Abstract
Abstract : The Direct Measurement Explorer-A (DME-A) satellite was launched in November 1965 into a near-earth orbit ranging between altitudes of 500 and 3000 km to sample and measure charged particles. The attitude control system is used to keep the spin axis aligned with the orbit normal and to maintain the spin rate. Spin axis control is achieved by a chargeable permanent magnet system which is operated upon command and reacts with the earth's field to produce precession of several degrees per minute. With this system the spin axis was kept within 10 degrees of the orbit normal for several weeks at a time, although larger deviations have been tolerated. The spin rate was observed to decay at 0.05 rpm per day. Periodic use of the spin rate control system has compensated for spin decay. This system is analogous to a DC motor in which the entire satellite is the armature. (Author)
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