"drdoody" wrote in message
...

"Dan DeConinck" wrote in message
m...
Hello ,

Why is Mars rovers lifespan is only 90 days ?

Com Sats last years.
Pioneer is 20+ yrs and still talking.

Thanks Dan



I always wondered why they couldn't send a rover with a better power
source
than solar panels. Perhaps RITEG would work better and be more durable?

Of course, if NASA sent up a probe that lasted for years and not months,
they might not be able to justify sending as many probes as they do.

It's a very complex issue.

With Spirit/Opportunity (and Pathfinder), there are two
main problems... dust and the cold/hot temperatures.

If you're using solar panels, dust is going to accumulate
on them over time. Your going to get less and less power.
Some have suggested various mechanisms for removing
the dust, but they are all untested and add precious weight
to the craft when they might not work. Compressed air,
as just discussed here recently, would require high velocities
to work in thin Martian air, and of course you'd have a
limited supply. Running a compressor to compress
Martian air for use would probably consume too much
time, energy, and mass.

A simply brush or wiper might work, but then again might
just as easily scratch up your solar panels and become
clogged with dust. Perhaps more intriguing is the use of
electrostatic fields to remove most of the dust without
mechanical intervention.

So why not dump solar panels entirely and use RTGs
like we did with Viking and other space probes? Because
for a long time here anything with "nuclear" in it was bad
PR. Even Cassinni had protests recently. However, it
does seem now that without a radical environmentalist
in the White House and with changing attitudes over time,
RTGs are becoming viable again, and newer probes will
use them. However, Mars remains close enough to the
sun that the use of solar power remains quite attractive.

The bigger issue is dealing with the thermal changes and
their effect on battery performance over time. These
probes have to sit in an atmosphere and against the
surface, not sealed in a vacuum like satellites. It's not
that these problems are not solvable, but they require
a lot of mass to deal with. At some point it becomes
prohibitive, because you don't have money to send
another Viking, so you have to pick between a full
suite of science instruments that will only survive 90
days, or one camera that will last for years.

Another important issue with long-lasting probes is the
fact that we don't have the network to support them.
DSN is already overtaxed with trying to get data from
all the probes out there now, and some missions have
been ended or curtailed specifically because the data
they would return is not as important as data from
other missions.

Pioneer was still going? Sure, but almost none of the
science it returned was being received, and what was
received was mostly not processed. And FYI, Pioneer
11 stopped talking in 1995 and Pioneer 10 stopped
talking in 2002 (although we did get a faint signal last
year).

Bruce