NASA TM X-67823 Gas-Core Rocket Diagram

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This is the preliminary design for a Gas-Core Open-Cycle nuclear thermal rocket from NASA TM X-67823 Gas Core Rocket Reactors-A New Look. I posted an artistic render of this spacecraft a few days ago, here The R.A. Heinlein.


This design was the basis for the radiator cooled Gas Core Rocket presented in my gallery here Earth Orbit Escape Burn. Obvious differences are the lack of a lengthy structural truss and rectangular rather than triangular radiator panels.

My previous Gas-Core rocket incorporated data from NASA TM X-67927 Crew Radiation Dose From The Plume of A High Impulse Gas-Core Nuclear Rocket During A Mars Mission which set out guidelines for  a crew/nozzle separation distance between 100 and 200 meters.

This is the spacecraft as initially envisioned. How does this compare to my modified design in terms of radiation hazard? The main difference is my modified design has the command module at 200 meters from the gas core reactor, effectively cutting the radiation dose in half.

Going from the stated size of the rectangular panels in the study 51.5 meters (168 feet) in length, the command module in this design is just about 102.96 meters (337 feet) from the nozzle of the gas core rocket, just over the minimum safe distance. However the radiator panels are far outboard, arrayed around the nozzle and directly exposed to the highly radioactive plume. The shadow shield in this design is positioned inside the hull at about the position of the aft reaction control thrusters. The radiators would certainly reflect radiation from the reactor far forward along the hull. Considering that the command module is completely fared in, I would imagine the radiation hazard could be mitigated by embedding the command module in a thick shell of 5% Borated Polyethylene.

Data for 5% Borated Polyethylene Neutron Radiation Shielding can be found here DEQ Tech Scroll down at the link.

Hydrogen Atom Density/cm^3: 7.5 x 10^22
Natural Isotope Distribution: 99.98% 1H
Boron Atom Density/cm^3: 3.0 x 10^21

Total Density: 1.08 g/cm^3 (67 lb/ft^3)

Radiation Properties:
Macroscopic Thermal Neutron Cross Section: 2.00 (cm^-1)                        
Gamma Resistance: 5 x 10^8 rad
Neutron Resistance: 2.5 x 10^17 n/cm^2

Fast Mars Round Trips

The Mars round-trip mission performance of the radiator-GCNR system is compared to that of several alternative engine concepts in NASA TM X-67823, see Fig. 8 in the linked PDF. Initial mass in Earth orbit (IMEO), a rough measure of initial cost, is plotted against the round-trip mission time. The radiator GCNR is compared to a SCNR (solid core nuclear rocket) and higher mass/lower delta-v GCNR missions and to a theoretical low-thrust/high isp fusion propulsion system.

In "Courier" mode all the available mission time is used for Earth-Mars transits. The 80 day Mars courier mission would require about 3,350 kg of uranium and 670,000 kg of hydrogen. These amount to about 3/4 of the 900,000 kg IMEO.

The radiator gas core rocket is based on NASA TM X-2772, a preliminary design study of a 6,000 megawatt open-cycle gas-core nuclear rocket engine. The engine has a thrust of 196,600 newtons (44,200 Lbs) and a specific impulse of 4400 seconds. The nuclear fuel is enriched uranium-235 and the propellant is hydrogen.

The courier mission spacecraft is comprised of a command module, payload, jettisonable liquid hydrogen tankage, and interconnecting structure. The GCNR provides the four burns required – Earth-orbit escape, Mars-orbit capture, Mars-orbit escape and Earth-orbit capture at mission’s end. The core vehicle comprising the GCNR engine, its uranium storage and supply system, the command module, and part of the hydrogen tankage, is recovered in Earth orbit to be refurbished and reused.

The spacecraft departs from, and the core vehicle returns, to a 600 mile apogee parking orbit.

Related Art

The R.A. Heinlein

Open-Cycle Gas-Core Nuclear Thermal Rocket

Mars Courier Mission, Earth-Orbit Escape Burn With Radiator SFX

Mars Courier Mission, Earth-Orbit Escape Burn

Mars Courier Mission, Earth-Escape Tank Jettison

Open Cycle Gas Core Nuclear Thermal Rocket

Radiation Design by CG Modeling

Gas Core Rocket New Radiation Simulation