Pluto Flyby

On Tue, 31 Aug 2004 23:27:21 -0700, Alain Fournier
wrote:

Eric Gisse wrote:
On Tue, 31 Aug 2004 10:38:27 +0000 (UTC), Sander Vesik
wrote:


In sci.space.policy Stefan Dobrev wrote:

(Henry Spencer) wrote in message ...

In article ,
Keith F. Lynch wrote:

What will happen to Cassini when its mission is over?

...

As I've noted before, when the time comes that on-board resources are
running low and the beancounters' patience is exhausted, there will be
great pressure to end the mission in some spectacular, definitive way that
gets some good science return while positively killing the spacecraft.

What about getting into orbit that frequently crosses the rings?
Close-ups of the rings would be spectacular. And we might get lucky to
get a couple of crossings before it finally hits something.

Why contaminatethe rings with manmade grabage?


...because it would be useful. What is the ring anyway, other than a
lot of junk?

Aren't those rings made out of all the lost airline baggage?

Alain Fournier

Who knows?!

Taking Cassini through the rings sounds like an even better idea now!

In article ,
Keith F. Lynch wrote:
... the bulk of the decline in power output is not from the decay of
the Pu-238 -- it has a half-life of nearly a century -- but from the
accumulation of radiation damage in the semiconductor thermoelectric
elements.

Isn't the radiation entirely alpha particles, which are easy to block?

No, unfortunately there is some gamma radiation as well -- alpha decay
rarely has the decency to decay to exactly the ground state of the
resulting nucleus, and the extra energy comes out as gammas -- plus
minor odds and ends from secondary processes.

It's not just for thermal reasons that spacecraft designers try to put the
RTGs as far from the electronics and instruments as possible -- out on
booms, or in the case of Cassini, down at the bottom of the propulsion
module. And even so, some instruments see an elevated level of background
noise because of them.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

In sci.space.policy Paul Blay wrote:
"Sander Vesik" wrote ...
In sci.space.policy Stefan Dobrev wrote:
What about getting into orbit that frequently crosses the rings?
Close-ups of the rings would be spectacular. And we might get lucky to
get a couple of crossings before it finally hits something.

Why contaminate the rings with manmade grabage?

Do the maths.

According to my WAG "drop in the ocean" would be overstating the matter.
It isn't as if there's the potential of affecting local lifeforms.

dunno. if it gout grounded up in the process, it might affect the
meallicity of some ringlet. If it really got dispersed over all of
the rings tehn sure, but that is not that likely.

--
Sander

+++ Out of cheese error +++

In sci.space.policy Eric Gisse wrote:
On Tue, 31 Aug 2004 10:38:27 +0000 (UTC), Sander Vesik
wrote:

In sci.space.policy Stefan Dobrev wrote:
(Henry Spencer) wrote in message ...
In article ,
Keith F. Lynch wrote:
What will happen to Cassini when its mission is over?
...
As I've noted before, when the time comes that on-board resources are
running low and the beancounters' patience is exhausted, there will be
great pressure to end the mission in some spectacular, definitive way that
gets some good science return while positively killing the spacecraft.

What about getting into orbit that frequently crosses the rings?
Close-ups of the rings would be spectacular. And we might get lucky to
get a couple of crossings before it finally hits something.

Why contaminatethe rings with manmade grabage?

...because it would be useful. What is the ring anyway, other than a
lot of junk?


I'm not sure i'ddescrie the contents as junk

--
Sander

+++ Out of cheese error +++

Sander Vesik wrote in message ...
In sci.space.policy Stefan Dobrev wrote:
(Henry Spencer) wrote in message ...
In article ,
Keith F. Lynch wrote:
What will happen to Cassini when its mission is over?
...
As I've noted before, when the time comes that on-board resources are
running low and the beancounters' patience is exhausted, there will be
great pressure to end the mission in some spectacular, definitive way that
gets some good science return while positively killing the spacecraft.

What about getting into orbit that frequently crosses the rings?
Close-ups of the rings would be spectacular. And we might get lucky to
get a couple of crossings before it finally hits something.

Why contaminatethe rings with manmade grabage?
How is that worse then contaminating Titan/Saturn/whatever you crash
it into?

If I had to crash it, the ring crash/passages looks to me to give the
most spectacular, if not the most scientificantly interesting return.

Stefan

P.S. Spectacular in terms of images/data returned before crash, not in
terms of 'spectacular damage to the ring system'. ;-)

In article ,
(Steve Harris ) writes:
But I think that a better solution involves a simple heat pipe, for
getting heat from the RTG to the core of the [Titan] lander.

Heat pipes are standard spacecraft hardware. I'm sure they will be
considered when the time comes.

If you rig up your RTG so it pumps enough heat to the Titan lander
core by conduction to make up for convection/advection away by that
thick cold atmosphere, then the same conductive input will fry the
thing in vacuum, on the way to Titan. So obviously the heat input has
to be switched on, about the time the crawler lands. Of course this is
what will make engineers first think about electical heating.

More likely the engineers will think about how to use radiative
cooling during transit or about a mechanical heat switch, possibly
one activated by temperature. Or the heat pipe itself can be made
temperature dependent, with poor conduction at high temperature.
Your idea of adding the working fluid to the heat pipe doesn't look
like an attractive approach, at least at first glance. Aside from
moving parts and possible failures thereof, you need a place to store
that fluid before it goes into the heat pipe, and containers are
usually heavy.

[resistive heating]
We might consider that SOME of it could potentially be replacable,
just by capsules of Pu-238,

Yes, these have been used on Mars landers; perhaps elsewhere. I
wouldn't be surprised to see them on a Titan lander. Of course it
will be quite some time before anybody starts detailed design. By
then there may be even better ideas.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
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