Fine pointing of military spacecraft
Sands, Timothy A.
Agrawal, Brij N.
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In 1923, Herman Oberth, considered by some to be “the father of it all” for spaceflight, wrote a book called “Die Rakete zu den Planetenräumen” (i.e., “Dreams of Planets”) inspiring today's modern spaceflight. Amongst his suggestions was placing a telescope in space, so astronomical observations may be made without atmospheric distortion. Nearly a century later, the Hubble Space telescope is imaging distant stars with high accuracy. If Hubble were placed on the ground of the West Coast of the United States, it would able to target a small coin placed on the Lincoln memorial on the East Coast of the United States. This startling accuracy has become useful for military spacecraft missions as well even though the mission is much more challenging. Military spacecraft perform aggressive slew maneuvers to acquire targets, but the actuators are complicated by singularities that can often lead to loss of attitude control during aggressive maneuvers. After acquiring the target, the spacecraft must rapidly settle and track the target as the spacecraft races by overhead. This dissertation addresses these challenges by introducing a new optimized geometry for installation of the spacecraft actuators to minimize the impact of singularities. Methods are discussed to orient the direction of maximum slew capability in a desired direction. In addition to the optimal geometry, a new algorithm is presented that reduces those remaining singularities that could lead to loss of attitude control. A newly developed algorithm is proven to fly through the singularities without losing attitude control. The advancements introduced here increase aggressive maneuver performance aiding military spacecraft rapidly acquire earthly targets. After acquiring the target, several new, very simple adaptive control algorithms are introduced that adjust the control strategy based on tracking errors. If the spacecraft has trouble tracking a target, the control is adjusted to eliminate the tracking error. Using simplified techniques, target tracking accuracy is increased compared to current spacecraft control methods. While many promising, advanced techniques look good on paper, real-world factors like noisy signals and disturbances are often confounding. Most importantly, the claims made here are proven experimentally on a free-floating spacecraft simulator.
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