Investigation on the effects of the planetary radiation pressure on solar sails

The vast majority on literature on solar sailing has thus far considered solar radiation pressure (SRP) as the only contribution to the sail force. However, when a sail orbiting a planet is considered, a new contribution can be added. A planet, being a body in thermodynamic equilibrium with its environment, emits the so called Black-Body Radiation. This radiation is emitted uniformly in all direction, with most of the energy emitted in the infrared range. The specific spectrum and intensity of this radiation depends only on the body temperature. Moreover, the radiation coming from the Sun will hit the planet and it will be reflected diffusely from the planet surface into the outer space as a function of the position of the Sun. This radiation is known as Albedo and it varies with geological and environmental features. The sum of the Black-Body Radiation Pressure and the albedo will be called Planetary Radiation Pressure (PRP). Hence, this work studies the combined effects of both SRP and PRP on a planetary sail. In particular, two case-studies have been considered, i.e. Earth and Venus. Considering a grid of points around the planet it has been found that in proximity of the Earth the effect of PRP can be significant under specific conditions, while around Venus PRP is by far the dominating contribution, providing better performances of the sail. These combined effects have been studied for single- and double-side reflective coating sail and including the presence of an eclipse region. Results show potential increase in the net acceleration and a change in the optimal attitude to maximise the acceleration along a given direction. Moreover, an optimal trajectory for increasing the semi-major is shown with and without PRP, to quantify the difference on a real-case scenario. For a sail orbiting around Earth the increment, considering the PRP, is of 0.1% however, this grows up to 4% if the sail is in a Venus-centred orbit.