Onwards to Uranus and Neptune! Options

[Holder of the Tw...]

Don't forget one other possiblility, aerocapture followed by a satellite swingby to raise the periapsis. In Neptune's case you might be able to use Triton. For Uranus, well... probably not.

[tedstryk]

Don't forget one other possiblility, aerocapture followed by a satellite swingby to raise the periapsis. In Neptune's case you might be able to use Triton. For Uranus, well... probably not.

A problem with that is that the uncertainties concerning Neptune's atmosphere translate to a very uncertain trajectory. It would be very hard to pass close enough to Triton to get the desired effect without risking lithobreaking.

[Holder of the Tw...]

There are various ways to address that problem. Observations of stellar occultations of Uranus and Neptune can help refine the models of their upper atmospheres. This is especially true of space based observations where you can observe a broader range of the spectrum, plus less noise in the signal.

Then there is the heatshield. The manned Gemini and Apollo capsules had off-center shields that allowed for some adjustment and piloting of the trajectory during entry. The same principle can be applied to aerocapture. With a sensitive enough inertial guidence system and enough built-in intelligence, the craft could fly its way through the upper atmosphere to the proper outcome for orbital speed and direction (within a reasonable initial approach, of course).

Finally, the craft doesn't have to immediately aim for Triton on the way out. The orbit would be a long loop outward that could have a period of maybe half a year. Such an orbit would be very sensitive at apoapsis to small adjustments leading to large changes in targeting later on, putting Triton well within range. On the way back to Neptune you make a close pass to the moon and ... there you go. It might be possible to "flatten out" the orbit, lowering apoapsis and raising the periapsis at the same time.

Plus, I don't think it really would take all that much fuel at apoapsis to raise the orbit out of the atmosphere, so a satellite flyby might not be all that necessary to save the spacecraft (highly desirable, though, to reduce the period).

[tasp]

There is a thread here somewhere (sorry don't have time to check right now) about aerobraking at Triton. As I recall, the scale height of that atmosphere is useful for the technique, and having an orbit about Neptune with your low point at the height of Triton's orbit might be handy.

[Juramike]

There is a thread here somewhere (sorry don't have time to check right now) about aerobraking at Triton. As I recall, the scale height of that atmosphere is useful for the technique, and having an orbit about Neptune with your low point at the height of Triton's orbit might be handy.

Uhhh, wait a minute, are you recommending to use Triton's atmosphere for aerobraking?

[Floyd]

tsp my be confused. Two earlier post were talking about Neptune aerocapture and swingby of Triton to raise periapsis--while avoiding lithobreaking.

[tasp]

Here it is.

[Gsnorgathon]

Would it be possible to use an atmosphere probe to get enough info to mitigate the risks of aerocapture? It seems you'd want to have an atmosphere probe along for the ride anyway.

(And btw - isn't it lithobraking, rather than breaking? Though I guess both ultimately amount to the same thing... (and in Triton's case, wouldn't it be cryobraking? (And if you cried when your probe cryobraked and cryobroke, would anyone be so cruel as to call you a cryobaby?)))

[Greg Hullender]

I always assumed that "lithobreaking" was a deliberate joke. I prefer to call it "impact." :-)

--Greg

[tedstryk]

I always assumed that "lithobreaking" was a deliberate joke. I prefer to call it "impact." :-)

--Greg

Yes, you assumed correctly. The "break" instead of "brak" was a tongue-in-cheek reference to what happens when one hits the lithosphere.

[Juramike]

Would it be possible to use an atmosphere probe to get enough info to mitigate the risks of aerocapture? It seems you'd want to have an atmosphere probe along for the ride anyway.

You'd want the atmospheric probe to return data well before trying an aerocapture. You'd need the parameters well in advance to plan and design for how much fuel to carry for the retro-burn, the ballute design, etc..

Atmospheric probes might make the next Neptune mission aerocapture possible, but not the first one.

[briv1016]

In conjunction with the Decadal Survey, the "Giant Planets Panel" had a study performed in regards to a Neptune Orbiter/Flyby/Probe.

http://www.spacepolicyonline.com/pages/ima...0NeptuneRMA.pdf

[Drkskywxlt]

In conjunction with the Decadal Survey, the "Giant Planets Panel" had a study performed in regards to a Neptune Orbiter/Flyby/Probe.

http://www.spacepolicyonline.com/pages/ima...0NeptuneRMA.pdf

Unless something changed, this study also had a recommendation and co-sponsorship from the Satellites Panel due to the likely high emphasis on Triton science.

[vjkane]

Unless something changed, this study also had a recommendation and co-sponsorship from the Satellites Panel due to the likely high emphasis on Triton science.

This assessment was commissioned as part of the first wave of mission assessments selected prior to the science community input. (See http://futureplanets.blogspot.com/2009/11/...ssessments.html). My understanding is that there will be several tens (low tens?) of rapid mission assessments and around a dozen full mission architectures and costings.

What I found interesting in this Neptune/Triton assessment was that the cheapest orbiter mission is probably about $1.5-2B, while the more capable missions are in the $3+B range. (Scaling from a New Frontiers flyby cost factor.) This suggests that there is an intermediate class of missions possible between flybys and full Flagship missions.

Fitting an intermediate mission into a $12B decadal budget with a moderate Mars program and JEO, however, would be difficult.

[Greg Hullender]

I'm just absorbing the fact that a 14-year mission launched in 2035 (the latest date mentioned) would enter its extended mission just after I turn 90.

--Greg