some time ago, helvick posted the following excellent analysis of the
MER solar power situation as an extrapolation of a diagram showing Watts/hours
against Sols.
http://www.unmannedspaceflight.com/index.php?act=Attach&type=post&id=580
(originally posted in: http://www.unmannedspaceflight.com/index.php?showtopic=947&st=180&p=10722entry10722)
What makes this chart (let's call it Helvick's Power Chart, HPC so useful, is it's taking into account all relevant factors contributing to the remaining power life time of the rovers: seasonal solar input, gradual attenuation by dust accumulation, and (last not least the "pushing" of the cleaning events.
So here is my suggestion to use this thread/topic for updating this chart
whenever new power figures (watts/hours) and/or new cleaning events are
reported by JPL.
This would be a great way to always get an overview of the best guess of the maximum remaining rover life time (i.e. the limit imposed by the solar power...
which, of course does not take into account failure for other reasons, but would be a nice estimate of the maximum expected lifetime of our little heros
The latest JPL power report
Would it be possible for the power output to reach some sort of balanced state?
I mean, you have dust setting and dust removing powers at work here. So, if the cleaning events come in a regular enough fashion, it would mean that the power output would remain above a certain level.... for ever???
Or do the solar cells degenerate anyway, regardless of dust? (But in a much lower rate I would guess).
I think it'll be like gambling. Sometimes you win, sometimes you loose,but eventually, the house will always win and the output drops below a critical level.
Doug
Update to the original chart.
I'm stuck down at the bottom of a net free zone updating over GPRS so I'm just dipping in briefly. This is my current "best" guess based on the very few sample points we've been given. I also cleaned up my earlier data somewhat however it is now more obvious that the two main factors I didn't take into account, Tau and Rover Orientation, played a significant part in the very healthy Power state in the Sol 350-Sol 500 timeframe. Very slick orientation gave Oppy better than 100% of the theoretical level I calculated for it from Sol 275 to Sol 340 or so. The benefits of finding a nice sheltered Sun facing slope in mid winter are pretty clear.
Anyway - I'd love more data and really want to work this out a bit better but here's where i'm at so far
The charts are great, but you might consider adding something to them to indicate when they were made. Right now there's no easy way of telling the difference between actual values and predicted values just from looking at the charts.
Oppy exceeds maximum power estimate? Is this because it was resting on the slopes of endurance crater at a favorable angle?
Just a thought - is there some whr info in the mobility reports?
Doug
Well this power chart is outstanding, exactly what's needed for presentations.
may I suggest adding a few real time earth dates (month/yr), perhaps every 100 to 150 Sols, at bottom.
Also, Martian seasons on top to correlate with estimated max power
thanks.
Another variation..
Added a table for Martian Seasons in Mission Year 1\2 (Solstice\Equinox) and Landing anniversary date.
Changed X-Axis to reflect Earth Date (M\D\YY) & Spirit sol
Added shading to indicate the current date (split between "known" data and extrapolated data)
I'm still looking for more precise data on the actual power and want to work on building a better model for the "Estimated Max Power" data - I got the data for this by lifting some values from an insolation chart I found online and making some outrageous assumptions but really want to recalculate that based on actual orbital data\lattitude.
The pointing data that Michael Howard has put together for MMB makes me think that I should be able to get sufficiently accurate information on the actual orientation\inclination of the Rovers to work out pretty accurate "maximum theoretical power"
Thanks again, Helvick for this great analysis !
I bet, even JPL's own models couldn't hardly be more elaborated than your's
speaking of the JPL team: have you considered mailing them for more accurate solar power data ?
maybe someone of them is reading this forum
You may get more info my dredging thru all the workbook sol-by-sol documentation.
Doug
helvick, your chart looks great but I'm little disappointed by the fact that Opportunity was so close to a "power death" one year ago!
If true, rover was unable to move or make complex operations. Indeed, it moved, taking many pictures and using robotic arm too!
http://marsrovers.jpl.nasa.gov/gallery/all/opportunity_n184.html
http://marsrovers.jpl.nasa.gov/gallery/all/opportunity_f194.html
Also press release didn't mention any power issue (http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20040804a.html), so there is something wrong?
I'll post any and all values I find in the documentation
Spirit
Sol 360 : 410 whrs
oh
That's the only one I could find
Just a thought - would you be prepared to share the .xls ( if that's what your using ) of the data?
Doug
From the latest update:
http://marsrovers.jpl.nasa.gov/mission/status.html#opportunity
"The team has been watching Opportunity's power very carefully. It seems that Opportunity is losing some of the power boost it received during the last cleaning event. The solar array wake up time has been getting later each day and is currently 9:48 Mars Local Solar Time. The team has been planning accordingly, taking steps to preserve power where appropriate."
Is 9:48 Mars solar time based on whose clock? 24 hours, a proportion of a Sol or what...
...this is NOT intended to start a thread on Martian clocks, calendars, etc!
summer solstice on mars tomorrow (Aug 16)
Just back from a talk by SS and I have the latest power figures:
As of "yesterday" (Sol 580?) Sprit was at 880WHr.
Oppy was at around 600WHr.
But...
Steve said in response to a question about remaining rover life that he didn't think that dust would be the cause of rover death. Rather there is not a lot of redundency in a lot of the electonics. There are a lot of electronic components that if they fail would be end of mission just like that
As Steve said "We plan every day as if it's our last, because it might be."
James
Problem is, they've been planning *every* day as if it will be their last since each vehicle's sol 1. Squyres himself, in his book, speaks of being very high-strung about anything that would take away a productive sol, because they only had 90 (or less!) to work with. He also speaks of the team getting more laid-back and less nervous about their babies dying anytime soon as they doubled, then tripled, then quadrupled their design lifetimes.
I wonder how hard it is to maintain that kind of emotional energy, to assume that your project (and your present Life As You Know It) is going to die soon -- keeping at that fever-pitch for month after month, caught in the tension between assuming you'll be dead tomorrow and hoping you'll survive indefinitely. I would think that would be nearly as exhausting, in the long run, as living on Mars time.
-the other Doug
Of course, I'm sure Steve is more relaxed about it as time goes on but there is no getting away from the fact that sudden rover death is likely at some point so it's the way they have to work. The trick is not worrying about it! SS did mention today about how it's a hard way to work, making long term plans but making sure you are getting the maximum return day by day given you don't know what will happen tomorrow.
All I was trying to point out was that what with solar panel cleaning events and being able to stuggle on coping with several mechanical failures that at this point an electronic failure is seen (by SS) as the way the rovers will probably die. Thus all these power projections, while interesting probably arn't particuarly relevent to rover lifetimes.
James
12/5/2005
Significant New Power Information from JPL is here:
PIA03607: Solar Power on Mars
http://photojournal.jpl.nasa.gov/catalog/PIA03607
Original Caption Released with Image:
This chart illustrates the variation in available solar power for each of NASA's twin Mars Exploration Rovers over the course of approximately two Mars years. Two factors affect the amount of available power: the tilt of Mars' axis and the eccentricity of the Mars' orbit about the sun.
The horizontal scale is the number of Martian days (sols) after the Jan. 4, 2004, (Universal Time) landing of Spirit at Mars' Gusev Crater. The vertical scale on the right indicates the amount of available solar power as a ratio of the amount available at the equator when Mars is closest to the sun (perihelion). The red line indicates power availability at Spirit's landing site (Gusev). The blue line indicates power availability at Opportunity's landing site (Meridiani).
The vertical scale on the right applies to the dotted line, indicating the latitude north or south of Mars' equator where the noon sun is overhead at different times of the Martian year.
and more here
PIA03608: Solar-Panel Dust Accumulation and Cleanings
http://photojournal.jpl.nasa.gov/catalog/PIA03608
Original Caption Released with Image:
Air-fall dust accumulates on the solar panels of NASA's Mars Exploration Rovers, reducing the amount of sunlight reaching the solar arrays. Pre-launch models predicted steady dust accumulation. However, the rovers have been blessed with occasional wind events that clear significant amounts of dust from the solar panels.
This graph shows the effects of those panel-cleaning events on the amount of electricity generated by Spirit's solar panels. The horizontal scale is the number of Martian days (sols) after Spirit's Jan. 4, 2005, (Universal Time) landing on Mars. The vertical scale indicates output from the rover's solar panels as a fraction of the amount produced when the clean panels first opened. Note that the gradual declines are interrupted by occasional sharp increases, such as a dust-cleaning event on sol 420.
Sweet!
[Meant to post in tech forum. Sorry.]
Helvick- is there a new version of the power chart available? ( notice some discussion about power in the Spirit at winter quarters thread.
Doug - can we move this thread to the tech forum? (I was confused by it being in the oppy thread - newbie mistake?)
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