I almost didn't get to drive the rovers.
As one of the five developers of the software used to build the command sequences and rehearse and visualize the rover activities, I really wanted to be one of the people using it in flight. Unfortunately, only three members of the team were selected to be Rover Planners (a job title we believe was chosen in place of Rover Drivers to make the job sound very boring and reduce competition for it). I was not one of them.
I was originally slated to be a downlink analyst looking at the telemetry from the rover to assess the driving and arm operations. This entailed months of training to learn how to run somebody else's software, a much more difficult task than using your own. Fortunately for me, and unfortunately for someone else, a position opened up on the Rover Planner team and I was transferred over. This entailed more months of training to learn the procedures, but the fuse was very short since Spirit was careening towards its landing. The fact that I knew the software tools already was the saving grace that allowed me to be ready to go on landing day.
Looking back on these six years, I'm tired, but amazed, when I think about how much we've accomplished and continue to accomplish. During the prime mission, I remember hearing Steve Squyres say how much we would like Spirit to go explore the hills in the distance but that we would never get there. Well, we have driven to the top of those hills and down the other side.
I remember when Opportunity drove into Purgatory and the Rover Planners immediately said that we needed to back out of the sand dune. After months of testbed activities and review, the decision was made to back out of the sand dune. I can remember looking over at Scott Maxwell, another Rover Planner, and saying to each other "This is so cool!!" (We still say that).
Some of my favorite memories are of giving talks to school kids about what I do, though one of my saddest was being asked by one of the kids, an honor student, if the moon landings were faked. I especially enjoyed calling up Car Talk and asking the guys how to keep our electric vehicle running through the winter on Mars. I laugh when I think about a recent talk I had with Scott when the right front wheel of Spirit seemed to work again after four years of being dragged around. Scott said he didn't know if we were driving with six wheels or only five. Immediately I jumped in, Dirty Harry-style, with, "I know what you're thinking punk. Are we driving with six wheels or only five? To tell the truth, I don't know myself. The question you have to ask yourself is, 'Do I feel lucky?' Well, do ya', punk?"
As we work on getting Spirit out of the current sand trap, I feel manic-depressive about our chances. One day I am sure we will have no problem but the next day I am equally convinced that all is lost. This is about the toughest situation we have ever had to get out of. When we are stuck, it seems as if we are always running out of daylight, which translates to power. It happened at Tyrone, it happened at Tartarus, and it has happened at Troy.
Hmmm, maybe we should stop giving names to locations that start with T.
The Mars Exploration Rovers, Spirit and Opportunity, have been exploring the geology of Mars for nearly five years - well beyond their expected lifetime of three to six months. In that time they have made amazing discoveries, most importantly finding proof that Mars was once a much wetter planet that may have been capable of supporting life. Spirit has been exploring a region around a small mountain range that seems to have once had hot water or steam, the very kind of place life might have originated on Earth. Opportunity has been investigating craters in the plains that provide views deep underground and show evidence of flowing water in the ancient past.
I am a roboticist at JPL, and just one member of the large team of people who work together to enable Spirit and Opportunity to explore. My work focuses on getting robots to do things intelligently, both by developing software for robot autonomy and by operating our two spacecraft on the surface of Mars. Spirit and Opportunity have become like old friends to the operations team. Every day we are anxious to hear the latest news and see the snapshots taken from the new places they are visiting. Working with the rovers never gets routine as each new location brings new circumstances and new problems to solve.
The challenges of operating Spirit and Opportunity have continued to grow and change as they age, and we have had to develop new ways of driving and operating the robotic arm as capabilities decrease. We are discovering how to operate these rovers in ways for which they were never designed. The discovery process requires a lot of imagination and a lot of practice, both on Earth with our engineering rover and on Mars. It’s this kind of completely new and unanticipated problem that is the most fun for engineers like myself to solve.
Both rovers are now starting to show their old age of 4¾ years (that’s at least 300 in rover-years!), and some parts do not function quite as well as they used to. Spirit has to drive more slowly and constantly monitor her progress to make sure she is staying on the right path to compensate for a broken right front wheel that tends to dig into the soil. Opportunity has limited reach with her instrument arm due to a failed shoulder joint, and has to approach science targets in a very precise way. Despite these limitations, both rovers are now about to embark on difficult journeys which will require them to set new milestones and we will need to learn new ways of driving yet again.
After surviving a very difficult winter, Spirit is soon going to be heading south toward some interesting geological features: a hill called von Braun and a depression called Goddard. Scientists hope investigating these unique features will provide insights into the Martian past. They are looking for additional evidence of hot springs or steam vents that have been hinted at by other observations in this region. Based on comparisons to similar locations on Earth (like deep sea vents), this could be an ideal place for life. Reaching these exciting features requires a long drive through sandy terrain in a very short period of time before next winter arrives. This will mean pushing Spirit to new levels of performance.
Opportunity is finishing up her observations of the 800-meter Victoria crater and then will begin a 12-kilometer, two-year odyssey toward a huge crater (about 22 kilometers across) to the southeast. As this means more than doubling the total distance Opportunity has driven in her lifetime, we are excited to be developing new methods to make record distance drives safely. This will require relying on the rover’s onboard autonomy to keep her safe more than ever before as we drive each day well past what we can see.
Spirit and Opportunity’s story of continued exploration - boldly striking out after one new goal after another, far beyond their design lifetimes - is a genuinely inspiring one. It’s as if Magellan circumnavigated the Earth, then paused and said, ‘You know, that’s not good enough. Let’s go to the moon, too.’