Huygens' Titan Descent

"muldar" skrev i en meddelelse
...

it still is one HUGE success. Monumental, really. Just too bad the major
news networks didnt even mention it or show a photo tonight.
This sorry state of socially irresponsible affairs in the USA must end
soon.

You think this sorry state of affairs is confined to the USA? Since I
don't have cable or sat dish, I can take only the two TV channels that are
carried on airwave here in Denmark. One is the old national TV channel that
was the monopoly station in the old days. On this channel there was heavy
coverage on the new opera house that was inaugurated in Copenhagen on the
same day as the Huygens landing, both in the regular news and as a special,
hours-long program. There was nothing about the Huygens landing. The other
channel did have something, but not much. And also heavy coverage of the
new opera house.
Thank heavens for the Web. :-) (I'll check it later when there isn't so
much run on the relevant sites.)

Jon Lennart Beck.

richard schumacher wrote:

A lifetime of weeks would have required nuclear heaters at least,
and perhaps a nuclear thermal electric source as well. That means
more mass, probably more then anyone wanted to pay to send.
..
But Huygens had already 35 nuclear heater units onboard...

wrote:
richard schumacher wrote:


A lifetime of weeks would have required nuclear heaters at least,
and perhaps a nuclear thermal electric source as well. That means
more mass, probably more then anyone wanted to pay to send.

.
But Huygens had already 35 nuclear heater units onboard...


I believe you may be mistaken. On the other hand, you might just be wrong.

Uncle Bob

Probably both, but mostly engineering.

RTGs generate a LOT of heat, witch would be difficult to deal with
inside the closed reentry shell of that small probe.

For instance, an RTG generating 200W eletric power generates 2000W heat
power.

It's also heavy, generates radiation, witch is bad for the
instruments... etc.

Tim Killian wrote:
Was the lack of an RTG on Huygens a political decision, or a true
engineering limitation?



Scott M. Kozel wrote:



The Huygens spacecraft could not utilize an RTG or solar power, so it
was limited to un-rechargable batteries, and given the number of
instruments on board, battery capacity was limited to a matter of hours.

Uncle Bob wrote:

wrote:

But Huygens had already 35 nuclear heater units onboard...

I believe you may be mistaken. On the other hand, you might just be
wrong.

Uncle Bob

From
http://saturn.jpl.nasa.gov/multimedi...y20041221b.pdf

"To ensure that none of the equipment falls below its storage-
temperature limit the probe carries 35 Radioisotope Heater Units,
each generating 1 W."

Read it and weep.

In article om,
Uncle Bob wrote:

wrote:

A lifetime of weeks would have required nuclear heaters at least,
and perhaps a nuclear thermal electric source as well. That means
more mass, probably more then anyone wanted to pay to send.

.
But Huygens had already 35 nuclear heater units onboard...


I believe you may be mistaken. On the other hand, you might just be wrong.

No, my mistake, he's quite correct. 35 units each generating 1W. See
http://saturn.jpl.nasa.gov/multimedi...by20041221.pdf
But an RTG for communication power would have been much more massive.

Others have pointed out that, with no good idea of Titan's surface
during design, Huygens was intended as an atmosphere probe. Any surface
science return was pure gravy.

A lifetime of weeks would have required nuclear heaters at least, and
perhaps a nuclear thermal electric source as well. That means more
mass, probably more then anyone wanted to pay to send.

not to forget that try landing heavier probe somewhere quite unknown
would probably lead to assured failure

it s good to get back something !

In article , says...
In article ,
Tim Killian wrote:
Was the lack of an RTG on Huygens a political decision, or a true
engineering limitation?

Yes. :-) Within the priorities, mass limits, and cost constraints of the
project, there was definitely no engineering possibility of an RTG. (The
"priorities" part is that Huygens was mainly an atmosphere mission with
only a secondary role as a lander, as witness its primary mission being
153 minutes -- 150 minutes of descent, 3 minutes on the surface.)

The priorities, mass limits, and cost constraints were ultimately mostly
political decisions at one level or another. I don't believe there was an
explicit political "no RTG" decision -- Huygens did have a whole bunch of
RHUs (plutonium heater capsules) -- but the mission as defined couldn't
really afford one (in dollars, mass, or engineering complications) and
didn't really need one.

So an RTG wasn't practical for several reasons on this mission; however,
it's been reported that the batteries were rated for 7 hours. If that's
true, what if they had included a programmable timer in the probe? Just
before release the timer could have been programmed with the expected
times when Cassini would be in a position to again receive data.
Between data windows the probe would mostly power down, just running low
current instruments like temperature and air pressure, recording data,
conserving batteries, and keeping warm with it's RHUs. If need be,
Huygens could have powered down completely between passes, but only
getting current data during a pass would be much less interesting. When
Cassini was again in the sky Huygens would again wake up and transmit
the collected data and take a new snapshot. They might have gotten 4 or
5 more passes out of the thing.

Of course for any of that to work several other things would have to be
true, not the least of which is that the RHUs would be enough to keep
the inside of the probe warm during weeks of near or complete power down
on that cold cold moon.

Marc

In article ,
Marc 182 wrote:
Of course for any of that to work several other things would have to be
true, not the least of which is that the RHUs would be enough to keep
the inside of the probe warm during weeks of near or complete power down
on that cold cold moon.

Exactly. Unfortunately, there was also a requirement that the RHUs not
roast the inside of the probe before launch and while in space, including
quite a while spent relatively near the Sun. So in practice, they
couldn't do the whole job, and a noticeable fraction of Huygens's power
consumption was for heaters.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

In article , says...
In article ,
Marc 182 wrote:
Of course for any of that to work several other things would have to be
true, not the least of which is that the RHUs would be enough to keep
the inside of the probe warm during weeks of near or complete power down
on that cold cold moon.

Exactly. Unfortunately, there was also a requirement that the RHUs not
roast the inside of the probe before launch and while in space, including
quite a while spent relatively near the Sun. So in practice, they
couldn't do the whole job, and a noticeable fraction of Huygens's power
consumption was for heaters.

I checked the public Huygens engineering webpage. It had about 35 watts
of RHU heat available. In a foam-wrapped package, essentially an ice
chest with a small heater in it, it seems like it could have made it
through. But then again, that bitterly cold and dense atmosphere would
be so much better at conducting/convecting heat away than space is that
I can see at least upgraded insulation being required. You might keep
the weight the same with super materials like areogels, but not the
cost.

Still, the instruments I was thinking of continuing to run don't need
much heat, if any, atmospheric pressure and temperature. You definitely
don't want to heat your temp sensor! Now that I think about it, you'd
want to run your microphone too, you can hear rain. Mix data from those
with remote optical sensing of clouds from Cassini and ground based
telescopes and you've got a pretty good weather station going. Then
you've just got to keep your radio, computer, electronics, and batteries
warm, which I suspect the RHUs were positioned to do anyway.

So long as I'm dreaming here, and discarding everything else I've said,
it would have been nice if they had just programmed the gas
chromatograph to make one more run starting at the end of the nominal
mission, 180 seconds after landing. That hot spacecraft ("hot" being a
very relative term here) was probably boiling all kinds of interesting
stuff off of the surface and a GC is great at unambiguous identification
of organics.

But, of course, they never expected it to live for any length of time on
the surface... or did they? I wonder what the thinking was when they
slipped in the big batteries. Anyway, I'm glad they did. ESA did an
awesome job and I'm thrilled!

Marc