The US army is expected to test its new Long Range Hypersonic Weapon today near the Caribbean over the Atlantic, weapons experts say.
The LRHW, also known as Dark Eagle, is the US military’s latest attempt to field a weapon that can travel at five times the speed of sound – Mach 5 – or faster.
Etienne Marcuz, a French defence analyst, said on X the Dark Eagle test could be imminent based on Notices to Air Missions (Notam) issued over the previous test area, from Cape Canaveral, Florida.
A Notam is issued by a country’s aviation authority to warn aircraft in advance of a hazardous change to flying conditions on a flight path.
The US Federal Aviation Authority website displayed two Notams around in the airspace south-east of Cape Canaveral on Thursday.
“Those Notams are almost identical with the ones of previous launch attempts (as this test has been postponed several times)” Mr Marcuz wrote on X.
While Mr Marcuz expected the test to go ahead, several last year and up until March were cancelled or failed.
Hypersonic engineering challenge
At Mach 5, hypersonic weapons or aircraft move at around 1.6 kilometres per second, travelling hundreds of kilometres in a few minutes and giving enemy forces almost no time to prepare missile defences.
Dark Eagle, a ground-launched weapon fielded in co-operation with the US Navy, features a booster rocket and glide vehicle, which separates from the booster to descend unpowered to the target from high altitude at more than 6,000 kilometres per hour.
According to a Congressional Research Service report this month, the missile’s glide vehicle is “reportedly based on the Alternate Re-Entry System,” which has been in development since around 2018. The US now has at least eight hypersonic weapon projects after decades of research. Some experts say China and Russia were able to pull ahead in the field after initial US efforts became fragmented between different service branches.
While hypersonic weapons travel at Mach 5 or above, there are different interpretations of what this means for a weapon, with the most basic definition relating to speed. By this definition, the weapon is capable of withstanding extreme temperatures from friction travelling through air, where the leading edges of the missile can reach 1,800 celsius or higher.
Typically, ballistic missiles – decades-old technology – fall into this hypersonic definition.
Missiles such as Russia’s Kinzhal aero-ballistic missile, launched at high altitude from a fast-moving MiG 31, also fall into this category.
The US military, however, defines hypersonic weapons as those being able to manoeuvre at these speeds, rather than remain on a relatively predictable trajectory.
This makes them extremely difficult to shoot down, but also creates extreme engineering challenges.
“Extensive flight testing is necessary to shield hypersonic missiles’ sensitive electronics, to understand how various materials perform, and predict aerodynamics at sustained temperatures as high as 3,000° Fahrenheit,” the US Congressional Budget Office reported last year.
Manoeuvrable hypersonic weapons, according to their advocates, would also be much harder to shoot down because they can change course in the atmosphere, at lower altitudes than ballistic missiles, giving air defences less time to react. The lower something flies, the closer it is to the curvature of the Earth, shielding it from radar until it emerges in the “radar horizon”.
But experts say that manoeuvring in the atmosphere also reduces speed significantly. No manoeuvrable hypersonic weapon has been used in combat and numerous US tests for the devices have had mixed success, including several tests for the Dark Eagle which either failed or were cancelled, according to the Congressional Research Service.
Key challenges remain temperatures that rise sharply with every additional Mach – according to scientists David Wright and Cameron Tracy, temperatures at Mach 15 are 30 times hotter than at Mach 5.
Such high temperatures can cause serious problems for sensitive microelectronics that guide the weapon, one of the challenges engineers are trying to solve with advanced heat shielding materials.
