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Wolverine
2004-Nov-12, 07:19 PM
I know Spirit and Opportunity have been racing against the clock since landing, but am curious: what exactly is the lifespan of the onboard battery systems? Looked through a variety of information and specs at JPL and Cornell, but was unable to find anything specific.

What piqued my curiosity was seeing the following statement in the article covering the power boost (http://www.space.com/news/rover_mystery_041105.html):


Opportunity is now at about 820 watt-hours and remains very close to full capability. Spirit, which is in a less advantageous position to point its arrays toward the sun, has 350 to 400 watt-hours daily.

Since we're in the 300% arena now, I would imagine that solar arrays would be the weakest link, but if the MERs benefit from further anomalous power increases, what are the ramifications where the batteries are concerned?

ToSeek
2004-Nov-12, 07:44 PM
I found this interesting article (http://www.space.com/businesstechnology/technology/mer_batteries_030903.html) about the batteries, but not much about their expected lifetime. The primary concerns I've heard mentioned so far are the solar arrays and the mechanical systems. No one's expressed any worries about the batteries that I can remember.

Wolverine
2004-Nov-12, 10:16 PM
Nice article, thanks. :)

I know the questioned I raised above is merely a secondary or tertiary concern, was just trying to pin it down since the subject came up with some friends last night, and we were left scratching our heads.

Cugel
2004-Nov-13, 01:06 PM
http://www.batteryuniversity.com/parttwo-34.htm
This site provides some more information. According to them a lithium ion battery has a life time of 500 cycles (upper limit). However, this estimate is based on batteries for laptop computers. My 'guestimate' for the rover batteries would be something like 1000 cycles (being state of the art).
As the batteries are recharged once every day this would result in a lifetime of between 500 and 1000 sols.

Regards.

slinted
2004-Nov-13, 01:48 PM
this took forever to find (let this be another frustrated call for NASA to get their information releases organized), but it has the info:
http://technology.jpl.nasa.gov/spotlights/index.cfm?page=spotlight_detail&ItemId=47
MER Battery Characteristics:
16 Li ion cells of 10 Ah
Two parallel strings of 8 cells each.
Energy: 600 Wh
Voltage : 32 -24 V
Capacity: 20 Ah at RT
Operating Temp Range: -20 C to 30 C
Cycle Life: 1000 cycles
Calendar Life: 5 Years

01101001
2004-Nov-13, 06:16 PM
http://technology.jpl.nasa.gov/spotlights/index.cfm?page=spotlight_detail&ItemId=47
Cool. Thanks.

I know it would be quite a blow, but what percentage of capability would a rover have after complete battery failure, given that its solar cells are still functioning?

Could it still wake up when the sun was high enough, receive commands, move a little ways, take some measurements, and transmit the results, before the sun was too low?

Wolverine
2004-Nov-13, 07:33 PM
Thanks, slinted! 8)

ToSeek
2004-Nov-15, 03:07 PM
http://technology.jpl.nasa.gov/spotlights/index.cfm?page=spotlight_detail&ItemId=47
Cool. Thanks.

I know it would be quite a blow, but what percentage of capability would a rover have after complete battery failure, given that its solar cells are still functioning?

Could it still wake up when the sun was high enough, receive commands, move a little ways, take some measurements, and transmit the results, before the sun was too low?

I would think so, though the programming would likely revert to what's in permanent memory, rather than what's on RAM. That might require some workarounds unless the permanent memory is on EEPROMs, which can be reprogrammed if need be.

01101001
2004-Nov-15, 07:00 PM
I would think so, though the programming would likely revert to what's in permanent memory, rather than what's on RAM. That might require some workarounds unless the permanent memory is on EEPROMs, which can be reprogrammed if need be.
I see, from articles about Spirit's January filesystem problem, 3 types of memory, the (fast) volatile RAM they probably use to execute from and temporary storage, nonvolatile flash they use for more permanent storage (similar to hard disk is use) mostly for data files, and nonvolatile EEPROM for holding the software image. It looks like they lose the contents of RAM every night.

They survived the temporary flash failure (which more fairly seems to have been a file-managment software problem), and subsequent clearing/reformatting of the flash. They also updated the flight software after that, I presume in EEPROM, to handle that sort of flash failure more gracefully.

Come to think of it, Opportunity's heater-switch problem has had them using a deep sleep over nights where they take the batteries off the main power bus, as I recall, requiring power from the solar panels to enable and trigger wake-up. Maybe that's been good practice for when the batteries are finally unavailable 24-solhours (whatever they call them) per sol.

I think they will still be able to get a little work done if the batteries fail.

tlbs101
2004-Nov-15, 10:58 PM
Consider that that batteries on the some of the GPS satellites have been cycling for well over a decade. Several comm. satellites have been up for years, now (although they use their batteries less often).

I don't know if the batteries used on the rovers are the same as those used in long-lived satellites, but I'm sure they are of the same proven reliability class.

ToSeek
2004-Dec-29, 06:07 PM
From Slashdot (http://science.slashdot.org/comments.pl?sid=134247&cid=11206524):


I was at a presentation by one of the members of the rover science teams six weeks ago.

If there are no surprises, he was talking about the rovers possibly lasting till June or July. By that time, he was suggesting that the rover's batteries would no longer be able to hold enough charge to keep the things operating.

01101001
2004-Dec-29, 06:52 PM
From Slashdot (http://science.slashdot.org/comments.pl?sid=134247&cid=11206524):


[...] he was talking about the rovers possibly lasting till June or July. By that time, he was suggesting that the rover's batteries would no longer be able to hold enough charge to keep the things operating.
Odd, given given this MER Battery Technology Spotlight item (http://technology.jpl.nasa.gov/spotlights/index.cfm?page=spotlight_detail&ItemId=47).


MER Battery Characteristics:
16 Li ion cells of 10 Ah
Two parallel strings of 8 cells each.
Energy: 600 Wh
Voltage : 32 -24 V
Capacity: 20 Ah at RT
Operating Temp Range: -20 C to 30 C
Cycle Life: 1000 cycles
Calendar Life: 5 Years
I wonder if they have new experimental data that contradicts these specs. Or, did a lot of their life get used up in pre-launch and cruise?

Bamf
2004-Dec-29, 07:06 PM
From Slashdot (http://science.slashdot.org/comments.pl?sid=134247&cid=11206524):


[...] he was talking about the rovers possibly lasting till June or July. By that time, he was suggesting that the rover's batteries would no longer be able to hold enough charge to keep the things operating.
Odd, given given this MER Battery Technology Spotlight item (http://technology.jpl.nasa.gov/spotlights/index.cfm?page=spotlight_detail&ItemId=47).


MER Battery Characteristics:
16 Li ion cells of 10 Ah
Two parallel strings of 8 cells each.
Energy: 600 Wh
Voltage : 32 -24 V
Capacity: 20 Ah at RT
Operating Temp Range: -20 C to 30 C
Cycle Life: 1000 cycles
Calendar Life: 5 Years
I wonder if they have new experimental data that contradicts these specs. Or, did a lot of their life get used up in pre-launch and cruise?

I think when the batteries finally die, they'll create an open circuit, rendering the solar panels (and all the rest of the electronics) useless.

Also, the (expected) cycle life number probably doesn't take into account the 90C temperate swings the rovers get every day (-60C at night, +30C in the daywith all the electronics running)

frogesque
2004-Dec-29, 07:26 PM
The whole kit was only designed with a 90 sol lifespan; that we've got this far is a tribute to the engineering that went into those two little critters. Push, pull, coax, coerce, pray to your God or gods if you have to but they have surpassed all expectations and will continue to do so for a bit yet.

Probably 5 years is optimistic, another 3 months pessimistic. Without specialized knowlege I just have a gut feeling that they are about mid life and thankfully not having a crisis over it :lol:

Doodler
2004-Dec-29, 07:28 PM
From Slashdot (http://science.slashdot.org/comments.pl?sid=134247&cid=11206524):


[...] he was talking about the rovers possibly lasting till June or July. By that time, he was suggesting that the rover's batteries would no longer be able to hold enough charge to keep the things operating.
Odd, given given this MER Battery Technology Spotlight item (http://technology.jpl.nasa.gov/spotlights/index.cfm?page=spotlight_detail&ItemId=47).


MER Battery Characteristics:
16 Li ion cells of 10 Ah
Two parallel strings of 8 cells each.
Energy: 600 Wh
Voltage : 32 -24 V
Capacity: 20 Ah at RT
Operating Temp Range: -20 C to 30 C
Cycle Life: 1000 cycles
Calendar Life: 5 Years
I wonder if they have new experimental data that contradicts these specs. Or, did a lot of their life get used up in pre-launch and cruise?

I think when the batteries finally die, they'll create an open circuit, rendering the solar panels (and all the rest of the electronics) useless.

Also, the (expected) cycle life number probably doesn't take into account the 90C temperate swings the rovers get every day (-60C at night, +30C in the daywith all the electronics running)

Actually, you probably tapped it right there. The operating range of the battery lists -20C as the low. I'll bet even with the warmers running, they're still getting a blast or two that's causing greater wear.

I'm also certain that they designed the rovers with the intent that they would have 90 sols of hardcore 100% operational capacity, with any program extentions operating under the impression that the hardware would be undergoing steady performance decay. Short of a major breakdown of the equipment, they had to know going in, that if they got through the landing in good shape, they'd have a lot of extra innings to play with them after the main mission was done.