Outgassing and vaporization considerations in milliwatt generators designed for 20-year missions

• Main Authors: Hiller, N, Allen, D, Elsner, N, Bass, J C, Moore, J P
• Format: Conference Proceeding
• Language: English
• ISSN: 0094-243X

Ongoing experimental work and theoretical models indicate that milliwatt thermoelectric generators that operate in a sealed-off vacuum environment will be useful for long-term operation, such as the PASCAL 20 year Mars mission and the CryoScout mission. Considerations for long-term operation include outgassing of the multifoil vacuum insulation before pinch off and vaporization of the (Bi, Sb)2(Se, Te)3 thermoelectric materials during long-term operation. Tests underway indicate the multi-foil insulation can be pre-outgassed before assembly so further outgassing in the sealed generator is minimized. Experimental data and vaporization models for a Th of 250 C thus far indicate that the small amount of vaporization of materials used in the thermoelectric module do not significantly effect the generator vacuum or the module power output. These tests and models indicate that both potential modes of degradation can be controlled and minimized. Although performance data on the generator materials only extend for several hundred hours, the good performances in a limited time, combined with an understanding of the materials behavior, indicate that milliwatt generator holds promise for providing sufficient and reliable power for space missions lasting up to 20 years. (Author)