Zubrin’s Pioneer Astronautics Selected for NASA Grant to Develop Radiator-free Engine

by Douglas Messier
Managing Editor

Bob Zubrin’s Pioneer Astronautics has been selected for a NASA Small Business Innovation Research (SBIR) award to develop a radiator-free engine (RFE) that could be used in nuclear electric and solar thermal electric propulsion systems.

“In the RFE, cold water propellant or hydrogen used as the heat rejection dump for a dynamic cycle heated by a nuclear reactor, enabling Carnot efficiencies as high as 0.79 for water or 0.99 for hydrogen,” the proposal’s technical abstract said. “Some of the propellant that is boiled or sublimated off is then sent to an electric propulsion system, which ejects it from the spacecraft at high velocities to produce thrust….

“The Radiator Free Engine (RFE) enables very high power to mass ratio NEP and solar thermal electric propulsion. RFE systems could be used to transport payloads from LEO to the Deep Space Gateway. RFE systems could use water as propellant, enabling the Artemis Moonbase to support both cis-lunar and interplanetary transportation,” the abstract said.

“RFEs could enable fast trips between Earth and Mars. RFE reactor systems could also be used to supply power on surface of the Moon, Mars, and Titan. RFE lunar surface vehicles could go into shadowed craters to mine ice,” the abstract added.

The SBIR Phase I award is worth up to $125,000 for six months.

A summary of the proposal follows.

SBIR PHASE 1 AWARD
Amount: up to $125,000
Duration: 6 months

Radiator Free Engine
Subtopic Title: Dynamic Energy Conversion for
Space Nuclear Power and Propulsion

Pioneer Astronautics
Lakewood, CO

Principal Investigator: Robert Zubrin

Estimated Technology Readiness Level (TRL):
Begin: 2
End: 4

Technical Abstract

The Radiator Free Engine (RFE) is a new technology enabling very high power to mass ratio nuclear electric propulsion. In the RFE, cold water propellant or hydrogen used as the heat rejection dump for a dynamic cycle heated by a nuclear reactor, enabling Carnot efficiencies as high as 0.79 for water or 0.99 for hydrogen. Some of the propellant that is boiled or sublimated off is then sent to an electric propulsion system, which ejects it from the spacecraft at high velocities to produce thrust. Potential RFE conversion systems include Brayton, Rankine, and Stirling cycles.

The RFE can be operated in either steady state or in pulsed modes, with the later enabling very high thrust/mass ratios. Potential alternative RFE propellants include nitrogen, methane, CO2, and ammonia stored in either liquid or frozen phases. Because its thermal to electric conversion efficiency is about a factor of 3 higher than conventional NEP systems, and it does not require radiators for heat rejection, the RFE can achieve power to mass ratios an order of magnitude higher than conventional multi megawatt power systems.

Other advantages of the RFE include its ability to use cheap, dense propellants that are plentiful or producible in space. In the proposed program, the potential performance of the RFE will be analyzed, design options compared, technical concerns addressed, and the concept validated by means of computer analysis and laboratory tests.

Potential NASA Applications

The Radiator Free Engine (RFE) enables very high power to mass ratio NEP and solar thermal electric propulsion. RFE systems could be used to transport payloads from LEO to the Deep Space Gateway. RFE systems could use water as propellant, enabling the Artemis Moonbase to support both cis-lunar and interplanetary transportation. RFEs could enable fast trips between Earth and Mars. RFE reactor systems could also be used to supply power on surface of the Moon, Mars, and Titan. RFE lunar surface vehicles could go into shadowed craters to mine ice.

Potential Non-NASA Applications

Solar thermal RFE space transfer vehicles could support LEO to GEO transfer of commercial satellites, and cis-lunar transportation. RFE propulsion would be extremely attractive for asteroid development, since water ice is present on many asteroids. RFE technology could also be used to support high efficiency power generation on Earth.