The Defense Department should financially compete long-range hypersonic cruise missiles with ballistic and boost-glide systems if it determines there is no potential role for long-range hypersonic cruise missiles distinct from conventional prompt global strike (CPGS), according to an expert on missile issues.

James Acton, a senior associate in the Carnegie Endowment for International Peace’s nuclear policy program, said in his report released on Sept. 3, Silver Bullet? Asking the Right Questions About Conventional Prompt Global Strike, this approach would help ensure that the CPGS program delivers value for its investment. Acton said there’s a possibility the Air Force could be duplicating a mission already assigned to the service’s Global Strike Command (AFGSC) because the office of the assistant secretary of the Air Force for acquisition is liaising about warfighter requirements for long-range hypersonic cruise missiles with Air Combat Command (ACC) instead of AFGSC. Acton said ACC is largely responsible for tactical operations while AFGSC is responsible for CPGS. 

If the Pentagon determines there isn’t a potential role for long-range hypersonic cruise missiles distinct from CPGS, Acton told Defense Daily  all candidate CPGS technologies, both ballistic and cruise, should be funded out of the CPGS account, enhancing direct competition. Acton said the development of short-range hypersonic cruise missiles, if any, should be continued to be funded separately. 

“It seems to me like there is a risk that the Air Force is developing hypersonic cruise missiles for the same missions that the Office of the Secretary of Defense (OSD) is developing conventional prompt global strike,” Acton told Defense Daily. “It seems suboptimal to have different people working on the same issues without a degree of competition between them.”

An Air Force spokesman said the service wouldn’t be able to respond by press time to a question regarding if they were duplicating CPGS investment.

Acton told Defense Daily when he started writing the report about six months ago, DoD officials were talking about making an acquisition decision during fiscal year 2013, which ends Sept. 30. Acton said an acquisition decision for CPGS may be a year or two away at this point.

CPGS, in simple terms, is the Pentagon’s goal of being able to hit any location on earth from long-range in 60 minutes with a conventional, not nuclear, weapon. Acton said in his report advocates argue CPGS could be used to counter antisatellite weapons or sophisticated defense capabilities or to kill high-value terrorists. Acton said critics worry that CPGS weapons could create serious strategic risks, most notably of escalation, including to a nuclear level, in a conflict.

Challenges facing the development of long-range hypersonic cruise missiles include aerodynamics, Acton said in his report. Since cruise missiles travel slower than rocket-launched maneuverable re-entry vehicles (MaRV), their aerodynamic regime is better understood. But hypersonic cruise missiles face an additional aerodynamic challenge that MaRVs do not: shaping and controlling the flow of hypersonic air through the “scramjet” engine to ensure stable combustion. Acton said this challenge is often compared to lighting a match in a hurricane and keeping it burning.

Supersonic Combustion RAMjet engines, or Scramjet, are also being developed toward the goal of a hypersonic cruise missile, Acton said in his report. Scramjet engines take oxygen needed by the engine to combust from the atmosphere passing through the vehicle, instead of from an on-board tank. This helps make the vehicle smaller, lighter and fast. But because a scramjet engine must already be moving forward quickly to function effectively, Acton said scramjet-powered vehicles need another type of engine to propel the vehicle to high speeds.

Acton said in his report the Scramjet technique was successfully employed by the Air Force in the X-43A and X-51A programs. A X-51A, developed by Boeing [BA], successfully flew for a record three minutes, 30 seconds at a top speed of Mach 5.1 in a May Air Force Research Laboratory (AFRL) test. This was the fourth X-51A test performed by AFRL. Acton said the X-51A was funded separately from CPGS, but the two have similar goals.