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Posted by: vjkane Jan 14 2013, 05:27 PM

MOD NOTE: New topic split from previous posts http://www.unmannedspaceflight.com/index.php?showtopic=7568.

There have been various concepts in the US planetary community for similar missions. I'm not sure if any made it to the status of formal proposals to the Discovery program. Eventually some space agency is likely to do this.

Posted by: Phil Stooke Jan 14 2013, 06:27 PM

Of course, the concept of a multiple small body mission is similar to the ill-fated CONTOUR. I hope we will see this mission happen - I would like to see a large sample of small bodies studied over the years. We're already doing quite well, but there is such diversity still to see.

Phil

Posted by: vjkane Jan 14 2013, 09:00 PM

At least several Discovery-class concepts/proposals looked at using solar electrical propulsion to randezvous/orbit several asteroids. There have also been many concepts, one dedicated (CONTOUR), a couple of extended mission (EPOXI, Stardust) of multiple ballistic flybys.

Posted by: Explorer1 Jan 15 2013, 06:44 AM

I wonder how many asteroid encounters would be possible for a space-crafting going retrograde around the sun; delta-v issues aside, couldn't a huge number of flybys happened in close succession, with a kind of 'running into the rain' effect? Since Ulysses got into a polar orbit with a flyby of Jupiter, couldn't the planet fling something else right around? Or would it require multiple flybys over decades?

Posted by: jgoldader Jan 15 2013, 11:34 AM

I tossed out a thought earlier about stationing a craft at one of the EML points, waiting for targets of opportunity or just good close flybys. With enough good trajectory planning and delta-v you might be able to get back to the EML to wait for additional opportunities. Another possibility- we saw demos several years ago of "brilliant pebbles" hovering and maneuvering in tethered tests on the ground. Maybe we could put up a bus carrying half a dozen of those, augmented with a better propulsion system. Sort of nanosatellites, launched at good targets from EML. Payload maybe a webcam and a decent optical imager; are there enough mineral features to justify a 1-1.6 micron passively cooled imager or spectrometer?

Jeff

Posted by: TheAnt Jan 15 2013, 11:42 AM

@vjkane: Oh yes EPOXI/Deep impact have taken a peek at 2 comets, and impacted one, with one asteroid coming up in 2020. And lets not forget about Dawn here.

Regardless of direction, the spacecraft still would have to be at the proper position at the right time for one encounter, the same orbital mechanics would still apply. Perhaps it could add one or two encounters to a mission, the time for meaningful observations would be close to zero though.

Posted by: tedstryk Jan 15 2013, 02:38 PM

A DAWN-type mission (with more appropriate instruments for flybys as opposed to systematic mapping from orbit) that instead of orbiting goes for a diverse, large selection of asteroids would be a real winner in my book.

Posted by: Phil Stooke Jan 15 2013, 04:07 PM

"....couldn't a huge number of flybys happened in close succession, ...."

But even travelling retrograde, space is still mostly empty. The number of targets encountered on any realistic trajectory will still be very small.

Phil

Posted by: JRehling Jan 15 2013, 08:04 PM

I imagine someone came up with the idea before I did, but I mentioned the idea of a retrograde asteroid belt mission years ago:

http://www.unmannedspaceflight.com/lofiversion/index.php/t4087.html

The devil's in the details as to how you could find a path to optimize the number of close flybys. I think the key idea is not to pick ten asteroids and ask how to visit them but to consider the set of >10K asteroids and see which retrograde orbit out of the almost infinite permutations visits the largest number of asteroids.

The value of such a mission would be a function of how diverse the asteroids are. If every asteroid visited falls into four types, you may as well just visit four asteroids. If there's some stunning surprise there that you see in a quick/close encounter with the Kth asteroid, then you want to visit K asteroids, where K may be high.

More discussion at that linked thread.

Posted by: vjkane Jan 15 2013, 10:17 PM

The ill-fated CONTOUR mission had a concept somewhat like that. If I remember correctly, following its prime missione, it was to have regular Earth flybys that would allow it to target new comets.

Posted by: vjkane Jan 15 2013, 10:23 PM

I've been wondering if a team would propose a mission similar to Dawn to visit additional main belt asteroids. In some ways, the New Frontiers candidate mission to the Trojan asteroids would do that with 1-2 flybys and orbiting one body http://futureplanets.blogspot.com/2011/01/trojan-and-centaur-mission-concepts.html

However the flight times are long and that imposes a ~$5M/year penalty during cruise. At the recently completed OPAG meeting, Alfred McEwen (HiRISE PI and PI for the proposed Discovery mission) said that the Discovery budget was really isn't large enough for outer planet missions (although he said several teams made proposals in the hopes that NASA's desire to fly an ASRG power system would tip NASA towards a longer mission). Those long flight times equally hurt a lot of asteroid and comet rendezvous missions, although they can use solar panels instead of plutonium for power.

Posted by: jgoldader Jan 16 2013, 02:40 PM

I'm sort of fixated on the idea of staging a multiple-encounter, flyby spacecraft out of one of the EML points, to which it would return after the encounter. SEP gives large delta-v but very slowly, so how about a spacecraft with a chemical engine to enable quick departures from EML, then using SEP to return to EML and await the next opportunity? I've never thought about the delta-v budgets before, so perhaps this is just a stupid (errr, uninformed?) idea, but maybe somebody here has done the math.

Jeff

Posted by: tedstryk Jan 16 2013, 02:57 PM

DAWN could certainly have done multiple encounters from its prograde orbit using its ion engine if that was its only purpose.