A Free Molecule Micro-Resistojet: An Interesting Alternative to Nozzle Expansion
Abstract
The growing trend of using significant numbers of small spacecraft, thus enhancing the performance of communication and surveillance tasks previously done by a few much larger vehicles, has created a requirement for low power, highly efficient propulsion systems It is clear that this class of small satellites will require station keeping with low mass, low thrust, low impulse bit (I-bit) thrusters, orbital transfer and rendezvous capabilities, multiple orbital plane changes, and de-orbit provisions. Small satellites are not only mass limited but also seriously power limited. For the mass range below 50 kg, a figure of merit is 1 W/kg available for propulsion, although this could be increased during orbital transfer or plane change maneuvers. Small mass, power efficient thrusters (microthrusters) need to be developed. There is a growing realization that in many cases microthrusters will not be simply scaled down versions of present thrusters. For example, chemical thrusters have difficulty maintaining efficiency at small scales due to increases in frozen flow and viscous losses. For ion electric propulsion, the increase in surface to volume ratio as the size decreases makes the scaling of these thrusters to small size, while maintaining efficiency, extremely difficult. In this paper, an electric thruster that is scalable to spacecraft in the kilogram to hundreds of kilogram range is discussed. The Free Molecule Micro-Resistojet (FMMR) satisfies the various issues resulting from extreme size reduction and appears to be scalable to rather large size without penalty. The FMMR is intended primarily for use as an attitude control thruster. As shown by Muntz and Ketsdeve, there are only quite modest differences between the performance of a free molecule orifice expansion and limit isentropic expansion with respect to I(sub sp).
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 13, 1998
- Accession Number
- ADA397946
Entities
People
- Andrew D. Ketsdever
- Dean C. Wadsworth
- E. P. Muntz
- Stephen Vargo
Organizations
- Air Force Research Laboratory