Scott Maxwell stared at his bedroom ceiling in the hours after his first drive, restless with excitement. All systems were go, and he'd sent the commands by the time he left the Jet Propulsion Laboratory. Now he was supposed to sleep before his next shift on Mars time. But he knew that on the fourth planet from the sun, the Spirit rover's wheels had started to move.
"I was thinking that at that moment, there is a robot on another planet, doing what I told it to do. I could not imagine going to sleep," Maxwell recalls. "It just blew my mind. And I still think it's amazing that what I do with my day job is reach out my hand across 100 million miles across of empty space, and move something on another planet."
Maxwell is one member of a team of engineers and scientists who have spent nearly a decade working with NASA's intrepid Mars Exploration Rovers, Spirit and Opportunity, maneuvering them across windblown Martian terrain and into groundbreaking new discoveries. Many of them, along with a new cadre of researchers, will also command the new Mars rover Curiosity, set to land in three weeks. That rover is far more complex and more powerful, and designed to last much longer than the twin rovers' initial three-month lifespan. But the MER mission, as it's known, set the stage in many ways - including how to live and work as a Mars rover driver.
The humans do their work in a fairly unremarkable setting, wearing normal clothes perched at normal computers, holding conference calls inside normal cubicles in southern California. Yet they're driving little cars on Mars, an incredible feat that never ceases to amaze team members like Maxwell. It is not easy, neither on the team members' own health - living on Mars time is hell for some - nor on their personal relationships. But ask them, and they'll say it's been the trip of a lifetime.
Waking up to drive a rover on Mars is complex from the moment you hit the snooze button. In the early days of a mission, engineers live according to the Martian clock. A Martian day, called a sol, is about 40 minutes longer than an Earth day, so engineers show up for their shifts 40 Earth-minutes later each day. Mars timekeeping requires some detailed calculations. From the perspective of a rover driver, it's awful - unless you're Maxwell, who claims to love it.
Morning people like Deborah Bass, a scientist at JPL who worked on MER and the Phoenix lander, and Ray Arvidson, the mission's deputy principal investigator, describe Mars time less than fondly. "Oh, it hurts," Arvidson says. "It's like coming back from a trip to Europe every day." Nowadays, the MER team plans ahead so they can work normal Earth schedules, but 300 to 400 people will revert to Mars time and its bizarre timelines after Curiosity lands.
"At this moment, there is a robot on another planet, doing what I told it to do. It just blew my mind." Spirit and Opportunity are solar-powered, so they have to work during the Martian day to ensure they have enough juice. Though Curiosity has a nuclear generator, it, too, will work mostly during the day so its cameras and instruments can see. That means planning is key, according to Bass.
"We want to be ready so as soon as that little spacecraft wakes up on Mars, we have a whole set of stuff for it to do," she says. "We send it at like 5 in the morning on Mars, and that's the start of the day. So we say we work the Martian night shift."
Thanks to Mars time, this makes for some long days and nights, and managers at the Jet Propulsion Laboratory have to make sure people go home to bed. "It is so compelling, it can be challenging to shut it off and go home," Bass acknowledges.
It's also challenging because team members feel real affection for the rovers and each other, and want to be there for every new step. The mission has served as a bedrock for people who have worked together for more than a decade, surviving deaths in their families, divorces and other traumatic experiences. Initially, engineers and scientists were tied to one rover or the other, and came to know them closely, discussing Spirit and "Oppy's" personalities the way the rest of us might discuss our pets.
"They are personalities we imbue them with, but they're not less real for that. If you ever had a first car, and you loved that car - maybe it was cantankerous, maybe it was great - that car is somebody to you. This is like that, on steroids," Maxwell says. "To the extent that you can say this about the rovers - that it has a personality and is ‘somebody' - the character that she is, is the product of the whole team that is operating her."
THE DAILY GRIND
Despite all the emotion and excitement, even Mars rover driving starts with meetings. The MER team's morning starts with a planning session; the science team, led by Steve Squyres of Cornell University and by Arvidson, a professor at Washington University in St. Louis, head discussions of what the rover ought to do. Then engineers including Maxwell pass the instructions along to the rover itself. (At this point it's rover, singular, because Opportunity is the only one still functioning; its twin Spirit lost contact after becoming mired in sandy soil.)
The speed-of-light delay from Mars to Earth means there's a long lag time between commands sent, commands executed, and confirmation. In the mission's early days, maneuvers were painfully slow and simple as the team learned how the rovers would respond. Later, the rovers got artificial intelligence upgrades to help determine interesting targets. This was helpful, because a lot can change on Mars in a few minutes - rampaging dust storms, loose soil, and other unexpected things can spoil the best-laid plans.
"Imagine driving your car to the grocery store with a delay like that. Nothing happens for 20 minutes, and when it does happen, you don't know about it, because your rear window doesn't update for another 20 minutes." "Imagine driving your car to the grocery store with a light time delay like that. Nothing happens for somewhere between 4 and 20 minutes, and when it does happen, you don't know about it, because your rear window doesn't update for another 4 to 20 minutes," Maxwell says. To avoid excruciating waits, the team now programs Opportunity (and formerly Spirit) with a series of tasks, up to three days' worth over a weekend. After so many years, they're confident in the rovers' response times and capabilities, so they don't have to test every little command with exacting detail. The Curiosity mission will do that for some time, though.
Late afternoon rover time, Opportunity stops driving and sends pictures to Earth, using its high-gain antenna and a relay from the Mars Odyssey orbiter. That's when Maxwell and his team get to work for the next day. As they write commands, they can move a virtual rover in a custom-built, video-game-like software platform, which serves as an avatar for the one on Mars. The computer version helps validate the commands.
"When it executes, there's not going to be anybody there to hit the panic button, so anything that might go wrong, we have to think of that in advance," Maxwell says.
But sometimes, Mars throws a curveball, and there's nothing anyone can do.
LOSING SPIRIT
Both rovers had a few kinks early on; their solar panels filled with dust again and again, and Spirit lost control of one of its six wheels a couple of years into the mission. Some instruments eventually wore down, like the diamond in the Rock Abrasion Tool the rovers used to grind into rocks. But none of these limitations presented serious problems. Then on May 1, 2009, the hobbled Spirit fell into a trap.
"It was like an ice skater might break through the surface; Spirit broke through what looked like this very friendly terrain," Maxwell recalls. "It was softer, fluffier terrain, so it was really hard for her to get traction in."
The team went to JPL's rover test bed, a sandbox with a full-size duplicate rover where they could try some maneuvers. They had a plan in place and started sending commands just before the onset of Martian winter - and then another wheel failed. Still, Maxwell and his team figured out a method that would basically help Spirit swim out of the trap, building a pile of dirt behind it. They made 30 centimeters of progress before the sun dropped too low on the winter horizon, and Spirit's solar panels were tilted the wrong way. Spirit went into hibernation, and as far as anyone knows, she never woke up. NASA sent more than 1,300 attempts to hail the rover before finally giving up last year.
"Victory was within our grasp, but we just didn't have the time. It was devastating," Maxwell says.
The experience sparked Arvidson's interest in the terramechanics of Mars, studying the properties of soil at different depths and under crusts. He's a co-investigator on a new terramechanics experiment using Curiosity, which will use detailed telemetry from the rover to help it plot a safe course, avoiding sand traps like the one that caught Spirit. It will also help scientists understand how crusted soil forms, and their relation to the modern Martian water cycle. It's based on a system Arvidson built to free Spirit. "I decided that will never happen again," he says.
Every two seconds, the system records the rover's pitch, yaw, roll and motor currents, simultaneously building a topographic map. Then these figures drop into a computer model. The Curiosity system will work in a similar manner. Here's an example of the MER project, called Artemis.
Along with helping future Mars missions, all of the rover drivers' work - life on Mars time, late nights and missed appointments - has captured the public's imagination, and served to change the way we see our neighbor planet. No longer is the red planet, named for the god of war, such a foreign place; now it's a dirt-filled, rusty-colored landscape where humans can virtually scamper around. The rovers are just about an average person's height, and they see the world in stereo color vision, as Maxwell points out.
"When you see Mars through their eyes, you're seeing it like you would through your own eyes," he says. "We can't go there yet with our squishy, frail human bodies, but we can send robots that can send you home vacation photos of what Mars would be like if you were there yourself."
Despite all the public's affection over the past decade, the rovers have now slipped from most people's minds, just as regular space shuttle launches sometimes failed to make the newspapers. But Opportunity is still bringing home new discoveries all the time.
"In 1969, we landed a human being on the moon. You go out at night and look at that big thing in the sky - people were walking on that, for goodness' sake. But by Apollo 17, everybody was bored with it," as Maxwell puts it. "So we're not front page news everyday, I get that. But for me, it just never gets old."
Arvidson echoes his sentiment: "We're driving rovers on another planet. How can it not be fun?"
 |  |
No comments:
Post a Comment