It's also why they had to make it out of exotic materials to be able to handle the speed. Even at high altitude, friction from the speed would cause the entire aircraft to heat up and start glowing at certain parts.
Also why they have to refuel it as soon as it gets into the air, because it would leak like a sieve on the ground, as there had to be gaps allowed due to the expansion of the metal when it heated up.
Exactly.
Hypersonic flight is not what most people seem to think. The biggest thing is that they can only operate at hypersonic speeds at extremely high altitudes. You are not going to have a "sea skimming" hypersonic missile, that is a complete contradiction.
In fact, even at Mach 4+ the thing got so hot that they had to create a special fuel with a high flash point specifically so it would not ignite inside of the tanks at hypersonic speeds. It was so "thermally stable" that is was also used as coolant and lubrication inside the engine, and had to be run through the ending as coolant in order to rea a high enough temperature where it would even burn as fuel. And because it is so thermally stable, it does not "boil off" at extreme temperatures,
And here is the interesting part, I tried to find the boiling point of water at that altitude. And was fascinated to find that the calculators literally broke down and returned the nonsensical figure of -14f as the boiling point of water! Quite literally if you put water at that altitude it would boil away before it froze unless it was in a pressurized container. That is how special the fuel has to be in order to operate at those altitudes and speeds.
Of course, that is why the "Russian Hypersonic" missile uses none of that.
In fact, most people are completely wrong about it and have no actual idea how it operates.
Very simply, it is just a ballistic missile that is launched from an aircraft instead of the ground. It is launched from an aircraft, then climbs to a high altitude as if it was a land launched ballistic missile. It then enters a completely unpowered flight profile which due to gravity and terminal velocity attains hypersonic speeds. The exact same way that any other ballistic missile can.
And their claims of "accuracy" have largely been destroyed, as those used in Ukraine have been hitting targets almost at random. Apartment buildings, unoccupied office buildings, road intersections, and other things of no military value. This has caused their claims of "pinpoint accuracy" and "ability to hit mobile targets" into serious question.
And yes, PATRIOT and other air defense systems have been taking them out.
And even launching ballistic missiles is nothing new. The US back in 1974 actually successfully launched a Minuteman ICBM in flight from a C-5. But much like the idea of "hypersonic missiles" themselves, they never followed it up because ultimately it was realized it was a rather stupid capability to have in the first place. In the military, there is such a thing as "too fast".