Touch and Go Days
Pasadena, Opportunity mission, Sol 14, Spirit mission, Sol 35
This generation of Mars rovers have begun testing and using the first constellation of satellites that can act as complex communication relays. Numbering three in total the orbiters include the Mars Odyssey, Global Surveyor and Express. Jennifer Trosper, the mission manager for the Spirit rover, said, "We did a demonstration with Mars Express, to save a file sent to the rover from orbit, so we have our interplanetary network going, " both ways. "Spirit is in great health. We are moving forward with its science mission."
|The round, shallow depression in this image resulted from history’s first grinding of a rock on Mars. The rock abrasion tool on NASA’s Spirit rover ground off the surface of a patch 45.5 millimeters (1.8 inches) in diameter on a rock called Adirondack during Spirit’s 34th sol on Mars, Feb. 6, 2004. The hole is 2.65 millimeters (0.1 inch) deep, exposing fresh interior material of the rock for close inspection with the rover’s microscopic imager and two spectrometers on the robotic arm. This image was taken by Spirit’s panoramic camera, providing a quick visual check of the success of the grinding. The rock abrasion tools on both Mars Exploration Rovers were supplied by Honeybee Robotics, New York, N.Y. |
Previously the orbiters would receive and relay data from the surface back to Earth, but now the rovers are receiving telemetry and data from orbit to store. In addition to communications, the constellation overhead allows the rovers to anticipate where to drive, as the birds-eye view now shows a relatively clear path from the Spirit rover’s current location to its next long traverse. The Spirit rover plan is shaping up to be a driving mission, according to mission planners who look towards a crater in the distance called Bonneville. "We believe from the satellite images, it does look like there’s a path to the crater."
With three orbiters and two rovers, Mars is getting intense scrutiny. Matt Wallace, the mission manager for the other twin rover on the opposite side of the planet said the Opportunity site’s precise location is still days away. "We know we’re on Mars, in a cool site in a crater. In the last three to five days, we have gathered a good amount of information, but we’ll wait for the localization experts to give the scoop as to exactly where Opportunity is."
Measure Twice, Cut Once
Among the mission accomplishments so far, according to Trosper, "we brushed Adirondack with the rock abrasion tool. We put Mossbauer and APXS [spectrometers[ on the rock." The team anticipates digging their first hole in Martian rock as a milestone event in interplanetary work. Below the dusty surface, scientists anticipate they will find crystalline or rocky grains that tell the story of the site's geological origin. "We will do an actual RAT later [on Saturday]."
|This image shows the Mars Exploration Rover Spirit’s "hand," or the tip of the instrument deployment device, poised in front of the rock nicknamed Adirondack, the rover’s first science target since developing communication problems over two weeks ago. In preparation for grinding into Adirondack, Spirit cleaned off a portion of the rock’s surface with a stainless steel brush located on its rock abrasion tool and seen here at the end of the yellow arrow. The image was taken by the rover’s panoramic camera.|
"The plan," for Spirit, said Trosper, "will be to finish the RAT and beginning to drive towards Bonneville crater. We believe we will be able to get there. How to use traversing and autonavigation capabilities. We will tell it exactly where to drive, then for a meter or so, let the rover determine its own next way-point. Each sol we will extend the distance for autonavigation. We will use the [instrument deployment device], IDD, and remote sensing."
The story of how Spirit reached a stand-down for two weeks has been summarized as corrected and better understood. Glenn Reeves, the software architect for both rover missions indicated that Spirit’s journey has been partly "the story of how we got from crisis to relief. "
"The short summary of the problem and timeline of how we got to a solution," said Reeves, was one of too many files. "The problem is as we accumulated additional files, the system consumed additional memory, and we ran out. Our reaction", meaning the rover’s self-diagnosis to its memory limit, "was severe, and we corrupted the file system. That lead us to seeing the system in a reset cycle. During the design period, we anticipated it and kept it in cripple mode. We got in crippled mode and were able to stabilize the vehicle on Sol 21. We then were able to debug a system…200 million miles away. The slowest dial-up provider, given the distance, and the
number of times we could communicate, we were able to extract as much information every time we could talk to it. "
"Our reaction," said Reeves, "was to get all the files we could, then erase the flash memory. Consuming all the memory is a rather severe error, and the vehicle reinitialized by resetting. But the [original] number of files consumed the same memory each time it was reset. Beginning on Sol 18, the 21st of January which seems like a long time. It took a couple of days to get [any] information out of the vehicle. "
The software team’s initial hunch seems to have proven true, said Reeves: "Out of memory was correct. The subsequent problem was managing to corrupt the file system. We erased all the flash. Then created new file system. It is not dissimiliar to what you might do on your home PC, when a hard drive is too corrupt to use."
"We can work around this problem indefinitely," said Reeves. "We will try to identify the issue more quickly, but we will monitor the amount of RAM at the beginning of the day and during the day. On both vehicles, there are monitors to limit activity as RAM stores during the day. The bug is we should have restricted the memory. We have now set an internal configuration value. We’re anticipating one to two days to get the change for flight software. We have a good way to avoid the problem, so I’m not sure we will try to change [too much]."
Given Spirit’s three week headstart at its landing site, the mission timeline for the first rover is ahead of what is happening at the Opportunity site, despite the software delays. Spirit now has pioneered a little known experimental capability of its instrument package, the chance to brush dust without actually cutting into rock. One-fourth of the robotic arm’s diagnostics are devoted to getting below the dust on various field rocks, but looking at the Gusev site from a distance had led most scientists to conclude that wind had cleared much of the dust already. However to test what is rock and what is dust, scientists planned to brush the rock called Adirondack lightly, rather than cutting into it with their high-speed diamond drill.
Diamond Drills and Snouts
Describing what might at first sound like intense dental work, Steve Gorevans, a specialist in the tool from Honeybee Robotics, spoke about the subtle differences on Mars that this experiment revealed. "The first time use of the RAT was to brush a rock, a less well-known capability", than cutting. "Adirondack looked clean but scientists wanted to preserve a cemented coating, brushing only loose material away. The idea came to get the cemented coating. And there are stainless steel bristles for brushing, which was intended to remove debris from a cutting hole. But we used it for 5 minutes", and managed to remove dust while still preserving the cement coating on Adirondack.
|The Opportunity rover’s hazard avoidance camera snapped this picture of the outcrop and the feature called ‘Snout’ on the far right side of an arc that is thought to be bedrock and stretches half the circumference of the crater.|
Gorevans said the major work came from imaging the rock’s cemented layer with the microscope, but added "As Mohammed Ali would have said, ‘This is the greatest interplanetary brushing of all time.’ We think we preserved the loose coating. The material on the surface shows literally no resistance, no motor effort to remove. "
Ken Herkenhoff, a geologist with the US Geological Survey in Flagstaff, Arizona, said the Spirit sample is likely volcanic, with a thin dust layer on top of cemented coatings. "Under microscopic imaging, the brushed rock shows a dramatic change. There was quite alot of dust on a rock, Adirondack, that we thought was relatively clean. We’re seeing mineral crystals, as we continue to abrate the rock. What this looks like is a volcanic rock, a basalt, as it looked like in pancam."
"The dust [top-layer] is consistent with what we see under microscopic imager, about a couple of microns thick." A micron is about 1/100th the thickness of a human hair. "We see clumps of dust around the edge, agglomerates of dust, so it looks like it sticks together, but not strongly enough to keep it from being brushed away easily."
"We can’t rule out electrostatic cohesion," noted Herkenhoff, when referring to the clumpiness of the dust on such a dry site. "Certain minerals, clays, tend to aggregate (by molecular attraction called van der Waals forces) and that allows it to adhere more easily. Mars is much drier, electrostatics may play a role we don’t anticipate yet. I’d expect we’ll be rethinking some of the previous remote sensing results. Some of the Mars Pathfinder results, had been interpreted as thin dust coatings. At the Spirit site, completely ‘dust-free’ will be difficult to find. "
The use of the most complex exploration instrument on-board involves the robotic arm and its four diagnostics. Matt Wallace reported that parallel activities to Spirit are now happening for Opportunity. "We completed exercising [Opportunity's] instrument arm. We approached the right hand side of the outcrop, to a rock named Snout. That was another 1.6 meters, after driving the first 3 meters since egress. We came up slightly short of the outcrop, about half a meter, and we will complete that drive Saturday. The outcrop runs about 180 degrees along the rim, so we see it in front and back" camera-views.
As to why the drive didn’t butt up against the outcrop, Wallace said, "We saw some soil slippage, and the vehicle is tipped back about 13 degrees. We think we are looking at dry sand, and above 10 degrees we see simulations with significant slip just from the soil mechanics. We get between 10 to 20 percent slip during these traverses. We’ll be able to accomodate that pretty efficiently."
In summarizing what remains over the next few days, Wallace said "We will take a touch and go picture of the soil, restow the arm, and prepare for a full suite of instrument exercising on Snout. We will start an arc along the bottom of the outcrop, stopping at choice viewing locations, potentially dropping down the arm to get microscopic images as we go."
Wallace concluded the day’s assessment: "The spacecraft is healthy and happy doing the job she was sent there to do."