Valves and sensors continue to be tricky to operate on SpaceX's Dragon spacecraft, as the company rushed to verify a sensor data before its Crew 7 mission from NASA took off from the Kennedy Space Center in Florida earlier today. The Crew 7 launch was scrubbed earlier and officials from NASA and SpaceX explained the reasons behind the delay at the post launch teleconference. At the event, SpaceX's Benjin Reed shared that a sensor reading saw SpaceX quickly verify data for a potential propellant leak and the go ahead for the mission was given a mere two minutes before launch after the off nominal nitrogen tetraoxide reading was discovered as the crew arm separated from the Crew Dragon before liftoff.
SpaceX Reevaluated Oxygen Valves For Crew Dragon Before Crew-7 Lift Off
SpaceX's CRS 28 mission created some stir earlier this year after a valve demonstrated problems while the Cargo Dragon was docked to the International Space Station (ISS). After the spacecraft returned to Earth, the firm and NASA evaluated the valves and examined them to ensure that the problem does not take place again in a future mission. Their investigation revealed that a valve on the Cargo Dragon was corroded due to acid buildup from a moisture leak. At the Crew 7 mission's flight readiness review press conference, SpaceX and NASA officials confirmed that they had developed a strategy to ensure that even if the problem occurred in the future, a workable solution to mitigate it was present.
NASA's Steve Stich explained that during Crew 7's dry dress rehearsal saw an Oxygen sensor behave abnormally. This sensor is part of a set of five, and it measures the Oxygen and air that is injected into the cabin for crew life support. This sensor was replaced, and the vehicle was cleared for launch. The reason behind the delay in the mission was SpaceX's decision to reevaluate all of the valves for the spaceship to check their force margins. These margins calculate the force that would be required to open the valves in case of an anomaly. Among these valves, the ones that feed air and oxygen into the cabin took longer to understand and caused the delay.
Understanding the force margins of the valve wouldn't be the last hurdle before a successful launch, though. SpaceX's Reed shared that before liftoff, as the crew arm separated from the Dragon, SpaceX detected a small nitrogen tetraoxide reading on one of the sensors. The crew arm transports the astronauts inside the spacecraft, and its removal is one of the few steps before rocket engine ignition for liftoff.
An NTO leak is concerning due to its toxicity and it is one of the first things that ground and recovery crews scan the Dragon for after it lands in the ocean. This is to ensure that there is no leakage that can harm either the crew during their egress (exit) from the Dragon or the crews that access the ship after its return.
After the leak, which was nearly a quarter of a part of a million, was discovered, SpaceX assigned three different engineers to run independent calculations to determine if the amount of NTO coming from the service section's exhaust would pose any harm during the full 210 days of the mission. These calculations were finished just two minutes before launch before the Dragon was cleared for liftoff. They confirmed that if there was leak, then over the course of the mission, it would be typical of a system of its kind.
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