Discussion Uranus and Neptune mission concepts

[DaveS]

I had a chance to see Galileo, Magellan, and a little of Cassini not only in orbit but Deployed from the shuttle with both the IUS and Centaur.

Cassini? That is a big NO-GO as it is way too heavy. Galileo was the max on the lightest orbiter in the fleet running the engines at 109% (Full Power Level, FPL).

Alone Cassini's propellant mass at launch was more than Galileo total.

 

[barrygolden]

Yes David your right about the weight but it looked pretty cool on a centaur. Maybe if they used those new SRBs it might have been closer

 

[Nicholander]

On an unrelated note, I just had an idea on how you could fix the RTG radiation problem: You can put 2 small holes (That needless to say, can be closed.) in the aeroshell where during cruise the RTGs can extend out of, so they aren't as close to the spacecraft. And before aerocapture they are then retracted, the holes closed and aerocapture starts. After the braking maneuver (I'm assuming the aeroshell is detached after aerocapture) the RTGs are simply extended, as the shield has been separated, so no need for any holes to be opened.

 

[K_Jameson]

This is a clever idea, although implies some sort of mechanical complication of the aeroshell design. I can suppose that, after seven and a half years of flight, problems in the hermetic closure of the "holes" during the aerocapture can emerge. The expected approach velocity to the Neptune atmosphere is nearly 31 km/sec, the heat environment very severe and even a small leak can be fatal. Obviously, if the holes are in the aft of the spacecraft, a less critical area, the problem is in part bypassed.

After some lecture of a long and exhaustive document about a similar design (the link is somewhere in this topic), i'm convinced myself that the problem of the RTG heating can be solved with an active cooling system with external radiators. I have the need to shift outside as many component as possible, to reduce the dimensions of the aeroshell and thus the overall weight of the spacecraft (the aeroshell is the heaviest component), so my idea could look like this:



At the front, the aeroshell, divided in heat shield (bottom), upper shield (up) and backshell. The spacecraft is enclosed in the aeroshell, that is about 2.2 meters long.

At rear, a hollow cylindrical cruise stage, with the radiators for the RTG cooling and all the equipments for the cruise (star trackers, sun sensors, low and medium gain antennas for the ordinary telemetry).

The cruise stage is detached minutes before the entry interface; after the aerocapture, the aeroshell opens and the probe is released, proceeding for the subsequent orbital maneuvres (perapsis raising, apoapsis adjustment).

---------- Post added 04-01-15 at 09:41 AM ---------- Previous post was 03-31-15 at 07:07 PM ----------

This is the full document:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20060012088.pdf

Look at the pag. 26 for the thermal problem.

 

[K_Jameson]

Regarding the launch and the launch vehicle.
I found another good launch window, Feb-23-2031, that requires only 6.71 km/s for Earth departure instead 7,34 km/s.
This value could enable, altough very narrowly, a launch with the Eridanus spaceplane, using a kick stage that currently don't exist but can be obtained from the Jarvis C third stage, that was already designed with in mind the possibility of an adaption for Eridanus in the same fashion of the Shuttle-Centaur project (Eridanus-Jarvis?).

I know that the rationale for this choice is only the coolness factor... ;-) If the reason and the realism will prevail, the spacecraft will be launched on the Jarvis C unmanned rocket...

This new launch window has the problem of a Jupiter flyby at some 5 radii, that is in well inside the deadly radiation belts...

 

[Nicholander]

Well, how much radiation would the spacecraft get during the Jovian flyby exactly? And what would be that amount of radiation's effects?

 

[K_Jameson]

The dosage for a single, high speed pass within the radiation belts, although significant, should not be a great problem and I think that the aeroshell can act as a sort of "vault" for the main electronics. Surely the radiation absorbed in the quick Jupiter flyby will be superior to the dosage expected in the entire Neptune/Triton mission.

For comparison, Shakespeare/Pope will pass at over 32 jovian radii, that is well beyond the Callisto orbit and the Jupiter radiation belts.

 

[K_Jameson]

Some Easter work.
Conceptual mock-up of the "Trieste" spacecraft in navigation configuration, showing the cruise stage and the aeroshell. The cruise stage features various equipments: four RTG radiators, a 0.5 meters steerable high gain antenna, a backup horn-type medium gain antenna, two low gain antennas, two foward-looking navigation and approach cameras, a sun sensor, star trackers.





Despite the appearances, Trieste is a rather small spacecraft, only 3.6 meters long with the cruise stage. The aeroshell is 2.53 x 1.52 x 1.12 meters. Included Hatsune Miku for scale reference (Pipcard, i couldn't resist!).



Current best estimate of the total weight is around 1450 kg (can be obviously subject at change).

---------- Post added at 10:11 PM ---------- Previous post was at 09:52 PM ----------

The spacecraft mated with the Jarvis upper stage. The kick-stage employed in case of an Eridanus launch will be shorter and with various other modifications for allowing insertion in the cargo bay.

 

[K_Jameson]

Progress on the Neptune/Triton orbiter. Folded configuration with external aeroshell in transparence.



Being a very small spacecraft, the science package will be somewhat minimal, even in comparison with the Shakespeare/Pope spacecraft. Most of the instruments (NAC, WAC and a compact IR/UV spectrograph) are placed on a pivoting platform.

 

[K_Jameson]

Despite personal problems, I'm trying to maintain some momentum on these projects, altough only on a conceptual level, for now...
My efforts to rescale the aeroshell for allow an Eridanus launch has produced, ultimately, a spacecraft with no physical room for all the instruments I want. Even a minimal science package, New Horizons class, is difficult to fit in a such small vehicle. I'm thinking to rescale the entire spacecraft 1.5 times to allow a more substantial science package, at the cost of more weight, that definitely will preclude every attempt of an Eridanus launch.
Thus, the workhorse Jarvis C is back in game. The unmanned launcher has exactly the required performances.

A new idea for the spacecraft's name is NEXT-Trieste. "NEXT" stands for Neptune Triton EXperimental EXplorer.
The name "Trieste" is explained above in this topic.