I have blogged before about NASA and concerns about their supply of radioisotopes used to power spacecraft. NASA has just announced that it will halt work on the Advanced Stirling Radioisotope Generator (ASRG), a new nuclear generator intended for the next generation of space probes. It was intended to replace the Multi-Mission Radioisotope Generator (MMRTG) that has been the power source of the U.S. space exploration program for decades. Basic research and development on the ASRG will be transferred from the U.S. Department of Energy to the Glenn Research Center. Budget constraints were cited by NASA as the reason for the change. NASA will continue to utilize the MMRTG for future probes.
The MMRTGs contains about ten and a half pounds of PU-238 and generates around one hundred and twenty five watts of electricity at the start of its life. The more efficient ASRG uses about two and a half pounds of PU-238 to generate one hundred and forty watts of electricity when first put into service. PU-238 has a half life of eighty seven years. With a projected mission time of about fourteen years, both generators are able to provide needed power for the whole mission. The ASRGs are about four times as efficient as the MMRTGs which means that four times as many probes could be launched for the same amount of PU-238 if the probes were powered by ASRGs.
NASA says they have sufficient plutonium-238 for the near future but it is estimated that NASA only has enough PU-238 for one more big mission which may be the Mars mission planned for 2020. The U.S. is going to restart production of PU -238 which was halted in 1989. However, only two to three pounds of PU -238 will be produced each year. The New Horizon mission to Pluto required about twenty four pounds of PU-238. It would take about ten years to produce that much PU-238 with the current projected production levels. This would mean that big space probes could only be launched about once a decade. NASA had to purchase PU-238 from the Russians for the recent Curiosity Mars mission.
On the other hand, a Jupiter mission slated for 2016 will not have a nuclear power generator on board. Due to the great distance from the sun to Jupiter, three huge solar panels will be used to power the probe. Without nuclear power generators, U.S. exploration of the outer solar system will be impossible. This may prevent the Europa mission or the Titan lander mission from being carried out.
Only the U.S. space program has launched missions to the outer solar system. Unless something changes, it is likely that missions to the outer solar system will be few and far between. This would be a serious blow to the exploration of the solar system. If you care about the U.S. space program, write to your Congressmen and the President urging the production of more PU-238 and the resurrection of ASRG manufacture. The Planetary Society is also a good place to register support for the future of the U.S. space program.
Diagram of the Advanced Stirling Radioisotope Generator:
