Mike White, the Pentagon’s Assistant Director for Hypersonics has made comments confirming that fears of a communication blackout during hypersonic flight are unfounded. He stated that during tests ground stations were able to maintain contact with the hypersonic glider and receive telemetry data. The most recent of these tests, Flight Experiment 2, was conducted last March.
These fears were not without cause since manned space vehicles such as the Apollo crew capsule and Space Shuttle experienced communication blackouts with ground stations during re-entry. This is caused by the formation of plasma around the vehicle due to the obscene drag involved during reentry which blocks radio signals. However, as pointed by Mike White, hypersonic gliders and manned re-entry vehicles have fundamental design differences with regards to drag. For example, the Space Shuttle was intended to shed a tremendous amount of energy during re-entry, starting the process at Mach 25 and eventually landing at 200 mph. Hypersonic gliders are designed for the opposite. They are intended to maintain as much energy as possible during the flight and have been designed to be aerodynamically efficient rather than the bluntly shaped manned re-entry vehicles.
The ability to communicate is vital to effectively employing these weapons against certain targets such as naval vessels. A key advantage of hypersonic weapons is their ability to redirect hundreds of kilometers from their ballistic path. This enables them to follow moving targets but also to switch targets mid-flight. These both require a forward observer such as low observable UAVs like RQ-180, or possibly in the case of China, high-speed UAVs like WZ-8.
Naturally, if the forward observer is unable to directly communicate with the weapon this breaks the cooperative engagement chain. With all this said NASA was able to overcome the communications blackout through the creation of the Tracking and Data Relay Satellite System which does as its name suggests, acting as a relay between space vehicles and ground stations. If communication had been an issue such a method could be used albeit increasing the reliance on satellite networks which the military is actively avoiding.