Why is Mars rovers lifespan is only 90 days ?

Hello ,

Why is Mars rovers lifespan is only 90 days ?

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

Thanks Dan

"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.

Doc

"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

Bruce Sterling Woodcock wrote:


"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.

Why wouldn't they put a bursh on one, and an electrostatic
cleaner on the other and see which one works the best? After 90 days, and
too much dust has collected on the solar cells, the vehicle is trash
because they are worried about scraching the solar panels? Doesn't quite
make sense to me.


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.

I thought they were having trouble with too much heat (too much
insulation). I would have thought that even with badly degrade batteries,
as long as they were good enough to keep the insides warm during the night,
they could still operate on solar cells alone, during the day, when the
rover can see and communicate with earth. That is if the solar cells aren't
dirty.



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.

This seems like the more likely reason, planned obsolescence because there
aren't enough resources to collect the data, or so they can reduce the
supporting work force.

Craig Fink

In message t, Craig
Fink writes
Bruce Sterling Woodcock wrote:

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.

This seems like the more likely reason, planned obsolescence because there
aren't enough resources to collect the data, or so they can reduce the
supporting work force.

That's always seemed remarkably poor economics to me, and fortunately I
can't think of many examples.
Spending $500 million to a billion on development, launch, and primary
mission and then refusing to spend another million for a year's data
just doesn't make sense. Much more sensible to run it into the ground,
past any reasonable extended mission, and even then do something
interesting, like Magellan testing aerobraking.
"Die with music" as the Russians apparently say.
--
Rabbit arithmetic - 1 plus 1 equals 10
Remove spam and invalid from address to reply.

Jonathan Silverlight
wrote:

Craig Fink writes
Bruce Sterling Woodcock wrote:

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.

This seems like the more likely reason, planned obsolescence because there
aren't enough resources to collect the data, or so they can reduce the
supporting work force.

That's always seemed remarkably poor economics to me, and fortunately I
can't think of many examples.
Spending $500 million to a billion on development, launch, and primary
mission and then refusing to spend another million for a year's data
just doesn't make sense. Much more sensible to run it into the ground,
past any reasonable extended mission, and even then do something
interesting, like Magellan testing aerobraking.
"Die with music" as the Russians apparently say.

The data needs to be processed after it is copied to tape on the Earth.
So much data comes down from a mission, that is the reason why most of
the data from the Voyagers and Pioneers 10 and 11, has never been
analyzed, because of the amount of trained people needed to analyze the
data.

Given the advances in hardware and software, many times more data is
produced by today's deep space missions.

I thought they were having trouble with too much heat (too much
insulation).

That's a temporary issue while the rover is still on its platform.

The real problem is not temperature as such, it is temperature changes.
One of the recent press images has the temperature swings between day and
night - it's a regular seventy-degree (Celsius) jo-jo. Insulation and
heaters dampen that out somewhat, but at some point in time a crucial
solder joint will break, and there goes your probe.

Jan

Jan C. Vorbrüggen wrote:

I thought they were having trouble with too much heat (too much
insulation).

That's a temporary issue while the rover is still on its platform.

True, it'll be interesting to see if it is temporary or better than they
expected when they get off the platform.


The real problem is not temperature as such, it is temperature changes.
One of the recent press images has the temperature swings between day and
night - it's a regular seventy-degree (Celsius) jo-jo. Insulation and
heaters dampen that out somewhat, but at some point in time a crucial
solder joint will break, and there goes your probe.


It would be interesting to see the temperature swings inside the rover.
Maybe they'll put it on their web site sometime.

Dampen, or ?eliminate? the temperature swings in the main electronic bay.

If the insulation is performing better than expected, this could possibly
reduce the duty cycle of the batteries. Battery life time is dependant on
how they are used. A reduction in duty cycle might give them more cycles.

Also, I found the high resolution pictures of the landing site interesting.
All the dust devil trails, many of which look like they start at surface
features like craters that disturb the wind. Maybe dust won't settle on the
solar cell because the landing site is a high wind area.

Craig Fink

On Sat, 10 Jan 2004 13:08:35 GMT, "Bruce Sterling Woodcock"
wrote:

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.

OK, I'm curious. When was the last time we had a "radical environmentalist
in the White House"? Teddy Roosevelt? Did he oppose the use of RTGs?

OK, I'm sure you meant Clinton, but his environmental record wasn't all
that great. Not exactly a world leader on the issue, let alone "radical".
Remember the environmental objections to NAFTA? Did he care?

God, we are so not ready to leave the Earth and start colonizing space...

Dale

Dale wrote:

"Bruce Sterling Woodcock" wrote:

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.

OK, I'm curious. When was the last time we had a "radical environmentalist
in the White House"? Teddy Roosevelt? Did he oppose the use of RTGs?

OK, I'm sure you meant Clinton, but his environmental record wasn't all
that great. Not exactly a world leader on the issue, let alone "radical".
Remember the environmental objections to NAFTA? Did he care?

He may have been referring to Algore.