Photo from space of the interior of MAPLE, with the transmission array to the right and the receivers to the left. (Image: SSPP)

Wireless power transfer was recently demonstrated by MAPLE — Microwave Array for Power-transfer Low-orbit Experiment — one of three key technologies being tested by the Space Solar Power Demonstrator (SSPD-1), the first space-borne prototype from Caltech’s Space Solar Power Project (SSPP), which aims to harvest solar power in space and transmit it to the Earth’s surface.

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. For SSPP to be feasible, energy transmission arrays will need to be lightweight to minimize the amount of fuel needed to send them to space, flexible so they can fold up into a package that can be transported in a rocket, and a low-cost technology overall.

“Through the experiments we have run so far, we received confirmation that MAPLE can transmit power successfully to receivers in space,” said SSPP Co-Director and Professor Ali Hajimiri, who led the team that developed MAPLE. “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.”

“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,” said Hajimiri.

Beyond a demonstration that the power transmitters could survive the launch and space flight, and still function, the experiment has provided useful feedback to SSPP engineers.

Space solar power provides a way to tap into the practically unlimited supply of solar energy in outer space, where the energy is constantly available without being subjected to the cycles of day and night, seasons, and cloud cover — potentially yielding eight times more power than solar panels at any location on Earth.

When fully realized, SSPP will deploy a constellation of modular spacecraft that collect sunlight, transform it into electricity, then convert it to microwaves that will be transmitted wirelessly over long distances to wherever it is needed — including locations that currently have no access to reliable power.

“In the same way that the internet democratized access to information, we hope that wireless energy transfer democratizes access to energy,” said Hajimiri. “No energy transmission infrastructure will be needed on the ground to receive this power. That means we can send energy to remote regions and areas devastated by war or natural disaster.”

Individual SSPP units will fold up into packages about 1 m3 in volume and then unfurl into flat squares about 50 m per side, with solar cells on one side facing the sun and wireless power transmitters on the other side facing Earth.

SSPD has two main experiments besides MAPLE: DOLCE (Deployable on-Orbit ultraLight Composite Experiment) 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.

For more information, contact Kathy Svitil at This email address is being protected from spambots. You need JavaScript enabled to view it.; 626-395-8022.