— In addition to the wealth of scientific data they have produced over the past four and a half years, NASA’s rovers Spirit and are providing those planning future Mars missions with some critical lessons learned along the way about the challenges inherent in long-term operations on the martian surface.
In a presentation here June 9 during a conference about the Mars Sample Return proposal from the International Mars Architecture for the Return of Samples (iMARS) Working Group, Steve W. Squyres of Cornell University, principal investigator for the two Mars Exploration Rovers, listed 10 must-do elements for such an endeavor based on NASA’s experience with the rovers since January 2004:
1. Mobility
Staying in one place means limiting the mission to samples that might not be representative. Landing-site selection and landing accuracy can reduce the need for mobility, but the rover still needs to move around to get a suite of samples characterizing the selected site.
2. Longevity
Spirit found some of its most interesting samples only after 1,200 martian days. And if longevity is the goal, plutonium power is the preferred option. “Martian dust gets on everything,” including the rovers’ solar arrays. “If you have no reliable power, you are forced into inactivity, waiting for a gust of wind. If plutonium is off the table, then we need to dramatically oversize the solar arrays.”
3. Agility
Rovers need to handle steep terrain, even when the landing site is supposed to be flat ground. The high-resolution HiRise camera aboard NASA’s Mars Reconnaissance Orbiter has been invaluable in revealing obstacles that would not otherwise have been detected. “Negotiating a maze of ripples and ridges that may look small can take forever. Having good overhead images is extremely important,” Squyres said.
4. Use the Mars impact craters to the mission’s advantage.
They have spared rovers the need to dig through strata. “You get access to materials that would be impossible to reach, and they can also deliver good stuff to you,” Squyres said.
5. Don’t let pride or the sense of adventure prevent a return to sites already visited.
“We have a strong aversion to turning around and going back,” Squyres said. “You can count on one hand the number of times we did it in the beginning. Now we’ve started to recognize the value of returning to places.”
6. Think twice before heading into sites that have high potential but may trap the rover.
“You need to calculate the risk to the rover in going to places even if fabulous samples are likely,” Squyres said. “We have compromised by taking small ‘toe dips’ and then retreating.” Testing vehicles in a field setting, with program managers there to see it in action, also is helpful.
7. Getting below the surface of a rock is important.
“Huge variations in chemistry reveal themselves only then. Also, don’t ignore pebbles. Being able to pick them up is important too.”
8. Be creative with the available tools.
“We have occasionally driven over rocks to crush them under the wheels, then backed up to look at it.”
9. Image compression is important.
“Rover-driving speed is driven by the quality of the images you have to look at the terrain. You will have limited bandwidth, so get good image compression.”
10. Manage your teams for the long haul.
“It is very, very tough to live on Mars sols [days]. A Mars day is 24 hours and 39 minutes long. I did it for four months. It’s difficult.” Also important, Squyres said, is to have science and engineering teams work together, in the same locale, for the first few months of a mission to get to know each others’ reactions. “Distributed operations is effective, but you need to start with face-to-face operations,” he said.
