Sitting in the emptier office, she plunged into the analysis, although the pesky laws of physics turned an afternoon of rote celestial tennis practice into a forces free-for-all. Earth’s gravity exerted its force on the satellite and had to be accounted for in the trajectory’s system of equations. Earth’s oblateness—the fact that it was not perfectly spherical but slightly squat, like a mandarin orange—needed to be specified, as did the speed of the planet’s rotation. Even if the capsule were to shoot off into the air directly overhead and come back down in the same straight line, it would
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