At some point in the next few weeks, a B-52H bomber will carry a rocket high into the air and send it to its target at an unprecedented speed, according to the U.S. Air Force. If all goes according to plan, the missile will accelerate to more than five times speed of sound before inserting a dummy second phase that will quickly “disintegrate” somewhere in the atmosphere.
The missile, known as AGM-183A, is supposed to be the first hypersonic weapon – or an Air-Launched Rapid Response Weapon (ARRW) – in the US arsenal. It must move so fast through the atmosphere – about 20 times the speed of sound – at such low altitudes that it is impossible to fire enemy missile defense systems from the air. And its speed means it can be useful for destroying ‘high-quality, time-sensitive targets’, the air force said in a statement.
Hypersonic missile designs, including this one, usually involve two phases.
First, a rocket accelerates the weapon to many times the speed of sound, while remaining at a much lower altitude than Intercontinental Ballistic Missiles (ICBMs) that bow above the atmosphere before delivering their nuclear charge.
Second, it releases a glider that carries the weapon for the last leg of its journey to the target, driving the atmosphere like a wave bouncing and braiding over waves – adding another ripple to each attempt to take it down shoot.
That lower altitude, in theory, makes a hypersonic weapon harder to detect and harder to destroy: it’s harder to detect for the same reason that it’s harder to see an airplane when you are on the ground at an airport 8 km away stands as a plane 10 miles away in the air approaching that airport to land; the closer an object is to the ground, the more things – from trees to buildings to another plane – hinder. And a hypersonic missile is theoretically harder to shoot down for the same reason; most missile defense technology is designed to intercept an ICBM near the apex of its arc through space. Up there, a missile defense system has a clearer line of sight to the target and the ICBM itself moves in a more predictable way.
A Mach 20 hypersonic glider would actually move at the same speed as a decade-old ICBM, which could accelerate to similar speeds during its spaceflight, but would have to travel a much longer distance to reach the same target. (This is the difference between driving in a straight line from New York to San Francisco and driving between the two cities with a stopover in the Arctic Circle.)
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The US is not the only country working on hypersonic weapon technology. As Live Science reported earlier, Russian President Vladimir Putin first announced his country’s own hypersonic weapons program in 2018, promising that the country’s hypersonic weapon would reach Mach 20.
Pavel Podvig, a military analyst, told Live Science at the time that such weapons were unlikely to be useful.
“It was described as a weapon in search of a mission,” he said. “My opinion is that you do not really need this kind of ability. It does not change much about the ability to reach targets.”
This is because ICBMs are already quite capable of evading missile defense systems. The US has the most advanced missile defense technology in the world; and according to physicist Laura Grego of the Union of Concerned Scientists and many other analysts simply do not work it out. It is therefore not clear why a hypersonic rocket would be needed to hit any other country. The Air Force does emphasize the idea that an ARRW can be useful against ‘time-sensitive’ targets because of its high speed (at least compared to non-ICBM missiles commonly used to deliver non-nuclear weapons).
The danger of hypersonic weapons, Podvig said, is that they are not covered by existing treaties designed to prevent gun races.
And there is still a lot of uncertainty surrounding the technology. “These systems create greater risks of [strategic] wrong calculation, “Podvig said,” and it is not clear whether we can handle the risks effectively. “
Meanwhile, there are questions as to whether hypersonic technology will work at all.
The upcoming test will only demonstrate the missile itself, not the glider, which is the latest technology. (Rockets that go very fast have been around for a long time. Gliders that fly many times faster than an F-16 does not have.) And, as The Drive pointed out, this test was also delayed. The missile arrived at Edwards Air Force Base in California on March 1, and the service originally said the test would take place by March 6. The statement on March 5 extended the timeline to ‘the next 30 days’ without any explanation.
Meanwhile, an independent analysis published in 2020 in the journal Science and Global Security argued that “fundamental physics” severely limited the usefulness of these weapons. They showed that the physics of atmospheric flight prevented these weapons from ever going fast enough to significantly surpass ICBMs, and that it would be relatively easy to detect a hypersonic rocket launch with the right satellite. The idea that hypersonic missiles would provide a revolutionary upgrade of ICBMs, according to the researchers, is a “social” phenomenon, not a scientific one.
Originally published on Live Science.