Neptune Orbiter, Another proposed mission Options

[Rob Pinnegar]

This seems like a good place to start off the Uranus and Neptune forum: with the next ice-giants mission.

I will admit to not knowing a whole lot about the Neptune Orbiter With Probes (NOWP), other than the fact that it's in the planning stages, and a few other details I've gathered from Wikipedia and various other Internet sources. Anyone care to get this one going with a bit more information?

[dvandorn]

Does Triton *really* have enough of an atmosphere to allow for efficient aerobraking? At least, without a gazillion passes before you're significantly slowed down?

-the other Doug

[Toma B]

Does Triton *really* have enough of an atmosphere to allow for efficient aerobraking?  At least, without a gazillion passes before you're significantly slowed down?

-the other Doug

NO IT DOES NOT!
The atmospheric pressure at Triton's surface is about 15 microbars , 0.000015 times the sea-level surface pressure on Earth...that's not enough for any kind of aerobraking...
Mars has average presure of 7 milibars, that is why MRO will have to spend many months aerobraking and don't forget that it uses only upper parts of atmosphere where presure is much less than that...
The average pressure on the Earth surface (sea level) is 1000 millibars....
In order to use that little atmosphere on Triton for aerobraking our unlucky spaceprobe would have to fly verry,verry,verry dangerously close to surface...
Edit:
Some approximate calculatins based on these facts:
Mars atmosphere is 143 times less efficient in aerobraking then atmosphere of Earth is...
Triton atmosphere is 467 times worst then Mars...
So it would take gazillon passes through it to slow down significantly...
Solution : USE ROCKET ENGINES!!!

[JRehling]

Mars atmosphere is 143 times less efficient in aerobraking then atmosphere of Earth is...
Triton atmosphere is 467 times worst then Mars...
So it would take gazillon passes through it to slow down significantly...

The proposal is certainly complicated, but your calculations are not relevant. Aerobraking would not take place at the surface, but high up, and Triton would have a high scale height. Whereas aerobraking at Earth would involve a short skip through the upper atmosphere, aerobraking at Triton would involve about 1000 km through gas not that much less dense than at Triton's surface.

Of course, if you want a source of gas to really slow down through, Neptune is right next door. The problem is, if aerocapture is used on the way in, the resulting orbit would probably be one that would make it very difficult to later pass through Neptune's atmosphere again -- unless a low peri-neptune were maintained throughout the mission.

A more feasible combo mission might be an orbiter/Triton lander duo. One heatshield for braking in Neptune's atmosphere would be utilized. The craft would be stacked as follows:

Heatshield
Triton lander
Neptune orbiter

On arrival, the stack would aerocapture into a Neptune orbit with peri-neptune very near the cloudtops. The orbit would be highly eccentric, and intersect Triton's, allowing several flybys to perform initial reconnaisance and landing site selection. Then, on one apo-neptune, the orbiter's thruster would point the stack onto a path into Neptune's atmosphere. Then the orbiter would separate, leaving the heatshield on the lander. The lander would decelerate through Neptune's atmosphere, and emerge on an "orbit" that would just barely make it to Triton at apo-Neptune, at a low velocity relative to Triton. Then a ballute system might be able to bring the lander down. The orbiter would continue on indefinitely.

Seems inordinately difficult. Also, I don't see a Triton lander being part of the next mission to that part of the solar system. I'd bet on a Neptune entry probe first.