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!!!

[helvick]

Mars atmosphere is 143 times less efficient in aerobraking then atmosphere of Earth is...

Not really. Despite having only a few millibars surface pressure Mars' atmosphere is denser at high altitudes than the earth's and extends further so it is not any worse than the earth's for orbital aerobraking. The cross over point is at around an altitude of around 70km if I recall correctly and orbiter aerobraking takes place much further out than that. The problems arise for landing craft as the lower density near surface atmosphere leads to much higher terminal velocities. Again I'm just going by recollection here but I think martian terminal velocities are about 5-10x Earth ones so from a lander aerobraking perspective I reckon it would be more accurate to say that Mars was about 10 times less efficient.

Triton's atmosphere does seem to be just too thin to be of much use but it would be worth running some calculations on it to be certain. More on this later when I can find my drag calculations spreadsheet.