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Hybrid small fission reactor pressurized Xenon capsule as ion powered NEP stage; a NASA 2015 SBIR proposal

March 26, 2014

 Hybrid small fission reactor pressurized Argon/Helium (or Xenon)capsule as ion powered stage; a NASA 2015 SBIR proposal

based on this link,

and this link

hypothesis ,

The SpaceX Dragon capsule pressure vessel with a known volume must have a known surface area, with a known volume surface area and a known  M2 we can compute the gas law for the Dragon capsule with an Argon/Helium atmosphere and a small fission reactor radiator of 2.4 meter length at 250 C

We do not know what the ATM(pressure)  of the Dragon capsule would be with the small fission reactor radiator or its energy translation to the Dragon capsule Stirling engine would be but gas law should allow for this and the black body heat to the Dragon capsules hull and its subsequent escape to space.

Many small fission reactor studies show that 10% of thermal heat becomes electricity and one study  shows that more than half of the heat escapes through the small fission reactor through its radiator. I am thinking that a pressurized capsule that captures the radiators heat might improve this by an order of magnitude.

This may not be a good enough argument for two Dragon capsules docked to one another serving as a deep space probe SEP stage do to weight.

We hope in future to form a team to flesh out the gas law, heat translation to the spaceX Dragon hull and to the secondary Stirling engines

Small fission reactor and the pressurized capsule both power  Ion powered SEP stage, the capsules trunk or service module doubles as a planetary probes SEP stage.

CON OPS, Trades,

possibly the stage and the capsule are pressurized with Xenon.

small fission reactor

electrical power from thermocouples (think RTG’s)

electrical power from small fission reactor stirling engines using fluids internal to reactor( see studies)

waste heat from small fission reactor radiator to capsule pressure vessel atmosphere using Gas Law,

capsule pressure vessel  heated atmosphere powers  secondary stirling engines

electrical power to trunk or service module that contains SEP Ion engines

remaining heat in capsule Argon/Helium atmosphere radiates out to space through capsule skin

as fission power system ages and cools Xenon pressurized capsule uses xenon as SEP fuel (less need for Xenon as coolant/heat sink)

service module/trunk shields reactor from science payload and avionics


service module/trunk separates with first capsule  retains reactor, science payload flys on,

service module/trunk separates with radiator, science payload with reactor flys on( reactor powers down to support science only)***

*** implies that second capsule is the science payload heading to deep space

Second capsule may be the with a heat shield  capable of aerobraking to its planetary destination/


  Centaur/Delta upper stage/DUUS/ACES duel chemical Ion powered  hybrid small fission power in space stage


In space stage performs injection burn with LH2 and O2,use IVF thrusters and fuel cells to deplete remaining fuel.pressurized in space stage with Xenon in both tanks.Small fission reactor and radiator are housed inside LH2 and O2 tanks.small fisson reactor produces power in three ways, thermocouples,stirling engines and a second set of stirling engines in between the Xenon tanks. the second set of stirling engines uses heated xenon from the radiator “waste heat”

In space stage uses Xenon in tanks surrounding the reactor(shielding) to power ion engines after chemical engine cut off.We think a centaur small fission reactor ion power stage would be too heavy without the chemical boost phase

A large massive small fission reactor ion power in space stage makes since if it is in powered flight in the outer solar system for extended periods and/or it serves as a power plant after powered flight.It is helpful to retract the RL-10 engine aft skirt or engine nozzle to enable ion engine operations.

What needs to be done;

(A) model small fission reactor weight and waste heat to Xenon tanks with Gas law

(B) model Xenon heat to interior surface area of in space stage tanks and loss to space with black body radiation law

(C)we need to model stirling engines in between the two Xenon tanks as one tank will be hotter than the other!

(D) the radiator will displace LO2 so we need to stretch the LO2 tank



A Small Fission Power System for NASA Planetary Science Missions NASA TM-2011-217099 – 1Dec11 25pp 20120000789_2012000894

We know the values for the radiator heat rejection for various small fission reactors

or Brayton  systems with Helium/Argon mix




We do not know volumes for in space stages or the surface areas of the LH2 and O2 tanks for the exiting or proposed upper stages and in space stages please help!


some Centaur tank volumes in this dated paper,


We still need tank surface areas to possibly compute heat loss with a heated pressurized Xenon atmosphere


this concept would work with in space stages docked to capsules or cargo vehicles  re purposed as science/planetary probes.


Edit April 2014,


quote ,

”   LH2 volume ~1,700 ft3

LO2 volume ~600 ft3


The Centaur tank sidewall is ~25 ft long and 10 ft in diameter.  You can calculate the area from this.


We fly SOFI on the sidewall on all missions for insulation.  Some missions also have MLI.

End Quote









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