Other spacecraft questions

As there seems to be no group for such things in this hierarchy, here goes.
Why is the Juno spacecraft seemingly tied to this specific number of orbits,
namely 33? Also why is it using Solar, I'd have thought that just using
Solar would mean that it in fact should have a very long life as it won't
run the risk of the decay of the heat producing core as nuclear powered
craft do.. yet.. which brings me onto the next question, why is the Mars
rover using a nuclear generator? I would have though ti more of a danger to
land one on Mars than have one in space at Jupiter in fact.
Where are all the usual protesters about launching such devices.
For what its worth, the method of landing Curiosity on Mars looks highly
prone to failure to me.

Brian

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In article ,
says...

As there seems to be no group for such things in this hierarchy, here goes.
Why is the Juno spacecraft seemingly tied to this specific number of orbits,
namely 33? Also why is it using Solar, I'd have thought that just using
Solar would mean that it in fact should have a very long life as it won't
run the risk of the decay of the heat producing core as nuclear powered
craft do.. yet..

There is a limited amount of the proper isotope for creating new RTG's.
I thought that was common knowledge in these groups.

which brings me onto the next question, why is the Mars
rover using a nuclear generator? I would have though ti more of a danger to
land one on Mars than have one in space at Jupiter in fact.
Where are all the usual protesters about launching such devices.
For what its worth, the method of landing Curiosity on Mars looks highly
prone to failure to me.

You're forgetting all of the news releases about the past Mars Rovers.
Many times their solar panels were coated in Mars dust, limiting their
power. Also, over the Maritain winter, there isn't enough (solar) power
to run heaters to keep many of the Mars rovers and probes alive and they
succumb to the cold of winter.

Solar is a p.i.t.a. at Mars because of the dust and the seasons
(winter).

Solar is a p.i.t.a. at Jupiter because the amount of solar power
available is much less than here at earth, which is why it needs such
fracking huge arrays in the first place. Also at Jupiter, the high
radiation environment will degrade the output of the solar panels faster
than in a typical earth orbit which is designed to minimize exposure to
radiation from earth's radiation belts.

Jeff
--
" Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry
Spencer 1/28/2011

On 8/10/2011 7:50 AM, Jeff Findley wrote:
In ,
says...
As there seems to be no group for such things in this hierarchy, here goes.
Why is the Juno spacecraft seemingly tied to this specific number of orbits,
namely 33? Also why is it using Solar, I'd have thought that just using
Solar would mean that it in fact should have a very long life as it won't
run the risk of the decay of the heat producing core as nuclear powered
craft do.. yet..
There is a limited amount of the proper isotope for creating new RTG's.
I thought that was common knowledge in these groups.

And besides that, solar cell technology has advanced to the point where
solar power is now economically and practically feasible for this sort
of mission.

I would imagine the plan to de-orbit after 33 orbits is either to
investigate what happens during entry to the Jovian atmosphere, and/or
due to limited funding to continue the mission beyond that point, but I
haven't been able to find a definitive statement on either.

For what its worth, the method of landing Curiosity on Mars looks highly
prone to failure to me.

What part of that method are you having a problem with? It's too big to
use the "bouncing airbags" method of the previous rovers.

Bob M.

In sci.space.shuttle message , Wed, 10 Aug
2011 08:12:32, Brian Gaff posted:

As there seems to be no group for such things in this hierarchy, here goes.
Why is the Juno spacecraft seemingly tied to this specific number of orbits,
namely 33? Also why is it using Solar, I'd have thought that just using
Solar would mean that it in fact should have a very long life as it won't
run the risk of the decay of the heat producing core as nuclear powered
craft do.

Jovian radiation environment would be expected to kill its brain within
not much longer than that, as it is, they're kept in a heavy Titanium
box.

The orbit round Jupiter is very elliptical and exactly timed. 15 passed
will cover the surface at 20 degree intervals, then a slight plane
change and the next 15 go half-way between. After that, it will have
completed the intended work.

It will be crashed into Jupiter to ensure that it does not, in its old
age, crash into a satellite.

Solar power is sufficient; Juno will always face the Sun, will not be in
eclipse at Jupiter, and will only briefly be in eclipse during the Earth
fly-by.

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