SpaceX just hit another big milestone today on the road to launching astronauts for NASA starting next year, with a successful test fire campaign of their Crew Dragon’s maneuvering thrusters and abort engines at Cape Canaveral Air Force Station.
The test comes nearly 7 months after an anomaly blew up a Crew Dragon during the original test firing of its abort engines back on April 20, which was traced to a leaky valve which allowed liquid oxidizer – nitrogen tetroxide (NTO) – to enter high-pressure helium tubes during ground processing.
“Personnel determined that a slug of liquid propellant in the high-flow helium pressurization system unexpectedly caused a titanium ignition event resulting in an explosion,” explained NASA in a press release. “Based on that investigation’s findings and months of testing, SpaceX redesigned components of the system to eliminate the possibility of slugs entering the high-flow pressurization system.”
The abort system is critical in that it is intended to safely launch a crew away from a failing rocket, whether on the launch pad or during launch itself. Crew Dragon employs eight SuperDraco thrusters for an abort emergency, which are paired up in pods of four around the spacecraft, with each engine providing a thrust of 16,000 pounds.
SpaceX initiated several actions to correct the problem moving forward, such as, “eliminating any flow path within the launch escape system for liquid propellant to enter the gaseous pressurization system”, said the company earlier this year. “Instead of check valves, which typically allow liquid to flow in only one direction, burst disks, which seal completely until opened by high pressure, will mitigate the risk entirely.”
“The engine tests began with two burns for a duration of one-second each for two of Crew Dragon’s 16 Draco thrusters,” says NASA. “The Draco thrusters are used for on-orbit maneuvering and attitude control, and would also be used for re-orientation during certain in-flight launch escapes. Following these initial Draco thruster burns, the team completed a full-duration firing for approximately nine seconds of Crew Dragon’s eight SuperDraco engines. The SuperDraco engines are designed to accelerate Dragon away from the F9 launch vehicle in the event of an emergency after liftoff.”
“In quick succession, immediately after the SuperDracos shut down, two Dracos thrusters fired and all eight SuperDraco flaps closed, mimicking the sequence required to reorient the spacecraft in-flight to a parachute deploy attitude and close the flaps prior to reentry,” added NASA. “The full sequence, from SuperDraco startup to flap closure, spanned approximately 70 seconds.”
With the static fire tests of the spacecraft’s thruster and engines now complete, SpaceX and NASA will review the data and perform detailed inspections, before scheduling a launch date for one final big test of the spacecraft; the In-Flight Abort Test.
NASA conducted a similar test earlier this year with their Orion Crew Capsule, and a scary incident last year on a Russian Soyuz rocket and spacecraft proved exactly why such a capability is absolutely needed, when the crew of Soyuz MS-10 experienced a failure with their rocket, forcing them into a dangerous high-G ballistic descent back to Earth.
Fortunately they survived, but things easily could have turned out the opposite. Even a proven system like Soyuz can’t escape the inevitable. Things will go wrong, and the upcoming Crew Dragon In-Flight Abort Test will ensure future Dragon crews can safely escape an in-flight emergency.
Additionally, SpaceX has lost two missions to failing rockets in recent years; one on the launch pad (AMOS-6) and one on launch – a Cargo Dragon mission for NASA (CRS-7). And while both NASA and SpaceX state the issues which caused those accidents are resolved, it does not change the fact that those events are exactly why an abort capability is needed for crews to begin with.
SpaceX already conducted a Pad Abort Test in 2015, which launched from SLC-40 off a specially made truss to simulate the spacecraft atop a Falcon-9 rocket. The 21,000-lb prototype took flight quickly under 120,000 lbs of axial thrust from its eight SuperDraco engines, ascending 3,500 ft in six seconds before jettisoning its trunk and deploying a pair of drogue chutes, followed by a trio of main parachutes and splashdown less than a mile offshore.