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Galileo To Taste Jupiter Before Taking Final Plunge
DP writes:
Ron Baalke wrote: RELEASE: 03-297 GALILEO TO TASTE JUPITER BEFORE TAKING FINAL PLUNGE In the end, the Galileo spacecraft will get a taste of Jupiter before taking a final plunge into the planet's crushing atmosphere, ending the mission on Sunday, Sept. 21. The spacecraft has been purposely put on a collision course with Jupiter to eliminate any chance of an unwanted impact between the spacecraft and Jupiter's moon Europa, which Galileo discovered is likely to have a subsurface ocean. At some heights in the Jupiter atmosphere the physical conditions might be suitable to sustain life. Since temperature increases inward, at some level it must traverse the 0-100 C interval in layers where water and organic molecules must be present, and well shielded from cosmic rays. Apparently NASA seems to be sure enough that either no life can exist within Jupiter, or that Galileo will be completely sterilized before entering such "comfortable" atmospheric layers. The important thing is, NASA seems to be sure enough that the spacecraft will surely be destroyed and, if little bits of anything survive, they won't be sending back radio signals. Most of NASA's planetary missions since Voyager have ended when someone found an Absolutely Compelling Scientific Reason why the spacecraft should be deliberately crashed into the nearest large object. This is probably because the Pioneer and Voyager missions ended by seeing NASA spend many megabucks over many years maintaining ground teams and facilities to pick up a steadily declining trickle of bits, only to face boos and catcalls when they eventually zeroed the budget and pulled the plug on the Plucky Little Spacecraft What Was Still Bravely Exploring The Cosmos. Which isn't to say that there aren't people who are seriously concerned about the contamination issue and seriously certain that a Jovian entry event will thoroughly sterilize the craft. But I am skeptical that this is the dominant motive behind the move. -- *John Schilling * "Anything worth doing, * *Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" * *Chief Scientist & General Partner * -13th Rule of Acquisition * *White Elephant Research, LLC * "There is no substitute * * for success" * *661-951-9107 or 661-275-6795 * -58th Rule of Acquisition * |
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Galileo To Taste Jupiter Before Taking Final Plunge
probably because the Pioneer and Voyager missions ended by seeing NASA
spend many megabucks over many years maintaining ground teams and facilities to pick up a steadily declining trickle of bits, only to face boos and catcalls when they eventually zeroed the budget and pulled the plug on the Plucky Little Spacecraft What Was Still Bravely Exploring The Cosmos. In Galileo's case, it was almost out of attitude-control fuel. The time would have been near when it lost attitude control and could no longer communicate with Earth because of that. No need to pull the plug. Jan |
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Galileo To Taste Jupiter Before Taking Final Plunge
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Galileo To Taste Jupiter Before Taking Final Plunge
"Jan C. =?iso-8859-1?Q?Vorbr=FCggen?=" writes:
probably because the Pioneer and Voyager missions ended by seeing NASA spend many megabucks over many years maintaining ground teams and facilities to pick up a steadily declining trickle of bits, only to face boos and catcalls when they eventually zeroed the budget and pulled the plug on the Plucky Little Spacecraft What Was Still Bravely Exploring The Cosmos. In Galileo's case, it was almost out of attitude-control fuel. The time would have been near when it lost attitude control and could no longer communicate with Earth because of that. No need to pull the plug. Los of attitude control doesn't mean you can no longer communicate with Earth, it just means that you need to make the extra effort to suck bits through the low-gain antenna in random orientation[1]. So the need to pull the plug is all the more urgent. [1] Not that this would be as big a deal for Galileo as for most spacecraft, of course... -- *John Schilling * "Anything worth doing, * *Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" * *Chief Scientist & General Partner * -13th Rule of Acquisition * *White Elephant Research, LLC * "There is no substitute * * for success" * *661-951-9107 or 661-275-6795 * -58th Rule of Acquisition * |
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Galileo To Taste Jupiter Before Taking Final Plunge
Henry Spencer wrote: In article , Gordon D. Pusch wrote: 1.) Galileo's impact velocity will be so high it will wiff to plasma. 2.) Jupiter's environment is most likely too alien for anything that evolved on Earth to survive there --- even in the "water zone." 3.) Jupiter has almost certainly already been hit by terrestrial material ejected by asteroid impacts... Possibly not since life evolved, though; it takes a really huge impact to get stuff off Earth. The other two points I generally agree with. The Chicxulub meteor wasn't big enough? Hop http://clowder.net/hop/index.html |
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Galileo To Taste Jupiter Before Taking Final Plunge
DP wrote in message ...
After all meteorites do reach the ground keeping cold core although entering the atmosphere with similar speeds as Galileo. No, meteorites do not reach Earth's surface "with similar speeds as Galileo." Galileo is hitting Jupiter a lot faster. Some components of Galileo (presumably the one with plutonium) must be built to resist terrestrial atmosphere re-entry. That's a bit different than Jovian atmosphere re-entry. Like, a lot slower. Cassini's RTGs were expected to (IIRC) burn off 33% of their mass if Cassini hit Earth during its sling shots past Earth. Cassini swung by Earth at 19km/s. Galileo hit Jupiter at 48km/s. 2.5 times the entry velocity translates into 6.25 times the kinetic energy to be converted into heat per kilogram of spacecraft. |
#17
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Galileo To Taste Jupiter Before Taking Final Plunge
Los of attitude control doesn't mean you can no longer communicate with
Earth, it just means that you need to make the extra effort to suck bits through the low-gain antenna in random orientation[1]. I think that's not true for Galileo - even with a well-oriented low-gain antenna, they got a data rate around 100 bits per second using the 70m antennas for reception. They were making pointing turns of a few degrees every once in a while. I would think that with, say, the pointing off by 10 degrees, the data rate would be essentially zero. Jan |
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Galileo To Taste Jupiter Before Taking Final Plunge
"Mike Miller" wrote in message m... DP wrote in message ... That's a bit different than Jovian atmosphere re-entry. Like, a lot slower. Cassini's RTGs were expected to (IIRC) burn off 33% of their mass if Cassini hit Earth during its sling shots past Earth. Cassini swung by Earth at 19km/s. Galileo hit Jupiter at 48km/s. 2.5 times the entry velocity translates into 6.25 times the kinetic energy to be converted into heat per kilogram of spacecraft. I don't understand why kinetic energy increases quadratically with speed while the energy it costs to increase speed itself seams to be directly proportional to the speed. After all, speed = acceleration * time. What's wrong with my reasoning? Wim |
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Galileo To Taste Jupiter Before Taking Final Plunge
Wim Dekker wrote:
"Mike Miller" wrote in message m... DP wrote in message ... That's a bit different than Jovian atmosphere re-entry. Like, a lot slower. Cassini's RTGs were expected to (IIRC) burn off 33% of their mass if Cassini hit Earth during its sling shots past Earth. Cassini swung by Earth at 19km/s. Galileo hit Jupiter at 48km/s. 2.5 times the entry velocity translates into 6.25 times the kinetic energy to be converted into heat per kilogram of spacecraft. I don't understand why kinetic energy increases quadratically with speed while the energy it costs to increase speed itself seams to be directly proportional to the speed. After all, speed = acceleration * time. What's wrong with my reasoning? Wim Who said energy was proportional to speed? What context? |
#20
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Galileo To Taste Jupiter Before Taking Final Plunge
"Wim Dekker" writes:
"Mike Miller" wrote in message om... DP wrote in message ... That's a bit different than Jovian atmosphere re-entry. Like, a lot slower. Cassini's RTGs were expected to (IIRC) burn off 33% of their mass if Cassini hit Earth during its sling shots past Earth. Cassini swung by Earth at 19km/s. Galileo hit Jupiter at 48km/s. 2.5 times the entry velocity translates into 6.25 times the kinetic energy to be converted into heat per kilogram of spacecraft. I don't understand why kinetic energy increases quadratically with speed while the energy it costs to increase speed itself seams to be directly proportional to the speed. After all, speed = acceleration * time. What's wrong with my reasoning? The implicit assumption that acceleration is proportional to energy or power. In fact, power = acceleration * velocity, so when you do the integral you do get energy = 1/2 * mass * velocity^2. Yes, there are many propulsion systems which provide constant thrust for a constant applied power. But they do this, at low velocities, by applying energy to something other than the acceleration of the vehicle (specifically, acceleration of the exhaust), and at high velocities, by exhausting reaction mass that has already been accelerated to high velocity at great cost in energy. When you do the integral over the trajectory of the vehicle, you find that the energy applied is = 1/2 * mass * velocity^2 -- *John Schilling * "Anything worth doing, * *Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" * *Chief Scientist & General Partner * -13th Rule of Acquisition * *White Elephant Research, LLC * "There is no substitute * * for success" * *661-951-9107 or 661-275-6795 * -58th Rule of Acquisition * |
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