[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.

[TheChemist]

spirit is travelling down a fairly steep north facing slope while the Noon sun is still in the Southern Sky.

Spirit was facing north while climbing up Husband Hill. It can't be facing north again going down on the opposite side

[helvick]

Spirit was facing north while climbing up Husband Hill. It can't be facing north again going down on the opposite side 

Good point. I'm not sure of the orientation to be honest but I recall that SS did say they needed to get off slope quickly while the power situation was favourable. I took that to mean that the downward route was predominantly North facing. Looking at the route map it appears that the orientation is probably generally south easterly, tilted at an average of around ~10%. That shouldn't cause too much of a drop in power on it's own.

I'm still convinced that orientation is the main problem, it may be that the missing power is caused by the fact that she's in a valley now and the effective sunset is a lot earlier that it was when she was on top of the hill.

Can anyone estimate what her orientation and average tilt has been over the past week or so?

[sattrackpro]

Can anyone estimate what her orientation and average tilt has been over the past week or so?

Don't know about average tilt numbers, but she has not been in ideal conditions for charging ever since she began going down into the inner basin, being tilted away from the most sun, being on a South facing slope and the Sun going lower in the North every day - hence the race to get to a North facing slope soon... and you're cetainly right about the 'valley' local, also limiting exposure a bit by early mountain-caused sunsets - and to some degree, sunrises, I would expect.

Note though, that long pauses (like at Comanche, and this latest 'bright spot') have helped build up power at each layover. During those stops, to do science observation, the batteries get a chance to catch up a bit.