Hypersonic Medium Range Boost-Glide Vehicles

A clear (July 3, 2018) discussion of hypersonic cruise missiles and boosted hypersonic glide vehicles. Will the physics of speed and the atmosphere causing overheating forever be an obstacle?
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Drawing from KQN's 30 January 2019 comment below this Submarine Matters' article of 29 January 2019:

The French Armed Forces Minister, Florence Parly, on January 21, 2019 announced France will be developing a missile boosted, then hypersonic (Mach 5+), glide vehicle by 2021. The glide vehicle is designated the Vehicule Manoeuvrant eXperimental (V-MaX) or experimental manoeuvring vehicle in English.

There might possibly be a proliferation of 1,000-3,000 km range missiles (MRBM)
 (eg. China's DF-21)(see below) as the launch platform for hypersonic gliders.

Even though Australia has been experimenting with hypersonic flight since 2007 (if not earlier) any Australian project would need to be a joint program (with the US, UK or France) on an unknown time-frame. A launch platform might conceivably be torpedo tubes in Australia's future submarines, modified F-35As, vertical launch systems in existing Hobart class destroyers or future Hunter class frigates.

At a minimum, the modified ballistic (glide) trajectory may point to a conventional warhead, rather than a nuclear warhead (with nuclear ambiguity inviting a nuclear response (eg. from China). China is developing the hypersonic DF-ZF (previously called "WU-14" by the US).

BACKGROUND

Courtesy wiki: Boost-glide trajectories in the military sense are reentry trajectories extending the range of reentry vehicles by employing aerodynamic lift in the high upper atmosphere. 

In most examples, boost-glide roughly doubles the range over the purely ballistic trajectory. In others, a series of skips allows range to be further extended, and leads to the alternate terms skip-glide and skip reentry.

The concept was first seriously studied as a way to extend the range of ballistic missiles, but has not been used operationally in this form. The underlying aerodynamic concepts have been used to produce maneuverable reentry vehicles (MARV) to increase the accuracy of some missiles.

More recently the traditional form with an extended gliding phase has been considered as a way to reach targets while flying below their radar coverage.

"...research was eventually put to use in the Pershing II's MARV reentry vehicle. In this case, there is no extended gliding phase; the warhead uses lift only for short periods to adjust its trajectory. This is used late in the reentry process, combining data from an inertial navigation system with and Goodyear Aerospaceactive radar seeker.^[17] Similar concepts have been developed for most nuclear-armed nation's theatre ballistic missiles.

In contrast to these maneuvering warhead concepts, there has been growing interest in the traditional boost-glide concept not to extend range per se, but to allow it to reach a given range while flying at a much lower altitude. The goal, in this case, is to keep the reentry vehicle below radar coverage until it enters the terminal phase.

Such a system is assumed to be used on the Chinese DF-21D anti-ship ballistic missile, which is also believed to maneuver during the terminal phase to make interception more difficult. 

China's later DF-26, a development of the DP-21, may be armed with the WU-14 later named DF-ZF, a hypersonic glide vehicle that has been successfully tested six times by the Chinese.^[18] Similar efforts by Russia led to the Kholod and Igla hypersonic test projects, and more recently the Yu-71 hypersonic glide vehicle which can be carried by RS-28 Sarmat.^[19][20]

Hypersonic Glide Vehicles could be used for delivering quick nuclear decapitating strikes.^[22]

In March 2018, Russia unveiled hypersonic glide vehicle Avangard.

COUNTER-MEASURES

While flying below the operational envelope of Exoatmospheric Kill Vehicles, the tradeoff with HGVs in comparison to conventional MIRVs are many-fold, including no needle in a haystack protection from missile decoys and both less speed and altitude as they near the target, all of these characteristics result in HGVs having poorer survivability odds when placed against lower-tier interceptors.^[24] 

Some examples of which include the high thrust mach-10 Sprint missile, its US derivatives and the still operational mach-17 Russian 53T6, ABM-3 Gazelle. Moreover, the possible re-emergence of nuclear or hit-to-kill stratosphere reaching guns, guided and triggered by forward operating flight-path sensors (such as the 2016 Hypervelocity Projectile (HVP) in development for the M109 howitzer) also will decrease HGV survivability odds.

Other more speculative counter-hypersonic vehicle measures may involve laser or rail gun technologies.^[25]

KQN, Wiki and Pete