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{{Refimprove|date=September 2010}}
A '''radioisotope rocket''' or '''radioisotope thermal rocket''' is a type of [[Thermal rocket|thermal]] [[rocket engine]] that uses the heat generated by the decay of [[radioactive]] elements to heat a [[working fluid]], which is then exhausted through a rocket nozzle to produce [[thrust]]. They are similar in nature to [[Nuclear thermal rocket|nuclear thermal rockets]] such as [[NERVA]], but are considerably simpler and often have no moving parts. Alternatively, radioisotopes may be used in a '''radioisotope electric rocket''',<ref>{{cite journal |last1=Schmidt |first1=George R. |last2=Manzella |first2=David H. |last3=Kamhawi |first3=Hani |last4=Kremic |first4=Tibor |last5=Oleson |first5=Steven R. |last6=Dankanich |first6=John W. |last7=Dudzinski |first7=Leonard A. |title=Radioisotope electric propulsion (REP): A near-term approach to nuclear propulsion |journal=Acta Astronautica |date=1 February 2010 |volume=66 |issue=3 |pages=501–507 |doi=10.1016/j.actaastro.2009.07.006 |bibcode=2010AcAau..66..501S |hdl=2060/20110016114 |hdl-access=free }}</ref> in which energy from nuclear decay is used to generate the electricity used to power an [[
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 {{cvt|1500
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 {{cvt|1.3
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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==Technology development==
[[TRW Inc.|TRW]] maintained a fairly active development program known as '''Poodle''' from 1961 to 1965, and today the systems are still often known as '''Poodle thrusters'''. The name was a play on the larger systems being developed under [[Project Rover]], which led to NERVA. In April 1965 they ran their testbed engine for 65
==Photon
{{see also|
Even without an exhaust, the [[Radiation pressure|photon pressure]] of the energy emitted by a thermal source can produce thrust, although an extremely tiny amount. A famous example of spacecraft thrust due to photon pressure was the [[Pioneer anomaly]], in which photons from the onboard radioisotope source caused a tiny but measurable acceleration of the Pioneer spacecraft.
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