496. Mass Moment of Inertia Computer Program Used in Optimizing a Gravity Gradient System

Paper

Abstract

A wide variety of avionic devices and techniques, expected to have broad application to future meteorological, communication, navigation and military systems, will be evaluated on NASA’s Applications Technology Satellite. A Gravity Gradient Stabilization System constitutes one of the primary experiments to be flown on ATS.
There are three systems to be launched in the following sequence by Atlas-Agena boosters:
1. Medium Altitude Orbit, Gravity Gradient Stabilized – One Vehicle
2. Synchronous Orbit, Spin-Stabilized – Two Vehicles.
3. Synchronous Orbit, Gravity Gradient Stabilized Satellite – Two Vehicles
The primary purpose of the Medium Altitude Satellite will be to conduct a wide range of gravity gradient experiments to verify analytical models heretofore investigated only by computer studies.
A digital computer program has been constructed for rapid calculations of mass moments of inertia, which are changed by deploying booms (with tip masses) at various attitudes. The description of this computer program and gravity gradient stabilization are the main object of this presentation.
Gravity Gradient Stabilization offers a means of significantly improving the reliability of long-life earth satellites. Gravity Gradient Stabilization is based on the principle that any earth satellite will align its long axis, or axis of minimum moment of inertia, with the local vertical. By properly configuring a satellite, it is possible to make the satellite point to the earth. Since a long slender shape is desired but is inconvenient to launch, this shape is achieved after launch by deploying long booms with tip masses at the end.
The ATS Gravity Gradient Experiment requires that the inertial properties of the satellite be varied during orbit by ‘scissoring’ the booms. A computer program has been set up in FORTRAN IV for use with the I.B.M. 7094 computer to compute these inertias. The program has been set up so that the inputs are direction cosines, boom lengths, tip masses, rod inertias, and pivot point locations. Previous programs used required detail center of gravity locations for each item that was moved (for example the Nimbus Solar Paddle movement).
The main advantage of this computer program is its efficiency. Also, it should point out the fact that there are probably many ways which the computer can be used to our advantage that have not as yet been tried.