23.04.2019

Six weeks after the spacecraft completed its orbital launch debut, SpaceX’s first flight-proven Crew Dragon capsule suffered a catastrophic explosion seconds before a planned SuperDraco test fire.

In the last nine years, SpaceX has successfully built, tested, launched, and recovered Cargo and Crew Dragons 18 times, including five instances of Cargo Dragon capsule reuse, all with minor or no issues. The April 20th event is the first time in the known history of SpaceX’s orbital spacecraft program that a vehicle – in this case, the first completed and flight-proven Crew Dragon capsule – has suffered a total failure. Regardless of the accident investigation’s ultimate conclusions, the road ahead of Crew Dragon’s first crewed test flight has become far more arduous.

According to information acquired by NASASpaceflight.com, SpaceX was in the middle of a series of static fire tests meant to verify that the flight-proven capsule was in good working order after Crew Dragon’s inaugural mission to orbit. The spacecraft was to be tested near SpaceX’s Cape Canaveral Landing Zone facilities, where the company has a small but dedicated space for Dragon tests. Crew Dragon C201’s testing began earlier on Saturday, successfully firing up its smaller Draco maneuvering thrusters. This transitioned into a planned SuperDraco ignition, what would have been the first such integrated test fire for capsule C201.

SpaceX planned to rapidly reuse Crew Dragon C201 for an upcoming in-flight abort (IFA) test, in which the spacecraft would be required to successfully escape from Falcon 9 at the point of peak aerodynamic stress (Max Q). Based on a leaked video of the failure, one or several faults in Crew Dragon’s design and/or build led to a near-instantaneous explosion that destroyed the spacecraft. Sound in the background seems to indicate that the explosion occurred several seconds before the planned SuperDraco ignition, a major concern given their pressure-fed design.

As pressure-fed rocket engines specifically designed to be the basis of a launch escape system, Crew Dragon and its SuperDraco thrusters are meant to be ready to ignite at a millisecond’s notice once they are armed in a flight-ready configuration. It’s safe to say that ten seconds away from a specifically planned ignition is one of those moments, although there is a limited chance that SpaceX’s static fire procedures intentionally diverge from an abort-triggered ignition. Regardless, the fact that Crew Dragon was destroyed before the ignition of its SuperDracos is not an encouraging sign.

Instead of a problem with its high-performance abort thrusters, it can be tentatively concluded that Crew Dragon’s explosion originated in its fuel tanks or propellant plumbing. Such an immediate and energetic explosion points more towards a total failure of propellant lines or valves (or their avionics), while another – and potentially far more concerning – cause could be one of Crew Dragon’s pressure vessels. In a space as enclosed as a Dragon capsule, the rupture of a pressure vessel could trigger a chain reaction of pressure vessel failures, freeing both oxidizer (NTO) and fuel (MMH). Known as hypergolic propellant, NTO and MMH ignite immediately (and violently so) when mixed.

It’s quite possible that the accident investigation to follow will be SpaceX’s most difficult and trying yet. Regardless of the specific cause, the footage of Crew Dragon C201’s demise does not support any positive conclusions about the fate of astronauts or passengers, had they been aboard during the violent explosion. Seemingly triggered in some way by the very system meant to safely extricate Crew Dragon and its astronauts from a failing Falcon 9 rocket, major work will need to be done to prove to NASA that the spacecraft is safe. Sadly, Boeing’s Starliner spacecraft – funded in parallel with Crew Dragon under NASA’s Commercial Crew Program – suffered a far less severe but no less significant failure during a static fire test of its own abort thrusters. Boeing was forced to remove the impacted hardware from its flight plans to extensively clean, repair, and rework the service module.

NASA is now faced with the fact that both of the spacecraft it supported with CCP have exhibited major failures related to their launch escape systems. Crew Dragon’s catastrophic explosion comes as a particularly extreme surprise given how extensively SpaceX has already tested the SuperDraco engines and plumbing, as well as the successful completion of the spacecraft’s launch debut. In the process of DM-1 launch preparations, Crew Dragon likely spent a minimum of 80 minutes with its SuperDraco thrusters and propellant systems primed and ready to abort at any second, apparently without a single mildly-concerning issue.

Godspeed to SpaceX and NASA as they enter into this challenging and unplanned failure investigation.

Quelle: TESLARATI