Physical limits of solar collectors in deflecting Earth-threatening asteroids

This paper investigates the physical limits of a solar collector for orbit deflection of near-Earth asteroids (NEAs) on a collision course with Earth. For decades of warning time a small change of NEA orbital velocity Δv by a few mm/s might suffice to alter the collision path into an Earth fly-by and consequently avert a local or even global catastrophe. In principle this can be achieved by a spacecraft that carries a large solar collector. The latter focuses sunlight onto the NEA surface in order to vaporize surface material, hence transferring a continuous momentum to the NEA. We model evaporation process and vapour expansion to show that the functionality exists. From the analysis of focussing misalignments and collector degradation we find that a considerable operational effort is required to maintain operating conditions. The most important result is that the collector lifetime is limited to only a few minutes. Therefore a solar collector might only be applicable to NEAs with size < 250 m if Δ v < 0.1   mm / s is required. We also discuss capabilities for the prolongation of collector lifetime and hence an increase of NEA application size range.