A Magnetic Unloading System for an Ultra Stable Unmanned Spacecraft

Many Magnetic Control or Unloading Systems have been presented at technical conferences over the past few years. Now one is a reality - a production line item - in the NASA-Grumman Orbiting Astronomical Observatory (OAO). The OAO magnetic control system utilizes the earth's magnetic field - itself a source of disturbance torque - as a spatial lever arm, upon which to transfer accumulated angular momentum in a wheel control system or to control directly the orientation of the spacecraft. No longer considered in the "tail fin" category, it ls a primary control system, the importance of which can be seen when it is compared with a pneumatic control system. This paper comments on a theoretical magnetic control system design advanced by Messrs. Paiken and Fleisig (and other authors Ref. 5,6,7), and traces the solution of equipment design problems. This includes the selection of iron core torquers, rather than large air core coils; the environmental and reliability criteria of long life spacecraft; the static and dynamic testing of the systems; and use of existing control system signal information. The discussion supplements a previous paper; "Momentum Control of the OAO Spacecraft Utilizing the Earth's Magnetic Field" by GAEC's Paiken and Fleisig. This was presented at the International Astronautical Congress, Paris, France, in September-October 1963, and described the initial block diagram design, computer simulations and studies.