kilowatt thermionic reactor power plant for unmanned electrical propulsion applications. The total power plant/propulsion unit would weigh approximately 18,000 pounds and would be configured for launch by a Titan III-class booster. Such a system may be suitable for a Jupiter orbiter mission. Brayton Cycle Technology.-The objective of this program is to investigate the performance and life limits of the Brayton cycle for use with either isotope or reactor heat sources. Initially, the program is aimed at developing the technology for a 2-10 KWE space power system which would use an isotope heat source. A combined turboalternator-compressor unit, mounted on gas bearings, has now been operated for 1,014 hours. Startup and shutdown characteristics were determined and performance demonstrated. Other individual components of a power conversion system were also placed in test. The first test of a complete 2-10 KWE power conversion system designed for eventual use with an isotope heat source giving a turbine inlet temperature of 1,600° F. was initiated in the Plum Brook Space Power Facility. In the tests, which used an electrical heat source, 592 hours of running were achieved and a conversion efficiency of 22 percent demonstrated at 1,400° F. turbine inlet temperature. (Fig. 4-2.) Isotope Power.-The SNAP-19 radioisotope thermoelectric generator (RTG) power units on the Nimbus B2 satellite continued to supply useful power 9 months after launch. Performance data are continually being evaluated to provide a basis for design and performance prediction of RTG's for future space missions. The SNAP-27 RTG power supply for the Apollo Lunar Surface Experiment Package (ALSEP) was placed on the moon during the Apollo 12 mission. Performance to date has been as predicted and satisfactory. NASA selected RTG's to be the primary power source for the Pioneer F and G missions and for the Mars Lander of the Viking mission. Arrangements were made to obtain suitable power units through the AEC. Several required experiments to evaluate RTG/ spacecraft interactions in these missions were identified. Programs to define and resolve RTG/spacecraft integration and operational problems and tests of RTG's for stability and long-term reliability were continued. Figure 4-3. SNAP-8 system; endurance hours as of December 31, 1969. SNAP-8 Technology Development.-The objective of the SNAP-8 program is to develop the technology for a 35-50 KWE space power system which will use a nuclear reactor as the heat source. During this period, the boiler and turbine, which in past years experienced major difficulties, successfully completed 10,000 hours of testing, and all major components of the power conversion system have now achieved a demonstrated life of 10,000 hours, with some components reaching 14,000 to 20,000 hours. (Fig. 4-3.) An experimental program to define system startup and shutdown dynamic characteristics was completed, using a breadboarded power conversion system located at the Lewis Research Center. (Fig. 4-4.) Data essential for designing the power conversion system for testing with the reactor were obtained. The Atomic Energy Commission terminated testing of the seconds NAP-8 reactor after 7,000 hours of power operation because the fuel element cracking observed in the test of the first reactor was also occurring in this reactor. The reactor will be opened for an examination to determine the cause of this problem. The Electric Propulsion Program Electric propulsion systems are of interest for difficult auxiliary propulsion missions, such as long-term satellite station keeping, and for many primary propulsion applications, such as those involved in planetary exploration. The development of the technology required for such applications continued to progress. Auxiliary Propulsion.-Cesium contact ion engine experiments were carried on ATS-V (launched August 12), but their operation will depend on whether satisfactory spacecraft performance can be achieved. These engines, designed for satellite east-west station keeping at a thrust level of about 10-5 lbs., were first operated on ATS-IV (20th Semiannual Report, p. 95). North-south station keeping requires a higher thrust level (10-3 lbs). The bombardment ion engine appears best suited for this role because of its economical use of electrical power, and plans were made to include an engine of this type on the ATS-F. (Fig. 4-5.) Following the successful life tests of resistojets described in the 21st Semiannual Report (p. 89), recent space station studies have included the use of such engines in the baseline designs. Initial |