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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.
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.
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.
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.