What's the fastest atmospheric missle that demonstrated a useable radome?

Question

I read that

DoD has stated that its hypersonic boost-glide missiles will be able to emit and receive radio signals, such as those from the Global Positioning System (GPS). That statement implies that portions of a missile’s glide body where transmitters and receivers are located will remain below the temperature threshold for plasma formation in the surrounding air, as DoD’s modeling suggested might be the case. [...]

Although the sensitive electronics necessary for communications must be adequately shielded from a missile’s exterior temperatures, the missile needs to have windows (called radomes) through which signals can be emitted or received. The materials for such radomes are inherently difficult to develop because they must allow radio frequency or infrared radiation to pass through them while also providing significant thermal shielding.

What's the fastest atmospheric flight that still demonstrated a useable radome, e.g. for GPS or remote command etc.?

Answer 1

That would be the Space Shuttle.

A more detailed, in-depth overview of the various antennae and their radome/window design can be foud in this document: INVESTIGATION OF HIGH TEMPERATURE ANTENNAS FOR SPACE SHUTTLE

The Space Shuttle's highest heat flux was reached at 63-68 km altitude, which corresponds to ~5,500 m/s velocity during the reentry phase. However, this did result in a temporary communications blackout.

This leaves about 3,300 m/s as the highest airspeed at which a production hypersonic vehicle, namely the Space Shuttle, could successfully communicate while in the atmosphere.

Heat flux can be mapped to altitude via the graph below.

The paper this graph comes from, Plasma-Radiofrequency Interactions Around Atmospheric Re-Entry Vehicles, also mentions experiments that have achieved communications at higher velocity. "As a general rule, the steeper the trajectory ... the lower is the altitude at which recovery occurs."

The RAM-C reentry vehicle used a very simple blunt cone shape. As the image shows, most of the vehicle was covered by a plasma sheath, so the nose was left as an antenna window. It still had a blackout phase above 5,200 m/s. This gives about 5 km/s as the experimental limit for very restricted communications.

For missiles specifically, currently the one operational hypersonic, the Zircon at 2,650 m/s, is slower than the Space Shuttle. DoD designs target further lower speeds, in favor of range, so it's very likely that they will be able to communicate.