Preliminary model for radiometric design and analysis of the breakthrough starshot initiative

A model has been developed for preliminary examination of radiometric properties pertaining to the Breakthrough Starshot Initiative. This project aims to send a nanocraft to the Proxima Centauri system. The nanocraft will deploy a solar sail driven by a 100 GW laser beam at 1064 nm projected from a segmented aperture of several kilometers in diameter¹. The radiometric model uses both MATLAB and FRED to quantify and characterize the light returning from the sail while also predicting the nanocraft’s kinematic motion. Photon counts and wavelengths along with craft position, velocity, and acceleration at any time throughout the duration of the launch are among the quantities modeled. Since the nanocraft is to be accelerated to 20% the speed of light, relativistic effects must be considered². In particular, the Doppler shifted reflected drive light is of significance since it may be suitable for wave-front sensing once the shift is sufficient to separate it from the unshifted drive light at the projector. Additionally, estimates of the photon flux support predictions of the amount of light the system will be able to collect for wave-front sensing. All of these quantities are calculated using an iterative process which takes known initial conditions and integrates forward in time to provide the desired properties at every time interval. The model allows system parameters (e.g., reflectivity of the sail, BRDF profiles, projector fill factor, etc.) to be varied for optimization of the drive system design. The model will continuously be updated as advancements in both projector and sail designs are made. An expanded model including other phenomena, such as sail self-emission, transmission, and irradiance distribution patterns at the solar sails, will follow.