Critical Look at the Solar Photon Thruster Concept

A solar photon thruster is a class of solar sail using multiple reflecting surfaces. Herein, the details of solar photon thruster design are investigated to allow comparison against more typical solar sail configurations. Many potential problems with the solar photon thruster concept have been sidestepped in the literature. Therefore, issues relevant to solar photon thruster operation were investigated, such as the following questions: 1) What are the realistic thrust levels and performance that such a vehicle might experience? 2) Do lightweight materials capable of handling the high heat fluxes, where the light is concentrated and reflected, exist? 3) How significant are the reflection losses due to having multiple reflective surfaces? 4) Can a large flexible mirror really focus the light sufficiently well to allow the solar photon thruster concept to work? It is found that any solar photon thruster will have a significantly inferior performance to a similarly sized flat solar sail. The maximum reflectivity of the surfaces typically used by solar sails and solar photon thrusters is determined; it is also found that the thermal issues of concentrating sunlight to a small focus are difficult but manageable and that using a large flexible metallized plastic surface as the main light-collecting surface, although suitable for a normal solar sail, is an extreme challenge for the solar photon thruster concept.