We now know the probable cause of the unsuccessful Starship test flight that caused parts of the rocket to fall over popular tourist destinations in January, forcing airlines to reroute flights.
According to SpaceX, the upper stage of the Starship spacecraft experienced a stronger-than-expected harmonic response. By harmonic response, engineers mean vibrations amplified by resonance. This, in turn, caused an increased load on the propulsion system, which likely led to the rocket exploding before it could reach space.
On January 17, the 33 Raptor engines of the Super Heavy launch vehicle successfully operated during the launch, and the launch vehicle was able to both launch and complete its full combustion. The upper stage ignited its own Raptor engines during separation from the launch vehicle. Although the launch vehicle eventually returned to the ground, where it was picked up at the launch site, there was a slight hiccup in the process. The low power of the ignition system of one of the engines led to its premature shutdown, but the other 12 engines worked normally. SpaceX said that a potential problem of this nature has already been identified and eliminated for future flights by upgrading the ignition system.
Things did not go so smoothly with the second stage of the Starship. Approximately two minutes after the engine started burning, “a flash was observed in the rear of the ship near one of the Raptor vacuum engines,” SpaceX explained. “This tail section, commonly referred to as the ‘attic,’ is a non-pressurized area between the bottom of the liquid oxygen tank and the aft heat shield. Sensors in the loft detected an increase in pressure, indicating a leak after the fire.”
Shortly thereafter, another flash was spotted and a fire broke out in the attic, leading to a controlled shutdown of several engines. Communication with the ship was lost.
“Contact with Starship was lost before the rules for destroying the autonomous flight safety system, which was fully operational when contact was lost,” SpaceX said. “It was observed that the ship broke apart approximately three minutes after the loss of communication during descent. Post-flight analysis indicates that the safety system operated autonomously and the disintegration occurred within the flight termination system’s expectations.”
The investigation, launched by SpaceX under the supervision of the US Federal Aviation Administration (FAA), was ordered by the FAA after the incident. The malfunction caused debris to rain down over the Atlantic Ocean, some of which landed in the populated areas of the Turks and Caicos Islands. No one was injured, although locals reported finding rocket debris on their property and along local beaches.
SpaceX presented a more optimistic picture of the consequences, saying that all the debris “fell within the pre-planned debris response area and did not contain hazardous materials, nor is it expected to have a significant impact on marine species or water quality.”
“While the early completion of a flight test is never a desirable outcome, the measures taken prior to the launch have demonstrated their ability to keep the public safe.”
Starship is an ultra-heavy-lift launch vehicle that plays a key role in NASA’s future plans. One of the planned variants will deliver astronauts to the Moon as part of the space agency’s Artemis program. Others will be able to transport a huge amount of cargo into orbit, such as Starlink satellites.
The next test launch of the rocket is scheduled for Friday, February 28. As a result of the investigation, several modifications were made to the rocket design, including changing the fuel supply lines to the vacuum engines and adjusting the temperature of the rocket fuel. Vents and a purging system were also added to the loft to make it more fire-resistant.
Rockets are incredibly complex, and several Starship tests have failed. The first, in April 2023, resulted in significant damage to the launch pad. The rocket itself exploded after about four minutes of flight. The second flight test went better, as key milestones were achieved despite the fact that both the booster and upper stage were destroyed. Subsequent tests have revealed even more problems, and SpaceX has already successfully re-launched the upper stage twice during its return to earth. It is obvious, however, that there are still shortcomings that need to be addressed.
