Space Propulsion - IAP/TU Wien

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Space Propulsion limit cycle without external torque A limit cycle without external torque swings the spacecraft back and forth between preset angular limits. When the spacecraft drifts across one of the angular limits Θ L , the attitude-control system fires a thruster pair for correction. The spacecraft rotation reverses and continues until the opposite angular limit is reached, at which time the opposite thruster pair is fired. It is important that the smallest possible impulse be used for the corrections because the impulse must be removed by the opposite thruster pair. cont‘d
limit cycle cont‘d Space Propulsion nFL Θ = t I v t b c Θ tot = nFL I v 2 ⎛ Pw ⎜ ⎝ 2 tcP + 2 w ⎞ ⎟ ⎠ total angle of rotation Θ ↓ replacing 2t b P w (EQ 86) Θ L = 1 2 nFL I v t b t c = nFL 4I v P w t c the limit settings + Θ L are one-half of the coasting angle ↓ Θ = 2 Θ L (neglecting small rotations during accel & brake) nFP mp, cyc = 2 I sp w each cycle includes two pulses; the propellant consumed per cycle is Propellant consumption is small for low thrust, short burn time, and high specific impulse in pulsing operation. Pulsing engines are characterized by minimum impulse bit I min I min = (F.P w ) min The minimum impulse bit is a characteristic of a given thruster/valve combination cont‘d
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Space Propulsion - IAP/TU Wien

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