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#11
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MERs: what limits their lifetime on Mars surface?
In article ,
Brian Thorn wrote: My main complaint is that they are reportedly "testing the turn to drive off in another direction." Now, they going to rehearse the maneuver and not drive off until Thursday (Sol 12, I think). Why wasn't this tested before they got to Mars? Quite likely it was... but conditions are different there, and the price for screwing things up is severe, so they're being careful. -- MOST launched 30 June; science observations running | Henry Spencer since Oct; first surprises seen; papers pending. | |
#13
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MERs: what limits their lifetime on Mars surface?
Assuming all systems check out o.k. and the rover drives off into the
Martian sunset towards the distant hills in one direction, what is the maximum possible range we can expect it to cover in the remaining 80 or so Sols of primary mission left? I have faint memory, that it was something like 10km. But they are there to do science, so they try to spend all their time drilling rocks instead of driving to sunset. Maybe if there were something really extraordinary (like Arnold Schwarznegger) in few km distance they might go for it. |
#14
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MERs: what limits their lifetime on Mars surface?
"Henry Spencer" wrote in message ... In article , Brian Thorn wrote: My main complaint is that they are reportedly "testing the turn to drive off in another direction." Now, they going to rehearse the maneuver and not drive off until Thursday (Sol 12, I think). Why wasn't this tested before they got to Mars? Quite likely it was... but conditions are different there, and the price for screwing things up is severe, so they're being careful. Spencer Considering the cost of the mission it would seem sensible to have equipped the MER with a SRIMECH or to design it with a self-righting capability. Those wheels look awfully small in OD to me. Horatio. |
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MERs: what limits their lifetime on Mars surface?
In message - Brian Thorn
Fri, 09 Jan 2004 21:18:53 -0600 writes: On Fri, 9 Jan 2004 00:24:19, om (Arie Kazachin) wrote: Reading various bits of info about Mars rovers on various sites I haven't noticed (or missed?) any info about their life expectancy on the Mars surface. 90 days. http://marsrovers.jpl.nasa.gov/mission/tl_surface.html "Eventual End of Mission Toward the end of the surface phase for both missions, both power and telecom capabilities will be decreasing, as the Earth and the Sun Except for decreased bitrate, why increased distance should be a telecom show-stopper? If Voyagers can still be communicated, isn't the maximal distance from Mars well within the capabilities of the DSN? become more distant from Mars, dust falls on the solar panels, the batteries lose capacity, and the Sun moves further North past the landing site latitude. Eventually, somewhere near Sol 91 it is expected that the rover will be unable to store up enough thermal or battery energy to prevent its components´ overnight temperatures from falling below flight allowable levels. That will sooner or later result in failure of one or more of those components, silencing the rover forever." Taking a step forward and thinking about future landers/rovers, I'm wondering what can be designed differently (at sane price) in order to make a rover lifetime MUCH longer: 1) Solar panels: will making them able to rotate slightly over 90 deg. and vibrate a little be enough for the accumulated dust to fall of? Or maybe to have some blower directed at the panels to blow the dust away? Apart from dust, what other causes (like radiation, for example) will cause gradual degradation in the power output? At what rate? 2) From what I understand, current MERs must retain power at all times, which means - when battery fails during the cold night, the MER is dead and stays this way, is that correct? I wonder what it would take for the rover to be able to "self power up" when the solar panels start producing enough power in the Martian morning? What is the minimal temperature during Martian night? I understand it's well below the "military standard" semiconductors storage temp. of -65 C (couldn't find space-rated range), how difficult would it be to keep the electronics within storage temp. range? How long will raioactive heaters last? Is it feasible to thermally isolate the electronics sufficiently for it to be warmed during the day and not get too cold before morning? Apart from the electronics, what else can be permanenly damaged by low temperature? 3) Dust accumulation in moving parts: how severe this problem is? ************************************************** **************************** * Arie Kazachin, Israel, e-mail: * ************************************************** **************************** NOTE: before replying, leave only letters in my domain-name. Sorry, SPAM trap. |
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what limits their lifetime on Mars surface?
Henry Spencer wrote:
They're called RHUs, Radioisotope Heating Units. They use Pu-238, just like RTGs although in rather smaller quantities. The one snag is that you can't turn them on and off, so you have to go easy with them to avoid overheating. Yes and no. Pioneers 10 and 11, if I recall correctly, had things like venetian blinds which opened or closed depending on temperature. I believe they used no electronics, but just bimetallic strips. Something like that ought to work even better on Mars than in vacuum. -- Keith F. Lynch - - http://keithlynch.net/ I always welcome replies to my e-mail, postings, and web pages, but unsolicited bulk e-mail (spam) is not acceptable. Please do not send me HTML, "rich text," or attachments, as all such email is discarded unread. |
#17
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MERs: what limits their lifetime on Mars surface?
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#18
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MERs: what limits their lifetime on Mars surface?
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#19
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MERs: what limits their lifetime on Mars surface?
As I Understand it, the staff at JPL and the various parts of the dep space
nework and other supporting agenecies is only paid up for running the mission for 90 days, after which somebody needs to authorize more funding to continue the missions, if the rovers are still functioning then... |
#20
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MERs: what limits their lifetime on Mars surface?
In article ,
Arie Kazachin wrote: Toward the end of the surface phase for both missions, both power and telecom capabilities will be decreasing, as the Earth and the Sun Except for decreased bitrate, why increased distance should be a telecom show-stopper? If Voyagers can still be communicated, isn't the maximal distance from Mars well within the capabilities of the DSN? It's not a "show-stopper"; they never said it was. It does reduce the bit rate. A contributing factor that they don't mention is that once their primary mission is over, they will have lower priority for DSN resources, notably the big 70m antennas, and their bit rate will fall considerably for that reason also. Taking a step forward and thinking about future landers/rovers, I'm wondering what can be designed differently (at sane price) in order to make a rover lifetime MUCH longer... Nuclear power -- RTGs -- is the biggie, so that there is ample power for electrical heating during the night. Viking Lander 1 was still going strong six years after landing, when a command error pointed its antenna at the ground and communication was lost. 1) Solar panels: will making them able to rotate slightly over 90 deg. and vibrate a little be enough for the accumulated dust to fall of? Maybe. Nobody really knows, due to lack of data on Martian dust. Fine dust can cling quite tenaciously to smooth surfaces. Or maybe to have some blower directed at the panels to blow the dust away? It's conceivable, but given the low pressure it would need quite high gas velocities. Electrostatic dust removal is probably a better choice. Apart from dust, what other causes (like radiation, for example) will cause gradual degradation in the power output? At what rate? Nothing very significant. 2) From what I understand, current MERs must retain power at all times, which means - when battery fails during the cold night, the MER is dead and stays this way, is that correct? Not quite. When the battery fails, the electronics are exposed to much more drastic temperature swings, which will probably kill them quickly. I wonder what it would take for the rover to be able to "self power up" when the solar panels start producing enough power in the Martian morning? That's not hard. Mars Pathfinder and Sojourner both could do that, and the MERs probably can too. The problem is temperature cycling, not power cycling. Mars Pathfinder went silent shortly after its battery died. What is the minimal temperature during Martian night? At Spirit's location, -90degC is a typical summertime overnight low. how difficult would it be to keep the electronics within storage temp. range? Not hard at all, if you have lots of power. Without it, very difficult. How long will raioactive heaters last? Many years, but because you can't turn them *off* during the day or when the electronics are most active, they can't do the whole job. Is it feasible to thermally isolate the electronics sufficiently for it to be warmed during the day and not get too cold before morning? Not really practical. The temperature swings are too extreme, and it's too difficult to make the details work. Apart from the electronics, what else can be permanenly damaged by low temperature? The electronics are really the main issue. 3) Dust accumulation in moving parts: how severe this problem is? On the Moon, very serious. On Mars, nobody knows. -- MOST launched 30 June; science observations running | Henry Spencer since Oct; first surprises seen; papers pending. | |
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