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SpaceX will aim to again catch the Super Heavy booster in Starship’s coming eighth flight test.
SpaceX has made design changes to the Starship launch system for its eighth flight test in response to the spectacular breakup of the upper stage during its most recent test, which it believes was caused by a harmonic response that stressed the onboard hardware, leading to a fire and loss of the vehicle.
The next flight could happen on Feb. 28, pending regulatory approval, SpaceX said on its website. The objectives set for the test include Starship’s first payload deployment, which it failed to achieve last time, and reentry experiments geared toward returning the upper stage to the launch site. SpaceX will again aim to replicate the success it has had twice in catching the Super Heavy booster first stage.
“Several hardware and operational changes have been made to increase reliability of the upper stage,” the company said. Those include changes to fuel feedlines connecting the vacuum engines, propellant temperature changes and a new operating thrust target.
In its Feb. 24 mishap report, SpaceX said: “The most probable root cause for the loss of ship was identified as 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. The subsequent propellant leaks exceeded the venting capability of the ship’s attic area and resulted in sustained fires.” The unpressurized attic is the section between the bottom of the liquid oxygen tank and aft heat shield.
SpaceX said the first indication that something was going wrong came about two minutes into the burn of the second stage when a flash was detected near one of the six Raptor engines. Sensors then detected a rise in pressure, suggesting a leak. Two minutes later another flash occurred, sparking sustained fires in the attic. Five of six Raptor engines then shut down and communications with the vehicle was lost 8 min. 20 sec. into flight, SpaceX said.
Three minutes after contact was lost the vehicle broke apart. “Post-flight analysis indicates that the safety system did trigger autonomously, and breakup occurred within Flight Termination System expectations,” SpaceX said.
The company said it subsequently performed a 60-sec. static fire with the Starship due to fly in the upcoming test. It involved different thrust levels and Raptor configurations to try and replicate and address the issues that led to the mishap.
SpaceX said additional changes being made to reduce flammability include adding more vents and introducing a new purge system utilizing gaseous nitrogen to reduce propellant leak risk. “Future upgrades to Starship will introduce the Raptor 3 engine, reducing the attic volume and eliminating the majority of joints that can leak into this volume,” it said.
In the next flight, SpaceX plans to deploy four Starlink simulators sized to replicate the next-generation of its low-Earth-orbit communications satellite system. The upper stage will also aim to relight a Raptor engine while in space. The company also aims to collect data on the upper stage’s heat shield. “Starship’s reentry profile is designed to intentionally stress the structural limits of the upper stage’s rear flaps while at the point of maximum entry dynamic pressure,” SpaceX added.
The Super Heavy booster also sports new features, including a more powerful flight computer, upgraded power and upgraded power and network distribution.
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