Power for Interstellar Lightsails

The Starshot mission will send the first probe to fly by a planet of a nearby star, such as Proxima Centauri, returning 100 kbits of data from that destination in about 20 years. In order to achieve high acceleration from a 100 GW laser and a 20-year relativistic trajectory through our solar system and interstellar medium (ISM), gram-scale Starshot probes need lightweight power and energy storage. Mechanical interfaces must attach to merely molecules-thick structures. In roughly 1 gram, this power subsystem's performance is driven primarily by communications needs: it must make a total of 14 kJ available at 20 μW periodically during the 20-year mission and must deliver 1W peak power at the beginning of life and then just after the spacecraft's encounter with a target extrasolar planet. Despite thin-film photovoltaics' ability to meet the initial and end-of-life power needs, several moderately near-term technologies show promise for supplying power for a minimally viable space vehicle, while others offer higher capability but with greater technological risk. Chief among the nearer-term solutions are isotope-based power and energy-storage approaches, which nevertheless require substantial maturation if they are to meet the high specific power and energy requirements of this mission while also conforming to Starshot's unique mechanical and environmental constraints. Energy scavenging from the ISM and near-lossless power storage are the riskier approaches which, despite their low readiness at present, may prove enabling for next-generation lightsails.