Editing Resistojet rocket

{{Short description|Method of spacecraft propulsion}}
A '''resistojet''' is a method of [[spacecraft propulsion]] ([[Electrically powered spacecraft propulsion|electric propulsion]]) that provides thrust by [[heat]]ing a typically non-reactive [[fluid]]. Heating is usually achieved by sending [[electricity]] through a [[resistor]] consisting of a hot incandescent filament, with the expanded gas expelled through a conventional nozzle.<ref name="electric-propulsion-encyclopedia">{{Cite encyclopedia |title=Electric Propulsion |encyclopedia=Encyclopedia of Physical Science and Technology |publisher=Academic Press |location=San Diego |url=https://alfven.princeton.edu/publications/browse/ep-encyclopedia-2001/ |last1=Jahn  |first1=Robert G. |date=2002 |edition=3rd |volume=5 |pages=125–141 |last2=Choueiri |first2=Edgar Y.}}</ref>

Resistojets have been flown in space since 1965 on board military [[Vela (satellite)|Vela satellites]]. However, they only became used in commercial applications in 1980 with the launch of the first satellites in the [[Intelsat|Intelsat-V]] program. Many GEO spacecraft, and all 95 [[Iridium satellite constellation|Iridium]], used Aerojet [[MR-501]]/[[MR-502]] series resistojet engines.<ref name="electric-propulsion-encyclopedia" /><ref>{{Cite conference |last1=Hoskins  |first1=W. Andrew |last2=Cassady |first2=R. Joseph |last3=Morgan  |first3=Olwen |last4=Myers |first4=Roger M. |last5=Wilson |first5=Fred |last6= King |first6=David Q. |last7=Kristi deGrys |date=October 6–10, 2013 |title=30 Years of Electric Propulsion Flight Experience at Aerojet Rocketdyne |url=http://electricrocket.org/IEPC/7vc5f5xg.pdf |conference=33rd International Electric Propulsion Conference |page=2 |id=IEPC-2013-439}}</ref> Nowadays resistojet propulsion is used for [[orbit insertion]], [[Spacecraft attitude control|attitude control]], and [[deorbit]] of [[low Earth orbit|LEO]] satellites, and do well in situations where energy is much less of a constraint than mass, and where propulsion efficiency needs to be reasonably high but low [[thrust]] is acceptable.{{citation needed|date=February 2011}}

Resistojets have also been proposed as means of using biowaste as reaction mass, particularly in conjunction with [[hydrazine]]. Studies focus on the characteristics of steam and carbon dioxide as major constituents of a biowaste stream, and typically use [[cubic zirconia]] as a [[heating element]].<ref name="A Design Study of Hydrazine and Biowaste Resistojets">{{Cite report |url=https://ntrs.nasa.gov/citations/19870004992 |title=A design study of hydrazine and biowaste resistojets |last1=Page |first1=R. J. |last2=Stoner |first2=W. A. |date=September 1, 1986 |pages=22–27 |id=NASA Contractor Report 179510 |last3=Barker |first3=L.}}</ref>

== Advantages ==
Many satellite missions necessitate an ability for minor alterations in trajectory even after the craft has been inserted into orbit. Most satellites use [[Monopropellant rocket|monopropellant]] rocket motors or [[cold gas thruster]]s for such orbital adjustments. Both methods, however, suffer from some limiting drawbacks: Hydrazine, the most commonly used monopropellant, is highly expensive and due to its volatile nature unsuitable for smaller satellites that are sent to space as secondary cargo. Cold gas thrusters, while utilizing relatively cheap, inert and therefore "safe" gasses like nitrogen, suffer from low [[specific impulse]] in comparison to monopropellant motors. Resistojets are designed to bridge the gap between these two methods of propulsion, offering the safety of an inert propellant coupled with specific impulse nearing that of hydrazine.<ref>{{Cite journal|last=Gibbon|first=Dave|date=2002|title=The Development of a Family of Resistojet Thruster Propulsion Systems for Small Spacecraft|url=https://digitalcommons.usu.edu/cgi/viewcontent.cgi?referer=&httpsredir=1&article=1769&context=smallsat|journal=Surrey Space Centre, University of Surrey|volume=|pages=1|via=}}</ref>

== Disadvantages ==
The main disadvantage of a resistojet design in comparison to simpler cold gas thrusters is the need for a power supply, which takes up space and is therefore sometimes a prohibitive factor for [[Small satellite|Microsat]] missions. In addition, the increased technical complexity of a resistojet relative to simpler solutions results in a greater risk of technical failure.

Since they do not take advantage of chemical combustion, resistojets (and [[Arcjet rocket|similar designs]]) have a lower thrust that is orders of magnitude lower than those of more conventional [[Solid-propellant rocket|solid fuel]] and [[Liquid-propellant rocket|liquid-propellant]] rockets. As a result, they are unsuitable for orbital maneuvers that require high delta V over shorter periods.

== Physical principles ==
Resistojets can be considered an evolution of traditional cold gas thrusters, which are the simplest form of rocket engine available. Their fuel tank holds the propellant, which is then led into the nozzle where it decompresses, propelling the craft forward. In a resistojet, a resistor is used to heat the fluid before it enters the nozzle, making it expand more forcefully, resulting in higher specific impulse.

A resistor is an electrical component which converts electrical energy into heat. Therefore, the thrust of a resistojet engine can be regulated by simply altering the wattage flowing through the resistor.

Heating a fluid by 300&nbsp;°C in such a way results in a 41% increase in specific impulse. If heated by 900&nbsp;°C, specific impulse could be doubled in comparison to a cold gas thruster using the same propellant.

==See also ==
*[[Solar electric propulsion]]
*[[Arcjet_rocket|Arcjet rocket thruster]]

==References==
{{Reflist}}

==External links==
* [http://arc.aiaa.org/doi/pdf/10.2514/6.2005-4260''A Xenon Resistojet Propulsion System for Microsatellites''] (Surrey Space Centre, University of Surrey, Guildford, Surrey) (Purchasable document) 
* [http://www.esa.int/esaCP/SEMNEYAOE1G_UnitedKingdom_0.html Two new ESA satellites successfully lofted into orbit] (European Space Agency)
* [https://web.archive.org/web/20130604101644/http://www.alta-space.com/index.php?page=resistojet Resistojet Propulsion System for Microsatellites] (Alta, Italy)
{{spacecraft propulsion}}

[[Category:Rocket propulsion]]