A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Space Science » Science
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

Galileo To Taste Jupiter Before Taking Final Plunge



 
 
Thread Tools Display Modes
  #11  
Old September 22nd 03, 12:37 AM
John Schilling
external usenet poster
 
Posts: n/a
Default 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 *

  #12  
Old September 23rd 03, 03:06 PM
Jan C. Vorbrüggen
external usenet poster
 
Posts: n/a
Default 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
  #14  
Old September 25th 03, 10:20 PM
John Schilling
external usenet poster
 
Posts: n/a
Default 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 *


  #15  
Old September 26th 03, 02:04 AM
Hop David
external usenet poster
 
Posts: n/a
Default 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

  #16  
Old September 26th 03, 12:49 PM
Mike Miller
external usenet poster
 
Posts: n/a
Default 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  
Old September 26th 03, 01:12 PM
Jan C. Vorbrüggen
external usenet poster
 
Posts: n/a
Default 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
  #18  
Old September 29th 03, 11:27 AM
Wim Dekker
external usenet poster
 
Posts: n/a
Default 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




  #19  
Old September 29th 03, 09:32 PM
stmx3
external usenet poster
 
Posts: n/a
Default 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  
Old September 29th 03, 10:06 PM
John Schilling
external usenet poster
 
Posts: n/a
Default 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 *





 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT +1. The time now is 09:42 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.