Back to the Moon with Nuclear Rockets

This joint study came up with advanced fuel designs, suchas "twisted ribbon" fuel elements, which could be adjusted accordingto the desired exhaust temperature. The proposed enginewas designed for a specific impulse of 940 to 960 seconds,about double that of today's advanced liquid hydrogenchemical engines. Reactor tests at Semipalatinsk demonstratedhydrogen propellant exhaust temperatures of 3,100 K for morethan 1 hour, and 2,000 K for 2,000 hours.In 1993, the U.S. participants in the program suggestedthat a joint effort would bring significant benefits to all thecountries involved. Using the existing CIS test facilities wouldmean that the United States would not have to spend timeand resources to duplicate them. The economic situation ofthe Russian and other CIS scientists and engineers would beimproved, and their expertise put to good use. By the end ofthe Bush administration, however, it was clear that neitherthe White House nor the Congress was willing to pay for anyFigure 4AUGMENTING THE NUCLEAR ENGINE WITH OXYGENThe Borowski team has also developed a "trimodal" design for the nuclear tl ermal rocket,which introduces liquid oxygen (LOX) into the flow stream of the supersonic hydrogen exitingthe nozzle, to increase the thrust and flexibility of the engine. The hydn >gen and oxygencombust spontaneously.In the liquid-oxygen-augmented nuclear thermal rocket design, an increas ng amount ofoxygen added to the lighter hydrogen exhaust stream will increase the thrust of the engine,by increasing the mass of the exhaust. At the same time, however, it reduces t le specific impulseof the system, by slowing down the exhaust.The table demonstrates that while the specific impulse decreases by abc uf 45 percent,from about 940 to 515 seconds, if the ratio of oxygen/hydrogen is 7.0, the er gine thrust-toweightratio increases by nearly 440 percent. This increased thrust through o> ygen augmentation,Dr. Borowski states, means that "big engine" performance can be obtained withsmall nuclear engines.visionary manr ed space program, and the nuclear propulsionresearch was a >ain put on a back burner.Despite this situation, a team of experts led by Dr. StanleyBorowski from NASA Lewis Research Center, wanted to ensurethat whei the nation made the decision to go back tothe Moon, nuclear propulsion would be seriously considered,because it is far superior to chemical propulsion or tovarious low-th ust options that are less attractive for mannedspace travel. Over the past five years, Borowski's team hasgreatly extendi d the capabilities of the CIS Nuclear ThermalRocket design.Every space ;raft in operation today, whether manned ornot, requires .in on-board electricity supply to power theelectronics, co nputers, and scientific instruments for the mission.In the ca< 2 of the Space Shuttle, chemical fuel cells providethis energ r, which is required not only for spacecraft operationsbut also for life support. Spacecraft with longermission times in Earth orbit,such as the RussianMir space station, the InternationalSpace Station,commercial communicationsand other satellites,and near-Earth scientificsatellites carry large solararrays that convert solarenergy into electricity.Outer Solar System roboticspace probes, suchas the Galileo spacecraftwhich is orbiting Jupiter,or the Cassini spacecrafton its way to Saturn, carrya few pounds of radioactiveisotopes which produceheat as they decay,and this energy can beconverted to very smallamounts of electricity, adequateto power the instrumentson board. But if nuclearenergy is used as thepropulsion system of tomorrow'slunar vehicles, aready supply of electricityfor use on board can beproduced from the samereactor that is poweringthe engines.Borowski suggests thatthe nuclear-powered submarine,in which the reactorheat produces highpressuresteam to driveturbines for the ships propellerand turbines thatproduce all of the ship'selectricity, is a good modelfor extending the duty ofthe nuclear reactor on a21stCENTUR> Summer 1999 59