Huygens shortlived?

In article ,
Ian Stirling wrote:
There is nothing really prohibiting a mission that just gathers data/sleeps
between communication attempts.
You'd need to add several things.
A RHU, to keep it warm enough for the batteries to work.

Unfortunately, Huygens already had a whole bunch of RHUs.

The problem with RHUs is that there is no way to switch them off when your
electronics are active and you don't need quite as much heat. Or when
you're closer to the Sun, early in the mission, and need rather less heat.

Even setting that aside, it's rather tricky to set things up so that the
RHUs supply *all* your heat but not too much, especially in an atmosphere
whose detailed thermal characteristics are not well known. (And then
there's the possibility that you might be floating in a liquid...)

In practice, you need some way to *control* the internal temperature.
Much the simplest way to do that, unfortunately, is to have the RHUs
supply only the very smallest amount of heat you might ever want, and make
up the extra with electrical heat. There are more elegant ways of doing
this, but they add complexity and often moving parts, and spacecraft
designers tend to distrust them.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

Christopher M. Jones wrote:

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.

My understanding is Huygens was designed to survive such
a landing and continue to function while floating in
hydrocarbons.

I could be mistaken however.

Steve

Steve Pope wrote:
Christopher M. Jones wrote:
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.

My understanding is Huygens was designed to survive such
a landing and continue to function while floating in
hydrocarbons.

I could be mistaken however.

I think the better phrasing would be that it was designed
with some thought that they'd like to to survive landing,
and that they were aware that it might land on land or
a liquid ocean, but that it wasn't really a huge design
priority.

If it had landed on very very solid strong material,
it would probably have broken. Same for on a loose
soil, but on top of a big enough rock.

If it landed in a liquid with enough sideways velocity
or tilt, I think it would have tipped over (and then
probably have sunk). It had moderate dynamic stability
afloat in likely liquid sea materials for Titan;
nothing like what you'd want to see for a real long
term surface probe.

They had a tight weight budget and dollar budget,
and did what they could to keep it survivable on
the surface, not knowing what that surface was
going to be.


-george william herbert

George William Herbert wrote:
Steve Pope wrote:
Christopher M. Jones wrote:
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.

My understanding is Huygens was designed to survive such
a landing and continue to function while floating in
hydrocarbons.

I could be mistaken however.

I think the better phrasing would be that it was designed
with some thought that they'd like to to survive landing,
and that they were aware that it might land on land or
a liquid ocean, but that it wasn't really a huge design
priority.

They planned for the contingecy of a liquid landing. One of the UK
experiments was a densometer for analysing the liquid.

Dave

Steve Pope wrote:
Christopher M. Jones wrote:


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.


My understanding is Huygens was designed to survive such
a landing and continue to function while floating in
hydrocarbons.
Yes. For three minutes.

Greetings!
Volker

George William Herbert wrote:

They had a tight weight budget and dollar budget,
and did what they could to keep it survivable on
the surface, not knowing what that surface was
going to be.
Maybe next time they try to aim for an ocean.
Much easier to land on.

Lots of Greetings!
Volker

In article ,
George William Herbert wrote:
If it had landed on very very solid strong material,
it would probably have broken...
If it landed in a liquid with enough sideways velocity
or tilt, I think it would have tipped over...

Add to this: if it had landed intact but tipped up at a substantial tilt,
nothing dire would have happened to it... but Cassini wouldn't have been
able to hear it. The antenna wasn't fully omnidirectional: it put most
of the transmitter output out nearly horizontally.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

...If the surface is slush-like
or tarry, a the usual wheeled rover isn't going to
make much progress and the liquid areas may have some
of the more interesting chemistry. In several of the
areas, the terrain looks like marsh with many channels
and small lakes. It will be a real challenge, but IMHO
what is called for is something amphibious, perhaps
even a hovercraft or a balloon. After all, since there
is an atmosphere, let's make use of it.

Indeed, given the low gravity and dense atmosphere, some sort of blimp
seems like might be the way to go. You could either just hang your
surface instruments off of it, or use it as the landing system for
surface probes, e.g., you fly around until you have found a good spot
to set down your rover. The latter would save you from needing a main
parachute in your landing system. I suppose the practicality of that
depends on the wind conditions. Winds were apparently fairly mild at
low altitude for Huygens, but are still largely unknown.

Power might be a bit of a problem too, as RTGs seem to be your only
long term option, and they have poor power to mass ratios, meaning your
blimp will be slow. Still, if you are content to drift most of the
time, and only do station keeping in low wind, that shouldn't be
impossible. The RTGs could also heat your gas envelope for improved
lift.

Steve Pope wrote:
My understanding is Huygens was designed to survive such
a landing and continue to function while floating in
hydrocarbons.

I could be mistaken however.

It was designed to have the maximum possible survival
rate in the event of a landing in liquid that the
designers could give it, within the design constraints.
However, this chance was not much. A pool of liquid
hydrocarbons at near liquid Nitrogen temperatures makes
an awfully efficient coolant. So much so that had
Huygens landed in liquid methane it would have ended
its operational life very quickly thereafter.

The crux of the issue is that Huygens' design is
fundamentally incompatable with long duration, or even
medium duration, surface science, let alone on Titan.
It needs not only greater longevity in general but
also different instruments and different overall design.
I think the inflatable wheeled rover / aerobot* is
probably the best design for this sort of thing available
at the moment. It would use 3 separate Helium filled
balloons as wheels in a rover. These would enable the
craft to operate as an aerobot during and after descent
(it could also take the place of parachutes), which would
permit it to perform extensive surveys of the atmosphere
and surface. Later the balloons can be partially
deflated to approach or touch down on the surface, for
higher resolution imagery or surface science. Finally,
while on the surface the Helium could be replaced with
ambient atmosphere, transforming the vehicle to an
amphibious rover. It looks to be an enormously capable
design, with quite a lot of potential.


(*) http://www.lpi.usra.edu/meetings/out...1/pdf/4023.pdf

http://www2.jpl.nasa.gov/adv_tech/rovers/summary.htm

Christopher M. Jones wrote:
I think the inflatable wheeled rover / aerobot* is
probably the best design for this sort of thing available
at the moment. It would use 3 separate Helium filled
balloons as wheels in a rover.
Yes, and they could have any amount of spare wheels waiting to
be inflated.

Lots of Greetings!
Volker