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MSL reasons for delay
centsworth_II
post Jul 11 2009, 06:44 PM
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QUOTE (djellison @ Jul 11 2009, 11:45 AM) *
If having a vertical panel is the answer, how come we still have to clean our TVs and Monitors?

The dirt that sticks to a monitor is nothing compared to what built up on Spirit's panels before their latest cleaning. For that matter, the top of a computer monitor gets a lot dustier than its face. I would expect a vertical panel to get as dirty as the MER camera lenses. Not too bad.
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dtolman
post Jul 13 2009, 07:48 PM
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QUOTE (SpaceListener @ Jul 11 2009, 10:06 AM) *
And hope that these probably existence of solar panels must have their own self cleaning mechanics by applying the learned lessons from MER's experience.


After all the delays, overruns, and setbacks (they can't even power the darn thing now?), I'm wondering if learning anything is even possible - they're just trying to keep their heads above water...
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dtolman
post Jul 13 2009, 07:55 PM
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Isn't it a little late in the game to figure out that the amount of power available is insufficient to power the vehicle? Assembly is supposed to start in 6 months, and they're still worried about basics of the design...
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SFJCody
post Jul 13 2009, 08:06 PM
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I hope there's a TV documentary crew following MSL. The travails of this vehicle will surely be fascinating to watch.
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SpaceListener
post Jul 13 2009, 08:22 PM
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dtolman,

I think that this might be a leak news from news media since it has no further detail information about the reason. If NASA informs this, I hope it would be well covered and explained.

About this I have many questions and I am not able to know what is the real reason. It would be to too early to get well acquainted.

I think that NASA must know it perfectly whether if it is or not necessary after studying their cons and pros. The main electrical energy would be based of nuclear and the solar ones would be interpreted as an supplemental and not as critical energy. On the other hand, it would to be insufficient to supply an extra needed energy due to a new requirements, or present instruments that might need an additional not planned electrical energy needs.

An additional battery capacity would be the most sounding acceptable but up to here, it is not worth to further discuss without knowing their cons/pros.
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mcaplinger
post Jul 13 2009, 08:24 PM
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QUOTE (centsworth_II @ Jul 11 2009, 07:48 AM) *
My favorite solution is to mount the panels on vertical surfaces, like the sides of the electronics box. They would give less power with the sun overhead, but more with the sun near the horizon.

Obviously, they would only produce power when the sun was near the horizon and when they were on the sunlit side, assuming the rover was always parked with the panel pointed east or west. If the panel was pointed west, they wouldn't produce anything in the morning.

Fixed near-vertical panels have some use at higher latitudes, but not really near the equator. You can work out the math for various latitudes and orientations, but the cosine losses are quite dramatic, to the point of unworkability.


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helvick
post Jul 13 2009, 09:51 PM
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This isn't completely true - vertically placed panels will always get some diffuse light (generally about 5-15% of direct insolation on Mars) and reflected insolation (1-2% usually, higher when local albedo is high) . And when atmospheric opacity is high (Tau>~2) there is more diffuse than direct insolation although the overall levels are down to a fraction of ideal conditions. However if all you are looking for is a small amount of extra power then covering the vertical surfaces with panels will always give you some power.

A major problem that I see with it is that the extra weight and additional power management circuitry would lead to something else being removed which would be very bad.
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dtolman
post Jul 14 2009, 01:25 PM
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SpaceListener,
The main source of this seems to be an article in Nature - http://www.nature.com/news/2009/090710/ful...s.2009.664.html.

I didn't see this in the summary, so it probably bears repeating. From the article (concerning cost and power overruns respectively):
QUOTE
The cause of the latest overrun is problems with motors, gearboxes and avionics controls. After switching from a dry to a wet lubricant, engineers have had trouble verifying the reliability of motors for the rover's robotic arm. Moreover, McCuistion says, a new snag was recently discovered: some of the premier instruments — the Sample Analysis at Mars or SAM instrument set — will suck twice as much power as was expected, and that means the rover needs to carry bigger batteries.


I'm assuming here that the "batteries" are the RTGs. not the L-I kind...is there sufficient P-238 unclaimed to supply larger batteries? as of early 2008, I read reports in the media that the unclaimed supply in the system was measurable counting on one hand (in kilograms). Or maybe they can find a clever way to shutdown systems to allow the SAM to run on the existing power supply.

Hopefully the latter is a viable solution. I doubt they can add kilograms of battery, without cutting weight from somewhere else...
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mcaplinger
post Jul 14 2009, 01:53 PM
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QUOTE (dtolman @ Jul 14 2009, 06:25 AM) *
I'm assuming here that the "batteries" are the RTGs. not the L-I kind...I doubt they can add kilograms of battery, without cutting weight from somewhere else...

No, they are talking about the secondary batteries (I forget if they are using Li-ion or something else.) The RTG doesn't provide enough peak power to run the systems directly, so it has to be used to trickle-charge the batteries.

As for mass, I expect that they have enough mass margin to add batteries if there is no operational workaround. At least our cameras are coming in well under on both mass and power relative to predictions (not that we were very big either way.)

And for JPL bashers, note that SAM is provided by GSFC, not JPL.


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dtolman
post Jul 14 2009, 02:17 PM
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mcaplinger - thanks for the clarification. It can get confusing trying to parse power supply issues when everything ends up getting called "a battery" in the media.

Also - if anyone is interested - there is related information in this presentation to the NASA Advisory Committee (courtesy naswatch/spaceref):
http://images.spaceref.com/news/2009/PSS.Jun.09.Mars.pdf

The slide of interest from the presentation:
QUOTE
• Rover power system design does not meet present mission requirements, requiring additional battery capacity, and possibly solar array
– Increased energy requirements to keep actuators above safe operating temperature
– Almost double energy requirement to operate/conduct SAM instrument science/sample analysis scenarios
• The SAM instrument has not completed its environmental qualification program, and the wide range
pump has not demonstrated life qualification (hours of operation and start/stop) requirements.


The bullets above make it sound more serious (at least to me), than the Nature summary. Does anyone have any idea if the problem is that they can't run the SAM with other operations running, or if they can't even draw enough power to run the SAM even by itself?
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mcaplinger
post Jul 14 2009, 02:26 PM
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QUOTE (dtolman @ Jul 14 2009, 06:17 AM) *
Does anyone have any idea if the problem is that they can't run the SAM with other operations running, or if they can't even draw enough power to run the SAM even by itself?

Almost certainly the first one. These are total energy problems, not instantaneous power problems. As such there are most likely operational workarounds, though they may not be very attractive.


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Guest_Enceladus75_*
post Jul 16 2009, 01:52 AM
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I think MSL was just too big a leap, technology wise, from Sprirt and Oppy.

Cost and time overruns are a serious problem among NASA missions - and MSL is yet another prime example of this. sad.gif
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BrianL
post Jul 16 2009, 02:37 AM
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I would say that Spirit and Oppy were a much bigger leap in technology from Sojourner, over a comparable time period, yet things seemed to work out just fine for them.
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dvandorn
post Jul 16 2009, 02:55 AM
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Brian? Read "Roving Mars" by Steve Squyres sometime. The MERs came so close to cancellation so many times, it's almost a running joke.

Spirit and Oppy were once spoken of by Ed Weiler, who had the yea-or-nay vote on continuing with them, as things that "would look just great over at Air and Space." Unflown. Forever.

The MERs also got a major descope after the "final" design had been approved -- the Raman spectrometer was axed, something that Squyres has said all along is his greatest regret from the design and assembly phase.

So, no -- the MERs didn't have an easy path. It's almost miraculous that they even got launched. And their costs overran something fierce (I don't remember the original bid numbers vs. the eventual cost through the end of the primary mission, but it was something like a 60% to a 100% overrun.) Their development cycles were every bit as fraught with peril as MSL's has been, perhaps moreso.

-the other Doug


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mcaplinger
post Jul 16 2009, 03:42 AM
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QUOTE (dvandorn @ Jul 15 2009, 07:55 PM) *
And [MER's] costs overran something fierce (I don't remember the original bid numbers vs. the eventual cost through the end of the primary mission, but it was something like a 60% to a 100% overrun.)

Relative to the original 2003 proposal, it was probably more like 3-4x. Even more relative to the original Athena proposal. Not that a final cost accounting for MER is easy to come by. That's why I can only sigh in frustration when someone suggests that flying copies of MER would be cheap and risk-free.


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