WASHINGTON – NASA and SpaceX have delayed the launch of a Cargo Dragon mission to the International Space Station after discovering a potential propellant leak in the spacecraft’s thrusters.
In a statement in late June, NASA said the launch of the CRS-25 mission, scheduled for June 10, was being postponed after “elevated vapor levels” of monomethylhydrazine (MMH) were detected in part of the spacecraft’s Draco engine system. The cause of the increased reading is currently being investigated.
The Dragon spacecraft uses Draco thrusters for orbital maneuvers, including approaching and exiting the space station and de-orbiting at the end of the mission. The engines use MMH and nitrous oxide propellants, a storable, hypergolic combination. The cargo version of Dragon lacks the more powerful SuperDraco engines that SpaceX developed for the Crew Dragon starship’s demolition system.
NASA said the elevated readings were noticed as propellant was being loaded into the spacecraft, but didn’t say when that happened, other than that the problem was “identified over the weekend.” NASA and SpaceX officials said they met on June 6 to discuss the issue “and the best way forward.”
The agency said Dragon’s MMH and nitrous oxide propellants were dumped so engineers could study the problem. “Once the exact source of the elevated readings is identified and the cause determined, the joint NASA-SpaceX teams will determine and announce a new target launch date,” it said.
The dragon will deliver more than two tons of supplies and equipment to the ISS. The mission’s science payloads, highlighted in a NASA briefing June 2, include an Earth science instrument that will study mineral dust in the atmosphere, experiments to study how stitched wounds heal in microgravity, and the aging of the immune system, and a student- developed an experiment that uses biopolymers to make bricks from materials found in the regolith of the Moon and Mars.
The engine problem is the second problem involving a Dragon spacecraft in recent weeks. NASA announced on May 24 that SpaceX would replace the heat shield structure for the next Crew Dragon spacecraft, which will launch in September on the Crew-5 mission. This heat shield failed an acceptance test in early May.
NASA revealed the problem with the heat shield in a statement that denied a published report that hypergolic propellants leaked during reentry of the Crew Dragon spacecraft flying the Ax-1 private astronaut mission in April, damaging the heat shield.
“The data associated with the Dragon crew’s recent re-entry was normal – the system was without a doubt operating as intended,” the agency said last month. “During the return of a manned Dragon mission, there was neither a hypergol leak nor a heat shield contamination that caused excessive wear.”