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Posted by: K-P Jan 13 2008, 12:51 PM

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?

Posted by: J.J. Jan 13 2008, 02:57 PM

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.

Posted by: K-P Jan 13 2008, 07:08 PM

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...

Posted by: Greg Hullender Jan 13 2008, 08:01 PM

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

Posted by: stevesliva Jan 13 2008, 08:33 PM

Jupiter-Sun gravity assist can get you going even faster. Of course the flyby will then be extremely brief.

Posted by: ugordan Jan 13 2008, 08:46 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.

Posted by: ngunn Jan 13 2008, 09:09 PM

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.

Posted by: cawest Jan 14 2008, 02:15 AM

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.

Posted by: stevesliva Jan 14 2008, 02:34 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.

Posted by: cawest Jan 14 2008, 06:34 AM

when will a "Grand Tour" set be available next? that would add alot of Dv, like the Voyagers.

Posted by: ugordan Jan 14 2008, 09:18 AM

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.

Posted by: Greg Hullender Jan 14 2008, 05:51 PM

You have to do it at night.

--Greg :-)

Posted by: Greg Hullender Jan 14 2008, 05:55 PM

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

--Greg

Posted by: ugordan Jan 14 2008, 09:53 PM

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)?

Posted by: stevesliva Jan 14 2008, 10:14 PM

There are some more details (and numbers for Ulysses) here:
http://www.niac.usra.edu/files/library/meetings/annual/jun00/393McNutt.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.

Posted by: ugordan Jan 14 2008, 10:28 PM

A 15.4 km/s burn within 15 minutes. Well, that's optimistic to say the least. Currently, you could have either 15 km/s or a 15 minute short burn, but not both. The only thing I can think of right now is a massive (and we're really talking about a MASSIVE) ion engine powered by god knows what. Massive solar arrays lofted all the way to Jupiter to be able to provide enough juice for the 15 minutes of hellish perihelion passage at 4 solar radii?

We'll be seeing nuclear reactors in space probes sooner than this, IMHO.

Posted by: JRehling Jan 14 2008, 10:45 PM

At least solar radiation would not be in short supply at 4 solar radii. I think that, if anywhere, is where the energy would come from.

Posted by: ugordan Jan 14 2008, 11:01 PM

True, but one has to think about how hot the semiconductors in the solar panels can get before dying on you. A quick, back of the envelope calculation gives 64 megawatts of solar radiation per square meter at 4 solar radii. That's running a tad hot.

Posted by: bobik Jan 25 2022, 08:13 AM

Recently, https://iki.cosmos.ru/ researchers have analysed possible https://arxiv.org/ftp/arxiv/papers/2112/2112.13017.pdf for launch in 2029–2034.

Posted by: Antdoghalo Jan 29 2022, 03:10 PM

I like the Neptune flyby one. It gives us an excuse to revisit Neptune along the way while the planets northern summer is beginning allowing mapping of Triton's northern hemisphere. Perhaps we could throw in an imaging encounter with one of the inner moons of Neptune too. Two birds with one stone.

Posted by: StargazeInWonder Jan 29 2022, 10:59 PM

2050 would be about equinox on Triton and would allow mapping of a lot of unseen territory, but note that Neptune's seasons are not the same as Triton's seasons.

https://www.researchgate.net/figure/Variation-of-the-subsolar-latitude-on-Triton-over-time-Triton-experiences-periods-with_fig1_355707178