In 1970, NASA’s Apollo 13 crisis revealed that while a spacecraft plumped into earth’s environment, the hot ionized air formed around the craft disrupted the radio communication. This resulted in a communications blackout that lasted a minute longer than expected, leaving ground control in suspense over whether the three astronauts aboard had survived.
Studies found that whenever a vehicle travels at a hypersonic speed, moreover at a speed five or more times faster than speed of sound – an envelope of hot, ionized air encircles the vehicle. This “plasma sheath” acts a mirror against electromagnetic signals in most of the cases and disables any kind of radio communication to occur with anything outside the vehicle.
Researchers have been working on a new kind of antenna for future spacecrafts that might help the vehicle stay in touch with ground control, despite any kind of fiery sheaths of superhot plasma around them. Xiaotian Gao & Binhao Jiang, physicists from Harbin Institute of Technology in China have found a way to solve the communication blackout problem and revealed that they might be able to use that “plasma sheath” itself to boost and enhance signals from antennas to maintain communication during hypersonic flight. This technology might also help keep communication lines open to other hypersonic vehicles, such as military planes and ballistic missiles.
The researchers further explained that when the electromagnetic fluctuations of radio antennas are in sync with those of their surroundings, a phenomenon known as resonance can amplify radio signals. One example of resonance is the way a playground swing will climb higher from repeated pushes. Another well-known example of resonance can be seen when an opera singer hits just the right note to cause a champagne glass to resonate and shatter. The researchers have suggested adding a carefully designed layer of electrically insulating material onto communications antennas that would essentially store electrical energy. Further, in combination with the plasma sheath, this "matched layer" would generate resonant conditions during hypersonic flight, and radio signals could propagate through.
The Scientists have noted that for the resonance to work, the thickness of this matched layer and the plasma sheath must be smaller than the wavelengths of the radio signals used for communication. The properties of the plasma sheath can vary during flight, complicating any efforts to generate resonance, but the researchers suggested the matched layer can compensate for these changes if it is made from a material whose electromagnetic properties can be altered electrically.
Prior studies and approaches have tried to solve this communication blackout problem, however they have had shortcomings. For instance, using magnetic fields to control the plasma sheath, or injecting water or other liquids into the plasma sheath to make it more permeable to radio signals were some of the approaches. But these methods require extra power and weight. Scientists have also suggested changing the shape of hypersonic vehicles, because sharp-nosed vehicles have thinner plasma sheaths than blunt-nosed ones. But sometimes, blunt-nosed bodies are preferable because they can withstand heat better and slow down more quickly.
The researchers noted that their new approach has a number of advantages over prior attempts to solve the communication blackout problem. However, Gao and his team have cautioned that this finding is only a theoretical prediction and needs to be verified by further experiments. The researchers do not plan to build such a hypersonic communication system themselves and would require engineers from all over the world to help solve this problem by using their approach.
Learn more about this technology at in the Journal of Applied Physics.
