Scientists look at communicating with hypersonic vehicles using plasma resonance

Artist's concept of a returning Apollo Command Module showing the plasma sheath(Credit: NASA)

Returning spacecraft hit the atmosphere at over five times the speed of sound, generating a sheath of superheated ionized plasma that blocks radio communications during the critical minutes of reentry. It's a problem that's vexed space agencies for decades, but researchers at China's Harbin Institute of Technology are developing a new method of piercing the plasma and maintaining communications.

According to physicists Xiaotian Gao and Binhao Jiang of the Habin Institute, by redesigning the spacecraft antenna, it may be possible to maintain communications by setting up resonance in the plasma sheath. Essentially, this involves turning the layer between the spacecraft and the sheath into a capacitor in the antenna circuit. This causes the sheath to act as an inductor. Together, they create a resonant circuit.

"Once the resonance is reached, the energy can be exchanged between them steadily and losslessly, like real capacitance and inductance do in a circuit," says Gao. "As a result, the electromagnetic radiation can propagate through the matched layer and the plasma sheath like they do not exist."

According to the researchers, the tricky bit is to keep the matched layer and the plasma sheath smaller than the length of the radio waves. However, Gao believes that it's possible to tune the craft's antenna to compensate

"We don't need to know exactly the properties of the plasma layer, but we need to know the ranges for these properties," says Gao. "The matched layer will be adjusted by an automatic control system, so we only need to know the ranges to make sure this whole system can work appropriately."

This isn't the first attempt to solve the blackout problem, but the team says that this is a lighter and simpler method that doesn't rely on the shape of the spacecraft to work. The researchers also say that the method could be applied not only to returning spacecraft, but also future hypersonic passenger aircraft, missiles, and ICBMs

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