**12. Human exploration missions**

492 Radioisotopes – Applications in Physical Sciences

convertor manufactured by Sunpower. Characterization testing was performed for typical

Fig. 18. ASRG engineering unit readied for extended testing at NASA Glenn Research

After successful characterization tests the EU was put on extended operation with electrically heated GPHS simulators as shown in figure 18. A cold gas is passed over the EU to maintain proper thermal operating conditions. The EU is planned to demonstrate 14,000 hours of operation in validating the design's viability for flight on a NASA science mission (Lewandowski and Schreiber, 2010). The EU has achieved over 11,000 hours (April, 2011)

In addition to the MMRTG and ASRG efforts are underway to develop other technologies such as advanced thermoelectric couples (ATEC), thermophotovoltaic (TPV) systems and

The ATEC effort is developing and demonstrating thermoelectric couples with efficiencies greater than 10% with degradation losses less than 1% per year. Part of this effort is developing high temperature complex advanced materials with twice the state of practice

TPV uses photovoltaic cells tuned to certain spectra emitted by a radioisotope heat source. Development efforts include studies of the optical properties and optimization of the emitter, filters and collectors to achieve efficiencies of greater than 15% with low

launch and space environments.

Center (Photo Credit, NASA Glenn).

with a prototypical flight controller.

the Stirling duplex system.

efficiency.

degradation rates.

**11. Future radioisotope technologies** 

To this point, discussions have focused on lower-power science mission objectives. However, the concept of high efficiency energy conversion could find application in human exploration, particularly relating to the Moon and Mars. Multi-kilowatt power level radioisotope systems have application for the Moon due to its long 356-hour night period and on Mars due to its distance from the Sun, atmospheric dust attenuation and short winter day periods at higher latitudes.

Fig. 19. A concept for a multi-Kilowatt radioisotope power system deploying a fission reactor on the surface of Mars, (Artist concept credit: Bob Souls, John Frassanito and Associates, Courtesy of NASA).

Radioisotope power systems provide continuous power avoiding necessity of solar arrays and battery or fuel cell storage (for night time energy) and the wait to recharge them. Relative mission risk could also be reduced since solar array size for many of these

U.S. Space Radioisotope Power Systems and Applications: Past, Present and Future 495

Bennett, G. L. (1995). Safety Aspects of Thermoelectrics in Space, In: *CRC Handbook of* 

Bennett, G. L. et al. (2006). Mission of Daring: The General-Purpose Heat Source

Cataldo, R. L. (2009). Power Requirements for the NASA Mars Design Reference

Corliss, W. R. & Harvey, D. G. (1964). *Radioisotopic Power Generation*, Prentice-Hall, Inc.,

Dick, P. J. & Davis, R. E. (1962). Radioisotope Power System Operation in the Transit

Gendler, S. L. & Kock, H. A. (1949). Auxiliary Power Plant for the Satellite Rocket: A

Greenfield, M. A. (1947). *Studies on Nuclear Reactors, 6: Power Developed by Decay of Fission Fragments*, NAA-SR-6, North American Aviation, Inc., Los Angeles, California Hammel, T. E., Bennett, R., Otting W. & Finale, S. (2009) Multi-Mission Radioisotope

Hoye, T. J., Tantino, D. C., Chan, J. (2011), Advanced Stirling Radioisotope Generator Flight

Johns Hopkins University Applied Physics Laboratory (JHU/APL). (1980). *Artificial Earth* 

Jordan, K. C. & Birden, J. H. (1954), *Thermal Batteries Using Polonium-210*, MLM-984, Mound

Lipp, J. E. and Salter, R. M., eds. (1954), *Project Feed-Back, Summary Report* (2 volumes) R-262,

Lewandowski, E.J. and Schreiber, J.G., (2010). Testing to Characterize the Advanced Stirling

Moseley, H. G. J. & Harling, J. (1913). The Attainment of High Potentials by the Use of Radium. *Proceedings of the Royal Society* (London), A, 88 (1913), p. 471 Pitrolo, A. A., Rock, B. J., Remini, W. C. & Leonard, J. A. (1969). SNAP-27 Program Review,

*General Meeting*, Denver, Colorado, 17-22 June 1962

One Year, RAND Corporation, Santa Monica, California, 1949

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RAND Corporation, Santa Monica, California, 1954

1995

2006

Jersey

Colorado, 2009

*2011*, Albuquerque, NM, 2011

Laboratory, Miamisburg, Ohio, 1954

and Astronautics, Nashville, TN, 2010

*Report of the RPS Provisioning Strategy Team*, 8 May 2001

Engineers, New York

*2009*, Atlanta, GA, 2009

*Thermoelectrics*, Rowe, D. M., CRC Press, ISBN-10 9780849301469, New York,

Radioisotope Thermoelectric Generator (GPHS-RTG). AIAA 2006-4096, *4th International Energy Conversion Engineering Conference*, San Diego, California,

Architecture (DRA) 5.0. *Proceedings of Nuclear and Emerging Technologies for Space* 

Library of Congress Catalog Card Number 64-7543, Englewood Cliffs, New

Satellite. Paper No. CP 62-1173. *American Institute of Electrical Engineers Summer* 

Radioactive Cell-Mercury Vapor System to Supply 500 watts for Durations up to

Thermoelectric Generator (MMRTG) and Performance Prediction Model. AIAA 2009-4576, *7th International Energy Conversion Engineering Conference,* Denver,

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Paper 699023 in *Proceedings of the 4th Intersociety Energy Conversion Engineering Conference*, held in Washington, D.C., 1969, American Institute of Chemical

applications are too large and therefore require stowage during mobility and subsequent deployment for recharging multiple times. For Mars, radioisotope systems could be used in several applications (Cataldo, 2009). Opportunities to travel to Mars occur every 26 months. Many human mission scenarios call for pre-deployment of equipment on the opportunity preceding the piloted flight to simplify launch and mission logistics. One concept for a radioisotope system is a power cart capable of several applications with mobility as a key feature. For example, supplying power to deploy a shielded fission reactor several kilometers from a habitat could be accomplished in several days without the use of large solar arrays. The power cart would have communications capability to Earth via orbiting assets to control its movements and its re-location to future sites.

Once the crew arrives on a subsequent opportunity, the power cart could be used with a pressurized rover. This scenario would allow the crew to perform long-range roving (over ~100's km) to significantly extend the scope of exploration from a single landing site. The power cart could also provide back-up power to the habitat should that become required. Should the base power system be solar instead of fission power a radioisotope-powered habitat back-up system could save significant mass during decreased array output during due to a global dust storm. A radioisotope power system could offer significant flexibility in mission planning for human missions as well as robotic science missions. In addition, since a crew would be available for repairs, maintenance or upgrades, the radioisotope fuel could be placed in a redundant cart with new conversion hardware extending the use of the fuel for many follow-on missions (Cataldo, 2009).

#### **13.Conclusions**

The U.S. has had a very successful 50 years of using RPS to power some of the most challenging and scientifically rewarding space missions in human history. These RPS have provided power at or above that required levels, and generally for longer than the original mission specification. RPS can truly be an enabling technology for both robotic probes and human exploration of the Solar System and beyond.

#### **14. References**

*Apollo 11 Lunar Landing Mission Press Kit*, NASA, Release NO: 69-83K, June, 1969


applications are too large and therefore require stowage during mobility and subsequent deployment for recharging multiple times. For Mars, radioisotope systems could be used in several applications (Cataldo, 2009). Opportunities to travel to Mars occur every 26 months. Many human mission scenarios call for pre-deployment of equipment on the opportunity preceding the piloted flight to simplify launch and mission logistics. One concept for a radioisotope system is a power cart capable of several applications with mobility as a key feature. For example, supplying power to deploy a shielded fission reactor several kilometers from a habitat could be accomplished in several days without the use of large solar arrays. The power cart would have communications capability to Earth via orbiting

Once the crew arrives on a subsequent opportunity, the power cart could be used with a pressurized rover. This scenario would allow the crew to perform long-range roving (over ~100's km) to significantly extend the scope of exploration from a single landing site. The power cart could also provide back-up power to the habitat should that become required. Should the base power system be solar instead of fission power a radioisotope-powered habitat back-up system could save significant mass during decreased array output during due to a global dust storm. A radioisotope power system could offer significant flexibility in mission planning for human missions as well as robotic science missions. In addition, since a crew would be available for repairs, maintenance or upgrades, the radioisotope fuel could be placed in a redundant cart with new conversion hardware extending the use of the fuel

The U.S. has had a very successful 50 years of using RPS to power some of the most challenging and scientifically rewarding space missions in human history. These RPS have provided power at or above that required levels, and generally for longer than the original mission specification. RPS can truly be an enabling technology for both robotic probes and

Bates, J. R., Lauderdale, W. W. & Kernaghan, ALSEP Termination Report, NASA, Reference

Bennett, G. L., Lombardo, J. J. & Rock, B. J. (1984). US Radioisotope Thermoelectric

Bennett, G. L. and Lombardo, J. J. (1989), The Dynamic Isotope Power System: Technology

Generators in Space. *The Nuclear Engineer*, Vol. 25, No. 2, March/April 1984, pp. 49- 58, ISSN 0262-5091. Reprinted from the paper "U.S. Radioisotope *Thermoelectric Generator Space Operating Experience* (June 1961 – December, 1982)", *18th Intersociety Energy Conversion Engineering Conference*, Orlando, Florida, 21-26 August 1983, American Institute of Chemical Engineers, New York, New York, 1983, ISBN 10

Status and Demonstration Program. Chapter 20, In*: Space Nuclear Power Systems* 1988, El-Genk, M.S. and Hoover, M. D., Orbit Book Publishing Company, ISBN-10

*Apollo 11 Lunar Landing Mission Press Kit*, NASA, Release NO: 69-83K, June, 1969

assets to control its movements and its re-location to future sites.

for many follow-on missions (Cataldo, 2009).

human exploration of the Solar System and beyond.

0894640291, Malabar, Florida, 1989

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**13.Conclusions** 

**14. References** 


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General-Purpose Heat Source Radioisotope Thermoelectric Generator (GPHS-RTG). AIAA-2010-6598, *8th International Energy Conversion Engineering Conference*,
