Mission News

JPL Media Teleconference
01.28.10
 
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Operator: Thank you for standing by.  At this time, all participants are in listen-only mode.  After today's presentation, there will be a question-and-answer session.  At that time, to ask your questions press *1 on your phone.  Today's conference is being recorded.  If you have any objections you may disconnect at this time.

I would now like to introduce your host for today's conference.  We have Mr. Dwayne Brown.  Sir, you may begin.

Dwayne Brown: Thank you, Operator.  Good afternoon, everyone.  My name, again, is Dwayne Brown, with NASA's Office of Public Affairs.  Let me say Happy New Year, and welcome to the Mars Exploration Rover Spirit teleconference.

We obviously have a lot to cover, so I will introduce today's speakers and we will then open it up for questions and answers.

First up will be Doug McCuistion, Director of the Mars Exploration Program here at NASA headquarters in Washington.  Following Doug will be John Callas, Project Manager for the Mars Exploration Rovers at NASA's Jet Propulsion Laboratory in Pasadena, California.  Following John will be Ashley Stroupe, rover driver, Mars Exploration Rovers, also at JPL. And someone who probably doesn't need an introduction – he has been the face of science for the rovers and you all know him very well, Steve Squyres, principal investigator for the Mars Exploration Rovers. And he is from Cornell University.

So with that, I'll turn it over to Doug.

Doug McCuistion: Thanks, Dwayne.  Welcome, everybody.  As everybody knows, Spirit is in a difficult situation.  Spirit has encountered a golfer's worst nightmare – the sand trap that, no matter how many strokes you take, you can't get out of it. But, you know, this is not a day to mourn Spirit.  This is not a day of loss at this point and you'll hear that story much more explicitly with our panelists. 

Spirit will continue to make contributions to science and to the understanding of Mars.  It'll continue to excite the public globally, I believe.  And you'll hear about that science from Steve later. 

The Mars Exploration Rover Project consists of both Spirit and its sister ship, Opportunity, on the other side of the planet. Just celebrating its sixth anniversary on the surface two days ago, it is still doing great science and still exploring roving and driving.  It's in a trek from Victoria to Endeavor Crater.  It's found quite a few exciting things along the way in the sand dunes between meteorites and other materials.  It's now approaching an extremely young crater named Concepcion that's probably the youngest crater we've ever had the opportunity to explore.  This will be very, very exciting in the next weeks and months for Opportunity.

So the Rover Project still roams the planet and still is doing exciting things, regardless of Spirit becoming a stationary platform at this point.  Its driving days are likely over for all intents and purposes, and you'll hear more about that.  However, its contributions will continue.  The public will still be engaged.  We will continue our exploration goals.  Steve will expand on this, as I said.  But of course, a little bit more information will be provided first on the challenges that Spirit has.  The winter on Mars is coming.  We have to have the right tilt to the solar rays and we have to prepare Spirit so that it can do this exciting science after the [unintelligible crosstalk] is over. 

I would encourage people to please put their mute buttons on.  We're getting a lot of background noise. 

At this point, I'd like to pass it over to John Callas and Ashley Stroupe to discuss a little more of the engineering status and what's coming up in the winter and what the challenges for Spirit are. John?

John Callas: Thank you, Doug.  Good afternoon, and good morning to those on the West Coast.  As Doug mentioned, Spirit is embedded. She's been embedded for about ten months now and we have been engaged in a very ambitious process and attempt to extricate the rover.  But during the embedding process, we had yet another setback – we lost functionality in another wheel.  You may recall about four years ago we lost functionality in the right front wheel. We have since lost functionality in the right rear wheel, so we now have only four functioning wheels on this vehicle and the extrication process has been extremely challenged because of that.

But the most immediate issue for Spirit right now is surviving the next Martian winter.  We're in the Southern Hemisphere.  The sun is moving to the north.  The winter solstice is around the middle of May so we're a few months away from that solstice point.  And we're clearly seeing a decrease in energy levels for the rover.

In past winters we've always been able to position the rover such that we could tilt its solar rays to the north to maximize the generation of energy by those arrays.  Our solar rays are not particularly dusty right now, as they have been in past winters, but the embedding has left the rover with an unfavorable tilt.  We're tilted right now about nine degrees to the south and what we would really like is a level rover or a rover that's tilted to the north.  And shortly, you'll hear Ashley describe what's remaining in terms of motion activities before we settle down for the winter.

Let me talk about what the winter prospects are for the rover.  We'll be experiencing decreasing energy levels.  In our current tilt, if we aren't able to substantially improve our tilt, we'll see energy levels drop before levels that are sufficient to keep the rover constantly active through the winter. Right now we estimate we'll need about 160 watt-hours on a sustained level each day to maintain the rover activities -- in other words, what we call Earth and control.  This means that we're able to talk to the rover each day. 

What is likely to happen if we can't improve the tilt is we'll trip what we call a low-power fault, in that we don't receive as much energy each day as the rover consumes, and so it takes that deficit out of the batteries and eventually the batteries drop below a minimum state of charge and the rover goes into this fault mode where it basically shuts down. It causes the rover to literally hibernate.  Pretty much everything is turned off except the master clock and every photon that hits the solar rays then goes into charging the batteries.

Now, what happens when the rover is in this state is that the clock sets a timer each day and when that timer expires the rover then wakes up just a little bit to check its status.  It checks to see how charged the batteries are, and if the batteries have charged back up enough the rover will then wake up and attempt to communicate to the Earth, or it will allow us to communicate to it.  But if the batteries are not charge enough it will go back to sleep right away.   So the rover will be like a polar bear, hibernating.  And it could be for many months.  It could be of the order of six months that the rover will be in this state. So we have to be prepared to go through a period where we're not hearing from the rover for an extended length of time.

Now, this is not like the Phoenix mission. This rover is still electrically active. It's just that it has insufficient power to be awake each day and so it's taking the necessary steps to preserve that power.  The concern and the challenge is that the temperatures are going to get cold for Spirit. Normally we keep the rover warm by actually having it on.  This is similar to running your car engine to keep the heat on.  But since the rover will be deeply sleeping during this period the temperatures will drop, and we're concerned that the temperatures are going to get very cold. 

The sensitive electronics are designed with withstand temperatures as low as –40°C when they're operating and as low as –55°C when they're not operating.  We expect that the electronics will get below –40°C, perhaps around the mid-forties, so –45°C, during the depth of winter.  But the electronics will be off.  When the rover checks to see whether to wake up each day, that's typically done around the middle of the day when the temperatures are warm enough. And we expect, at that point, the electronics to have warmed back up due to sunlight to above –40°C.  So right now the estimate is that the rover, even though it's getting cold, will stay within its design limits.  But I'll caution that those design limits were tested for a brand new rover, fresh out of the box.  And this is a rover that's been on the surface of Mars now for over six years and has endured thousands of grueling temperature cycles.  So there's no guarantee that the rover would be able to survive these colder temperatures.  I mean, these will be temperatures that are colder than anything we've seen before on the surface of Mars.  And we will have this extended period of time of not hearing from the rover, so that's going to be frustrating and challenging for the team.  But it's something that we'll just have to be disciplined about in that eventually when power allows the rover will wake up and begin to talk to us and then we can resume activities in the spring.

So at this point I'll turn it over to Ashley and have her describe the remaining steps we have to go before we batten down for the winter.

Ashley Stroupe: Thanks, John.  As John mentioned, ideally the solar panels should be pointed as closely to the sun as possible in order to maximize the energy that the rover receives.  And this not only will help the rover keep warm but should also be able to shorten that period of time when the rover is in that low-power state, which also improves Spirit's chances of being able to return to full functionality after the winter. 

So we're focusing on trying to maneuver the rover to improve the positioning of the solar panel.  Right now the rover is pitched approximately flat and it is rolled significantly onto its left side.  Ideally, given where Spirit is parked, we would really prefer her to be pitched downward and either flat or even rolled slightly to the right.  The best way to try to improve both the pitch and the roll would be to get the left rear wheel of the rover lifted up.  And our last few drives actually were dedicated towards attempting extrication but also were aimed towards improving this northerly tilt.  We're sitting slightly on the edge of this little crater, with the outside rim of the crater behind us.  And as we back up, the rover is moving that left rear wheel towards the outer edge of the crater and is slowly climbing up.  And in fact, on our last drive we saw a significant improvement in our northerly tilt of about one to two degrees over a short distance of a few centimeters. 

So this is the maneuver we're starting with. We're going to do as much improvement as we can by trying to lift that left rear wheel by continuing to drive backwards and try to improve both the roll and the pitch.  There are some other things we can do if that doesn't improve it enough.  We can attempt to rotate the rover in place a little bit, trying to make it so that the roll isn't pointed quite as much towards the south as it currently is. And we have had some success in being able to turn the rover in place just driving the wheels on one side versus the other.

So that's our primary mission right now, is to get those solar panels pointed more towards the sun to improve not only the amount of energy she'll get and the internal temperatures but also the amount of time that she'll have to be in this dark hibernation period. 

Then of course after winter we will continue to use the mobility system as best we can to follow the science.  There's a significant amount of science left to be done at this site, which in just a moment I'm going to pass off to Steve to talk about.  And we will continue to make the full capabilities of this rover at the scientists' disposal when we hopefully come out of winter.

With that, I will pass it off to Steve to talk about the fantastic science campaign we have planned for the spring.

Steve Squyres: Thanks very much, Ashley. As you heard from John, we have hope that Spirit will survive this cold, dark winter that we have ahead of us and be ready to do more science come springtime.  So I want to talk a little bit about what we can expect.

Spirit was built with six wheels and when you have a rover with six good wheels on Mars you feel a relentless imperative to drive it. Driving brings you into new terrain and enables new discoveries, so as long as this rover has had its mobility capability we keep moving.

But when you have a four-wheel rover – which is effectively what we have now – and when its mobility is very limited, that imperative to drive is relaxed.  And what that does is it enables us now to focus on new classes of science that you can only do from a platform that isn't moving around a lot.  So I'm going to take you through some of the science that we expect to do.

The one that I am most excited about is one that involves tracking the radio signal from Spirit.  This is totally new.  This is something we have never done before.  By tracking the radio signal from the rover very carefully, it's possible to very accurately determine the rover's motion through space in three dimensions.  Now, if the rover is not driving then the motion that it undergoes simply results from two things – the motion of Mars in its orbit, which is something we understand extremely well, and the spin of Mars about its axis.  Mars spins on its axis and it turns out that because of gravitational interactions with the sun and the moons of Mars, Mars's spin axis wobbles ever so slightly. So if we can track the motion of the rover very precisely and watch Mars spin, we can characterize very precisely the nature of that wobble.

Now, the reason that's important is that the way in which Mars wobbles depends on its internal structure.  And when you go through the math what you find is that if Mars has a solid core of iron it'll wobble in a certain well-defined way. But if that core is liquid, it'll wobble in an ever-so-slightly different way.  And by tracking the rover's position long enough and carefully enough, we can distinguish between the two.  So we believe that by simply tracking an essentially stationary rover for about six months and characterizing the wobble precisely, we think we can actually determine whether the core of Mars is liquid or molten – totally new science, never been done before, really fundamental stuff.  This is something that I didn't really think much about when we first put a rover on the surface of Mars because we were thinking about the geology of the surface.  But when you delve deeply into what this vehicle is capable of, you find new tricks.  And this is one that we're extremely excited about. 

Another thing that we can do is study the way in which the Martian atmosphere interacts with the Martian surface.  When you're driving, the scenery is always changing and so your view of a particular piece of real estate on Mars is different one day than it is to the next and that makes it difficult to detect changes. And in fact, there could be some patch of Mars that you're interested in but you drive over a ridge, you drive out of sight, and you can't even see it anymore.  If you stay pretty much fixed in location you can look at the same patch of Martian terrain over and over again and you can watch it change.  The wind blows on Mars, it blows dust around, it blows sand around – these transport processes are fundamental to shaping the Martian surface today, and yet they're very hard to study from a vehicle that's always moving.  Once you've parked for a while, you can look at the same patch over and over again and you can characterize the changes that take place. 

And we will do that on macroscopic scales by using our cameras to look off into the distance.  We can do it on microscopic scales too.  We can take a piece of soil in front of us, hover the microscope over it, take the picture, and then take another picture days or even weeks later and see the grains move.  So we are going to be able to characterize the way Martian wind stirs up the soil in a fashion we've never been able to do before.

Finally, we can do a really comprehensive job of characterizing the soil in the vicinity of the rover.  Spirit didn't get stuck here by coincidence.  Spirit got stuck here because this is a really strange set of soil that we have roamed into.  The soil here is not like normal Martian soil.  It's extraordinarily rich in sulfate salts, and it makes it horrible stuff to drive in and that's a big part of why Spirit got stuck where it did. But scientifically, this stuff is tremendously important.  We think that these sulfate salts initially formed when there were steam vents – geologists would call them [fuma] rolls – at this location, where hot caustic steam was coming out of the ground and changing the chemistry of the local soils.  And then, perhaps billions of years later, there were other water processes that caused these salts to move around.  Some of these salts are very soluble in water, and when we look very carefully at the structure of the soil in front of us in three dimensions we can see evidence for layering.  We can evidence that more soluble salts, the ones that you can dissolve in water, have actually moved around.  And that suggests that thin films of water have formed in the past and salts have moved around.

And right now, we've got a moderately good picture of the structure of the soil in this location.  But by having a lot of time to make measurements with the instruments on the end of the arm, we can characterize the soil in much greater detail. And, as Ashley pointed out, we expect to be able to use the wheels on the rover come springtime to slightly reposition the rover – to swing it back and forth a little bit, to move it forward and backwards a little bit – bringing new patches of soil within reach of the arm and enabling us to really characterize this very, very interesting salt-rich soil at this location much more thoroughly than we have been able to, really, anywhere else on Mars. 

So the bottom line is we're not giving up on Spirit.  Since the start of this mission, we've really done everything that we can to try to squeeze very last little bit of science out of these rovers.  We're going to keep doing exactly that.  And once springtime comes, if the vehicle is still alive and talking to us we feel that there's a lot of really exciting science ahead, including some stuff that I think is truly groundbreaking. 

And with that, I will hand it back to Dwayne.

Dwayne Brown: Thank you all.  Before we take questions – and the operator will give you instructions – a few things of note: first of all, we will have replays of this teleconference for the remainder of this week.  The toll-free number is 866-502-6119.  For international media, it's 203-369-1860.

We have a number of television representatives on the line.  Please go to NASA TV and look at the schedule.  There will be some very interesting video and comments featuring Doug McCuistion.  Check the NASA TV schedule.  We'll be feeding that.  And also, for our radio reps, we have some digital high-quality sound bites from Doug as well at the new Web site.  So for television and radio, we have those available to you. 

Last, but certainly not least, the incredible folks at JPL that do our education and outreach – it's certainly safe to say that the rovers are loved by thousands and certainly millions worldwide.  It's an inspiration-of-science icon, and folks have been engaged in sending e-mails and the outreach folks have come up with a very, very cool and cute idea for students and folks worldwide to send their comments via postcards.  If you go to www.nasa.gov/rovers you will see that, and if you have any further questions on how that mechanism works please feel free to call the JPL office.

With that, Operator, I'll turn it over to you to facilitate the Q&A.

Operator: Thank you so much.  [Directions for Q&A].  The first question comes from Joe Palca of NPR.  Your line is open.

Joe Palca: Hi, guys.  I have two quick questions of a technical nature.  One is: has either of the rovers been put into this hibernation mode before? And the second question is about this notion of which direction is backwards.  As I remember, it backed into its predicament and so backwards was forwards and I'm not sure word to use.

John Callas: The question about if we've been in this hibernation mode – this is what's called a low-power fault.  The only time that either rover experienced that was shortly after landing with Spirit.  We had the Sol 18 anomaly and there it was a problem that the vehicle was caught in a continuous reset.  And so it wasn't sleeping – it was consuming energy from its batteries and it tripped this low-power fault.  But we have not had an extended period of time under low-power fault.

And I'll further add that we're likely to trip this low-power fault multiple times, in that the rover will attempt to wake up and will not have sufficient charge to the battery and it'll trip the fault again. So it's likely to be a cyclic process during the winter.

In regards to your second question about which way is backwards, the rover was driving backwards heading south when it became embedded in this location we call Troy.  So when Ashley was talking about driving backwards recently, we're continuing in the southerly direction but the rover is pretty much pointed north.  It's actually more northwest at this point. But the direction is still pretty much to the south, with the rover facing backwards at that point.

Joe Palca: Thank you.

Operator: The next question comes from Eric Hand of Nature.  Your line is open.

Eric Hand: Hi, all.  This question, I guess, is for Doug or for Steve perhaps.  Can you tell me what the annual operations cost would be for Spirit while it was roving and what you expect the cost to be once it begins in its stationary mode?

Doug McCuistion: That's mine, Steve.  The budget for the rovers as a pair – in other words, for the project – is about 20 million a year.  What it will be for one roving and one not roving – I don't have an answer to that yet. We have a senior review coming up in February that is our regular annual review of all of our operating missions and what their science plans and related budgets are, and that's done by an independent panel.  As I said, that will occur in February and that will feed into the regular budget process that begins in the March/April timeframe. 

So it all depends, Eric, on how much work the science is, how much repositioning we want to do, and things like that.  I can tell you it's really not clear at this point whether there will be a change in their budget.  We'll figure that out over the next number of months and when we see how Spirit handles the winter as well.

Eric Hand: Thanks.

Operator: The next question is from Emily Lakdawalla from Planetary Society. Your line is open.

Emily Lakdawalla:   I have two questions.  One is: just to be clear, are you going to try extrication again in the spring or are we done with extrication and Spirit is now a stationary lander?  The question is: I know that Mars Pathfinder also did some radio tracking and I know it didn't last as long, but is Spirit better by virtue that it's going to be longer or does it have a better radio system?

Doug McCuistion: I'll take the first one and then, Steve, can you answer the second one in regards to Pathfinder?

Steve Squyres: Yes, sir.

Doug McCuistion: Okay.  Right now, the rover is embedded in the Troy location.  We do not believe that it's extractable.  If it is, being a four-wheel-drive rover instead of a six-wheel-drive rover – and the two wheels that John mentioned that are failed are both on the same side – it certainly couldn't really make any headway.  As you recall, those wheels do not spin freely. They are fixed, so you're dragging them. So we believe that the mobility of this rover is complete and that extrication may be by accident.  But right now our plan is to worry about getting through the winter and then enabling this science campaign, as Steve said. The radio science, the geophysical radio science, is really a high priority in the science community.  We've never done it before, and that is our first priority.

Steve Squyres: And, Emily, with respect to your second question, there have actually been three opportunities in the past to track radio signals from landers on the surface that are far from the pole, the two Viking landers and Pathfinder as well. 

Pathfinder contributed a bit to this understanding, but because the Pathfinder mission was much shorter in duration than the tracking period we're talking about it was not able to resolve the issue of the state of the Martian core.  The Viking landers, of course, were tracked for a very long period of time but they used a different communications frequency, and that was one that was substantially affected by electrons in the solar plasma and prevented the kind of science that we're talking about.  So this is a unique and new opportunity.

Emily Lakdawalla:   Thank you.

Operator: The next question is from Tariq Malik of space.com.  Your line is open.

Tariq Malik: Thank you very much.  This is Tariq Malik from space.com.  I think my question is either for Steve or John.  I'm just curious about your thoughts on being at this point where you can't declare Spirit mobile.  It seems like it was a valiant campaign and effort to try to free the rover. Do you have thoughts on that shift in mindset from operating a rover to now a stationary science tool?  Is it bittersweet at all?  Are you sad?  Were there hopes all the way to the end?  If you can give us an idea on that, that would be great.  Thank you.

Steve Squyres: I'll take a swing at that one.  It's kind of a poignant moment for us, you know?  We built these vehicles with the intention of driving around on the surface, and Spirit has done that magnificently for the better part of six years.  So seeing us shift our focus to a different class of activities – you know, it's a change and it's one we're going to have to adapt to.

I will say, though, that it's a much, much better alternative than some other ways that I could see this mission going.  There are a number of ways in which one of these missions could end, and some of them you can imagine being very abrupt.  If we had an abrupt end to this mission of any sort, it would preclude doing the kind of science that we're looking at for Spirit, going ahead.  And we'd never be able to do some of, for example, this geophysical stuff that we're so excited about. 

If, instead, the natural evolution of the vehicle is we go from being highly mobile to less mobile to very, very hard to move significant distances – which is where we are now – it enables a class of science that you wouldn't be able to do otherwise.  And if the final scientific feather in Spirit's cap is that we can determine whether Mars has a solid or liquid core – man, that's pretty cool.

So, you know, it's an adjustment and it's something we're going to take some time to get used to.  But I'm feeling actually really good about this.

Operator: The next question is from Craig Covault, at spaceflightnow.com.  Your line is open.

Craig Covault: A couple of questions: first, from an earthly calendar perspective I guess I'm not quite clear on when your science awakening will be started.

John Callas: As I mentioned, we're likely to fall into this winter hibernation beginning in the March/April timeframe.  And winter solstice is in the mid-May timeframe, but it's not going to be a symmetric kind of time behavior.  So right now, we're looking at late summer Earth time, the August/September timeframe, of coming out and resuming our science campaign at that point.

Craig Covault: Okay.  And a more general one, perhaps for Steve: a rover kind of gives you the ability to have a new landing site about every other day.  Even though you've been there at Troy for several months, once you come out on the other side of winter do you still have enough to do there that it's going to be very much like landing at a brand new landing site for you?

Steve Squyres: Yeah, I think it is.  And the key thing here, Craig, is that this isn't just any old spot on Mars. As I said earlier, we got stuck here for a reason and the reason is that this is bizarre soil.  This is very anomalous stuff.  It doesn't behave like almost anything else that we have seen. Not only does it have these high concentrations of salt, including the highest concentration of sulfates that we've seen anywhere on the planet with either rover, but they're layered.  And they're layered in a very intricate and interesting fashion. 

We were driving along, it turns out, on a crust of this stuff that was sort of strong enough to support the rover for a while, and then we broke through it.  So there's a really interesting story here that we've only really begun to understand. And we're very fortunate that this new landing site, as you put it, has turned out to be an exceptionally interesting one.

Craig Covault: Thank you.

Operator: The next question is from Alan Boyle of MSNBC.  Your line is open.

Alan Boyle:  I wanted to ask about the thought processes over the last few days.  It sounded as if there were some activity, some movement, and some hope that the rover could get going again.  Was it a case of hopes being raised and then deciding, well, this is reality?  How did the ups and downs of that process to decide to focus on survival take place?

Steve Squyres: Ashley, you're probably the closest to this as a rover driver. Would you like to answer that one?

Ashley Stroupe: Sure.  We changed our approach to extrication about a week and a half ago, driving backwards. We had seen actually surprisingly good performance.  Instead of moving on the order of millimeters we'd been moving 5+ centimeters per day, which had given us a tremendous amount of hope that we might be able to pull this vehicle out.  But we're running out of time, so at this point even if we wanted to preserve the option to continue extraction later we don’t have time to complete that process before winter.  So we're going to have to really focus on guaranteeing that we still have the spring to do this science campaign and then whatever else follows on – whether that be extrication in four-wheel driving or something we haven't even imagined yet.

But at this point, we've been really focused I think as a team more on the day to day – you know, trying to get the most for this rover. I don't think we've necessarily fully changed our mindset in our heads just yet in terms of changing to more stationary ops.  So we'll just have to see where that takes us when the spring comes.

John Callas: Let me just add to what Ashley's saying.  The seasons are determined by Mars, not determined by the mobility of the vehicles so we had always been in a mode of preparing for the next winter.  And that has dominated the activities for the last several weeks, if not months, on the vehicle.  So, yes, we are running out of time.  We're getting to a point where no matter what we want to do we have to prepare for winter, and that's where we're focused right now.

It turns out that moving the vehicle backwards in a path towards extrication is actually the right thing to do in preparing for winter. And we have had some good results lately, but the reality is whether the rover is embedded or not we need to prepare for winter now.  And that's what we're doing. 

Operator: The next question is from Chris Lintott of BBC, Sky at Night.  Your line is open.

Chris Lintott:   I wanted to ask about the implicit weather forecast that was contained in some of the things that were said at the top of the call, in that you expect the temperatures to drop below the –40 level but not reach the critical –55.  I wonder if you could say more about whether that's based on previous winters at Spirit's site, on some sort of weather prediction model – where that base is coming from and what the error bar is on that critical prediction.

John Callas: We have gone through three winters so we have experience and we have actual data from the previous seasons.  And they do vary in terms of temperature.  I mean, some winters are colder than others.  So we've taken that experience base and we have a detailed thermal model, computer model, of the rover and we've then propagated that forward in time, given what we expect the range of environmental conditions will be.  We then look at what the resulting temperatures are, and that's what our model tells us.

And our models have been pretty good, to within a few degrees.  Now, if the winter is particularly colder than we're expecting then the temperatures could get commensurately colder as well.  But I'll just mention that the rover electronics are insulated inside a box and that box also has what are called RHUs.  These are radioisotopic heaters.  So even though the rover is not powered, a small amount of thermal energy is being expended to keep the electronics warm.  So the interior of the rover never gets as cold as the exterior of the rover.

Chris Lintott:   Thank you.

Operator: The next question comes from Irene Klotz of Reuters.  Your line is open.

Irene Klotz:  Thank you very much.  I had a couple of questions.  First, is there anything besides trying to adjust the tilt of the rover that you want to do before this winter shutdown?  Any instruments that need to be saved, et cetera?  And the second question has to do with Phoenix, if anybody knows if there are still attempts to contact that lander and, if not, when you called that off.  Thanks.

John Callas: I'll speak to the first question.  Just to remind people, our rovers shut down every single day. They take naps and things get turned off.  But there are specific things we will be doing in addition to adjusting the tilt of the rover to prepare Spirit for the winter.  There are different parameters that control the behavior of the rover and we'll be adjusting those parameters.

For example, one of the things we'll change is normally when the rover trips a low-power fault it attempts to communicate.  It attempts to turn on its transmitter. Well, that's a big power hog so what we're going to do is we're going to tell the rover just to listen during these times.  So it'll save that energy that way but of course in that case we have to be proactive in an attempt to talk to the rover, which we'll do. 

So it'll be things like that.  These will be basically parameters that control behaviors within the rover electronics that we'll be modifying.  Those are essentially the only things that we need to do in addition to improving our tilt to get ready for winter.

Doug McCuistion: As far as Phoenix is concerned – to your second question, Irene – this is a very different situation.  Phoenix was never expected to make it through the winter.  It wasn't designed to handle the kinds of temperatures that it was going to see in the Martian Arctic, essentially encased in ice through the winter.

What we do is we listen for it.  It's designed so that it comes up and basically sends communication signals, and we listen for it with the orbiters – mainly Odyssey. We had a three-day period in January where we did not expect to hear from it.  Because of the time of year we don't there's enough power, but we wanted to listen anyway.  We did not hear anything.  We have another couple of opportunities in the February/March/April timeframe that we will be listening but my guess is it's highly unlikely that we'll hear anything from Phoenix.  That's the situation with that.

Operator: The next question comes from Todd Halvorson of Florida Today.  Your line is open.

Todd Halvorson:  Thanks very much.  I'm wondering if somebody can tell us what the environmental conditions will be for Opportunity at the same time that Spirit is going through this long, dark winter. And can somebody maybe put some odds on the chance of survival for Spirit?

Steve Squyres: I can handle the first part of that.  I'll leave the odds up to John Callas.  Opportunity is in a very different thermal environment.  The primary reason is that it's much closer to the Equator.  The Opportunity landing site is only a few degrees off the Martian Equator, whereas the Spirit landing site is at 16 degrees south.  And because the tilt of the Martian spin axis is pretty similar to that of Earth, the seasons that you encounter when you're off the Equator are substantially more severe than they are when you're near the Equator.  So Opportunity is continuing -- even though Opportunity is actually pretty dirty right now; we haven't gotten a good wind gust there in a while, though we certainly expect to because that's been the norm there in the past – Opportunity has always been an active vehicle through every Martian winter and we certainly expect it to be through this one as well.  So the environmental conditions at the Opportunity site are just way, way more benign than they are at Spirit's.

John, I'll leave the odds to you.

John Callas: Okay.  I won't give you odds but I will tell you this is a much more difficult and dangerous situation for Spirit.  We are going into a regime where the vehicle is going to get colder than it ever has on Mars.  Yes, it's within the design limits but that again was for a brand new rover, not one that's been six years on the surface of Mars and been battered by thousands of diurnal temperature cycles. 

Also, we feel that Spirit's best chance for survival is when we're able to stay in touch with her.  You know, it's kind of like we're parents and we're sending our kids off to college and the angst we go through when they're on their own, and we feel that as long as we can talk to them, advise them, and encourage them they stand their best chance of success.  It's the same kind of thing with Spirit, because if we were able to maintain communication with the rover we could look out for trouble.  We could see, we could advise Spirit on how to reapportion her limited resources to maximize chance of survival.

If we go into this low-power fault we won't have that opportunity, and Spirit will pretty much be all on her own.  She's designed to go through this but, again, I'll caution: that was for a brand new rover. 

[Todd Halvorson]:   [Unintelligible] I was wondering if somebody has the total project cost for both rovers to date and the number of scientific papers that have been generated as a result of these rovers to date.

John Callas: I can give you an indication of the total cost.  This is counting design, development, testing, launch, prime mission operations, and up through the current extended mission operations.  We're above 900 million dollars. 

Steve Squyres: And the number of scientific papers -- it's been a lot.  I don't have a good count in my head. John, do you know that number?

John Callas: No, I don't, Steve.  It's a lot.

Steve Squyres: More than I can keep track of, I'll tell you that. 

Dwayne Brown: This is Dwayne.  I'll get you guys a good number and those who want the accurate number, just give me a call, Todd or anyone else.

Operator: The next question comes from Miles O'Brien of This Week in Space. Your line is open.

Miles O'Brien: Hi.  This question is for Ashley.  Ashley, can you walk us through the process of tilting Spirit?  How do you go about that?  Is it like rocking a car back and forth that's been stuck in a ditch?  If you can describe it in some way, that would be helpful.

Ashley Stroupe: Sure.  Unfortunately, rocking a car back and forth in a ditch works because you can build up some momentum with your acceleration.  We have basically no acceleration with this vehicle so we have to rely on the ground beneath us, with the wheels solidly on that ground, to provide the tilt.  So what we're trying to count on right now is the fact that we're sitting on a hill, and if we can back up that hill and lift the rear of the rover that's going to naturally point the solar panel towards the sun.  We've been doing this backing for the last several days and we've actually successfully moved about twenty centimeters now backwards up this hill, and on this very last drive we actually caught that hill a little bit and we actually really significantly improved our tilt by about one to two degrees.

So we're going to continue that process of trying to back the rover up the hill.  And once those rear wheels and possibly even the middle wheels have caught that hill that should give us a significant change in the tilt.

Miles O'Brien: And to follow up on that – and maybe this is for John Callas – what's the delta in the amount of power you're likely to be able to capture from the sun if you're successful getting that tilt a little bit better?

John Callas: Just to give you a sense of scale, it's actually a pretty steep function because not only is there a cosine theta effect – for those of you who still remember your high school geometry – but there's also an angle dependency to the dust and shadowing from the mass on the rover.  So we get about a 5-6-watt hour improvement for each degree improvement in northerly tilt.  That's a pretty big number for a rover that needs 160 watt-hours to get through the winter without tripping a low-power fault.

Steve Squyres: And if I could jump in quickly here, I've actually got an answer to the previous question regarding papers.  As of one year ago – there have been a few more since then, actually quite a few since then – we had published ninety-one papers in peer review journals, and that includes two special issues of the journal Science and one special issue of the journal Nature.  And we have published 407 abstracts at professional conferences. 

Operator: The next question comes from Nancy Atkinson of Universe Today.  Your line is open.

Nancy Atkinson:  Hi.  How much time do you have to get the rover into a good position, and how much longer do you expect the rover to be able to send back images and data before shutting things down for the winter?

John Callas: Well, we estimate we have maybe three weeks of driving activity that we can do.  Now, we can't drive every day because of the amount of power so we probably have a handful of drives left before there's insufficient power to keep moving the rover.

And then it's probably sometime around the March/April timeframe where we run out of the ability to communicate to the rover each day because of power.  So two more weeks of driving, a couple more months before we won't have any more images coming back each day.

Nancy Atkinson:  Okay.  And the worst-case scenario – if there's a long period of time where you don't hear from the rover in the spring, has any thought been given to how long you will attempt to communicate with it?

John Callas: Well, it's a very complex problem, in that the rover will actually experience probably two levels of fault protection and then a third communication complication because of this duration.  Not only if we do have reduced power will we trip the low-power fault, but if we go too long without talking to the rover it also trips what's called an up-loss timer, where the rover hasn't heard anything from the Earth in quite a bit of time and so it takes action based on that. 

And then the third thing is we only keep about as much as six weeks of communication tables on board the rover.  These are the tables the rover uses for normal communication. And that will have run out.  So all of these things fall together to make a complex recovery effort for the rover and it's very hard to say how long we would try, because we would have to try many, many things before we exhaust the list of things to do.

Nancy Atkinson:  Okay.  Thank you.

Operator: The next question is from Raphael Jaffe of Aerotech News.  Your line is open.

Raphael Jaffe:  Regarding the radioisotope thermal generators, how many watts do these put out?  And are there several of them, and would Doug comment on whether Mars Science Lab has such devices in case they run into trouble like this several years from now?

Doug McCuistion: John, do you want to talk about the RHUs first?

John Callas: Yes.  There are eight one-watt RHUs.  There are three on each of the two batteries and there are two inside the rover electronics module, so eight watts total.

Raphael Jaffe:  I see.  And is that really substantial and more or less saving the mission?

John Callas: Well, you have to remember that the electronics in the batteries are inside an insulated box.  So what you're working against is what heat leaks out of the box, and that's what you need to replace.  Now, these RHUs won't be able to replace all that leaks out but they do mitigate some of it.

Raphael Jaffe:  I see.  And would, I guess, Doug comment on my Mars Science Lab question?  Does the Science Lab have such things?

Doug McCuistion: The Mars Science Lab design is very different.  Instead of a series of radioisotope heating units – RHUs – it has a single RTG, radioisotope thermal generator.  It actually produces power through the decay of plutonium for charging the batteries on MSL.  It does not have individual RHUs.  So that RTG that is on MSL will basically do the same thing but in bulk, so it produces heat that creates electricity to charge the batteries but also provides heat to the electronic systems.  So the short answer is yes, it can do a similar thing by providing heat from radioactive decay for the life of the mission if it runs into trouble.

Operator: The next question comes from Ken Kramer of Spaceflight Magazine.  Your line is open.

Ken Kramer: Hi. Thank you.  First, congratulations on a fantastic mission.  My question is for Steve.  If you could talk about the core, the current thinking of the core on Mars – and have you thought about this idea?  Could you have done this on the previous winters at all?

Steve Squyres: Good questions, Ken.  With respect to current thinking on the Martian core, there is a very strong belief that Mars does have an iron core because when you look carefully from orbit with a magnetometer what you see are remnants of an ancient magnetic field, somehow generated inside of Mars, that remain frozen in some of the oldest [crystal] material on Mars.  When you crystallize magma in the presence of a magnetic field, magnetic mineral grains like magnetite can line up with that magnetic field like tiny compasses.  And then that magnetization gets frozen into the rock and you can see it from orbit. 

So there's compelling evidence that Mars once had a pretty powerful internally generated magnetic field and that probably required a core of iron that was liquid and was convecting to set up the dynamo that created the magnetic field.

Now, Mars does not have a powerful internally generated magnetic field today so something has changed inside the planet.  Has the core frozen solid?  Has it only frozen partly?  What's the actual state of the core?  That's something that we hope to determine.  But there is good reason to believe that Mars does have a core and that at least in the distant past it was liquid.

Your second question again – remind was – was?

Ken Kramer: It was about during the previous winters – could you have collected this data? When did you come up with the idea?

Steve Squyres: The idea has actually been around for quite a long time.  We have a team member named Bill Folkner who has been with us since very early in the mission and has been very patiently waiting for this to happen.  In previous winters we have placed our priorities elsewhere.  We've been doing other things with the vehicle.  Now, that doesn't mean we have no data at all – we actually have sort of gone through and done what you might call some data mining and extracted the tracking data that's useful from previous periods where the rover has been stationary, particularly the time that it's already been at Troy.

So we're going to take those little fragments of data that we've already collected and then add to that in a really organized fashion as we go forward.  We don't have a lot of data on this yet but it's something we're going to start doing soon.

John Callas: Let me just add to what Steve said.  In the previous winters, we've always been power-constrained. And to do this technique the best way possible requires the rover to turn on its transmitter, which is one of the biggest power consumers.  So we haven't had the power environment before to do this while the vehicle has been stationary and come springtime this will be really the first time where we've had sufficient power, but a vehicle that we're not planning on moving much.

Ken Kremer: Thank you.

Operator: Your next question comes from Laura [Lima] of [Deutsche Well – echo on line]. Your line is open.

Laura [Lima]:   Hi.  This is Laura.  I'm curious about two things.  One of them is: assuming that Spirit is not able to move much more into a better angle, is there still going to be enough power generated that at some point, regardless if it's stuck there, it will be able to turn on and so the only matter here is it will turn on earlier if it gets more energy than if you maneuver it to the right position?  And then the second question would be along the lines of: assuming that it does turn on in maybe six months or so, then how long does it take – how many measurements will you be able to take – before you're able to determine what the core of Mars actually is?

John Callas: I'll address the first one.  We seem to have an echo on the line, so I hope people can hear me. In terms of power, the issue right now is as you described it.  If we can get a favorable tilt we may avoid this low-power fault and the rover would be active throughout the winter.  I mean, it's not going to be conducting much activity but we will be able to communicate regularly with it.  So if we can get that favorable tilt, we might avoid this.

If we don't get that favorable tilt – if we're stuck, for example, where we are today – then we are likely to trip this low-power fault in the order of a few months and then have this quiet period that could extend for six months. 

But the timing of all this is very uncertain. It depends on many factors – how dusty the sky is on Mars, how much dust is remaining on the solar rays, what the temperature environments are on the planet, etc.  So we can't be precise at all at this time on the timing of these things.

Steve Squyres: And with respect to your question about the time to determine the core state, it depends on a lot of factors.  It depends on how much power is overhead, how many minutes a day we can track its signal, and so forth.  But the simulations that we've run to estimate this suggests that we have a good chance of determining the core state in about six months of tracking.

Operator: The next question is from Rachel Courtland of New Scientist.  Your line is open.

Rachel Courtland: I just wanted to clarify this six-month issue.  I think earlier you said that the rover might be back up and running as early as August or September.  Do you have a sense of –

Steve Squyres: Rachel, I guess your question is to me as to our sense on how long the vehicle will be in this class and state.  Again, think of the Spirit as a hibernating polar bear.  When does the polar bear stick her nose out of the ice cave and start roaming on the surface?  It again depends on the final tilt of the vehicle, the dust on the arrays, the amount of dust in the atmosphere on Mars, how cold the environment is on the planet, etc.

When we take past years, past winters on Mars, and apply those to what we think the state of the vehicle will be going forward we get a number like six months of hibernation.

Operator: That does conclude the Q&A session of today's conference. I'd like to turn the call back over to Mr. Dwayne Brown.

Dwayne Brown: Thank you.  I want to thank our participants and all of the media joining us, of course.  All the participants will be available for follow-up media interviews.  Call their respective public affairs offices or call them directly.

And of course, for all the latest and greatest about the Mars rovers go to www.nasa.gov/rovers.  Thanks for joining us, everyone, and have a great day.  And over to you, Operator.

Operator: Thank you for joining today's conference.  This has concluded and you may disconnect.

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