PARIS — The U.S. Air Force Research Laboratory (AFRL) has answered with a qualified “yes” the question of whether a British company’s revolutionary air-breathing rocket engine, designed for a horizontal-takeoff vehicle climbing to orbit with a single stage, holds promise.

AFRL’s Aerospace Systems Directorate looked at Reaction Engines Ltd.’s Synergetic Air-Breathing Rocket Engine, SABRE, as part of a Cooperative Research and Development Agreement.

The key component of the engine is its heat exchanger, designed to convert incoming air from 1,000 degrees Celsius to minus 150 degrees Celsius in one-hundredth of a second.

SABRE Reaction Engines
Synergetic Air-Breathing Rocket Engine, SABRE. Credit: Reaction Engines

As announced by Reaction Engines March 15, AFRL’s assessment is generally good news for a company that has been trying to win support for its technology for well over a decade.

The British government in 2013 agreed to invest 60 million pounds ($90 million) into Reaction Engines as seed money to enable the company to entice private capital to provide complementary funding for a prototype engine to be built in 2017.

The European Space Agency has looked at SABRE and concluded that the technology holds promise, but that much more work remains to be done.

AFRL’s conclusion is that SABRE is an interesting technology that is technically feasible and that may find earlier applications in two-stage-to-orbit rockets or defense applications.

Left out of AFRL’s assessment was a clear sense of how much investment would be needed to build what Reaction Engines calls its Skylon vehicle.

“Our analysis has confirmed the feasibility and potential performance of the SABRE engine cycle,” AFRL program manager Barry Hellman said in an April 15 statement released by Reaction Engines. “While development of the SABRE represents a substantial engineering challenge, the engine cycle is a very innovative approach and warrants further investigation.”

“The question to answer next is what benefit SABRE could bring to high-speed aerospace vehicles compared to other propulsion systems,” Hellman said. “Although application of the SABRE for single-stage-to-orbit space access remains technically very risky as a first application, the SABRE may provide some unique advantages in more manageable two-stage-to-orbit configurations. Furthermore, the heat exchanger technology also warrants further investigation for applications across the aerospace domain.”

Reaction Engines said in a statement that the company and AFRL are planning further joint work on the SABRE, including “testing of SABRE engine components and exploration of defense applications for Reaction Engines’ heat-exchanger technologies.”

The company previously had identified several nonaerospace applications as potential markets for SABRE-based technologies including power generation and water desalination.

ESA governments in December committed to a 10-year, nearly $10 billion package of spending on next-generation expendable rockets. But the agency’s governments set aside a modest sum of money to explore reusable rocket technologies.


Peter B. de Selding was the Paris bureau chief for SpaceNews.