On Thursday, June 6, Starship S29, stacked atop Super Heavy Booster 11, launched from Starbase, Texas, at 7:50 a.m local time. Teams gathered invaluable data, achieving reusability milestones while certifying changes from previous flights. “We've gone from utterly insane to merely late!” said Elon Musk, referencing the lofty goals for Starship, which seem one step closer after each test flight.

Starship lifted off with 32 of 33 Raptor engines igniting on the Super Heavy booster. Despite one engine being down, the vehicle ascended as expected along its planned trajectory, demonstrating the critical engine-out capability and redundancy built into Starship since its development. After the hot-stage separation, the Super Heavy booster turned around and successfully performed a soft landing in the Gulf of Mexico, seven minutes and 24 seconds into the flight. The booster itself is around 20-stories tall.

Starship continued its flight to orbit, maintaining its orientation throughout the coast phase before re-entering the Earth’s atmosphere over the Indian Ocean. Teams captured real-time telemetry and high-definition video throughout the re-entry courtesy of Starlink, another achievement. Starship successfully navigated the phases of peak heating, sustaining the maximum temperature generated during re-entry and maximum aerodynamic pressure, the point of greatest stress while reentering the thicker parts of Earth's atmosphere. As Starship neared the ocean surface, it initiated a belly-flop maneuver and ignited three center Raptor engines, allowing for a soft splashdown in the Indian Ocean, culminating the flight 66 minutes after liftoff.

“This is like a 20% lucky outcome because both the Booster had a soft landing and the Ship had a soft landing in the ocean,” said Elon after the successful test.

A key objective of this flight was to demonstrate a soft water landing for the Super Heavy booster. Data from the third flight indicated that the filter supplying liquid oxygen to the Raptor engines was blocked, causing a loss of pressure in the engines’ turbopumps and resulting in an early boostback shutdown and re-ignition failure during the landing burn. For this flight, SpaceX modified the hardware inside the oxygen tanks to improve propellant filtration capabilities, along with additional hardware and software changes to increase the startup reliability of the Raptor engines during landing.

Flight 4 certified these changes as the Booster separated from the Starship, initiated a flip maneuver, and successfully ignited 13 Raptor engines for the boost back burn to return to the targeted landing site in the Gulf of Mexico. The hot-stage ring was jettisoned from the Super Heavy, a temporary measure to keep the booster within its mass constraints for the landing burn. Future Starship iterations will feature a lighter, integrated hot-stage ring for full reusability. 

Unlike the Falcon 9, Super Heavy doesn’t perform an entry burn as its steel structure is designed to handle atmospheric pressures and heating. As the booster entered the thicker parts of the atmosphere, it used its large grid fins to finely maneuver itself toward the landing zone. It ignited 12 of the 13 Raptor engines for the landing burn, switching to only the center 3 to softly land on the water. Despite the fiery landing burn and visible debris, the booster maintained its orientation and landed precisely in the Gulf of Mexico. This successful soft landing marks a first in Starship’s flight tests, bringing teams closer to reliably retrieving the booster.

Starship continued on its planned trajectory, just shy of achieving orbit at 151 kilometers in altitude, traveling at a speed of 26,500 kilometers per hour. Not achieving a stable orbit is intentional to ensure Starship safely re-enters the Earth’s atmosphere in case SpaceX loses communications with the vehicle, a very real possibility during these tests. The previous flight saw Starship in a slow, but uncontrolled roll throughout its coast phase, resulting in an irregular atmospheric entry with more intense heating on both protected and unprotected areas. The cause was determined to be the clogging of several of the Ship’s valves responsible for roll control. With additional roll control thrusters onboard Ship 29, it maintained a stable configuration during its coast phase as it made its way to the Southern Indian Ocean. There were some hiccups in getting the external views for most of the coasting phase, but the VADER team – the Video/Audio Design & Engineering Resources team responsible for all the launch broadcasts – kept 3 million cumulative viewers on X (formerly Twitter) captivated with the serenading classical music of Johann Strauss II.

Forty-five minutes after liftoff, the views from Starship began streaming in as it entered the Earth’s atmosphere, traveling at over 26,700 kilometers per hour at an altitude of 107 kilometers. Plasma started surrounding the leeward side of the Starship protected by 18,000 hexagonal ceramic tiles. During this phase, the vehicle experienced temperatures of over 1400 degrees Celsius (2600 F). In the initial phase of re-entry when the atmosphere is thin, Starship’s flaps were tucked in and the vehicle was solely controlled by its thrusters. Four minutes and thirty seconds into the atmospheric re-entry, Starship successfully passed the point of peak heating.

The vehicle survived the highest temperatures, but as it descended into the thicker parts of the atmosphere, air pressure began to build up and interact with the Ship’s heat shield. The Ship started shedding a significant amount of speed, but also parts of its heat shield, particularly near the hinge of its right forward flap. The heat shield broke apart bit by bit at the hinge, and the high temperatures began melting the stainless steel structure, despite its very high melting point.

Starship continued its fiery re-entry as its guidance system adapted to the damage on the forward flap to maintain a stable trajectory and successfully made it through Max-Q, the point where the atmosphere exerted the maximum pressure on the Ship during re-entry. As Starship shed most of its speed to subsonic levels, the damaged flaps were still adjusting to maintain a stable trajectory. It achieved terminal velocity at an altitude of 2 kilometers before igniting three Raptor engines to perform the belly-flop maneuver and the landing burn to reduce speed and land on the Southern Indian Ocean. Despite maintaining the landing trajectory, damage to the flaps caused the landing to occur 6 kilometers off the intended area.

Flight 4 provided SpaceX teams with ample data, which they called the "payload" of the test, to drive improvements needed to achieve Starship's lofty goals, set by SpaceX, NASA, and the United States, to land astronauts on the Moon under the Artemis Program. It also validated SpaceX’s controversial choice of stainless steel over lighter carbon composites.

Based on Super Heavy’s precise landing in the Gulf of Mexico, SpaceX will attempt to land the world’s largest and most powerful rocket booster on the launch pad using the Chopsticks on the Orbital Launch Tower. “Unless something comes up that we think is problematic, we will try to bring the booster back and catch it with the giant mechazilla arms,” said Elon Musk regarding landing Super Heavy back on the launch pad. 

He clarified that similar to Falcon 9’s return-to-launch-site landing profile, Super Heavy will target an area over the Gulf and maneuver itself to the launch site if all its systems are healthy.

As the booster performs the landing burn over the launch pad, the chopstick arms on the launch tower will close in and hold the booster using the lifting pins, the same way the booster was mounted on the launch pad before the launch. This could not only enable rapid launch cadence but will also save mass by eliminating the need for landing legs. 

“It will take us a while to perfect capturing a rocket out of the air with mechazilla arms, but once we do it will save so much [mass],” said Elon.

Starship’s heat shield will also be improved as SpaceX will be switching to new hexagonal tiles, which Elon claims are twice as strong as the current ones. These tiles will be laid on top of a secondary heat shield layer to ensure the vehicle survives even if a tile is cracked or displaced. This layer, made of felt-based silicone, is ablative, meaning it absorbs the intense heat by gradually wearing away. While it may not be ideal for reuse, it will ensure future Starships return without extensive damage. 

Elon says that with these and many more changes, the next flight of Starship will be in about a month, with the goal of returning Super Heavy to the launch pad while ensuring a clean re-entry and soft landing of the Starship from orbital velocities.

Elon reiterated the challenges they continue to face with the ceramic tiles, which can handle the temperatures but are difficult to ensure they remain on the Ship after multiple violent high-energy re-entries, saying, “[Starship heat shield] tiles are ceramics; they are like a coffee cup or dinner plate, so you’ve got a whole bunch of dinner plates stuck on the side of a rocket which is shaking like hell.”

SpaceX plans to iterate on Starship and Super Heavy via such integrated test flights. The end goal with this program is for both vehicles to require minimal repairs and increase the launch cadence to mirror an airline-like operation. It’ll reduce the launch costs, make it cheaper to explore space, and finally achieve SpaceX’s primary goal of establishing a city on Mars.