Oh, I see. It was about time for a conspiracy theory! 8)

I removed it. Look in the history of that page for older revisions with Jerry's changes.

(Oh whatever, here's a direct link to Jerry's last revision: http://en.wikipedia.org/w/index.php?...oldid=11954151 )

Ok, regarding the jumps in the velocity and acceleration reconstructed from radar data, the explantion is quite simple.

The radar locks between certain altitudes. It starts giving reliable data from ~25 km and losses lock again just a few hudred meters above the surface.

The radar was turned on higher that 25-30 km and its initial data was off-place. Then it started giving good data, until it lost lock again just before impact, as expected

Anyone should take in mind all these engineering limitations before interperting this data.

And for a further description, scroll down to Radar Sounds on this page, which was posted on the Planetary Society's website in January:
http://planetary.org/sounds/huygens_sounds.html

Thanks Andreas!

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

Where did you get the idea that Huygens was suspended under two parachutes? The main parachute was jettisoned after 15 minutes and then the stabilization chute was deployed.

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

That is a pretty damn good estimate, since all I had was an approximate initial velocity (4000m/s), and I was calculating the distance to Titan's orbit, not to Titan. Also, I was only considering one relevant vector.

I pulled the seperation distance out of my butt - it is totally irrelevant...curious though, if I do run the numbers, the relative velocity at seperation was 11 m/s?...Oh, Cassini did the orbital seperation firing at day 5, not day ten.

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jwj

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

Thank you. I agree the big jumps in the plot are most likely due to "ambiguous" and "unambiguous" radar locks, that are distance and terrain dependent. My interpretation is clearly speculative - it will be nice when a vertical scaling can be assigned to the numbers.

There is the issue though, that, neglecting the big jumps, neither the velocity nor the acceleration are consistent with the descent profile: the acceleration, relative to the ground, should be flat, with only a very slight sin wave due to the rocking. Likewise the velocity should be a constant 1.5 m/s. Both the acceleration and the velocity show three clear episodes of change. (Down and up at ~25 seconds, down at ~62 seconds.)

Also, the altitude is slightly higher when the signal is locked at 13 seconds than it was when it lost lock at 12 - I hadn't thought about it before, but this could be a real change in the elevation of the surface of Titan...mmm I suppose the others could, too...But that does not answer why the velocity was so flat, when it should have been a fairly constant 1.5m/s during the last 65 seconds, not suddenly accelerating to 1.5 m/s just before landing.

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jwj

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

This is a bit offtopic for this thread, and probably any further discussion of this should go to another thread.

In a post several days ago, Jerry repeated a rather egregious bit of Bad Astronomy which has been circulating urban myth style for some time now. It's a pet peeve of mine, so I can't stand to let it go by without comment (so much so that I finally registered after lurking on this board for quite a while).

It is misleading to state that there was only one near-miss, or that the O-rings always resealed themselves prior to Challenger. There were several flights on which O-ring damage or even blowby took place.

This explanation of the putty's purpose in the joint design is completely false. It was not behind the O-rings as a second line of defense. Nor was it intended to flow into O-ring gaps. The putty was actually the material directly exposed to the combustion chamber. The sequence of materials was: combustion chamber, putty, airgap, primary O-ring, airgap, secondary O-ring, airgap, grease bead (to seal the joint against moisture while the rocket was on the pad).

The putty's purpose was twofold. It provided thermal insulation to protect the rubber O-rings from hot combustion gases (which was why it had asbestos filler, not the reason you imply). It also acted as part of the mechanism which 'actuated' O-ring sealing via gas pressure.

This latter role has to do with the fact that the Shuttle O-rings (as many O-ring seals do) required application of pressure to 'seat' the O-ring and create a seal. The putty's role in seating the O-ring was to act like a piston. As combustion chamber pressure pushed on one side of the putty seal, the putty flowed a bit into its channel, compressing the air in the airgap behind the putty. As soon as airgap pressure built up enough to seat the primary O-ring, a seal was formed. Once the O-ring sealed, pressure in the airgap would rise to equilibrium with the compression chamber, stopping the putty from flowing any further.

So far as I am aware, the putty never actually flowed into an O-ring joint during any flight. Doing so would actually interfere with proper operation of the O-ring.

(As an aside, if the SRB engineers had relied on putty to flow into O-ring gaps and seal them, it seems likely that it wouldn't have taken nearly as many flights to have an accident. If the putty could flow into gaps, it would keep on flowing through them, not stop and provide a seal. What you'd have is a joint that would leak putty until enough putty was used up to create a channel for gas flow, and then you'd have a combustion gas leak.)

And here we get to the bit which seems to be pure fabrication by some unknown person with an anti-environmentalism bent. I identify that as a motive because the putty story is nearly always attached to material which beats up on asbestos remediation or other environmental topics; this is perhaps the first time I haven't seen it used that way. (Ironically I tend to agree that asbestos remediation sometimes causes more problems than it solves, but that's an entirely different can of worms.)

As refutation, I quote from testimony included in the Rogers Report (the report of the Presidential Commission which investigated the accident):

So, the kernel of truth behind the urban legend is that the Shuttle program was evaluating non-asbestos putties due to concerns about future supply. The contradiction with the legend is that nothing had actually been done yet! STS-51L and all previous flights used zinc chromate putty with asbestos filler. There were two different suppliers but the material was pretty much the same. And it wasn't a change made just before STS-51L; there were twice as many flights with the newer supplier than with the older supplier.

(All flights after STS-51L used no putty at all, since the redesigned SRB field joint has none.)

Clearly you have never bothered to check what the report actually says. The Rogers Commission report (note: not the 'Feynman report'), available online here, does in fact discuss the putty as a possible contributing factor. The role it may have played in allowing a leak is complex, and not completely certain.

(edited for better grammar)

It would be a huge improvement if your Huygens scenario were merely speculative. It is, however, a complete fantasy that you have concocted and only exits in your fevered imagination. It never happened in the real world.

Jerry, more than one person has told you that the probe acquired the expected duration of data collection on the parachutes and more than a hour on the ground. I know one of the people doing data reduction for the GC/MS. I asked her directly about a chart she helped prepare for Toby Owen's presentation at the press conference a week after the mission. It was a graph showing number of counts for nitrogen and methane. The horizontal scale was given in clock time onboard the probe (as CET): 2 hours and 27 minutes on the parachutes and about 1 hour and 10 minutes on the surface. She said that those times were taken from the probe's timer/clock, not from the nominal expected times from the pre-entry mission profile. Ralph Lorenz gave the talk on the Surface Science Package at last month's LPSC. He said directly that they also got 2:27 of data during descent and about 1:10 on the ground.

Your imagined timeline for the entry is complete bunk.

I'm rather relieve to read this, thank you. I was miss-informed, I was told (by someone who should have known) that a new putty had been used, in spite of the fact it did not perform the same in testing. My point was that there was not a conspiracy to hide anything, and I was unaware of this dialogue.

FWIW, I have no political motivation in this, and anyone who has followed the plight of workers involved in the manufacturing of asbestos shouldn't be saddened by the curtailment of the industry.

__________________
jwj

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

Just to be clear, I wasn't saying you had a political motive–actually, this was probably the first time I've seen the putty story where it was not connected to axe-grinding about environmentalism.

Aerich: welcome on the board! Nice first post. =D>

Jerry: so, what should be? Huygens with shield all the way down and no data until landing or shield ejected as expected?

BTW, could someone tell me which instruments (if any) could perform their task with the shield still attached to Huygens?

Only HASI, which actually operated starting from 1270 km, just before the entry begun (and only part of HASI, not all of it - because it also had some deployable booms that could only operate after heat shield release).

Thanks for infos; so, if I correctly understood (from here) only the accelerometers inside Huygens worked before shield ejection?

Thank you, this is the type of verification I have been looking for all along! It identifies the source, both instrumentally and the scientist.

No it is not. Look what would have happened if I am right:

Huygens software was designed to optimize the data stream to Cassini, keeping the buffers full of the data considered most important in each altitude segment. Huygens only had a lookup table to determine the altitude above ~ 30km, so if the descent through the upper atmosphere was much faster than expected, the altitude vrs. Time table is meaningless.

Below ~40 km, Huygens had both the time-at-altitude table and the radar data to consider, but a sanity check was run on the radar data, and if it didn’t pass, the look-up table was still used to decide what altitude the probe was at - If the gravimetric force was greater than expected, the accelerometers may have still been recording accelerations above the expected gravimetric force, so the probe would have assumed it was still falling, even though it was sitting on the ground.

The software would not have even polled the penetrometer data until the time-at-altitude chart was complete. Once it did, it would then send the landing report to Cassini, more than an hour after the landing actually occurred!

Whether this scenario is possible or not depends upon which data Huygens was using to determine altitude below 40 km – the radar data, or the time-at-altitude data. There was a single bit flag sent with the report saying which was used (the radar data was also duplicated in the housekeeping report). Elias has told us that the accelerometer and Doppler Radar reconstruction only differed slightly from the ‘origin descent profile’, but what data was used in the original construction below 40 km? Radar, or the look-up table?

__________________
jwj

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

(peeks in)



AAAAUUUGGGH!!!!!!!!!!


(flees)

__________________
Two years ago moved from my town
I was looking up past the city lights
But the city lights got in my way

See the constellation ride across the sky
No cigar, no lady on his arm
Just a guy made of dots and lines

-from "See The Constellation"
by They Might Be Giants

Jerry, once again, the time of the probe impacting the surface was determined independently of the playback of the data from the probe to the orbiter. The Greenbank facility detected the deployment of the 2.9 meter stabilizing parachute at the correct expected time and also detected the time of touchdown.

Your timeline and sequence of events remains utter bunk.

Since you have garnered no support here for your fantisized scenarios (except for mayb Lunatik and perhaps someone else early on), I'm curious how many other folks think that any of your assertions about Huygens are plausible. For example, have you run any of this past any of the other signers of the Open Letter to Closed Minds?

This has been what we've been telling you for two months. Remember this timeline from here posted on Jan 21?