In January, a space solar power prototype was launched into orbit and has successfully demonstrated its ability to wirelessly transmit power in space and beam detectable power to Earth for the first time.
The prototype, called the Space Solar Power Demonstrator (SSPD-1), is part of Caltech’s Space Solar Power Project (SSPP), which aims to harness solar power in space and transmit it to the Earth’s surface.
One of the key technologies being tested within SSPD-1 is called MAPLE (Microwave Array for Power-transfer Low-orbit Experiment). It consists of a lightweight array of flexible microwave power transmitters driven by custom electronic chips made from low-cost silicon technologies. MAPLE uses these transmitters to beam energy to specific locations.
To make space solar power feasible, the energy transmission arrays need to be lightweight, flexible, and cost-effective. MAPLE addresses these requirements by utilizing lightweight and flexible components, which can be transported in rockets and deployed in space.
MAPLE’s development was led by Ali Hajimiri, a professor at Caltech and co-director of the SSPP. Hajimiri states that through their experiments, they have confirmed MAPLE’s successful transmission of power to receivers in space. They have also demonstrated the ability to program the array to direct its energy towards Earth, which they have detected at Caltech. This confirms that MAPLE can survive in space and operate effectively.
The array of power transmitters in MAPLE utilizes constructive and destructive interference to shift the focus and direction of the transmitted energy without the need for moving parts. Precise timing-control elements enable dynamic focusing of power to specific locations using the coherent addition of electromagnetic waves. This ensures that the majority of the energy is transmitted to the desired location.
MAPLE includes two receiver arrays located approximately one foot away from the transmitter. These receivers convert the received energy into direct current (DC) electricity, which is then used to light up a pair of LEDs. This demonstration showcases the successful wireless energy transmission over a distance in space. However, it’s important to note that the experiment is not sealed, so it is exposed to the harsh space environment, including temperature fluctuations and solar radiation, similar to what large-scale space solar power units would face in the future.
According to Hajimiri, the wireless energy transfer demonstrated by MAPLE is a first in space, even with expensive rigid structures. He emphasizes that they have achieved this milestone using flexible lightweight structures and their own integrated circuits.
The energy transmitted by MAPLE was detected by a receiver on the roof of Caltech’s Gordon and Betty Moore Laboratory of Engineering. The received signal matched the expected time, frequency, and frequency shift, confirming the successful transmission of energy from orbit.
Apart from surviving the launch and space flight, the experiment has provided valuable feedback for SSPP engineers. The power transmission antennas in MAPLE are arranged in clusters driven by custom flexible integrated circuit chips. The team is currently assessing the performance of individual elements within the system by analyzing interference patterns and measuring differences between various combinations. This process will help identify and address irregularities, providing insights for the next generation of the system. However, this assessment may take up to six months to complete.
Space solar power offers a way to tap into the abundant solar energy available in outer space, which remains constant without the constraints of day and night cycles, seasons, and cloud cover. It has the potential to yield up to eight times more power than solar panels on Earth’s surface. The vision of SSPP involves deploying a constellation of modular spacecraft that capture sunlight, convert it into electricity, and transmit it wirelessly via microwaves over long distances, providing power to locations currently lacking reliable access.
The flexible power transmission arrays developed by Caltech are crucial for the design of their sail-like solar panel constellation. These arrays can unfold once in orbit and facilitate wireless power transmission. Sergio Pellegrino, co-director of SSPP, highlights the importance of these flexible arrays in realizing Caltech’s vision.
Hajimiri expresses the hope that wireless energy transfer can democratize access to energy, similar to how the internet democratized access to information. With this technology, energy can be sent to remote regions or areas affected by war or natural disasters without the need for ground-based energy transmission infrastructure.
The Space Solar Power Project (SSPP) began in 2011 after philanthropist Donald Bren, inspired by an article in Popular Science, approached Caltech’s then-president to discuss the creation of a space-based solar power research project. Over the years, the Brens, through the Donald Bren Foundation, have made donations exceeding $100 million to fund the project and establish endowed professorships at Caltech.
Donald Bren expresses his admiration for the hard work and dedication of the brilliant scientists at Caltech, who have brought us closer to the realization of providing abundant, reliable, and affordable power for the benefit of all humankind.
Caltech President Thomas F. Rosenbaum highlights the importance of renewable energy transition and the challenges it currently faces in energy storage and transmission. He sees space-based solar power as an elegant solution, which has taken a significant step forward thanks to the Brens’ generosity and foresight. Rosenbaum emphasizes the potential of space solar power to provide uninterrupted renewable energy to the world.
Harry Atwater, one of the principal investigators of the project, emphasizes the significance of demonstrating wireless power transfer in space using lightweight structures. He sees this as a crucial milestone towards space solar power and its global accessibility.
The Space Solar Power Project envisions individual units folding into 1 cubic meter packages, which will then unfurl into flat squares measuring about 50 meters per side. These squares will have solar cells on one side facing the sun and wireless power transmitters on the other side facing Earth.
The SSPD-1 prototype was launched aboard a Momentus Vigoride spacecraft on a SpaceX rocket mission called Transporter-6. Momentus has been providing ongoing support to Caltech, including data communication, commanding and telemetry, and resources for optimal imaging and solar cell lighting.
In addition to MAPLE, the SSPD includes two other main experiments: DOLCE (Deployable on-Orbit ultraLight Composite Experiment) and ALBA. DOLCE is a structure that demonstrates the architecture, packaging scheme, and deployment mechanisms of the modular spacecraft. ALBA consists of 32 different types of photovoltaic cells to assess their effectiveness in the harsh space environment.
While ALBA’s solar cell tests are ongoing, DOLCE has not been deployed at the time of the press release. Results from these experiments are expected to be available in the coming months.