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New Images from Galileo
deglr6328 writes "New images of Jupiter's Moon Io, along with a false color image of the first isolated ammonia ice cloud discovered on Jupiter; were released yesterday on the Galileo Probe homepage. The probe is currently transmitting back (at it's maximum transmission rate of about 120 Bits per second!) data on previously recorded observations of Ganymede, Jupiter's main ring, Europa and the Jovian Aurorae. Magnetometer measurements that are now being taken in a 100 day survey of Jupiter's huge magnetosphere will be used in a joint investigation with the Cassini spacecraft, which will be making it's closest approach to Jupiter in about two months. After a broken antenna, 5 years in the Jovian environment, 2 extended missions and a total dosage of nearly 4 times the designed radiation exposure, Galileo is still doing spectacular science."
The reason for the low bitrate is the fact that they are not using the main antenna, which failed to open long ago. Instead the engineers ingeniously reprogrammed the craft to use a low-gain antenna to transmit scientific data. The high-gain antenna was meant to transmit 134,400 bits per second (about one imaging frame per minute). Many software tricks had to be applied, as well as the use of better receiving equipment on earth, for the mission to continue as planned. Prior to the software upgrades, the low-gain antenna had a bitrate of only 8-16 bits per second! See http://www.jpl.nasa.gov/galileo/hg a_f act.html.
http://minduploading.org
I don't know what is more impressive:
1) NASA launching a spacecraft of this kind period
2) Having it still work at all
3) Having people smart enough to jury rig it to STILL WORK! Can you imagine trying to fix something MILLIONS of miles away? That's amazing...way to go NASA.
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Let me give you the lowdown
"You'd think for a few hundred million dollars they'd find something better than an AOL account?"
Galileo was launched in 1989 and probably took
two tears to build. Also keep in mind that "dependable" is far more important than "cutting edge" technology so they would have used older tech. ( I think the space shuttle is just now upgrading to pentiums from 486 'puters).
120bps is pretty impressive.
AdFuel
gave the area of compression algorithms in mathematics something of a kick in the ass, so to speak. IANAMathematician but Galileo doesuse some extremely clever tricks to achieve its mission. Three main types of compression functions are used:
1.)a low-complexity integer cosine transform algorithm, which is an integer-based version of discret cosine transform (ie. JPEG)compression, ICT algorithm, this is new and was developed at JPL.
2.) 2x2 summation mode (which includes a factor of 2 hit on resolution).
3.) Bit Adaptive, Rate-Controlled compression(BARC) a lossless compression
A science virtual machine was created in the the command and data subsystem(main computer) and integrated into the existing operating system to support editing, compression, and packetization of the science data. So Galileo was REPROGRAMMED FROM EARTH (using an upload speed of about 10 bits/second!!) on it's way to Jupiter, with the new compression algorithms. I think those scientists deserve a huge amount of credit for thier achievments.
- "Hear that?! The percolations are imminent! Cease your ingress!"
Alright, before I hear any more complaints about the data rate, keep in mind that Galileo is 50 light minutes from Earth. It's one thing to get 100Mbps over twisted pair copper between machines a kilometer apart, but quite another to do it by radio over about 900,000,000 times that distance (by some quick back of the envelope calculations) with a broken antenna.
Bottom line: don't mess with NASA -- chances are one of their engineers wrote your network driver.
Corgha
When Galileo was built, NASA put a Big Huge Beefy antenna on there, that would deploy like a flower bloom, and provide Lotsa Data.
Now, this is a directional antenna - it puts out lots of data but only in a narrow cone. So they needed a backup antenna, for when the main one was not deployed or if it was not pointed right, just for basic communications (i.e., "Galileo, point main antenna towards earth"). So this antenna is omnidirectional but very small bandwidth (since you don't need bandwidth, after all.)
Yeah, the big one broke. So they have to use the dinky one for all the _data_ communication, too. :-P
This would be like your monitor burning out and having to figure out a way to use your PC speaker to do file management.
For the record, I don't think NASA can be completely blamed for the failed main antenna on Galileo.
Earlier this year I heard Bob Mitchell speaking about Galileo and Cassini - he's pretty much been at the top of both missions. One of the reasons that the main antenna failed to open was because it had to open in the first place, so it was a lot more complicated. (Ideally they would have built it fixed open, like Cassini is designed.)
It had to be redesigned and sent up with the antenna folded up so they could fit it in the space shuttle cargo bay. The reason it had to go up in the space shuttle was because of political interference where people wanted the shuttle to be used for some high profile missions to revive it a bit from the Challenger blowing up in 1986.
Cassini couldn't have the same problems because it was launched with the antenna open. Instead of the space shuttle, they just threw it on the back of one of these, which would have been preferable for Galileo aswell, since they can get much more effective propulsion to kick it off.
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Remember the Van Allen radiation belts around Earth? They're composed of energetic charged particles (protons and electrons), excited to high energies by the magnetosphere, and are held in their spiraling paths by the terrestrial magnetic field. Before they were discovered (in the late 50's, by James Van Allen), people like Werner Von Braun had planned to put manned satellites in a two-hour orbit -- about 1075 miles up. This turned out to be in the lower Van Allen belt, and the radiation hazard was far too great for safety, so manned spaceflight now is generally in orbits below 250 or 300 miles.
But it's Jupiter we're talking about, and the jovian magnetic field is much stronger than Earth's; the jovian equivalent of the Van Allen belts are millions of times more energetic than the terrestrial belts. Just to give you an idea of what this means to people, compare the exposure at Jupiter (say, in the neighborhood of Io) to that around Earth.
When the Apollo astronauts went to the moon, they had to penetrate the Van Allen belts twice, going out and coming back; in doing so, they received about 2 rem radiation dose. This isn't too much: the U.S. limits radiation workers to about 25 times this, each year, based on the cancer risk. When you talk acute doses -- say, you do a pass by Io, which is in the middle of the jovian belts -- the whole-body exposure which is 50% fatal within 30 days (when untreated) is around 250-300 rad (under these circumstances, 1 rad ~ 1 rem).
Jupiter's radiation belts are millions of times stronger than Earth's, so if an astronaut spent the same time in them (about 3 hours total on a lunar mission -- but Jupiter's much larger, and so your speed would have to be hugely greater to make the transit in that time) they'd get an exposure of millions of rem. In other words, they'd be dead almost immediately -- an exposure of mere seconds would probably be lethal.
Galileo is radiation-hardened, since it was intended to survive in this environment; however, it's been there for almost three times its design limit, and it must be getting pretty fried by now. As a matter of fact, last year when it made its first really close flyby of Io, there was concern that the radiation would corrupt the computer memory and cause it to go into safe mode, or blind the camera's CCD. When that didn't happen, everyone was relieved -- and they promptly did it again!
The radiation environment is severe enough that they actually expect the spacecraft to be physically destroyed in a few hundred million years, if they left it in Jupiter orbit.
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Politics is about making compromises. Religion isn't. --Michael Horton
Jovian clouds are generally understood as comprising three distinct cloud layers: an upper layer of ammonia crystals, a middle layer of ammonium hydrosulfide, and a thick bottom layer of water and ice crystals. It's good finally to see some corroboration from the trenches.
-- Anne Marie
The value of data alone that the probe is obtaining is well worth the value of increasing the transmission ability.
The slow transmission speed is due to the fact that the main (high-gain) parabolic-dish antenna failed to open correctly on its way to Jupiter. According to the JPL web site, the main antenna was supposed to be capable of up to 134 Kbps.
Instead, they had to use the less powerful, omnidirectional backup antenna, which has worked admirably over the years. Go JPL.
--
Is it okay to cry "Movie!" in a crowded firehouse? --Steve Martin
You'd think for a few hundred million dollars they'd find something better than an AOL account?
Something wonderful will happen Dave.