The Martian lives of Spirit and Opportunity

updated 9:27 p.m. ET Oct. 12, 2009

At times, it seems like NASA's Mars rovers Spirit and Opportunity will last forever on the red planet.

Since 2004, the twin rovers have explored different parts of Mars with amazing longevity that has astounded scientists almost as much as the data the robots have beamed back to Earth. Spirit and Opportunity have shed light on the history of water on Mars in the distant past, explored Martian hills and meteorites, and even rolled inside craters to probe ever-deeper into the planet's geologic history.

Today, Opportunity has added yet another Martian meteorite — the third of its mission — to its grab bag of red planet discoveries. Opportunity began heading toward the lumpy rock, which has been named "Shelter Island," on Oct. 1 and is reaching out to study the meteorite using its robotic arm. It is eventually headed to a distant, giant crater called Endeavor.

Spirit is stuck up to its wheel hubs in a Martian sand dune that has thwarted all escape attempts to date. Engineers are still trying, though, and the rover's power and science instrument systems are in good shape.

Mars rover engineer Ashley Stroupe, who works on the mission at NASA's Jet Propulsion Laboratory (JPL), discussed Spirit and Opportunity's exploits with SPACE.com readers during a recent Live Forum. Here are some of Stroupe's answers to reader questions on the rover mission's challenges and what it's like to drive two cars on Mars:

Has the Mars Rover team examined the possibility of using the Spirit rover's instrument arm to maybe help push it out of its current predicament?

INTERACTIVE Ten greatest Mars hits and misses Getting spacecraft to Mars is risky business. Fewer than half of the attempts have succeeded.

Dr. Stroupe: Several people have questions about using the IDD [Instrument Deployment Device, or robotic arm] to help get Spirit out. The IDD is very low in mass and was only designed to exert the forces needed to firmly place instruments on science targets.

That means moving it around barely shifts the rover's center of gravity and attitude. The arm can only exert at most about 20 pounds of pressure, which is only 13 percent of what would be needed to lift the rover's mass on Mars. With that level of force we again could only minimally affect the rover's attitude, and would not be able to move rocks of any significant size. And if we tried, we would definitely risk damaging the instruments or the IDD itself. If all else fails, we may give one of these strategies a try and hope that the small difference is enough, but these are all very risky, and so far down our list of options.

Do you have a time frame in mind for trying to get Spirit unstuck? Are there budgetary issues to consider as well or will the project keep going as long as Spirit responds?

Dr. Stroupe: We do not have any particular time frame in mind. We're driven by being sure we have the absolute best plan we can have in order to maximize our chances of success. This is likely to be at least a few more weeks. At this point, the success of the plan is our primary driver, not calendar and not budget.

We are still finishing up our ground testing and haven't yet started driving on Mars. That is probably at least a few weeks away.

How much easier is it to plan the next day's drive now than in the beginning?

Dr. Stroupe: The rovers are actually robots, and as such are highly autonomous. We give them an entire day's worth of activities at once (in the morning) and then at the end of the day they call home and let us know how they did. During the day, they execute the plan, and keep themselves safe from conditions that arise that were not foreseen. Once in a while, during an emergency, we command the rovers real-time, but this almost never involves driving or using the robotic arm.

We have developed a lot of experience and a lot of tools to help us since the beginning of the mission. However, every day and every place is different and brings new challenges. While I wouldn't say it has really gotten easier, I think I can say it is has gotten a lot more efficient.

Do Spirit and Opportunity handle differently when you command them from Earth, or is it more like once you've driven one rover, you've driven them all? And do you have a favorite?

Dr. Stroupe: Actually the rovers do behave differently! Spirit and Opportunity are first in very different terrains, and so you have to drive them differently. Also, they have aged differently and have driven us to use very different strategies. We have to drive Spirit mostly backward to drag the broken right front wheel, and we have to drive Opportunity with the robotic arm out in front since one of the joints broke and we can't stow it anymore. So, it's definitely not "drive one, drive them all."

I do have a favorite - Spirit is my favorite - but I love Opportunity too!

MORE FROM SPACE

Space Section Front

Month in space: Powerful pictures   Astronauts land with families on their minds Cosmic Log: Signs of Mars life? ... and more Powerful laser simulates stellar jet Solar tsunamis are real, NASA says Rocket man fails to fly from Morocco to Spain Is case finally closed on 1965 UFO mystery? Space telescope to probe sun’s atmosphere Space agencies argue over delayed launch Cosmic Log: Play the galactic slots Space Section Front   Add Space headlines to your news reader: