In a partial response to a report alleging evidence of several significant anomalies during a recent private astronaut launch that could affect a crew of NASA astronauts launched last month, the space agency issued a statement denying these allegations. However, the same statement simultaneously revealed that SpaceX had recently discovered a different issue with a different Crew Dragon spacecraft component during ground testing.
May 23, space explored released a report alleging that a SpaceX Crew Dragon spacecraft encountered major problems during Axiom-1, the company’s first fully private astronaut launch to the International Space Station (ISS). According to information from sources and a possible internal memo from SpaceX, part of Dragon’s toxic thruster leaked during the 17-day flight, damaged or weakened parts of its heat shield, and “[caused] dangerously excessive wear on re-entry. In general, the report seemed well-researched and even alleged that NASA’s Engineering and Security Center (NESC) had opened an investigation. Additionally, when approached for comment, neither NASA nor SpaceX were initially willing to speak officially, which also meant neither had denied the charges.
A day later, NASA provided an official statement to Space Explored explicitly denying that there had been a propellant leak, heat shield contamination, or excessive heat shield wear during any of the “recent reentries of Dragon’s crew”.
NASA also dismissed concerns about reusing a previously used Cargo Dragon 2 heat shield structure on Crew-4, which was launched just two days after Axiom-1 was recovered and is expected to spend four to five more months in orbit. He also noted that reusing Dragon’s heat shield floor tile – structures that experience the most re-entry heating and are submerged in salt water after each mission – are extremely limited and have only been attempted occasionally Cargo Dragon missions.
Simultaneously, NASA revealed that “a new composite heat shield structure intended for flight on Crew-5 failed an acceptance test” at SpaceX’s Hawthorne, Calif. Dragon factory. The failure of the unrelated test was blamed on a manufacturing defect and NASA gave no signs of serious concern in its statement, suggesting the problem may be less serious than it appears. In response, NASA says SpaceX will simply use a different heat shield composite structure for Crew-5, which is slated for launch no earlier than (NET) September 2022.
Data associated with recent Dragon crew re-entries was normal – the system was working as expected without issue. There were no hypergol leaks when returning from a crewed Dragon mission or contamination with the heat shield causing excessive wear. SpaceX and NASA perform a full technical review of the heat shield thermal protection system after each return, including before launch of the Crew-4 mission currently on the International Space Station. The composite structure of the heat shield (structure under the tile) was redone according to the normal planning and renovation processes. The thermal protection system on Crew-4’s main heat shield was new, as it has been for all human spaceflight missions. SpaceX has only demonstrated the reuse of select PICA (Phenolic-Impregated Carbon Ablator) tiles, which is a lightweight material designed to withstand high temperatures, as part of the heat shield on cargo flights.
NASA and SpaceX are currently determining the hardware allocation for the agency’s next SpaceX Crew-5 mission, including the Dragon heat shield. SpaceX has a rigorous testing process to put every component and system through its paces to ensure safety and reliability. In early May, a new composite heat shield structure intended for flight on Crew-5 failed an acceptance test. The test did its job and found a manufacturing defect. NASA and SpaceX will use another heat shield for the flight that will undergo the same rigorous pre-flight testing.
Crew safety remains the top priority for NASA and SpaceX and we continue to target September 2022 for the launch of Crew-5.
Some quirks remain. While NASA’s explicit rebuttal should be considered the final definitive word on the matter, it is still highly unusual that NASA and SpaceX have refused or been unable to quickly and publicly deny the claims hours later. have been questioned. It could simply be a consequence of NASA and SpaceX’s internal and external miscommunication or both parties’ love of withholding information from taxpayers about the systems and technologies those same taxpayers paid for.
On the other hand, after the break-in of Crew Dragon’s Demo-2 with higher than expected heat shield wear in 2020, it’s almost impossible to imagine that NASA and SpaceX would have launched Crew-4 two days later. the recovery of Axiom-1. without verifying with certainty that the erosion of the heat shield was within normal limits. SpaceX’s enhanced Dragon Phenolic-Impregnated Carbon Ablator (PICA-X) heat shield tiles are would have been designed to erode [PDF] less than a centimeter of their thickness around 2017 ~ 7.5 cm (3 in) after each re-entry. Musk went even further, stating in 2012 that “[PICA-X] can potentially be used hundreds of times for re-entry into Earth orbit with only minor degradation each time. If it were true, it would be extremely difficult, even for a quick post-flight inspection of Axiom-1’s Dragon capsule, to miss what Space Explored described as “dangerously excessive wear.”
In theory, during recovery, even a tiny propellant leak should also have been immediately detected by SpaceX’s recovery team, as the very first part of the hands-on process involves a small team with gas masks and detectors s approaching the floating pod to ensure it is safe for others to approach. Crew Dragon’s liquid monomethylhydrazine (MMH) and dinitrogen tetroxide (NTO) fuel are highly toxic in small amounts and MMH is a known carcinogen.
All told, news of a potential thruster leak and abnormal heat shield performance appears to have been a false alarm, though – coincidence or not – a seemingly minor anomaly with an unmanned Crew Dragon heat shield structure did occur earlier this month. Despite this anomaly, Crew-4 and Crew-5 are proceeding normally, and NASA appears to be content with Crew Dragon’s performance on several recent launches and recoveries.
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