Inside the fuel tank of the Falcon 9. Image: SpaceX
After the surprise explosion of Space Exploration Technologies Corp. (SpaceX)’s Starship SN10 prototype, the company’s CEO and chief engineer, Mr. Elon Musk, went to Twitter to give details behind the crash. SpaceX is testing the higher-phase prototypes for its next-generation launch vehicle called the Starship – which Mr. Musk hopes it will fulfill the fundamental goal of the company to make humanity a multi-planetary species.
Prototype of the spacecraft landed hard due to tank problems due to earlier correction after the first prototype accident, explains musk
The prototype that SpaceX tested last week was the third vehicle to successfully lift and execute an intricate landing shot maneuver in the air. However, it was the first to end up in one piece, with the other two failing to generate enough pressure to counteract gravity.
Its predecessors, SN8 and SN9, crashed for various reasons. While the latter’s accident was due to a programming decision made by SpaceX – a mistake Musk admitted – the former crashed due to insufficient fuel pressure in the secondary tank of the vehicle above. Rocket tanks must maintain their internal pressure as fuel escapes, otherwise the engine may not generate stable thrust.
A view of a fuel tank (secondary) tank, one similar to the one that caused SpaceX’s Starship SN8 to crash when it tried to land. Image: Elon Musk / Twitter
Before SN9, SpaceX used autogenous pressure to maintain that tank pressure. This involves the exhaust of the Starship Raptor engines and the feedback in the tank to ensure that there is no vacuum.
After the accident, however, the company used Helium to put the tanks under pressure, similar to the Falcon 9. Musk confirmed this in a Tweet, but warned that it was not yet a long-term solution. An inside view of the Falcon 9 second phase’s liquid oxygen tank below shows how this is done. At the bottom of the frame are two black composite overflow pressure vessels (COPVs) that inject helium into the tank to prevent the fuel from drifting away into the air space of the tank. What engineers also call ‘baffles’ are visible – something we’ll explain below.
Fuel tank pressure, slider bars can contribute to insufficient fuel flow to raptor car
The decision to switch to Helium is the main reason that SN10 could not land properly. Musk confirmed in a tweet yesterday that he had explained that some of the helium used for the pressure of the tank might get into the Raptor engine. This would have reduced the thrust generated during the landing, causing SN10 to land at a speed of 10m / s.
For a vehicle that is nearly 12 stories long, the force that causes such a velocity during an impact on the ground is unlikely to be absorbed by Starship. landing well. However, the legs themselves would not have stood a chance, even if the tanks would work normally, as three of them did not lock in place after deploying during the landing attempt.
The liquid oxygen tank is visible inside the Falcon 9 second during a Starlink launch in April last year. Image: SpaceX, edited by Wccftech
It appears that methane has leaked into the secondary fuel tank of SN10, causing some of the helium to enter the system. Almost all rocket tanks (and some others) have structures in them called ‘baffles’. This counteracts the forces that cause the liquid to move violently in the tank and weaken the percentage.
According to Musk, although they could succeed in preventing methane from moving around inside Starship, they might also have had a ‘bridge’ for gaseous methane above the fuel’s liquid surface to get into the engine in the form of bubbles.
Screen channels inside rocket tanks serve as conduits for fuel to ensure adequate flow for engine ignition – especially after a turn maneuver has been performed. Images of the first phase tanks of the Falcon 9 showed the presence of such channels, which work with the second phase printer to drive fuel to the bottom of the first phase tank to re-ignite.
It is possible that Musk is speculating about bubbles coming inside the Raptor, as he recalls a similar problem that SpaceX encountered with the Falcon 1.
SpaceX is currently installing propellant tanks at its launch site in Boca Chica, where the next Starship prototype – SN11 – is currently waiting its turn to clear tests before launch. Musk hopes to send an unmanned mission to Mars by next year and also aims for large aircraft in 2022.