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

These are all the power generation numbers I have from the Rover updates:
http://marsrovers.jpl.nasa.gov/mission/status_spiritAll.html
http://marsrovers.jpl.nasa.gov/mission/sta...rtunityAll.html

Most of these are specific references but some are not absolutely specific e.g. for the Spirit Sol 219 to 231 update the power level is quoted as "Power is always a major concern as available energy fluctuates between 300 and 400 watt-hours per sol" so I've taken that somewhat arbitrarily as 300whr on Sol 219 and 400whr on Sol231.

Opportunity
Sol Whr
639 720
633 528
630 496
629 470
628 479
627 593
526 650
524 500
456 650
450 620
339 836
333 630
321 546
312 840
316 730
257 700
250 660
199 610
100 610

Spirit
Sol Whr
575 900
572 875
422 800
421 700
420 600
419 400
418 350
284 400
231 400
219 300
204 288
203 370
80 700

New Scientist Rover Updates.
All of these are a bit approximate in terms of dates and exact power levels.

New Scientist 16 Feb 2006
Opportunity
Sol 734 600whr
Spirit
Sol 754 450 whr
Sol 704 550whr

New Scientist 23 December 2004
Opportunity
~Sol 310 "over 900 whr".
Spirit
~Sol 330 600 whr

New Scientist 30 October 2004
Opportunity
June 2004(~Sol 126 to Sol 155) "dropped to 500-600 whr"
Mid September 2004 (~Sol 230) 700whr

Steve Squyres Mission To Mars
Jan 3 2006
Spirit
Sol 711 500whr

August 31 2005
Spirit
Sol 581 956whr

April 17 2005:
Spirit
Sol 457 "Over 800 whr"

And I found this in the April 17 2005 update - "We think that the rovers can't survive at power levels much lower than 280 watt-hours". That's where the minimum power level reference comes from.

The Planetary Society Rover updates.
There are quite a few power numbers quoted but only a handful are specific.

TPS MER Update November 30 2005
Opportunity
Sol 638 720 whr

TPS MER Update October 27 2005
Spirit
~ Sol 645 "High 700's"
Opportunity
~ Sol 625 "High 600's"

TPS MER Update September 22 2005
Spirit
~Sol 621 885whr
Opportunity
~ Sol 601 630whr

TPS MER Update July 28 2005
Spirit
~Sol 557 600-650 whr
Opportunity
~Sol 537 600-650 whr

TPS MER Update June 5 2005
Opportunity
Sol 463 620whr
Sol 476 650whr

TPS MER Update March 25 2005
Spirit
~Sol 435 860whr
~Sol 421 800whr
Opportunity
~Sol 401 "the 600's"
There is also a note that Spirit hit a minimum of 550 "for a while"

TPS MER Update 9 December 2004
Opportunity
~Sol 310 "800-900 whr"

TPS MER Update 22 October 2004
Spirit
~Sol 176 ~400whr
~Sol 236 - Sol 285 "400 - 500whr"
Opportunity
~Sol 126 - Sol 215 "500 - 600whr"
~Sol 216 - Sol 235 "averaging 660whr"
~Sol 236 - "than 700whr"

TPS MER Update 19 August 2004
Spirit
~Sol 223 400whr
Opportunity
~Sol 202 550-600whr

TPS MER Update 3 June 2004
Opportunity
~Sol 128 ~500whr
Note This mentions that Deep Sleep saves Opportunity ~170 whr per sol.

Just got word from JB

"Spirit is down to about 360-370 Whr and Opportunity is down to about
540-55 Whr"

Doug

Time for a graph. anyone?

Bob Shaw

Here ya go
Spirit
Click to view attachment

Power is down significantly compared to my prediction at the last check point. My previous estimate had it at 416whr for Sol 774. At this rate it would drop below 300 whr on Sol 829 and below 280 on Sol 849. If a more hospitable environment isn't ound she would drop to 245whr between sol 923 and 938

Opportunity
Click to view attachment
Opportunity is also down somewhat - I had anticipated it would be at 571 whr at this point . At this rate the minimume power level looks to be 405whr between Sol 902 and 924.

The lower power levels for both rovers might indicate that dust levels are up (which would be unexpected I think) or it might just be unfavourable orientation.

Opportunity
Click to view attachment
Opportunity is also down somewhat - I had anticipated it would be at 571 whr at this point . At this rate the minimume power level looks to be 405whr between Sol 902 and 924.

[/quote]

So the Trek to Victoria could become a race against the time. If this trend (dust-induced power loss dropps more rapidly than predicted/expected) then we will hit the "operational limit" in significantly less than 100 Sols.
So in order to rech the Victoria slopes in time we should be really making not much less than 20 meters per Sol of driving *on average* which seems pretty fast IMO

Any guesses about the average meters per day Oppy could realistically make in the terrain towards Victoria ?

And, ehr yes: keep up praying for those cleaning events

At the moment I still don't think that Opportunity will fall below a level at which it can still drive for at least an hour a day but if it is dust deposition that is causing this rather than orientation or an increase in Tau then who knows.

Depends on the type and density of dunes and we don't really know what's ahead yet. On a good pavement she should be able to cover 20-40m even when power drops to 400whr. Around Sol 320/325 she covered 60-80m on sols when she was generating not much more power than she is now (540-600whr)

Oh yes.

From the laest update

Helvick , does your projection account for Spirits current tilt?

No. My estimates are based on a horizontal orientation and have never taken tilt into account which is a major flaw that I never got round to fixing. Spirit's current tilt adds around 15% extra power to those numbers so the current estimated value from my last chart of around 270whr would go up to around 310whr which agrees pretty well with the reported value. The minimum values from Sol 923-938 will be around 285whr which is very low but higher than the worst that was seen in the climb up Husband Hill.

Helvick, is your estimated output for sol 923-938 considering also further dust deposition?
If not, I'm a little worried...

All of my "projections" include a 0.18% cumulative degradation in performance per sol to account for dust deposition so a minimum of around 285whr/sol give or take a couple of watts should be right unless she goes and falls off that rock.

thanks!

Now, how about is the power level of Oppy. I see that latelly, Oppy is only permited to drive around 30 minutes per sol. However, up to know, Oppy still have not posed to tilt to north facing. I seems that Oppy has enough solar energy to rover for some days. Then , when do you believe that Oppy will not be allowed to traverse further?

Rodolfo

Where do you get that 30 min drive time from? And couldn't the reason be that they could drive for longer, but they don't want to? Unknown terrain etc.

Opportunity current (Sol 856): ~ 382whr
Minimum: 339whr from Sol 937 to Sol 965.

~280whr is (according to SS) the minimum required for basic survival. So we have around 100whr/sol to play with right now and that will drop to 60 or so at the minimum. The rovers burn about ~100w when driving but there are all the other things that have to be done (enabling the gyros\accelerometers, uplink\downlink relay, taking the end of drive images, Sun\Tau measurements) which probably add up to around 20-30whr. So we've got about an hour's driving capability at most right now and it will be dropping to 30 minutes or so as SH winter insolation hits its minimum.

The duration of transverse done by Oppy lately was around 30 minutes according tot he calculations which I have made. The Oppy's average speed is around 3.5 cms/sec, that is about 62.5 meters / 30 minutes. Hence, I deduct that Oppy is taking about 30 minutes of driving knowing that Oppy stops every 45 seconds to perform any navigation analysis related for 15 seconds before to resume again the drive. That is the driving distance would be 30*3/4 a little more than 22 minutes to cover a distance of 46 meters.

On the other hand, I was acquainted by the JPL Marsrovers news that they were planning to drive the Oppy toward VC between 30 minutes to 2 hours depending to the energy reserve level.

Hope I have cleared to your inquiry!

Helvick, Thanks of your input!

Rodolfo

http://marsrovers.nasa.gov/mission/status_...All.html#sol874

No mention of how much power this requires. I wonder how it affects the amount of science that can be done.

Alan:

Think of the effect if the heaters *didn't* get turned on: EOM.

Bob Shaw

>For the first time on either rover, Spirit's battery heaters turned on at
>8:15 a.m. local solar time on Mars on Sol 865 (June 9, 2006).
>The heaters activate automatically when local temperatures drop to
>about minus 19 degrees Celsius (minus 2 degrees Fahrenheit).

In "Roving Mars," SS notes (at p. 341) that Opportunity survived at temperatures as low as -46 C (as measured in Mini-TES) the first time they tested Deep Sleep, in May 2004.

In light of this, I'm confused by the recent status report which suggests that this is the first time either Rover has experienced temperature as low as -19 C. Or is the point that the temperatures had never fallen so law during daytime? Or maybe Mini-TES is colder because it's up in the mast?

TTT (puzzled in NYC)

There's a difference.

That -49 was the temperature of the lens inside Mini TES.

The -19 is the temperature of the battery.

They're both inside the WEB, but the battery does more work, more of the time, so stays warmer for longer - it's the 'hot spot' of the entire WEB I would imagine.

Doug

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

Hang in there buddy.

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.

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.

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.


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.

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?

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.
Click to view attachment
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.
Click to view attachment

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.

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.

You're correct - the Dust Loss number is a rate not an absolute value - it's an estimate of the rate of change in efficiency of the power generating system from Sol to Sol. ie the power is reduced by that percentage each Sol.

To take an example period the Dust Loss [Rate] is 0.03 from Sol 853 to 882.
On Sol 855 the relative efficiency of the panels compared to Sol 1 is 53.6106%.
On sol 856 it is 53.5945%.
The Sol 856 number is 99.97% of the Sol 855 number. You don't add the values directly, you reduce them by that percentage so you get an exponential decay type curve eventually rather than a straight line, or would be if it lasted long enough and was constant.

Hi helvick,

do you also have the dust accumulation loss rate estimates for Opportunity ?

(and what's the current WHR generated by Oppy right now (must be around 400 Whr, right ?)

I'm concerned by your observation that even with spring season coming, the negative effect of the dust loss rate seems to "overtake" the positive effect of increasing solar insolation

If for Oppy it's similar to the spirit figures (0.1-0.3 % per Sol) then this could limit the remaining
lifetime to less than 100 Sols ... just barely sufficient to reach Victoria at all and then
leaving not much time for doing the science there
( of course we could hope for future cleaning events but, unfortunately we can not rely on that to actually happen ...)

Helvick.

One thing that struck me last night. The amount of incident sunlight absorbed by dust on the panels must be quite inclination dependent. (Think of the size of the shadow of a dust grain, or the path length through a thin dust film as the the angle varies) Maybe this is the reason for the power falling off faster than expected?

If this is the case then as we appoach the solstice the rate of change of this effect should decrease and even better, give more power than expected as spring arrives.

Does this make any sense?

James

Interesting idea - this certainly would make sense for beam insolation. The assumption that I made was that the "loss" in power due to dust could be described by a simple efficiency percentage as that seemed to be what the mission planners had thought. Now that I think about it it doesn't make a lot of sense to think it could be so simple.

I think I need to try to model this to see how it might effect power throughout the day and as the Sun's altitude changes from Sol to Sol.

Diffuse light (which accounts for around 30% of power generated at the moment) is definitely not affected in the same way - by definition it comes from all incident angles after all.

Hi Helvick,

do you also have current dust accumulation loss rate estimates for Opportunity ?

(see also my former posting above)

I haven't carried out the same exercise for Oppy yet - I'll try and post it later this evening.

I'd agree that it is not affected in quite the same way -but the effect will also will affect diffuse light. That element of diffuse light arriving vertically will be affected less than the element of the diffuse light arriving obliquely.

I'll leave you to model it!

Rob

Aargh! True there is an effect and it will change the distribution of light on the panel but I have a gut feeling that it will generally cancel itself out. Reflection will play a fairly significant part in it too. Hmmh, some more thinking is in order.

Anyway quick back of the envelope calculations for the beam case show that for the best case situation (midday sun directly overhead) a 33% physical covering of dust would cause a performance degradation of ~45-50%. Exactly the same amount of dust in mid winter (with a maximum solar elevation around 63deg) would cause a degradation of 70-75%.

However that also assumes completely non reflecting dust grains. If they reflect anything (which they do) then a significant percentage of the reflected light will end up becoming available to the panel which could even increase the efficiency of the panel at low solar angles if the dust was quite reflective. Not a simple task to model well I think.

Interesting. Got to think about this more and do some real digging into last years data to see if I can spot any trends.

Just found some great news from the folks at JPL - they definitely disagree with my guess that dust deposition rates were high and getting worse. From todays Spirit update

For that to be true the dust deposition rate at the moment would need to be very low (~0.05% per sol). Clearly that's good news.
So to celebrate I've effectively trashed my earlier attempt at the power chart and mapped out a possible version using the above data, a much more friendly dust loss rate from the published table for Spirits panel efficiency for her first year, and including two cleaning events (corresponding to the sol 421 and 520 events).
Click to view attachment
That would allow for quite a bit of activity (ie like trying to move) from around Sol 1100.

Even without any cleaning events under these conditions she would have enough juice to survive fairly easily and be able to keep up the current programme of long term observation while waiting for a bit of a clean.
Click to view attachment

The problem with Opportunity is that there is very little data - the last update I can find that mentions power was the 400whr number at the end of May.
Using the same assumptions as for Spirit above I get the following for Opportunity at the moment. Power has just about hit its lowest level for this winter (~370) and will stay around there for a while (say around Sol 925\930) and then will slowly creep up to ~420 at around Sol 1080 and then begin to decline back to 300 whr as Tau increases with SH Spring\Summer. Any cleaning events will significantly change that of course.
Click to view attachment

Thanks Helvick !

It's encouraging, that even with your conservative estimate and even without cleaning events,
there seems to be sufficient power for Oppy until at least around Sol 1150

BTW.: I really love those excellent diagrams of yours

More good news on the power front, this time for Oppy - from todays JPL update:

So Oppy is in very good shape and getting better. The following chart shows that even without any further cleaning Opportunity should have enough power generating capability to last through to next winter.
Click to view attachment
I think I'm going to break out the Laphroaig and have a wee dram to celebrate.

Spirit hasn't been so lucky (yet) but they have confirmed that her power generating capability is not expected to fall below 275 watt hours which is very good news.

Yippie !!

this is very good news !
Thanks Helick, for the prompt power chart update ...

I see you like to celebrate in style.

Great news, helvick. I think we definitively need another mission extention, something like another earth year (up to sol 1350). This would allow Opportunity to complete Victoria Crater exploration and, hopefully, Spirit will be able to climb the Mc Cool hill (but probably we need a cleaning event too!).

yes: comleting Victoria exploration and Mc Cool Summit - that would be the absolute dream of the perfect mission !


so let's just pray that the hardware will last long enough ...
<sol 1350 vision>
Oppy is dragging its broken IDD on 3 wheels accross the bottm of Victoria while Spirit finishes a one-eyed McCool Summit Panorama after having creeped to the top at a pace of 2-meters-per day
</sol 1350 vision>

:-) The Islay single malts are ideal for special events - Laphroaig in particular really is a delightful mix of heaven and hell that I can only ever drink slowly and in small quantities so there's no fear of ending up with a hangover afterwords which is definitely a good thing since a Laphroaig hangover would probably be an awful thing indeed.

About Oppy news are very good and what about the news about Spirit. It is matter of crossing fingers or not? Just withstand for few days until after August 8. Will Spirit survive that time?

About Nirgal's comment, how bad will be the both girls, they will end like pirates, limping on the roads.

Rodolfo

From the August 4, 2006 mission status for sols 915-921

"Spirit is collecting about 280 watt-hours of electrical power each sol from the rover's solar array"

http://marsrovers.jpl.nasa.gov/mission/status.html

From the August 11, 2006 mission status for sols 922-928

"Spirit continues to collect about 280 watt-hours of electrical power each sol from the rover's solar array"

http://marsrovers.jpl.nasa.gov/mission/status.html

The winter solstice has passed (Aug 8, 2006).