First wireless transmission of power demonstrated in space

Caltech's space solar power demonstrator has delivered its first key operational outcome with wireless transmission of power in space.

While such wireless transmission has been demonstrated on the Earth, its delivery in space is believed to be a first and a verification of Caltech's MAPLE (Microwave Array for Power-transfer Low-orbit Experiment) technology – one of the three key technologies under test in the demonstrator, which was launched on January 3.

"Through the experiments we have run so far, we received confirmation that MAPLE can transmit power successfully to receivers in space," says Ali Hajimiri, Bren Professor of Electrical Engineering and Medical Engineering at Caltech (California Institute of Technology) and co-director of the Space Solar Power Project, who led the development of the MAPLE instrument.

He adds that the group also has been able to programme the instrument to direct its energy toward Earth, which could be detected at Caltech and is indicative of its ability to survive the trip into space and to operate there.

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MAPLE consists of an array of flexible lightweight microwave power transmitters driven by custom electronic chips that were built using low-cost silicon technologies and enable the array to beam the energy to a desired location.

The focus and direction of the energy that is beamed out is achieved using the properties interference, the project team explains. Precise timing-control elements dynamically focus the power selectively on the desired location using the coherent addition of the electromagnetic waves.

The demonstration features two separate receiver arrays located about 30cm away from the transmitter to receive the energy, convert it to DC electricity and use it to light up a pair of LEDs.

This was tested by lighting up each LED individually and shifting back and forth between them.

The instrument also includes a small window through which the array can beam the energy, which was detected by a receiver on the roof of the Engineering Laboratory 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 other notable aspect is that the experiment is not sealed and subject to the harsh environment of space, including the wide temperature swings and solar radiation to which a large scale instrument would be subject.

In addition to the demonstration that the power transmitters could survive the launch into space and operate there, the development team intend to assess the performance of the individual elements – a process they believe could take around six months.

The power transmission antennas are clustered in groups of 16, each group driven by an individual chip and evaluation of the interference patterns of smaller groups should enable irregularities to be detected and traced back to individual units.

The other two main experiments on the demonstrator are DOLCE (Deployable on-Orbit ultraLight Composite Experiment), a structure approximately 1.8m square to demonstrate 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 space environment.

The ALBA tests of solar cells are ongoing, but so far the team has not yet attempted to deploy DOLCE.

Caltech's successful power beaming demonstration has emerged just days after news reports from Japan have suggested that country could be deploying a series of small satellites in orbit to start beaming solar energy to the Earth by 2025.

The initiative is being led by Kyoto University professor Naoki Shinohara, who has been working on the challenge for over a decade.

Other countries in the space solar race include China, the UK and Europe, while in the US another initiative is the Air Force Research Laboratory's Space Solar Power Incremental Demonstrations and Research Project (SSPIDR), which is developing a novel ‘sandwich tile’ to collect and beam the solar energy to Earth.

The Arachne demonstration of the sandwich tile is also slated for launch in 2025.

With space based solar requiring panels of about 2km in extent to deliver 1GW of power, similar to that of the average nuclear reactor, there are still considerable technological and financial challenges to overcome to bring it to fruition.