Submission + - Hypersonic Radio Black-Out Problem Solved (technologyreview.com)
KentuckyFC writes: Russian physicists have come up with a new way to communicate with hypersonic vehicles surrounded by a sheath of plasma. Ordinarily, this plasma absorbs and reflects radio waves at communications frequencies leading to a few tense minutes during the re-entry of manned vehicles such as the shuttle. However, the problem is even more acute for military vehicles such as ballistic missiles and hypersonic planes. Radio black out prevents these vehicles from accessing GPS signals for navigation and does not allow them to be re-targeted or disarmed at the last minute. But a group of Russian physicists say they can get around this problem by turning the entire plasma sheath into a radio antenna. They point out that any incoming signal is both reflected and absorbed by the plasma. The reflected signal is lost but the absorbed energy sets up a resonating electric field at a certain depth within the plasma. In effect, this layer within the plasma acts like a radio antenna, receiving the signal. However, the signal cannot travel further through the plasma to the spacecraft. Their new idea is to zap this layer with radio waves generated from within the spacecraft. These waves will be both absorbed by the plasma and reflected back inside the spacecraft. However, the key point is that the reflected waves ought to be modulated by any changes in the electric field within the plasma. In other words, the reflected waves should carry a kind of imprint of the original external radio signal. That would allow the craft to receive external signals from GPs satellites or ground control. And the same process in reverse allows the spacecraft to broadcast signals too.
