Abstract. The second mission of the small expendable deployment system (SEDS-II) followed the successful mission of SEDS-I, which deployed freely a small instrumented probe on a 20-km tether. Unlike SEDS-I, the deployment of SEDS-II was controlled to provide a small libration amplitude and tether velocity at the end of deployment. The preflight goal for SEDS-II was a maximum libration of less than 10 deg and a final velocity of less than 1 m/s. The control problem was made difficult by the limited capabilities of the SEDS sensors and onboard computer and the large uncertainties inherent in the response of the actuator (brake) and the plant (deployer). The nonlinear, nonautonomous control problem is divided in two parts by using a numerically formulated feedback linearization, i.e., by devising 1) a nonlinear control (reference) trajectory and 2) a linear control about the reference trajectory. An ad hoc feedback law that forces the perturbed system to follow the reference trajectory is derived by using a linearized variational model. The controller is then tested, through computer simulations, for large deviations of the model parameters on the nonlinear model. The relevant flight data are also presented and compared to the reference values to demonstrate the validity and robustness of the control law, which provided a maximum libration amplitude of less than 4 deg and a final tether velocity of less than 0.02 m/s

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I SUPPLEMENTARY NOTES1s. ABSTRACT IThis note briefly reviews the Skylab attitude and pointing control system (APCS) requirements and the way in which they became altered during the prelaunch phase of development. The actual flight mission (including mission alterations during flight) is described. The serious hardware failures that occurred, beginning during ascent through the atmosphere, also are described. The APCS's ability to overcome these failures and meet mission changes are presented. The large around-the-clock support effort on the ground is discussed. Finally, salient design points and software flexibility that should afford pertinent experience for future spacecraft attitude and pointing control system designs are included.

No abstract

I SUPPLEMENTARY NOTES1s. ABSTRACT IThis note briefly reviews the Skylab attitude and pointing control system (APCS) requirements and the way in which they became altered during the prelaunch phase of development. The actual flight mission (including mission alterations during flight) is described. The serious hardware failures that occurred, beginning during ascent through the atmosphere, also are described. The APCS's ability to overcome these failures and meet mission changes are presented. The large around-the-clock support effort on the ground is discussed. Finally, salient design points and software flexibility that should afford pertinent experience for future spacecraft attitude and pointing control system designs are included.