National Interest:
There is a great deal of talk about hypersonic weapons and their possible impact on the battlefield. Some consider them the ultimate weapon of war, others feel they are merely an evolutionary development along a predictable track.
So just how dangerous could these weapons become in the future? Who is developing them? Would America be able to defend against them? To get some answers, I put these questions to Center for Strategic and Budgetary Assessments senior fellows Bryan Clark and Mark Gunzinger.
Kazianis: Hypersonic weapons are all the rage in defense circles these days—a recent article in Politico seems to suggest as much. Which country would you say at this point is furthest along in its research on deploying an actual usable hypersonic weapon? What are the potential bottlenecks in such advanced R&D?
Clark & Gunzinger: The United States, China and Russia are all aggressively developing hypersonic weapons. In terms of operationalizing a usable weapon, I believe the United States and Russia are very close. China has hypersonic technology, but is mostly working on boost-glide weapons that are essentially ballistic missiles with a hypersonic missile as the warhead. These will be too large and costly to be an operationally useful weapon system that is used in significant numbers. The United States and Russia are also working on air-launched hypersonic weapons that are smaller, less expensive and more operationally relevant.
There are few real technical bottlenecks at this point. The biggest technical challenge is the fact you essentially need two different motors to power the missile: one to get the missile up to supersonic speeds (> Mach 1, or about 750 mph), and another to then take the missile up to hypersonic speeds (> Mach 5, or about 3,750 mph). The kinds of motors that work at lower speeds, such as turbojets and turbofans, will not work at higher speeds, which require scramjet or ramjet motors. Conversely, the higher-speed motors don’t work at lower speeds. This can increase the cost of the weapon significantly, because you need to boost the missile to high speed and then use a scramjet or ramjet to attain and maintain hypersonic speeds.
There are essentially two ways to get a missile up to the speed where a scramjet or ramjet will work. One is a “boost-glide” weapon in which a large rocket boosts the missile to high altitudes and speeds before its ramjet or scramjet ignites and powers the missile at hypersonic speed to a target. The other is an air-launched weapon that uses the launch aircraft to get the missile to a high altitude and speed; after launch, a small booster rocket takes the missile to high enough speeds for the ramjet or scramjet to take over.
The latter weapon could be far less expensive than a surface-launched weapon. Some U.S. manufacturers are looking at reducing the cost of air-launched hypersonic weapons by using inexpensive rocket boosters (see below) to accelerate it to high speeds, and using additive manufacturing (“3-D printing”) to build the hypersonic ramjet/scramjet motor. Additive manufacturing enables them to produce the motor less expensively because it eliminates the need for extensive machining to create the motor’s combustion chambers and fuel systems…
