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Artist’s concept of Hypersonic Air-breathing Weapons Concept (HAWC) vehicle. (Credit: DARPA)

WASHINGTON: The US recently completed a successful “free flight” test of a hypersonic missile, according to the Pentagon, but reportedly kept the test quiet in an effort to avoid escalation with Russia over Ukraine.

The Defense Advanced Research Projects Agency (DARPA) announced the test today, calling it the “second successful flight in DARPA’s HAWC [Hypersonic Air-breathing Weapon Concept] program.”

“This Lockheed Martin HAWC flight test successfully demonstrated a second design that will allow our warfighters to competitively select the right capabilities to dominate the battlefield,” Andrew “Tippy” Knoedler, HAWC program manager in DARPA’s Tactical Technology Office, said in a DARPA release. DARPA is partnered with the Air Force on the HAWC program. “These achievements increase the level of technical maturity for transitioning HAWC to a service program of record.”

Lockheed’s free flight test was supposed to happen in late 2020, but was delayed due to technical issues. Raytheon’s competing version of the HAWC system was successfully tested in September 2021.

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According to DARPA, in the new test the missile was released from a “carrier aircraft,” was boosted by a scramjet engine and then “quickly accelerated to and maintained cruise faster than Mach 5 (five times the speed of sound) for an extended period of time. The vehicle reached altitudes greater than 65,000 feet and flew for more than 300 nautical miles.”

The DARPA announcement came hours after CNN reported the successful test, saying it took place in mid-March but that the Biden administration kept it quiet to avoid sending an escalatory signal to Russia.

Last month Russia claimed the first battlefield use of a hypersonic missile in combat operations in Ukraine, which US President Joe Biden later confirmed.

“We do understand that at least in one instance, they used a hypersonic missile,” Pentagon Press Secretary John Kirby told reporters on March 22, while questioning exactly why the Russians would use it to reportedly take out a storage facility. “That’s a pretty significant sledgehammer to take to a target like that. So, it’s not exactly clear what their intentions were.”

Kirby said the US did not consider the Russian use of a hypersonic missile a “game changer” in the Ukraine conflict.

Last fall the defense world was set abuzz by reports that the Chinese had tested its own hypersonic weapons system, one the US later said was part of a fractional orbital bombardment system (FOBS).

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Of its own hypersonic missile, DARPA’s Knoedler said, “We are still analyzing flight test data, but are confident that we will provide the U.S. Air Force and Navy with excellent options to diversify the technology available for their future missions.”

Scramjets take in oxygen from the atmosphere, rather carrying bulky oxygen tanks — as boost-glide rocket boosters do. Thus, air-breathing hypersonic missiles can be made smaller, to be carried by fighter jets rather than big, heavy bombers.

But flying at greater than Mach 5 (scramjet powered cruise missiles are estimated to be able to fly at about Mach 7) through the atmosphere also creates friction, heating up an air-breathing hypersonic weapon in ways a boost-glide design, which spends most of its time in a near-vacuum, does not. Scramjets remain experimental, as do many of the materials designed to keep temperatures on the missile down so that avionics and other subsystems can function.