A resistojet is a method of

spacecraft propulsion Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. In-space propulsion exclusively deals with propulsion systems used in the vacuum of space and should not be confused with space launch or atmospheric ...

( electric propulsion) that provides thrust by

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...

ing a typically non-reactive

fluid In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...

. Heating is usually achieved by sending

electricity Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as describe ...

through a

resistor A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active e ...

consisting of a hot incandescent filament, with the expanded gas expelled through a conventional nozzle.Electric Propulsion article in Encyclopedia of Physical Science and Technology, 3rd Edition, Academic Press, San Diego, v.5, pp. 125-141, 2002
/ref> Resistojets have been flown in space since 1965 on board military Vela satellites. However, they only became used in commercial applications in 1980 with the launch of the first satellites in the INTELSAT-V program. Many GEO spacecraft, and all 95

Iridium Iridium is a chemical element with the symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, it is considered the second-densest naturally occurring metal (after osmium) with a density o ...

, used Aerojet MR-501/ MR-502 series resistojet engines. Nowadays resistojet propulsion is used for

orbit insertion Orbit insertion is the spaceflight operation of adjusting a spacecraft’s momentum, in particular to allow for entry into a stable orbit around a planet, moon, or other celestial body. This maneuver involves either deceleration from a speed ...

attitude control Attitude control is the process of controlling the orientation of an aerospace vehicle with respect to an inertial frame of reference or another entity such as the celestial sphere, certain fields, and nearby objects, etc. Controlling vehicle ...

, and

deorbit Atmospheric entry is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. There are two main types of atmospheric entry: ''uncontrolled entry'', such as the entr ...

of LEO satellites, and do well in situations where energy is much more plentiful than mass, and where propulsion efficiency needs to be reasonably high but low

thrust Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that ...

is acceptable. Resistojets have also been proposed as means of using biowaste as reaction mass, particularly in conjunction with

hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...

. Studies focus on the characteristics of steam and carbon dioxide as major constituents of a biowaste stream, and typically use

cubic zirconia Cubic zirconia (CZ) is the cubic crystalline form of zirconium dioxide (ZrO2). The synthesized material is hard and usually colorless, but may be made in a variety of different colors. It should not be confused with zircon, which is a zirco ...

as a

heating element A heating element converts electrical energy into heat through the process of Joule heating. Electric current through the element encounters resistance, resulting in heating of the element. Unlike the Peltier effect, this process is indepen ...

.NASA Contractor Report 179510, The R. J. Page Company Santa Ana, California, pp. 22-27, 1986
/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 Monopropellants are propellants consisting of chemicals that release energy through exothermic chemical decomposition. The molecular bond energy of the monopropellant is released usually through use of a catalyst. This can be contrasted with bipro ...

rocket motors or

cold gas thruster A cold gas thruster (or a cold gas propulsion system) is a type of rocket engine which uses the expansion of a (typically inert) pressurized gas to generate thrust. As opposed to traditional rocket engines, a cold gas thruster does not house any ...

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 Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine (a rocket using propellant or a jet engine using fuel) creates thrust. For engines whose reaction mass is only the fuel they carry, specific impulse is ...

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.

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 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 similar designs) have a lower thrust that is orders of magnitude lower than those of more conventional

solid fuel Solid fuel refers to various forms of solid material that can be burnt to release energy, providing heat and light through the process of combustion. Solid fuels can be contrasted with liquid fuels and gaseous fuels. Common examples of solid fuel ...

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

References

External links

Xenon Resistojet Propulsion System for Microsatellites''
(Surrey Space Centre, University of Surrey, Guildford, Surrey) (Purchasable document)

(European Space Agency)
Resistojet Propulsion System for Microsatellites
(Alta, Italy) {{spacecraft propulsion Rocket propulsion

Advantages

Disadvantages

Physical Principles

See also

References

External links