Caltech claims to have beamed energy to Earth from satellite

Tech has potential to power war-torn spots and remote regions

Researchers at a US university claim to have beamed energy from a satellite in orbit to a detector on Earth, demonstrating that harvesting energy from solar panels in space is technically possible.

The eggheads at the California Institute of Technology, aka Caltech, said they used a satellite launched into orbit in January to demonstrate the ability to transmit power wirelessly in space, and also to beam detectable power back to Earth.

Known as the Space Solar Power Demonstrator (SSPD-1), the satellite is the first technology prototype from Caltech's Space Solar Power Project (SSPP) to make it into orbit.

SSPP was founded a decade ago, with the objective of harvesting solar power in space and transmitting it to receivers on the ground, as The Register has previously reported.

All electromagnetic radiation carries energy, which can be seen in radios that are powered by the received radio signal itself. The trick is being able to direct energy to a desired target instead of it radiating in all directions.

The business end of the SSPD-1 satellite is the Microwave Array for Power-transfer Low-orbit Experiment (MAPLE) – an array of flexible, lightweight microwave power transmitters driven by custom electronic chips to direct a beam of energy to wherever it is needed.

An interplay of constructive and destructive interference between individual transmitters directs the beam, so that a bank of power systems is able to shift the focus and direction of the energy it beams out. This is similar to the technique used in military phased-array radar systems to scan the horizon without physically moving the antenna.

In this case, the transmitter array uses precise timing control to focus the power on the desired location using the coherent addition of electromagnetic waves, according to Caltech – so that the majority of the energy transmitted is focused on the desired target location.

However, in this case, the energy didn't have to travel very far. MAPLE includes two receiver arrays about a foot (30.5cm) away from the transmitter to receive the energy. When the energy is received, it lights up some LEDs to demonstrate the system is working.

This isn't much of a test. MAPLE also features a small window on the satellite through which the array can beam the energy. This was used to transmit a test signal to a receiver on the roof of a laboratory at Caltech's campus in Pasadena.

Although this only delivered a tiny amount of energy, Ali Hajimiri, Bren Professor of Electrical Engineering and co-director of SSPP, claimed the achievement as a first.

"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," he declared in a statement.

"Through the experiments we have run so far, we received confirmation that MAPLE can transmit power successfully to receivers in space. 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."

The satellite has other experimental hardware in addition to MAPLE. Deployable on-Orbit ultraLight Composite Experiment (DOLCE) is designed to test deployment mechanisms for a lightweight foldable structure to support the solar panels, while ALBA is a collection of 32 different types of photovoltaic cells. They are arrayed to assess which types operate best in space.

Looking to the future, the SSPP project said it aims to deploy a constellation of satellites to collect sunlight and beam the energy by microwave to wherever it is needed – including locations that have no reliable access to power. This is assuming the equipment achieves enough efficiency to make the effort worthwhile.

"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," Hajimiri said.

The idea behind solar power from space is that energy is always available without being subject to the cycles of day and night, seasons, and cloud cover, the SSPP states – potentially yielding eight times more power than solar panels on the ground.

However, a previous study by the European Space Agency (ESA) into solar collecting satellites calculated they would have to be somewhere in the region of a kilometer or more across in order to beam down around 2GW of power to the surface – which would match the output of a nuclear power plant.

It looks like the SSPP will be aiming for more modest goals, at least for now. ®

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