Onwards to Uranus and Neptune! Options

[ugordan]

I believe trajectory search and optimization software nowadays uses Keplerian orbits and patched conics to find plausible/optimum trajectories (and things like impact parameter or miss distance during flybys) and then when a "conceptual" trajectory is selected, it's precisely worked out by numerical integration and taking into accounts other factors such as solar light pressure, etc. That last part might be iterative and computationally more expensive, but it's all within reach of modern computers.

[JRehling]

[...]

[simonbp]

This has got me thinking about if you could pull off a Uranus/Neptune Orbiter for less than $850 million...

Aerocapture is obviously the way to go, and the Titan Explorer orbiter seems a good place to start. It masses ~1800 kg wet, while the cruise stage ~1500 kg, mainly fuel. If we drop the balloon and lander, we cut out roughly 2/3 the mass of the cruise stage, giving a payload mass of ~2300 kg. That's about half the mass of TE. The option then is either to use a low-end EELV (Atlas 401, Delta IV sans SRBs, or Falcon 9) for a single launch (more likely), or launch two spacecraft (one Neptune, one Uranus) on an Atlas 551 (much more cost effective, but less likely).

The point is, I don't think it's a given that a ice giant orbiter has to a ridiculously expensive Battlestar Galactica style mission like Cassini. It's just like Mars Sample Return; if you're willing to use new technology (aerocapture and ASTG in this case) and make compromises, you can turn a perpetually paper mission into reality...

Simon

[cawest]

There is the opportunity, brought up in another thread, for a Jupiter > Saturn > Neptune tour with launch opportunities 2016-1018. It could then go on to visit one or more KBOs. A presentation on this opportunity as a New Frontiers candidate was made to a group reviewing the program in November, I think.

An ideal mission would drop a probe into the Saturn atmosphere as well as Neptune. It would also do a close fly-by of Triton. Don't know if the orbital mechanics will allow this and still do the probe relay.

This had me thinking... why can we not have three droppers, one at each? This would make an orbit of Neptune cheaper. How do you ask.. if you drop of a probe into Jupiter, Saturn, and before you make Neptune orbit you have less mass to slow down. what do you all think?

[ugordan]

you have less mass to slow down.

What about mass you actually need to launch? Does it go down as well?

[tasp]

This has got me thinking about if you could pull off a Uranus/Neptune Orbiter for less than $850 million...

Simon

Not to put you off of working through cost savings for interesting mission concepts, but my ideas for a 'cheap' Neptune orbiter were pretty thoroughly discredited and chewed up here a while back . . .

[Greg Hullender]

I think the problem with launching a Neptune and Uranus probe in the same rocket is that the next obvious launch window for that is about 80 years away.

Of course, gravitational assists are complicated beasts; there could well be some complicated sequence that managed to split them up at the right point and get them both to the right places, but it'd be a wonder to behold.

--Greg

[JRehling]

[...]

[Greg Hullender]

I thought about that, but I think the trouble is that one of the two is going to get a pretty lousy gravitational assist, and given the distances involved, that seemed like a loser -- and maybe not even enough delta-V to get both to their targets.

And, as you say, every year it gets worse.

--Greg

[cawest]

What about mass you actually need to launch? Does it go down as well?

it would be less fuel mass to launch than a reguler orbiter.

[Greg Hullender]

How does that follow? You'd clearly have less mass to launch if you didn't drop anything at the earlier planets.

--Greg

[simonbp]

Well then drop the second vehicle and fly the one with a faster trajectory. Point is, I still think it's possible to build a very capable New Frontiers-class Neptune Orbiter...

Simon

[Greg Hullender]

I hear you. I'd love to see a serious proposal. Say, starting with $90 M for a Falcon 9 Heavy to put 12 tons in GTO. What can you do with 12 tons in GTO with about $800M to spend on it? And, assuming no other never-before-flown technology.

--Greg

[Big_Gazza]

$90 M for a Falcon 9 Heavy to put 12 tons in GTO.

Sorry, but i'll believe it only when I see it fly. And even if it ever does, it'll cost way more than 90M.

[Greg Hullender]

Sorry, but i'll believe it only when I see it fly. And even if it ever does, it'll cost way more than 90M.

Good points, but my question is "taking Falcon 9 Heavy on faith -- but nothing else, does that change the picture? That is, is the launch vehicle cost the only thing that keeps us from having a New Horizons-class Uranus or Neptune orbiter?"

--Greg