The US Air Force bets on hypersonic missiles

The Air Force has successfully fired its air-launched hypersonic rapid response weapon (ARRW) from a B-52 with initial success. This promising development suggests rapid weapons development for the service as it tries to close the gap between China and Russia.

Lockheed Martin leaves the ARRW

However, although early tests indicate initial success, the service is canceling the ARRW program with Lockheed Martin. Air Force acquisition executive Andrew Hunter informed Congress of the Air Force’s decision but said he saw value in continuing research and development and will continue other companies’ programs.

According to Air Force acquisition chief Andrew Hunter’s written response to the Air Force’s subcommittee on tactical air and ground forces, the service “does not currently intend to pursue the procurement of the ARRW when the prototype development is complete.”

failed tests

The Breaking Defense article quoted senior officials in the service as explaining that a recent ARRW test simply didn’t go well, although not many details are given.

What is important about the ARRW is that hypersonic weapons development has advanced considerably, as the ability to launch and maintain hypersonic speeds has long been a challenge for the Pentagon. Although Hunter did not say definitively that the service would “never” buy the weapon, he did clarify that progress toward production after the prototype phase would stop.

hypersonic development

Last year, the ARRW was successfully fired from a B-52, according to Air Force reports. “After separating from the aircraft, the ARRW’s propellant ignited and burned for its predicted duration, reaching hypersonic speeds five times the speed of sound,” an Air Force statement said last year.

Much was probably learned from this experiment, in which the ARRW looked promising. However, more recent testing has cast doubt on the weapon’s future.

Why did Lockheed’s tests fail?

The technical reasons for the failed test and cancellation are not known, probably for safety reasons, but the failure or challenge is reminiscent of some of the difficulties hypersonic flight poses.

Several key issues need to be addressed for an air-launched weapon to achieve and sustain hypersonic speeds. Thermal management is critical, as materials simply cannot withstand the heat generated at hypersonic speed unless they promise new compounds capable of maintaining flight conditions at unprecedented temperatures.

This is a topic of great interest to the Pentagon, as the Army and probably the Air Force and Navy are experimenting and testing new combinations of composite materials capable of supporting sustained hypersonic flight. Experiments are being carried out at the Army Research Laboratory to discover new materials capable of supporting hypersonic flight.

The hypersonic challenge

Aside from guidance and targeting technology, the other main challenge of hypersonic flight is the issue of airflow and the boundary layer. Hypersonic weapons, projectiles, or one day even hypersonic drones will have to be designed to maintain heading and flight path with smooth or “laminar” airflow to avoid disturbances.

Conversely, turbulent airflow can cause the molecules and particles surrounding the hypersonic projectile to shift, upsetting the balance and knocking the weapon off course.

 Addressing this problem successfully involves advanced assessment of the aerodynamics surrounding hypersonic flight, which concerns the projectile’s materials, shape, and configuration.

The specific way in which the shapes are configured is designed with careful attention to airflow and aerodynamic phenomena related to surrounding airflow. Similar aerodynamic principles are considered when designing combat aircraft to optimize vectoring through airflow management, enable efficient aerial maneuvers, and reduce aerodynamic drag.

The USAF and hypersonic flights

The Air Force has been trying and testing hypersonic flight for many years since the Waverider X-51A reached hypersonic speeds of Mach 5 but did not maintain them. The Waverider could reach hypersonic speeds using scramjet propulsion but not fully maintain them. However, a record was broken, and in 2013 the X-51 could reach Mach 5 for 210 seconds, a breakthrough that inspired further developments.

With this background and the initial advances of the ARRW, the Air Force likely plans to move quickly in developing new hypersonic weapons. Other promising hypersonic weapons programs are underway, and the Pentagon will almost certainly continue to prioritize and accelerate their development.