IPB

Welcome Guest ( Log In | Register )

8 Pages V  « < 4 5 6 7 8 >  
Reply to this topicStart new topic
Is Europa really the "highest priority" of the community?, Cleave said it was at LPSC?
JRehling
post Mar 21 2006, 03:32 AM
Post #76


Senior Member
****

Group: Members
Posts: 2530
Joined: 20-April 05
Member No.: 321



QUOTE (BruceMoomaw @ Mar 20 2006, 07:00 PM) *
In any case, since it seems likely that it will be a long time before we get any kind of closeup look at Io again (Europa Orbiter wouldn't come near it, although it's now a long-shot possibility that the next New Frontiers mission selected may be a Jupiter-orbiting Io mapper), it seems worthwhile looking into any possibility.


I know the published "sample" trajectories for Europa Orbiter didn't feature a close Io flyby, but would it be possible to perform one before JOI on initial arrival? Well, obviously it's possible, but would it cost too much delta-v? I imagine it would involve flying past Io and then on to about Europa orbital radius before firing the engines. That would also start the clock ticking on the radiation survival lifetime, and briefly taking on more rads than the nominal mission, but only for hours. And the flyby would not have to be very close, either; it may be sufficient to "split the difference" between Io and Europa orbital distance to accomplish the main scientific goals.
Go to the top of the page
 
+Quote Post
Guest_BruceMoomaw_*
post Mar 21 2006, 03:43 AM
Post #77





Guests






Looks like my whole idea was another pipe dream. I can't find anything on Juno's bit rate, even in Steve Matousek's otherwise excellent description ( http://trs-new.jpl.nasa.gov/dspace/bitstre...4/1/05-2760.pdf ), although an earlier strawman description of a similar mission had a 4000 bps rate. However, a drawing on page 4 of Matousek's report makes it clear that -- throughout its 32-orbit primary mission -- Juno can't possibly make a close flyby of Io (or Europa). And any extended mission will last no more than a month or so, since they want to make damn sure that the craft doesn't malfunction from radiation before they can steer it into Jupiter and thus make sure of missing Europa -- in fact, they may even end its mission after only about 16 orbits or so if they think they have enough data by then. They could, I suppose, maybe arrange a close flyby of Io if they had one hell of a lot of spare delta-V, but I can't see how they could have enough fuel margin left for that. (On the bright side, just by having a spectral resolution twice as good as Galileo's, the near-IR spectrometer on Juno could get a little more long-range compositional data on Io.)
Go to the top of the page
 
+Quote Post
Guest_BruceMoomaw_*
post Mar 21 2006, 03:53 AM
Post #78





Guests






John Rehling's idea for Europa Orbiter just might be workable -- IF they want it badly enough.

EO, since it will now use a VEEGA gravity assist to get to Jupiter, will have a hell of a lot of payload margin -- about 340 kg worth (after it gets into Europa orbit), which is why they're considering a lander. An alternative use being very seriously considered for at least some of that mass margin is to instead increase its shielding, since EO can extend its lifetime in Europa orbit (currently 3 months) by 1 month for every 100 kg more shielding. An alternative use for that shielding could be to allow it to make a few close Io flybys before entering Europa orbit. However, this might also require additional propellant, depending on the design of its Jupiter-orbiting phase (the plan for EO, from the start, has been to have it make a gravity-assist flyby of Ganymede to help brake into Jupiter orbit, instead of using Io as Galileo did).

It's also true that the larger instrument payload they now plan for EO would be well-designed to study Io as well -- high-res and medium-res cameras, near-IR and mass spectrometers (and maybe X-ray and UV ones too), a thermal mapper, fields and particles instruments.
Go to the top of the page
 
+Quote Post
Guest_BruceMoomaw_*
post Mar 21 2006, 04:03 AM
Post #79





Guests






While I'm on the subject of Europa Orbiter and the Jovian radiation belts: one important factor in NASA's advisors saying that it's time to go ahead with the thing is that -- thanks to the additional shielding mass made possible by using inner-planet gravity assists to reach Jupiter -- it has now been decided that our existing technology is already adequate to provide it with the radiation-hard electronics it will need. This is also partly because a lot of additional work has been done in the last few years to develop rad-hard electronics, during the work on EO's previous lighter-weight incarnation and then on JIMO. The computer on Deep Impact and MRO can confidently withstand 1 Mrad, and a lot of other similarly hard new electronics have also been developed.

Using the VEEGA trajectory, by the way, TRIPLES the mass of EO compared to the direct-to-Jupiter trajectory which they (for reasons that baffle me) originally had planned for it.
Go to the top of the page
 
+Quote Post
mcaplinger
post Mar 21 2006, 04:07 AM
Post #80


Senior Member
****

Group: Members
Posts: 2504
Joined: 13-September 05
Member No.: 497



QUOTE (BruceMoomaw @ Mar 20 2006, 08:03 PM) *
This is also partly because a lot of additional work has been done in the last few years to develop rad-hard electronics, during the work on EO's previous lighter-weight incarnation and then on JIMO. The computer on Deep Impact and MRO can confidently withstand 1 Mrad, and a lot of other similarly hard new electronics have also been developed.

Don't believe all the JPL hype. The RAD750 is only hard to ">100 Krad" and if they'd meant 1 Mrad, they'd have said that. And it's not all that obvious how you can build an Mrad-hard imager, though we'll do it if you toss a few million our way smile.gif


--------------------
Disclaimer: This post is based on public information only. Any opinions are my own.
Go to the top of the page
 
+Quote Post
Guest_BruceMoomaw_*
post Mar 21 2006, 04:34 AM
Post #81





Guests






Well, that's what they kept assuring all of us (repeatedly) at the Europa meeting. It's not my fault if we were being fibbed to...
Go to the top of the page
 
+Quote Post
mchan
post Mar 21 2006, 04:34 AM
Post #82


Member
***

Group: Members
Posts: 599
Joined: 26-August 05
Member No.: 476



QUOTE (BruceMoomaw @ Mar 20 2006, 08:03 PM) *
Using the VEEGA trajectory, by the way, TRIPLES the mass of EO compared to the direct-to-Jupiter trajectory which they (for reasons that baffle me) originally had planned for it.

Giving in to the no-nukes-in-space folks fears of the end of the world from an accidental re-entry during an Earth flyby?
Go to the top of the page
 
+Quote Post
mcaplinger
post Mar 21 2006, 04:46 AM
Post #83


Senior Member
****

Group: Members
Posts: 2504
Joined: 13-September 05
Member No.: 497



QUOTE (BruceMoomaw @ Mar 20 2006, 08:34 PM) *
It's not my fault if we were being fibbed to...

It's arguably your fault if you state it as absolute truth without going to any effort to verify it, though.


--------------------
Disclaimer: This post is based on public information only. Any opinions are my own.
Go to the top of the page
 
+Quote Post
Stephen
post Mar 21 2006, 05:56 AM
Post #84


Member
***

Group: Members
Posts: 307
Joined: 16-March 05
Member No.: 198



QUOTE (BruceMoomaw @ Mar 21 2006, 03:43 AM) *
Looks like my whole idea was another pipe dream. I can't find anything on Juno's bit rate, even in Steve Matousek's otherwise excellent description ( http://trs-new.jpl.nasa.gov/dspace/bitstre...4/1/05-2760.pdf ), although an earlier strawman description of a similar mission had a 4000 bps rate.
That document alludes (p8) to the spacecraft using the Ka band (albeit: "For the GS measurements, Ka-up and downlink is only available from the DSN station Deep Space Station (DSS)-25 at Goldstone, California").

What bit rate would be expected from a Ka band link between Jupiter & Earth?

EDIT: I think I may have found the info to that last query in this PDF document, albeit maybe not specifically for Juno. Check out:

http://hrdd.grc.nasa.gov/resources/Pdfs/Outerplanetary.pdf

======
Stephen
Go to the top of the page
 
+Quote Post
JRehling
post Mar 21 2006, 08:01 AM
Post #85


Senior Member
****

Group: Members
Posts: 2530
Joined: 20-April 05
Member No.: 321



QUOTE (mcaplinger @ Mar 20 2006, 08:07 PM) *
And it's not all that obvious how you can build an Mrad-hard imager


Vacuum tubes?

cool.gif
Go to the top of the page
 
+Quote Post
dvandorn
post Mar 21 2006, 08:10 AM
Post #86


Senior Member
****

Group: Members
Posts: 3419
Joined: 9-February 04
From: Minneapolis, MN, USA
Member No.: 15



Oh, gee -- that reminds me of an sf story I once read. It was written in the late '40s, and had its plucky 22nd-century-spaceship-pilot-hero turning on his ship's electronics and waiting, "as man had been forced to wait since the dawn of the electronic age, for the vacuum tubes to warm up."

biggrin.gif

-the other Doug (who is old enough to remember those TV tube sales carts and the joys of finding a given tube to replace one that had blown out...)


--------------------
“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
Go to the top of the page
 
+Quote Post
edstrick
post Mar 21 2006, 09:02 AM
Post #87


Senior Member
****

Group: Members
Posts: 1870
Joined: 20-February 05
Member No.: 174



I last tested vaccuum tubes in the early 90's, keeping my mothers electric organ going. The only tube tester in town was at "Tinkertronics" and was very very tired, mechanically. Hard to get good tube pin contact and the like.
Go to the top of the page
 
+Quote Post
Guest_AlexBlackwell_*
post Mar 21 2006, 06:35 PM
Post #88





Guests






QUOTE (JRehling @ Mar 21 2006, 03:32 AM) *
I know the published "sample" trajectories for Europa Orbiter didn't feature a close Io flyby, but would it be possible to perform one before JOI on initial arrival? Well, obviously it's possible, but would it cost too much delta-v? I imagine it would involve flying past Io and then on to about Europa orbital radius before firing the engines.

Galileo did exactly the same thing: Io flyby->JOI->Perijove Raise Maneuver.
Go to the top of the page
 
+Quote Post
djellison
post Mar 21 2006, 07:44 PM
Post #89


Founder
****

Group: Chairman
Posts: 14431
Joined: 8-February 04
Member No.: 1



I think JUNO might actually do harm for the 'Europan' cause.

Imagine the discussion up on the hill,

"They're pitching for a mission to Europa"
"Where's that?"
"It's one of the moons of Jupiter, the one that's made of icebergs or something"
"Didn't we just DO Jupiter with that JANO or JOURNO or something?"
"Hmm - you're right - I say we go somewhere else"

I'm sure JUNO is of excellent scientific value, but you can see it leading toward another pause in Jovian exploration.

Doug
Go to the top of the page
 
+Quote Post
Guest_AlexBlackwell_*
post Mar 21 2006, 08:03 PM
Post #90





Guests






QUOTE (djellison @ Mar 21 2006, 07:44 PM) *
I think JUNO might actually do harm for the 'Europan' cause...I'm sure JUNO is of excellent scientific value, but you can see it leading toward another pause in Jovian exploration.

I'm not too sure of this. The Level 1 science objectives in the Decadal Survey for the Flagship-class "Europa Geophysical Explorer" are very distinct from the New Frontiers-class "Jupiter Polar Orbiter with Probe(s)" aka Juno. While the latter may contribute second tier science for the former, and politicians might seize on this continue delaying a Europa mission, the EGE Level 1s remain. So as long as the scientists have any input in the process, I don't see Juno doing any real harm to a Europa mission.
Go to the top of the page
 
+Quote Post

8 Pages V  « < 4 5 6 7 8 >
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 28th March 2024 - 10:31 AM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is funded by the Planetary Society. Please consider supporting our work and many other projects by donating to the Society or becoming a member.