Boeing's venture capital arm invested outside the U.S. (again), putting funds behind a space company (again).

The U.S. industrial giant joined Rolls-Royce and defense company BAE Systems in a $37.6 million fundraising round for U.K.-based propulsion company Reaction Engines. This is both the second foreign investment and the second space investment for Boeing HorizonX Ventures, which contributed to the $15 million funding round for Australian satellite company Myriota last month.

Reaction Engines' advanced propulsion "could change the future of air and space travel," according to Boeing HorizonX vice president Steve Nordlund.

"We expect to leverage their revolutionary technology to support Boeing's pursuit of hypersonic flight," Nordlund said in a statement.

Reaction Engines, which has now raised more than $140 million over the last three years, is developing a hybrid jet and rocket engine. In theory, the company's SABRE engine will be capable of operating as a jet at take-off and transitioning to a rocket at higher altitudes.

The company estimates that SABRE, or "Synergistic Air-Breathing Rocket Engine," will be capable of reaching speeds of Mach 5 while operating as a jet, using Reaction Engine's "air-breathing" technology. Then SABRE will flip to rocket power, taking the spacecraft to low Earth orbit and reaching speeds of Mach 25 – more than 19,000 miles per hour.

"Reaction Engines [is] an innovative UK company that is helping push the boundaries of aviation technology," Rolls-Royce chief technology officer Paul Stein said in a statement.

With about 150 employees, the firm is testing engine components, with the aim of a ground-based test of a SABRE engine core in 2020. Reaction Engines has a contract with the U.S. Defense Advanced Research Project Agency for airflow testing and is building a new facility in the U.K. for further tests.

The investment comes at an opportune time in the United Kingdom, which put into law the Space Industry Bill on March 15. The new legislation is part of the country's effort to establish a legal basis to bring the global space industry to U.K. soil, especially looking to attract the space tourism and satellite industries to new spaceports.