Dinosaur Wars: Earthfall by Thomas P Hopp

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  A little over an hour later, Clem approached her orbit’s perigee and her impact point at Phaeon Crater. She fired two small side-thruster jets and rotated to the precise pitch and yaw to aim at the central pyramid. Then she adjusted her antenna pointing-angle and began transmitting a series of approach radar-images back to earth. As the pull of lunar gravity accelerated her down to her target, she calculated the few remaining parameters more precisely than any she had ever calculated before, because she no longer needed to plot out lengthy sequences of events far into the future. Her operations would cease in 1.996608 minutes.

  At impact-minus 1.000000 minutes she began to relay to earth the requested data: laser altimeter readings, 1.7344 km, 1.6860 km, 1.4253 km; a photo of the target impact point on Phaeon’s central pyramid, now 1,928 meters away.

  From the geometry of the radar images, she recalculated the match between her programmed aim-point and the gap under the pyramid’s cannon. With 45.3333 seconds to go, she determined that her aim point was slightly off, specifying an impact on the crater wall beyond the pyramid. She calculated a fine adjustment based on her updated 3D map of Phaeon and fired guidance thrusters briefly. With her newly calculated impact point squarely on the gap beneath the cannon she ignited her main engine. A smooth parabola of blue flame erupted from its bell-shaped nozzle, propelling Clementine forward at ever-increasing velocity. The time to impact clicked down to 7.0130 seconds and counting. Clem continued to transmit radar-image data to earth as she checked her velocity relative to the surface. It was up to 7,780 km/hr and increasing, sufficient for an impact of 2,278,093 ergs—more energy than any of her subsystems were built to withstand…