On SpaceX Rocket, Caltech Prototype Tests Way to Beam Solar Power to Earth

January 06, 2023 by Darshil Patel

On SpaceX's recent launch, Caltech sent its Space Solar Power Demonstrator (SSPD) into orbit to harvest solar power in space and transmit it to Earth.

While solar energy is one of the most abundant energy sources, it is intermittent on the Earth's surface and heavily depends on the weather. Sunlight, however, can be accessed continuously in space. Solar energy harvesting in space can generate around five times the energy of a similar solar panel on Earth. To put this into perspective, a study by the National Space Society in 2007 estimated that a half-mile band of photovoltaics in geosynchronous orbit can generate energy equivalent to all the oil remaining on Earth for one year.


Caltech's Space Solar Power Demonstrator

Caltech's Space Solar Power Demonstrator. Screenshot courtesy of Caltech


Researchers are now studying not only how to capture solar energy in space but also how to transmit that energy to Earth via microwave or infrared laser beams. The California Institute of Technology (Caltech) recently announced that its prototype, called the Space Solar Power Demonstrator (SSPD), launched into orbit on Jan. 3. The demonstrator will test key components designed to harvest solar power in space.

The Caltech Space Solar Power Project (SSPP) has attracted over $100 million in funding from Donald Bren, chairman of Irvine Company and a lifetime member of the Caltech Board of Trustees. The multifunctional demonstrator collects sunlight, converts it to electricity, and transfers energy wirelessly through radio frequency (RF) using ultralight structures for integration. It was part of the Momentus Vigoride spacecraft, carried by a SpaceX rocket on the Transporter-6 mission.


Technologies Deployed for SSPD

The engineers working on the SSPD explored new technologies, architectures, composite materials, and structures to overcome the challenges of heavy solar cells and power transmission. They created parts and solar cells lightweight and durable enough to be deployed in the unpredictable conditions in space.

The 50 kg SSPD will test three key components for the project:


  1. DOLCE (Deployable on-Orbit ultraLight Composite Experiment): A six feet by six feet structure that tests a new architecture for solar-powered vehicles and a phased array antenna. It uses ultrathin composite materials for exceptional efficiency and flexibility. Its modularity and deployment mechanism would make up a kilometer-scale constellation forming a power station.
  2. ALBA (Italian for “dawn”): A collection of 32 different types of photovoltaic cells that assesses the cell types under harsh space conditions. A successful test will provide data on which solar cells operate efficiently and reliably in these environments.
  3. MAPLE (Microwave Array for Power-transfer Low-orbit Experiment): An array of lightweight microwave power antennas that work with precise timing control focusing on two different receivers on Earth, demonstrating selective distant power transmission to multiple specific targets on demand. It performs functional verification and evaluates the system performance under different space conditions. 


Engineers attaching DOLCE to the Momentus Vigoride spacecraft

Engineers attaching DOLCE to the Momentus Vigoride spacecraft. Image courtesy of Caltech


Other components include a box of electronics interfacing with the Vigoride computer that controls these experiments. This box consists of cameras to monitor the experiment's progress.


How Does the Directional Wireless Power Transfer Work?

The concept of power transmitter arrays is based on interference. If one source transmits energy in space, it will be omnidirectional. However, when two or more sources transmit, there will be an area where there is constructive interference, which means the energies from all sources add up. Similarly, there are areas where the energy waves cancel each other, namely destructive interference.


Flexible antenna sheet as the power transmitter array

Flexible antenna sheet as the power transmitter array. Image courtesy of Caltech


If all the transmitters in the antenna array are in phase (transmitting simultaneously), a high-power beam with high directionality will form. The Caltech researchers precisely control the timing of each antenna in an array, changing its directionality and transmitting the energy to multiple receivers at the same time. Antenna separation and its phases play an important role in beamforming.


Illustration of the phased array antenna

Illustration of the phased array antenna. Image courtesy of Wikimedia Commons [CC0 1.0]


Launching the Demonstrator into Orbit

The SSPD was carried by the Momentus Vigoride spacecraft on a SpaceX rocket as a part of the Transporter-6 mission. The rocket took around 10 minutes to reach the desired altitude, after which the Momentus spacecraft was deployed into orbit.

The Caltech team plans to start their experiments in a few weeks. Some of these tests, like DOLCE, will be performed quickly. Others, however, will take more time. The evaluation and collection of solar cell data will take up to six months to get new insights into which technologies are effective.