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Time to land: SpaceX details what went wrong with Starship, fourth flight imminent

Starship fully stacked on the launch pad during the launch rehearsal

SpaceX is getting closer to the fourth integrated test flight of Starship, the world’s biggest rocket of all time. While the company didn’t make it in time for a May attempt, as originally hinted by its founder Elon Musk, space enthusiasts won’t wait too long to see the giant fly again.

Musk said on X (formerly Twitter), that the launch should happen around June 5. This time, though, the plan is supported by ongoing preparations at Starbase in Boca Chica, Texas, where Starship completed the launch rehearsal on May 20.

On top of Musk’s recent remarks, SpaceX has shared a blog post clarifying some details about the 3rd flight attempt – what went wrong and what the engineers did to address these issues.

During the third integrated test flight, which occurred in mid-March, Starship completed a full ascend burn after a successful separation from the Super Heavy booster stage. The hot-staging process, during which the Starship ignites its engines while still attached to the booster, was an important milestone for SpaceX engineers.

However, the booster then didn’t soft-land in the waters of the Gulf of Mexico, as originally planned. Despite the Super Heavy booster ignited 13 Raptor engines (the stage has 33 engines in total, however, just a portion is used on the way back) for the so-called “boostback burn,” six engines began shutting down, SpaceX describes:

“The booster then continued to descend until attempting its landing burn, which commands the same 13 engines used during boostback to perform the planned final slowing for the rocket before a soft touchdown in the water, but the six engines that shut down early in the boostback burn were disabled from attempting the landing burn startup, leaving seven engines commanded to start up with two successfully reaching mainstage ignition. The booster had lower than expected landing burn thrust when contact was lost at approximately 462 meters in altitude over the Gulf of Mexico and just under seven minutes into the mission.”

The flight data analysis revealed that the most likely root cause for the early boostback burn shutdown was continued filter blockage where liquid oxygen is supplied to the engines, leading to a loss of inlet pressure in engine oxygen turbopumps.

Even though SpaceX experienced similar problems during the second flight and implemented hardware changes to prevent the issue from happening again, the problem reoccurred. Therefore, the engineers will implement additional hardware inside oxygen tanks to further improve propellant filtration capabilities, as well as additional hardware and software changes to increase the startup reliability of the Raptor engines in landing conditions.

The Starship experienced its own set of problems after reaching the orbit. During the coast phase when the Raptor engines are not firing anymore, the attitude control of Starship is maintained via roll control thrusters. However, it seems that the valves responsible for roll control were clogged.

As a result, Starship didn’t attempt to relight a Raptor engine as was originally planned, and the spacecraft entered the dense parts of the atmosphere without the ability to keep its intended orientation. Thus, it was not only the heat shield, but also other parts of the rocket that faced the immense heat of the gloving plasma.

The flight test’s conclusion came when telemetry was lost at approximately 65 kilometers in altitude, roughly 49 minutes into the mission. For the fourth attempt, SpaceX will add more control thrusters to improve attitude control redundancy and upgraded hardware for improved resilience to blockage.

These won’t be the only changes for Flight 4. For example, Super Heavy will jettison the hot-stage adapter following the boostback burn to reduce booster mass for the final phase of the flight.

SpaceX says that from now on it will turn its focus from achieving orbit to demonstrating the ability to return and reuse Starship and Super Heavy. That includes Super Heavy successfully soft-landing and Starship surviving the controlled reentry, especially through the point of max reentry heating.

It is important to say that even though Starship lost roll control and disintegrated in the atmosphere, the debris didn’t impact outside of pre-defined hazard areas. Therefore, if the Federal Aviation Administration (FAA) identifies no public safety impact – as expected – a launch license modification for the next flight can be issued without formal closure of the mishap investigation, which would otherwise delay the next attempt even more.

Just a few days ago, Jeff Bezos’ Blue Origin got lucky, when its New Shepard rocket flew astronauts to space after a long hiatus, but one of its three main parachutes didn’t fully inflate before the landing. The Observer reported, that the FAA does not consider this a mishap, therefore it will not require an investigation.

If you don’t want to miss Starship’s fourth launch, don’t forget to keep an eye on our regular summary of upcoming flights – Neowin’s Paul Hill and his This Week in Rocket Launches.

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