UK company Reaction Engines has tested its innovative precooler at airflow temperature conditions equivalent to Mach 5, or five times the speed of sound. This achievement marks a significant milestone in its ESA-supported development of the air-breathing SABRE engine, paving the way for a revolution in space access and hypersonic flight.

The precooler heat exchanger is an essential SABRE element that cools the hot airstream generated by air entering the engine intake at hypersonic speed. 

“This is not only an excellent achievement in its own right but one important step closer to demonstrating the feasibility of the entire SABRE engine concept,” said Mark Ford, heading ESA’s Propulsion Engineering section.


Test facility in the USA

The Synergetic Air-Breathing Rocket Engine (SABRE) is uniquely designed to scoop up atmospheric air during the initial part of its ascent to space at up to five times the speed of sound. At about 25 km it would then switch to pure rocket mode for its final climb to orbit.

In future SABRE could serve as the basis of a reusable launch vehicle that operates like an aircraft. Because the initial flight to Mach 5 uses the atmospheric air as one propellant it would carry much less heavy liquid oxygen on board. Such a system could deliver the same payload to orbit with a vehicle half the mass of current launchers, potentially offering a large reduction in cost and a higher launch rate.

Pre-cooler airflow

Reaction Engines constructed the precooler test item in the UK, then shipped it to its specially constructed facility at the Colorado Air and Space Port in the US for its test campaign.

This ground-based test achieved the highest temperature objective of the company’s ‘HTX’ hot heat exchanger test programme: it successfully quenched airflow temperatures in excess of 1000 °C in less than 1/20th of a second.

SABRE-based spaceplane

The tests demonstrated the precooler’s ability to cool airflow at speeds significantly in excess of the operational limit of any jet-engine powered aircraft in history. Mach 5 is more than twice as fast as the cruising speed of Concorde and over 50% faster than the SR-71 Blackbird aircraft – the world’s fastest jet-engine powered aircraft.

This most recent test builds upon the success of previous HTX hot tests undertaken in April which saw the precooler successfully operate at temperatures of 420 ᵒC – matching the thermal conditions corresponding to Mach 3.3 flight.

HTX test system

ESA, via the UK Space Agency, has invested €10 million in SABRE development, together with £50 million (€58 million) from UKSA. ESA also performs a technical oversight role on behalf of UKSA. In March, the two agencies reviewed and validated the preliminary design of the demonstrator engine core of SABRE, which Reaction Engines will use to undertake ground-based testing at its under-construction TF1 test facility at Westcott, Buckinghamshire, UK.

Reaction Engines co-founder and current Chief Technology Officer Richard Varvill emphasised that this achievement was the culmination of more than 30 years of effort: “This is a momentous landmark for Reaction Engines in the development of its SABRE engine, which has the potential to revolutionise both access to space and high-speed flight by powering aircraft to five times the speed of sound.


European Space Agency 23rd October 2019


Artist's impression of a supermassive black hole planetary system (Credit: Kagoshimal University)

Up untill now we have never thought that Black Holes might have planets in orbit, except for a few science fiction stories. It just goes to show that science fiction writers can be visionaries. Now, Professor Keiichi Wada of Kagoshima University, Japan, says: “With the right conditions, planets could be formed even in harsh environments, such as around a black hole,” This suggestion emerged from his work in active galactic nuclei, which are highly luminous objects energized by supermassive black holes.

Black holes, by their extensive and strong gravitational field, would be able to gather around themselves considerable volumes of dust and gas. In regions where the intense radiation from close to the black holes' absolute event horizon, is attenuated by the depth of orbiting dust clouds, theoretic studies indicate that planets can form.

The sheer quantity of material that a supermassive black hole could gather, as compared with far less massive stars, coupled with the much larger volume of space subjected to the black holes gravitational field, means that many more planets than might be found in a typical stellar system could be formed.

“Our calculations show that tens of thousands of planets with 10 times the mass of the Earth could be formed around 10 light-years from a black hole,” says Eiichiro Kokubo, a professor at the National Astronomical Observatory of Japan who studies planet formation. “Around black holes there might exist planetary systems of astonishing scale."


At present, there do not seem to be any observational techniques that would make such planetary systems visible. Our own galaxy contains a black hole, so far as can be determined, and it is known to have close stellar companions whirling about it. Viewing planet-sized objects at 30,000 light years distance would require resolving powers unattainable by Earth-based telescopes.

Article: The Astrophysical Journal, 886:107 (7pp), 2019 December 1




Propulsion methods for launchers, upper stages, satellites, etc

Astronomy of planets in other star systems.