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Adding to the many remarkable properties of graphene, they are also highly efficient in converting heat directly to electricity: SUTD team proposes low-temperature thermionic converter with graphene cathode; about 45% efficiency. 9 March 2015 http://www.greencarcongress.com/2015/03/20150309-sutd.html For spacecraft operating too far from the Sun or needing too much power to use solar cells, radioisotope thermoelectric generators (RTG's) have been used, and nuclear space reactors have been proposed in regards to manned missions. RTG's however have very poor efficiencies in the range of 3% to 7%: https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator#Efficiency And the nuclear space reactors that have been tested only have efficiencies in a similar poor range: http://www.world-nuclear.org/information-library/non-power-nuclear-applications/transport/nuclear-reactors-for-space.aspx though a proposed nuclear space reactor could have ca. 25% efficiency. The new research on graphene however suggests it could get efficiencies in the range of 45% in converting heat directly to electricity. And using graphene rather than heavy metals for the thermoelectric conversion would also save significantly in weight. The greater efficiency at a lighter weight might make possible proposed nuclear electric space propulsion systems such as VASIMR that could cut trips to Mars to weeks travel time instead of months. The Mars Society president Robert Zubrin had criticized VASIMR on the grounds that it would require an unreasonablly lightweight nuclear power system for the power it put out: The VASIMR Hoax By Robert Zubrin | Jul. 13, 2011 http://www.spacenews.com/article/vasimr-hoax But taking into account both the higher efficiency and the lighter weight, a graphene based thermoelectric conversion system may allow the required lightweight power system for VASIMR or other nuclear electric propulsion systems. Bob Clark
