Whr Figures, From various sources Options

[djellison]

I've been looking at the new entries at the PDS for WHR quotes, to compile as good a list of actual quoted Whr values as I can......so if you find one, add it to this thread and I'll update this post with figures....any source as long as it's an actual figure and an actual sol.


B0515 - 418 Whrs
B0522 - 462 Whrs

[bigdipper]

From 14 July Spirit Update: sol 897-904 Solar array input down to 280 whrs

Hang in there buddy.

[helvick]

From 14 July Spirit Update: sol 897-904 Solar array input down to 280 whrs

I've noted elsewhere that spirit appears to be losing power generating capacity at a slightly faster rate than I expected when assuming a constant rate of power loss due to dust of 0.18% per Sol.

This latest reported whr number seems to indicate that we might be seeing the effect of local winds picking up and increasing the rate at which dust is being deposited on the panels but it could also be that Tau is increasing earlier this year than last.

From Sol 811 to Sol 853 panel efficiency decreased by ~0.08% per sol.
From Sol 853 to Sol 877 panel efficiency decreased by ~0.10% per sol.
From Sol 877 to Sol 891 panel efficiency decreased by ~0.33% per sol.
From Sol 892 to Sol 899 panel efficiency decreased by ~0.41% per sol.

If that rate continues then Spirit will be in a very bad way. After mid winter insolation increases at less than 0.4% per Sol and power generation capacity would just continue to decline rather than picking up again as summer rolls in.

[centsworth_II]

...spirit appears to be losing power generating capacity at a slightly faster rate than I expected when assuming a constant rate of power loss due to dust of 0.18% per Sol.

I wonder if the computer trouble that Spirtit had in the first days of its mission, which lead to a near complete discharge of the battery, reduced the battery life.

I also wonder if plans are in the works for an attempt at repositioning Spirit to get a better angle to the sun, or if it has been decided to let Spirit live or die as it sits. The danger of repositioning is that it could unintentionally lead to a worse and perhaps deadly power situation.

[helvick]

I wonder if the computer trouble that Spirtit had in the first days of its mission, which lead to a near complete discharge of the battery, reduced the battery life.

It may have but I think we've established that the Lithion batteries used by the MER's should be good for a few thousand Sols unless temperatures drop so far that they actually get damaged. The couple of weeks of trouble at the start probably didn't do Spirit's any good but I don't think they damaged it either.

I also wonder if plans are in the works for an attempt at repositioning Spirit to get a better angle to the sun, or if it has been decided to let Spirit live or die as it sits. The danger of repositioning is that it could unintentionally lead to a worse and perhaps deadly power situation.

Spirit has already been manoeuvred into a position with one wheel perched on a rock giving her a very favourable northerly tilt that has increased the power she generates by about 20%. Without that tilt she would currently be generating only 220-230 whr or so per sol. An ideal tilt could increase the power gain by a further 10% or so but it would be an incredibly risky exercise. I don't think anyone would try it now, if they got it wrong and she ended up horizontal it might be impossible to recover from.

[centsworth_II]

So it looks like the die is cast. Spirit is in the orientation that she is in. The dust buildup is what it will be. And a cleaning event (frost congealing of dust?) will happen or not.

On the bright side, is a large part of the minimum power requirement for life due to heating needs? Will those needs decrease as spring approaches so that even if power levels continue to decrease, the minimum power requirement for life will also decrease as rising night temperatures reduce heating needs?

[helvick]

There have been requests (well a request) for an update of my power estimate charts. To better illustrate my comments above I've reworked the presentation a bit in an attempt to illustrate the current power situation. So far I've only sone this for Spirit but I'll post one for Opportunity as soon as I can.

The critically important line is the solid red one. The future estimate (the portion of all of the line to the right of the dashed purple vertical line) is based on the current power level and the solar panel's effective efficiency today extrapolated out using the actual Tau and my own estimate of the dust deposition rate from precisely 1 martian year earlier. The basic conclusion in this is that without any cleaning she's not going anywhere.

So I also made a much more optimistic version that includes the effect of similar cleaning events to those seen last year at the same time as they occured just to see what effect those would have.


Max-Power is the theoretical maximum that the panels could generate at a given point in time given the known Tau values and assuming that the panel is flat and there is no dust on it. It should be accurate to within about 5% or so. This is in Watt hours (left axis)
Est Power is my interpolated estimate of the actual power generated at any given point. As far as the historical data is concerned this line agrees with JPL's published Solar Panel Efficiency chart to within +-1.5% which I'm quite happy with. This is in Watt hours (left axis)
Dust Loss is my own estimate of the actual rate of dust deposition at various points in time. I derived this by testing various values for each period in order to make my estimated power line approach the reported power number for each published power value except in cases where we know there was a cleaning event. This is a percentage per Sol and uses the right axis (it's generally ~0.2% but has peaked over 1% on occassion)
Tau is an average Tau value for each Sol taken from the published Tau charts. Uses the right axis.
Today and Last Year. I put in these two vertical indicator lines for today and 1 martian year ago to give folks some sort of visual guide to put the other chart lines into context.

[bigdipper]

If I read the dust loss plot correctly the _rate_ of loss is plotted as opposed to the cumulative loss due to dust, right?

Trying to add/subract the curves didnt' quite work. Looking at sols +/-830-851 noticed ~0 dust loss (but not 0 loss due to dust).

BTW: 570+ downloads of the HPC excel zip file means you have more than one adoring fan.