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Posted by: gndonald Nov 8 2006, 02:44 PM

This is something I've been thinking about over the last few days and I'd like to post it here for discussion.

I got an idea for a Jupiter probe, which I term the Jupiter Distant Orbiter.

The instrument fit is primarily particles and fields, with the objective being to map the radiation belts/magnetic field from outside the orbit of Callisto. The probe would also be fitted with a 'HiRISE - style' camera to enable photography of the moons/Jupiter.

The orbit used would be one that is highly inclined so that the probe is never occluded by Jupiter itself.

Comments?

Posted by: djellison Nov 8 2006, 02:59 PM

Umm - http://newfrontiers.nasa.gov/missions_juno.html ?

A HiRISE type camera doesn't work too well if you're not in a regular low orbit - a normal framing camera would make a lot more sense.

Doug

Posted by: ugordan Nov 8 2006, 03:06 PM

I see one obvious problem with your approach: orbit insertion burn cost. If you do the JOI burn outside of Callisto's orbit, you expend much more fuel than a close periapsis burn would. It's not very economic.

Posted by: vjkane2000 Nov 8 2006, 03:46 PM

A spacecraft with a camera with the focal capabilities of the HiRise camera (you would want it to be framing) would be able to do considerable monitoring of Jupiter and Io as well as many flybies of Ganymede and Callisto. Such a spacecraft could use solar power; see the ESA mission study on a two craft mission to Jupiter. One would be a distant orbiter (although without a HiRISE-like camera) and the other a Europa orbiter.

Such a mission plan could be adopted to an international mission. The Europeans, for example, could do the distant orbiter and a larger camera could be put on the spacecraft. Then a simpler and less expensive Europa orbiter could do the close up Europa studies. If the Americans built the latter, it could be powered by RTGs.

One of the key advantages of the split mission according to the European mission is that the distant orbiter could be a relay for the Europa orbiter, simplifying its design and power requirements.

Posted by: Rob Pinnegar Nov 8 2006, 04:35 PM

True, but the probe wouldn't necessarily have to start out in a distant orbit. A few flybys of the Galileans could be used to raise the periapsis to near Callisto's orbit. But it'd need fuel to get to a distant orbit from there, of course.

As for a possible orbit, I suppose the Ganymede 2:1 resonance is probably too close to Callisto to be stable. Maybe Ganymede 3:1? I'm just suggesting this on the assumption (possibly faulty) that deliberately dropping the probe into an Io-Europa-Ganymede resonance might help stabilize it against perturbations from Callisto. But I don't know the subject well enough to confirm that myself.

It's not a bad idea, but I think there are better ones out there for "passive" spacecraft. One -- I think it came from John Rehling, correct me if I'm wrong -- was to use Jupiter's gravity to throw a probe into a retrograde solar orbit that would pass through the asteroid belt. The retrograde orbit would permit the probe to encounter asteroids much more frequently than would a probe in a prograde orbit.

However, I'm not sure if anyone here has done the calculations to see whether this is feasible, and what could be done with the orbit after the Jovian encounter (presumably through encounters with inner planets). If it's workable, it could give us fairly close-up views of quite a few asteroids, and a Jupiter close flyby as a bonus.

Posted by: tasp Nov 8 2006, 04:55 PM

I don't recall how difficult this orbit would be for a spacecraft to achieve (eccentricity is quite high and no Jupiter flyby for orbit shaping) but a craft launched from earth to pass Jupiter roughly 60 degrees ahead in it's orbit, with 4 years of flight exterior to Jupiter's orbit would then cross 60 degrees behind Jupiter as it headed sunward. Such an orbit could encounter a mainbelt asteroid and a leading Jupiter Trojan out bound, and a trailing Jupiter Trojan and another mainbelt asteroid in bound. Time this right and maybe you get to go past Chiron, too.

Set up the orbit to return to the vicinity of earth in a multiple of 365 days, and you can flyby earth closely, mod the orbit some, and maybe go somewhere else interesting. (maybe pump up the orbit and go check out some possible Saturnian Trojans, or a comet far from the sun)

Posted by: vjkane2000 Nov 8 2006, 05:16 PM

Here is a link to the ESA study. Their distant orbiter had pretty limited capabilities, presumably to keep costs down. If this was a joint mission, that limitation would be less stringent.

Posted by: JRehling Nov 8 2006, 05:41 PM

That was my idea. It would lead to the spacecraft passing a new asteroid radially (in many cases, off-plane or at considerable difference in solar distance) every few HOURS. The small fraction of passes that happened by random chance to be close would allow many dozens of close flybys per year. With planning (crank up the supercomputer) and modest changes to the trajectory, a really great variety of close (fast, but close) flybys would be possible.

Posted by: vjkane2000 Nov 8 2006, 09:16 PM

This time with the link! http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=35982

Posted by: monitorlizard Nov 8 2006, 10:51 PM

If studying asteroids is desired, a Jupiter Distant Orbiter with HiRISE resolution imaging could look at some of the outer satellites of Jupiter (read: captured asteroids). I realize these are WAY out from Jupiter, but there are several ways to approach the problem. One, design your Jupiter approach (pre-orbit insertion) to pass at least one outer satellite. Two, if I remember correctly, some of these satellites are in very loose clusters or at least constitute families of satellites, so may allow orbits to be designed that could pass more than one in a reasonable length of time. Three, a HiRISE-class imager would allow improvements over earth-based or Hubble imaging from a fairly large distance, so close flybys might not be necessary to get good science.

Posted by: Rob Pinnegar Nov 9 2006, 01:28 AM

Unfortunately, that one can be tough. The spacecraft pretty much has to approach along the plane of Jupiter's orbit around the Sun. Those outer satellites have pretty large orbital inclinations... they spend hardly any time near that plane, and can be millions of kilometres above or below it. But, in principle, it's not impossible.


It is true that some of the satellites are in families, but "families" here refers to similarities between their orbital ellipticities and inclinations. This doesn't mean that the satellites in a family are anywhere near each other at any given time. That said, perhaps there's a way to exploit these relationships.

It's a tough problem.

Posted by: tasp Nov 9 2006, 01:44 AM

Any chance the Jupiter L1 or L2 positions are tantalyzingly close to the outer satellites?

Any halo orbits about L1 that interesected the outer Jupiter satellite 'cloud' might give us a low delta vee chance to look at some of them . . . .

Posted by: djellison Nov 9 2006, 08:09 AM

If that were the case then the outer satellites would be too close to L1/L2 to remain in orbit

Doug

Posted by: tasp Nov 9 2006, 03:01 PM

Halo orbits around L1 apparently can be largish, but maybe not large enough . . .

http://solar-center.stanford.edu/FAQ/QL1.html

Posted by: Spacecadet Dec 21 2006, 10:31 PM

Somethings to keep in mind...

A camera (any camera), especially a high-end one like HiRISE, will be very difficult to deploy in the Jovian environment. The radiation would make much more difficult to build, and HiRISE was not exactly easy (or cheap ) to build in the first place.

Why a camera? What will you learn? Instruments are deployed on spacecraft to answer scientific questions. What questions will a camera answer?

The ESA mission study is pretty aggressive. The level of radiation shielding they assume for the instruments is paltry compared to the 5mrad assumption of radiation dosage. It is difficult to make digital electronics that can take 50-100 krad... let alone 5mrad with minimal shielding.

I also find the masses/power of the instruments to be very suspect... I usually check http://nssdc.gsfc.nasa.gov/ and look for similar instruments. You will probably be able to build lighter more capable instruments in the future... but not by factors of 2 or more... especially since you will have to use older, lower performing parts to withstand the radiation.

Posted by: Roly Dec 22 2006, 08:40 AM

There was an interesting Jupiter Distant Orbiter-esque proposal at OPAG earlier in the year. It was called the Ganymede Observer I believe, and its main feature was the MIDAS (Multiple Instrument, Distributed Aperture?) platform - which (apparently) enabled considerably more science return for equivalent volume/mass. Looked like an impressive innovation, that MIDAS, despite the potential integration problems, ITAR etc.

I wonder if it could be part of an New Frontiers 3 "Galileo 2" type proposal. Or as part of the Europa Explorer for better than MRO resolution of interesting regions (especially repeat coverage over time).

Incidentally, does ICER compression still work properly at Europa? I presume it is durable enough with the radiation environment, given that ICT worked (I'd love to know the full story behind that, the few papers I saw, one from 1991, and the snippets on how hard it was to implement on the AACS processor is terrifying.)

Roly

Posted by: ugordan Dec 22 2006, 09:34 AM

ICER is just a compression algorithm. If you can manage to build a processor hardened enough to reliably execute instructions I don't see why it wouldn't work. I don't know about those snippets about Galileo (would love to find out more!), but I assume an AACS processor just wasn't general purpose "enough" to readily support heavy trigonometry calculations.