So it seems for the amazing Mars Exploration Rovers that another sol has come and another milestone has been reached.

Opportunity has passed the Viking 1 lander for operational time on Mars - 2245 sols.
While Spirit remains in hibernation, there's no way to know whether she has the record.
I'm sure that Opportunity will happily stand aside for Spirit when we hear from her again

Here's a banner logo and desktop image to mark the milestone.

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Enjoy

I believe I'll not be the only one to enjoy. Thanks.
What we can say for sure is: Opportunity is the first spacecraft contacting Earth holding the record of longevity on another Planet.
Very soon, she'll be the oldest spacecraft to rove on another planet.
Come on Spirit, you CAN'T stand it, can you?

Great idea (and visual) Astro0 !!!
Here is my interpretation.
A tribute also to MarsEngineer !
Enjoy also !
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Cool, although hopefully 2010 won't stick.

Do you mean Rob participated also to Viking program?

Not in the Viking program, but I know Rob since 1993 when we started the Mars Pathfinder program. I was then working with Cheick Diarra launching the Mars Outreach with JPL and we had a lot of discussions with the engineering team about the MESUR Pathfinder mission. Then, the only way to compare how to land on Mars was Viking which life duration on Mars to attain was some kind of a dream ...
When Rob started the MER mission, no one would have bet that the MER could have the possibility of beating the life duration of VL1... except those having seen the exceptional engineering skills of Rob who did care a lot about the quality of launched equipments and their testing ("do testing and do more testing", that's the success mantra of JPL).

When MER was launched my personal bet was that :
(i) with solar panels and their random cleaning ;
(ii) the real possibility of batteries failure due to harsh Martian conditions ;
(iii) the improvement of technologies derived from MPF ;
(iv) the improvement of the quality of equipments and electronics since MPF ;
(v) the bigger budget than MPF ;
(vi) the greater managing experience of the MER team having now the success of MPF in their hands ;
=> the MER life duration could be in the range of 1 to 2 Mars years maximum, having ended as a stationary lander by failure of its mobility system.

This is why I give 5 s to Rob, because not only he bet the VL1 record, but the MER rovers still have their wheels working (partially for Spirit).
I think that Rob is on the very top of the list of the best Mars engineers since the beginning of Mars exploration !

...as well as an encredibly good communicator (I miss him posting here). I also listen to him in Pasadena on Spirit landing day with the Planetary society and "nearly" met him once : http://www.unmannedspaceflight.com/index.p...ic=3765&hl=

Really interested in your last post vikingmars. I know that the rovers had a 'warranty' of 90 days but it was fascinating to hear from someone more 'in the know' than I what their private hopes for the mission were. Although the forum covers many other spacecraft and planets my primary interest at the current time is the rovers (and how I discovered this forum). The recent slowdown on posts regarding Spirit has emphasised to me how fortunate we are that the rovers have so far exceeded their expectations.

I guess if I was being really greedy, I would hope that both Spirit and Oppy can continue until MSL lands. The idea of all quiet on the MER forum is too hideous to contemplate. So my thanks go to Rob and all those involved.

Neil

ps Do we have a 'warranty' expectation and landing date for MSL yet?

You are right !
Here is a version without numbers... Enjoy also
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... and that's why I love this place so much, right there...

Thank you Olivier!

I am flattered by you (& Climber) ....

Actually a bit embarrassed too...because I really have to say that I am getting far far too much credit here!
These endeavors are the result of many many talented people from all over our blue planet. I am very very lucky to have been in the right place at the right time which allowed me to work with such talented and fantastic people (like Olivier) who work hard to try to make this really amazing stuff happen. In countless ways it is a privilege to do this work.

Yes, I had HOPED that MER would last a year or so. Remember all we had to go on in 2001 for estimating the rover's dust accumulations was the results from Pathfinder and Sojourner in 1997. Back then we saw a very consistent 0.25% loss of solar array power every sol on both of these vehicles. That's all we had to go on. On MER when we looked at where we thought that quarter percent took us using the largest (origami) arrays we could fit in our tetrahedral "box" and we compared that with the amount of power needed to stay warm and actually DO something (unlike poor Spirit of late, she really has not been pulling her weight) we found that we ran out of power after about 110 sols or so. (In fact we were so worried about even making it 90 sols that Dara added another folding set of solar panels to our early design.) We of course speculated that the dust accumulation would level off at some point and that the rovers could actually require less power in the dead of winter than we assumed, but we were simply guessing. I tended to look on the bright side and privately suggested that they might survive a winter ... who could say? In fact what has happened to Spirit this year (minus getting stuck) was exactly the scenario that we envisioned for the end of the mission in 2004.

We were also pleasantly surprised at how well the rover's internal temperatures stayed within bounds. The MER thermal isolation design was a lot better than we did on Pathfinder (a little aerogel here ... a little cable isolation there ... ). The MER mechanical & thermal engineering team was amazing.

Olivier is right, I have been betting on another year for quite a while now for both rovers. Steve S. has been on the losing side.
I don't know if Spirit will make it this time.

There was one thing that we did not have to worry about in our MER design - we did not have to consider several tons of dry ice breaking our solar panels. (Poor Phoenix!)
What's left of Phoenix's solar panels?

-Rob

- and it's into the history books for you lot!
An awe inspiring achievement that brought Mars to us all, congratulations.

So, Rob, did the team never consider the possibility of dust removal by wind forces? There were no design considerations in the direction of "let's make the surface of the solar arrays really slippery"?

Would be fascinating to know which lessons from the MERs have made it into MSL. Keep up the good work on that one! (Seems we will have some Avatar-like imaging goodness from Curiosity, if EDL turns out well!)...

Oerstad, we did consider wind. We even considered going up to the "Mars" low pressure wind tunnel up at NASA Ames with a bag of dust and a fan in hand. The problem was that we did not have a Mars dust stimulant that we trusted. Our expectations were that the dust - at least the first few microns of it - would be "sticky" due to Van der Waals forces or other triboelectric effect. We suspected (and still suspect) that our intuition about materials interaction goes out the window when in a low pressure, highly desiccated environment with materials we do not understand.

One factor that dampened our enthusiasm for testing on MER was that we knew that the dust was NOT cleaned on MPF's (nor Sojourner's) solar panels after dust devils went by in the summer of 1997. Although we could not see them, the dust devils were measured using the atmosphere pressure transducer and the hot wire anemometer (part of the ASI/MET experiment). We could see the pressure drop as it went by and see the change in wind direction at the same time. (Look up Dr. Tim Schofield.)

So..... dust devils, no cleaning. We could not count on it. Instead we made the solar arrays bigger. But why does the wind successfully (completely?) clear the arrays on MER? We don't know. Perhaps it is because the rover is higher off the ground than MPF and higher above the boundary layer. Perhaps it is the airspace below the panels that allow the wind to flow faster over the arrays. Is it perhaps that MER winds bring dust with them and scour (sand blast) off the existing dust? Perhaps the dust devils are NOT the cause of the MER cleaning and that some other wind phenomena is doing it (like a passing front that has sustained winds). Without an atmosphere science experiment on board MER, we simply do not know.

In our work, we often have to learn to live with simply not knowing and instead learn to imagine and assume the worst case. The worst case seemed to be the 1/4 percent per sol of dust with no end in sight. That is how we design these beasties. The trouble is, even our worst imaginings might not be good enough ... fortunately we tend to err on the conservative side just enough to win in the end.

People ask me why the rover's lasted far far more than the original 90 sols .... did we over-design them? One could say "well of course!", but ... think about it, if NASA had asked us to design to last exactly 90 sols (with no designed-in life-limiting "timer" like MPF had with its Ag-Zn battery), could we have? No. If we had tried, the rovers would have lasted either 3 sols or 300. When it comes to reliability, we can only design for inequalities: we design for MORE than 90 sols (90 sols plus various design-in and tested margin). If we had designed for ZERO margin above 90 sols, then we might have lost them on sol 3. That would not do. Our contract with NASA and Steve was to last 90 sols or more. If MER had died on Sol 91, we still won (just), but if it died on sol 80 we would not.

On MSL we do have a a life-limiting timer: the MMRTG. We know that no amount of wind will make it generate more power as it ages. But at least we have a guaranteed supply of trickle-charging into the batteries. We have traded limited life for reliable power over a wide latitude band and over a Mars year.

You asked about lessons from MER to MSL (and from Phoenix to MSL). The list of lessons is too long to type. Interestingly, due to design and mission differences there are some aspects of MSL that just are not well informed by any previous surface mission. In some aspects we are in new engineering territory (again). MSL really is a big challenge, easily as big as MER.

Good night,

-Rob

This might be a silly question, but why wasn't it possible to make the solar panels tiltable so the dust would simply slide off when they were set vertically?

That's been asked a thousand times. Go look at your TV. It's vertical, right... but the screen's still dusty. tilting them vertical is probably not going to do much.

Plus - such a mechanism has it's own failure modes, complexities and risks. A dirty solar array is far far better than one that's stuck vertical.

Maybe if somebody goes back to solar on Mars one day, there'll be a little fan on the instrument arm. On a RAT tool, with prop blades that swing out with the centrifugal force when rotating. Then they can be latched tight for RAT'ing and unlatched for blowing. I'm not sure it will be worth it, though, with the added complexity and considering the stellar record of the MER panels!

MarsEngineer, Thanks so much for your reply! - so much fascinating info about your MER lifetime expectations. Might pop a few questions in the MSL forum one day, I'll alert you to them

Some time ago, I read something, somewhere (yes, very helpful, I know) about a proposal for induced electrostatic cleaning of solar panels. Has anyone any idea how practical such a thing might be? (Seems to me it might come in handy for optics as well.)

I can't speak for anyone else but as an engineer I have to take my hat off and bow to the master and his team. We've seen discussions about wipers, fans, electrostatic plates, tilting and shaking panels and a host of other solutions to a problem that the team eliminated by designing the best possible system they could to meet the objectives they had been given.

The pre-flight assessment said 0.25% power loss due to dust deposition per Sol. So they built a set of arrays that would give them 90 Sols of mission even with 0.25% per sol losses. Anything better than that was a bonus and here we are 2000 and whatever sols later with at least 50% of the mission still powering along and we can't rule out the other 50% waking up sometime. Come on folks - if you can't see that as a vindication of good, no scratch that, awesomely great design then you really do need to reconsider your standards (in my humble opinion at any rate).

I'd say that pretty much conclusively proves that fans, wipers, electrostatic wotsits and tilting panels would all have been a pointless waste of valuable time and money and the decision not to invest time and energy into them was a very smart move by MarsEngineer and his band of MERry men (and women).

...and mass. With mass such a precious commodity in terms of launch and EDL criteria, adding gizmos to clear the solar panels would mean giving up something else. Or possibly investing in a bigger booster and redesigning the landing system... which, now that I think about it, is exactly what you said... time and money.

Helvik, such a sensible comment. Bravo!

I think what would have given, would have been the large multiple folding arrays - after all, with a cleaning gizmo such large arrays wouldn't have been needed to make it through the primary mission. This would have given us less power in the summer and if it failed (or plain didn't work, given how little we knew/know about the mechanics of the dust) then they would have have had a much more serious problem during winter.

I personally don't think they would be roving today if it hadn't been for the simple yet oh so effective array design that the team came up with. All hail the MER engineering team for getting us a frankly astonishing 2.255 THOUSAND sols into a 90 sol mission!

Here's a trivia question that maybe the mission team can set an intern down to calculate during a slow time. What is the TOTAL wattage collected stored and consumed by each/both rovers to date?

Probably in the 500-1000 kwhr range I'd have thought. Ish.

I'd estimate we're approaching a MWhr of total energy usage for each rover. It would be a simple matter to integrate under the power curves in Dilo's statistics plots. Then we could all celebrate when each rover hits 1 MWhr.