A high-temperature airflow test site designed to evaluate a key technology in the Reaction Engines’ hypersonic air-breathing combined cycle Sabre rocket engine is under assembly at Front Range Airport near Watkins, Colorado.
Construction of the facility follows the award earlier this year of a U.S. Defense Advanced Research Projects Agency (DARPA) contract to test the engine’s pre-cooler heat exchanger, or HTX. The test work, which is due to start in 2018, will focus on running the HTX at airflow temperatures in excess of 1,800 deg F (1,000 deg C), representing inlet conditions at Mach 5.
The HTX is designed to chill airflow down from this temperature to minus 150 deg. C. in less than 1/20th of a second, and is a vital element of the Sabre concept which extracts oxygen from the atmosphere. The chilled air is passed from the HTX to a turbo-compressor and into the rocket combustion chamber where it is burned with sub-cooled liquid hydrogen fuel.
Tests of the heat exchanger, which is made from thousands of thin-walled tubes to provide a high surface area to low weight, represent a major milestone for Reaction which has seen growing U.S. interest in elements of Sabre since the concept was first independently validated by the U.S. Air Force Research Laboratory in 2015. Each tube in the HTX is joined to an inlet and outlet manifold, which allows coolant to be injected and removed for the cooling process.
Reaction says the work is designed to build upon previous successful testing of the precooler heat exchanger at ambient temperature conditions. Adam Dissel, president of Reaction Engines Inc., adds: “the facility’s ability to deliver controlled temperature profiles over flight-like run durations at significant airflow represents a unique capability that can fill additional testing demand beyond HTX.” Inlet air for the facility will be heated by a General Electric J79 engine.
Dubbed TF2, the Colorado test site will also be made available to industry, technology developers, and universities, following evaluation of the HTX. Reaction Engines in the UK is meanwhile continuing to develop the TF1 engine test facility at Westcott where the first ground-based demonstration of the Sabre rocket engine will take place. The UK site will incorporate a hydrogen/air-breathing pre-burner to condition the air for core evaluation and is adjacent to a test facility where Reaction’s rocket nozzle tests have also been conducted.
Core testing is provisionally targeted for 2020 and will focus on the low fuel consumption potential of the cycle, as well as operability work covering transients, start-ups and shut-downs. The second phase will evaluate the integrated engine for the first time from around 2021 by linking up pre-coolers and thrust chambers to take the engine through the full operating range with heated inlet air. For the third phase covering flight testing, Reaction is considering an X-plane type flight demonstration program. Targets for the flight test engine include inlet and bypass demonstrations, complete propulsion integration, maintainability and reliability.