The Nitinol Heat Engine (NHE) uses a shape-memory alloy of nickel and titanium to convert thermal energy directly to mechanical power and through a generator, to electricity. An NHE was analyzed and designed to produce power from solar irradiation in space, with radiative cooling to a deep-space heat sink. A model NHE was built and tested in a space chamber simulating the radiation and space environment, and produced results agreeing with performance predictions. Other space NHE using Space Station waste heat are also discussed. Such space NHE are demonstrated to be cost-competitive with photovoltaic cells as a source for space power.