One Martian Year!, And still going strong... Options

[dot.dk]

One martian year coming up in a few hours!

Nov. 19, 12:23:40 PM UTC if my math is correct

It's hard to describe what a fantastic achivement this is. So I'll just say:



Let's keep on roving!


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[elakdawalla]

Planetary Radio, Monday, November 28, 2005:
A Martian Anniversary for Spirit and Opportunity!

We celebrate a Martian year of exploration by the Mars Exploration Rovers with Jim Bell, Cornell planetary scientist, member of the MER science team, and new Planetary Society board member.

[Guest_Sunspot_*]

Planetary Radio, Monday, November 28, 2005:
A Martian Anniversary for Spirit and Opportunity!

We celebrate a Martian year of exploration by the Mars Exploration Rovers with Jim Bell, Cornell planetary scientist, member of the MER science team, and new Planetary Society board member.

Ask him whats going on with Opportunity

[Guest_exobioquest_*]

Is there an article somewhere on the forum dedicated to discussing how long MER will last?

Who many cleaning events have there been? Is there a chart of solar cell output levels for either rover? Will solar cell output ever become a problem at this rate?

How long will the batteries last? How many cycles have they taken and when is the end of the warranty date for them?

What aliments does each rover have as of now?

[helvick]

Is there an article somewhere on the forum dedicated to discussing how long MER will last?

Who many cleaning events have there been? Is there a chart of solar cell output levels for either rover? Will solar cell output ever become a problem at this rate?

How long will the batteries last? How many cycles have they taken and when is the end of the warranty date for them?

What aliments does each rover have as of now?

I don't think there's been a dedicated thread but I've dug into this quite extensively, some might say obsessively.
Anyway I have a bunch of excel spreadsheets that I put together earlier this year that estimate what the power should be but I've only been able to find ~25 published data points for Opportunity and 14 for Spirit so it is very hard to actually chart the performance of the panels. One of them is posted here somewhere but the data is very much out of date and it is based on a bunch of assumed data. I also have a bunch of Perl scripts that I hacked together more recently to create a pretty decent Insolation model that in the end don't significantly improve on the Excel spreadsheets ability to predict future power generation levels.

The team have reported about a half dozen cleaning events per rover. Some were relatively small (Opportunity is believed to have had a couple of 5% events while in endurance) but both rovers have had 2 or three major cleanings that improved power generating capability by 20% or more, all of those happened in the last 12 (earth) months.

One of the published papers by the team stated that the power loss due to dust deposition followed the expected pattern for the first 100 or so sols (ie 0.18% reduction per sol) however only two actual data points were ever published for those periods (Opportunity Sols 80 @ 610 watt hours and 93 @ 593 Watt hours). As far as I can make out power continued to degrade pretty much exactly as per the predicted model until Sol 204 for Spirit and Sol 198 for Opportnity. Spirit got into some complex geography at that point so orientation caused power problems for a while but Opportunity was delving into Endurance and benefiting from a favourable orientation that boosted power by about 25%.

I'm reasonably sure now that that dust deposition rate decreased significantly once the atmosphere cleared up about halfway through SH Autumn (at around Spirit Sol 130 or so), then we had the major cleaning events about halfway through winter (December 04 for Spirit and Jan 05 for Opportunity). Dust deposition seems to have remained low until a few months into spring (around may of this year) as the amount of dust in the atmosphere rose again. It is reasonable to assume that the rovers are once again subject to approximately 0.18% reduction in power per sol and that degradation will continue until around Sol 780-800 (Mid April 2007).

Recent published power numbers (Opportunity 720 Watt hours on sol 628, Spirit 650 at around the same time) lead me to believe that the current worst case scenario (no more cleaning events) would have the rovers hovering around 300 Watt hours per sol generating capacity around Spirit sol 870, June 14 2006. That's pretty low but it's survivable and should still allow some activity particularly if the drivers\planners are creative about finding North facing slopes to park on.

My best guess now is that since the major threat of dust storms has pretty much passed for this martian year there is no reason to think that either of the rovers cannot generate enough power to survive through the winter. The power situation improves fairly rapidly after that provided my guesses about the reduction in dust deposition rates are correct.

I was of the opinion that the batteries were likely to fail as we closed on 1000 sols but someone else (I forget who) posted here that they should be good for 2000 or more charge cycles (I think). If that's true then power is not going to be a death threat. I think they go through a charge cycle per Sol more or less but can't be sure of that - I do know that they got a surprise recently when Oppy failed to charge one of it's batteries which led me to assume that bringing the batteries up to a full charge was a standard daily procedure.

The MiniTES instruments seem to be the most likely components to break first simply because they are temperature sensitive and they are no longer being heated at night. Oppy's has already caused a bunch of problems and it should have frozen to death in the middle of winter when they adopted deep sleep.

Other than that Spirit's RAT is burned out, or virtually burned out. We've had front wheel problems on both rovers but neither seems hugely problematic. Oppy has a stuck heater but deep sleep seems to be enough to cope with that. They may be problems with Oppy's IDD at the moment, we don't know.

I'm more optimistic about their long term survivability as rovers now than I have been in well over a year but then again something nasty could happen at any time.

[Guest_exobioquest_*]

Thank you all for the data

So from the charts and all if they are going to die this martian year its going to be in mid winter (sol ~900+/-50) either (unlikely) solarpower input to low, or thermal cycling of the electronics causing a lethal "stroke" which should be at its worst in mid winter because of the low temps and low power causing the need for things like deep sleep. If they survive that they are set for another martian year! Though a electronics break down could happen anytime and chances increase with every sol I'm guessing winter is when the rate of chance increase goes up fastest.

So here is my prediction, but don't call be psychic or a warlock if I’m right:

Opportunity will wake up some cold winter day and as the electronics warm up something will snap: as is the semi-frequent(?) reboots might be a sign of micro-cracks forming in the soldering causing echoes and noise in the signals and increasing the chance of bad bits. After the snap opportunity might either be stuck in a set of infinite reboots or might not wake up at all (the BIG sleep). Of course we on earth won’t know what happened because of a lack of telemetry, even worse Opportunity might be able to weakly reply but not be commendable (like road-kill that is still alive and trying to crawl away, traumatizing sad to watch!), once Opportunity is finally put out of its misery it will be only a matter of time until it happens to Spirit, maybe the winter after or any random day after 1000sols.

[helvick]

If they survive that they are set for another martian year! Though a electronics break down could happen anytime and chances increase with every sol I'm guessing winter is when the rate of chance increase goes up fastest.

That's it.
Overall the Solar Panels have performed very well and the pre flight models of their behavior seem to have been totally validated. These rovers have been lucky though and we would do well not to forget that. The 90 day mission had sensible safety margins but they have survived this far by the slimmest of margins, well Spirit has at any rate.