National Aeronautics and Space Administation
The Multi-Mission Radioisotope Thermoelectric Generator for Science Exploration Presented by: David Woerner | RTG Integration Manager | NASA Jet Propulsion Laboratory | [email protected] | (626) 497-8451
The Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) was developed to serve as a power source for a variety of space missions, from planetary surface to deep space interplanetary missions. Its special capability to handle the harsh surface environment of Mars makes it unique among recent RTGs, which could not survive on the surface of Mars. The special design characteristic of an isolated and hermetically sealed thermoelectric converter compartment enables long term performance in a multitude of environments. The MMRTG converts thermal energy, supplied by the Department of Purpose Heat Source (GPHS) modules, to electrical energy. The MMRTG produces electrical power when heat generated from the decay of the radioisotope fuel in the GPHS modules flows through the MMRTG Model thermoelectric couples located around the heat source. The resulting temperature gradient across the thermoelectric couples generates a voltage via the Seebeck effect. The generator produces power when a load is placed across the thermoelectric string, allowing current to flow. Waste heat is rejected to the MMRTG in Thermal Vacuum Chamber environment via radiator fins attached to the housing [1].
Thermoelectrics [2] MMRTG Characteristics Summary The MMRTG thermocouple is based on Parameter Value [3] the proven design heritage of the Pioneer Power, electrical (BOM*) 110 We required Power, thermal (BOM*) 2,000 W [3] / ~1750 W and Viking RTGs. The thermoelectric th th materials (PbSnTe, TAGS, and PbTe) Design Lifetime 17 yrs (14 yrs operational) [3] Diameter 64 cm (25 in) [3] have demonstrated extended lifetime Height 66 cm (26 in) [3] and performance capabilities, and are Mass 45 kg (94 lbs) [3] based upon those used for the two Viking Voltage Range 23-36 V dc [2] spacecraft that landed on Mars in 1976. Max Fin Root Temperature 200 C Random Vibration Qual Limit 0.2 g2/Hz [2] The MMRTG has 16 thermoelectric Pyrotechnic Shock Qual Limit 6,000 g [2] modules connected in electrical series. * BOM (Beginning of Mission) is defined as launch MMRTG fit check on Curiosity Each module contains 48 thermoelectric couples in an electrical series/parallel ladder arrangement for reliability. Extended Operation Testing of MMRTG Two module box tests are underway at Teledyne Energy Systems, to measure the long-term performance of MMRTG Engineering and Qualification Units [5] thermoelectric couples. The boxes are being operated at two The MMRTG Engineering Unit (EU) is currently under life different temperatures to envelop potential mission operating assessment testing at the University of Dayton Research Institute conditions of the MMRTG. in Dayton, Ohio. Life assessment testing began with an electrical heat source simulator in 2007, and so the EU has accumulated more than approximately 6.85 years on test, as of 2013 [4]. The EU was previously tested to demonstrate the MMRTG flight Mission Performance: Mars Science design could meet the extreme Multi-Mission qualification Laboratory requirements. The test program was divided into five major The Mars Science Laboratory (MSL) segments: electrical performance, thermal vacuum, vibration, mission successfully landed on Mars on pyro-shock, and magnetics. August 6, 2012, when it began science operations for its primary mission. Future EU tests under consideration include: both long-term and operating very well on diurnal thermal cycling; the surface of Mars, providing power transient power output analysis; helium leak testing; and possible above predictions and operating within chassis short characterization. its flight allowable temperature limits. The MMRTG Qualification The generator produced approximately Unit will begin life ) 114 We at the beginning of the surface assessment this summer, e mission [8]. and subsequent tests will
The MSL mission provided the first evaluate performance Power (W experience with integrated design and parameters against original operation of a thermoelectric power QU data for baseline performance validation. The Time (years) source, a solar array, and rechargeable F1 and EU MMRTGs Normalized Power Output [5] Lithium-ion batteries on an interplanetary mission. Given the assessment will simulate as internal fault protection measures of the MMRTG, MSL interfaced deep space cruise as opposed the MMRTG directly with the power bus [7].
125.0 Monthly Maximum 120.0 Average Power, We Monthly Minimum COMING SOON: Get Access to More 115.0
110.0
e MMRTG Information
, W 105.0 r
100.0 Interested in Proposing a mission using an MMRTG? U.S. Powe 95.0 Citizens who are U.S. NASA affiliates may request approval to 90.0 85.0 Library 80.0 at http://rps.nasa.gov in Fiscal Year 2016. Jul-13 Jul-14 Aug-12Sep-12 Oct-12 Nov-12 Dec-12 Jan-13 Feb-13 Mar-13 Apr-13 May-13 Jun-13 Aug-13Sep-13 Oct-13 Nov-13 Dec-13 Jan-14 Feb-14 Mar-14 Apr-14 May-14 Jun-14 Aug-14Sep-14 Oct-14 Nov-14 Dec-14 Jan-15 Feb-15 MMRTG EU, F1 and Pioneer Change vs. Time [4] Actual values from the MSL MMRTG on Mars For more details email the RPS Program at [email protected].
Literature cited [1] Hammel, T. E., Bennett, R., Keyser, S., Sievers, R., Multi-Mission Radioisotope Thermoelectric Generator (MMRTG): Proven Power for Next Generation Radioisotope Power Systems, 10th International Energy Conversion Engineering Conference, Atlanta, Georgia, 2012. [2] Fleurial, J-P., Caillat, T., Nesmith, B.J., Ewell, R.C., Woerner, D.F., Carr, G.C., Jones, L.E., Thermoelectrics: From Space Power Systems to Terrestrial Waste Heat Recovery Applications, 2011 Thermoelectric Applications Workshop, San Diego, California, 2011. [3] MMRTG Fact Sheet, RPS Program, 2013, [3] MMRTG Fact Sheet, RPS Program, 2013, https://solarsystem.nasa.gov/rps/docs/MMRTG Fact Sheet update 10-2-13.pdf [4] E.H. Thomas, B. Russell, K.S. Robert, K. Steven, O. William, G. Leo, Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) Performance Data and Application to Life Modeling, 11th International Energy Conversion Engineering Conference, San Jose, California, 2013. [5] Barklay, C. D., Tolson, B.A., Sjoblom, C.W.O., Harriss, R.J., Lifecycle Testing of the EU/QU MMRTG, University of Dayton Research Institute, 2/25/15. [6] Woerner, D.F. (2015). Another update on the multi-mission radioisotope thermoelectric generator powering the curiosity rover. Journal of Thermoelectricity, 1, 68-78. ISSN 1607-8829 [7] Jones, L., Moreno, V., Zimmerman, R., The F1 Multi-Mission Radioisotope Thermoelectric Generator (MMRTG): A Power Subsystem Enabler for the Mars Science Laboratory (MSL) Mission, Nuclear and Emerging Technologies for Space, Albuquerque, New Mexico, 2013. [8] Woerner, D., Moreno, V., Jones, L., Zimmerman, R., Wood, E., The Mars Science Laboratory (MSL) MMRTG In-Flight: A Power Update, Nuclear and Emerging Technologies for Space, Albuquerque, New Mexico, 2013. www.nasa.gov