Richard Madonna: Powering Earth from Orbit with Caltech’s Space Solar Initiative

Image courtesy of Caltech.

As global energy demands continue to rise and geopolitical conflicts threaten stable energy supplies, it becomes increasingly important to identify clean, reliable, and renewable national energy sources. Among the most ambitious efforts toward this goal is Caltech’s Space Solar Power Project (SSPP), a research effort led by three principal investigators: Harry Atwater (Engineering and Applied Science Division Chair), Ali Hajimiri (project co-director), and Sergio Pellegrino (project co-director). These professors oversee the laboratories, personnel, and funding needed to carry out the research and develop the technologies. Dr. Richard G. Madonna serves as the project manager and system engineer and works closely with the technical teams. 

EcoAero had the opportunity to interview Dr. Madonna. His extensive background, compromising a Ph.D. in theoretical physics, four years of service in the U.S. Air Force, and prior work with Northrop Grumman, has contributed significantly to the development of the groundbreaking ideas at SSPP.

The earlier Space Solar Power Initiative (SSPI), conducted from 2014 to 2017 in partnership with Northrop Grumman, developed a 10 cm by 10 cm “sandwich” module designed for geosynchronous orbit (GEO). The module used photovoltaic cells on one side to collect solar energy and radio-frequency (RF) systems on the other side to wirelessly transmit power. This concentrator-based concept used mirrors to intensify sunlight onto narrow photovoltaic strips.

However, manufacturing the mylar concentrator mirrors proved difficult, and in GEO the mirrors would only allow energy collection for half of each orbit. The team explored options such as collecting sunlight from both sides of the module and transmitting RF energy in multiple directions.

Image courtesy of Caltech.

When SSPP began, the concentrator approach was determined to be a dead end. The team shifted to a flat, dual-sided tile architecture, using a 3:5 compound semiconductor material that is more resistant to radiation damage than gallium arsenide and provides a high power-to-mass ratio. This design resembles Earth-based solar panels but is optimized for space radiation.

The current SSPP tile concept uses long strips composed of photovoltaics on both sides and an antenna array on one side. These are layered onto a flexible integrated circuit board, allowing deployable antennas to transmit collected power to Earth.

This research could significantly advance space-based solar power. One full system could power a small town, effectively replacing a coal plant. The modular nature of the architecture allows scaling by adding more tiles as needed.

The team studied the feasibility of operating at GPS-altitude orbits. For this assessment, the stronger radiation environment—more challenging than GEO—was temporarily ignored to examine potential benefits. They concluded a constellation of at least four space solar power satellites would be required to ensure continuous power to a single region. To remain economically competitive with GEO, the other satellites would also need to sell power to other regions when not serving the primary target. This introduces a business model unfamiliar to domestic utilities and presents commercial risk. The team did not evaluate Tundra orbits. Research into radiation-tolerant versions of current SSPP technologies would be required before such constellations could be implemented.

In 2023 (January–November), SSPP completed an on-orbit demonstration of three core technologies on Momentus Space’s Vigoride-5, launched aboard SpaceX Transporter-6. The payload, called Space Solar Power Demonstration-1 (SSPD-1), included:

• DOLCE: deployable structure and mechanism (Pellegrino)

• MAPLE: wireless power transfer (Hajimiri)

• ALBA: photovoltaic experiment (Atwater)

The mission returned valuable technical data.

Image courtesy of Caltech.

Challenges remain, including thermal management, radiation tolerance, orbital logistics, and phased-array deployment at scale. Still, SSPP represents meaningful progress toward practical, space-based renewable energy.

At EcoAero, we believe that sustainability should be valued above all else in space, no matter the time or cost necessary. While the future of space energy generation is still unknown, the Space Solar Power Project holds promising results towards greener energy creation for the modern world. This technology and drive are a heartening step towards the future of space.