SpaceX is gearing up for another Starship launch, blaming a previous failure on structural issues and fuel pressurization problems.
The launch is currently scheduled for Sunday, August 24, with the launch window opening at 1830 CT (2330 UTC). The mission will be similar to previous ones, including a payload deployment of simulated Starlink satellites and a relight on one of the upper stage's Raptor engines while in space.
There are no plans to try to catch the Super Heavy Booster on this mission. Instead, SpaceX plans to drop the booster into the Gulf of Mexico after intentionally disabling one of the three center engines used for the final phase of landing. The plan is to gather data on the ability of a backup engine to complete the landing burn. The booster will then hover over the ocean using only two engines before eventually dropping into the water.
As with previous failed tests, the upper stage will feature changes to its tiles to stress-test vulnerable areas during reentry and catch fittings to check out their structural and thermal performance. The changes are aimed at a future return of Starship to the launch site. The vehicle (and its deployed payload) will be on a suborbital trajectory and, if it survives reentry, will be destroyed upon splashdown.
SpaceX hasn't had a lot of luck with its enormous Starship rocket, after some early successes, including a catch of a returning Super Heavy booster by chopsticks on the rocket's launch tower.
Flights 7, 8, and 9 have all experienced anomalies, usually resulting in some impressive fireworks. Most recently, the company dispensed with all that launching nonsense and opted to explode a Starship on the ground.
As well as tentatively scheduling the launch of the tenth flight test, SpaceX provided details on what had happened during the ninth flight test and the likely cause of the explosion during testing.
SpaceX lost the Super Heavy Booster on the ninth flight test, attributing the loss to a higher angle of attack experiment. According to SpaceX, the booster reached a peak angle of 17 degrees, but rather than the splashdown expected, an "energetic event" occurred shortly after the landing burn started. The final telemetry was received when the booster was approximately 1 km over the target area.
SpaceX reckons that the experiment resulted in the fuel transfer tube experiencing structural loads above its capability and then… boom.
The solution? Don't do that angle of attack again.
The upper stage, Starship, made it to space this time, but leaks sent the vehicle into a spin, or (in SpaceX language) "an off-nominal attitude". The problems meant that the payload deployment was skipped, as was the Raptor engine relight. The final telemetry from Starship was received approximately 59 km above the Indian Ocean.
According to SpaceX, the most probable cause of the loss of Starship was a failure on the main fuel tank pressurization diffuser, located inside the nosecone on the forward dome of the main fuel tank. The company said that the failure was visible in footage from inside the vehicle as the component, which is designed to spread the flow of fuel, failed. This allowed liquid methane to enter the nosecone while also causing pressure to drop in the main tank.
The plan to resolve the issue is a redesigned diffuser. SpaceX said the new design "underwent a more rigorous qualification campaign, subjecting it to flight-like stresses and running for more than ten times the expected service life with no damage."
Finally, the company blamed a fault with a Composite Overwrapped Pressure Vessel (COPV) in Starship's payload bay section for the explosion at the pad. The damage was "undetectable or under screened" according to SpaceX, but resulted in structural failure and an "energetic event."
SpaceX said it will update the inspection criteria for COPVs, add more proof tests, and operate the vessels at lower pressure. New covers will also be added, and the company said it had come up with a "new non-destructive evaluation method" to check for internal damage.
SpaceX has form when it comes to COPV problems. A Falcon 9 exploded in 2015 when a COPV tank came loose during flight, impacting the LOX tank of the vehicle's second stage. Then, the blame was placed on iffy steel in the rods holding the tank in place rather than the tank itself.
The US Federal Aviation Administration (FAA) accepted SpaceX's findings regarding the flight 9 mishap and said, "SpaceX identified corrective actions to prevent a recurrence of the event." The agency gave SpaceX the nod to continue with Starship Flight 10.
SpaceX noted that just two flights remain with the current generation of Starship. Hopefully, that does not mean there'll be a whole new set of anomalies and mishaps to look forward to in the next generation. ®
Source: The register