The rover spent most of Wednesday, April 21 - Sol 106, performing remote sensing of the inside of the new, old crater, acquiring mini-TES measurements, and PanCam panoramas and NavCam images, along with some PanCam pictures looking back toward Bonneville Crater. The team found familiar drift deposits in Missoula -- the wind blown deposits that tend to accumulate in these craters. Just as in Bonneville, the deposits are on the upwind side, and have the same "characteristic features and composition," said Des Marais. "Therefore, they represent a replicate measurement of what we observed at Bonneville."
On Thursday, April 22 - Sol 107, Spirit took some atmospheric and cloud observations with her PanCam and mini-TES, then used the PanCam to home in on three specific targets at Missoula -- Gratteri Piazza, Wallula Gap, and Clark Fork. That done, the rover took off to the southeast, driving some 242 feet [73.8 meters] and jogging around a sandy hollow to the east of Missoula. From that position, the robot field geologist acquired additional PanCam and NavCam images.
During the weekend, Spirit roved on, stopping at an area called Site 35. On Sunday - Sol 110 she took MI pictures of an area of soil called Waffle Flats, then placed her Mössbauer spectrometer on that spot for a 90-minute integration. With her Mössbauer working, the robot field geologist took PanCam and mini-TES observations of the area for both localization and science purposes, reaffirming her ability to multi-task.
Spirit then stowed her instrument deployment device (IDD) and began a 262.5 - foot [80-meter] drive, half of it directed by rover planners and half of it with the rover using her autonomous navigation software. During the autonomous navigation portion, she detected a hazard; consequently, she did not complete the final short-drive that had been planned at the end of the journey. Images from the front hazard avoidance camera, however, showed no visible sign of a hazard, leaving rover controllers with a bit of a mystery to investigate.
After acquiring some more PanCam images of her surroundings and the drive direction, and completing some atmospheric science with the PanCam and mini-TES, Spirit revved up her engine again on Monday, April 26 - Sol 111, and successfully drove 199.5 feet [60.8 meters] toward her ultimate destination in the hills to the east of the Columbia Memorial Station, the landing site named by the MER team in remembrance of the shuttle tragedy. The rover then took some more pictures with her PanCam and NavCam of the drive direction, and ended her day by taking some mini-TES observations of the soil in front of her, and a coordinated mini-TES and PanCam study of the atmosphere.
Spirit slept in on Tuesday, April 27 - Sol 112, conserving her energy for an afternoon drive. Beginning her day at 11:45 a.m. Mars local solar time, the rover first gathered some soil and atmospheric observations with her mini-TES and PanCam, and then hit the Gusev highway. Her updated autonomous navigation software proved its worth once again this sol. During a long auto-navigation segment, the rover encountered a hazard and was able to back up and find a way around it with relative ease. Actually, Spirit continued to drive backwards toward her intended goal point, using the rear hazard avoidance cameras to navigate the way. When the allotted drive time was up, she turned back around and made one last short drive to her resting place for the night. Spirit's odometer records backwards and forwards driving and so logged another 290.7 feet [88.6 meters] for the sol, although the true distance traveled toward the Columbia Hills was actually about 197 feet [60 meters].
"The R-9 flight software delivery that we sent to the vehicle a few weeks ago has been aiding tremendously," Wallace said at the press conference." We're able to drive about three times farther than we were able to drive with previous software capability," even with the challenging landscape. The terrain at Gusev is a mixture of soft sand and depressions, craters, small rocks and large rocks, and rock fields, and is not easy to navigate. Even so, Wallace said, "the vehicle has been performing beautifully and is making good progress toward the Columbia Hills." In fact, he added, "in just the last few days we have done drives of 60.8 meters [.037 mile] and the longest drive to date at Gusev Crater [Tuesday] of 88.5 meters [.054 mile]." Those drives pushed Spirit's total mileage to .8 mile [1,315 meters].
On Wednesday, April 28 - Sol 113, Spirit was woken up earlier than normal, at 9:00 a.m. Mars local solar time, to do some morning atmospheric science. One objective of the early sky scan was to image the morning clouds with the PanCam. The rover then began a detailed examination of a soil spot called MayFly. During her inspection of the area, Spirit took PanCam and mini-TES images in parallel, conducted a two-hour Mössbauer spectrometer integration, and finished off with a close-up look with her MI. She then stowed her IDD to prepare for digging a trench.
While the rover's planners intended for Spirit to use her wheels to dig a trench from her position at the MayFly spot, hazard avoidance camera images of the area revealed a potato-size rock that could have potentially fallen into the wheel hollow in the process. Rather than take that risk, the controllers decided to back the rover up 3.9 inches [10 centimeters] to a clearer spot. After the final positioning, the robot field geologist used her wheels to dig a 2.4-inch [6-centimeter] trench. She finished the sol with hazard avoidance camera images of the trench, which were used to plan for the instrument work she conducted on Thursday, April 29 - Sol 114, using her Mössbauer, APXS, and MI.
During the last couple of weeks, Spirit has been moving from an area dominated by material dispersed by crater-forming impacts into an area with fewer rocks. "We are transitioning now into a geologically different region . . . a different geologic province. Nothing could be more striking evidence of this than the view ahead of a landscape that has fewer and smaller rocks than the region explored so far," Des Marais said.
Scientists will be using Spirit's observations at ground level to better define and describe the region's geology compared to observations from orbiting spacecraft, something that could improve interpretation of orbital data for the whole planet.
"One of the major goals that we're going to try to achieve as we make this traverse is to ground truth, to see what's really there to compare with what we see from orbit, and to provide some real meaning behind the orbital observations that are made," said Des Marais.
As of today, Spirit still has about a mile [1.8 kilometers] to go to reach the Columbia Hills. That should take another 50 sols or so, whistle-stops included, so that the rover should pull up to the western base of the hills by mid to late June. "The important point for this traverse is that we're going to be favoring much more remote sensing, on-the-fly observations compared to the detailed arm work we had the luxury of doing in the vicinity of Bonneville Crater," pointed out Des Marais. "Our challenge is to do a reasonable job of characterizing what's there, recognizing that we've got this schedule we have to keep."
OPPORTUNITY FROM MERIDIANI PLANUM
Sols 83 - 94
Following a fairly extensive study and trenching of the Anatolia fracture site, Opportunity hit the Meridiani highway and has spent much of the last week and a half or so trekking to and examining Fram Crater. About 26-feet [8-meters] in diameter, Fram Crater is one of the four chosen waypoints on the rover's route to the much larger, 262-foot [80-meter] diameter Endurance Crater, her major destination.
On Monday, April19 - Sol 84, the rover conducted some remote sensing observations and analyses with her MI and Mössbauer spectrometer, and then continued her journey with an 82-foot [25-meter] drive to Fram Crater, taking images of her surroundings on the way. The following day, rover engineers woke the robot field geologist with the song "Take Me Out to the Ball Game!" by Jack Norworth, in honor of all the baseball-related target names that had been chosen. After some morning remote sensing, Opportunity moved up to the rim area of Fram Crater, then used the instruments on her IDD to more closely examine a rock target, dubbed Pilbara, to uncover its geochemistry and mineralogy. Then, on Wednesday, April 21 - Sol 86, the rover took out her rock abrasion tool (RAT) and went to work on Pilbara so the team could look into the interior of the rock.
"We had hoped we would find an in-place outcrop, but in fact what we did find was [an outcrop] that was very disrupted by the impact process," said science team member Scott McLennan. "On the other hand, it seems to be quite a bit fresher, so we gleaned that this impact was younger than the one at Eagle Crater," where Opportunity landed January 24. Still, the team didn't see much there "that was entirely different," he added. So, while they did decide to conduct some detailed work on Pilbara, the lack of unique findings at Fram overall, and "the fact that it was so disrupted," McLennan said, influenced the team's decision not to spend a whole lot of time there.
Meanwhile, the MER team has continued to 'tweak' the rovers' systems and instruments, and is now employing a new, more aggressive approach it developed for commanding the RAT. In the event of a stall, the tool is now programmed to retreat from its target and attempt to grind again. This allows the grinder to essentially reset itself instead of aborting its sequence altogether and waiting for further commands from rover planners.
As a result, Opportunity broke yet another record, grinding for nearly two-and-a-half hours to produce an impressive 0.28-inch [7.2 millimeter] hole in Pilbara. It was, informed McLennan, "a rather spectacular, very successful RATing . . . the deepest RAT we've had so far on the mission."
The plan for the rest of that sol called for placing the APXS on the new hole to determine the elemental composition of the exposed area. When the drivers determined that the rover position would not allow for a safe integration of the instrument, however, they amended the plan so that the rover would back up and reposition herself for a safe placement of the spectrometer after the RAT completed the grind.
Even before the APXS integration, though, the science team members found that the rock's interior was 'studded' with the now famous 'blueberries,' the small, iron-rich spherules that are one part of the evidence for past water in the region.
On Thursday, April 22 - Sol 87 the rover completed the collection of the desired compositional information from Pilbara, with Mössbauer and APXS integrations, and MI close-ups images of the new hole. On Friday - Opportunity's Sol 88, the rover team decided that while Fram Crater was an intriguing depression, the potential hazards and the time involved in investigating it made it more of a tour stop than a destination. So, with the goal of Endurance Crater topping the agenda, the rover finished her investigation of Pilbara, with a final Mössbauer measurement, and a mini-TES of the recently carved RAT hole.
The set of activities that Opportunity performed on Pilbara and around the rim of Fram Crater offer, McLennan said, a look at representative rocks and soil from the area, which are already being compared to the Eagle Crater rocks and soils. "The chemistry and mineralogy turn out to be almost a dead ringer for materials we found at Eagle Crater," he said. That noted, there are, he added, "some features, such as the laminations of the bedding features within the material" and "some of the rocks' surfaces," which are, "in some places a little bit different than what we had seen at Eagle Crater."
Although the team has decided not to go into Fram, they will be looking for these same kinds of differences as Opportunity gets closer to Endurance, McLennan said. "And if we don't see this kind of material [anywhere else], we have thought about possibly coming back," he said. At the moment, however, there are no plans to return to Fram.
Last weekend, Opportunity pushed on to Endurance, successfully driving onto the plains for a photometry experiment [measurement of light detectable by the human eye]. The 108-foot [33-meter] south-easterly drive ended with a front wheel 'scuff' in the soil. On Saturday, April 24 - Sol 89, the rover used her MI to photograph a soil patch called Nougat within the scuff, then followed that with a Mössbauer spectrometer reading of the target. She also conducted some remote sensing with her mini-TES before calling it a day.
On Sunday, April 25 - Sol 90, Opportunity woke up ready, willing and more than able to complete her primary mission. Happily for the MER team, all the rover really had to do was finish the day to meet the last of the official mission success criteria. But this rover has proved to be a true mover and shaker throughout this mission and so she continued her work with as much 'enthusiasm' as she has since landing on the Red Planet. As she conducted more of the multi-sol PanCam and mini-TES plains photometry observations, she multi-tasked with her APXS collecting data on Nougat and another soil target, Fred Ripple.
After completing some more remote sensing and taking a Mössbauer spectrometer read on Fred Ripple, Opportunity cruised into her extended mission on Monday, April 26 - Sol 91, by driving 131.2 feet [40-meters] in the southeasterly direction. That put her just 525 feet [160 meters] from the rim of Endurance Crater. McLennan likened the images of Endurance that she took from that location to a Rorschach test. "From a distance, everybody sees what they want to see, but as we get closer, we start to see more and more detail," he explained. "Some of us can see what we think are sort of bedding like features, others have seen erosional features, but we are all convinced that there's some very, very interesting science to do at Endurance Crater. "The team members won't really know what they' want to do though, he said, until the rover gets closer.
Opportunity spent most of Tuesday and Wednesday, her Sols 92 and 93, edging her way closer to Endurance Crater, driving 347.8 feet [106 meters} to put her just 229.7 feet [70 meters] from the rim. The rover's routine for these two sols was to take pre-drive and post-drive remote sensing observations, then pictures in the crater direction in between mid-day, energy-conserving naps. The team expects that the rover will reach the rim of Endurance today, her Sol 95.
Once at the rim, Opportunity will spend some time taking images with her various cameras, as well as capturing some remote science, and when she sends home a view into the big crater, scientists and engineers will begin deciding whether the rover should try to enter that crater.
"We will be taking some imagery to make assessments "relative to traversibility, with an eye towards trying to understand whether or not we'll be able to get down into the crater," Wallace said at the press conference. Of course, the more challenging notion, he added, is whether or not the rover would be able to get back out of the crater. "As you all remember, we did have to take two shots at getting out of Eagle Crater, so soil properties and slopes and traversibility will all need to be taken into consideration to make that assessment."
At some point in the next week or so, rover engineers are planning to put Opportunity into Deep Sleep mode for the first time. This is the new software capability that will allow them to minimize the energy being lost as a result of the stuck instrument arm heater. The team has practiced the procedure "extensively" at JPL in a flight-like environment on the test vehicles and, said Wallace, "we are confident that the capability has been well wrung out" and that Opportunity "will wake up" from her delta downtime refreshed and ready to rove on.