The Storm, Dust storm of 2007 Options

[ugordan]

Uranium heaters? Pardon me for being ignorant here, but what isotope would that be? U-233, 235 and 238 all have very low specific heat output as I remember.

[fredk]

Plutonium. From this press release:

Each rover has eight radioisotope heater units that supplement electric heaters for keeping batteries and electronics within their operating temperature ranges. The radioisotope heater units use the decay heat from plutonium-238. Each of them provides about one watt of heat. They aid the rovers' survival on very low-power days and through cold nights, though the electric heaters are also necessary.

Eight watts over 24 hours gives 192 Whrs per sol. If most of that heat is useful rather than waste, that's actually a very significant addition to the array output these sols!

[ugordan]

Yep, that sounds about right. Plutonium-238 dioxide, the same stuff as commonly used in RTGs.

[Del Palmer]

I'm wondering why the turning on of the emergency heaters would be so bad? Is it so that they cannot be otherwise turned on, except automatically when the low temperature limit is reached? Is there a particular reason to run other electronics instead of the heaters, which I would think would be most efficient in warming the WEB?

It all comes down to how much heat you need versus how much heat you can afford. Consider the following analogy: If your room temperature in winter is 11 C, and the minimum you can personally tolerate is 13 C, you may be able to reach 13 C by just leaving your computer and CRTs on for longer periods. Switching on a heater will bring the room up to a much more comfortable 18 C, but at a hefty cost.

[akuo]

If your room temperature in winter is 11 C, and the minimum you can personally tolerate is 13 C, you may be able to reach 13 C by just leaving your computer and CRTs on for longer periods. Switching on a heater will bring the room up to a much more comfortable 18 C, but at a hefty cost.

Continuing your analogy, why not use the heater to bring it up to 13 degrees C if that's all you need? Which is really my question, don't they have control over the heaters except for the emergency situation triggered by the low temperature? I would think using the heaters would be more efficient in heating the WEB than eg. running the processor.

[helvick]

From a thermodynamic point of view all of the means of heating would be the same since all of the energy gets dissipated as heat eventually (assuming we're talking about stuff happning within the WEB at any rate).

Given that, it would seem (to me) to be better to use the electronics systems to heat themselves where possible as the heat in question would be distributed directly through the thing you most want to heat up and you get the benefit of the other work at the same time.

[Del Palmer]

Continuing your analogy, why not use the heater to bring it up to 13 degrees C if that's all you need? Which is really my question, don't they have control over the heaters except for the emergency situation triggered by the low temperature? I would think using the heaters would be more efficient in heating the WEB than eg. running the processor.

The survival heaters are thermostatically controlled - you can't bring them on until they reach the critical low, and turning them off would require Deep Sleep mode (something that's not possible during the day).

[Del Palmer]

There are 8 of them as I understand it - 6 on the battery, 2 on the REM. They each chuck out abotu 1W of heat. They've been doing so since the day they landed - and - except for decay - will carry on doing so for some time to come. Essentially they're there making a bad situation slightly less bad than it might be. they wont keep an entirely dead rover warm enough for survival - they just shave a bit off the heating requirements.

Oh, they do more than just shave a bit off the heating requirements. It's a sobering thought to consider that without the RHUs, the rovers wouldn't even have been able to last 90 Sols due to depleted batteries.

[Chmee]

Here are both HST July observations (July 23 and 27).

Hey who took our Mars and put this imposter in its place? It looks like a cue ball
That storm is amazing. Although tthe rovers are struggling, I think we are garnering much new information by having 'ground-truth' on this.

[ustrax]

I think we are garnering much new information by having 'ground-truth' on this.

I'm avoiding to visit this thread since its beggining, call it a defensive procedure, but I must agree with you, this possiblity of gathering local knowledge about martian storms by the rovers is another jewel to the crown of glory of this mission.

[nprev]

Oh, no doubt about it; this storm may well prove to be the primary engineering/environmental data acquistion triumph of the MERs with respect to future lander mission designs, at least the solar-powered ones.

Of couse, as the dust settles it will be clinically interesting to see if it affects any other systems, particularly moving parts...though I suspect there won't be any effects since the MER team hasn't missed a beat yet with respect to contingency planning & design. (You guys are just unbelievable! )

[MarsIsImportant]

Hey who took our Mars and put this imposter in its place? It looks like a cue ball
That storm is amazing. Although tthe rovers are struggling, I think we are garnering much new information by having 'ground-truth' on this.

If there was any doubt that this is a global dust event, then it should be gone now. Both images show an extremely dusty atmosphere; yet, the second one clearly shows that the intensity of the storm has maintained and spread considerably further over the entire planet within 4 or 5 days. There are only a few spots relatively dust free now. And relative is a pretty inaccurate term here...like basically maybe the pole! Yet even the pole seems slightly obscured in the 27 July image.

[tedstryk]

If there was any doubt that this is a global dust event, then it should be gone now. Both images show an extremely dusty atmosphere; yet, the second one clearly shows that the intensity of the storm has maintained and spread considerably further over the entire planet within 4 or 5 days. There are only a few spots relatively dust free now. And relative is a pretty inaccurate term here...like basically maybe the pole! Yet even the pole seems slightly obscured in the 27 July image.

I wouldn't go that far. It isn't the same face of the planet, and the south polar cap isn't properly aligned with the south pole, so it may simply be closer to the limb.

[imipak]

....the MER team hasn't missed a beat yet with respect to contingency planning & design. (You guys are just unbelievable! )

Yes, amazing resilience, so far anyway!

I think it's interesting that the widely-quoted minimum power requirements of 280-ish Whr is clearly *not* the minimum, and that the engineering team don't seem particularly surprised by that(?) (In this 2004 post by Helvick the 280Whr figure is attributed to Steve Squyres.)

BTW -- this will be old news for the experts here, but I just came across this interesting doc from a JPL "MER Thermal Design workshop" in 2002, which shows the heaters alone as requiring 172 Whr/day (page 22.)

[raketmensch]

I think it's interesting that the widely-quoted minimum power requirements of 280-ish Whr is clearly *not* the minimum, and that the engineering team don't seem particularly surprised by that(?) (In this 2004 post by Helvick the 280Whr figure is attributed to Steve Squyres.)

BTW -- this will be old news for the experts here, but I just came across this interesting doc from a JPL "MER Thermal Design workshop" in 2002, which shows the heaters alone as requiring 172 Whr/day (page 22.)

But minimum survival power should depend on environmental conditions, which vary. It'd be greatest for Spirit in the winter, when temperatures are coldest. It'd be considerably less in the summer. And it'd be least of all (fortunately!) during a dust storm, when nighttime temperatures are moderated by all the dust in the atmosphere. So I think that any quoted minimum power requirement (or power draw by the survival heaters) has to be considered in the context of the conditions on Mars at the time.