What's with the wave-like effects that appear to correspond to MARCI's imaging strips and propagate to the east? I presume those are just imaging artifacts though they do look a bit like surface illumination effects?

Remember - this isn't a snapshot of the whole planet at one time - it's slices of planet at 3pm local - and thus you get lighting effects from one side of each stripe to the other.

Doug

I'm aware of the slices, but I forgot to take into account the wide FOV the instrument has that encompasses a range of local times, not just 3 PM. Shame, the "waves" distract from the dust clouds visible in the animations Astr0 and Emily posted and almost give a feeling of wave nature to the storm. In case of the dust storm there's probably an additional factor of optical depth of the atmosphere when looking way off nadir.

Gusev remained at Tau = 4.0 for 1259, for those few not watching Mark's page closely.

Pre-storm, I was wondering whether the decision to go with a nuclear-powered MSL was wise in the light of the MER's solar-electric longevity.

I have no doubts now.

Andy

The standard Tau measurements are carried out at various times and adjusted to account for the transit through the additional air mass resulting from off zenith pointing e.g. take this extract from Spirit's published tau data

CODE

Product_ID                   ,   L_s, R_au,      Sol,    AM,     Flux,    TAU, Rel_err
"2P134460532ESF2700P2600L8M1",  15.1, 1.594,  90.703,  3.790, 179.723,  0.523,   0.003
"2P134522131ESF2700P2678L8M1",  15.5, 1.595,  91.397,  1.355, 576.685,  0.600,   0.011
"2P134525203ESF2700P2600L8M1",  15.5, 1.595,  91.431,  1.184, 647.670,  0.589,   0.009

The fractional part of the Sol field indicates the local time (4:52pm , 9:32am, 10:20am) at the time the measurement was taken, AM is the air mass is approximately the secant of the Zenith angle at that time. The tau measurement is made by accounting for the additional air-mass and the expected Flux reading given the effective solar constant (derived from the R_au measurement - the distance from the sun).

As you say though this becomes increasingly tricky when tau is high and the senith angle is high - ie with nearly horizontal views to the horizon.

The reason that dust storms are so deadly at high tau is because critical parts of the rover get too cold, right? The lack of power is not a problem in itself, as the rover can hibernate.

So why not go with solar-electric power, plus insulation and a small radioisotope heat generator to keep the main body warm? Things like arms, that are not warmed by the heat generator but still need to be kept warm, would have the same system of heaters that the MERs do -- the difference being that those heaters would be the only electrical load during hibernation. I believe that even the worst dust storms should allow enough energy to keep those heaters going -- especially given the lower-atmosphere heating observed during dust storms.

The advantages of such a system would be lower total power-system mass (I think), lower development costs, and possibly a longer lifetime (going by the MER experiences) if, as I seem to recall, the reactor only has a several years lifetime.

Bill

A couple of decades.

Doug

Another advantage of a nuclear powered MSL is that it can work at night. Dust storms would not slow progress, and continuous night studies could be a very significant development. The MSL could operate basically 24/7 if need be.

I do think there could be some additional advantages if a combined approach could be developed for future missions. Also, maybe a soft brush could be included to manually sweep clean any solar arrays. I also hope that better wheels are developed. I would think something could fairly easily be developed to last a few thousand miles worth of surface travel. The problem might be staying within weight constraints.

I was wondering about this, and that's why I asked the MSL experts this question. The Answer tells us that it won't have the capability to operate 24h a day, because the batteries still need to be charged by the RTG. 7 hours each sol adds up to significantly more what the MERs do, though.

That's why a combined approach might be useful. It might be too late to change the MSL design; but I don't think it will be the last rover. Also, 7 hours per Sol is an average. If the batteries are fully charged, then I believe that it could operate longer.

With a combined approach, then closer to continuous 24/7 could be achieved. However, the batteries might not last as long. So there are multiple trade offs.

I just think it would be a waste to completely throw away the advantages of solar power. The MER proves the application of the technology. I just want a brush so that we don't have to wait for the wind to blow.

Get rid of the brush, get rid of the arrays use an RTG and you've fine. And remember - there is another short-link in the chain. People. You can't have a rover that operates 24/7 - not least of all because you'd have to take floodlights with you - but also because you need downtime for the operations team to design the next sols sequence based on the results of the previous sequence. The downtime inbetween can be used a little like the rover's nights have been from time to time - APXS/Mossbauer integrations ( in the case of MSL - APXS integrations and the SAM suite )

You want to add arrays, a big arm with a brush ( which is more mass, more volume, more money )
That RTG is going to be producing X Watts, every hour of every sol, and that figure is more than is required to operate the vehicle. There isn't any sense in adding a further power source when you could spend the mass, volume and money elsewhere (like, a slightly larger RTG for instance). The very point of the RTG is that it gives a perfectly predictable, reliable power source for as long as you need it (over a primary mission of a martian year) - it's eliminates every down-side of the solar arrays in one - excuse the pun - sweep.
Doug

I always wondered why they couldn't emulate a good strong gust of wind by drawing in some Martian "air" and using a method of blowing off the dust.

Locate a nozzle in the centre of the array in such a way that as it spins as it blows and you could cover a large percentage of the array. Likely only needs to be pretty small and lightweight too.

You don't need floodlights. You just use infrared sensors. There is a whole host of instruments that you don't need lights for. It all depends upon what kind of science you want the rovers to do. You are correct that only certain things can be done during the day. Yet, valuable measurements could easily be done at night with the right instrument package.

The trade off because of human limitations is a valid point. Yet, team shift management can solve a lot of those problems. The real problem with approaching 24/7 is a commitment of time and money. It could be done and, in my opinion, would be worth it. But getting funding for such a program would be a problem.

NASA Mars Rovers Braving Severe Dust Storms:

http://www.jpl.nasa.gov/news/news.cfm?release=2007-080

On Tuesday, July 17, the output from Opportunity's solar panels dropped to 148 watt hours, the lowest point for either rover. On Wednesday, Opportunity's solar-panel output dropped even lower, to 128 watt hours.

Engineers calculate that skipping communications sessions should lower daily energy use to less than 130 watt hours.

A possible outcome of this storm is that one or both rovers could be damaged permanently or even disabled. Engineers will assess the capability of each rover after the storm clears.

Gulp... Only 128 Watt!

NASA news release.



"On Tuesday, July 17, the output from Opportunity's solar panels dropped to 148 watt hours, the lowest point for either rover. On Wednesday, Opportunity's solar-panel output dropped even lower, to 128 watt hours."


"To minimize further the amount of energy Opportunity is using, mission controllers sent commands on Wednesday, July 18, instructing the rover to refrain from communicating with Earth on Thursday and Friday. This is the first time either of the rovers has been told to skip communications for a day or more in order to conserve energy. Engineers calculate that skipping communications sessions should lower daily energy use to less than 130 watt hours"

Interesting quote from Richard Zurek:
http://www.jpl.nasa.gov/multimedia/audioclips/mer-20070720/

"If you're at the rover, for instance, sitting on the surface, and you're looking up at the sky, you're not going to see the sun's disk, even during the day because the cloud, the dust haze, is thick enough that the sunlight has been either absorbed or scattered."

How can this be? Spirit can still see the sun in those Tau images:
From Sol 1259 ( Tau 4 ):

Hum... That's explain the form of the Sun, a little stretched, by I longer exposure than a normal-tau day, due to Mars rotation during it?

"This is, I think, one of the most significant challenges we've faced over this entire mission," Squyres told SPACE.com today. "The nature of the risk is well understood, but the magnitude of the risk is not. We simply don't know what's going to happen next."
"Whatever we do, though, the problem is not going to get much better rapidly," he said. "I think that we have a good chance. If Mars really wants to kill these vehicles it can, but we have a lot of things working in our favor."

Solar power will continue to be used by missions that cannot afford the price of RTG goodness. Certainly, no NASA Mars Scout mission can afford an RTG.

Brushes are so 20th Century, how about an electrodynamic dust shield instead?
http://science.nasa.gov/headlines/y2006/19apr_dustbuster.htm

I saw videos of that electrostatic mechanism at the IAC'06 in Valencia - it was brilliant. Far FAR better than any mechanical system.

Doug

They are insulated and they already have had problems with over heating.

The real advantage is time of day independance.

I know folks who are working on the next gen of martian solar arrays. They are using panel vibrators to shake the dust off. Their testing under simulated martian conditions are showing that it should be able to keep the panels clean.

Meanwhile, even if kind of OT we get 2500 sols total today... and Spirit is very close to 100.000 pictures.

AND Spirit is only 20 sols away from beating Viking 2!

Back OT. From the space.com article:
If Mars really wants to kill these vehicles it can, but we have a lot of things working in our favor.

Question: what things?

Rocket scientists

THEMIS dust maps:
http://themis.asu.edu/dustmaps/

Really? I looked at the project website, and they were saying that the RTG was designed to provide an operating lifespan of 'a full Martian year'. The MERs are already at twice that timespan.

Bill

It'll last for years and years and years - like NH's or the Voyager ones.

Doug

MSL is being designed to last a full Martian year the same way the MERs were designed to last 90 sols.

The website describes the RTG power system as "giv[ing] the mission an operating lifespan on Mars' surface of a full Martian year (687 Earth days) or more." (my emphasis) All the page is saying is that the power system will work for a lengthy nominal mission. It's not discussing how much longer than the nominal mission the RTG can operate.

The prose could be a little more clear, but I think that mission designers are understandably wary of making comments that could be interpreted as predictions of exceptionally long lifespans for the equipment. The fact that the RTG will keep working for decades isn't very important unless lots of other systems are still working as well.

TTT

Phew! Story posted. This was a complex one and done in a bit of a rush so I'd appreciate an email if anyone finds any errors.

http://www.planetary.org/news/2007/0720_Th...Crisis_for.html

--Emily

Thanks Emily, great article,

I'm still in awe looking at the dimming horizon image in there...

The MCS stuff is great as well - really good to see what could be an outreach-challenging instrument get good airtime via TPS.

Doug

There's a lot more where that came from -- I only got those graphs an hour before I posted, so there's much more in there than I had time to explain. More from MCS next week -- that's the instrument that's REALLY designed to stuyd what's going on with the storm.

--Emily

Emily,

Wonderful story; it's exactly what I was hoping for as a backgrounder on the storm.

Is MCL still unable to perform vertical profiles?

TTT

Really excellent article Emily, thanks.

If I might make a request? It would be very nice if you could post a follow up article in a day or two once we get comm back from Oppy that goes into more detail on the on going orbital results as well as Rover status.

BTW You really should get that article to some of the major National/International newspapers. It would make a great Sunday Science article.

Emily,
As always, your article provides a clear and concise explanation of the situation. The dimming horizons graphic is outstanding.

Great work Emily, I always enjoy reading your articles!

Yeah, I agree with everyone else. That was really a well done summary, Emily. I'm still hopeful the storm is subsiding, and that the rovers will survive, but if not, we will still learn something...

Here is a set of 3 pics (calibrated and all that sort of things...) showing the fading of the local horizon at Gusev starting from sol 1122 to sol 1197 and finally ending at sol 1254.
Enjoy it (on Earth, NOT on Mars) !

Where did you get truly raw data to calibrate?

Yes, I have the same question : where?

Already mentioned in this thread:

Clean solar panels
Warmer temps
Relatively healthy craft
And I'm guessing the batteries are still fairly well charged since
they just now started severely cutting back on communication.

From Reuters :

The rovers have electric heaters to prevent vital core electronics from getting too cold. One concern is that absence of sunlight could make the rovers drain their batteries.
That worst-case scenario is still weeks off at a minimum, Callas added. He said that because it was now Martian summer for the rovers, there was a chance temperatures would not fall low enough to ruin the electronics even if the rovers were starved of power.

Sounds optimistic.

Idle question -- please consider me off my rocker, but I'm curious if anyone's anticipating the storm to warm some areas enough for a "water release event" in various crater walls.

The phase diagram shows that the window for liquid water at these pressures is very small. It's quite likely that these conditions putting both the liquid AND solid phase out of the question for much of the day.

Doug

Sorry my friends, but the the truth is not elsewhere and -unfortunately- I'm not working with secret "X-files" : the images are data from the Exploratorium and processed (+ rotated and cropped to show the same section of landscape) as usual... Anyway thanks for this kind interest of yours on my modest contribution to this nice "Storm" section...

CBS News radio in Los Angeles picked up the story (pretty doom & gloom... ), had an interview with Robert Zubrin...was there a press conference today?