Wheel Trouble, ...down to 5 good wheels? Options

[Bob Shaw]

FWIW, the Lunokhod wheels were, like the MER wheels, each equipped with an electric motor, but provision was made to 'blow' the motor if it stalled so that the wheel could freely turn. I don't think this feature was ever actually used.

Bob Shaw

[djellison]

Blimey - I'm reaching WAYYy back into the distant past here - I seem to remember that they were a few degrees above predicts whilst still sat on the lander, but I've not heard anything since then.

Trying to convert that heat into a 'power saving' obviously requires more MER facts than we mortals have.....

Call it 4 degrees. Say we have an equiv within the structure and contents of the WEB of say 20kg of water in terms of equiv thermal capacity.

Specific heat is 4186J, x 20, x4 - 334880 Joules of energy.

3600 seconds in one hour, 1 Whr thus provides 3600 Joules - so 4 degrees of heat in 20kg of water is 93 Whrs. I have no idea if that relates in any way shape or form to the potential for saved power onboard a rover, but it's a thought isn't it.

Still waiting for that sky hemisphere eh Mike

Doug

[helvick]

3600 seconds in one hour, 1 Whr thus provides 3600 Joules - so 4 degrees of heat in 20kg of water is 93 Whrs. I have no idea if that relates in any way shape or form to the potential for saved power onboard a rover, but it's a thought isn't it.

It is a thought alright. The original engineering requirements documents go into quite a bit of detail on the thermal performance and the amount of IR heat energy the Rovers would be subjected to on the surface. Looking at the charts it seems that the design specified downward IR flux that varied from 20-50 watt/m^2 throughout the day when Tau was low up to 20-75watt/m^2 when Tau was around 2. That amounts to between 600 and about 1000 whr/sol for the rovers since the downward IR seems to remain around about ~20watt\m^2 even at night.

All of this is very speculative though considering that we have no idea how well insulated the rover body is and even if we had such detailed thermal model data we still don't really know what the temperature limits actually are. It could be that the components can just handle much colder temperatures than they had been designed for or it could be that they are managing to remain warmer than expected. I suspect the former because the latter would surely have led to real overheating problems.

[djellison]

real overheating problems.

LIke the one's that resulted in cancelled UHF sessions whilst still on the lander, and turning the spacecraft off in the afternoons whilst atop Husband Hill

Doug

[helvick]

LIke the one's that resulted in cancelled UHF sessions whilst still on the lander, and turning the spacecraft off in the afternoons whilst atop Husband Hill

I was thinking that as I was typing but at that time the total insolation was almost 20% higher than the maximum that would ever have been planned for in the original mission and even with the most optimistic hope for extended operations so overheating at that point wasn't really surprising. I seem to recall though that overheating was mentioned much earlier in the mission too but I can't remember when so maybe the insulation is just working much better than intended.
My comment was based on my own opinion that it would be much more of a surprise that the insulation on the rover worked better than expected than having components survive more repeated heating\cooling cycles than they had been designed for.
Hopefully there will be some nice papers on this at some stage.

[mwolff]

[snip]

Still waiting for that sky hemisphere eh Mike

Doug

...in LOCO!

--mike

My comment was based on my own opinion that it would be much more of a surprise that the insulation on the rover worked better than expected than having components survive more repeated heating\cooling cycles than they had been designed for.
Hopefully there will be some nice papers on this at some stage.

rover naps were definitely inserted into the tactical planning process as a result of the need to "cool". you'll get
more reliable information from Emily, though. Atmospheric STG concerns about thermal issues was typtically limited to the amount of power that had to be used to pre-heat before overnight miniTES observations...

...in LOCO!
--mike
rover naps were definitely inserted into the tactical planning process as a result of the need to "cool". you'll get
more reliable information from Emily, though. Atmospheric STG concerns about thermal issues was typtically limited to the amount of power that had to be used to pre-heat before overnight miniTES observations...

...though apparently grammar wasn't a concern either.