The Caltech Space Solar Power Project (SSPP) launched into orbit in early January a prototype, the Space Solar Power Demonstrator (SSPD). The craft is intended to test several components of a system that is planned eventually to harvest solar power in space and beam the energy back to Earth.

If fully realized, SSPD would deploy multiple modular spacecraft to collect sunlight, transform it into electricity, then wirelessly transmit that electricity over long distances wherever it is needed.

A Momentus Vigoride spacecraft carried aboard a SpaceX rocket on the Transporter-6 mission carried the 50-kilogram SSPD to space on January 3. SSPD consists of three main experiments, each tasked with testing a different technology:

DOLCE (Deployable on-Orbit ultraLight Composite Experiment): A structure measuring 6 feet by 6 feet that demonstrates the architecture, packaging scheme and deployment mechanisms of the modular spacecraft that could eventually make up a kilometer-scale constellation forming a power station.

ALBA: A collection of 32 different types of photovoltaic (PV) cells, to enable an assessment of the types of cells that are the most effective in the punishing environment of space.

MAPLE (Microwave Array for Power-transfer Low-orbit Experiment): An array of flexible lightweight microwave power transmitters with precise timing control focusing the power selectively on two different receivers to demonstrate wireless power transmission at distance in space.

A fourth component is a box of electronics that interfaces with the Vigoride computer and controls the three experiments.

Data collection

SSPP began in 2011 after philanthropist Donald Bren learned about the potential for space-based solar energy manufacturing in an article in Popular Science. The first of the donations to Caltech (which are expected eventually to exceed $100 million) was made through the Donald Bren Foundation.

Data collection from the diverse types of PV cells will need up to six months to give usable insights into what types of photovoltaic technology will be best for the application. MAPLE involves a series of experiments, from an initial function verification to an evaluation of the performance of the system under different environments over time. 

Sergio Pellegrino, Harry Atwater, and Ali Hajimiri, the principal investigators of the Space Solar Power Project.Credit: Caltech

At the same time, cameras on deployable booms mounted on DOLCE and additional cameras on the electronics box will monitor the experiment’s progress, and stream a feed back down to Earth. The SSPP team said it hopes to have a full assessment of the SSPD’s performance within a few months of the launch.

Rethinking power delivery

Caltech said that everything about solar power generation and transmission needed to be rethought for use on a large scale in space. Solar panels are bulky and heavy, making them expensive to launch, and they need extensive wiring to transmit power.

To overcome these challenges, the SSPP team had to create new technologies, architectures, materials, and structures for a system that is capable of the practical realization of space solar power, while being light enough to be cost-effective for bulk deployment in space, and strong enough to withstand the punishing space environment.

The prototype antenna sheet for the power transmitter array that demonstrates the unit’s flexibility.Each orange square on the yellow tile is an antenna to be driven by a single transmitter.Credit: Lance Hayashida/Caltech

The DOLCE test unit was designed to demonstrate a new architecture for solar-powered spacecraft and phased antenna arrays. It uses the latest generation of ultrathin composite materials to achieve what the Caltech team said is “unprecedented packaging efficiency and flexibility.” 

In addition, the entire flexible MAPLE array, as well as its core wireless power transfer electronic chips and transmitting elements, was designed from scratch. 

The entire set of three prototypes within the SSPD was envisioned, designed, built, and tested by a team of about 35 people. 

Success or failure will be measured in several ways. Researchers said the most important test for DOLCE will be that the structure completely deploys from its folded-up configuration into its open configuration. For ALBA, a successful test would provide an assessment of which photovoltaic cells operate with maximum efficiency and resiliency. And MAPLE’s goal is to demonstrate selective free-space power transmission to different specific targets on demand.