NASA Dawn Asteroid Mission Told to "Stand Back Up", Reinstated! Options

[dvandorn]

Just 'cause I said I would...

Hopefully, though, this whole episode has made its point -- NASA isn't afraid to tell overbudget missions to stand down.

I just *really* wish we could get the magnetometer back on the beastie, though...

-the other Doug

[Mariner9]

I remember in one of the earlier Discovery mission proposals I read about a mission similar to CONTOUR which would flyby multiple asteroids. It wouldn't seem all that cost effective to only fly by 2-3 asteroids, but I know that in the early days of DAWN they were suggesting that they could fly past as many as 10-12 targets on the way there. I always found that number as overly optimistic, Dawn will have enough on it's plate just getting there, so if they manage 1-2 extra flybys it would be impressive enough. Something I read recently suggested they were now using lower numbers whenever the topic came up.

But has anyone given any serious consideration to taking a Dawn type ion propelled spacecraft and using all of the delta-vee specifically for as many fly-bys as possible? I would think with a couple Earth, Venus, or Mars flybys thrown in to make the orbit more elipitcal, they could potentially survey a very large number of targets.

It occurs to me that the instrumentation on DAWN might not be the best for fast flybys, but with the right package this might yield a lot more targets and results than a simple ballistic probe like CONTOUR. And that might make it worth it.

All of this is assuming that the Discovery office at NASA isn't really gun shy about ion drive missions right now.

[JRehling]

But has anyone given any serious consideration to taking a Dawn type ion propelled spacecraft and using all of the delta-vee specifically for as many fly-bys as possible? I would think with a couple Earth, Venus, or Mars flybys thrown in to make the orbit more elipitcal, they could potentially survey a very large number of targets.

Yeah, if you pick targets according to trajectories that net the highest sheer number, without any particular targets offering constraints, I would expect some fantastic possibilities.

Thinking outside the box, I wonder about using a Jupiter gravity assist to create a retrograde orbit that could be later circularized or near-circularized with propulsion and/or Earth gravity assists. It seems to me that flying backwards through the asteroid belt would very much increase the number of flyby possibilities, the same way that you would pass close to a LOT more cars on the highway driving 70 mph against traffic than you would driving 90 mph with traffic. In fact, this would mean no propellant would be needed to catch up to asteroids, or to lag behind them, and all of the propellant (once you achieve that orbit) could be used in "lateral" motion to create flybys. With 10,000 targets, and a full lap relative to the field taking place in about 2.5 years, the craft in retrograde orbit would fly by the radial vector of another asteroid every 2.5 hours! Assuming the asteroid belt is 1 AU wide, totally planar and with uniform distribution of the asteroids within it, the craft would fly within 0.001 AU (149,000 km) of an asteroid about three times a year even if you did nothing to aim for any targets! I would think that a campaign of lateral manuevers aiming for targets well in advance could lead to a mission ultimately achieving hundreds of flybys in a main mission of ten years.

Feasible?

[Bob Shaw]

Thinking outside the box, I wonder about using a Jupiter gravity assist to create a retrograde orbit that could be later circularized or near-circularized with propulsion and/or Earth gravity assists.

Feasible?

Now *that* is a really clever idea!

Simple, cheap, and (almost) free.

Any serious orbital dynamics guys out there? Or girls, I care not which!

Bob Shaw

[David]

Not me, but one thing occurs to me: aren't these byflights going to be awfully fast?

[JRehling]

Not me, but one thing occurs to me: aren't these byflights going to be awfully fast?

Yeah. About 50 km/s, which is about 3 times the relative velocity of, say, New Horizons at Pluto. But these worlds are pretty small, too, so you could aim for a daytime-side flyby, and reliably get a good "full asteroid" view during the minute or so that you have to squeeze off some multicolor frames. Looks like short exposure time, probably a pushbroom design, etc... we see some mission design specs that the high speed would require. Operational precision would be required. All told, though, if you're getting hundreds of flybys and a few are botched, you're still doing pretty well.