To Open The Sky
The Front Pages of Christopher P. Winter
Nuclear Thermal Rocket Tests
The NERVA (Nuclear Engines for Rocket Vehicle Applications) program conducted as many as twenty-three engine tests, achieving core power densities of 2kW per cm3 and coolant outlet temperatures of 2,500° C at pressures of 560 psia. Specific-impulse values of around 760 were achieved — twice that of the best chemical engines. Steady progress was made in engine efficiency and controllability, and in lowering the release of radioactivity. The XE-prime, the last engine in the series, was tested under simulated space conditions. It operated for a total of three hours 48 minutes (11 minutes at full power), starting and stopping 28 times. The table below, based on a page at the Web site of the Federation of American Scientists, provides sketchy information on these tests.
The NERVA program struggled with two major problems. The first was cracking of the ceramic fuel elements due to vibration. This was solved by redesigned engines that reduced vibration levels. The second was release of uranium into the exhaust stream caused by erosion of the fuel-element coatings and diffusion of uranium through them. At program termination, this contamination problem had been reduced but not eliminated.
TO PROBE FURTHER