Amid China and Russia Tensions, US Races to Build Hypersonic Weapons: Analysis

A B-52 prepares to launch the X-51 hypersonic test vehicle in 2013.

The Pentagon has created a “war room” to ramp up production of hypersonic weapons from a handful of prototypes over the last decade to “hundreds of weapons” in the near future, said Mark Lewis, modernization director for Pentagon R&D chief Mike Griffin. Those weapons will range from huge rocket-powered boost-glide missiles, fired from Army trucks and Navy submarines at more than Mach 10, to more compact and affordable air-breathing cruise missiles, fired from aircraft at a relatively modest Mach 5-plus.

According to Mark Lewis Pentagon wants both rocket-boost and air-breathing hypersonic cruise missiles at scale which can be fired various platform operated by all three branches of US military.

With hypersonics now a top priority for both Undersecretary Griffin and Defense Secretary Mark Esper, the Pentagon is trying to improve that stop-and-go track record with a new “hypersonic acceleration plan” – no pun intended, Lewis said. Griffin likes to compare the effort to the Cold War, when the US had a massive nuclear weapons infrastructure capable of building complex components by the tens of thousands.

Sydney J. Freedberg Jr. graphic from DoD data
Source Breaking Defense Data

Which hypersonic weapons the Pentagon buys also makes a major difference. “There are some technology choices we can make that lead us to more cost-effective systems,” he said. “I’m especially enthusiastic about hypersonic weapons that come off the wings of airplanes and come out of bomb bays, [because] I think those are some of the keys to delivering hypersonic capabilities at scale and moderate cost.”

Four Types of Hypersonics

To put it in simple terms – and I’ll beg the forgiveness of any aerospace engineers reading this – there are two kinds of hypersonic projectile, based on how they fly: one is an air-breathing engine flying through the atmosphere, like a jet plane or cruise missile; the other is a rocket booster arcing to the edge of space, like an ICBM. There are also two kinds of platform you can launch from: an aircraft in flight high and fast above the earth, or a relatively slow-moving vehicle on or below the surface, like an Army truck, Navy warship or submarine.

  • Air-launched boost-glide: Air Force ARRW (Air-launched Rapid Response Weapon). The Air Force also had another program in this category, HCSW (Hypersonic Conventional Strike Weapon), but they canceled it to focus on ARRW, which the service considers more innovative and promising.
  • Surface-launched boost-glide: Army LRHW (Long Range Hypersonic Weapon) and Navy CPS (Conventional Prompt Strike). Both weapons share the same rocket booster, built by the Navy, and the same Common Hypersonic Glide Body, built by the Army, but one tailors the package to launch from a wheeled vehicle and the other from a submarine.
  • Air-launched air-breathing: HAWC (Hypersonic Air-breathing Weapons Concept) and HSW-ab (Hypersonic Strike Weapon-air breathing). Arguably the most challenging and cutting-edge technology, these programs are both currently run by DARPA, which specializes in high-risk, high-return research, but they’ll be handed over to the Air Force when they mature.
  • Surface-launched air-breathing: This is the one category not in development – at least not in the unclassified world. But Lewis said, “eventually, you could see some ground-launched air breathers as well. I personally think those are very promising.”

The big innovation of boost-glide weaponry is that it replaces the traditional warhead with an agile glider. Once the rocket booster burns out, the glide body detaches and coasts the rest of the way, skipping nimbly across the upper layers of the atmosphere like a stone across the pond.

Navy photo
Launch of Army-Navy Common-Hypersonic Glide Body (C-HGB) in Hawaii on March 19, 2020.

But boost-glide has some big limitations. First, once the rocket booster detaches, the glide body has no engine of its own so it just coasts, losing speed throughout its flight. Second, precisely because the rocket launch is so powerful, it puts tremendous strain on the weapon, whose delicate electronics must be hardened against shock and heat. Third, the booster is big, because a rocket not only has to carry fuel, it has to carry tanks of oxygen to burn the fuel.

Sydney J. Freedberg Jr. graphic from DoD data
Breaking Defense graphic from DoD data

An air-breathing engine, by contrast, can be significantly smaller. It just has to carry the fuel, because it can scoop up all the oxygen it needs from the atmosphere. That means the whole weapon can be smaller, making it much easier to fit on an aircraft, and that it can accelerate freely during flight instead of just coasting, making it more maneuverable.

But while conventional jet engines are well-proven technology, they don’t function at hypersonic speeds, because the airflow pours their intakes far too fast. So you need a sophisticated alternative such as a scramjet, a complex, costly technology so far found only on experimental vehicles, like the Air Force’s revolutionary Boeing X-51.

Sandia National Laboratories graphic
Sandia National Laboratories glide vehicle, the ancestor of the Army-built Common Hypersonic Glide Body

All these factors suggest that the big boost-glide weapons are probably best launched from land or sea, the smaller air-breathing ones from aircraft in flight. But since boost-gliders go farther and faster than air-breathers, you still want them as an option for your bombers for certain targets.

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