m Open access bot: hdl added to citation with #oabot.
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→top: link specific isotopes; source for Fm is dead and others aren't coming up
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The basic idea is a development of existing [[radioisotope thermoelectric generator]], or RTG, systems, in which the heat generated by decaying nuclear fuel is used to generate power. In the rocket application the generator is removed, and the working fluid is instead used to produce thrust directly. Temperatures of about 1500 to 2000 °C are possible in this system, allowing for [[specific impulse]]s of about 700 to 800 seconds (7 to 8 kN·s/kg), about double that of the best chemical engines such as the [[LH2]]-[[LOX]] [[Space Shuttle Main Engine]].
However the amount of power generated by such systems is typically fairly low. Whereas the full "active" reactor system in a [[nuclear thermal rocket]] can be expected to generate over a gigawatt, a radioisotope generator might get 5 kW. This means that the design, while highly efficient, can produce thrust levels of perhaps 1.3 to 1.5 N, making them useful only for thrusters. In order to increase the power for medium-duration missions, engines would typically use fuels with a short [[half-life]] such as [[polonium
Another drawback to the use of radioisotopes in rockets is an inability to change the operating power. The radioisotope constantly generates heat that must be safely dissipated when it is not heating a propellant. Reactors, on the other hand, can be throttled or shut down as desired.
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