[X] My Assistant

[maycm]

From the following "Space" article LINK

Spirit’s solar arrays currently produce about 650 watt hours while Opportunity’s generate up to 700 watt hours, Laubach said. A minimum of 300 watt hours is required for Spirit to function, though Opportunity can operate on slightly less, she added.

What is the reason for the lower power requirements of Oppy?

I thought the two rovers were identical.

[djellison]

I think basically - you have to have the rovers 'on' for enough time during the day to pack the WEB with heat to keep it reasonably warm thru the night. Even with deep sleep it's so well insulated that it can keep at sensible temps in there thru the night.

However - once you get to a point when you spend most of your day just charging the batteries and not doing anything, then you're going to get a colder WEB before you go to sleep, and thus a much deeper thermal cycle in there over night. Once you get that deep cycling, then you're in the regieme that ends up with massive thermal cycling on batteries, on telecoms equip - you can't find lock with DTE comms, maybe even the UHF drifts so that Odyssey cant find it, then you get to a solar-power-only mode, and things just spiral from there.

I'm not sure how one might 'fix' that - but what I would do is just leave the rover 'sleeping' till abotu 3pm, and then keep the rover very very busy for an hour, then shut it down for deep sleep - that way you've packed as much energy in at the end of the day to get the WEB as warm as possible before night starts.

I'm guessing they're using that 275w figure as the point at which they cant do enough 'stuff' inside that WEB to keep it warm enough to remain healthy over night

BUT - that is all just my guessing. It might make sense to email an engineer about it

Doug