Low-cost debris deorbiting plus planetary protection

Abstract

Space debris can be deorbited by a coating of volatile material that evaporates in sunlight. Consider a roque CubeSat that gets splashed with black gel while on the night side of its orbit. As it emerges into the rays of the Sun, kinetic evaporation provides a retro force relative to the orbital velocity, causing speed to diminish. At midpoint of orbital dayside, the net force is downward, towards the Earth’s atmosphere, where drag increases. If sufficient gel remains unevaporated during the transition back to nightside, there could be acceleration, but the dose of gel is limited to avoid this. Gel balls can be delivered from a standoff distance such that orbital matching need not be perfect, saving time and fuel for the debris-hunter. Larger chunks of debris can be shot with multiple gel balls designed that rupture and wet the surface, similar to a paint marking capsule (“paintball”), to provide more retroforce. For very large objects, such as earth orbit-crossing asteroids, judicious application of volatile material can provide a net force away from the Sun, altering the trajectory sufficiently to avoid impact. This work considers the velocity distribution in a liquid assuming the Maxwell-Boltzmann equation, the vapor pressure using the Clausius-Clapeyron equation, and the evaporative flux using the explicit Schrage equation to model vapor kinetics from the Knudsen layer under direct solar irradiation. A concept of operations for a notional debris-hunter satellite design allows an estimate of debris mass that can be deorbited in a given period of time. From this, and an estimate of launch mass, the number and mass of space junk that can be removed from a higher low-earth orbit (LEO) can be calculated. These expenses are sufficiently smaller than the consequence of a Kessler syndrome to compel spacefaring nations to implement this proactive approach without delay.