By John McHale
MARS, 20 June 2008. Since the NASA Phoenix Mars Lander was deployed NASA engineers from the Jet Propulsion Laboratory in Pasadena, Calif., are quite pleased with the performance of the mission's electronic instruments, despite two minor bumps.
After landing the end of May, Phoenix transmitted a 360-degree panorama of its frigid Martian world, freed its nearly 8-foot robotic arm, tested a laser instrument for studying dust and clouds, and transmitted a weather report.
"We've imaged the entire landing site, all 360 degrees of it. We see it all," says Phoenix principal investigator Peter Smith of the University of Arizona in Tucson, Ariz. "You can see the lander in a fish-eye view that goes all the way out to the entire horizon "We are now making plans for where to dig first, and what we'll save for later."
Commands were communicated to Phoenix to rotate the robotic arm's wrist to unlatch its launch lock, raise the forearm, and move it upright to release the elbow restraint.
"We're pleased that we successfully unstowed the robotic arm. In fact, this is the first time we have moved the arm in about a year," says Matthew Robinson of NASA JPL. The arm deployment brings the Phoenix mission to a significant milestone.
"We have achieved all of our engineering characterization prerequisites, with all the critical deployments behind us," says JPL's Barry Goldstein, Phoenix project manager.
After a health check that tests the arm at a range of warmer and colder temperatures, the titanium and aluminum arm was to be tasked with its first assignment: to use its camera to look under the spacecraft to assess the terrain and underside of the lander.
The robotic arm will later trench into the icy layers of northern polar Mars and deliver samples to instruments that will analyze what this part of Mars is made of, what its water is like, and whether it is or has ever been a possible habitat for life.
Another milestone for the mission included the activation of the laser instrument called light detection and ranging instrument, or lidar.
"The Canadians are walking on moonbeams. It's a huge achievement for us," says Jim Whiteway Canadian Science lead from York University, Toronto. The lidar is a critical component of Phoenix's weather station, provided by the Canadian Space Agency. The instrument is designed to detect dust, clouds, and fog by emitting rapid pulses of green laser-like light into the atmosphere. The light bounces off particles and is reflected back to a telescope.
"One of the main challenges we faced was to deliver the lidar from the test lab in Ottawa, Canada, to Mars while maintaining its alignment within one one-hundredth of a degree," Whiteway says. "That's like aiming a laser pointer at a baseball at a distance from home plate to the center field wall, holding that aim steady after launch for a year in space, then landing."
Lidar data shows dust aloft to a height of 2 miles. The weather at the Phoenix landing site on the second day following landing was sunny with moderate dust, with a high of minus 30 degrees Celsius) and a low of minus 80 degrees C.
While instrument performance has been very successful since the mission reached Mars, NASA scientists had some apprehensive moments due to a couple of technological glitches.
Early last month Phoenix was having trouble getting soil samples into its analyzer. One of the main goals of the Phoenix mission is testing for water in the Martian soil. The first soil samples collected by the robotic arm did not initially make into the oven for testing, creating a lot of anxiety for Phoneix engineers.
Eventually the soil did make it into the Thermal and Evolved-Gas Analyzer instrument, or TEGA, which has eight separate tiny ovens to bake and sniff the soil to assess its volatile ingredients, such as water.
The oven might have finally filled because of the cumulative effects of vibrating the oven screen, or because of changes in the soil's cohesiveness as it sat for days on the top of the screen, says Phoenix co-investigator Bill Boynton of the University of Arizona.
A screen covers each of TEGA's eight ovens. The screen is to prevent larger bits of soil from clogging the narrow port to each oven so that fine particles fill the oven cavity, which is no wider than a pencil lead. Each TEGA chute also has a whirligig mechanism that vibrates the screen to help shake small particles through.
"There's something very unusual about this soil, from a place on Mars we've never been before," Smith says. "We're interested in learning what sort of chemical and mineral activity has caused the particles to clump and stick together."
In mid June some concern was raised among the Phoenix engineers regarding flash memory when Phoenix generated an unusually high volume of spacecraft housekeeping data causing the loss of some non-critical science data. Phoenix engineers were analyzing why this anomaly occurred at the time of publication.
"The spacecraft is healthy and fully commandable, but we are proceeding cautiously until we understand the root cause of this event," Goldstein said on 18 June, the day memory problems occurred.
Usually Phoenix generates a small amount of data daily about maintaining its computer files, and this data gets a high priority in what gets stored in the spacecraft's non-volatile flash memory. On 18 June the quantity of this data was so high that it prevented science data from being stored in flash memory, so the remaining science data onboard the next day, when the spacecraft powered down for the Martian night after completing its 22nd Martian day, or sol, since landing, was not retained. None of that science data was high-priority data. Almost all was imaging that can be retaken, with the exception of images taken of a surface that Phoenix's arm dug into after the images were taken.
To avoid stressing Phoenix's capacity for storing data in flash memory while powered off for overnight sleeps, the team commanded Phoenix that evening to refrain from any new science investigations on the next day and to lower the priority for the type of file-housekeeping data that exceeded expected.
"We can continue doing science that does not rely on non-volatile memory," Goldstein says. Most science data collected during the mission has been downlinked to Earth on the same sol it has been collected, not requiring overnight storage, but on some sols the team has intentionally included imaging that yields more data than can fit in the afternoon communication passes. This has been done in order to take advantage of the capacity to downlink additional data during communications passes on the following Martian mornings. In the short term, while the root cause of the unexpected amount of housekeeping data is being determined, the science team will forgo that strategy of storing data overnight.
Meanwhile, extra communication-relay opportunities were added to the schedule, so the science plan for the next day will be able to generate plentiful data without needing overnight storage.
The Phoenix mission is led by Peter Smith of the University of Arizona with project management at JPL and development partnership at Lockheed Martin, located in Denver. International contributions come from the Canadian Space Agency; the University of Neuchatel, Switzerland; the universities of Copenhagen and Aarhus, Denmark; Max Planck Institute, Germany; and the Finnish Meteorological Institute.