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Huygens News Thread, News as and when we find it
M_Welander
post Jan 14 2005, 05:19 PM
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The first images could be made available in a little over 2 hours from now.
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volcanopele
post Jan 14 2005, 05:24 PM
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QUOTE (M_Welander @ Jan 14 2005, 10:11 AM)
They believe they have got all the data from all experiments on Channel A (or B - there's some confusion?), however, the redundant Channel B (or A?) appear to be blank.

Channel A, mostly images, maybe blank. This would mean that we lost half the images.


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Baltic
post Jan 14 2005, 05:28 PM
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QUOTE (M_Welander @ Jan 14 2005, 04:51 PM)
I've found a really good webcast now:

Thanks for the links, you saved my day. smile.gif

Tom
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volcanopele
post Jan 14 2005, 05:33 PM
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The "fog" light on Disr came on biggrin.gif


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imran
post Jan 14 2005, 05:40 PM
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QUOTE (volcanopele @ Jan 14 2005, 05:24 PM)
QUOTE (M_Welander @ Jan 14 2005, 10:11 AM)
They believe they have got all the data from all experiments on Channel A (or B - there's some confusion?), however, the redundant Channel B (or A?) appear to be blank.

Channel A, mostly images, maybe blank. This would mean that we lost half the images.

Are you sure about this? Because according to Spaceflightnow the Doppler Wind Experiment may only have been affected.

"One of Huygens' six experiments, the Doppler Wind Experiment, relied in part on chain A of the probe's communications system. It was designed to measure wind speeds by detecting subtle changes in the frequency of radio transmissions as th craft is blown this way or that. If chain A did not work, scientists will lose measurements of that shift between Huygens and Cassini. But Sollazzo said similar measurements from Earth-based radio telescopes will allow scientists to collect similar data to make up the shortfall, assuming the data on chain A is, in fact, lost. "
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volcanopele
post Jan 14 2005, 05:48 PM
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QUOTE (imran @ Jan 14 2005, 10:40 AM)
Are you sure about this? Because according to Spaceflightnow the Doppler Wind Experiment may only have been affected.

"One of Huygens' six experiments, the Doppler Wind Experiment, relied in part on chain A of the probe's communications system. It was designed to measure wind speeds by detecting subtle changes in the frequency of radio transmissions as th craft is blown this way or that. If chain A did not work, scientists will lose measurements of that shift between Huygens and Cassini. But Sollazzo said similar measurements from Earth-based radio telescopes will allow scientists to collect similar data to make up the shortfall, assuming the data on chain A is, in fact, lost. "

I just sat in on a status report meeting and they mentioned that Channel A did not downlink and this would cause the loss of half of the DISR images.


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azstrummer
post Jan 14 2005, 05:49 PM
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Well, half's better than none. Shame the loss is in the images though. How many images are we talking about during the mission duration?
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Bjorn Jonsson
post Jan 14 2005, 05:51 PM
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That's weird, I understood A and B were redundant with one of the streams transmitted with a short delay to ensure fewer dropouts.
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pioneer
post Jan 14 2005, 05:52 PM
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QUOTE
I just sat in on a status report meeting and they mentioned that Channel A did not downlink and this would cause the loss of half of the DISR images


Aren't channel A & B redundant channels for Huygens to transmit the same data?
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volcanopele
post Jan 14 2005, 05:55 PM
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QUOTE (pioneer @ Jan 14 2005, 10:52 AM)
QUOTE
I just sat in on a status report meeting and they mentioned that Channel A did not downlink and this would cause the loss of half of the DISR images


Aren't channel A & B redundant channels for Huygens to transmit the same data?

As far as I know, they are not the same data. Maybe you are confusing this with the fact that Huygens will be retransmitting its data several times?


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pioneer
post Jan 14 2005, 06:03 PM
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dry.gif Perhaps I'm thinking of the Galileo atmospheric probe. Still, I think speculating that half the images are lost is a bit premature at this point.
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DavidVicari
post Jan 14 2005, 06:04 PM
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QUOTE (volcanopele @ Jan 14 2005, 05:55 PM)
As far as I know, they are not the same data. Maybe you are confusing this with the fact that Huygens will be retransmitting its data several times?

No... Huygens will not be re-transmitting its data several times. It sent all its data out in almost real time on two separate redundant channels. One channel was supposed to be delayed by something like 6 seconds so that a temporary comm. loss would not lose data.

Cassini will send its recorded data to earth multiple times and from multiple different memory locations.
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john_s
post Jan 14 2005, 06:11 PM
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This statement doesn't sound like half the images are lost:

From Spaceflight Now:

Engineers at the European Space Agency's Space Operations Center in Germany are receiving data from Huygens on chain, or channel, B but not from chain A. Both systems are identical and scientists should receive almost all of the desired data from chain B, Mitchell said.

"The way the probe system works, there are two transmitters on the probe and there are two separate receivers on the orbiter so we have two separate, distinct data links between the probe and the orbiter," he said. "These data links were deigned to be largely redundant, not 100 percent, but nearly so.
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volcanopele
post Jan 14 2005, 06:11 PM
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QUOTE (DavidVicari @ Jan 14 2005, 11:04 AM)
QUOTE (volcanopele @ Jan 14 2005, 05:55 PM)
As far as I know, they are not the same data.  Maybe you are confusing this with the fact that Huygens will be retransmitting its data several times?

No... Huygens will not be re-transmitting its data several times. It sent all its data out in almost real time on two separate redundant channels. One channel was supposed to be delayed by something like 6 seconds so that a temporary comm. loss would not lose data.

Cassini will send its recorded data to earth multiple times and from multiple different memory locations.

Sorry, I meant Cassini will be retransmitting Huygens data several times for redundancy.

Even though Channel A "may" be lost, DISR will still have plenty of nice looking panoramas from the data on Channel B. The Doppler Wind experiment data can be reproduced from the carrier signal on earth and from other Cassini instruments.


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M_Welander
post Jan 14 2005, 06:12 PM
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From what I've understood, the physical channels A and B (that is, the mechanisms used to create the channels) are redundant. However, the data from the instruments - which are not redundant - is interleaved between the channels in order to use this physical redundance to double the amount of data that can be transmitted during the short time available.

I could be wrong, though. But if I'm not, imagine this scenario, with a sequence of images:

ABABABAB

Now, if we're losing all A's, we'll still be able to get most of the science out of the B's, because we know where the A's where and so by looking at the B's can know what we've lost, either through interpolation or image reconstruction or reprojection or any other means of data recovery.
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