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.
Below are some details about the upcoming Ascent Abort Test
The following is from the FAA’s “Draft Environmental Assessment for Issuing SpaceX a Launch License for an In-flight Dragon Abort Test”, issued in November 2018:
“The abort test would involve observation, photography, and debris management associated with the breakup of the Falcon 9 first and second stages.
The launch scenario where an abort is initiated during the ascent trajectory at the maximum dynamic pressure (known as max Q) is a design driver for the launch abort system. It dictates the highest thrust and minimum relative acceleration required between Falcon 9 and the aborting Dragon. As the in‐flight abort would occur during the first stage portion of the launch trajectory, the second stage of Falcon 9 would be simplified
The abort test would start with a nominal launch countdown and release at T-0. The Falcon 9 with the Dragon attached would follow a standard ISS trajectory with the exception of launch azimuth to approximately Mach 1. The Falcon 9 would be configured to shut down and terminate thrust, targeting the abort test shutdown condition (simulating a loss of thrust scenario).
Dragon would then autonomously detect and issue an abort command, which would initiate the nominal startup sequence of Dragon’s SuperDraco engine system. Concurrently, Falcon 9 would receive a command from Dragon to terminate thrust on the nine first stage Merlin 1D (M1D) engines. Dragon would then separate from Falcon 9 at the interface between the trunk and the second stage, with a frangible nut system. Under these conditions, the Falcon 9 vehicle would become uncontrollable and would break apart. SpaceX would not attempt first stage booster flyback to KSC, CCAFS, or a droneship, nor would they attempt to fly the booster to orbit.
Dragon would fly until SuperDraco burnout and then coast until reaching apogee, at which point the trunk would be jettisoned. Draco thrusters would be used to reorient Dragon to entry attitude. Dragon would descend back toward Earth and initiate the drogue parachute deployment sequence at approximately 6 miles altitude and main parachute deployment at approximately 1 mile altitude.
Dragon recovery operations would be very similar to actions for normal Dragon reentry and recovery, although Dragon recovery during the abort test would occur approximately 9–42 miles from shore, and normal Dragon recovery is approximately 200 miles offshore.
The recovery vessel would recover all parachutes deployed by Dragon, as possible, including the two drogue and four main parachutes. Recovery of the drogue parachute assembly would be attempted if the recovery team can get a visual fix on the splashdown location.
However, because the drogue parachute assembly is deployed at a high altitude, it is difficult to locate. In addition, because of the size of the assembly and the density of the material, the drogue parachute assembly becomes saturated within approximately one minute of splashing down and begins to sink. This makes recovering the drogue parachute assembly difficult and unlikely.
The Dragon test vehicle is intended to represent the final flight configuration of Dragon-2. Systems, subsystems, and components critical to the success of in-flight abort would be in the final configuration. Non-critical systems would either be eliminated or simplified to reduce the complexity of the ground refurbishment process to conduct the abort test.
Dragon would contain approximately 5,650 pounds of hypergolic propellant, including approximately 3,500 pounds of dinitrogen tetroxide (NTO) and 2,150 pounds of monomethylhydrazine (MMH). Dragon would contain approximately 2,400 pounds of residual propellant after the abort test.
The booster would be a standard Falcon 9 first stage and configured in an expendable configuration for the abort test. Landing legs and grid fins would be removed.
No booster recovery burns would be attempted. As such, a full triethylaluminum-triethylborane (TEA-TEB) mixture used as a first and second stage ignitor would not be used. The booster would be capable of flying a mission profile that allows for the target abort velocity to be achieved.
The booster would include nine M1D engines and be configured to perform an ascent abort shutdown. Each engine is propelled by liquid oxygen (LOX) and rocket fuel (RP-1; highly refined form of kerosene) and produces 190,000 pounds of thrust at sea level (for a total of 1.71 million pounds of thrust from all nine engines). The booster would carry the standard set of flight instrumentation.
The second stage would be a standard Falcon 9 second stage, with the exception of the M1D vacuum engine. The components essential to propellant loading operations would be carried, but the thrust chamber, turbopump, thrust vector control actuators, and other components required for performing second stage burns, would be omitted, as the mission concludes part-way through the first stage ascent burn. Propellant loading would follow standard loading operations for the second stage.
During the initial flight of the Falcon 9 with the Dragon attached, the flight track would be normal. The separation of Dragon from Falcon 9 would occur approximately between 83 and 100 seconds after launch. Dragon and the trunk would separate from the second stage and continue to coast to its apogee, eventually dropping the trunk and deploying the drogue parachutes.
At the point where Dragon and the trunk separate, the first and second stage would become unstable and break up approximately 2–4 miles down range from the shore. After the main chutes deploy, Dragon would drift approximately 3 miles and land approximately 9–42 miles from shore.”
Only after both flight tests are complete, and once everything is to NASA’s satisfaction, will a GO be given for SpaceX to fly the first Dragon Riders to the International Space Station.