Quirks & Quarks·Analysis

A secret military space plane is carrying an experiment to harvest power from space

Bob McDonald's blog: A pizza box-sized prototype will demonstrate the possibility of solar power satellites, which have been a long-held dream of space enthusiasts.

Bob McDonald's blog: A pizza box-sized prototype will demonstrate the possibility of solar power satellites

The unpiloted X-37B military spacecraft is currently orbiting and flying an experiment to test technology for solar power satellites. (AP file photo)

An unmanned military space plane called the X-37B, which resembles a smaller version of the space shuttle, is carrying a device that converts solar energy into microwaves that could be beamed to Earth to provide emissions-free energy. This is proof-of-principle of an attractive idea that is not without risks, challenges, and enormous potential costs.

This concept of space-based solar power has been around for decades. It holds promise as a technology that could capture huge amounts of free energy from the sun and convert it into clean electrical energy. In space, sunlight is more intense because it doesn't pass through the atmosphere, and a satellite in the proper orbit could remain in sunlight almost 24/7 collecting energy. That power could be converted into an intense microwave energy beam aimed at receivers on the ground which would convert it into clean electricity.

The X37-B space plane has flown in space five times before, and is capable of staying in orbit for more than a year. But the military has been tight-lipped on what exactly it has been doing up there during most of these highly classified missions. This flight, which launched May 17, carries rare scientific payloads they are willing to talk about.

The solar power experiment is called the Photovoltaic Radiofrequency Antenna Module Flight Experiment (PRAM-FX). Designed by researchers at the U.S. Naval Research Laboratory, the proof-of-concept device is only about the size and shape of a pizza box. One side is covered with solar cells that turn sunlight into electricity, which is then converted to microwaves. 

This pizza box-sized device will fly in space to demonstrate the possibility of capturing solar power and converting it into microwaves to be beamed to the ground. (U.S. Naval Research Laboratory)

While this experiment is to test the efficiency of the system in space, it will not be sending a microwave beam to the Earth. However, the military is interested in developing future technologies that would allow them to beam energy from space to provide power for troops in the field, drive vehicles and even unmanned aircraft without carrying fossil fuels.

The idea of sending power without wires goes back to 1890 when Nicola Tesla experimented with devices to transmit energy using electromagnetic waves. While Tesla was not able to fulfil his dream of powering the world, today we do have things like wireless charging for devices that are close to each other. 

While it sounds like science fiction, beaming energy from space is technically feasible, but likely at least decades away from reality due to many challenges — first among them: scale.

Solar power satellites would have to be very large in order to capture enough solar energy, and also have very large antennas to transmit the beam to Earth. These monstrosities would be much larger than the International Space Station, which itself is larger than a football field. The ISS cost upwards of $100 billion to build, so that gives you some idea of what an even larger — though possibly simpler — solar power satellite might cost. 

Solar power satellites would likely dwarf the International Space Station which is already the size of a football field. (NASA)

On Earth, a very large receiver called a rectenna would be needed to capture the beam and turn it into electricity. Then there is the issue of having powerful microwave beams shining down on the Earth, potentially creating a hazard to everything from aircraft to migrating birds. An alternative might be to use lasers, but they come with their own hazards. Obviously, the areas above the ground stations would have to be no-fly zones.

Despite the enormous challenges, scientists say just one of these satellites could meet the energy needs of a major city such as Toronto or Vancouver and surrounding areas. This grandiose concept of providing reliable clean energy from space has been quietly in the back rooms of the space program for decades. 

As companies such as SpaceX bring the cost of space flight down, and the negative impacts of burning fossil fuels becomes more apparent, perhaps the pizza box experiment flying in space now will grow into a vision of plentiful, clean power in the distant future.  

Video describing the experiment from the U.S. Naval Research Laboratory

About the Author

Bob McDonald is the host of CBC Radio's award-winning weekly science program, Quirks & Quarks. He is also a science commentator for CBC News Network and CBC-TV's The National. He has received 12 honorary degrees and is an Officer of the Order of Canada.