The US Air Force has plans to improve radio communication over long distances by detonating plasma bombs in the upper atmosphere using a fleet of micro satellites. Since the early days of radio, we have known that signals that cannot be picked up by day may be heard clearly at night from hundreds of kilometres away.
This is down to changes in the ionosphere, a layer of charged particles in the atmosphere that starts around 60 kilometres up. The curvature of Earth stops most ground-based radio signals travelling more than 70 kilometres without a boost but by bouncing between the ionosphere and the ground they can zigzag for much greater distances. At night the ionosphere is denser and more reflective.
It’s not the first time the US have tried to improve radio communication by tinkering with the ionosphere. HAARP, the High Frequency Active Auroral Research Program in Alaska, stimulates the ionosphere with radiation from ground-based antennas to produce radio-reflecting plasma.
Now the USAF wants to do this more efficiently, with tiny satellites – such as CubeSats – carrying large volumes of ionised gas directly into the ionosphere.
There are at least two major challenges. One is building a plasma generator small enough to fit on a CubeSat. Then there’s the problem of controlling how the plasma disperses once released.
The USAF has awarded contracts to three teams sketching out different approaches. The best proposal will be selected for a second phase in which plasma generators will be tested in vacuum chambers and exploratory space flights.
General Science in Souderton, Pennsylvania, is working with researchers at Drexel University in Philadelphia on a method that involves using a chemical reaction to heat a piece of metal beyond its boiling point. The vaporised metal will react with atmospheric oxygen to produce plasma.
“It’s not the first time we’ve tried to improve radio signal by tinkering with the ionosphere,” said the programs director.
Another team, Enig Associates of Bethesda, Maryland, and researchers at the University of Maryland, want to rapidly heat a piece of metal by detonating a small bomb and converting the blast into electrical energy. Different shaped plasma clouds can be generated by changing the form of the initial explosion.
However, it’s not clear whether the USAF will succeed.
“These are really early-stage projects, representing the boundaries of plasma research into ionosphere modification,” says John Kline, who leads the Plasma Engineering group at Research Support Instruments in Hopewell, New Jersey. He thinks one of the biggest stumbling blocks will be packing enough power to generate plasma on to small satellites.
“It may be an insurmountable challenge.”