From: henry@spsystems.net
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. | henry@spsystems.net
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