1. Melting Probe Progress Meeting: 24-06-2008 Radioactive Power Supply for the Melting Probe E. Kaufmann, N.I. Kömle, M. Steller, G. Kargl Space Research Institute of the Austrian Academy of Sciences ESA-Contract 19272 Progress Meeting 24.06.2008

2. Melting Probe Progress Meeting: 24-06-2008 2IWF/ÖAW GRAZ Radioisotope Heater Unit (RHU) I Polonium based RHUs Used in 5 Russian Space Missions  -emitter  shielding with a thin, lightweight mantle V3-R70-4 RHUs  thermal capacity of 150-170 W th Half life 138 days, therefore not usable for long time missions 210 Po-based thermal source V3-R70-4

3. Melting Probe Progress Meeting: 24-06-2008 3IWF/ÖAW GRAZ Radioisotope Heater Unit (RHU) II Plutonium based RHUs Poor conductor for heat and electric current Chemical widely not active  -emitter  thin, lightweight mantle Diameter of 2.6 cm and a height of 3.2 cm Include 2.7 g PuO 2 Provide about one W th Half life 87.74 years Mass ~40 g

4. Melting Probe Progress Meeting: 24-06-2008 4IWF/ÖAW GRAZ Angle RHU Designed for the Mars-96 Martian surface units Heat source for this RHU is the so-called Pantera radioisotope thermal source based on 238 Pu Pantera heat source can not be considered independently of the Angle RHU/RTG system The Angle RHU has additional shielding and protective layers, mass ~0.2 kg, 40 mm diameter, 60 mm height Coupled to a small thermo- electric converter which provides minimal electric power of approximately 200 mW e 238 Pu based Pantera thermal source Angle RHU. Point 1 shoes the Pantera source

5. Melting Probe Progress Meeting: 24-06-2008 5IWF/ÖAW GRAZ RHUs as heaters for the Melting Probe Due to the free space inside the Melting Probe only 3 RHUs can be placed inside, which leads to only 3 W th Using Angle RHUs is no alternative because of their size not one of them would fit into the Melting Probe The radiation of the RHUs has strong influence on the electronics since the RHUs can not be turned off  shielding inside the probe would be necessary, which reduces the space for sensors and increases the mass The concept of different heating circuits that can be used separately or in combination for corrections of the direction of the penetration channel is not able since RHUs can not be turned on and off as necessary in such a case Alternative: Use of RHUs as energy source for accumulators on a surface station

6. Melting Probe Progress Meeting: 24-06-2008 6IWF/ÖAW GRAZ Radioisotope Thermoelectric Generator (RTG) Electric energy is produced by heat that is obtained from the natural decay of a radioactive isotope It contains a heating element e.g. a RHU or a GPHS (General Purpose Heat Source), a thermoelectric generator and a cooling device One side is heated by the radioactive source, the other side is a big dark area which is cooled through radiation of heat energy into space. Conventional conversion methods have efficiencies of ~2-8%, requiring high amounts of radioactive fuels to generate small amounts of electric power.

7. Melting Probe Progress Meeting: 24-06-2008 7IWF/ÖAW GRAZ Mission to Europa Use of RTGs depends on the target of the mission As direct heating source for a Melting Probe RTGs are to big and to heavy For a mission to Europa RTGs like the ones used for Cassini would be necessary for the satellite carrying the lander which includes the Melting Probe Cut-drawing of the GPHS-RTG of Cassini

8. Melting Probe Progress Meeting: 24-06-2008 8IWF/ÖAW GRAZ