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Space Propulsion - IAP/TU Wien

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eaction wheel, cont’d<br />

<strong>Space</strong> <strong>Propulsion</strong><br />

Example 9: Reaction Wheel Unloading<br />

How much propellant does it take to unload one of the Magellan wheels, and<br />

how long does it take? (JPL Venus Mission, 1994)<br />

The Magellan wheel characteristics are:<br />

maximum momentum = 27 N-m-s<br />

maximum wheel speed = 4000 rpm = 418.879 rad/s<br />

The thruster pair to be used has the following characteristics:<br />

thrust = 1 N; moment arm = 2m<br />

pulsing specific impulse 1500 m/s.<br />

the propellant mass required to unload it is<br />

m<br />

H<br />

LI<br />

27<br />

=<br />

2*1500<br />

p =<br />

=<br />

sp<br />

0.009<br />

[ kg]<br />

engine burn time required to unload is<br />

H 27<br />

t = = = 6.75<br />

nFL 2*1*2<br />

[ s]

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