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Posted by: Nirgal Jul 28 2005, 10:03 AM

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=10722&#entry10722)

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

underlines the remarkable accuracy of the HPC:
helvick posted the chart on May 18 (aronud Sol 460) predicting the 500 Watts/hour for around Oppy-Sol 540 (note, that the chart shows Spirit-Sols),
which is very well in agreement with the new JPL report !

Now, with 650 Watts at Sol 530 after the cleaning event, the "critical-below-300-Watt-drop" would be deferred from (approx) Sol 680 to Sol 750, in other words:
about 70 extra Sols as a gift from the cleaning event ;-)

Posted by: Cugel Jul 28 2005, 11:23 AM

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).

Posted by: Bob Shaw Jul 28 2005, 12:27 PM

The batteries have a limited number of discharge/recharge cycles, and thermal stresses may eventually cause dry joints in circuits etc, but in principle a solar-powered spacecraft which is protected from the worst ravages of the sun and has no attitude control issues can last a l-o-o-n-g time. Whether or not it'd be doing much, though...

...still, we've heard elsewhere on this forum that DODGE is still alive, and the old Pioneer solar orbiters also lasted an extraordinary amount of time, so who knows!

Posted by: djellison Jul 28 2005, 12:32 PM

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

Posted by: tedstryk Jul 28 2005, 05:55 PM

Well, depends how you look at it. Spirit and Oppy might win in the power situation category in the sense that this cleaning is efficient enough to allow them to live until they fall victim to some other kind of component failure that ends the mission. I will add that I really hope that these things continue their extended lives long enough to take full advantage of MRO...otherwise it seems that its communications package may go to waste, other than the Phoenix interlude, if MSL keeps getting pushed back.

Posted by: helvick Jul 28 2005, 06:56 PM

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

Posted by: ToSeek Jul 28 2005, 07:26 PM

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.

Posted by: deglr6328 Jul 28 2005, 10:15 PM

Oppy exceeds maximum power estimate? Is this because it was resting on the slopes of endurance crater at a favorable angle?

Posted by: djellison Jul 28 2005, 11:09 PM

Just a thought - is there some whr info in the mobility reports?

Doug

Posted by: dvandorn Jul 29 2005, 05:43 AM

I'm reminded of the lyric to the song "The Gambler" -- I should write up a whole lyric, but the line that springs to mind is:

"And somewhere in the darkness,
Ol' Spirit, she broke even..."

-the other Doug

Posted by: mars loon Jul 30 2005, 03:42 PM

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.

Posted by: helvick Aug 5 2005, 05:41 PM

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"

Posted by: Nirgal Aug 5 2005, 10:08 PM

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

Posted by: helvick Aug 5 2005, 10:13 PM

Well if they are reading - Pretty please?

I don't want to bug anyone about it but if someone is reading this who can publish the data or point me to it if it's already online then I'd be very appreciative.

Posted by: djellison Aug 5 2005, 11:02 PM

You may get more info my dredging thru all the workbook sol-by-sol documentation.

Doug

Posted by: dilo Aug 6 2005, 04:43 AM

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?

Posted by: helvick Aug 6 2005, 08:28 AM

Dilo,

There is certainly something wrong

First it was Spirit that hit rock bottom in terms of power, http://www.jpl.nasa.gov/missions/mer/daily.cfm?date=8&year=2004 look at the entry for 8/3/04, on sol 204 power dropped to 288 watt hours, Ouch! is right that's dangerously low. I also notice that my X-Axis Labels are offset a bit too much, the dip down to thewards the "Rover Death" line happened on sol204 but it looks like sol 225 from the chart labels, gotta fix that.

The chart includes both Spirit and Opportunity so it's a bit cluttered, I probably should split them apart and I'm beginning to think this thread should be in the "Imagery and Tech Issues" section as it's not Opportunity specific.

Secondly I only have about 25 data points from the daily updates between the two rovers and a further 5 or so from the Planetary society updates so a lot of the chart is interpolated. I really should add clear markers for the known data points.

Posted by: helvick Aug 6 2005, 09:04 AM

I've been looking but haven't found anything apart from the occassional references in the Mission Managers daily reports which match the data points I already have. Lots of downloading and digging to go.

Posted by: dilo Aug 6 2005, 09:43 AM

Ok, (damn!) now is clear... I fully agree with idea to split the two rovers in different plots... thanks.

Posted by: djellison Aug 8 2005, 09:59 AM

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

Posted by: helvick Aug 9 2005, 02:05 PM

Here ya go. I've split the chart into two separate ones and tidied things up enough to be happy for folks to dig into if they feel the need.

Please feel free to crticise, point out errors and suggestions for improvement.

I dropped the shading box that highlights the split between "known" and extrapolated data, I wasn't too happy with the fact that it made it look as if the historical data was actually known - 99% of the data points are estimates as you will see if you look at the spreadsheets.

New known data points are just added into the relevant cell for the sol (Panel Output Confirmed Values column) on the Worksheet tabs and everything automatically recalculates.

It's zipped because it's a bit large (1.9Meg) - which is a bit excessive I know but I was working on making it easier to read rather than efficient. Seems outrageous for something to make sense of about 25 3 digit numbers.

Posted by: general Aug 9 2005, 06:56 PM

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."

Posted by: helvick Aug 9 2005, 08:24 PM

Now if I had built my own Insolation table from 1st principles I'd be able to work out how serious that actually is. I'm making progress on that but I haven't got the kinks worked out yet (and learning more about eccentricity, equations of time, Zenith angles and all the rest than I'd ever thought I'd needed to know :-) ).

Based on my Insolation data I'd expect wake up time to be getting very slightly later in any case as total insolation peaked 4-6 weeks ago, although it's fairly flat at the moment as we pass through the SH Summer Solstice. Time to get back to work on my Equation of Time for Mars spreadsheet I think.

(Edit to correct Equinox to Solstice )

Posted by: Bob Shaw Aug 9 2005, 10:30 PM

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!

Posted by: helvick Aug 9 2005, 11:04 PM

The Mission times are based on a 24 "hour" per Sol clock, that's what you get in the http://www.giss.nasa.gov/tools/mars24/ application. AFAIK all Martian missions use it. Both Rovers use a Mission Time defined so that it would coincide with Local Solar time at a point about midway through their prime missions at their respective sites so theres a +-12 martian hour difference between them.

The precise details are bending my head at the moment so I'll stop there as I could go on ad nauseum.

Posted by: alan Aug 15 2005, 12:54 AM

summer solstice on mars tomorrow (Aug 16)

Posted by: jamescanvin Aug 22 2005, 06:27 AM

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

Posted by: dvandorn Aug 22 2005, 07:56 AM

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

Posted by: jamescanvin Aug 22 2005, 08:40 AM

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

Posted by: abalone Aug 27 2005, 02:29 PM

Can't believe how clean Oppy looks. Could have rolled out of the factory yesterday....

Posted by: djellison Aug 27 2005, 03:16 PM

The altenative being rover imortality

Doug

Posted by: jamescanvin Aug 29 2005, 12:47 AM

We can only hope!

Once we have a manned base on mars they could be tele-operated in real time and be much more productive.

Maybe around Sol 7000?

James.

Posted by: mars loon Dec 6 2005, 07:01 AM

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.

Posted by: helvick Dec 6 2005, 07:07 AM

Sweet!

Posted by: mars loon Dec 6 2005, 07:16 AM

Lots of new info especially for your fine efforts

Posted by: bigdipper Jul 8 2006, 04:50 PM

[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?)

Posted by: MizarKey Apr 27 2007, 07:47 AM

I thought about starting a new thread, but this one has such good info in it already...

I've looked back at http://marsrovers.jpl.nasa.gov/gallery/all/opportunity_p948.html and compared them to http://marsrovers.jpl.nasa.gov/gallery/all/opportunity_p1156.html and it's hard to see much difference. There may be some cleaning there, but has power improved over what was projected in the charts linked above?