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Bad Performance?
Wyl2006
post May 11 2006, 06:19 PM
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I am wondering about two special things:


1. Why was the Imager system of Cassini not set on a scan platform? I am really wondering that more than the half possibilites for RADAR-cartography are lost to do other experiments? This seems not an excellent technical solution.

2. Why was the Huygens camera build with such bad resolution? Also the "test images" done at the LPI parking area would give a lot of questions if people were not said that these things in the picture are trees.

Some experiments with a simple CCD-camera at 1/1000 of the illumination given on Earth shows clearly that better pictures could be done without problems, and there are better compression algorithms.

As the soviet space probe has shown during the 70s and 80s, it is possible to make panorama photos from a torrent surface during a flyby of the bus without serios problems.

I am really wondering on those funny self beloving of some ESA-"professionals" and the things told about these bunch of lousy photos they have gotten.

Some experiments with a simple CCD-camera at 1/1000 of the illumination given on Earth shows clearly that better pictures could be done without major problems.

I am working on that topic making cameras for supervision and examination for night and day.

Greetings: Wyl
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Guest_Richard Trigaux_*
post May 11 2006, 06:54 PM
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The main concern with Huygens was the data rate: very low. For this only reason, the images were of poor quality. Sounds too were only audiograms, not sounds.


Of course this is deceiptive, especially when we compare with the beautiful MER images. But it was this or nothing. Hope that the next Titan lander will have a larger data bandwidth. But for this it will need a radio relay orbiting around Titan, and... nuclear power. (RTG).

The scan platform on Cassini? Canceled because of cost, and no anticipated use of it. A decision that many will regreet, when it will come to fly by Enceladus at 25kms altitude.

Problems in conception? See the thread on ITAR.

Other problems? None as far as I know. Cassini does well and the engineers and technicians have all reasons to be proud.
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remcook
post May 11 2006, 07:08 PM
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QUOTE (Richard Trigaux @ May 11 2006, 07:54 PM) *
The scan platform on Cassini? Canceled because of cost, and no anticipated use of it.


no anticipated use?! The science planning has increased many times in complexity.
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centsworth_II
post May 11 2006, 07:25 PM
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QUOTE (Richard Trigaux @ May 11 2006, 02:54 PM) *
The scan platform on Cassini? Canceled because of cost....A decision that many will regret...


A stuck scan platform would also be cause for much regret.
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tedstryk
post May 11 2006, 08:10 PM
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The problem is that the Radar requires use of the same Antenna that is used to communicate with earth. So if it were aligned with the remote sensing instruments, Cassini could never use its High Gain Antenna while it was observing anything!


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djellison
post May 11 2006, 09:02 PM
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QUOTE (Wyl2006 @ May 11 2006, 07:19 PM) *
I am really wondering on those funny self beloving of some ESA-"professionals" and the things told about these bunch of lousy photos they have gotten.


Welcome to UMSF - but carefull on the 'self beloving' stuff - no need for insults.

The camera was built in the very early '90s, with a tiny volume, mass, power and data budget and sent to a very dim, cold, harsh environment - and given those constraints it was about as good as it could possibly have been. Given that, its origin is unimportant - but just to set the record straight, the camera was infact a US contribution to Huygens
http://www.lpl.arizona.edu/DISR/ - so if you feel the need for totally unjustified criticism, then lay it at their door, not ESA's.

Doug
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remcook
post May 11 2006, 09:12 PM
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for all those people who say 'my camera can do better', it would be fun to fully flight-test a normal digital camera. That means full environmental test and shake it! It would be interesting to see how a normal camera would do after such a test.
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Guest_BruceMoomaw_*
post May 11 2006, 09:13 PM
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The scan platform was removed from Cassini in 1992 -- along with a second scan platform for its fields and particles instruments, and a separate receiver antenna for Huygens' signals -- because at that time Cassini was in an extremely severe fiscal crisis. Congress was on the very brink of cancelling it because of its high cost -- only those design simplifications, plus very intense pressure from the ESA, kept Congress from doing so. And NASA asked the Space Studies Board for an appraisal to make sure that the new design would still be scientifically cost-effective: http://www7.nationalacademies.org/ssb/crafcassini1092.html .

As for the DISR: as other commenters have pointed out, the cameras' resolution was kept low simply because cameras are first-class data hogs, and making their resolution higher would have required much stronger transmitters and power supplies for the probe. (Without the cameras, Huygens' data rate could have been cut from 8000 bits/second to only about 200 -- as was the case with the Pioneer 13 Venus entry probe.) And, given those necessary limitations, the DISR team -- who were American, not European (led by Martin Tomasko of the Univ. of Arizona) -- chose to make a tradeoff between somewhat reduced resolution and greater total area coverage of Titan's surface. I don't think anyone can say they were wrong to do so. (The GCMS on Huygens, by the way, was also provided by the U.S.)
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Mariner9
post May 11 2006, 10:33 PM
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It has already been noted, but it is worth repeating: the descent camera was built a looooong time ago. At least, a long time ago in digital technology time frames.

Whenever you look at data being returned by a space mission, you really have to factor in the timeframe that the mission was developed.

In Cassini's case, it started being studied by JPL around 1980-81. They entered into talks with the ESA a few years later. Preliminary designs for Cassini were undoubtably being looked at by the mid-late 80s. Formal approval for the mission happened around 1989. As soon as these spacecraft start into the true design period, one of NASA's big things is flying proven hardware. So the designers probably were somewhat hindered from even including state of the art for 1989 .... so roll the clock back a few years from there.

For missions such as Galileo it was even worse. Essentially the spacecraft was re-designed several times, split into a probe carrier and orbiter, then merged back, and then the whole thing put into storage for a couple years after Challenger exploded. When it flew, it took a 6.5 year course to Jupiter, instead of the originally planned 3. So all told, when the first pictures of Ganymede started rolling in around July of 1996, the camera producing them was based on CCD technology from the mid 70s.
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Guest_BruceMoomaw_*
post May 12 2006, 01:38 AM
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Yes -- I still find it staggering that the Galileo Project, as a whole, stretched over half my lifetime. It was first seriously planned in 1976 (then called "Jupiter Orbiter and Probe"); it was cancelled by the House Appropriations Committee in 1977, only to have its funding restored in a very rare override of that committee by a full House vote; and its instruments were selected way back yonder in late 1977 (except for the Extreme UV Spectrometer and a total-radiation-dose monitor, which were added in the mid-1980s).

In the 1980s -- thanks entirely to the Shuttle's foibles, culminating in the Challenger disaster -- its launch was delayed by almost 8 years, its arrival at Jupiter by 11 years, and the mission's basic design was radically changed FIVE times. (And, as the crowning irony, if it hadn't been for every one of those delays -- including Challenger -- the mission would have failed totally and it wouldn't even have been America's fault. Messerschmidt built its small thrusters as part of a NASA deal with West Germany, and it wasn't until mid-1987 that it was discovered that they would all have burned out or exploded within a few months of launch, requiring a frantic last-ditch thruster redevelopment effort.) When that craft finally burned up in Jupiter's atmosphere, it was literally the end of an era for me.
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centsworth_II
post May 12 2006, 02:40 AM
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QUOTE (BruceMoomaw @ May 11 2006, 05:13 PM) *
...the DISR team... chose to make a tradeoff between somewhat reduced resolution and greater total area coverage of Titan's surface. I don't think anyone can say they were wrong to do so.


Limitations or no, the Huygens images stand as some of the most fantastic ever taken anywhere in the solar system. They are more than sufficient to reveal the totaly alien yet eerily familiar landscape of Titan. I'm no space exploration history expert, but as far as I know they are the best (only?) descent panoramas ever taken.
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Mariner9
post May 12 2006, 07:42 AM
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I think you are correct.

The Veneras only transmitted from the surface of Venus.

MERs had descent imagers, but I only recall a few fuzzy pics. and those are not panoramas.

Similar with Ranger, except the descent photos on the approach to the moon was the entire point of the mission. Lots of pics: straight down. No panoramas.

I don't remember any other missions having descent imaging at all, although the Lunar Surveyors might have.


I'm voting for a Discovery Mission with a Venus probe... that parachutes very, very slowly to the surface, with the entire point being to take as many panoramas as possible as it drifts slowly across the landscape. And, well I suppose while it is there it might as well do some sort of mineralogical study on the surface that the Veneras didn't get, this time with an incredible ammount of context information from the descent imaging .... but that's the scientists for you, always wanting some actual meat to the mission. Me, I admit I mostly want the pics. smile.gif
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Guest_Richard Trigaux_*
post May 12 2006, 07:55 AM
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Having worked in the area, and especially in testing components, I can confirm that electronic parts used in today space are in fact much in late compared to state of the art. The reasons are many, as well explained above by several; but there is also a delay simply in qualifying a component for space: it must work in a large range of temperatures (which usually constrain designers to use military-grade components) and especially with high doses of radioactivity. Especially the Huygens camera had to bear, in turn:
-Earth van Allen radiations
-interplanetary radiations
-neutron flux from the RTGs, for two more time than planned (no, one time, confused with Galileo. I corrected after the two further posts, thanks for seeing the bug).
-Saturn van Allen, which is enough to kill a man.
Integrated circuits are especially sensitive to radioactivity, which can create errors, break them abruptly ir degrade their performances until they stop working. Radiation probing a complex part like a CPU or a CCD requires years, build test circuit, expose the components to various radioactive conditions, do statistics, etc. I don't know how they did (this is included in design time) but we consider we can have relief if the Huygens camera was still working and gave images.

So it is really unfair to compare a 2006 digital camera working in a comfortable human environment, and a mid 70 integrated circuit still working after years in such a cold temp and destructive radioactivity.

A far space mission is a bit like a human life: it takes a long time, has its infancy, its great moments, its long waitings, and its death. And the world evolves significantly during all this time...
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Guest_Analyst_*
post May 12 2006, 08:15 AM
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QUOTE (Richard Trigaux @ May 12 2006, 07:55 AM) *
A far space mission is a bit like a human life: it takes a long time, has its infancy, its great moments, its long waitings, and its death. And the world evolves significantly during all this time...


Well said.

Why "neutron flux from the RTGs, for two more time than planned"?

Analyst
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ugordan
post May 12 2006, 08:21 AM
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I'd just add that the primary factor determining the low resolution of the images was the data rate. Do you even realize how low a bitrate 8 kilobits is? That's 7 times slower than today's dial-up modems are! Plus you have other instruments requiring bandwidth as well!
Another factor in determining the quality of the images is that the CCD chip on the camera accumulated 7 years of cosmic ray radiation damage -- you can't possibly expect the same level of quality as using a test device back here on Earth!
Saying today's digital cameras would blow the Huygens DISR away is nonsense. Your typical digital camera creates 8 bit images as opposed to Huygens' camera 12 bit images. Huygens had 16 times more sensitive dynamic range than your ordinary camera -- a capability that was crucial to even make out the faint surface features through the omnipresent haze. If you launched a 8 bit camera, you'd get nothing except haze (which reduces contrast and hence dynamic range) all the way down to the vicinity of the surface. So much for the superiority of commercial cameras. Finally, the compression algorithm for the images was IIRC made even before JPEG was standardized.
You really can't stress enough that any technology we launch into space is "obsolete" the moment it's launched. Think about that the next time you wish to complain about the quality of the data. When I first read details about Huygens's data rate and what number of images they were expecting to take in 2 hours time, I immediately thought "no way! that's going to look ugly!". When the images finally came back, I was actually pleasantly surprised because I had no expectations of superb imagery. In fact, the surface image was actually mindblowingly clear.
IMHO, given the circuimstances and the time when the probe was developed, I think it performed perfectly. The people who made the damn thing have every right to be "self beloving".

QUOTE (Analyst @ May 12 2006, 09:15 AM) *
Why "neutron flux from the RTGs, for two more time than planned"?

I was wondering about that as well. Maybe he thought two times more than had a direct-to-Jupiter flyby trajectory were executed. That trajectory option was never doable, given the sheer mass of the spacecraft. Cassini actually did pretty well - under 7 years to Saturn (as opposed to how long it took Galileo to Jupiter) and in fact there was no need for a backup, 11 year trajectory. On the other side, Huygens stayed attached to Cassini only a month or so longer than planned so that didn't have a big impact.


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