A Plume-Impingement Shepherd: Rocket Exhaust Pressure on the Surface of a 90-Metre Asteroid

This paper computes a shepherd that hovers 60 m above a 90 m asteroid of mass 725,236,664 kg and directs the exhaust of a 200 N engine at the surface. A plume transfer fraction of 0.31 gives an effective force of 62 N on the body and an acceleration of 8.55e-08 m per second squared. Over 6 days of hovering, consuming 35,265 kg of propellant, the shepherd delivers 44.3 mm per second against a requirement of 27.2 mm per second for a 6,000 km displacement with five years of warning, a margin ratio of 1.63 and a computed separation of 9,789.9 km. This is a computed study of a deflection system for planetary defence, with no targeting or weapon application. It is simulated, not measured.