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Mission Update by Steve Squyres

(Return to archived mission updates list)

June 2005
June 29, 2005

It's been an uncommonly good week so far for both rovers. It's funny with these vehicles... we have some stretches of time where it seems nothing much happens, or where various frustrating little glitches slow us down in some way or another. And then we'll have other stretches where everything seems to work exactly the way we want it to. This week has been one of the latter ones.

Our drive last weekend with Opportunity was perfect, and it put the part of Purgatory Dune that we wanted to study right into the arm's "work volume" -- the territory that the arm can reach. We then developed a very aggressive three-sol plan to learn everything we can about the dune: Microscopic Imager, APXS and Moessbauer in the old wheel tracks, MI and APXS out on the surface next to the tracks so we have something to compare it to, and Mini-TES to tell us about the thermal inertia of the soil. We're two sols into our three-sol campaign now, and so far it's gone perfectly. I wish I could really describe here the great job the Opportunity engineering team has done this week, managing power down to a tenth of an amp-hour each sol so we can squeeze every available drop of science out of the vehicle. The sol we planned today will wrap it up, and the sol we're going to plan tomorrow will be the one we've waited two months for... driving away from Purgatory Dune.

So, if you're watching our images, in another few days you'll see Opportunity on the move again, at long last. And if you watch closely, you'll see something that might freak you out a little... we'll be driving north.

No, we haven't decided to turn tail and run away from Erebus Crater! But after a careful study of all the images we have, we've concluded that the best way to map a path to the south is to start by going north a little bit, and taking some pictures off toward both the east and the west. Those images will complement ones we have already, and should allow us to plan the best possible southward path. So there'll be two or three drives to the north first, a lot of imaging, and then the long hard push south toward Erebus.

Over at Gusev, Spirit continues to shine. We've been really nailing our drives there lately. It hasn't hurt that the recent terrain has been just about the firmest ground we've seen anywhere at Gusev crater. We don't really understand this, frankly, but if you look at recent Hazcam and Navcam images you'll see that we're barely even leaving tracks, the ground is so hard. It makes for great traction and great climbing. I'm still not confident that we'll make it to the summit, since the images seem to show a transition to softer ground with more loose rocks ahead. But we're enjoying the conditions while we've got them.

And to make things even better, we seem to have found a nice piece of layered bedrock. This turned up right underneath the rover early this week after one of our long drives, and the timing was perfect. We've named it "Independence Rock", and we've maneuvered into position on it to do some arm work over the coming holiday weekend. We like to try to give the operations team a few days off on holidays, but of course we need to keep the rovers busy every sol. If we're trying to drive every sol we need to come to work and plan every day, since the terrain around the rover is always new and different. But when we're going to be parked in one place for several sols, we can plan multiple sols in advance and give people a little time off. So the Spirit team planned three sols yesterday and will be planning three more tomorrow, giving everybody on Earth the holiday off but keeping Spirit busy looking at Independence.

Of course we're dying to know what Independence really is. We haven't seen any MI images of it yet, but in the Pancam images it's finely layered, with a strange kind of porous texture. It looks a bit like Peace and Alligator, and a bit like Methuselah. Methuselah was one of the many high-titanium, high-phosphorous, low-chromium outcrops we saw all over the place on Cumberland Ridge, and Peace and Alligator were a couple of very weird sulfate-rich outcrops that we found our climb up to Larry's Lookout. I've felt all along that Peace and Alligator were probably the most important rocks we've found at Gusev, and it would be very cool to find another one like them. If I had to bet money I'd bet that Independence is similar to Methuselah, but I've been fooled by Mars so many times now that I think it's better not to make any bets. We'll find out very soon. And then it'll be time to resume the climb.

June 25, 2005

It's been slow going at Meridiani lately. We need to take a good hard look at Purgatory Dune with the instrument arm, but we've also got to show this dune a lot of respect... it got us once, and we don't want it to get us again. So as we're maneuvering into position on it, we're using a great deal of caution.

There are dozens of safety checks we can use when we operate these rovers. We can turn slip checking on, and we can abort a drive if we see more slip than we want. We can monitor the rover tilt, or the angles in the suspension system, or wheel currents, or you name it... and abort a drive if we don't like what we see. The big question in a situation like this is how tightly -- i.e., how conservatively -- we should set our limits. Do you abort a drive if you see more than 50% slip? Or 30%? or 20%? What about tilt, what about motor current? We've got most of our safeguards on as we approach Purgatory, and we've been setting the limits very conservatively, to make sure we keep the vehicle safe in this treacherous terrain. Of course, the unavoidable consequence of staying safe in a situation like this is that you also tend to go slowly... occasionally tripping one of the limits and aborting a drive. That has happened to us a couple of times recently, and we're still a few tens of centimeters short now of the place where we want to do the arm work. We're commanding another drive over this weekend, and we'll see on Monday where it puts us. Once we finally are in position, we're going to bang out the arm work as quickly as we can, and then be on our way. It'll feel very good finally to be moving again.

At Gusev, we're really moving... and it feels very good! Our journey to the south side of Husband Hill is well under way now. We've been spiraling up and around the west side of the hill, heading generally south and gaining elevation as we go. I've been surprised, as I think the whole team has, at how well this part of the climb has gone so far. Other parts of Husband Hill have been very tough going, but for some reason we're moving over this part of the hill very well. We've knocked off several drives of 20+ meters lately, which is really good for this kind of terrain, and there was one drive where we gained about three meters in elevation. Our drive paths have been nearly straight south lately, but now we're starting to curl around toward the east, more in the direction of the summit.

So now there are two big questions: Are we really going to go for the summit? And what will we see once we get our first good view to the south?

I really don't know about the summit. We all want it, of course... who wouldn't? We're doing the first mountaineering on another planet, and it would be a little frustrating fto get this close and not make it to the top. (I'm a climber when I'm not doing science, and Chris Leger, who has been the lead rover driver for Spirit much of the time lately is a really accomplished rock climber... so we both want this thing.)

However...

Mountaineering is not the point of this mission, obviously! We're here to do science, and we're only going to go to the summit if it makes sense scientifically. But there's a good chance that it will. The summit is directly between us and the terrain to the south that we want to explore, so going over the top may be a pretty efficient route to the good stuff. Also, the summit really is going to offer a pretty good view. Geologists in the field routinely climb to the top of the highest hill to get a good look at their surroundings and plan what they're going to do next, and we may want to do that here as well.

What it ultimately comes down to, I guess, is how hard the climb is. If we can get on top without wasting a lot of sols on our trek to the south, then we're definitely going to do it. But if we find the climbing is too hard and there's a significantly faster route to the south side, then we'll do that instead. So I simply don't know what's going to happen. But for now the going is good, so it's east, up, and we'll just take it sol by sol.

And then what will we see? We don't really know. The views toward the south right now are enticing, but so far we haven't seen much that we hadn't already seen before, albeit from a lower elevation. Orbital images of the south side of Husband Hill show some terrace-like structures that might be exposed layers, so those may be a major target once we get over there. There's also a big dark area that we think is probably a dune field, as many dark splotches on Mars are. And there are other features that we're simply not going to understand until we get a good look at them. The downhill run into the Inner Basin should in principle go pretty quickly once we start on it, but it gets very steep in places, so we're going to have to be careful. Anyway, we've got interesting times ahead, and everybody on the team is pretty pumped up right now.

June 15, 2005

Spirit's on the move. We've finished up our work in the whole Larry's Lookout/Jibsheet/Methuselah region and begun the long climb up and around to the south side of Husband Hill.

Our last big activity before we left was to check out the rock we named Backstay. This turned out really well, and it was a great example of how this machine works. First we used Pancam to survey the whole scene around the rover and figure out what was where. That showed us where Backstay was and what it looked like. Next we used Mini-TES to check out a lot of the interesting-looking rocks in the Pancam scene, to get a handle on what they might be made of. That gave us a hint that Backstay might be something new, and made us decide to go after it. Then we used the rover's mobility system to drive over to Backstay and put it within reach of the arm. After that we used the RAT to clean off the rock's surface, followed by MI, APXS and Moessbauer on it to see what it was really like. And the answer, to everyone's delight (particularly the Mini-TES guys, who had been the advocates for going to Backstay in the first place) was that it is indeed a martian rock type that we'd never seen before. It's a basalt, as you might guess just from looking at the pictures, but one with more titanium, more aluminum, less iron and more potassium in it than the basalts we saw out on the plains. We can't tell where it came from, of course, since it's probably a piece of impact ejecta, and maybe one that's pretty far from home. But it's definitely something new and interesting for the geochemists to puzzle over.

And with that, we're off into unknown territory once more. It really does feel good to be on the road again. (In fact, somebody put up a picture of Willie Nelson at today's Spirit SOWG meeting just for that reason!) The current plan is pretty much just drive-drive-drive for awhile unless something interesting and unexpected pops up in the images. So look for nice new vistas to the south as we work our way around the hill.

Good progress too at Meridiani, though we're being slowed down a bit right now by being in the period we call "restricted sols". This is what happens when Earth time and Mars time line up inconveniently, so that we have to plan each sol on the basis of what happened on Mars not yestersol, but the sol before. Despite being in restricted sols, we've gotten Opportunity through most of the three-point turn we're using to get her facing back toward Purgatory Dune. The next step will be to get into a safe position on the dune to try some arm work on it before we move on.

And dust is down a little at both sites, and Mini-TES on Opportunty seems happy and healthy. So life is good.

June 11, 2005

We've had a good weekend so far at Meridiani. Our objective at the moment is to turn Opportunity around so that we can safely approach Purgatory Dune and investigate it with the instrument arm and with our Mini-TES instrument. Rather than do a 180-degree turn in place -- which is possible but a little funky with a stuck right front steering actuator -- we're doing a three-point turn instead. We're partway through it now, and it's going really well... there has been very little slip, and much of the fine-grained debris that had been adhering loosely to the wheels has now fallen off. So we're very pleased with the progress so far. More progress should follow shortly.

So wait a minute, you may be thinking... Mini-TES? Wasn't the Mini-TES instrument on Opportunity malfunctioning? You may recall that the Mini-TES on Opportunity wasn't working properly awhile back, presumably due to the dangerously cold temperatures it sees each time we use Deep Sleep. But we've been keeping an eye on Mini-TES, and the last few times we've used it, the thing has worked just fine. Something's wrong inside the instrument, but whatever it is, the problem is an intermittent one, and right now the instrument seems to be okay. We're confident that using the instrument won't make matters worse, and in a situation like that the thing to do is to use it... aggressively. So for now the Opportunity Mini-TES is back in business. We'll see what happens.

And in the "it's always something" department... we are now facing a new threat to both vehicles. It is dust storm season on Mars. Dust storm season happens once per martian year, during the southern summer when the input of solar energy into the martian atmosphere is highest. And southern summer is now upon us. The atmospheric dust levels at both of our landing sites are high and climbing, and in fact the dust level at the Opportunity site is the highest we've ever encountered. It's not a serious threat yet, but it's a worry, and we're watching the dust levels in the atmosphere very closely.

The thing to realize about dust storms is that the threat is not high winds, nor is the primary threat dust buildup on the solar arrays. Instead, the primary threat is simply the attenuation of sunlight by dust that is suspended very high in the atmosphere, and the resultant loss of power from our solar arrays. RIght now we've got power to spare on both vehicles, and there is no imminent danger. But martian dust storms are notoriously hard to predict. In some years things are pretty quiet, and in other years what starts out as a small regional storm can blow up quickly into a monster that covers the whole planet, with solar attenuation that could be very bad for our vehicles. We have no way of knowing what's going to happen this year.

With both vehicles in such good shape, and with the solar arrays as clean as they are at the moment, we can handle a lot of atmospheric dust and come through it okay. And even if things do get very bad, there are a number of tricks we can use to save power and ride it out until the atmosphere clears. Still, we've learned that exploring Mars involves nearly constant peril, and dust storm season is looming as the next significant peril we may have to face.

June 9, 2005

Today is something of a landmark for us. As of the end of today's MER-B Command Approval Meeting, which will take place late this evening on the west coast of the US, and probably close to midnight here on the east coast, we will have planned one thousand sols on the surface of Mars... 490 for Opportunity and 510 for Spirit.

The uplink process for these vehicles is intense, engrossing and exhausting. At some point I probably should sit down and describe it in these pages. For today, though, I'll just tip my hat to all of my friends, colleagues and comrades -- engineer and scientist alike -- on the MER uplink team. 1000 sols is a remarkable accomplishment.

Good things are happening on both sides of the planet. At Meridiani, we'll soon begin our first maneuvers to reorient the rover so that we can study the feature that got us and then be on our way again. And the feature that got us now has a name: Purgatory Dune. We weren't calling it anything back when we were stuck in it, but now that we're out, it seemed there ought to be a name for the thing.

At Gusev, Spirit is parked at Backstay and crankin' away. Once we're done with Backstay, we're going to do a quick drive-by of Methuselah to get a little more imaging on it that'll help tell us which way the rocks are tilting. And with that done we'll be ready to move on.

If you've been reading these pages, you'll note that I haven't said yet where we're going after Methuselah. I wasn't playing games... the reality was that we hadn't decided. It's a much tougher call than you might think, because there are some very interesting outcrops down in Tennessee Valley, and some really good-looking stuff on the far wall of the valley. But after a lot of thought we have finally decided, and the decision is to head up Husband Hill. We're not going to try a frontal assault this time. Instead, we're going to spiral up and to the right, working both upslope and also cross-slope simultaneously. Whether we'll actually reach the summit is an open question at this point. But we're convinced that the route we've chosen offers the quickest path to a view of whatever's on the south side of the hill... and that's what we want to see next.

June 4, 2005

Boy, this has been a good day.

We've had a feeling over the past several days that this was coming. On each of the last few drives, the rover slipped a little bit less than it had been for most of the extraction. In addition, the right bogey (the part of the suspension that the right middle and right rear wheels are mounted on) recently started moving in a way that suggested that the wheels were finally coming over the crest of the dune. And we knew from all our earth-based testing that when a stuck rover breaks free, it tends to do it very abruptly. So all the signs were suggesting that the big breakout was almost upon us. Still, it's hard to describe how good it felt to check out the downlink this morning and see all six wheels back on solid ground again. You develop pretty strong feelings for these vehicles once you've spent enough time with them, and when one of them gets into trouble you really sweat it until the trouble is over.

So what comes next? The first thing we're going to do is simply take a very hard look at the stuff we were stuck in. Much of the worst terrain was under the belly of the rover through all of this, down where we couldn't see it. From our new position, everything that was under us for all those weeks is now visible. So we're going to take a little while just to look at where we were. We may also turn to take a look at our tracks (or trenches, or whatever you want to call them) with some of the instruments on the arm. But we'll see about that one... we'll only do it if we're convinced it's safe.

After that -- and there is no timetable for any of this -- we will begin a cautious set of moves to get us on our way again. And just so there's no doubt about it, this little incident is not going to deter us from continuing our southward exploration. South is where we think the best science is, and we're not going to turn tail and run because of one unfortunate episode. Now if we find after continued driving that the southward road is simply impossible, then it'll be time to start thinking about something else. But for now, south is where we plan to go.

And lest I forget our other baby in all the excitement... Spirit is doing very nicely. We were just about to hit the gas and head on out of here, but in the last couple of days something interesting and unexpected came up. Mini-TES, our infrared spectrometer, is a very nice compositional survey instrument. In other words, it's a tool we can use quickly to look around and learn something about what rocks are made of. We've been doing lots of Mini-TES observations on the rocks around Spirit for awhile now, it's gotten to the point that nearly every rock type is pretty familiar. But late last week, we came across a rock called Backstay that looks, to Mini-TES, a bit different from anything we've ever seen before. It's a loose rock, not bedrock, so it may be a piece of impact ejecta from someplace far away. The Mini-TES spectrum is nothing wildly exotic... the thing certainly seems to be some kind of basalt. But if it's a flavor of basalt we haven't seen before, then it's definitely worth a quick look. And luckily, a quick look is possible. Just about the time that we realized that Backstay was something interesting, our most recent drive had put us just four meters away from it. So the plan for the next few sols is to drive to Backstay and figure out what it is before moving on to anything new.

Time to go celebrate...

June 4, 2005

We're out! The Sol 484 downlink from Opportunity just hit the ground, and all six wheels are on top of soil. More later when I've got some details, but I wanted to get the news out now while it's hot. We've been confident all along that this would happen but still... what a relief!

June 2, 2005

Steady progress on both sides of the planet.

At Meridiani, we've picked up the tempo a little bit. On each of the last two sols we've commanded 20 meters worth of wheel turns, and on each we've seen about 12 cm worth of motion. That's encouraging; it's a rate of progress at or above anything we've seen so far. Perhaps more significantly, we're starting to see some changes in the geometry of the rover's suspension that suggest that we're making real progress over the crest of the ripple, which we were straddling back when all this started. The right rear wheel is starting to come up now with respect to other parts of the suspension, which means that the right middle wheel (which we can't see) has to be going down. And if the right middle wheel is going down, that probably means that it has crossed the crest of the ripple and is starting to go down the other side. I'm still not ready to guess when we'll be on our way again, but it's really heartening to see the kinds of changes that we knew we'd need to see before we could get free.

Over at Gusev, we've finished up our work on Larry's Lookout. In fact, we've only got a few odds and ends to tie off now before we leave this region for good. The most important of those will be to motor back toward Methuselah and get one more set of Pancam images there, aimed primarily at allowing us to make some fairly precise calculations of the orientation of the layering... what geologists call strike and dip. Once that's done, we'll be ready to leave the whole Lookout/Jibsheet/Methuselah region behind, and strike out toward new territory.