- On April 20, the new SpaceX spacecraft destined for NASA astronauts exploded during a ground test in Florida. Nobody was hurt.
- The seven-person capsule, called Crew Dragon, exploded because of a valve problem, SpaceX Executive Secretary Hans Koenigsmann announced Monday.
- Koenigsmann said that an investigation is "80 percent complete" and added that he did not know if Crew Dragon would be launched with astronauts before the end of the year.
- A NASA official called the discovery of the problem "a huge gift for us" to make the ship safer.
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SpaceX thinks know what caused the explosion of its new spacecraft Crew Dragon during a test on April 20th.
This capsule-shaped vessel is designed to carry NASA astronauts to and from the International Space Station, but it must first pass a series of important tests.
In April, SpaceX conducted an unarmed ground test, which was used to warm up a flight test on a rocket. The abandonment test is designed to prove that spacecraft evacuation propellers can safely transport astronauts (in case of a problem with a rocket).
But instead of showing that the exhaust boosters were operating normally, the procedure sent clouds of harmful pink smoke into the air over Cape Canaveral, Florida.
SpaceX called the anomaly incident the same day and a video revealed the next day shows that the dragon's crew explodes on its test bench. In May, Hans Koenigsmann, vice president of SpaceX's insurance mission, confirmed that the test had destroyed the company's ship.
Today, nearly three months after the accidental explosion, Koenigsmann said the investigators had "accomplished 80%" of their work and thought they had discovered what was wrong.
"We know the system is leaking," Koenigsmann told reporters at a teleconference on Monday. This "provoked a violent reaction" once the evacuation system was activated, he added.
Kathy Lueders of NASA also joined Monday's press call. She manages the commercial crew program of the agency, through which SpaceX is paid to develop, build and test Crew Dragon.
"In many ways, it was a gift for us, because it was a field test," Lueders said. "We were able to find a problem with the hardware and be able to find it and be able to evaluate the hardware."
What SpaceX thinks a leaking valve has destroyed his ship Crew Dragon
In March, the capsule in question, Crew Dragon, was put into orbit, docked at the space station, and then returned to Earth. The mission was one of the few unprepared demonstration tests required by NASA. SpaceX then recovered the vehicle from the ocean, checked it and refurbished it.
In anticipation of the next stage of the company – its flight dropping test originally planned for the summer – SpaceX employees have locked the refurbished capsule on a bench. ;trial.
The test consisted of two steps. The first was to use low pressure thrusters, called Dracos, to show that they could maneuver the capsule in space. The next was a high-pressure engine start-up called Super Dracos, which powers the spaceship's exhaust system.
The smaller Draco engines started for about five seconds and Koenigsmann said the test was successful. However, hell was unleashed when the spacecraft began to pressurize its Super Draco system.
SpaceX, NASA, the US Air Force and other members of an investigative team have spent weeks picking up pieces of Crew Dragon. They also examined the data from the spacecraft and replayed high speed videos in search of a cause.
Koenigsmann revealed on Monday that investigators had discovered burn marks inside the pressurization system's check valves: a component designed to prevent the liquid oxidizer from penetrating until the system can project it into the engines at the correct speed. The explosion also coincided with the activation of the system, he added.
The best presentiment of the investigators at this point, said SpaceX in a statement, is that during the processing of the spacecraft used, a "plug" of the liquid oxidizer for the Super Dracos – a toxic substance called tetroxide Nitrogen – leaking through the check valve and into the pressurizing tubes.
When this system was activated, it almost instantaneously increased the pressure to 2300 psi (more than 150 times the normal atmospheric pressure at sea level). At this point, the liquid plug has shot like a bullet towards the safety valve.
"It almost destroyed the check valve and caused an explosion," said Koenigsmann. "This effect was not expected."
While the investigation is underway, Mr. Koenigsmann said the proposed solution was to replace the check valve, which can be turned on and off, with a "check valve" opening in a sense of high pressure. A rupture valve will not allow any leaks, he said, but the component is more difficult to test because it is disposable. (The solution is to test many other valves made in the same batch.)
SpaceX hoped to launch its first astronauts by the end of the year, but Koenigsmann expressed doubts about the respect of this schedule.
"We will fly when we are ready," he said.
SpaceX and NASA did not immediately respond to additional questions regarding the failure and its plans to test the exhaust system engines again after a fix.
What does SpaceX say about the Crew Dragon explosion?
Below is the complete and detailed SpaceX statement on the subject:
On Saturday, April 20, 2019 at 18:13 UTC, SpaceX performed a series of static tests on the test vehicle dropping flight Crew Dragon on a test bench located in the SpaceX Landing Zone 1 at Cape Canaveral Air Force Florida.
The Crew Dragon design includes two distinct propulsion systems: a low-pressure dual-propulsion propulsion system with sixteen Draco in-orbit propellers, and a high-pressure twin-propulsion propulsion system with eight SuperDraco propellers for use only in case of throw escape. After the successful demonstration mission of the vehicle to and from the International Space Station in March 2019, SpaceX performed additional tests of the vehicle's propulsion systems to ensure their functionality and to detect any problems with the system prior to a flight. abandonment test in planned flight.
The initial tests of twelve Draco thrusters on the vehicle were successfully completed, but the launch of the final test of eight SuperDraco thrusters resulted in the destruction of the vehicle. In accordance with pre-established safety protocols, the test area was cleared and the team monitored winds and other factors to ensure public health and safety.
Following this anomaly, SpaceX assembled an accident investigation team composed of NASA representatives and observers from the Federal Aviation Administration (FAA) and the National Transportation Safety Board (NTSB). a complete failure tree to determine the probable cause. SpaceX has also worked closely with the US Air Force (USAF) to secure the test site, as well as to collect and clean up debris as part of the investigation. The site was operational prior to the launch of STP-2 by SpaceX's Falcon Heavy and the landing of two first-stage side boosters in Landing Zones 1 and 2 on June 25, 2019.
Initial analyzes of the data indicated that the anomaly had occurred about 100 milliseconds before the ignition of the eight SuperDraco Crew Dragon propellers and during the pressurization of the vehicle propulsion systems. Evidence shows that a leaked component allowed the liquid oxidizer – nitrogen tetroxide (NTO) – to penetrate helium tubes at high pressure during treatment. ground. A plug of this NTO was driven at high speed through a helium check valve during rapid initiation of the launching exhaust system, resulting in a structural failure of the check valve. return. The failure of the titanium component in a high pressure NTO environment was sufficient to cause the check valve to ignite and resulted in an explosion.
In order to understand the exact scenario and characterize the flammability of the titanium internal components and the NTO of the check valve, as well as other materials used in the system, the investigation team on the Accident conducted a series of tests at the SpaceX rocket development site in McGregor, Texas. . Debris collected at the Florida test site, which revealed a burn in the check valve, informed Texas testing. In addition, the SuperDraco thrusters recovered from the test site remained intact, highlighting their reliability.
It should be noted that the reaction between titanium and high pressure NTO was not expected. Titanium has been used safely for many decades and on many spacecraft around the world. Nevertheless, the static firing test and the anomaly provided a wealth of data. The lessons learned from the test – and others of our comprehensive test campaign – will further enhance the safety and reliability of SpaceX's flying vehicles.
SpaceX has already initiated several actions, such as eliminating any flow path in the launching exhaust system so that the liquid propellant enters the gaseous pressurization system. Instead of check valves, which usually allow the liquid to flow in one direction, bursting discs, which seal completely until opened by high pressure, will completely mitigate the risk. In-depth testing and analysis of these mitigation measures have already begun in close coordination with NASA and will be completed well in advance of future flights.
With several Crew Dragon vehicles in various stages of production and testing, SpaceX has postponed space craft assignments to stay on track for commercial crew program flights. The spacecraft Crew Dragon, initially assigned to SpaceX's second demonstration mission to the International Space Station (Demo-2), will conduct the company's flight dropping test. The spacecraft initially assigned to the first operational mission (Crew-1) will be launched as soon as it is part of Demo-2.