**11. Future radioisotope technologies**

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 Stirling duplex system.

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 efficiency.

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 degradation rates.

The Stirling duplex concept combines a power convertor as in the ASRG with a thermodynamic Stirling cycle cooler. This concept provides both power in the range of 100- 300 We and 1100 Wth cooling, allowing its potential use for missions in harsh hightemperature environments.
