Significance of Starship Flight Four

SpaceX character is expressed in their rockets

Epic Flight 4, credit SpaceX

On June 6 SpaceX performed the fourth test of their spectacular Starship, the world’s most powerful rocket. This flight achieved everything SpaceX planned, from launch through to successful landing of both stages in the ocean. Even the mass-media found it in their soul to praise this feat despite their predilection of finding fault with all things Musk. However, praise or criticism apart, this flight test has deep significance for SpaceX considering how well Starship performed.

Mars Tough

Classically the launch phase has always been viewed as the most hazardous part of any space flight, although now rocket landings are possible that easily takes the prize for pucker factor. Certainly this will be the case for Mars colonists as the rapidly descend through its tenuous atmosphere, while searching for a safe place to land. Fortunately these early tests of Starship have shown the vehicle is incredibly tough, due to its strength of design and construction. The primary material used is S30X, a special formulation of stainless steel alloy which has proved enormously resilient. Good example: on Starship’s first test flight the vehicle failed to achieve stage separation so the onboard computer decided to trigger the Flight Termination System (FTS). Promptly shaped charges punctured the propellant tanks of both stages – but the rocket shrugged it off, as if to say: “so what.” Only after the vehicle smashed into the dense lower atmosphere (akin to a belly-flop off the high board) did it finally give up the ghost.

Similarly, the flight 4 Starship encountered a problem when superheated plasma was channeled through the hinge gaps at the base of its forward flaps. This dislodged some ceramic heat protection tiles at the base of the flap allowing plasma to enter the flap’s structure, similar to how plasma entered the wing of Space Shuttle Columbia during its final flight… Surprisingly, despite these flaps being burnt through in places, Starship managed to survive the transition from hypersonic to subsonic and achieved a soft splashdown in the Indian Ocean. Special mention goes out to the flight computer which somehow compensated for the reduced control authority caused by the flaps altered geometry... This suggests SpaceX are using something like a high machine intelligence to full AI to control the vehicle, which provides precisely the level of safety needed to carry people.

“Like [Crew] Dragon there can be no failures ever, everything has got to be tested to six ways to Sunday. There has to be tons of margin. There can never be a failure ever for any reason whatsoever.” ~ Elon Musk

Notably Elon suggests this hinge gap problem has already been solved for the next flight and further mitigated on Version 2 Starship where the flaps have been shifted leeward, to shelter the flap joints from plasma.

Probably important to note there were a couple of engine outs on the Super Heavy booster, one engine switched off immediately after launch and another failed to relight during its brief landing burn. However, the flight computer again managed to compensate for this reduced thrust, allowing both stages to complete their mission objectives, ending in soft landings in the ocean.

We were treated to video of these landings which demonstrates Starlink can maintain a good connection to the vehicle even through the plasma storm experienced during atmospheric reentry. This is important because SpaceX relies on flight data to iterate the vehicle design, and their multiple Starlink transceivers can deliver hundred of megabits per second of useful technical data.

Next Step

Fortunately the FAA won’t require a mishap investigation into flight 4 because it succeeded in all its major goals. This suggests flight 5 could follow fairly shortly, perhaps as early as July, considering SpaceX have already received a launch license for the ensuing flight and have 3 more launch vehicles waiting in the wings. Elon suggests on the next flight the Super Heavy booster could return to the orbital launch tower and be caught by the mechazilla arms, which promises to be spectacular. While recovering both stages is not strictly necessary to perform moon landings for NASA, stage reuse is an essential element of SpaceX plans for Mars colonization. This early success demonstrates that full reuse is within their grasp, literally taking this extraordinary company to the next level. All of the SpaceX employees crowded around mission control at their Hawthorne HQ seemed mightily buoyed by this event, proving all their hard work was justified. No doubt that goes double for their engineers at Starbase in Texas, and maintaining good morale is crucial for a project this size and importance.

The Future Approaches

At the 2017 International Astronautical Congress, Elon Musk revealed a passenger version of Starship could be used for point-to-point travel here on Earth. While many believed a huge rocket like Starship would be impractical for commercial transport, Elon later revealed the upper stage alone could travel 10,000 km without need of a booster. Essentially the upper stage would launch into a high ballistic trajectory then create lift by skipping along the upper atmosphere until reaching its destination. Flight 4 seemed to demonstrate this capability as it barely lost altitude crossing the Indian Ocean. Probably important to note Starship used a very high ballistic trajectory that resulted in it plunging into the atmosphere, instead of the ideal flatter trajectory used for point to point transport.

The US Air Force keenly follow Starship development and this recent flight could be foundational to future cooperation. For example: in 2022 they awarded SpaceX a $102m contract to study rocket cargo transport, which now appears more than possible following this successful launch and landing. We can probably expect another large contract to land on SpaceX’s door by they end of the year to cover the next phase of development.

“AFRL's fiscal 2025 budget plans show that the lab hopes to complete testing of the capability to air-drop cargo pallets down from Starship during FY25, and to launch a demonstration flight to ‘transport 30 to 100 tons of cargo to an austere site’ in late FY25 or early FY26.” ~ Breaking Defense

Of course the DoD can conceive of many other potential applications for Starship, including some “sensitive and potentially dangerous” military operations requiring they take full ownership of the vehicle. Who knows, Space Force might even want to operate their own crew missions once Starship enters service.

SpaceX too would love to launch their next generation of larger Starlink satellites, designed to take full advantage of Starship’s 8m payload fairing. First they must demonstrate they can safely deorbit the Starship spacecraft by relighting one of its Raptor engines in space, in what’s called a deorbit burn. Likely this will be demonstrated on the next flight of Starship, instead of relying on a high ballistic arc to guarantee reentry. All being well, it’s quite possible the few remaining Version 1 Starships will be scrapped to speed up introduction of Version 2, which promises even better performance.

In Conclusions

For years SpaceX have pursued their dream of space settlement and following the success of Starship flight 4 that dream has come tantalizingly close to reality. The 2026 schedule for Artemis 3 moon landings now seems possible, much to NASA’s relief.

“Congratulations SpaceX on Starship's successful test flight this morning! We are another step closer to returning humanity to the Moon through Artemis—then looking onward to Mars.” ~ NASA Administrator Bill Nelson

Assuming SpaceX manage to resolve the few remaining issues, such as engine restart and thermal protection, that should enable rapid recovery and reuse of Starship vehicles. Then effectively today is tomorrow...

Chris Prophet