Design for High Precision in Spacecraft Jet Attitude Control Systems.
ROYAL AIRCRAFT ESTABLISHMENT FARNBOROUGH (ENGLAND)
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While maintaining economy in the use of fuel, realization of the highest available control precision from a pure jet system could require the ability to provide jet pulses of various durations with accuracies in the region of 1 ms. Due to sensor noise and sensor and jet delays, this is not possible if the jets are commanded solely in response to sensor signals. Existing systems overcome this difficulty in an intuitive manner by deriving a quasi-rate measurement from the jet command signal. Such systems are difficult to analyse and lack the flexibility available in linear systems for obtaining a good compromise between the conflicting aims of low sensitivities to sensor noise and to disturbing torque. A new class of systems is proposed in which an electronic model of an idealized control system is carried in the spacecraft. Jet commands in the model also command the real jets. The modelled variables are slaved to the sensor outputs by follow-up servos whose speeds of response can be adjusted to seek the above compromise. The new procedures have been validated by construction of on-board electronics for an example system, followed by testing in association with analogue simulation. Author
- Unmanned Spacecraft