Caltech Space Solar Power Project

The Caltech Space Solar Power Project is one of the most significant privately-funded SBSP research programmes globally, supported primarily by a major gift from Donald Bren and conducted by a multidisciplinary team across Caltech's divisions of engineering and applied science. The project focuses on three tightly integrated technology challenges: ultralight photovoltaic cells optimised for space deployment, a flexible tile-based architecture that integrates solar collection, power conversion, and wireless transmission into a single modular unit, and precise free-space microwave power beaming using phased array antennas. The project's MAPLE (Microwave Array for Power-transfer Low-orbit Experiment) payload flew on the SSPD-1 (Space Solar Power Demonstrator-1) mission launched in January 2023 aboard a SpaceX Falcon 9. In orbit, MAPLE successfully demonstrated wireless power transfer in space and beamed detectable power to a receiver on Earth — marking a historic milestone as the first demonstration of space-to-Earth wireless power transmission from orbit. Caltech's architecture differs from large traditional SBSP concepts: rather than a single massive structure, it envisions a swarm of small modular spacecraft that collectively constitute a distributed solar power satellite. This approach potentially reduces launch complexity and in-space assembly requirements, though it introduces different challenges in formation flying and inter-module coordination.