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. |

Brian Thorn :

On Sun, 11 Jan 2004 18:10:52 GMT, (Henry Spencer)
wrote:

Someone at JPL needs to read that paragraph to the MER engineers. The
clock is ticking, folks. Get that puppy moving. No sense sending a
rover to Mars if you're too timid to drive it off the lander.

The timeline has always included a few days of checkout on the lander
before driving off. The MER engineers are fully aware that the clock is
ticking, but there's lots to do. They aren't sitting around dithering.

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?

If you watch any of the PBS shows you would know that it was tested on Earth.
What they are testing for is any damage/failures caused by the flight to
Mars or the landing.

Earl Colby Pottinger

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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.

"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.

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?


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NOTE: before replying, leave only letters in my domain-name. Sorry, SPAM trap.

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.
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In article , says...
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.

Also the lander itself is the largest obstacle anywhere in view.
Driving off of it may turn out to be the single most dangerous thing the
rover ever does.

Marc

In article ,
says...
Does JPL have any kind of 'range coverage' ambitions in mind or is it
all about geology and water search around the locale of the landing
site? My own wish would be to go for some exotic, elevated terrain
which is *different* to the Viking 1, 2 and MPF type open-field
scenes, which would be essentially repeat playbacks with no *new*
exposures in this mission.

I think it would be cool, once the primary mission is complete and if
the rovers are still capable, to do a maximum range traverse. Just pick
a direction and go at highest possible speed, only stopping to sample
stuff that looks really interesting. Maybe heading up the channel that
fed the crater lake would be the most interesting way to go.

I am very much looking forward to the next several weeks!

Marc

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...

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. |