This story was updated at 6:41 p.m. EDT.
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?
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 un-stuck? 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!
Would it be possible, given
Opportunity's experience with exploring inside craters, that
the rover could hunt for water ice at the bottom of an enormous crater like
Endeavor, when it arrives?
Dr. Stroupe: Anything is certainly possible,
though I don't think Opportunity is quite at the latitudes where they're
finding water. Given the thin Martian atmosphere, anything on the surface is
long gone and Opportunity can't dig very deep. So it isn't very likely, but not
impossible!
From the technical perspective, what
lessons has the team learned from rovers? Will this influence the design of
future planetary rovers like Mars Science Laboratory?
Dr. Stroupe: That is a very tough question to
answer because we have learned a lot. We have really learned much more about
the challenges of driving, and what works well on different types of terrain.
We have also learned how to drive aging rovers that don't have full
capabilities anymore - this is really an entirely new field of robotics because
here on Earth we just fix them when they break.
Unfortunately most of these lessons
are too late to incorporate into our next rover, which is already well into
production. But these will help us operate MSL and will be factored into future
mission designs.
What was the single most exciting
event that you participated in during your Mars rovers
project?
Dr. Stroupe: Wow this is a very tough question
because there have been a lot! Personally, my first drive on Mars was very
exciting for obvious reasons. Also, the day we discovered the first real
evidence of wide-spread
water at Spirit's landing site in Gusev crater
changed the way we all think about Mars, which was very exciting.
Would it be possible to have the
second rover Opportunity steer towards Spirit in the attempts of dislodging it
with a bump or a side-swipe, or would it be too risky or time-consuming to
attempt this?
Dr. Stroupe: The rovers are on completely
opposite sides of the planet. Unfortunately, it would take many, many years to
drive that far at 200 meters a day. No AAA on Mars!
How surprising has it been to see
the rovers last such a long time, and what are the biggest dangers to their
longevity now?
Dr. Stroupe: Honestly, it is very surprising.
While we knew they were designed and built to the absolute best of our ability
(and we have a lot of very talented and smart people here!), Mars is a very
dangerous place. The biggest surprise, and one without which we would not still
be on Mars, is that it can also be friendly. The Martian winds have kept the
solar panels clean, and without that we would have long ago passed the time
when we could no longer make enough power to survive.
At this point in their lives, it is
impossible to tell what might fail next. Many thing we
can learn to work around (like the motors on the arm and wheel that have
already broken) but other things we might not be able to work around. It
depends on how it breaks, when, and where.
How large is the team that drives
Spirit and Opportunity? Do you have to train with the simulator on Earth in a
sort of rover Driver's Ed? Can you give us an idea what it feels like - if you
ever think about it - to actually be driving a car on Mars?
Dr. Stroupe: The team is still fairly large, we probably have about 20 people working on each
rover each day that we plan. For driving, we do have very good simulators that
we use to test our sequences before we send them to the rover, and we also use
this for training. It takes a long time to be fully qualified and get your Mars
driver's license.
As for what it feels like - it's
really just awe inspiring. Probably the closest I'll ever get to being an
astronaut. Going to new places and being the first human eyes to see them is
profound and hard to describe. It's the best job I could imagine.
Click
here to read the entire Live Forum Mars rover session.
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