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Huygens' Titan Descent



 
 
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  #11  
Old January 15th 05, 02:30 AM
Scott M. Kozel
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"Glenn Mulno" wrote:

"richard schumacher" wrote:

I am a bit puzzled why they only made the probe last the few short
hours after it detached from cassini. They could of built a better
battery when Voyager I is like 28 year and still going. I know it is
like -300F and mechanical things won't operate long in that harsh
environment. Assuming the probe could survive the environment it would
of been nice to be able to tap it for everything possible.


The issue is how long the orbiter is in range to relay data from Huygens
to Earth. It's only a few hours, so a longer-life battery for Huygens
would have been pointless.


If that were the "only" reason then I would disagree. Cassini will be
passing by Titan again in a few weeks. I would think they could have held
data and then blasted it at the satellite each time it passed.

However, as I understand it that is not really why they kept the life to
only a few hours. I think it had more to do with just getting it down
safely, the weight of the probe on Cassini, cost, and probably just the
general expectation that conditions were not favorable to the life of the
unit being long.


The Voyagers and Cassini itself receive electrical power from a
Radioisotope Thermoelectric Generator (RTG). An RTG can provide
electrical power to a robust suite of spacecraft systems for 20 years or
more, but an RTG would have been way too heavy to install on the Huygens
spacecraft.

The Mars lander spacecrafts utilize solar cell panels to create
electrical power which is stored in rechargable batteries, and Mars has
very little cloud cover that would interfere with that system, and Mars'
night is similar in length to Earth's; so that system is workable on
Mars.

Titan has a dense, hazy atmosphere, and even in the clear, the Saturn
system is way too far from the Sun, making a solar power system to be
infeasible (the solar panel system would have to be gargantuan).

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.

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  #12  
Old January 15th 05, 04:29 AM
richard schumacher
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In article ,
"Glenn Mulno" wrote:

"richard schumacher" wrote in message news:no-spam-

I am a bit puzzled why they only made the probe last the few short
hours after it detached from cassini. They could of built a better
battery when Voyager I is like 28 year and still going. I know it is
like -300F and mechanical things won't operate long in that harsh
environment. Assuming the probe could survive the environment it would
of been nice to be able to tap it for everything possible.



The issue is how long the orbiter is in range to relay data from Huygens
to Earth. It's only a few hours, so a longer-life battery for Huygens
would have been pointless.


If that were the "only" reason then I would disagree. Cassini will be
passing by Titan again in a few weeks. I would think they could have held
data and then blasted it at the satellite each time it passed.

However, as I understand it that is not really why they kept the life to
only a few hours. I think it had more to do with just getting it down
safely, the weight of the probe on Cassini, cost, and probably just the
general expectation that conditions were not favorable to the life of the
unit being long.


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.
  #13  
Old January 15th 05, 05:36 AM
Henry Spencer
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In article ,
Glenn Mulno wrote:
However, as I understand it that is not really why they kept the life to
only a few hours. I think it had more to do with just getting it down
safely, the weight of the probe on Cassini, cost, and probably just the
general expectation that conditions were not favorable to the life of the
unit being long.


A long surface life would have required, at the very least, an RTG, which
would have run up the cost, mass, and various other complications quite a
bit. Moreover, Huygens was planned and sold as primarily an *atmosphere*
mission -- even the camera (which is a US contribution, incidentally) was
optimized as much for cloud imaging and sunlight measurements as for
surface pictures.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |
  #14  
Old January 15th 05, 05:45 AM
furtig
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I have another question. The one photo I have seen from the surface
(unprocessed?) seems to have plenty of light. I found this surprising and
am assuming this was considered in the planning stage and the photo system
is extra sensitive. (?) Any comments on the data size of the images.

--
Detective Tom Polhaus: " Heavy. What
is it?"
Sam Spade: "The, uh, stuff that dreams
are made of."
"Glenn Mulno" wrote in message
...
"richard schumacher" wrote in message news:no-spam-

I am a bit puzzled why they only made the probe last the few short
hours after it detached from cassini. They could of built a better
battery when Voyager I is like 28 year and still going. I know it is
like -300F and mechanical things won't operate long in that harsh
environment. Assuming the probe could survive the environment it would
of been nice to be able to tap it for everything possible.



The issue is how long the orbiter is in range to relay data from Huygens
to Earth. It's only a few hours, so a longer-life battery for Huygens
would have been pointless.


If that were the "only" reason then I would disagree. Cassini will be
passing by Titan again in a few weeks. I would think they could have held
data and then blasted it at the satellite each time it passed.

However, as I understand it that is not really why they kept the life to
only a few hours. I think it had more to do with just getting it down
safely, the weight of the probe on Cassini, cost, and probably just the
general expectation that conditions were not favorable to the life of the
unit being long.

Glenn




  #15  
Old January 15th 05, 08:19 AM
muldar
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Is this the same Sen. Robert C Byrd that opposed Martin Luther King
and asked J Edgar Hoover to put him in jail and throw away the key?
Strange times we live in.



Victor wrote:

http://www.space.com/missionlaunches...mm_050114.html

"For those at work who don't have streaming video available........."

LIVE coverage of Huygens' Titan Descent

6:05 a.m. EST:

Space News Writer Peter de Selding reports live from Huygens mission
control:

DARMSTADT, Germany-- A network of powerful ground telescopes has picked
up the signal of Europe's Huygens descent probe 1.2 billion kilometers
away, confirming that the probe is alive as it begins its descent into
the thick atmosphere of Saturn's largest moon, Titan.

European Space Agency officials at Huygens mission control here said the
signal -- no more than the equivalent of a telephone dial tone -- was
detected by a network of 18 telescopes deployed to listen for a signal
coming directly from Huygens.

The biggest of these antennas is the 100-meter-diameter Robert C.

Byrd Green Bank Telescope, operated by the National Radio Astronomy
Observatory in Green Bank, West Virginia.

The signal did not confirm anything beyond the fact that Huygens is
alive. But it was enough to cause a burst of applause here when
announced at 10:35 a.m. GMT (5;35 a.m. EST) today. 'There is a lot of
emotion in this room," said Jean-Pierre Lebreton, Huygens program
manager at ESA. "It's great news."

Leonid Gurvitz, mission manager for Huygens' communications with the
ground telescope network, said 18 telescopes including Green Bank had
been trained to pick up a signal and that it is the network itself, more
than any single telescope, that received the Huygens signal.

NASA's Cassini satellite, which carried Huygens to Saturn orbit, has
been moved into position to receive Huygens mission data during the
probe's 2.5-hour descent into Huygens' thick atmosphere.

A more-complete assessment of whether Huygens' parachutes have deployed
and its heat shield jettisoned to permit the start of observations is
expected to be received by science teams from Cassini around 11:20 a.m.
EST (1620 GMT) today.

6:00 a.m. EST: If it switched on as planned, a microphone instrument
aboard Huygens may allow researchers to recreate the sound of the
probe's descent as it plunged through Titan’s atmosphere, ESA mission
scientists said. The instrument may also record thunder, and Huygens
scientists hope to have at least initial data to present within 24 hours.

5:50 a.m. EST: Cautious ESA commentators stress the Huygens signal is
just a carrier tone. There is no confirmation that the six science
instruments aboard the probe are working as planned.

"It looks like we heard the baby crying," said Huygens mission manager
Jean-Pierre Lebreton from the floor of ESOC mission control. "But
clearly it tells us the probe is alive, the entry has been successful
and we are under parachutes."

5:35 a.m. EST: Huygens speaks from Titan! ESA has confirmed that the
Green Bank Telescope successfully detected a Huygens signal tone. The
signal, a confirmation that Huygen's transmitter is at least
functioning, and activated on time at about 5:18 a.m. EST.

About 600 people are at ESOC mission control for Huygens Titan descent
and some engineers crowded around computer monitors when the signal
confirmation was announced.

"It's a tremendously exciting moment," said John Dodsworth, Huygens
ground manager at ESOC.


  #16  
Old January 15th 05, 08:21 AM
muldar
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why dont the photo links work at this page?


Impact9 wrote:

This is pretty exciting stuff! I hope and pray Huygens lands safely and
this mission is a success. I'm watching the live feed from NASA TV and
refreshing a good number of websites monitoring the mission. Here's a
real good misson monitor link:
http://www.planetary.org/saturn/huygens_mission.html

-DH


  #17  
Old January 15th 05, 09:29 AM
muldar
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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.



Henry Spencer wrote:

In article ,
Glenn Mulno wrote:
However, as I understand it that is not really why they kept the life to
only a few hours. I think it had more to do with just getting it down
safely, the weight of the probe on Cassini, cost, and probably just the
general expectation that conditions were not favorable to the life of the
unit being long.


A long surface life would have required, at the very least, an RTG, which
would have run up the cost, mass, and various other complications quite a
bit. Moreover, Huygens was planned and sold as primarily an *atmosphere*
mission -- even the camera (which is a US contribution, incidentally) was
optimized as much for cloud imaging and sunlight measurements as for
surface pictures.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |


  #18  
Old January 15th 05, 11:36 PM
Al Dykes
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In article ,
muldar wrote:
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.


That's what you get for getting your news from TV :-)

NPR and BBC radio haev given it decent coverage so far, and it would
supise me if they don't have more on NPR's Sunday AM hour.
--

a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.
  #19  
Old January 16th 05, 12:19 AM
Tim Killian
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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.


  #20  
Old January 16th 05, 02:27 AM
Henry Spencer
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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.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |
 




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