Interdisciplinary Applied Mathematics

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Escaping Propellant Molecule Path


Expansion WaJl.T,


Thin Film Heater, T-, —>


Propellant Inlet


Heating Element Pedestal


1 hernial


Insulation


Valve, Filter. Propellant Tank


FIGURE 6.32. Diagram of the free molecule microresistojet. The width of the expansion slot w is much less than the mean free path in the stagnation chamber; w = 100 nm. (Courtesy of A. Ketsdever.)


Ж


-1


—S—FMMR, T -600K


— «■


— B- -Microaozzle, T = 30GK 0


— ■ .Micronozzle, T =600K


О


1-1—: 1-Г


Ф


J


1



No Collision Limit


■ ■ ■ 1 ■ J 1 . . …1_


1_1 1 1 1 nil_1_1_


I.-U.i-Ui-i .J. 1 1 1 1 fll 1 1 i 1 1 iil


80 75 70 65 60 55 50 45 40


0.01 0.1 1 Knudsen Number


0.0001 0.001


FIGURE 6.33. Free-molecule microresistojet: Specific impulse as a function of Knudsen number for argon. (Courtesy of A. Ketsdever.)


TABLE 6.3. Typical operating conditions and propulsion characteristics for different micronozzles.


Fabrication


Po (psi)


Throat


w


Re


Ft (mN)


-^sp


(secs)


DRIE (Bayt, 1999) Conventional


85


19


3492


9.91


66.63


(Grisnik et al., 1987) KOH


3.32


640


3000


9.65


61.96


(Janson and Helvajian, 1997)


25


250


3258


9


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