Starship: Total success for flight 4, one of the missions of the year

© SpaceX

There was a lot of anticipation in Boca Chica, Texas, on Thursday morning. In the SpaceX control center, however, confidence still reigned supreme a few minutes before takeoff. After all, this is not the first time that Elon Musk's company has tried to launch this rocket.

It is also not the first time that it has reached the stage of separation between the two stages (which was fatal during the 2nd flight). These parts of the flight, as well as the “cruise” phase of the ship, were already known to SpaceX before today's flight. So the overwhelming majority of expectations were for the ship's final minutes, its return to Earth.

What should we remember from flight 3 ?

SpaceX's Starship alone, without the Super Heavy first stage © SpaceX

In order to understand the challenges of this 4th flight for Starship, it is important to look back at the progress made by the company during the 3rd flight on March 14. By Pi Day, SpaceX had successfully launched Starship into space. The ship had, however, developed a significant roll. In other words, it rotated.

During its return to Earth, the ship passed through different layers of the atmosphere, adding friction around its frame. These abrasions are normally absorbed by the Starship's heat shield, located on its belly. But during this flight, and because of this roll, other parts of the Starship were in contact with plasma, extremely hot air.

The The ship ended up exploding at an altitude of about 60 kilometers. As for the first stage, which was also supposed to return to Earth to try to land in the Gulf of Mexico, the engines of this Super Heavy did not only partially turned back on. The rocket then arrived too quickly towards Earth and was destroyed 450 meters above the ground to avoid creating debris during impact.

What expectations for this 4th flight?

An illustration of the separation phase between the two stages of the Starship © SpaceX

A few moments before takeoff, SpaceX's expectations are clear regarding this new flight. The objective is to achieve the two phases of return to Earth. First for the first stage (Super Heavy), then a few tens of minutes later for the Starship.

In order not to repeat the errors of the third flight, SpaceX has modified some data on its rocket. The first is that the connecting ring between the two stages (a large block of very heavy stainless steel) will be ejected. It will not make the return path with the rest of the first floor. Its disappearance allows SpaceX to better distribute the masses and should facilitate the return to Earth of the first stage.

As for the ship itself, SpaceX appears to have made changes to the glue used to attach the ceramic heat shield tiles. The company nevertheless left, obviously voluntarily, two “holes” in the middle of this shield (see tweet above) to collect data on how the plasma moves around the ship.

The 4th Flight  : minute by minute

As expected, the first moments of this new flight went without problems. The rocket flew through the air at full speed. Of the 33 Raptor engines on the first stage, 32 performed flawlessly. For the first two minutes, the rocket flew to the right to gain altitude before separating.

The separation is did it go perfectly ? The seven engines of the main ship took over from the booster and the “ small ” hot-staging ring separated after 4 minutes and 15 seconds, moments after the  kick back boost  the slowing down phase of the first stage of the rocket to make it take its return trajectory towards Earth. 

Three minutes later, seven after liftoff, the first stage was back on Earth. A few hundred meters from Earth, Super Heavy restarted 12 of its engines to reduce its speed. SpaceX then succeeded, for the very first time, in stabilizing the first stage, causing it to reach zero speed for an instant.

This is excellent news for SpaceX which achieves one of its two main objectives for the day. On the live broadcast of the event, scenes of jubilation followed the return to Earth of the first stage of Super Heavy.

Starship returns home< /h2>

After this euphoria, it was the calmest moment of the mission. Starship conducted its “cruise flight” reaching a speed close to that necessary to enter orbit. For many minutes, we were then left with a black screen, SpaceX having lost the exterior cameras of its ship for a long time.

We do actually have acquisition signal. 11 internal cameras are transmitting. Figuring out why external cameras aren’t.

— Elon Musk (@elonmusk) June 6, 2024

After 40 minutes of flight, the images came back and we could see Starship more than 100 miles above sea level. The rocket was then carrying out the first phases of its descent towards Earth. Unlike the 3rd flight, the ship did not rotate, another very good news for SpaceX. Five minutes later, the first glimmers of plasma began to be seen around the ship, as it descended below 100 kilometers in altitude.

The rocket then slowed down in the densest layers of the atmosphere. It reached its maximum temperature at 75 kilometers above the surface. At more than 50 kilometers high, one of Starship's flaps (fins) began to burn. Partially destroyed, this fin nevertheless managed to guide the starship during a chaotic return to Earth.

The rocket nevertheless reignited its engines as planned in the final moments. It straightened up and reduced its speed. The second major objective of the day is achieved by SpaceX and Elon Musk. This bodes very well for the next flight, which is already on everyone's minds.

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