Huygens shortlived?

In article . com,
"dexx" wrote:

Is it true that Huygens ceased transmission less than 2 hours after
touchdown? Whilst it was a magnificent achievement to travel so far and
land perfectly, it seems a great shame that the probe was so short
lived. I'm suprised the designers didnt make it rugged enough and
powered enough to survive several days.

You need to understand the mission a little more. The probe
was designed to measure the atmosphere on Titan. The landing
part was a bonus. The probe ran on batteries. Batteries only
last so long, especially in the cold. To make the probe run
much longer, it would have required an RTG (nuclear battery).
That would have made the probe far heavier, causing all kinds
of mission compromises from launch, number of instruments,
and its chances of survival coming through the atmosphere.
Next, the probe only had so much power, so it needed the
Cassini to record the data and retransmit it back to earth.
Cassini was moving, and it was out of view of the probe
within 2 hours of the probe landing. There was no easy way
to keep Cassini in view of Titan for much longer without
totally redesigning the Saturn mission. As it is, the probe
worked great and proved the technology. There isn't too
much more the Cassini/Huygens team could have gotten without
doing a much more complex mission that would have sampled
the surface looking for life. Maybe next time.

-john-

--
================================================== ====================
John A. Weeks III 952-432-2708
Newave Communications http://www.johnweeks.com
================================================== ====================

"dexx" wrote in message
ups.com...
Is it true that Huygens ceased transmission less than 2 hours after
touchdown? Whilst it was a magnificent achievement to travel so far and
land perfectly, it seems a great shame that the probe was so short
lived. I'm suprised the designers didnt make it rugged enough and
powered enough to survive several days.

Cassini will not return to Titan for about a month
as it is in orbit round Saturn, not the moon. With
a given mass budget, you have to trade off more
batteries against losing an instrument. The optimum
design was probably to last as long as Cassini would
be above the horizon plus a little bit spare.

George

"dexx" wrote in message
ups.com...
Is it true that Huygens ceased transmission less than 2 hours after
touchdown? Whilst it was a magnificent achievement to travel so far
and
land perfectly, it seems a great shame that the probe was so short
lived. I'm suprised the designers didnt make it rugged enough and
powered enough to survive several days.


There is also the issue that transmission had to be relayed via the
Cassini spacecraft - meaning that Cassini had to be close to Titan and
also had to be above the horizon as fas as Huygen is concerned

If you have a look at the animation applet on the ESA website
http://www.esa.int/SPECIALS/Cassini-...6E2VQUD_0.html
you can see that Cassini's path isn't really favourable for that.

I reckon the 'above the horizon' condition won't be met for almost 2
weeks, by which time Cassini will be about 2 million miles from Titan.
The next Titan flyby isn't until 15th Feb.

"dexx" wrote:

Is it true that Huygens ceased transmission less
than 2 hours after touchdown? Whilst it was a
magnificent achievement to travel so far and land
perfectly, it seems a great shame that the probe
was so short lived. I'm suprised the designers
didnt make it rugged enough and powered enough to
survive several days.

Well, all that costs weight, and the probe was
designed to be an _atmosphere_ probe, not a surface
rover. Unlike you, the ESA community were overjoyed
with the two hour survival, they'd planned for three
_minutes_ of surface lifetime.

And now that the space explorer types have pulled
this one off in such grand style [my message to them
was "please accept a standing ovation from the
entire planet"], can't you hear them planning to
drop a "ruggedized Huygens" into the atmosphere of
one of the gas giants? Or is that probe already en
route?

xanthian.




--
Posted via Mailgate.ORG Server - http://www.Mailgate.ORG

On 16 Jan 2005 06:18:31 -0800, dexx wrote:

Is it true that Huygens ceased transmission less than 2 hours after
touchdown? Whilst it was a magnificent achievement to travel so far and
land perfectly, it seems a great shame that the probe was so short
lived. I'm suprised the designers didnt make it rugged enough and
powered enough to survive several days.


Even if it had more power the signal has to be relayed to
Cassini. Cassini kept it's focus on the Huygens probe for 2 hours
then turned toward earth to relay the temetry.
Form earth you could barely pick up the carrier signal.
Since Cassini continues on it's route through the saturnian system
you wouldn't be able to get a continuous transmission anyhow.
Besides the most important part of the mission was a spectral analysis
of Titan't atmosphere. The surface pictures were really just gravy.


--
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

Terrell Miller wrote:

dexx wrote:
Is it true that Huygens ceased transmission less than 2 hours after
touchdown? Whilst it was a magnificent achievement to travel so far and
land perfectly, it seems a great shame that the probe was so short
lived. I'm suprised the designers didnt make it rugged enough and
powered enough to survive several days.

one design limitation factor was the length of time that Cassini would
be "over the horizon" wrt the lander. Huygens doesn't have powerful
enough transmitters to relay the datastream directly to Earth, so having
longer batt life wouldn't do anything but waste money and resources if
it couldn't see its mothership and thus transmit data.

Building enough transmitter power to send to Earth directly would very
likely have major scalability issues, which in turn would have a direct
impact on other mission profiles (maybe they could have had a powerful
transmitter but little or no instrumentation to feed it data, f'rinstance).

Mission planning for any tpye of space vehicle is a series of tradeoffs
between various things: time, money, propellant, payload, *type* of
payload, mission duration, mission capability, etc. etc.

Bottom line: for any launcher and any vehicle and any mission profile,
there's only so much you can include. Add more of thing X and you have
to take away from things Y, Z and A'.

Perhaps more importantly, the more things you put in, the more effort to
integrate it all, the more effort needed to shave weight, and the more
potential for a mission-threatening screwup. How many missions have
failed, or even failed to get funded, because they were too ambitious?

--
John Halpenny


A cluttered desk is the sign of a cluttered mind.
I’m so glad my desk isn't empty.

"OG" wrote in message
...

May I just briefly say that when I started replying this thread only had
1 reply ;-)

OG

They were hoping for ~30 minutes of surface
data;

I believe some early predictions said only a few
seconds.

Ben

dexx wrote:
Is it true that Huygens ceased transmission less than 2 hours after
touchdown? Whilst it was a magnificent achievement to travel so far and
land perfectly, it seems a great shame that the probe was so short
lived. I'm suprised the designers didnt make it rugged enough and
powered enough to survive several days.

A lot of people have responded already, but I haven't seen the single
most critical point made yet.

There was no certainty as to what type of surface lay under the
clouds. We knew there were light and dark areas, what the temperature
and pressure probably were. But we didn't know if it was liquid or
solid, how much topology was there, whether it was smooth or rough
with rocks or ice boulders, etc.

Designing a probe to survive the landing with high confidence,
across the wide range of possible conditions, was just too hard.
ESA weren't entirely sure if Huygens was going to survive landings
on soil, rocks, or liquid surface anyways. One of Ralph Lorenz'
early focus areas was a paper quantifying the impact parameters
and survival chances for the various possible impact surfaces.

See:
http://www.lpl.arizona.edu/~rlorenz/huygensimpact.pdf


-george william herbert

Henry Spencer wrote:
[snip]
It would have greatly increased the cost and complexity, unfortunately,
because it would almost certainly have required an RTG. Moreover, several
days is not enough -- it'll be a month or two (I forget exactly) before
Cassini goes past Titan again. You can't really do a long-lived Titan
surface mission without better communications support, that is, either a
Titan orbiter or a lander that's big enough and heavy enough to carry its
own high-power transmitter and steerable high-gain antenna (plus the power
source needed to run them).

To be fair, an RTG powered lander might very well have had
enough power to send data directly back to Earth. At low
bit rate certainly, but probably fast enough to be workable.
Galileo was able to operate at pitiful data rates, with
spectacular results, for example.

However, the surface science capabilities of the probe didn't
justify massive expenditures to increase the return for that
portion of the mission. A new probe with different
instruments and a different design, perhaps, but not Huygens.
Also, I believe that it would have been enormously difficult
to design Huygens and provide a large enough RTG to keep it
operating in the event of a landing in liquid hydrocarbons,
which was, and still is, a substantial possibility for a
Titan lander.

Considering how long ago Huygens was built, and that it was
the first foray into a virtually unknown world, I think it
did spectacularly well. We can do better next time, but
partly that's because of the extraordinarily valuable data
Huygens has provided.