Data channel "glitch" on Huygens

I still do not have a clear picture of exactly what was lost due to the
glitches with the data channel on Huygens. Most reports just barely mention
the glitch and most do not even mention it and none are clear on just what
data was lost and what was recovered, and how it was recovered.

Some seem to indicate that nearly nothing was lost due to the fact that the
channels were redundant and the data was duplicated over both channels.
Others seem to indicate that the "recovered" data was due to the
"eavesdropping" of the earth-based radio telescopes. Yet other reports seem
to indicate that half (some 350 of 700) the images were completely lost (and
not recovered by some other means such as redundancy of channels or
eavesdropping from earth).

Can anyone shed some light on these issues and why the media seem shy to
dwell more on these matters as well on the notable successes of the mission.

hankman wrote:
I still do not have a clear picture of exactly what was lost due to the
glitches with the data channel on Huygens. Most reports just barely mention
the glitch and most do not even mention it and none are clear on just what
data was lost and what was recovered, and how it was recovered.

Some seem to indicate that nearly nothing was lost due to the fact that the
channels were redundant and the data was duplicated over both channels.
Others seem to indicate that the "recovered" data was due to the
"eavesdropping" of the earth-based radio telescopes. Yet other reports seem
to indicate that half (some 350 of 700) the images were completely lost (and
not recovered by some other means such as redundancy of channels or
eavesdropping from earth).

Can anyone shed some light on these issues and why the media seem shy to
dwell more on these matters as well on the notable successes of the mission.

The data transmisssion of the huygens probe was to go over two channels
of the cassini probe. Accidentally, only one of these channels was
actually switched on, so all taba going over the dead channel was lost.
OTOH, every group with an experiment on huygens could choose how they
utilized those channels for their data. Many groups chose to send
essentially the same data (or enough redundancy) over both channels,
sacrifying data amount for safety. They were ok.

The images experiment didn't and instead chose to send half of the
images over each channel, so half the images are lost. IMHO they
couldn't have done any better since any redundancy would have cost them
images anyway.

The doppler wind experiment chose to use one channel only, unfortunately
the dead one. So all of that data is lost too. Incidentally, a lot of
radio telescopes were able to track the probes descent with a precision
of 1km and from that trajectory much information about the winds could
still be gained so that the guy wanting to know about winds on titan
has some data nevertheless by analyzing how the probe got bounced around
during descend.

Hope this helps.
Volker

"hankman" wrote in message
...
I still do not have a clear picture of exactly what was lost due to the
glitches with the data channel on Huygens. Most reports just barely
mention
the glitch and most do not even mention it and none are clear on just what
data was lost and what was recovered, and how it was recovered.

Some seem to indicate that nearly nothing was lost due to the fact that
the
channels were redundant and the data was duplicated over both channels.
Others seem to indicate that the "recovered" data was due to the
"eavesdropping" of the earth-based radio telescopes. Yet other reports
seem
to indicate that half (some 350 of 700) the images were completely lost
(and
not recovered by some other means such as redundancy of channels or
eavesdropping from earth).

Can anyone shed some light on these issues and why the media seem shy to
dwell more on these matters as well on the notable successes of the
mission.

From comments made in the press conference, the original
intention was to copy the data on both channels so if
one was lost, the data still got through. What was said
led me to believe that happened for all the instruments
other than the camera.

For the images though, someone decided to use the channels
separately which was probably a good idea. I don't know what
the actual rate was but for illustration, instead of taking
say one picture every 30 seconds and sending it through both
channels you can take one every 15 seconds and send them
through alternate channels. In one channel dies, you still
get one picture a minute so you are no worse off but if both
channels work you get twice as many images instead of two
copies of each. The press would ignore it as the consequences
are minimal.

George

I am very anxious to know anything firm about the winds, especially velocity
at ground. One contention has been made from the mpeg of all frames that
either the ground was moving slightly (slow wave action?), or there were
winds? Others have said this motion is all from transmission artifactual. But
there had to be winds at ground level. Anything about those would be appreciated!

gbh

Volker Hetzer wrote:

hankman wrote:
I still do not have a clear picture of exactly what was lost due to the
glitches with the data channel on Huygens. Most reports just barely mention
the glitch and most do not even mention it and none are clear on just what
data was lost and what was recovered, and how it was recovered.

Some seem to indicate that nearly nothing was lost due to the fact that the
channels were redundant and the data was duplicated over both channels.
Others seem to indicate that the "recovered" data was due to the
"eavesdropping" of the earth-based radio telescopes. Yet other reports seem
to indicate that half (some 350 of 700) the images were completely lost (and
not recovered by some other means such as redundancy of channels or
eavesdropping from earth).

Can anyone shed some light on these issues and why the media seem shy to
dwell more on these matters as well on the notable successes of the mission.

The data transmisssion of the huygens probe was to go over two channels
of the cassini probe. Accidentally, only one of these channels was
actually switched on, so all taba going over the dead channel was lost.
OTOH, every group with an experiment on huygens could choose how they
utilized those channels for their data. Many groups chose to send
essentially the same data (or enough redundancy) over both channels,
sacrifying data amount for safety. They were ok.

The images experiment didn't and instead chose to send half of the
images over each channel, so half the images are lost. IMHO they
couldn't have done any better since any redundancy would have cost them
images anyway.

The doppler wind experiment chose to use one channel only, unfortunately
the dead one. So all of that data is lost too. Incidentally, a lot of
radio telescopes were able to track the probes descent with a precision
of 1km and from that trajectory much information about the winds could
still be gained so that the guy wanting to know about winds on titan
has some data nevertheless by analyzing how the probe got bounced around
during descend.

Hope this helps.
Volker