After two press releases from the Federal Aviation Administration (FAA) and SpaceX, the latter's chief, Mr. Elon Musk, has shared the full list of 63 changes that the firm needed to get done as part of its Starship test flight one mishap mitigation process. SpaceX's Starship Super Heavy booster with the upper stage spacecraft staked on top took to the skies in April earlier this year, and six months after the flight test, SpaceX appears to be ready to give the orbital test attempt another go.
Flying Starship to orbit on the first try is tricky since SpaceX has conducted only one test fight of the Super Heavy booster - the most complex component of the Starship rocket system. The initial stages of the Starship test program were focused on flying the second stage spacecraft due to SpaceX's close relationship with the National Aeronautics and Space Administration (NASA). NASA has awarded SpaceX a multi-billion dollar contract to land astronauts on the Moon - a first-of-a-kind chance for any company in the world.
SpaceX's Raptor Engine Remains Toughest Nut To Crack Ahead of Second Starship Test Flight
The Super Heavy booster required to fly fuel to an orbital propellant depot is crucial to the Starship architecture. This depot will fuel the spacecraft that will embark on future missions, whether to Moon or Mars. Fortunately for SpaceX, though, the firm has completed 57 of the 63 items required by the FAA for the next flight. According to Musk, six items are not part of the second test flight, but the FAA, it seems, is determined to ensure that the world's largest rocket in development is safe for both the environment and humans, as the previous test flight stunned many simply due to the scale of the impact that it created at the launch site.
A major reason behind the multiple hurdles that the rocket has presented SpaceX is the Raptor rocket engine. Unlike the Falcon 9 rocket's Merlin engine, which is an open cycle, gas generator design, the Raptor is a full flow, staged combustion and methane fueled rocket engine. This makes it significantly more powerful than the Merlin and offers efficiency improvements as all of the gasses flowing through it are redirected to the combustion chamber.
The cost of this efficiency is a tricker engine more prone to leakage. Judging by the latest details shared by Musk, items related to leakage are the only ones remaining out of the list of 63 actionable items that SpaceX has to fix after Starship's first test flight.
Congrats to SpaceX for completing & documented the 57 items required by the FAA for Flight 2 of Starship!
Worth noting that 6 of the 63 items refer to later flights. pic.twitter.com/YlPg3ywCZE
— Elon Musk (@elonmusk) September 10, 2023
Some of SpaceX's first engines, built during the early days of the Falcon program, used ablative chamber pressure since the engines were easier to design and build. However, the need to make engines more reusable caused the firm to change this design since these chambers have to be eventually replaced. Now, the combustion chamber is cooled by the super-chilled propellant flowing around the system, and the Raptor redirects these gases back inside the chamber to improve engine performance.
Another key benefit of the Raptor system is its fuel choice. The Merlin uses kerosene for fuel, which generates soot. The Raptor, however uses methane, which burns cleanly to improve engine maintenance.
Of the six items that remain unchecked on the list that Musk shared, five are directly related to the engine or its components. The six items include igniter seal designs, oxygen valve and seals, the hot gas manifold and avionics. The gas manifold was one of the first things that Musk talked about after the April test flight, explaining that:
The engines on the last rocket were somewhat of a hotchpotch so they were, those engines were built and tested over a period of a year. . .So we have what's called a hot gas manifold. It takes the fuel rich gas from the fuel site powerhead, transfers it to the main chamber. Or transfers it to an area above the main chamber where it then mixes it with ox rich gas and goes to the main chamber and combusts. We've made a number of improvements to that hot gas manifold, which is arguably the most risky, the riskiest part of the engine. It's also something that is subject to hot gas leakage, which is sort of methane rich hot gas leaking through the bolt holes of the fuel manifold. So that's something that gets very hot, and if it gets very hot, it can gap. So an improved design of the hot gas manifold, as well as higher torque up on the bolts of the hot gas manifold to minimize potential for hot gas fuel leakage at high pressure. That's one of the single biggest improvements.
There are really a tremendous number of changes between the last Starship flight and this one. Well over a thousand. So I think the probability of this next flight working is, you know getting to orbit, is much higher than the last one. You know, maybe it's like sixty percent, it depends on how well we do at stage separation.
Gas seals were one of the major things that SpaceX upgraded on the Merlin 1D over the previous version, as they were prone to leakage. This leakage is one of the biggest risks on any rocket, particularly those that use multiple engines.
Upgrades made to the Raptor engines for the next Starship flight include adding more methane sensors in the engine bay, designing components to 'capture' any leaks if they might occur, adding more sensors for pump temperature and improving the gimballing system. Judging by the requirements, another reason that the April test failed was because the 33 rocket engine system's gimballing system did not perform as expected, since SpaceX now has to lubricate the full gimbal assembly.
Of course, the 63 line items require adding numerous additional items. For instance, for some upgrades that might be part of future flights, SpaceX has to replace manifolds, flanges and valves. These upgrades have been made already, and the firm has added more than 90 cameras to monitor any leaks in the rocket that measures nearly four hundred feet in height.
Notably, managing these leaks and any resulting fires they cause is a key feature of the Starship April test flight mitigation report. SpaceX redesigned the fire suppression system for the next flights and increased its strength by 15 times. Engine bay fires are a regular feature of the first Starship test flights, which flew the upper-stage spacecraft.
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