[en] The light-weight radioisotope heater unit (LWRHU) is a ²³⁸PuO₂-fueled heat source designed to provide one thermal watt in each of various locations on a spacecraft. Los Alamos National Laboratory designed, fabricated, and safety tested the LWRHU. The heat source consists of a hot-pressed ²³⁸PuO₂ fuel pellet, a Pt-30Rh vented capsule, a pyrolytic graphite insulator, and a fineweave-pierced fabric graphite aeroshell assembly. To compare the performance of the LWRHUs fabricated for the Cassini mission with the performance of those fabricated for the Galileo mission, and to determine a failure threshold, two types of impact tests were conducted. A post-reentry impact test was performed on one of 180 flight-quality units produced for the Cassini mission and a series of sequential impact tests using simulant-fueled LWRHU capsules were conducted respectively. The results showed that deformation and fuel containment of the impacted Cassini LWRHU was similar to that of a previously tested Galileo LWRHU. Both units sustained minimal deformation of the aeroshell and fueled capsule; the fuel was entirely contained by the platinum capsule. Sequential impacting, in both end-on and side-on orientations, resulted in increased damage with each subsequent impact. Sequential impacting of the LWRHU appears to result in slightly greater damage than a single impact at the final impact velocity of 50 m/s

[en] The question of failures leading to abortions of space missions is of importance in terms of financial and scientific expenditures. However, if nuclear devices such as power sources of satellites are involved and re-entries are to be envisaged, these failures will become a matter of safety, too. The results found are that abortive mission failures lay in the range of 10% probability. A break down of accessible event data provides a sound basis for these results. The more complex question of safety can only be touched here. (orig.)

[en] Using parameters for unclassified astronomical observatories based on Maui and on the Kuiper Airborne Observatory, we have determined the level of confidence of monitoring a ban on nuclear power in earth orbit. Existing military and astronomical observatories can detect and identify operating nuclear power sources on satellites, such as the Soviet RORSAT and American SP100, with a very high level of confidence to distances beyond geosynchronous orbit. A cold reactor can be detected with a medium level of confidence with visual observations by close-flying reconnaissance satellites with medium confidence, and in the future with very high confidence with the interrogation of neutrons. The smaller thermal sources, RTG and DIPS, could be detected with medium level of confidence under certain conditions. Large pulsed reactors can be detected with a medium confidence level with visual observations from close satellites, and with a very high level of confidence with neutron interrogation

[en] The General Purpose Heat Source - Radioisotope Thermoelectric Generator (GPHS-RTG)- was designed and built by General Electric under the sponsorship of the Department of Energy, Office of Special Nuclear Projects, to power both the Galileo and Ulysses spacecraft. Separate STS launches of these two spacecraft were planned for May, l986, but have now been delayed. Galileo will carry two RTGs, providing over 5l0 watts of electrical power at the end of a 4.2 year mission, and Ulysses' single RTG will provide over 250 watts of electrical power at the end of a 4.7 year mission. These power levels and mission durations may differ for delayed launch schedules. To ensure that the GPHS-RTG is qualified for the Galileo and Ulysses missions, a formal program, consisting of extensive analyses, inspections, demonstrations, and tests, was conducted. Requirements for qualification included such categories as electrical performance, life characteristics, dynamic capability, thermal characteristics, active cooling system performance, magnetic properties, nuclear criticality, gas management provisions, electrostatic cleanliness, mass properties, neutron emission rate, and micrometeoroid survivability. This paper addresses selected topics from this list and presents data to show that anticipated performance will meet or exceed design requirements as specified for a May, l986 launch

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[en] The Viking-75 mission utilized the August/September 1975 opportunity to launch two spacecrafts to Mars for arrival in 1976 after about a one-year transit period. On arrival, each spacecraft, consisting of an orbiter and lander, will be placed in Mars orbit, with each lander subsequently descending from orbit to a soft-landing on the Martian surface. Two SNAP 19 RTG's (radioisotope thermoelectric generators) provide the primary source of electrical power and means of thermal control for each Viking lander. The RTG's will be switched on-load just prior to separation of the lander from the orbiter for checkout of the lander, and will remain on-load during entry and the remainder of the 90-day minimum surface mission

[en] The successful utilization of a radioisotope thermoelectric generator (RTG) as the power source for spaceflight missions requires that the performance of such an RTG be predictable throughout the mission. Several mechanisms occur within the generator which tend to degrade the performance as a function of operating time. The impact which these mechanisms have on the available output power of an RTG depends primarily on such factors as time, temperture and self-limiting effects. The relative magnitudes, rates and temperature dependency of these various degradation mechanisms have been investigated separately by coupon experiments as well as 4-couple and 18-couple module experiments. This paper discusses the different individual mechanisms and summarizes their combined influence on the performance of an RTG. Also presented as part of the RTG long-term performance characteristics is the sensitivity of the available RTG output power to variations of the individual degradation mechanisms thus identifying the areas of greatest concern for a successful long-term mission