Steve Trimble Details of the U.S. Air Force’s first hypersonic weapon show a concept not unlike the AGM-158B cruise missile, albeit 12.5 times faster.
Steve Trimble
Lockheed Martin AGM-158A missile An AGM-158A launched from a Boeing B-52H can reach a target more than 500 nm away in 10 min. Credit: Mike Tsukamoto/USAF illustration
With the U.S. Air Force preparing to begin long-delayed hypersonic flight testing, key details around the performance of the Lockheed Martin AGM-183A Air-Launched Rapid Response Weapon have been revealed. Meanwhile, some lawmakers have voiced impatience with the program’s progress as the Biden administration opens a new round of arms control talks, with hypersonic weapons as a potential bargaining chip.
A revealing picture of the speed, dimensions and guidance of the U.S. Air Force’s first air-launched hypersonic missile has come from an unlikely source. The new data confirms that the performance of the future AGM-183A differs widely from the Mach 22, 4,000-nm-range Hypersonic Technology Vehicle-2 (HTV-2), which DARPA last tested unsuccessfully in 2012.
Instead, the arrowhead-shaped, rocket-boosted AGM-183A’s glider can achieve ranges closer to the Lockheed Martin AGM-158B Joint Air-to-Surface Standoff Missile-Extended Range (JASSM-ER)—albeit starting from a gliding speed more than 12.5 times as fast as the jet engine-powered Mach 0.8 stealthy cruise missile.
The specifications of the roughly $13 million AGM-183A are revealed in the annual report of the Defense Department’s High-Performance Computing (HPC) Modernization Program, which supported the Air Force’s analytical assessments of hypersonic flight. The report also reveals more capabilities and limitations of the ARRW design.
The AGM-183A will be able to receive GPS data to home in on the coordinates of a fixed target, but the glider may lack the ability to receive inflight location updates to track moving targets. The AGM-183A also does not appear to be equipped with a radio-frequency or optical sensor to acquire fixed or moving targets on its own.
The mass of the 5,000-lb.-class ARRW appears mostly consumed by the nonglider element of the all-up round—a 25.9-in.-dia., 232-in.-long tube that includes a solid rocket motor that separates from the glider late in the ascent stage.
The glider carries a 150-lb.-class fragmentation warhead, made of highly dense tungsten metal. A sensor linked to the weapon’s height of burst triggers the warhead to explode and spray shards of tungsten shrapnel over a target area. Even with the high speed of the glider in the terminal dive phase of flight, the AGM-183A warhead’s effectiveness is limited to soft targets such as fixed radars.
By implication, the AGM-183A’s guidance and warhead technology mean it may not be suitable for striking moving or relocatable targets, as well as targets enclosed in hardened shelters or underground bunkers.
“The maximum speed [for AGM-183A] is substantially lower than for the HTV-2, which significantly reduces gliding range,” says James Acton, co-director of the Nuclear Policy Program with the Carnegie Endowment for International Peace. “Those also are the problems caused by heating.”
The AGM-183A’s listed range, described by the HPC program as greater than 500 nm, could be intentionally conservative. Acton, who is also a theoretical physicist, calculated that the lift-to-drag ratio of the HTV-2 is 2.6. “If the same were true for ARRW, then it would have a glide range of about 700 nm,” Acton says. Alternatively, the Mach 10 speed of the AGM-183A reduces the thermal management challenge, compared with the HTV-2, which could allow ARRW’s designers to use a higher lift-to-drag ratio.
“I wouldn’t be surprised if the total range for ARRW was substantially in excess of 500 nm, perhaps even 1,000 nm or so,” Acton says.
The guidance system depends on the AGM-183A receiving signals from the GPS constellation while gliding at hypersonic speed. Although friction heating is known to create a potentially signal-blocking plasma field around a hypersonic vehicle, the Mach 10 speed for ARRW may be slow enough to avoid that problem. In 2009, the Defense Science Board noted that the “plasma blackout” issue must be overcome for hypersonic reentry vehicles that require updates from satellite signals, whereas gliders with top speeds of Mach 10-12 will likely avoid the problem.
Meanwhile, U.S. defense officials are also working on a terminal seeker for hypersonic gliders. According to fiscal 2022 budget justification documents, the Army plans to integrate a radio-frequency sensor into the Long-Range Hypersonic Weapon (LRHW) by fiscal 2025, which is in time to field the ordnance with the second battery. Given that the LRHW shares a common glider with the Navy’s Intermediate-Range Conventional Prompt Strike (IRCPS) missile, a terminal seeker would allow both weapons to strike moving targets at sea or on land.
The common glider for the LRHW and IRCPS missiles completed a successful flight test on March 19, 2020, but the Air Force’s efforts to launch flight testing for the ARRW program have been stalled for several months. An attempt to complete the first Booster Test Flight (BTF-1) for the ARRW program failed, with the missile unable to be released in flight from a Boeing B-52H pylon. A follow-up test event is planned for sometime in July, though the Air Force does not say when.
But lawmakers have grown impatient with the delays to the ARRW program. Despite the absence of successful flight testing, the Air Force requested $161 million in the fiscal 2022 budget proposal to buy the first 12 AGM-183As. However, the defense panel of the House Appropriations Committee has pushed back. In a report on the defense subcommittee’s markup of the fiscal 2022 appropriations bill, lawmakers highlight that they want to slash the ARRW program’s procurement budget by $44 million—reducing the buy to eight missiles.
“The committee notes that the flight-test regimen for the rapid prototyping program has become increasingly delayed and compressed, increasing the concurrency risk to the first production lot of weapons funded in this account,” the report states.
The Pentagon’s hypersonic programs also face new policy questions. In June, a summit in Geneva between U.S. President Joe Biden and Russian President Vladimir Putin resulted in a common agreement to open talks on completing a new arms control pact. Since the summit, Russian diplomats have clarified that they intend to seek limits on the U.S. military’s planned arsenal of hypersonic weapons. For his part, Biden also says that the bilateral arms control talks will be focused on new weapons that reduce military response times for decision-makers on both sides.
