NASA and SpaceX have delayed Cargo Dragon’s CRS-25 space station resupply mission by two weeks after the company identified the cause of the spacecraft’s rare leak.
Instead of the original June 7 mission goal, which was eventually pushed back to June 10 and then June 28 when SpaceX discovered signs of a possible fuel leak near one of the many ‘Draco’ boosters of the spacecraft, NASA and SpaceX will now attempt to launch CRS -25 no earlier than (NET) July 11.
That makes CRS-25 something exceptionally rare: a SpaceX launch delayed more than a month by a glitch discovered just days before liftoff. Along with its increasing throughput and successful launch record, Falcon 9 has quickly become one of the most reliable and punctual rockets in service today. Once the rocket is on board, SpaceX will occasionally experience a day or two of delays caused by minor technical issues or bad weather, but anything beyond a few days has become exceptionally rare.
The same has generally been true for Dragon and Dragon 2, although Dragon 2 spacecraft are much newer and less experienced than Falcon rockets and often encounter minor issues. However, it has been years since a Dragon mission has been delayed several times. weeks just days before its original launch target. CRS-25 problems are extraordinarily rare for SpaceX.
On June 13, NASA distributed an update on these issues, revealing that SpaceX had narrowed the cause of the abnormal fuel vapor readings that delayed the launch to a single “Draco thruster valve inlet seal.” Dragon spacecraft have 16 Draco maneuvering thrusters, each of which has at least two “valve inlet seals” for fuel (monomethylhydrazine or MMH) and oxidizer (dinitrogen tetroxide or NTO).
Dragon’s smaller pressure-fed Draco thrusters operate at relatively low pressures, but the hypergolic (self-igniting) fuel and oxidizer they burn are extremely uncooperative and corrosive and create harsh conditions for the valves to live. and work. In general, valves are already a major source of headaches in spaceflight, where the thermal and chemical environments are bipolar and unforgiving in the extreme, the stakes are about as high as they are and the realities basic physics require all hardware to be as light and minimal as possible.
Given Draco’s impressive history, with hundreds of thrusters flown on dozens of different orbital Dragon missions since 2010, it’s likely that SpaceX will solve the problem without issue and prevent it from happening again. Yet the leak still serves as a reminder that reliably operating large and complex spacecraft is an immense challenge. When that spacecraft is destined to be reused, the difficulty is further amplified.
A slight silver lining, however, came from the latest delay: SpaceX’s next Starlink launch on June 17 no longer has to worry about encroaching on a NASA Dragon launch just 11 days later. In fact, though unlikely, SpaceX might even have time for a second Starlink launch from Pad 39A to fill the slight void CRS-25 created in June’s Falcon 9 manifesto.