SpaceX successfully performed an in-flight-abort test of their Crew Dragon capsule, on Sunday 19th January. This marks the final major test of the capsule, hopefully allowing it to become certified to carry astronauts to the International Space Station.

Credit: NASA

The Crew Dragon 2 Capsule launching on top of Falcon 9 booster B1046 at Kennedy Space Centre (Credit: NASA)

As predicted, the launch was spectacular. The unmanned capsule lifted off atop a Falcon 9 booster, powered by 9 Merlin 1D engines, the rocket ascended on a standard trajectory to the ISS, however, as programmed, the main engines throttled down just past the point of maximum aerodynamic load (max-Q). The automated computer system on board the capsule interpreted this as a failure of the launch vehicle and commanded the abort. At this point the SuperDraco thrusters on the Dragon capsule ignited, safely propelling the capsule away from the failing booster. Missing the aerodynamic capsule and the main engines not offering any control authority, the booster was effectively an open-ended aluminium can travelling, unguided, through a Mach 2 airstream, and after a few seconds, the huge aerodynamic loads caused the booster to disintegrate in a huge fireball. Interestingly, the second stage survived this explosion, although it didn’t survive impacting the ocean at around the speed of sound. SpaceX claims it will try to recover as much of the floating debris from the booster as possible.

Crew Dragon Aborting | Credit: SpaceX

A beautiful shot of the four SuperDraco thrusters pulling the capsule to safety (Credit: SpaceX)

Having ditched the booster, the Dragon capsule continued to coast until it reached apogee at approximately 45km, at which point it jettisoned the trunk which had been keeping it flying straight, nose forward, and prepared to descend through the atmosphere, facing the heatshield downwards. After a minute or so, the two drogue chutes were deployed to orient the capsule and begin slowing it for splashdown. The four main chutes were deployed soon after, but in a reefed state (i.e. not fully opened) so as to minimise sudden loads on the capsule. As the capsule gradually slowed, the parachutes were slowly unfurled to their final diameter. Moments after the capsule splashed into the sea, the live-stream showed one of the fast-response boats coming up to meet it.

Explosion of B1046 | Credit: Katie Darby

At the mercy of the hypersonic airstream, Falcon booster B1046 was ripped apart (Credit: Katie Darby)

In the event of an actual crewed abort, the splashdown location would not be so precisely known, so the capsule is required to be able to stay afloat for a minimum of 24hrs. If rescue boats couldn’t reach the capsule in time, military helicopters would provide life-rafts for the crew before surface craft were able to take them to safety. From the information given about this test from NASA, the capsule never experienced more than about 3.5g, well within human tolerance.

According to Elon Musk, the capsule is also able to abort during an overpressure event (an explosion of the booster), and the fact that the main engines were already throttling down makes no difference to the validity of this test, which was optional for SpaceX in the first place.

 

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

 

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Propulsion methods for launchers, upper stages, satellites, etc

Astronomy of planets in other star systems.