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Saturn Experiment Might Be Salvageable

Hemos posted more than 9 years ago | from the crossing-your-fingwers dept.

Space 27

komissar writes "The Seattle Times has a recent update on possible salvaging of the Atkinson Saturn experiment. With some work, the data may be recoverable."

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k wut (-1, Offtopic)

Anonymous Coward | more than 9 years ago | (#11455284)

lol

Great quote... (2, Insightful)

keiferb (267153) | more than 9 years ago | (#11455310)

"I think right now the key lesson is this -- if you're looking for a job with instant and guaranteed success, this isn't it."

That's from the professor in charge. On the plus side, he'll never forget to turn on one of his experiements ever again. =) Seriously, though, it's great to hear that the data may not be lost.

Re:Great quote... (3, Informative)

QMO (836285) | more than 9 years ago | (#11455453)

I couldn't see where it said that it was Atkinson that forgot. It seemed to give the impression that someone else was supposed to have done it, but it didn't really say.

Re:Great quote... (2, Informative)

KinkifyTheNation (823618) | more than 9 years ago | (#11455569)

On Thursday, Idaho scientist David Atkinson said that someone failed to turn on a radio receiver for the instrument he needed to measure the winds on Saturn's largest moon.

Re:Great quote... (3, Informative)

Unholy_Kingfish (614606) | more than 9 years ago | (#11456818)

It was ESA's fault (no one is saying exactly whose fault in ESA). They created the command sequences for the Casssini/Huygens decent. They missed flipping the bit to turning on one of the two receivers. How can you forget something so important? NASA/JPL/ESA did this as a "joint" venture, so ESA had that responsibility for the Cassini programming at that point in the mission.

Nothing new (4, Informative)

Frans Faase (648933) | more than 9 years ago | (#11455840)

Sorry, to say, but the article referenced does not give any new information. The data is lost and an attempt is being made to reconstruct the path of the huygens probe using the doppler shift of the signal picked up by several radio telescopes on earth. This require huge computational efforts which can take several months to be completed.

Computational efforts required on Earth only? (3, Interesting)

Anders Andersson (863) | more than 9 years ago | (#11457425)

I thought they were planning to use the radio telescopes for this (reconstructing the path of the probe) long before they learned that the Channel A receiver wasn't going to be operational. Or, what was that Very Long Baseline Interferometry experiment meant for? Merely detecting the presence of a signal?

I suppose that one advantage of doing the same measurements via two receivers (one on Earth, the other on Cassini) would be the ability to reconstruct the path in two dimensions, thereby learning not only how fast the probe travelled, but in what direction (sideways or down).

I guess most of that computational effort may be to properly extract the true signal from all the other noise they probably recorded, much like the SETI@Home project does in a distributed fashion. However, no amount of computation can properly compensate for the loss of a receiver listening from a different position, if that's indeed what the receiver onboard Cassini was meant to do. Even if they had a dozen radio telescopes on Earth listening simultaneously, they would all detect the same doppler shift, telling them essentially nothing but the speed of Huygens relative to Earth only. As it was close to mid-day where Huygens landed on Titan, the Sun (and Earth) were close to zenith, and we would primarily be measuring descent speed, not lateral speed.

Has anybody seen a scientific explanation of the details of the doppler wind experiment, such as what measurements the Channel A receiver was supposed to perform and how it would deliver its results to Earth? I'm pretty sure three hours of analog recording of a high-frequency carrier wave would constitute way too much raw data to transmit to Earth for later analysis, so I assume some processing must be performed already onboard Cassini. If so, performing the same process for the signal received directly via the radio telescopes shouldn't take considerably longer time, once it has been properly extracted from the noise.

Re:Computational efforts required on Earth only? (1)

Anders Andersson (863) | more than 9 years ago | (#11457637)

Ah, I now realize this is exactly what interferometry is about, detecting the same signal with multiple receivers and seeing how they differ in doppler shift. Even the Earth doesn't provide that much of an angle as seen from Titan, so I admit it would be an achievement if they managed to reconstruct the path based on the data they got.

Still, I guess the ability to measure such slight differences in doppler shift would depend more on the sensitivity of the receivers, than on computational power. They do need storage facilities for huge volumes of analog recordings though, capturing nanosecond discrepancies or whatever in the wave...

I disagree with your reading of TFA (2, Interesting)

MarkusQ (450076) | more than 9 years ago | (#11457839)


The head of the space probe mission to Titan said today that much of the data from a botched experiment designed by a University of Idaho professor was recovered by radio telescopes on Earth...Idaho scientist David Atkinson said that someone failed to turn on a radio receiver for the instrument he needed to measure the winds on Saturn's largest moon. Because of that error, data transmitted by the gear on the Huygens lander was not received by the Saturn-orbiting Cassini spacecraft for relay to Earth.
It sounds to me like they were able to receive the data from Earth, without needing to have it relayed by Cassini. It doesn't say anything about them attempting to reconstruct the path from here, but rather that they picked up the data transmitted by the wind-speed instrument directly.

--MarkusQ

Re:I disagree with your reading of TFA (-1, Flamebait)

Anonymous Coward | more than 9 years ago | (#11459739)

Article is unclear.
You are wrong.
GP is right.
HTH

Re:I disagree with your reading of TFA (2, Funny)

MarkusQ (450076) | more than 9 years ago | (#11463060)

Your is post terse.
Claims are unsubstantiated.
Source?

--MQ

Re:I disagree with your reading of TFA (1)

Frans Faase (648933) | more than 9 years ago | (#11466237)

The signal is extremely weak (the output was only something like 10 watt, similar to a mobile phone). As I understood it, they will only be able to reconstruct the carrier signal, and not be able to retrieve the actual data sent on that carrier signal. They are going to use frequency variations in the carrier signal to reconstruct the path of the probe. (These frequency variations are refered to as the Doppler effect.) The huygens probe at a set of detectors (some of them also using doppler effects) to measure its trajectory through the athmosphere. I am not sure whether the Doppler effect in the carrier signal from huygens to cassini was measured.

Re:I disagree with your reading of TFA (1)

MarkusQ (450076) | more than 9 years ago | (#11474824)

That doesn't make sense to me. Are you saying that the modulation of the carrier (for the data) was weaker than the dopler effect? That seems nutty. If it's true, how were they expecting to recover the data in the first place?

I mean, think about it--both the data and the dopler effect are going to show up as variations in the frequency of the carrier wave (or, if you prefer, in a change in the amplitude of the signals received at frequencies near the nominal carrier frequency). From the point of view of the system as designed, one of these was "signal" and the other "noise." Are you telling me that they designed the system to have more noise than signal?

--MarkusQ

Re:I disagree with your reading of TFA (1)

Frans Faase (648933) | more than 9 years ago | (#11478887)

I guess you are right. Probably they are going to use baseline interference instead to determine the position of the craft.

Binary phase-shift keying (1)

Anders Andersson (863) | more than 9 years ago | (#11480571)

I mean, think about it--both the data and the dopler effect are going to show up as variations in the frequency of the carrier wave (or, if you prefer, in a change in the amplitude of the signals received at frequencies near the nominal carrier frequency).

I find it a little confusing too, but as described in last year's IEEE Spectrum article on the Cassini relay doppler shift problem [ieee.org] , the radio link from Huygens used neither frequency nor amplitude modulation, but rather phase modulation:

Huygens is designed to generate telemetry at a rate of 8192 bits per second. Using a common modulation technique known as binary phase-shift keying, Huygens's transmission system represents 1s and 0s by varying the phase of the outgoing carrier wave. Recovering these bits requires precise timing: in simple terms, Cassini's receiver is designed to break the incoming signal into 8192 chunks every second. It determines the phase of each chunk compared with an unmodulated wave and outputs a 0 or a 1 accordingly [see chart, "
Going Through a Phase [ieee.org] "].

I would assume that detecting the signal at all means they can also detect its phase, regardless of how weak it is; it should merely require comparing it with an unmodulated signal generated at the receiving end. I don't know what carrier frequency they used, but I suppose precise timing in the nanosecond range is necessary, as we are literally dealing with the speed of light here.

Or, was Huygens transmitting an entirely different signal to Earth merely for this interferometry experiment? I doubt it, but various comments regarding this event seem to point in that direction. In particular, the analogy ESA officials made with the dialling tone you hear when you pick up a phone handset would make more sense then, as neither the dialling tone contains any data.

This is not clear.. (1, Interesting)

adeyadey (678765) | more than 9 years ago | (#11458569)

Does anyone know if they are trying to actually retrieve the A-channel data, or are they just analysing the carrier for dopler-shift to get the data for this experiment?

Its an important difference - if they can retrieve the A-Channel data, they can re-generate the lost picture data from that channel too..

Re:This is not clear.. (0)

Anonymous Coward | more than 9 years ago | (#11459311)

Just analysing doppler shift. Obviously.

Re:This is not clear.. (0)

Anonymous Coward | more than 9 years ago | (#11461441)

No, not obviously - RTFA..

Re:This is not clear.. (0)

Anonymous Coward | more than 9 years ago | (#11461616)

TFA is crap. They only analyse doppler shift.

Re:This is not clear.. (0)

Anonymous Coward | more than 9 years ago | (#11466880)

So its not clear from the article, right? QED.

Re:This is not clear.. (1)

Tablizer (95088) | more than 9 years ago | (#11476197)

Its an important difference - if they can retrieve the A-Channel data, they can re-generate the lost picture data from that channel too..

If I am not mistaken, the images were compressed (JPEG-like) when transmitted. Compressed images tend to be very sensative to missing portions. I think they would need a pretty clean signal to extract decent images, and I doubt they have that. You can probably get doppler info from choppy signals, but not compressed images.

Ambiguity (1)

danieljpost (455925) | more than 9 years ago | (#11459741)

See, that's the problem. "Someone" forgot to flip the bit. Makes it sound like they weren't sure who was supposed to do it. If the person who was supposed to turn the experiment on had only KNOWN that they were supposed to turn it on, this probably would have been done.

how did they know to start listening? (2, Interesting)

menscher (597856) | more than 9 years ago | (#11460449)

Silly question, but at what point did they realize there was a problem? If they didn't find out there was a problem until after failing to receive channel A data from the orbiter, then the radio waves from the probe would have already passed the Earth also.

Did they somehow know that they'd forgotten to flip the switch before any data was transmitted?

Or maybe the transmit time was several days, and they only missed the first few hours?

Just trying to make sense out of this, since the journalists obviously don't have a clue. Hopefully someone who worked on the project can respond.

They were already listening anyway (1)

Anders Andersson (863) | more than 9 years ago | (#11470242)

If they didn't find out there was a problem until after failing to receive channel A data from the orbiter, then the radio waves from the probe would have already passed the Earth also.

They learned that there was a problem when the Cassini relay transmission came in loud and clear at ESA, but with Channel B data only. At that time there would have been no point in enabling the Channel A receiver, as Cassini had already lost contact with Huygens.

The radio telescopes listened to the signal from Huygens directly, bypassing the Cassini relay (and therefore hearing the signal several hours earlier). They had planned to pick up the carrier wave anyway for doppler measurements, and have recorded the raw, analog signal for analysis. Now that half of the experiment was lost, they will have to cut to the point of the landing using a single scissor blade only. Try it with a piece of paper and one hand behind your back; it ain't easy (poor analogy, I know).

One-way light (and radio signal) travel time from Cassini to Earth is about 68 minutes. The Huygens transmission was some 4 hours long, but I don't know whether the recording was speeded up by Cassini when relaying it to Earth (it was supposedly relayed multiple times).

No, I don't work on the project, but a team at my university [space.irfu.se] designed and built one of the instruments onboard Cassini (a Langmuir probe, measuring space plasma characteristics).

Why only one chance at transmit? (3, Interesting)

Vellmont (569020) | more than 9 years ago | (#11462066)

I tried a few days ago, but couldn't find much information on the design of the Huygens probe. One thing I don't quite understand is why they only planned to transmit the data once, then leave Huygens for dead? Is it because of the extreme cold of the planet and they couldn't prove enough heating + insulation, or were there other factors involved? The vaccum of space is rather cold too, but electronics seem to work OK.

Re:Why only one chance at transmit? (1)

jim_davis (849479) | more than 9 years ago | (#11463804)

My understanding from a radio interview was that the lander was battery powered and that it was a power issue.

Re:Why only one chance at transmit? (1)

Tablizer (95088) | more than 9 years ago | (#11476136)

My understanding from a radio interview was that the lander was battery powered and that it was a power issue.

Further, Cassini only passes by Titan roughly about once every 2 months. The battery is not going to last for 2 months, and the probe may have sank in mud by then anyhow.

Probably the only way to have power for 2+ months is to use the contraversial "nuke packs" rather than chemical batteries. There is not enough sunlight to use solar power there.
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