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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
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© 2017 - 2021 William-Black
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NyrathWiz's avatar
Another masterpiece William! And I find your logic for lengthening the standoff of the GCNR to be impeccable. 
William-Black's avatar
Thanks Winchell,

A hundred meter truss and shadow shield friendly radiator configuration goes a long way toward addressing the re radiation, radiation embrittlement and neutron activation damage which would result from this configuration. Exactly the reasoning behind my design modifications evident across the entire series of previous posts. I think the cherry on the Sunday will be a radiation simulation showing the extent of re radiation this configuration would suffer, so that's on the schedule.
Centurion030's avatar
THAT would be nice-looking forward to it...
question - would the radiators directly beside the reactor not catch a lot of supplemental heating via neutrons? neutron enbrittlement might also be factor to think about
William-Black's avatar
Winchell Chung is spot on in his comment below. The points you raise are the matters of concern I saw in this design, and that is why I modified the design, as can be seen here
Mars Courier Mission, Earth-Orbit Escape Burn With Radiator SFX. As I state in the text above, and as is evident in all the previous linked posts, my design modifications explicitly address exactly the points you raise, adding a hundred meter truss and changing radiator geometry to fit within the shadow cone thrown by a properly positioned and scaled shadow shield fully mitigates those issues. 
NyrathWiz's avatar
Agricola64, I'd say Yes, neutron heating, neutron embrittlement, and neutron activation. Not to mention scattering the radiation around the shadow shield onto the crew module. All of which William is well aware of (as shown in his  Earth Orbit Escape Burn).

But that's how the NASA document showed radiator placement on this spacecraft, so that's how William modeled it. 
Centurion030's avatar
Nicely done as always! So, the command module is in between things?
NyrathWiz's avatar
Yes, according to the source technical report, all the propellant tanks will be discarded as they are emptied. Except for the last one.
For ease of jettisoning, the disposables are mounted forwards of the command module.
Centurion030's avatar
Thanks much!!!!!!!!!!!!!!!
doktorno's avatar
I remember seeing that design in magazine, that my father got in the 1970's :)…

During the Cold War the US government was publishing glossy magazines for Eastern Block countries to show the best things about USA, and among them was the quarterly (?) publication called "Ameryka", and it had a special issue about the future of space exploration.
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