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December 2005
December 23, 2005
Things have been going well at Gusev. We've spent most of the past
week looking at a rock right next to Comanche that we call Comanche
Spur. Like everything we've seen since we've descended off of Haskin
Ridge, Comanche Spur has undergone very little alteration and has a
lot of olivine in it. But the composition is different from what
we saw at Seminole and Algonquin, so we seem to have yet another rock
type at Gusev.
With the Comanche campaign wrapping up,
it was decision time... Allegeny Ridge or El Dorado? We
had a long meeting about that at mid-week, and the consensus decision
was to head for El Dorado. We should begin the drive on about Sol
704, and we're hoping it will go quickly. Expect Spirit to do a lot
of driving and (except at El Dorado) not much IDD work in the weeks
ahead.
Over at Meridiani, we have now gotten pretty good at operating
our balky arm without problems. And we've been at Olympia long enough
now that it's probably now the best-imaged place on the entire planet.
With all that imaging we've identified several other nearby targets
that we'd really like to take a look at. Unfortunately, though, it's
still going to be a little while before we can get moving again.
While we know how to work the arm, we're still figuring out the
best way to stow it. We no longer want to stow it under the front
of the vehicle, since a complete motor failure there would
incapacitate the arm permanently. Instead, we're looking at
"stowing" it somewhere out in front of the vehicle. That sounds
easy, but it's something really new... we've never tried driving
with the arm deployed, on either planet, so we've got to be
very careful. Being very careful means we have to do a lot
of calculations and tests on Earth before we're ready to try it
on Mars. So it'll still be a little while before we're ready to
drive anywhere.
And a final note: If you want to know about our take on water at
Meridiani, there is one good place to read about it... the papers that
we recently published in Earth and Planetary Science Letters. Check
them out.
December 15, 2005
Just a quick update today...
The big news, of course, is that Opportunity's IDD is working again! We
have confirmed that there is a broken wire in the winding of the motor,
and in order to compensate for it we have to double the voltage to that
motor. We've done that, and the IDD is moving.
We still have work to do here. Even though we know how to move it now,
we still have to experiment quite a bit with all the nitty-gritty
details of how to operate an arm in this fashion. Also, we're now
thinking that we may not want to stow the arm again underneath the
rover where we normally put it, since one more broken wire could
disable that joint completely. Instead, we're looking at other
ways that we might "stow" the arm out in front of the vehicle so that if
the joint dies completely, we'll still be able to use the other
joints.
Still, it sure is good to see it working again!
Over at Gusev, we're bearing down on Comanche. This thing is pretty
big, and it's going to look spectacular once we get next to it. Still
no telling what it's made of, but we should know soon enough.
Once we've done our work at Comanche, then we have a really important
decision to make. We need to keep moving quickly if we're going to
get to McCool Hill and its sunny north-facing slopes by winter. We
have two very enticing targets ahead of us after Comanche, and we've
got to pick one of the two... there isn't time for both. One is a
ridge off to the southeast that we've named Allegheny Ridge. The
other is a large patch of dark sand off to the southwest that
(with some inspiration from Edgar Alan Poe) we've named El Dorado.
We'll get to Comanche, take pictures of both, and then pick one
of the two... probably sometime next week. The seasons are changing
rapidly at Gusev, and time is of the essence.
December 11, 2005
It's been so long since I've written one of these that even my
father is starting to complain... so Dad, this one's for you. :)
In the time since I last wrote an update, we've passed a couple of
really major milestones. The first, of course, is that we've now
been on Mars for one full martian year. This, to me, is maybe the
most significant milestone we've hit. The others, like 90 sols,
one Earth year, and so forth, seem kind of artificial, since they
really have nothing to do with what's happening on the planet where
the rovers live. But
this one means that we've now seen Mars in all its seasons. The
seasons really do change in a very substantial way on Mars,
especially if you depend on solar power for survival. In the
months ahead we know that we can expect hazy skies to clear,
but we also know that the temperatures will drop dramatically,
especially at the Gusev site, and that the sun is going to sink
lower and lower in the northern sky. It shouldn't be too big a
deal at Meridiani, but for Spirit we're starting to think real
hard about where we're going to spend the winter, and making
plans to get there in time to stay alive.
The other big milestone is that we've finally published a big
batch of very detailed papers about the rocks at Meridiani, in
a special issue of the journal Earth and Planetary Science
Letters. This was a long time coming. It's very hard to get
science done and get papers written at the same time we're doing
flight operations every day! But the papers are out now, and
they provide a much more comprehensive description of what we've
found at Meridiani than we were able to do in the very short
papers that we published more than a year ago. Next up will be
another big volume of papers about the Spirit site, to be
published in the Journal of Geophysical Research in the next
couple of months.
On Mars, Spirit is well down off of Haskin Ridge and heading for
Home Plate. On the way, we've stopped off at three big outcrops,
named Larry's Bench, Seminole, and Algonquin. Algonquin is the
one that we're parked at now. They're all similar to one another,
and all dramatically different from anything we've seen anywhere
else. The rocks have undergone very little alteration, and
contain a lot of olivine... much more olivine than
we've seen anywhere else.
Next stop should be Comanche, a big and very red outcrop between
us and Home Plate. It looks like Comanche may be different from
Algonquin and the rest, based on Pancam and Mini-TES data...
we'll see what we see when we get there.
Over at Meridiani, progress has been slow. A couple of weeks ago,
we encountered a problem with the IDD, and we're still dealing with it.
The IDD on Opportunity, you'll recall, is the one that has a stuck
heater on the shoulder joint. What this means is that the shoulder
has seen much larger temperature ranges than any other piece of the
rover. Motors can encounter problems
if they undergo too much thermal stress, and
we found a couple of weeks ago that the "azimuth" joint on the
shoulder -- the one that swings the arm left and right -- wasn't
moving when we asked it to.
When something like this happens, you proceed carefully, since you
don't want to make the problem worse simply because you don't
understand it yet. So the engineers at JPL have been methodically
working their way through various fault scenarios, using tests
on Earth or tests on Mars to knock them off one by one until only
one's left. At first, we feared that it might be a mechanical
problem, perhaps like the one that incapacitated the right front
steering motor on Opportunity. But we've ruled out all the
plausible mechanical issues and narrowed it down to an
electrical problem, probably within the motor itself. More
analysis is needed, but it seems pretty likely that the
problem is a consequence of deep thermal cycling.
We're not out of the woods yet, and I'm not making any
predictions. However, the good news is that late last week we
got the motor to move properly. It was just a small move, but
by adjusting some of the parameters that control the motor we
were able to compensate for what we think may be the problem
inside the motor, and get it to move just the way we asked it to.
We're going to continue to take our time with this, but
I have high hopes that you may be seeing the IDD deployed
out in front of the rover again before too long. We may have
to operate it a big differently from here on out, but I'm
also optimistic that we'll be doing science with it again
pretty soon.
I'll try to do better with updates during the weeks ahead...
