Galileo WebChat - July 18, 1996
5PM - 6PM PDT

Stephen Licata GLL Mission Control Team: . . . . Thu, Jul 18, 4:56PM PDT
Hi, thanks to everyone who tuned in. I may only be able to stay a short while. Let me know if you have any questions about the mechanics of sending commands/receiving data from our struggling, brave spacecraft!

Geoff Collins, Brown University/Galileo Imaging Team: . . . . Thu, Jul 18, 5:01PM PDT (-0700 GMT)
Mark Dunk: I saw that on the front page of the NYTimes and the first thing I thought of (after WOW!) was hey, maybe this relates to Europa! There's a theory floating around that Europa's icy crust spins faster than the underlying rocky interior, the outer shell being decoupled from the interior by an ocean or a layer of warm, soft ice.

Duane Bindschadler Magnetometer/Dust Detector Team, JPL: . . . . Thu, Jul 18, 5:04PM PDT (-0700 GMT)
(to Warren Fish) good question! A few weeks ago I would've said that there *was* no convection going on inside Ganymede -- that it was a geologically dead hunk of rock and ice. But the magnetic field measurements force me to question my own view. There are three sources of heat that are possible:(1) decay of radioactive elements (important for Earth) (2) the original heat left over from planetary accretion (important for Jupiter), and (3) tidal heating (important for Io). Up to now, none of these have been thought to be sufficient to cause convection inside Ganymede up to the present day.

Geoff Collins, Brown University/Galileo Imaging Team: . . . . Thu, Jul 18, 5:04PM PDT (-0700 GMT)
Warren Fish: The core doesn't necessarily have to be molten to drive convection, it just has to be warmer than the outside. Convection can take place in the solid state, just very, very slowly. The Earth's mantle convects without being molten.

Stephen Licata GLL Mission Control Team: . . . . Thu, Jul 18, 5:20PM PDT (-0700 GMT)
Jim Harvey: The maximum downlink data rate we can get with the Galileo spacecraft is 160 bits per second using our low-gain (now only) antenna. This is based primarily on signal strength, extra data coding on the spoacecraft, interference with the radio signal across space (solar interference as well as just the loss over distance) and through the Earth's atmosphere (observing a spacecraft near the zenith is best), and the aperature and technology (i.e. super-cold detectors) on the ground antennas of the Deep Space Antenna and a 64-meter antenna at the parkes facility in Australia. With the high-gain antenna (which did not deploy as you know) we could have gone up to 134,000 bits per second. Still, to appreciate how much we DID recover from the loss of the High-Gain antenna, consider that we were looking at a maximum downlink data rate of only 10 bps without all the spacecraft and ground system modifications made in the last few years, and loaded onto the spacecraft this Spring. The uplink data rate is always the same - 32 bits/sec and we boost up the transmitter power on the ground usually to 100 Kw as necessary. The downlink transmitter on the spacecraft is around 30 watts, but I'm not sure exactly. For this past Ganymede 1 encounter, we got up to about 80 bits/sec.

Kelly Bender, Galileo Imaging Team, ASU: . . . . Thu, Jul 18, 5:02PM PDT (-0700 GMT)
wally - we shutter veryyyyyyy fast

Jim Kaufman, Galileo Imaging Team, JPL: . . . . Thu, Jul 18, 5:05PM PDT (-0700 GMT)
wally: We use short exposure times (to keep the blur down), and for the closest approach observations, something called Target Motion Compensation (TMC). In essence, we move the camera so that it tracks the target while we take the pictures.

Geoff Collins, Brown University/Galileo Imaging Team: . . . . Thu, Jul 18, 5:08PM PDT (-0700 GMT)
bjork: Nope, haven't found any ancient civilizations yet, but we've found enough coincidental arrangements of craters to keep the people looking for "faces" on other planets happy for a long time. :-)

Steve Collins Galileo Backroom (Attitude Control): . . . . Thu, Jul 18, 5:23PM PDT (-0700 GMT)
The attitude control subsystem figures out and controls which direction the spacecraft and camera platform are pointed. The AACS unit of which I am a member also is responsible for controlling propulsive maneuvers when we need to tweak galileo's orbit.

Jim Kaufman, Galileo Imaging Team, JPL: . . . . Thu, Jul 18, 5:07PM PDT (-0700 GMT)
Spacenut: We don't any closer to Io than about 400,000 km, I believe.

Lou D'Amario, Galileo Navigation, JPL: . . . . Thu, Jul 18, 5:08PM PDT (-0700 GMT)
Spacenut: The closest galileo will come to Io during the nominal tour is 244,000 km on orbit #3 on 11/6/96.

Ron Baalke, Galileo Outreach, JPL: . . . . Thu, Jul 18, 5:17PM PDT (-0700 GMT)
Comment on Lou D'Amario's remark that Galileo will pass by Io by 244,000 km on 11/6/96: that will be nearly 10 times closer than when Galileo took this Io image! (press button

Duane Bindschadler Magnetometer/Dust Detector Team, JPL: . . . . Thu, Jul 18, 5:11PM PDT (-0700 GMT)
sky bauman: As I understand it, there are currently two competing models for Io's magnetic field. The first say that it's like Earth's field -- internally generated. The second is that the magnetic field we observed is just a side effect of the interactions between Io, the Io plasma torus, and Jupiter's magnetic field. Some of the principal investigators on Galileo are presenting their preliminary results this week in Europe. I'm anxious to hear the results of their discussions.

Ron Baalke, Galileo Outreach, JPL: . . . . Thu, Jul 18, 5:11PM PDT (-0700 GMT)
Wisdom: Galileo uses RTG's for its power source because solar panels are not feasible at Jupiter's distance - it is too far from the Sun. Also, there is no nuclear reaction in the RTG's. The RTG hold plutonium, which gives off heat as it decays. This heat is then converted into electricity to power the spacecraft.

Duane Bindschadler Magnetometer/Dust Detector Team, JPL: . . . . Thu, Jul 18, 5:15PM PDT (-0700 GMT)
Wisdom: We really don't know exactly how much radioactive material is contained in Ganymede. Because we (usually) need actual samples to do better than make educated guesses, it's a tough problem. Planetary scientists have *generally* thought that Ganymede would contain a smaller fraction of radioactive elements than rocky bodies like Earth and Mars.

Spacenut: . . . . Thu, Jul 18, 5:18PM PDT (-0700 GMT)
I've been wondering if the same technology that is used to get electricity from the RTG's could be used to get electricity from wasted heat, like from a car's engine. If you had the entire engine block surrounded with these collectors (or whatever they are) you could convert the wasted heat to usable energy. Would this work?

Jim Kaufman, Galileo Imaging Team, JPL: . . . . Thu, Jul 18, 5:12PM PDT (-0700 GMT)
P0Z: The BW/xmission problem is part of the explantion. Also, during the closest approach period there just isn't enough time to make color images (the camera has a mechanical filter wheel, etc.) We are making color images when we are further away from a given target body.

Kelly Bender, Galileo Imaging Team, ASU: . . . . Thu, Jul 18, 5:15PM PDT (-0700 GMT)
POZ - yes the allocations of tape and downlink have affected how much color imaging we do; however, b &w is more that adequate for scientific analyses of all types. In addition, some places are pretty colorless, so B&W looks pretty much the same as the color (I'm thinking of Callisto here)

Duane Bindschadler Magnetometer/Dust Detector Team, JPL: . . . . Thu, Jul 18, 5:27PM PDT (-0700 GMT)
POZ: To expand a little on Kelly's answer -- One of the instruments on Galileo (call the Near Infrared Mapping Spectrometer or NIMS) will obtain a great deal of color information about the surfaces. By looking at a variety of wavelengths, NIMS data can be used to learn about the composition and texture of surfaces. The PPR (PhotoPolarimeter/Radiometer) also looks at spectral information and will be used to tell us about the surfaces of the Galilean satellites (and the atmosphere of Jupiter.)

Geoff Collins, Brown University/Galileo Imaging Team: . . . . Thu, Jul 18, 5:14PM PDT (-0700 GMT)
slevy: The evidence for a liquid interior on Europa is sketchy so far... modeling indicates that it could go either way, frozen or liquid. We just don't know enough about the conditions or the distribution of ice and rock in the interior yet. Gravity measurements from Galileo should help to constrain this problem.

Jim Erickson, Galileo Science and Sequence Office, JPL: . . . . Thu, Jul 18, 5:11PM PDT (-0700 GMT)
Apollo: Our New Millenium program has a Deep Space-1 project that will use ion propulsion. Its a program to test new technologies for later use in science missions.

Lou D'Amario, Galileo Navigation, JPL: . . . . Thu, Jul 18, 5:12PM PDT (-0700 GMT)
Apollo: A lot of attention is being paid to solar electric propulsion right now as a means to reduce trip time and increase payload mass. It's undergoing a renaissance of sorts. Of course, gravity-assist is still a mainstay of mission design.

Apollo: . . . . Thu, Jul 18, 5:13PM PDT (-0700 GMT)
Is ion propulsion feasible for intra-solar expeditions?

GllSeq1 : . . . . Thu, Jul 18, 5:16PM PDT (-0700 GMT)
Apollo: not sure this is the right forum, but- U can check the "New Millenium Program" homepage at button for new tech. info; in general- Solar Electric Propulsion will b tested on an Ion drive (single engine, not like the Star Wars' Twin-Ion-Engine fighters). :)

Spacenut: . . . . Thu, Jul 18, 5:14PM PDT (-0700 GMT)
What about some sort of robotic airplane in Jupiter's atmosphere instead of a balloon? Maybe it could scoop up hydrogen to power itself...

Geoff Collins, Brown University/Galileo Imaging Team: . . . . Thu, Jul 18, 5:18PM PDT (-0700 GMT)
anonymous: That's a really, really broad question. What concerns do you have? Personally, as a geologist, I want to know how the Earth works. By looking at other worlds with different conditions, we can test theories and improve our knowledge of our home planet...an important thing to have if we're staying on it for a while...

Duane Bindschadler Magnetometer/Dust Detector Team, JPL: . . . . Thu, Jul 18, 5:21PM PDT (-0700 GMT)
(re: helping us on Earth) There are a lot of reasons that folks give for studying the universe around us. In many cases, we've learned about the fundamental laws of nature -- and how to apply those laws to making our own lives better. There's also the fact that our expeditions to the planets represent the human spirit of exploration. So i think that we benefit both in a practical sense and by having our horizons expanded.

Kelly Bender, Galileo Imaging Team, ASU: . . . . Thu, Jul 18, 5:21PM PDT (-0700 GMT)
General answer - everything we learn about the Jovian system we relate to the Earth (from geologic processes to surface history) and our place in the solar system. Because the Earth is SO active geologically it is difficult to probe single processes (tectonism for example) without getting bogged down with other stuff. When we look at simpler surfaces we are able to use them as a 'lab'. That's part of the reason

anonymous: . . . . Thu, Jul 18, 5:17PM PDT (-0700 GMT)
Will the Galileo probe make any close encounters with the moon IO?

Kelly Bender, Galileo Imaging Team, ASU: . . . . Thu, Jul 18, 5:17PM PDT (-0700 GMT)
Jim, you want to handle the Io observing plan/ monitoring etc.?

Jim Kaufman, Galileo Imaging Team, JPL: . . . . Thu, Jul 18, 5:18PM PDT (-0700 GMT)
Ted Stryk: Since we aren't getting any high-resolution info on Io, the basic plan is to 1) fill gaps in Voyager data, 2) look for changes in the surface (from volcanic activity), 3) make topographic maps, and 4) look for known or new volcanic plumes.

Jim Kaufman, Galileo Imaging Team, JPL: . . . . Thu, Jul 18, 5:21PM PDT (-0700 GMT)
Ted Stryk: As for editing out black sky... We use that technique on the more distant Io images. We also use a technique called on-chip-mosaicking (OCM). This is basically, multiple exposure, where each exposure is located in a unused portion of the CCD frame. Each image is made in a different filter. Typically, we make 2x2 OCMs of Io.

Lou D'Amario, Galileo Navigation, JPL: . . . . Thu, Jul 18, 5:23PM PDT (-0700 GMT)
Seattle: Regarding close approaches to the outer satellites, we have looked at that. There are no really close approaches. I'm looking for that data.

Lou D'Amario, Galileo Navigation, JPL: . . . . Thu, Jul 18, 5:30PM PDT (-0700 GMT)
Seattle: Most of the close approaches to the outer satellites are in the range of 10-20 million km. There are a few less than 10 million km: Lysithea 3.2 million km on 6/1/96 (already occurred), Elara 5.5 million km on 4/17/97, and Lysithea again 5.1 million km on 10/18/97. So there are no real close encounters.

anonymous: . . . . Thu, Jul 18, 5:19PM PDT (-0700 GMT)
did the probe send pictures back from the surface of jupter

Jim Kaufman, Galileo Imaging Team, JPL: . . . . Thu, Jul 18, 5:24PM PDT (-0700 GMT)
anonymous: No, the probe did not send back any pictures from Jupiter. It mainly made measurements of atmospheric composition, temperature, wind speed, lightning discharges, etc.

K. Baines, Jupiter NIMS Co-I: . . . . Thu, Jul 18, 5:25PM PDT (-0700 GMT)
No: (1) The probe had no picture taking capability, and (2) there really is no "surface" accessible by anything (except maybe neutrinos!) ... Jupiter can be thought of as a big bag of fluid (gas for perhaps the outermost thousand kilometers, liquid H2 for the next 60,000 km or so ... The bottom few thousand kilometers might actually be a "hard surface", but it certainly isn't photographable!

Geoff Collins, Brown University/Galileo Imaging Team: . . . . Thu, Jul 18, 5:24PM PDT (-0700 GMT)
Sky Bauman: Ganymede's activity has probably been stopped for a long time (most of the surfaces have accumulated a lot of craters, and are old), so the activity was probably mostly due to the escape of heat from the planet's interior (radioactive heat, heat left over from accretion, etc.)

Duane Bindschadler Magnetometer/Dust Detector Team, JPL: . . . . Thu, Jul 18, 5:33PM PDT (-0700 GMT)
Sky Baumann: The primary theories to explain Ganymede's volcanic and tectonic history are (1) somehow Ganymede ended up with an unusually high concentration of radioactive elements -- enough to make it more geologically active than it's neighbor Callisto. (2) Tidal forces on Ganymede are more important than most scientists think, and were able to keep the interior warm for long enough. Those are the theories I'm familiar with. Any of you grad students out there who are more up to date on your reading?

Ron Baalke, Galileo Outreach, JPL: . . . . Thu, Jul 18, 5:25PM PDT (-0700 GMT)
Apollo: About what Galileo will do after its primary mission, press this button This is the Frequently Asked Question section on the Galileo home page.

Kelly Bender, Galileo Imaging Team, ASU: . . . . Thu, Jul 18, 5:26PM PDT (-0700 GMT)
Tim - names have to follow a certain convention. They go through the USGS and then on to the International Astronomical Union for approval. We'll keep your suggestion in mind - as I'm sure new things will be named.

Jim Kaufman, Galileo Imaging Team, JPL: . . . . Thu, Jul 18, 5:26PM PDT (-0700 GMT)
Tim Harvey: The International Astronomical Union is the governing body for naming objects (and features on the objects) in the solar system. I think naming something after Arthur C. Clarke would be a great idea!

Geoff Collins, Brown University/Galileo Imaging Team: . . . . Thu, Jul 18, 5:27PM PDT (-0700 GMT)
Tim Harvey: He certainly has earned it! I know in my lab, we keep joking about finding the monolith on the next image...(or finding Elvis)

K. Baines, Jupiter NIMS Co-I: . . . . Thu, Jul 18, 5:31PM PDT (-0700 GMT)
When the mag folks announced that strange magnetic field on Ganymede, it occured to me that good ol Arthur C may have been on to something after all.... So perhaps Ganymede is the place a crater or some other "anomoly" should be named....

Tim Harvey: As for getting a neat place on Europa named for Arthur C. Clarke, I'm not on the committe but I sure would bet on it! There will be so many neat new features coming into view. However, the naming committee usually has a theme that dominates all the larger features and crater/mountains. BTW, there are a few people here at JPL who have astreoids named after them, at the behest of one lady researcher here who discovers them in droves (it's her job!). Also, the asteroid Gaspa, first viewed up close by Galileo in 1991, has, I believe, a few regions on it named after two of the Galileo science officer managers who sadly passed away a few years ago.

Kelly Bender, Galileo Imaging Team, ASU: . . . . Thu, Jul 18, 5:27PM PDT (-0700 GMT)
Jim Kaufman - you want to handle Apollo's question about compression - BARC and ICT!

GllSeq1 : . . . . Thu, Jul 18, 5:29PM PDT (-0700 GMT)
Apollo: there is both editing (selecting certain areas) as well as compression to varying degrees (both lossy and/or lossless) done on the images b4 transmitting to earth. BARC (?) is lossless, and the lossy algorithms include ICT (integer cosine transform, a derivative of the digital kind- DCT).

Jim Kaufman, Galileo Imaging Team, JPL: . . . . Thu, Jul 18, 5:33PM PDT (-0700 GMT)
We used several different types of data compression: 1) ICT (Integer Cosine Transform), 2) BARC (Block Adaptive Rate Controlled), and 3) Huffman compression. 1) is lossy, 2 and 3 are lossless. BARCing uses less tape than the other two. ICT uses less downlink capabilities. PUHLEEEEZE don't ask me to explain them in more detail. My fingers can't handle the typing :-)

Stephen Licata GLL Mission Control Team: . . . . Thu, Jul 18, 5:35PM PDT (-0700 GMT)
John Kirikawa: Unfortunately, using the low-gain antenna does not save any energy. The problem is that the signal pattern sent to the area is better than omni-directional (an expanding sphere of ever-diluting energy) but it is still not to fairly focused "blast" that one gets from a high-gain antenna. Still, 30 watss (that's a ball park figure) of energy coming through an antenna, regardless of energy pattern, is still 30 watts! Ted Stryk: . . . . Thu, Jul 18, 5:25PM PDT (-0700 GMT)
How will the resolution of the Io images at closest approach compare with Voyager images?

Jim Kaufman, Galileo Imaging Team, JPL: . . . . Thu, Jul 18, 5:29PM PDT (-0700 GMT)
wally: We are planning on imaging the following bodies: Jupiter Io Europa Callisto Ganymede Jupiter's rings Amalthea Adrastea Metis Thebe

Cal Grant: . . . . Thu, Jul 18, 5:30PM PDT (-0700 GMT)
Jewel Eye - Ask your congressman! GLL folks: GREAT WORK! Keep it up!

John Krikawa: . . . . Thu, Jul 18, 5:32PM PDT (-0700 GMT)
JewelEye: yeah, I agree, I would love to see a Nova program on the probe. I'm quite sure we'll see a National Geographic article in 12-24 months, stunning as usual.

Geoff Collins, Brown University/Galileo Imaging Team: . . . . Thu, Jul 18, 5:33PM PDT (-0700 GMT)
JewelEye: I sure wish there was more coverage on the news! I guess people are apathetic, or scared of anything having to do with science, both of which would make me sad, or because the major networks figure that celebrities get more ad money than science...

Duane Bindschadler Magnetometer/Dust Detector Team, JPL: . . . . Thu, Jul 18, 5:39PM PDT (-0700 GMT)
Seattle: I'm not sure how long Galileo *could* continue to send back data. The primary constraints are power (the RTG's will eventually decay enough to be insufficient as a power source) propellant (if we can't make Galileo go where we want it to, it gets harder to get good science data), and the effects of radiation. The orbital tour is scheduled to continue through the end of '97. And extended mission could probably continue for another year or two. After that...?

Kelly Bender, Galileo Imaging Team, ASU: . . . . Thu, Jul 18, 5:33PM PDT (-0700 GMT)
Bob - the spacecraft will be taking its next set of images in Sept. Ganymede is, again, the closest approached target.

K. Baines, Jupiter NIMS Co-I: . . . . Thu, Jul 18, 5:34PM PDT (-0700 GMT)
HST is being utilized to get global images in many colors. The observations are keyed to the various Galileo passes. We just got in some GRS pixs the other day. We also are doing some groundbased global monitoring in the near-ir and visible from the NASA/IRTF in Hawaii and fropm Pic Du Midi in the Pyrenees. In all these programs, numerous Galileo Co_i's are in charge or heavily involved to ensure relevance to the Galileo mission...

Lou D'Amario, Galileo Navigation, JPL: . . . . Thu, Jul 18, 5:38PM PDT (-0700 GMT)
Mark: The orbits of the outer Jovian moons are constantly changing due to solar perturbations. Their orbits are not known very acurately. Any close approaches between these moons would have no effect, since there masses are so small. The large Galilean satellites are in prettyy stable orbits right now.

Geoff Collins, Brown University/Galileo Imaging Team: . . . . Thu, Jul 18, 5:45PM PDT (-0700 GMT)
Mark Dunk: Actually, the moons interact with each other to keep them right where they are! They're in orbits with resonant periods, and it would be very, very hard for them to break out of it. The moons of Uranus, however, are thought to interact very strangely indeed, with chaotic readjustments of orbital distances due to the very weak (like weird 7:13) resonances. Also, Saturn has a couple of moons that are co-orbital, they share the same orbit, but trade off on which satellite is in front of the other! If you have the shareware program "gravitation ltd." I can email you a co-orbital demo that I accidentally created.

Mark Dunk: . . . . Thu, Jul 18, 5:46PM PDT (-0700 GMT)
Geoff: I'm interested in the co-orbital info. (markdunk@flash.net)

Apollo: . . . . Thu, Jul 18, 5:47PM PDT (-0700 GMT)
I can obtain the 'gravitation ltd' program and I'd very much like to have the demo you mentioned if you don't mind sending it.. :)

Apollo: . . . . Thu, Jul 18, 5:48PM PDT (-0700 GMT)
As for my email address: (jschuhr@students.uwf.edu)

Gregory LaBorde - Galileo Testbed and Systems Engineer: . . . . Thu, Jul 18, 5:49PM PDT (-0700 GMT)
I'd like the demo too, Geoff! Maybe you should put it somewhere accessible?

Jim Kaufman, Galileo Imaging Team, JPL: . . . . Thu, Jul 18, 5:38PM PDT (-0700 GMT)
wally: Not sure what you mean by "What decides how the images are digitally altered for further examination?"

Apollo: . . . . Thu, Jul 18, 5:43PM PDT (-0700 GMT)
The difference in gravitational pull from orbiting bodies causes heat? Am I understanding that properly?

Jim Kaufman, Galileo Imaging Team, JPL: . . . . Thu, Jul 18, 5:44PM PDT (-0700 GMT)
Apollo: Tidal forces cause frictional heating in some orbiting bodies. This mechanism is thought to be the energy source for the volcanoes on Io.

Geoff Collins, Brown University/Galileo Imaging Team: . . . . Thu, Jul 18, 5:55PM PDT (-0700 GMT)
Apollo: What happens to tidally heat a satellite, say Io, is the following: Io is not a perfect sphere. Its shape is distorted by Jupiter's gravity, and it gets a "tidal bulge" facing Jupiter. If there weren't any other satellites, the tidal bulge would always face Jupiter. However, Europa swoops by every day to make Io speed up or slow down from its orbit, which makes Io rotate slightly from where it "should" be, and the tidal bulge tries to shift accordingly. This rhythmic shifting of the tidal bulge creates lots of friction and lots of heat. Another theory says that there might even be electric heating of Io, as Jupiter's magnetic field induces a charge across it!

Mark Dunk: . . . . Thu, Jul 18, 5:41PM PDT (-0700 GMT)
Thanks for the chat. Gig 'em, Aggies!

Kelly Bender, Galileo Imaging Team, ASU: . . . . Thu, Jul 18, 5:41PM PDT (-0700 GMT)
Spacenut - please ask your questions again, they are scrolling by so quickly and I can't seem to get back to them

Duane Bindschadler Magnetometer/Dust Detector Team, JPL: . . . . Thu, Jul 18, 5:42PM PDT (-0700 GMT)
Spacenut: I scrolled back a ways and couldn't find any of your questions. Would you care to repeat one and I'll gladly do my best to answer.

Spacenut: . . . . Thu, Jul 18, 5:47PM PDT (-0700 GMT)
Aha, the data transper rate is limited! So, I'll have to prioritize and cut back my questions. Sound familiar? Ok, anyway, one of them was, could you send a robotic airplane to Jupiter instead of a balloon? Perhaps it could scoop up hydrogen to power itself.

Duane Bindschadler Magnetometer/Dust Detector Team, JPL: . . . . Thu, Jul 18, 5:50PM PDT (-0700 GMT)
Spacenut: Yes, such a mission is possible. But balloons would probably be cheaper and last longer. Both are important considerations for such a mission.

Kelly Bender, Galileo Imaging Team, ASU: . . . . Thu, Jul 18, 5:55PM PDT (-0700 GMT)
Spacenut - as a geologist I don't know if airplanes would work at Jupiter - remember the high winds and up/down drafts. I think it would be dicy to control a robotic anything from earth in that environment. However, technology and programming races ahead - so maybe artificial intelligence would be used and make it possible. Just a thought, I'm way out of my league on this!

Jim Kaufman, Galileo Imaging Team, JPL: . . . . Thu, Jul 18, 5:55PM PDT (-0700 GMT)
Spacenut: I suppose it would be technically feasible, but probably prohibitively expensive. As for using hydrogen to power it... you would have to bring along an oxydizer with you.

Jim Kaufman, Galileo Imaging Team, JPL: . . . . Thu, Jul 18, 5:42PM PDT (-0700 GMT)
Ratman: I believe that GLL's current budget is on the order of several $M per year.

Ratman: . . . . Thu, Jul 18, 5:56PM PDT (-0700 GMT)
Okay, all of us members of the Planetary Society, L-5 Society, Ad Astra, and the rest can whip out our check books. I'll start collecting cans. Seriously, how about farming out some of the work to Universities and the like? The orbiter will be there money or no, and it seems a shame to waste the years and money it took to get it there. And I do write my congressman, which we all should do.

Kelly Bender, Galileo Imaging Team, ASU: . . . . Thu, Jul 18, 5:44PM PDT (-0700 GMT)
wally - the mars armada is going to start launching this fall. Here at ASU the TES instrument on Mars Global Surveyor is being handled. I, personally, am not working on any Mars stuff. I came to Galileo from Magellan (Venus) and will stick with Galileo til the end.

Matthew Fishburn, Imaging Team, NOAO: . . . . Thu, Jul 18, 5:56PM PDT (-0700 GMT)
As for the sticking of the high gain antenna, the final cause was determined to be a lack of lubricant at the joint which stuck agrivated by being shipped across the country several times because of launch delays. This was determined using tests on an identical antenna structure here on Earth.

Duane Bindschadler Magnetometer/Dust Detector Team, JPL: . . . . Thu, Jul 18, 5:43PM PDT (-0700 GMT)
Dangerous Curves: Thanks for dropping by!

Duane Bindschadler Magnetometer/Dust Detector Team, JPL: . . . . Thu, Jul 18, 5:47PM PDT (-0700 GMT)
Devin: Unlike the Earth, Ganymede is largely made up of water ice (roughly 50%). It's also smaller and colder than Earth. While it's not completely impossible that Ganymede has a molten iron core, it is very unlikely. And we did not expect to see a strong magnetic field at Ganymede -- at least most of us. The MAG principal investigator, Dr. Margret Kivelson, had actually made a prediction that has turned out to be pretty close. But to be honest, I'm not too sure she took her own prediction very seriously. :-)

Cal Grant: . . . . Thu, Jul 18, 5:49PM PDT (-0700 GMT)
The Ganymede images provided of the G1 orbit are from approx. 7500km away. I am wondering how some of the closer shots came out, was there movement artifact in images taken at <1000km?. Repeating JK's question.

Jim Kaufman, Galileo Imaging Team, JPL: . . . . Thu, Jul 18, 5:48PM PDT (-0700 GMT)
Glenn Macala, JPL: 1) Most definintely YES! 2) 129 images were recorded, 117 are currently scheduled to be played back. 3) We are getting several images per day 4). Only in certain regions will the resolution be slightly better than Voyager's.

Stephen Licata GLL Mission Control Team: . . . . Thu, Jul 18, 5:57PM PDT (-0700 GMT)
Data Coding: In addition to the coding schemes put onto the science data, the updated software on the spacecraft also performs two fancy coding routines to "bundle" the data units before sending them to the ground. The first is called Reed Solomon coding in which by a very complex algorithm, data bits are interspersed into the telemetry "frame" so they can be used as error correction markers later on. Secondly, by software and hardware processes we add another layer of coding called Viterbi or "convolutional" coding. This, to my limited understanding, is more like adding an extra few bits for every original bit of data, again in a complex algorithm, as a way of making a best guess to the data when it gets to the ground. For example, if you know that a single data bit has a binary value of "1" and the coding bits (which should also have matched it with 2-3 extra bits) also appear as "1's" on the ground, it looks like your data arrived safely to the Earth. If you have 3 "0's" and a single "1", then probably that one should have been a "0" originally. In theory, if this outer double layer of Viterbi decoding "survives" the trip to Earth, the Reed-Solomon coding will ensure a 100% recoverable data frame. By way of comparison, each telemetry "frame" sent by Galileo is 16,384 bits, but only ~23% are "actual data". Without these coding algorithms, though, we could not even approach the 160 bits/sec downlink data rate that may be possible at some points in the mission. NASA also beefed up our antenna receivers and arranged for multiple antennas to be able to work as an array or "co-collectors" of the signal so that while tracking the spacecraft from our best located site (Canberra, Australia) we could get the highest possible data rate. So you see, the Jupiter Operations improvements took alot of hard work both on the spacecraft and on the ground. We are all really appreciative of these very smart scientists and engineers!!!

Duane Bindschadler Magnetometer/Dust Detector Team, JPL: . . . . Thu, Jul 18, 5:55PM PDT (-0700 GMT)
Andrew: Almost all of the Io data is now on the ground. Scientists are working furiously -- many of them are at a conference right now discussing their results. I'm sure that you'll be hearing more about Io in the next few months. Keep a close eye out in early december, during the American Geophysical Union's Winter meeting in SF.

anonymous: . . . . Thu, Jul 18, 5:50PM PDT (-0700 GMT)
What is the latest thinking as to whether the probe entered in an unusual spot?

Ramblin Wreck: . . . . Thu, Jul 18, 5:50PM PDT (-0700 GMT)
What distance from Ganymede was the closest picture taken and were can I see it? Or has it been sent back yet?

Ted Stryk: . . . . Thu, Jul 18, 5:50PM PDT (-0700 GMT)
Why did you take images you didn't intend to sent back (12 out of 129)?

Jim Kaufman, Galileo Imaging Team, JPL: . . . . Thu, Jul 18, 5:58PM PDT (-0700 GMT)
Ted Stryk: In this orbit we are "downlink limited", i.e., we can record more than we have time to playback. Other orbits are "tape limited", i.e., we can play back much more than we can record on one pass through the tape recorder.

Gregory LaBorde - Galileo Testbed and Systems Engineer: . . . . Thu, Jul 18, 5:56PM PDT (-0700 GMT)
Jim is in his office (next door), but not on-line. He is busy sending e-mail. He said you'd know what he meant, Philippe.

Jim Taylor - telecom: . . . . Thu, Jul 18, 6:25PM PDT (-0700 GMT)
Hi, Philippe Poire -- Like you, it took me a good long time to scroll down through all the messages; it would be longer if I actually read them. It's been a busy day, partly taken up with explaining to our Science Office manager what our communications performance has been with the new system. Each station pass is a little different, and it varies. Someone earlier wondered if the high gain antenna might just pop open by itself. Well, our best efforts to free it have failed so far. If something did make the stuck ribs free themselves now, that could be seen in the changed dynamics of the spacefdraft. It would still take a deliberate effort on our part to drive the antenna fully open with its deployment motor. Someone else asked what the spacecraft's radio output power is. The transmitter (a traveling wave tube) outputs about 20 watts. By the time the losses are accounted for, about 15 watts actually is radiated from the antenna. Someone else asked if using the low gain antenna requires less spacecraft power. No. The traveling wave tube amplfier has two power modes: high and low. It's the "high" power mode that radiates 15 watts. If we had the high gain antenna, we could radiate the same 15 watts from that. But the high-gain beam would be much more concentrated, in the direction of the earth. The high gain antenna would have a higher *effective* radiated power, but it's the same basic 15 watts. I'm not going to be able to stay in this webchat all the while, but I'll peek back in a little later. Anyone who's interested in the Galileo Orbiter's telecommunications and would like to go into it in more detail, please e-mail me at f.h.taylor@jpl.nasa.gov. Thanks, and 'bye for now. Jim T.

6PM - 7PM PDT