The Caltech Space Solar Power Project (SSPP) has successfully launched into orbit a prototype, dubbed the Space Solar Power Demonstrator (SSPD), that 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. When fully realised, SSPP will deploy a constellation of modular spacecraft that collect sunlight, transform it into electricity, then wirelessly transmit that electricity over long distances to wherever it’s 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 carried the 50-kilogram SSPD into space. It consists of three main experiments, each tasked with testing a different key technology:
1. DOLCE (Deployable on-Orbit ultraLight Composite Experiment): A structure measuring two metres by two metres that demonstrates the architecture, packaging scheme and deployment mechanisms of the modular spacecraft that would eventually make up a kilometere-scale constellation forming a power station;
2. ALBA: A collection of 32 different types of photovoltaic cells to enable an assessment of the types of cells that are the most effective in the punishing environment of space;
3. MAPLE (Microwave Array for Power-transfer Low-orbit Experiment): An array of flexible lightweight microwave power transmitters (pictured below) 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 is a box of electronics that interfaces with the Vigoride computer and controls the three experiments.
The Caltech team plans to start running their experiments on the SSPD within a few weeks. Some elements of the test will be conducted quickly. ‘We plan to command the deployment of DOLCE within days of getting access to SSPD from Momentus. We should know right away if DOLCE works,’ said Sergio Pellegrino, Caltech’s Joyce and Kent Kresa professor of aerospace and professor of civil engineering, and co-director of SSPP.
Other elements will require more time. The collection of photovoltaics will need up to six months of testing to give new insights into which technology will be best for this application.
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 to Earth. The SSPP team hopes to have a full assessment of the SSPD’s performance within a few months of the launch.
‘No matter what happens, this prototype is a major step forward,’ said Ali Hajimiri, Caltech’s Bren professor of electrical engineering and medical engineering and co-director of SSPP. ‘It works here on Earth and has passed the rigorous steps required of anything launched into space. There are still many risks, but having gone through the whole process has taught us valuable lessons.’
Although solar cells have existed on Earth since the late 1800s and currently generate about four per cent of the world’s electricity, 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 envision and create new technologies, architectures, materials and structures for a system that is capable of the practical realisation of space solar power, while being light enough to be cost-effective for bulk deployment in space and strong enough to withstand the space environment.
‘DOLCE demonstrates a new architecture for solar-powered spacecraft and phased antenna arrays,’ Pellegrino said. ‘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.’
‘The entire flexible MAPLE array, as well as its core wireless power transfer electronic chips and transmitting elements, have been designed from scratch,’ Hajimiri said. ‘This wasn’t made from items you can buy because they didn’t even exist. This fundamental rethinking of the system from the ground up is essential to realise scalable solutions for SSPP.’
The set of three prototypes within the SSPD was envisioned, designed, built and tested by a team of about 35 individuals – a collection of graduate students, postdocs and research scientists. These individuals now 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, Caltech’s Otis Booth leadership chair of the division of engineering and applied science.