Researchers transmit space solar energy to Earth for the first time

Space solar power provides a way to tap into the virtually unlimited supply of solar energy in space. Solar energy from space is continuously available, unaffected by day and night cycles, seasons and cloud cover, which can produce up to eight times more energy than solar panels anywhere on the earth’s surface.

However, storing space solar energy, transmitting it to Earth and using it is still a challenge.

To overcome this problem, researchers at the California Institute of Technology (Caltech) have developed a Microwave Array for the Power-Transfer Low-Orbit Experiment (MAPLE) aimed at generating and transmitting solar energy from space to the Earth’s surface.

The space solar-powered prototype launched into orbit in January is now operational. It demonstrated its ability to wirelessly transmit energy into space and transmit detectable energy to Earth for the first time.

Being tested by the Space Solar Power Demonstrator (SSPD-1), it is the first space prototype of Caltech’s Space Solar Power Project (SSPP) which aims to harvest solar energy in space and transmit it to the Earth’s surface.

MAPLE consists of flexible, lightweight microwave power transmitters powered by custom electronic chips built using low-cost silicon technology. It uses a series of transmitters to transmit energy to desired locations.

For SSPP to be feasible, power transmission arrays must be lightweight to minimize the amount of fuel needed to send them into space, flexible enough to be folded into a package that can be carried in a rocket, and overall technology a low cost.

Using constructive and destructive interference between transmitters, a bank of power transmitters can shift the focus and direction of the energy they emit without any moving parts. A transmitter array uses a precisely timed control element to dynamically focus power to a desired location using a coherent combination of electromagnetic waves. Due to this, most of the energy is transmitted to the desired place.

To receive the energy, MAPLE has two separate receiver arrays located approximately one foot apart from the transmitter. It then converts the energy into direct current (DC) electricity and uses it to light a pair of LEDs to show the entire sequence of remote wireless energy transmission in space. MAPLE tested this by lighting each LED individually in the space and moving back and forth between them. The experiment is unsealed, so it is subject to the harsh environment of space, including the wide temperature swings and solar radiation that large-scale SSPP units will one day face.

MAPLE also includes a small window through which the array can transmit energy. This transmitted energy was then detected by a receiver on the roof of the Gordon and Betty Moore Laboratory of Engineering on the Caltech campus in Pasadena.

According to the researchers, the received signal appeared at the expected time and frequency and had the right frequency shift as expected based on its journey from orbit.

Through the experiments the researchers have conducted so far, they have received confirmation that MAPLE can successfully transmit energy to receivers in space. The researchers were also able to program the array to direct its energy towards Earth, which they detected at Caltech.

“As far as we know, no one has ever demonstrated wireless energy transfer in space, even with expensive rigid structures. We’re doing this with flexible, lightweight structures and our integrated circuits. This is the first” says Ali Hajimiri, Bren Professor of Electrical Engineering and Medical Engineering and co-director of SSPP.

“In the same way that the internet has democratized access to information, we hope wireless power transfer will democratize access to energy,” Hajimiri says. “No ground-based power transmission infrastructure will be needed to receive this power. This means we can send energy to remote regions and areas devastated by wars or natural disasters.”

Researchers have tested MAPLE on Earth and know evidence that power transmitters could also survive launch and spaceflight and still function. Furthermore, the experiment provided useful feedback to SSPP engineers. The power transmission antennas are assembled in groups of 16, each group driven by a fully customized flexible integrated circuit chip.

The research team is now evaluating the performance of individual components of the system by evaluating intervention patterns in small groups and measuring the differences between the different combinations.

The process could take six months to complete and will allow the team to fix irregularities and trace back to individual units, providing insights for the next generation of the system.

After thoroughly studying this system, the SSPP will deploy a constellation of modular spacecraft. These spacecraft will collect sunlight, turn it into electricity, then convert it into microwaves that will be transmitted wirelessly over long distances to wherever it’s needed, including places that don’t currently have access to reliable power.

“In the same way that the internet has democratized access to information, we hope wireless power transfer will democratize access to energy,” Hajimiri says. “No ground-based power transmission infrastructure will be needed to receive this power. This means we can send energy to remote regions and areas devastated by wars or natural disasters.”

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