APL Advances Propulsion Technology For Hypersonic Missile Applications

In support of the Navy program, the team is developing a dual-combustor ramjet (DCR) engine for a long-range hypersonic cruise missile with application to time-critical strike missions. In tests recently conducted at APL's Avery Advanced Technology Development Laboratory, researchers have demonstrated for the first time that pure JP-10 liquid hydrocarbon fuel — like that used in Tomahawk cruise missiles — can be successfully injected and burned in a supersonic combustion engine required to power a hypersonic missile. "We've successfully tested a full-scale combustor that's an accurate duplication of a tactical missile's engine geometry at conditions simulating Mach 6 flight," says Mike White, program area manager for Advanced Vehicle Technologies at APL.

The initial DCR engine concept was developed at APL through the mid-80s as part of a Navy missile technology program aimed at defending ships against aircraft carrying cruise missiles.

The DCR engine design is simple, safe and fuel-efficient compared to earlier supersonic combustion engine concepts. Those engines required fuel additives to burn properly, but the additives can be toxic or unsafe to carry aboard Navy vessels. "The DCR engine design avoids use of highly reactive and toxic fuels or complex heat exchangers required for other supersonic combustion engine concepts," says White.

APL's unique DCR engine design injects pure liquid fuel with air captured from the atmosphere into a fuel-rich pre-burner. The byproduct is then mixed with more captured air and combustion is completed downstream in a tandem supersonic combustor. "We've demonstrated that we can burn cold, liquid JP-10 fuel at Mach 6 very efficiently in an engine sized to propel a tactical missile at hypersonic speeds," says Steve D'Alessio, project manager for Dual Combustor Ramjet Technologies at APL.

The DCR engine is designed to fly at speeds up to Mach 6.5 (approximately 4,700 mph) at ranges exceeding 400 nautical miles. "It's a throttleable engine design," says White. "You can fly above Mach 6 and get ranges in excess of 400 nautical miles or, should the mission dictate, fly at Mach 4 to almost double the range."

Air-breathing engine designs have several advantages over rockets for hypersonic applications. They can provide a significant increase in range for a given missile weight. They can be powered all the way to the target, which means a missile can fly a programmed trajectory to improve lethality against hardened and protected targets. Air-breathing engine designs also enable target aim points to be updated during flight so that a target or its coordinates can be changed as necessary. The high degree of survivability that results from Mach 6 flight at high altitude also enables rapid mission planning and a high probability of mission success.

APL's efforts could greatly benefit the future of hypersonics, according to Gil Graff, weapons program manager in the Office of Naval Research, Strike Technology Division, which is sponsoring the work. "I think this effort matures a propulsion system that enables development of a low-cost, logistically suitable hypersonic weapon in the 2010 timeframe," says Graff. "We hope to demonstrate the validity of a hypersonic, long-range cruise missile for application to time-critical strike, and for use against hardened, buried and heavily defended targets for future war fighters."

Testing at APL's Avery Laboratory is scheduled to continue through spring 2001. The team plans to conduct additional tests of the fully integrated engine geometry in the fall. After completing the ground tests, the team's goal is to transition into a flight test program later this decade.

Throughout this program, APL is teaming with the Naval Air Warfare Center, Weapons Division, China Lake, Calif.; Naval Surface Warfare Center, Dahlgren Division, Dahlgren, Va.; Defense Advanced Research Projects Agency (DARPA), Arlington, Va.; Boeing, St. Louis; and Aerojet, Sacramento, Calif. The work is sponsored by the Office of Naval Research, Strike Technology Division, Arlington, Va.