Engineering topics
Publications and source records attributed to Nelson, John D..
A safehold mode has been implemented for Hubble Space Telescope that ensures a power-positive and thermally safe state without the use of rate gyros. This paper presents an overview of this zero-gyro sunpoint safemode, followed by details of the algorithm, the control system design, and results of simulations and of an on-orbit test of the algorithm.
The purpose of this paper is to document the on-orbit testing of the Zero-Gyro Sunpoint mode for Hubble Space Telescope, a safemode designed to ensure a power positive state without the use of rate gyros. This paper presents an overview of the test planning and test results.
Because of unexpected, thermally-induced disturbances originating in the Solar Arrays, the Hubble Space Telescope (HST) initially was unable to meet its pointing error specifications of 0.007 arcseconds (RMS) for observations lasting from a few seconds to several hours; and there immdiately began the effort to pin point the mechanism causing the problem and to redesign the onboard controller to accomodate the disturbance. Now, after a series of controller modifications, the pointing errors are well within the specicifcation for all of the orbit except for short intervals during transitons in and out of the Earth's shadow. This paper presents a chronology of the redesign process and flight data showing the current pointing performance. There is also a brief discussion of the modifications to the replacement arrays that will be installed on the HST in early 1994.
The purpose of this paper is to document the Zero-Gyro Sunpoint mode for Hubble Space Telescope, a safemode designed to ensure a power positive state without the use of rate gyros. This paper presents an overview of the Zero-Gyro Sunpoint algorithm, followed by details of the algorithm, control system design, and simulation results. A new, related safemode test, the System Momentum Test, is also discussed.