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Mission To Sedna, space mission to sedna
K-P
post Jan 13 2008, 12:51 PM
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I have tried to search but could not see any serious planning of sending a fly-by mission to Sedna. Does anyone have any info if the scientific community is planning such...?

In my opinion, Sedna would be very interesting target, far more interesting than any KBO etc. The fact that it spends most of the time outside heliopause under the influence of cosmic rays during aphelion could reveal some interesting results and also the reddish colour it has might be worth investigating. And good for us, at the moment it is approaching its closest point to Sun on its orbit, so mission to Sedna would not be such a big effort if done e.g. a'la NH with Jupiter gravity assist...? Maybe possible NH2 could be sent that direction.......?

Any comments, any info? Especially the fact that it is a body from outside the heliopause, could that add some interest towards it?


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J.J.
post Jan 13 2008, 02:57 PM
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Unfortunately, I don't see this happening any time soon, for two reasons:

1.) Sedna even at its closet will be more than two and half times farther than Neptune.
2.) It's well beyond the plane of the Solar System, complicating any trajectory.

To be fair, I think Sedna would be an extremely interesting target. Any serious attempt to reach it, though, will probably have to wait for new propulsion technology.


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K-P
post Jan 13 2008, 07:08 PM
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I don't think that the roughly 80-90 AU distance of Sedna at the moment is too overwhelming, after all we have four (two of them functioning still) probes on that distance (and beyond) at the moment, and if we put that little probe on top of Atlas 5 like NH or some other Heavy configuration we could reduce the travel time to a reasonable level (<20 years). RTG's and components can handle that.

The issue of Sedna been so much out of the ecliptic plane does not concern me, after all, at the moment both Voyagers are over 30 degrees above/below the ecliptic, so not much less than Sedna is. And as Ulysses has shown, Jupiter can swing probes in various directions. Of course we might lose some velocity/time if bending the route 40-50 degrees but I don't think that's a critical factor here...? And I believe we should also have quite many launch window opportunities if we do only single fly-by (Jupiter) and then off to Sedna.

But of course, all this is just a meaningless daydreaming and speculation unless somebody puts the money on the table...
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Greg Hullender
post Jan 13 2008, 08:01 PM
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Jupiter can speed you up or get you off the ecliptic, but it's a tradeoff. I'd love to see a proposal that used Jupiter AND an ion drive to try to reach Sedna in under 20 years. Something that wouldn't fly by so fast as to be useless, of course.

--Greg
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stevesliva
post Jan 13 2008, 08:33 PM
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Jupiter-Sun gravity assist can get you going even faster. Of course the flyby will then be extremely brief.
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ugordan
post Jan 13 2008, 08:46 PM
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How can you use Sun in a gravity assist? That's like using Earth in a gravity assist to get to the Moon. Unless you're thinking of a solar sail or ion engine providing delta-V during the Sun "flyby" in which case it makes a bit sense.


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ngunn
post Jan 13 2008, 09:09 PM
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We had a 'what missions would you like to see' - type thread some time ago and I included Sedna in my list. I agree it's important, but to make it worthwhile I'd want to be fairly sure that the mission could definitively answer the question Did Sedna condense from the same solar nebula as the rest of the planets, or did it originate elsewhere? I think I suggested multiple impactors and spectral analysis of the resulting debris.
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cawest
post Jan 14 2008, 02:15 AM
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i would not expect to see a mission to Sedna till after NH reaches Pluto. This would give the enginers an idea what kind of sensors they would need. waiting till after 2014 or so will give time for more development of engines (post launch), and launch tech.
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stevesliva
post Jan 14 2008, 02:34 AM
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QUOTE (ugordan @ Jan 13 2008, 03:46 PM) *
How can you use Sun in a gravity assist? That's like using Earth in a gravity assist to get to the Moon. Unless you're thinking of a solar sail or ion engine providing delta-V during the Sun "flyby" in which case it makes a bit sense.


Can't say I really know all the details-- Any gravity assist needs some sort of delta-V in the well, right? I think the Jupiter-Sun dual gravity assist was suggested for some interstellar probe. And I think it jettisoned a sun-shield when passing the sun, so there was delta-mass as well.
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cawest
post Jan 14 2008, 06:34 AM
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QUOTE (stevesliva @ Jan 14 2008, 03:34 AM) *
Can't say I really know all the details-- Any gravity assist needs some sort of delta-V in the well, right? I think the Jupiter-Sun dual gravity assist was suggested for some interstellar probe. And I think it jettisoned a sun-shield when passing the sun, so there was delta-mass as well.



when will a "Grand Tour" set be available next? that would add alot of Dv, like the Voyagers.
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ugordan
post Jan 14 2008, 09:18 AM
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QUOTE (stevesliva @ Jan 14 2008, 03:34 AM) *
Can't say I really know all the details-- Any gravity assist needs some sort of delta-V in the well, right?

Gravity assists work by changing speed relative to a third body. The speed w/respect to the body you're flying by doesn't change and this is what I meant. Sedna is in solar orbit so passing by the center body - the Sun will not give you any free delta-V. Jupiter works for other targets because it's not the center body of the system, rather it is in orbit around the Sun and you can steal a little bit of that energy.

I suspect the Sun flyby scenario actually doesn't imply a passive flyby, but a thrusting period (solar ion engine?) during a very low perihelion. This does boost your speed significantly, because you're deep in the gravity well and for every km/s of delta-V you burn, you get a higher hyperbolic excess velocity than burning that same delta-V far out. That's why for example New Horizons didn't need to get that obscene delta-V at Earth-Jupiter injection. Rather, a modest increase in ejection velocity out of parking orbit makes you spend less time in Earth's gravity well and gives you higher hyperbolic velocities. It sounds counterintuitive, but it works. If we really had to provide every single km/s our planetary probes get by the launch vehicle, we wouldn't be getting very far.


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Greg Hullender
post Jan 14 2008, 05:51 PM
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QUOTE (ugordan @ Jan 13 2008, 12:46 PM) *
How can you use Sun in a gravity assist?


You have to do it at night.

--Greg :-)
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Greg Hullender
post Jan 14 2008, 05:55 PM
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QUOTE (cawest @ Jan 13 2008, 10:34 PM) *
when will a "Grand Tour" set be available next?


The 4-planet one (JSUN) is every 176 years, so the next one should be about 2153.

--Greg
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ugordan
post Jan 14 2008, 09:53 PM
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Does anyone know how much heliocentric escape velocity Voyager 2 got off of the 4 flybys (ok, so Neptune flyby wasn't really to pick up speed) as opposed to how much can one get just by a single, aggresive Jupiter flyby (skimming the cloudtops if you will)?


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stevesliva
post Jan 14 2008, 10:14 PM
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There are some more details (and numbers for Ulysses) here:
http://www.niac.usra.edu/files/library/mee...0/393McNutt.pdf

The mission concept on slide 8 describes a retrograde trajectory to Jupiter, followed by a Sun gravity assist involving an yet-to-be-developed propulsion system. Not to mention that there are a lot of other yet-to-be-developed proposed technologies, like the optical communications and Americurium RTG.
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