SpaceX Starship hop debut aborted at the last second by Raptor engine

SpaceX’s full-scale Starship hop debut was aborted at the last second after an otherwise successful lead-up to the milestone, forcing the company to try again tomorrow.

Following a minor delay from August 2nd to August 3rd, SpaceX kicked off Starship SN5’s hop debut preparations relatively late into the 12-hour window, closing the highway and clearing the pad around 5pm CDT (22:00 UTC). The Starship SN5 tank section prototype was pressurized with ambient-temperature gas around the same time, while cryogenic liquid methane and oxygen propellant loading appeared to begin at roughly 6:20pm CDT (23:20 UTC).

Soon after, SpaceX CEO Elon Musk revealed that Starship was just 33 minutes away from launch, marching towards the first hop of a full-scale prototype at 6:56pm CDT. Unfortunately, possibly much less than a second before ignition, Starship SN5’s Raptor engine had different plans.

Musk says that one of Raptor engine SN27’s “spin start valves” failed to open moments before ignition, causing Starship to automatically abort the attempt. With more than an hour left in the window, SpaceX had time to briefly troubleshoot the bug and potentially turn the rocket around for a second attempt, but Musk announced some 50 minutes later that the company would stand down and try again tomorrow.

Musk’s description of the hop test abort sounds suspiciously similar to his description of the last abort of Starship SN5’s Raptor engine static fire test, in which a “fuel spin valve didn’t open.” If the root cause of both aborts is the same, there’s a good chance that SpaceX may need more time to properly investigate and fix the problem. A recurring issue is immediately much more concerning compared to a one-off bug, so there’s also a chance that SpaceX will go as far as replacing the Raptor engine currently installed on Starship SN5.

If things look more severe than SpaceX initially thought they were after the static fire abort and a replacement engine is necessary, Starship SN5 will have to complete another static fire test with the new Raptor before it can proceed to a second hop attempt.

Based on live views of the launch attempt from NASASpaceflight and LabPadre, Starship SN5 likely aborted a matter of milliseconds before Raptor SN27 ignition and perhaps just a second or two before liftoff. Just like SpaceX’s workhorse Falcon 9 and Heavy rockets, the vehicle’s flight computer is fully in control of the countdown a minute or two before liftoff and can automatically abort far faster than any human could possibly react. Held to the launch mount by hold-down clamps, Starship could have technically analyzed the engine’s performance after ignition and aborted the launch even later into the count.

Once hold-down clamp release is commanded, Starship SN5 will attempt to fly a roughly 150m-tall (500 ft) arc heading southeast of the launch mount. Perhaps 10 seconds prior to touchdown, Starship will attempt to deploy an array of six odd legs and gently land a few hundred feet from the pad. As of now, assuming Raptor’s finicky valve can be easily rectified, SpaceX will work towards a second Starship SN5 hop attempt sometime between 8am and 8pm CDT on Tuesday, August 4th.

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