Engineers carefully lower the DOLCE portion of the Space Solar Power Demonstrator onto the Vigoride spacecraft built by Momentus. (Image: Caltech/Space Solar Power)

On January 3rd, the Caltech Space Solar Power Project (SSPP) launched into orbit a prototype, dubbed the Space Solar Power Demonstrator (SSPD), which will test several key components of an ambitious plan to harvest solar power in space and beam the energy back to Earth.

Space solar power provides a way to tap into the practically unlimited supply of solar energy in outer space, where the energy is constantly available without being subjected to the cycles of day and night, seasons, and cloud cover.

The launch represents a major milestone in the project. When fully realized, SSPP will deploy a constellation of modular spacecraft that collect sunlight, transform it into electricity, then wirelessly transmit that electricity over long distances wherever it is needed— including to places that currently have no access to reliable power.

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

  • 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 would 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.

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

The collection of photovoltaics will need up to six months of testing to give new insights into what types of photovoltaic technology will be best for this 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. Meanwhile, two 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 hopes that they will have a full assessment of the SSPD's performance within a few months.

Numerous challenges remain: nothing about conducting an experiment in space is guaranteed. But regardless of what happens, the sheer ability to create a space-worthy prototype represents a significant achievement by the SSPP team.

Although solar cells have existed on Earth since the late 1800s and currently generate about four percent of the world's electricity (in addition to powering the International Space Station), 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 has had to envision and 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.

"DOLCE demonstrates a new architecture for solar-powered spacecraft and phased antenna arrays. It exploits the latest generation of ultrathin composite materials to achieve unprecedented packaging efficiency and flexibility. With the further advances that we have already started to work on, we anticipate applications to a variety of future space missions," said Professor Sergio Pellegrino.

"The entire flexible MAPLE array, as well as its core wireless power transfer electronic chips and transmitting elements, have been designed from scratch. This wasn't made from items you could buy — because they didn't even exist. This fundamental rethinking of the system from the ground up is essential to realize scalable solutions for SSPP," said Professor Ali Hajimiri.

The entire set of three prototypes within the SSPD was envisioned, designed, built, and tested by a team of about 35 individuals. "This was accomplished with a smaller team and significantly fewer resources than what would be available in an industrial, rather than academic, setting. The highly talented team of individuals on our team has made it possible to achieve this," said Hajimiri.

Those individuals — a collection of graduate students, postdocs, and research scientists — represent the cutting edge in the burgeoning space solar power field. "We're creating the next generation of space engineers," said SSPP researcher Harry A. Atwater, director of the Liquid Sunlight Alliance, a research institute dedicated to using sunlight to make liquid products that could be used for industrial chemicals, fuels, and building materials or products.

Success or failure will be measured in a variety of ways. For ALBA, a successful test will provide an assessment of which photovoltaic cells operate with maximum efficiency and resiliency. MAPLE's goal is to demonstrate selective free-space power transmission to different specific targets on demand.