A flexible prototype antenna sheet for Caltech’s power transmitter array. Each orange square on the yellow tile is an antenna driven by a single transmitter.
Credit: Lance Hayashida/Caltech

Last January, a novel prototype of space solar power-beaming technology was placed into Earth orbit.

Caltech’s Space Solar Power Project (SSPP) has announced the experiment has wirelessly transmitted power in space and beamed detectable power to Earth for the first time.

Called MAPLE, short for Microwave Array for Power-transfer Low-orbit Experiment, it is one of three key technologies being tested by the Space Solar Power Demonstrator (SSPD-1).

(Left to Right) Sergio Pellegrino, Harry Atwater, and Ali Hajimiri, the principal investigators of the Caltech Space Solar Power Project. Image credit: Caltech

A Momentus Vigoride spacecraft launched on January 3 aboard a SpaceX rocket on the Transporter-6 mission carried the 110-pound (50-kilogram) SSPD-1 to space.

Energy broadcasting

MAPLE consists of an array of flexible lightweight microwave power transmitters driven by custom electronic chips that were built using low-cost silicon technologies. It uses the array of transmitters to beam the energy to desired locations, according to a Caltech statement.

Caltech’s power transmitter array.
Image credit: Caltech

MAPLE was developed by a Caltech team led by Ali Hajimiri, Bren Professor of Electrical Engineering and Medical Engineering and co-director of SSPP. 

“Through the experiments we have run so far, we received confirmation that MAPLE can transmit power successfully to receivers in space,” Hajimiri reports in the Caltech statement. “We have also been able to program the array to direct its energy toward Earth, which we detected here at Caltech. We had, of course, tested it on Earth, but now we know that it can survive the trip to space and operate there.”

In-space photo taken from Space Solar Power Demonstrator (SSPD-1).
Image credit: Caltech

Image taken from Space Solar Power Demonstrator (SSPD-1).
Image credit: Caltech

LEDs: lighting the way

MAPLE is outfitted with two separate receiver arrays situated about a foot away from the transmitter to receive the energy, converts that energy to direct current electricity, and uses that energy to light up a pair of LEDs to exhibit the full run of wireless energy transmission at a distance in space.

MAPLE tested this in space by lighting up each LED individually and shifting back and forth between them.

MAPLE includes a small window through which the array can beam the energy. “This transmitted energy was detected by a receiver on the roof of the Gordon and Betty Moore Laboratory of Engineering on Caltech’s campus in Pasadena. The received signal appeared at the expected time and frequency, and had the right frequency shift as predicted based on its travel from orbit,” the Caltech statement adds.

Transmitted energy from space was detected by a receiver on the roof of the Gordon and Betty Moore Laboratory of Engineering on Caltech’s campus in Pasadena.
Image credit: Caltech

End of the power line. Space transmitted energy was detected by a receiver on the roof of Caltech’s Gordon and Betty Moore Laboratory.
Image credit: Caltech

Step-by-step evaluation

The Hajimiri-led team is assessing the performance of individual elements within the system, a meticulous process that can take up to six months to fully complete. The step-by-step evaluation will allow the team to sort out irregularities and trace them back to individual units, providing insight for the next generation of the system.

DOLCE is lowered onto the Vigoride spacecraft built by Momentus.
Image credit: Caltech/Momentus

Besides MAPLE, SSPD has two main experiments:

  • DOLCE (Deployable on-Orbit ultraLight Composite Experiment), a structure measuring 6 feet by 6 feet that demonstrates the architecture, packaging scheme, and deployment mechanisms of the modular spacecraft; and
  • 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.

The ALBA tests of solar cells are ongoing, and the SSPP has not yet attempted to deploy DOLCE as of press time. Results from those experiments are expected in the coming months.

Meanwhile, Hajimiri is beaming with satisfaction: “To the best of our knowledge, no one has ever demonstrated wireless energy transfer in space even with expensive rigid structures. We are doing it with flexible lightweight structures and with our own integrated circuits. This is a first.”

“The work at the space solar power program at Caltech continues to produce very useful technology for the future of space solar power,” John Mankins, President of Artemis Innovation Management Solutions told Inside Outer Space. He is an internationally recognized leader in space systems and technology innovation and a leading advocate of space solar power.

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