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

[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 One of them is posted here somewhere but the data is very much out of date and it is based on a bunch of assumed data.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.

[ljk4-1]

Guy Webster (818) 354-6278/5011

Jet Propulsion Laboratory, Pasadena, Calif.

George Deutsch/Erica Hupp (202) 358-1324/1237

NASA Headquarters, Washington

News Release: 2005-167 November 29, 2005

NASA Rover Helps Reveal Possible Secrets of Martian Life

Life may have had a tough time getting started in the ancient environment that left its mark in the Martian rock layers examined by NASA's Opportunity rover. The most thorough analysis yet of the rover's discoveries reveals the challenges life may have faced in the harsh Martian environment.

"This is the most significant set of papers our team has published," said Dr. Steve Squyres of Cornell University, Ithaca, N.Y. He is principal investigator for the science instruments on Opportunity and its twin Mars Exploration Rover, Spirit. The lengthy reports reflect more thorough analysis of Opportunity's findings than earlier papers.

Scientists have been able to deduce that conditions in the Meridiani Planum region of Mars were strongly acidic, oxidizing, and sometimes wet. Those conditions probably posed stiff challenges to the potential origin of Martian life.

Based on Opportunity's data, nine papers by 60 researchers in volume 240, issue 1 of the journal Earth and Planetary Science Letters discuss what this part of the Martian Meridiani Planum region was like eons ago. The papers present comparisons to some harsh habitats on Earth and examine the ramifications for possible life on Mars.

Dr. Andrew Knoll of Harvard University, Cambridge, Mass., a co-author of the paper, said, "Life that had evolved in other places or earlier times on Mars, if any did, might adapt to Meridiani conditions, but the kind of chemical reactions we think were important to giving rise to life on Earth simply could not have happened at Meridiani."

Scientists analyzed data about stacked sedimentary rock layers 23 feet thick, exposed inside "Endurance Crater." They identified three divisions within the stack. The lowest, oldest portion had the signature of dry sand dunes; the middle portion had windblown sheets of sand. Particles in those two layers were produced in part by previous evaporation of liquid water. The upper portion, with some layers deposited by flowing water, corresponded to layers Opportunity found earlier inside a smaller crater near its landing site.

Materials in all three divisions were wet both before and after the layers were deposited by either wind or water. Researchers described chemical evidence that the sand grains deposited in the layers had been altered by water before the layers formed. Scientists analyzed how acidic water moving through the layers after they were in place caused changes such as the formation of hematite-rich spherules within the rocks.

Experimental and theoretical testing reinforces the interpretation of changes caused by acidic water interacting with the rock layers. "We made simulated Mars rocks in our laboratory, then infused acidic fluids through them," said researcher Nicholas Tosca from the State University of New York, Stony Brook. "Our theoretical model shows the minerals predicted to form when those fluids evaporate bear a remarkable similarity to the minerals identified in the Meridiani outcrop."

The stack of layers in Endurance Crater resulted from a changeable environment perhaps 3.5 to 4 billion years ago. The area may have looked like salt flats occasionally holding water, surrounded by dunes. The White Sands region in New Mexico bears a similar physical resemblance. For the chemistry and mineralogy of the environment, an acidic river basin named Rio Tinto, in Spain, provides useful similarities, said Dr. David Fernandez-Remolar of Spain's Centro de Astrobiologia and co-authors.

Many types of microbes live in the Rio Tinto environment, one of the reasons for concluding that ancient Meridiani could have been habitable. However, the organisms at Rio Tinto are descended from populations that live in less acidic and stressful habitats. If Meridiani had any life, it might have had to originate in a different habitat.

"You need to be very careful when you are talking about the prospect for life on Mars," Knoll said. "We've looked at only a very small parcel of Martian real estate. The geological record Opportunity has examined comes from a relatively short period out of Mars' long history."

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Mars Exploration Rover project. Images and information about the rovers and their discoveries are available at http://www.nasa.gov/vision/universe/solars...m/mer_main.html .

[alan]

Sol 1 started on the Midnight before Spirit's landing.
There are 668.5921 Sols in a Martian tropical year.
It can be argued that the Marsiversary Sol should therefore start on Sol 669. *
However the the exact timing of the passing of 1 Martian year from the start of Sol 1 takes place at 14.21 local Martian time on Spirit Sol 669 due the 0.5921 fractional part.
Spirit landed at 14:26 local time (LST-A) on Sol-1 so the timing of 1 Martian year after that actually occurs at 4:47 on Sol 670.

* Using Earth Dates and Days.
Landing: January 4 2004 at 04:36 UTC.
Martian tropical year (in days) 686.9725.
Add the two and you get 03:56 on November 21 2005 for the actual event.

So Helvick, when does it become official for Oppy?

[djf]

Well, using 686.9725 days and a 05:05UTC landing time it seems to be 12 Dec 04:25 UTC...

% setenv TZ UTC

% date +%s -d "Jan 25 05:05 UTC 2004"
1075007100

% bc
686.9725*86400
59354424
1075007100+59354424
1134361524

% convdate -c 1134361524
Mon Dec 12 04:25:24 2005

[dilo]

Just made an Opportunity dedicated postcard.