The United States and Russia have been developing and using small radioisotope power sources for space for the last 40 years. They enabled all martian lander and extended lunar lander missions as well as spacecraft to Jupiter and beyond.
 
The European Aurora Programme envisages a series of automated missions to the Martian surface (with ExoMars in the near-term horizon), for which the use of small radioisotope power sources is a possible option. The full development of radioisotope power sources requires a dedicated infrastructure and substantial resources over several years, and is not foreseen to be performed in Europe. However, with safety being of utmost importance, the use of nuclear power sources requires a solid safety framework, an area in which specific European activity is deemed to be required. Russian devices are in principle available and technically suitable to European mission requirements.

The proposed activity aims at, and is required for, preparing and enabling the Agency to take a decision on the use of radioisotope power sources (RHUs/RTGs) on ExoMars. The most likely application of such devices in a near-future mission is for thermal control i.e. the heating of thermally sensitive components.

One point to note is that in relation to overall radioisotope power source activity, there is no intention to develop these technologies themselves within Europe. The activity detailed here, and indeed the overall European approach to RHUs, is based on enabling Europe to make use of externally procured devices in European spacecraft.

Given the importance of the safety aspects for all nuclear related activities, particularly in space, the present activity focusing on the safety aspects of Russian radioisotope heating units is essential to enable Europe to decide whether to use RHUs on European exploration missions in general and ExoMars in particular. This implies Europe must assess and eventually qualify Russian RHUs according to European standards and develop relevant handling and testing experience, to allow RHUs to be safely and effectively integrated, tested, validated and launched. Such tests are required to familiarise the Agency, European industry and a nuclear partner with the devices.

The activity aims at the following objectives:

• Safety assessment of Russian RHUs, and analysis of the results according to European standards (activity and dose level, reliability, resistance to radiation and meteorite damage, simulation of accidental situations)

• Detailed technical assessment of Russian RHUs: inspection and verification of all relevant characteristics (e.g. material properties under all foreseeable regular and accidental conditions, energy output, mass, activity and dose levels, lifetime)

• If compatible with Russian nuclear confidentiality aspects, assessment of the Russian RHU procurement/manufacturing procedures and facilities

• Determination of eventual additional actions to be taken in order to qualify the devices for the integration and launch on European missions/launchers (possible adaptation to accidental conditions of European launchers)

• Determination of potential adaptation needs of the European launch infrastructure (e.g. launch termination procedures)

• Eventually, depending on the outcome of safety assessments and programmatic decisions: additional qualification experiments and tests.