OK thanks. My only question remaining than is: do they measure an acceration (like the name suggests) or a change (derivative?) in acceleration, like Captain Swoop said?

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To the regular visitor of internet bulletin boards it is clear that it's an excellent idea your parents get to choose your real name.

True, but if you put those measurements on a graph you can see the changes.

Then again, if you want to calculate velocity and position you don't want the changes in acceleration, it's the acceleration itself you need to integrate once for velocity, and twice for position/distance.

Also, as Nicolas pointed out, acceleration (and velocity) are vectors, so you need to keep vertical and horizontal separate.

OK now it is fully clear to me.

I don't know the accelerometer layout of Huygens, but spacecraft that measure perturbations due to the earth's irregularities often have 2 accelerometers per direction, one at each corener of the craft.

The difference in acceleration is casued by the perturbation, the common value by surface forces.

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No, it didn't! That is you fantasy which you've failed to provide any corroborating evidence. We know that the parachute sequence happened within seconds of predicted time. We got signal acquistion on Earth at the predicted time. We know how long Huygens was under the chutes and when it landed.

Evidence? The parachute sequence happend within seconds of the predicted time. Quit ignoring these facts.

Evidence? As has been explained to you before, The TAT was NOT used to sequence the parachutes. Signal acquisition and telmetry data show that Huygens was where it was predicted to be. You cannot explain this away with your "quick descent theory".

LOL! That's quite the exercise in seeing what you want to see. How did you expect that the flimsy Mylar thermal blanket would survive re-entry? Why would there be an electrical harness attached to the heat shield and how did it survive re-entry?

Evidence? Signal acquisition and telemetry show that entry detection was within seconds of prediction.

Evidence? Since we know the parachute sequence was initiated within seconds of predicted time, this little fantasy makes no sense.

Trying to use the TAT as some kind of talisman to save your "theory" doesn't cut it. The TAT was updated with RAU data. How many times does this have to be explained to you? You can't claim the RAU's didn't work since we have the return data.

The lamp was activated at 400 meters based on radar altimeter data. Since we know the RAU's worked, there's no reason to suspect that the lamp didn't turn on when expected.

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"A mystic is a person who is puzzled before the obvious but who understands the nonexistent." -- Elbert Hubbard

No Jerry, you're the only one showing cheek.

Huygens knew when it was getting close to the surface based on return data from the acoustic sounder and the radar altimeter. It knew it hit the surface from the penetrometer data. To my knowledge the sun sensor didn't have any input into scheduling events after landing.

Evidence? You wouldn't design a system to to assign a timestamp to an event at some pre-determined time. You'd record the timestamp when the event occurred! That way, regardless of delays in scheduling or buffering, the data would have the correct timestamp. You're relying quite a bit on the TAT. Too bad it doesn't really help you case.

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"A mystic is a person who is puzzled before the obvious but who understands the nonexistent." -- Elbert Hubbard

So, little wind and plenty of turbulence. That's what your quotes were saying. Do you now admit that you were wrong when you attempted to forcibly interpret contradictions into these quotes?

Sorry, the picture isn't very helpful since it's hard to make out what it tries to be saying. The Doppler reconstruction assumed north/south winds to be negligible because that is what was expected and they could only measure east/west motion by using Doppler measurements. They need interferometry results for north/south movement reconstruction, which I don't think has been completed.

From what I read, he changed his conclusion based on his limited Doppler data due to additional data that is not contradictory.

And what about the measured variations they interpret as turbulence? Was Huygens tap dancing after landing?

Actually, it was based upon a ratio between the velocity and the speed of sound - Mach 1.5 - although you mostly right - they measure the velocity to determine this parameter. The most important thing, is that the probe must have been slowed enough by the atmosphere enough not to totally shred the parachutes.


The nail misses, if the ending was signaled by a timed or acceleration based event. If the landing accelerometers were not sampled until the the probe was good-and-ready to sample them, the time stamp cannot be used to validate the landing time. It should be easy to determine this with time-stamped radar data - and if you were able to see the radar plot I posted on Wikipedia, it is clear the descent during that minute looked nothing like the expected profile.

Yes, but I am hoping someone who knows more than me and you, and the specific sequence - for example, does the transmitter send a special signal to confirm the landing - would jump in and explain when I threw that out. I know the polling of the devices by the software is somewhat the way I have described it, but the more detail, the better.
I'm sure it has been, and will be, but not necessarily in the context of Newton and Einstein's curves not working.

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jwj

If you always believe what you already know, you can't learn anything - Liz

Supernova 1987A exploded recently.

Do you have a plausible answer? Nasa had a half dozen different explanations for the behavior of Galileo's wheels, which one is more plausable? Dark Matter, inflation, Dark energy, time dilation - all magic.

Actually, what I am hoping is the other way around: The behavior of the reaction wheels, if I were privy to the details, could better constrain the theory. I don't know if the wheels are using more power or less, or if there is a conflict as to the momentum expected in the wheel. Here are things that could be happening:

1) The wheel tracking roll, is recording more roll than expected - this could be true if the gravitational effects of the moon are tugging with a greater force than calculated, so the wheel gets in a tug-a-war with the other parts of the guidence system.

2) There could be certain resonant velocities in the wheels - any of the wheels - that interacts with one of the nature frequencies of Saturn - this would be the interference wave nodes involving both Saturn and her moons.

3) A true violation of the weak equivalence principle - the electrical force necessary to drive the wheel is greater or less than expected, screwing up the hysterises dampening parameters.

4) Something else.

I have always favored door 1), but this last episode sounds more like door 3), - effecting multiple types of stepper motors.

Don't you think it is odd that when both Galileo and Huygens were close to Jupiter and Saturn, reaction wheels have behaved curiously?

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jwj

If you always believe what you already know, you can't learn anything - Liz

The evidence is real - I will repost the radar on the Huygens article. I'll pull out the speculative comment, but graphs use real data - unscaled, but even these yield valid scientific information.

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jwj

If you always believe what you already know, you can't learn anything - Liz

No, you're wrong again. They weren't measuring velocity, they were measuring acceleration. The parachute sequence was initiated by the CASU when it detected it's acceleration limit.

Stating the obvious again.

The nail hits right to the heart of the matter. We know that the parachute sequence was within seconds of the predicted time. We know we got signal acquisition at the predicted time. We know Huygens was on the chutes for 2hrs 27min. There's no getting around these facts.

As I explained before, you wouldn't design a system to timestamp events at arbitrary times. You collect the timestamp when the event occurs. That way the data is valid regardless of whether we telemeter the data in real-time or we send you to Titan to download the information directly.

Quit trying to obfuscate the situation with these silly notions of which you have not a shred of evidence.

Where did you get the raw data to do this plot? Do you have access to telemetry the rest of us don't?

Whether there is a "special signal" or not is irrelevant. The landing can be inferred from the penetrometer data and by the timestamps on the images taken from the surface. We also have the reports from the Earth-based radio telescopes that detected the landing.

Why would they do such an analysis when there's nothing to indicate they should? This is all in your fevered imagination. The scientists and engineers involved in the project have to work in the real world.

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"A mystic is a person who is puzzled before the obvious but who understands the nonexistent." -- Elbert Hubbard

Why not? Planets go into retrograde all the time

Seriously, a Doppler signal that clearly demonstrates Hugyens landed at the correct time (or the moon stopped) absolutely kills my theory. Accelermeters that stored the landing force, then delivered this data to the computer when Huygens ask for it do not.

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jwj

If you always believe what you already know, you can't learn anything - Liz

Non sequitor. Was this supposed to mean something?

We're not talking about Galileo, were talking about Cassini. Why are you bringing up any of this? These other theories have no bearing on Cassini other than you don't like them. The difference between these theories and your musings is that they actually have some evidence to back them up.

Lots of flailing, but you've yet to show how any of this could effect one wheel and not the rest.

No. Balky reaction wheels are part of the space game. Take a look at the problems Hubble and the ISS have had. Your reading too much into this.

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"A mystic is a person who is puzzled before the obvious but who understands the nonexistent." -- Elbert Hubbard

Quit making stuff up. Do you have any evidence for this? You've conveniently ignored the last two times I explained this. Timestamps would be totally useless if you didn't record them at the time of the event. Why is this so hard to understand? Your only saying this to shoehorn the telemetry into your "quick descent" scenario. It doesn't work.

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"A mystic is a person who is puzzled before the obvious but who understands the nonexistent." -- Elbert Hubbard

That is my key point: The Doppler wind teams said the turbence ended at 60km, but the imaging team says no, the probe was rocking and tap dancing just before landflall. I think they are describing the same event, twenty minutes into the descent, seconds away from landing.

The balance of the Doppler day, recorded from the earth, showed a smooth descent, with a wind in the same direction that Titan was turning, at virtually no wind in the landing zone: All of it, on the ground.

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jwj

If you always believe what you already know, you can't learn anything - Liz

Parkes Tracking of the Huygens Probe:

What the DWE's principle investigator said about the Doppler data collected by the ground based telescopes:

Things that would have to be true for Jerry to be right:

1. Even though Titan pulled on Huygens much harder than predicted by Newtonian physics, Huygens magically hits the atmosphere on time anyway.

2. A "large glitch" in the Doppler data occurred, completely coincidentally, within 13 minutes of the predicted landing time.

3. Doppler data received before the landing "glitch" is inconsistent with a probe falling through the atmosphere while dangling from a parachute...and no one ever noticed this.

4. Doppler data received after the landing "glitch" is inconsistent with a probe sitting on the surface of Titan and instead looks a lot like the data received before the landing "glitch"...and no one ever noticed this.

5. We ignore every other excellent point that has been raised in this thread

The referenced article is not a "technical" article at all. It's more an informal recount of the work done tracking Huygens from the Parkes telescope in Australia. I think most reasonable people would agree that even just this article is evidence enough that we have a fairly good idea of the timeline of Huygens' descent (ie: the landing time isn't off by an hour).

I haven't religiously followed the Jerry portion of this thread but I believe, up until now, it's periodically been implied that various agencies are confused, dishonest or just plain stupid. But now it's real, published, accomplished scientists with names (and email addresses, and phone numbers, if you do a little searching) that Jerry has to say can't tell the difference between a probe falling through the atmosphere of Titan and a probe sitting motionless on the surface, using the equipment they are responsible for operating, at the Parkes radio telescope.