**10. References**

470 Radioisotopes – Applications in Physical Sciences

devices are relative thick and heavy compared to the usual solar cells. Further, these advanced cells would be radiation sensitive. Solar-powered Juno mission will be launched in August on 2011, to study Jupiter. The spacecraft avoid the intense radiation belts using a innovative polar orbit, obtaining a great visibility for both the solar light arriving from the

Large solar arrays would severely impact the design, mass and operation of the spacecraft. This structure would have to be deployable, i.e. it could fit inside the rocket payload, and then unfold once the SC reached the outer planet. The mechanical components to fold and unfold the arrays would increase notably the size and mass on the SC. The long solar arrays would also severely complicate the stability on the trajectory and the attitude for scientific observations and data transmission to the Earth. Large spacecraft size, indeed, would make

The electrical power requirements of the spacecraft for science instruments and telecommunications, lunch mass, and mission lifetime are all of critical concern in choosing

In space application, Radioisotope Power Systems takes some advantages over solar panels. In several space operations there are long periods of darkness, and RPS will be the best actual technology. For outer planet missions, RTGs are more useful than solar panels to generate electric power for feeding communication systems and scientific instruments on the spacecraft. Additionally, there are new space technologies that use natural resources with/without radioisotope power systems. Future mission such as Europa Jupiter System Mission (EJSM), which is a joined NASA/ESA mission, will intend to study Jovian system, focusing two particular Jovian moons. NASA-led will use one type of RPS on Jupiter Europa Orbiter (JEO) to reach Europa, whereas ESA will consider solar arrays for Ganymede exploration. NASA's Juno mission will use solar panels for Jovian system exploration, in spite of the low solar light reaching Jupiter. The JEO spacecraft is designed to meet the planetary protection requirements. The flight system will use five multi-mission RTGs (MMRTG) to generate 540 W of electrical power at the end of the mission. The high radiation environment (>50 the dose supported of Juno mission) makes the RPS more useful than solar array, because of the low solar wind reaching Jupiter. Waste heat from the

MMRTGs would be used for thermal control in order to reduce electrical power.

Safety analysis of RPS requires a combination of deterministic and probabilistic steps to accurately predict the probability of system failure. The system failure is defined as rupture of one or more of the internal containment capsules surrounding the radioisotope fuel. To reduce the accident probability, we would have to identify among credible accidents, and analyze typical accident scenarios and consequences for overall flight phases of the spacecraft. The Launch Accident Scenario Evaluation Program (LASEP) computer program analyze the overall response of the GPHS-RTG in the various on-pad and near-pad launch

Actual high-magnitude earthquakes events occurred in Japan in 2011, has severally damaged the Fukushima reactor. This marks the difficult to change the public opinion about nuclear energy. Besides, the low disposal of Plutonium-238 is a serious drawback. The reestablishment of this man-made radioisotope production will be more difficult with these

the maneuvers slower, which is critical for scientific data collection.

sun and communications.

the electrical power source.

**8. Conclusion** 

accidents.

Abelson, R. et al. (2004). Enabling Exploration with Small Radioisotope Power Systems*, JPL Pub 04-10,* Avalible from

http://hdl.handle.net/2014/40856


http://www.ans.org/pubs/magazines/nn/pdfs/1999-4-2.pdf


http://saturn.jpl.nasa.gov/spacecraft/safety/eisss2.pdf

Lange, R. & Carrol, W. (2008). Review of Recent Advances of Radioisotope Power Systems*, Energy Conversion and Management*, 49, pp. 393-401, ISSN: 0196-8904

**22** 

*USA* 

**U.S. Space Radioisotope Power Systems and** 

Radioisotope power systems (RPS) have been essential to the U.S. exploration of outer space. RPS have two primary uses: electrical power and thermal power. To provide electrical power, the RPS uses the heat produced by the natural decay of a radioisotope (e.g., plutonium-238 in U.S. RPS) to drive a converter (e.g., thermoelectric elements or Stirling linear alternator). As a thermal power source the heat is conducted to whatever component on the spacecraft needs to be kept warm; this heat can be produced by a radioisotope heater unit (RHU) or by using the excess heat of a radioisotope

As of 2010, the U.S. has launched 45 RTGs on 26 space systems. These space systems have ranged from navigational satellites to challenging outer planet missions such as Pioneers 10/11, Voyagers 1/2, Galileo, Ulysses, Cassini and the New Horizons mission to Pluto. In the fall of 2011, NASA plans to launch the Mars Science Laboratory (MSL) that will employ the new Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) as the principal

Hundreds of radioisotope heater units (RHUs) have been launched, providing warmth to critical components on such missions as the Apollo 11 experiments package and on the

A radioisotope (electrical) power source or system (RPS) consists of three basic elements: (1) the radioisotope heat source that provides the thermal power, (2) the converter that transforms the thermal power into electrical power and (3) the heat rejection radiator.

The idea of a radioisotope power source follows closely after the early investigations of radioactivity by researchers such as Henri Becquerel (1852-1908), Marie Curie (1867- 1935), Pierre Curie (1859-1906) and R. J. Strutt (1875-1947), the fourth Lord Rayleigh. Almost 100 years ago, in 1913, English physicist H. G. J. Moseley (1887-1915) constructed the first nuclear battery using a vacuum flask and 20 mCi of radium (Corliss and Harvey,

After World War II, serious interest in radioisotope power systems in the U.S. was sparked by studies of space satellites such as North American Aviation's 1947 report on nuclear space power and the RAND Corporation's 1949 report on radioisotope power. (Greenfield,

outer planet probes Pioneers 10/11, Voyagers 1/2, Galileo and Cassini.

Figure 1 illustrates the basic features of an RPS.

1964, Moseley and Harling, 1913).

**1. Introduction** 

power source.

thermoelectric generator (RTG).

**Applications: Past, Present and Future** 

Robert L. Cataldo1 and Gary L. Bennett2

*1NASA Glenn Research Center* 

*2Metaspace Enterprises* 

