WASHINGTON — Propellant leaks created by an unexpectedly strong harmonic response caused the loss of SpaceX’s Starship vehicle on a test flight last month as the company prepares for its next launch.
In a statement released Feb. 24, SpaceX provided new details about the seventh Starship/Super Heavy test flight Jan. 16, which ended with the Starship upper stage breaking apart over the Caribbean.
According to SpaceX, there was a flash in the aft section, or “attic,” of Starship near one of its six Raptor engines about two minutes after the vehicle separated from the Super Heavy booster. That was followed by a pressure rise in the section that suggested there was a propellant leak.
A second flash followed about two minutes later, after which there were “sustained fires” in the attic. “These eventually caused all but one of Starship’s engines to execute controlled shut down sequences and ultimately led to a loss of communication with the ship,” the company stated, with the last telemetry received about 8 minutes and 20 seconds after liftoff.
SpaceX noted that telemetry was lost before the autonomous flight termination system on the vehicle was triggered. That system instead activated about three minutes after the loss of communications with the vehicle.
The company concluded that the most probable cause for the loss of Starship was a “harmonic response several times stronger in flight than had been seen during testing, which led to increased stress on hardware in the propulsion system.” That increased stress caused propellant leaks that could not be fully vented from the attic and allowed the fires that led to the engine shutdowns.
As part of the investigation, SpaceX performed an extended static fire of the Starship built for the next mission, Flight 8, firing its engines for 60 seconds in the Feb. 12 test.
“The 60-second firing was used to test multiple engine thrust levels and three separate hardware configurations in the Raptor vacuum engine feedlines to recreate and address the harmonic response seen during Flight 7,” the company stated. “Findings from the static fire informed hardware changes to the fuel feedlines to vacuum engines, adjustments to propellant temperatures, and a new operating thrust target that will be used on the upcoming flight test.”
SpaceX said it is also adding vents and a gaseous nitrogen purge system to reduce the flammability of the attic section of the current version of Starship.
SpaceX is moving ahead with the next Starship mission, Flight 8. That is scheduled to launch as soon as Feb. 28 from the company’s Starbase site at Boca Chica, Texas, pending the Federal Aviation Administration’s approval of SpaceX’s investigation into Flight 7.
SpaceX said that Flight 8 will have many of the same objectives of Flight 7 that were not demonstrated, including deploying four mass simulators of next-generation Starlink satellites as a test of the vehicle’s payload deployment system. Starship will also test new technologies to protect it during reentry, such as metallic tiles with active cooling.
As with the previous flight, SpaceX will attempt a “catch” of the Super Heavy booster back at the Starbase launch tower. The booster includes changes such as upgraded avionics and power distribution systems, as well as an upgrade to igniters for the Raptor engines to address an issue on Flight 7 where one of 13 engines shut down at ignition during its boostback burn to return to the launch site.
“Starship’s seventh flight test was a reminder that developmental progress is not always linear, and putting flight hardware in a flight environment is the fastest way to demonstrate how thousands of distinct parts come together to reach space,” SpaceX stated in its summary of Flight 7. “Upcoming flights will continue to target ambitious goals in the pursuit of full and rapid reusability.”