Week of April 12, 2021

Hypersonic Weapons – Fad or Fact?


At the beginning of WWII, it was tanks.  After WWII, it was nuclear weapons, bombers, and missiles.  In the past few years, it has been drones.

Now it is hypersonic missiles.  China, Russia, and the US are engaged in a race to field the first practical hypersonic missile.

According to military experts, hypersonic weapons are the latest “leading edge” technology.  Travelling at five times the speed of sound, they are harder to detect and considerably more difficult to shoot down.  Russia sees them as the answer to America’s missile defense of North America and China sees them as the “golden bullet” that will defeat America’s super carriers.

The problem, however, is that hypersonic weapons are neither new, nor do they offer anything that current technology does not offer – for less money.

Hypersonic technology is about 80 years old and was first explored as a weapon technology during WWII.  Nazi Germany, who was the leader in rocket technology at that time, had considered it when looking at ways to attack America from Germany.  The first solution was a long-range bomber, but they took time to cross the Atlantic and were vulnerable to Allied long range air patrols.

The solution was a rocket that could travel at hypersonic speeds.  The Germans conceived a hypersonic boost glide missile called the Silbervogel (Silver Bird).  The problem was its cost, compared to the size of the weapons payload.

The post WWII era saw a demand to quickly hit distant targets in the most efficient way possible.  The answer was the ICBM.  It flew a ballistic flight plan, went up to a thousand miles in space at hypersonic speeds and landed with a degree of accuracy – at least accurate for nuclear weapons.  It was also the most economical solution.

The US continued to look at hypersonic flight and developed the Dyna-Soar hypersonic glider.  The program was cancelled because of its cost and the fact that there was no clear objective to the weapon.

The fact is that hypersonic weapons use nuclear technology from the 1950s, boost technology from the 1950s, and hypersonic glide technology from the 1960s – hardly a revolutionary weapon system.

However, afraid that it will fall behind, the US is pushing to develop a hypersonic missile as quickly as possible, and with the minimal testing.  The pace of testing indicates that this week’s hypersonic missile test failure off the coast of California will not be the last one.  The missile is designed to target high value strategic targets.

The Army hopes to field its first missiles in FY 23.

The US is focusing on the Hypersonic Conventional Strike Weapon and the air launched AGM-183A Rapid Response Weapon.

The Defense Department plans up to 40 hypersonic missile tests in the next five years – a fast track that could lead to problems if there are any test failures.  There are also few places like hypersonic wind tunnels that can test such a weapons system.

Russia has already fielded hypersonic missiles for strategic purposes – like replacing its current ballistic missiles.  The two missile systems are the Avangard and the Kinzhal.  The Kinzhal reportedly has speeds of up to Mach 10 and a range of 1200 miles.

The Russians are also testing an air-to-surface hypersonic missile for use on the Russian SU-57 jet fighter.

The Chinese are behind and are developing a hypersonic missile with a different tactical application.  They are developing an inexpensive Mach 5 scramjet, the SF-17.  Since it is cheaper, it can be deployed in massive attacks that could overwhelm the defense systems of an American carrier task force.  It is expected to enter service in the late 2020s.

The British and French navies are working on a hypersonic missile to replace the Harpoon and Exocet anti-ship missiles.  The missile, Pursues will have a ramjet engine and is expected to enter service in 2030.

For all the optimistic talk, hypersonic weapons face an invincible foe – physics.  That is why they were considered impractical in the 20th Century,

Hypersonic weapons will launch like traditional ICBMs.  However, instead of taking a ballistic path as an ICBM, the warhead will be attached to a hypersonic glide vehicle that can ride the shockwaves created by its high speed as it flies through the atmosphere.  Unlike ICBMs, it will fly at a much lower altitude, which will be below many missile defense system envelopes.

The key is the hypersonic glide vehicle, which is quite maneuverable at hypersonic speeds.  In a long-range flight, it skips across the edge of the atmosphere until it approaches its target.  Then, it rolls over and dives into the atmosphere.  It can maneuver by rolling clockwise or counterclockwise.  It does the same in a short-range missile, except it will stay in the atmosphere.

These glide vehicles have problems though.  As they fly through the atmosphere, they are subject to atmospheric drag and temperatures of thousands of degrees.  If one were to shape the glide vehicle to reduce the drag, it loses its hypersonic glide ability.  And, although it can maneuver at hypersonic speeds, doing so drastically reduces the speed and range.  Hypersonic flight depends on a narrow band of atmospheric density and speed.

This narrow band of atmospheric density and hypersonic speed drastically limits the ability of the missile to travel faster than the conventional ballistic missile taking the traditional ballistic flight plan.  This negates the argument that hypersonic missiles are dramatically faster than conventional ICBMs.

Although these hypersonic glide vehicles are fast, the heat created leaves a heat signature that is visible to satellites from thousands of miles away.  Both the US and Russia have early warning satellites that look for large heat signatures like those from ballistic missiles.  These thermal signatures are quite visible to satellite both in the boost phase and as the glide vehicle flies through the atmosphere.  Admittedly, modern anti-missile systems may not be able to intercept these fast-moving vehicles, but they can track them.

Hypersonic weapons are also subject to the age-old physics equation; Energy equals mass times velocity squared.  If one wants to make an object that travels Mach 1 to go Mach 5, the energy needed equals 5 squared, or 25.  That means that pushing a hypersonic glide vehicle at hypersonic speeds throughout its powered flight requires 25 times more energy then moving the vehicle at Mach 1.  No wonder the engineers of Nazi Germany, the Soviet Union, and the US moved away from hypersonic weapon technology back in the 1940s, 1950s, and 1960s.

The high speeds and heat incurred during its travel through the atmosphere also tests the structural integrity of the vehicle.  ICBM nosecones reach temperatures of a few hundred degrees Celsius.  Hypersonic vehicles will have skin temperatures of thousands of degrees Celsius.  Small imperfections in the skin can cause catastrophic failures.  Small pieces of shrapnel from an interceptor warhead will also cause a failure of the glide vehicle.

There is also the high temperature plasma that surrounds the glide vehicle during any high-speed flight in the atmosphere.  This is what causes the blackout with manned spacecraft reentering the atmosphere at the end of a mission.  This plasma will hinder communications and navigation.  This might preclude remote guidance changes or allow for the vehicle to use navigation satellites to make course corrections.

In the end, hypersonic flight represents a set of tradeoffs – tradeoffs that engineers felt was not worth it for several decades.  Drag forces at low altitudes reduce speed, which is only obtained by the considerable expenditure of fuel.  There are tradeoffs between speed, altitude, and maneuverability.  High speed through the atmosphere produces immense amounts of heat, which are detectable by satellites.

The key advantage of hypersonic flight is that current missile defenses cannot intercept them due to speed, flight paths that go under the envelope of defensive missile, and remarkable maneuverability.

However, as nations develop and perfect hypersonic missiles, there is another race going on to develop defenses that will negate the hypersonic missile.  Directed energy weapons and particle beams are already in the testing phase.

In the end, much depends on solving several major technological problems.  These problems were once faced by some of the greatest rocket scientists of all time, and they opted for simpler solutions.  Will this generation of scientists succeed when those others failed?