Caltech launches solar power prototype into space

The California Institute of Technology's Space Solar Power Demonstrator (SSPD) has been launched on a SpaceX Falcon 9 rocket, in a mission to test the viability of harvesting solar power in space.

The 110lb SSPD prototype was launched into space on the Transporter-6 mission, which lifted off from Cape Canaveral on Tuesday 3 January 2023. 

The demonstrator is part of the Caltech Space Solar Power Project (SSPP). The scientists behind the mission have designed three experiments to test several key components of an ambitious plan to harvest solar power in space and beam the energy back to Earth. 

Satellites in geosynchronous orbit receive sunlight for more than 99 per cent of the time – as they are not subjected to the cycles of a day and changes in weather – and at a much greater intensity than solar panels on Earth, making them a much more efficient source of energy. 

The launch of SSPD is the first step on a mission that could see the deployment of a constellation of space solar panels that could measure over half a mile wide. These will form a space power station that would be able to transform sunlight into electricity and wirelessly transmit it back to Earth.

Artist's rendering of what the Space Solar Power Demonstrator looks like when unfolded.

Artist's rendering of what the Space Solar Power Demonstrator looks like when unfolded. / Caltech

Image credit: Caltech/Space Solar Power Program

The SSPD is hitching a ride to orbit affixed to a Momentus Vigoride spacecraft, carried aboard a SpaceX rocket on the Transporter-6 mission. It consists of three main experiments, each tasked with testing a different key technology of the project. 

The first one is known as DOLCE (Deployable on-Orbit ultraLight Composite Experiment). It is a 6ft-square structure that demonstrates the architecture, packaging scheme and deployment mechanisms of the modular space solar panels. 

The second experiment has been named ALBA, and it has been designed to collect 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. 

Finally, MAPLE (Microwave Array for Power-transfer Low-orbit Experiment) is 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.

Engineers carefully lower the DOLCE portion of the Space Solar Power Demonstrator onto the Vigoride spacecraft built by Momentus.

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

Image credit: Caltech/Space Solar Power Program

The origins of SSPP date back to 2011, when philanthropist Donald Bren learned about the potential for space-based solar energy manufacturing in an article in the magazine Popular Science

Intrigued by the potential for space solar power, Bren approached Caltech’s then-president Jean-Lou Chameau to discuss the creation of a space-based solar power research project. In 2013, Bren and his wife, Brigitte Bren, a Caltech trustee, agreed to make a donation to fund the project. 
“For many years, I’ve dreamed about how space-based solar power could solve some of humanity’s most urgent challenges,” Bren said. “Today, I’m thrilled to be supporting Caltech’s brilliant scientists as they race to make that dream a reality.”

The rocket will take approximately 10 minutes to reach its desired altitude. A few weeks after the launch, the Caltech team on Earth plans to start running the three main experiments that make up the mission.

"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, a civil engineer at Caltech and co-director on the SSPD, in a press release. 

The unfurling is, in some ways, the easy part. The demonstrator has been tested down on Earth but how it holds up in space is yet to be seen. The ALBA and MAPLE experiments will take much longer to complete as scientists want to see how they function over time and in different environments.

Other elements will require more time, with the collection of photovoltaics needing up to six months of testing to give new insights into what types of photovoltaic technology will be best for this application.

The SSPP team hopes that they will 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, 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. We believe the space experiments will provide us with plenty of additional useful information that will guide the project as we continue to move forward.”

Although solar cells have existed on Earth since the late 1800s and currently generate about 4 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.

To ensure the success of the project, the SSPP team has 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 punishing space environment. 

“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 team at Caltech are, however, not the only scientists testing the potential of solar power generation. Last summer, China announced that the first launch for the construction of its solar power project in space had been scheduled for 2028 – two years earlier than originally planned – when a trial satellite orbiting at a distance of around 400km will test the technology used to transmit energy from the power plant to Earth.

In addition, the UK has also commissioned independent research supporting a £16bn British version of a solar power station in orbit by 2035.

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