June 16, 2024
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SpaceX details learnings from Starship Flight 3 and sets June 5 as planned launch date for Flight 4 – Spaceflight Now

Cameras aboard the Starship upper stage flown during Flight 3 (Starship IFT-3) show the vehicle surrounded by plasma as it re-enters the atmosphere on March 14, 2024. Image: SpaceX

SpaceX is preparing to launch its massive Starship rocket on its fourth flight test from its Starbase facility in south Texas on June 5. The planned launch date comes just under three months after Flight 3 on March 14.

In a pair of posts on its website, SpaceX outlined the learnings from Flight 3, the mission objectives for Flight 4, and the differences in the timing of everything between these two parts of the development campaign.

The Flight 4 launch window will open on June 5 at 7 a.m. CDT (8 a.m. EDT (1200 UTC). However, as SpaceX notes, they are still awaiting regulatory approval from the Federal Aviation Administration (FAA).

In this latest attempt, SpaceX will not attempt some of the additional flight elements it tested during Flight 3, such as operating the payload bay door or restarting the vacuum engines on the upper stage.

“The fourth flight test shifts our focus from reaching orbit to demonstrating the ability to return and reuse Starship and Super Heavy,” SpaceX said in a statement. “The primary objectives will be to execute a soft landing and splashdown in the Gulf of Mexico with the Super Heavy booster and achieve a controlled Starship entry.”

Learned lessons

In a blog post, SpaceX described a number of elements of Flight 3 that went as planned and others that caused the mishap. Among the successes was completing a propellant transfer demonstration, “moving liquid oxygen from a header tank to the main tank.”

“This test provided valuable data for eventual ship-to-ship propellant transfers that will enable missions such as returning astronauts to the Moon under NASA's Artemis program,” SpaceX said in a statement.

As with Flight 2, Flight 3 also saw a successful ascent of the rocket through stage separation. Building on that second flight, the most recent lap also saw Starship's upper stage undergo a full-duration climb.

However, during Flight 3, SpaceX said a blocked filter “where liquid oxygen is supplied to the engines” in the Super Heavy booster caused “a loss of inlet pressure to the engine's oxygen turbopumps.” He said this is likely the primary cause of an early shutdown of six of the 13 Raptor engines used during the boost firing.

SpaceX's Starship rocket launches for the third time in program history on Thursday, March 14, 2024. Image: Adam Bernstein/Spaceflight Now

When it came time for landing burn, the six engines that shut down prematurely were deactivated and of the remaining seven engines, only two were determined to have successfully achieved “main stage burn.”

“The booster had a lower landing thrust than expected when contact was lost at approximately 462 meters above the Gulf of Mexico and just under seven minutes into the mission,” SpaceX explained.

SpaceX said more hardware upgrades will occur within the oxygen tanks for Flight 4's Super Heavy booster and those beyond “to further enhance the filtration capabilities of the booster.” They will also add new hardware and software “to increase the starting reliability of the Raptor engines under landing conditions.”

During its re-entry from space, Starship's upper stage suffered a lack of attitude control, seen when the rocket began to roll involuntarily, leading to “the spacecraft seeing much greater heating than anticipated in both protected and unprotected areas”.

“The most likely cause of the unplanned sway was determined to be clogging of the valves responsible for sway control,” the company said. “SpaceX has since added additional roll control thrusters on upcoming Starships to improve attitude control redundancy and updated hardware to improve stall resistance.”

Timeline settings

In addition to some of the hardware and software modifications, eagle-eyed observers of the mission timelines will also notice some other key differences. One of the notable pre-launch changes has to do with the fueling process.

During Flight 3, SpaceX began by loading Starship's upper stage with liquid oxygen first at T-53 minutes, followed by loading liquid methane onto the ship two minutes later. Flight 4 turns it around and starts with liquid methane first at minutes T-49 and then liquid oxygen two minutes later.

Similarly, on the Super Heavy booster, flight 3 began with a liquid oxygen charge at T-42 minutes and then with liquid methane one minute later. Flight 4 begins with liquid methane at T-40 minutes and then liquid oxygen three minutes later.

SpaceX did not indicate the reason for the reversals in the fueling process, but they have been working extensively to modify the storage tanks for both liquid oxygen and liquid methane in the tank farm near the platform. The vertical tanks were replaced by horizontal tanks in recent months as part of work on land systems.

In total, the time to refuel Starship will be about four minutes shorter than the last flight. It's also only about 11 minutes longer than it takes to fully fuel a Falcon 9 rocket.

The release schedule is also somewhat modified. While the end of the mission, billed as “An exciting landing!” remains at approximately the same time (in the approximate 1 hour and 5 minutes), Flight 4 speeds up a lot by eliminating some of the additional flight objectives.

However, three key events were added to the timeline, one near takeoff and two towards the end of the mission.

After the Super Heavy booster performs booster burn, just before the four-minute mark, SpaceX will discard the hot stage adapter, which was added between Starship's first and second flights.

SpaceX said they are doing this “to reduce the mass of the booster for the final phase of the flight.”

The other two events added in this next lap include the so-called “landing spin” at T+01:05:38, followed by landing five seconds later.

“Flight 4 will follow a similar trajectory to the previous flight test, with Starship intended to land in the Indian Ocean,” SpaceX said. “This flight route does not require deorbitation for reentry, maximizing public safety while providing the opportunity to meet our primary goal of a controlled reentry to Starship.”

Road to launch

As SpaceX noted on Friday, the planned launch date of Wednesday, June 5, is dependent on FAA approval. The SpaceX-led mishap investigation after Flight 3 remains ongoing, but the company hopes to use a pre-existing clearance mechanism within FAA rules to return to flight before the investigation is completely over.

“During Flight 3, neither vehicle's automated flight safety system activated and no vehicle debris impacted outside of the predefined danger areas,” SpaceX said. “Pending the FAA's determination that there is no impact on public safety, a license modification may be issued for the next flight without formally closing the investigation into the mishap.”

When contacted for comment Friday, the FAA told Spaceflight Now it received SpaceX's request for a public safety determination and, if they agreed, SpaceX could fly while the investigation into the mishap continues.

“The FAA is responsible for and committed to protecting the public during commercial space transportation launch and reentry operations,” the FAA stated. “On April 5, SpaceX requested that the FAA make a public safety determination as part of the ongoing investigation into the Starship OFT-3 mishap. “The FAA is reviewing the application and will be guided by data and safety at every step of the process.”

A slide about Starship's version of the Human Landing System shown during a presentation this week by Logan Kennedy, NASA's surface lead for the HLS program. Chart: SpaceX/NASA

Carrying out as many launches as frequently as possible is important for SpaceX's development process and also for NASA. The rocket is contracted to support a crewed landing on the surface of the Moon during the Artemis 3 mission, which is currently scheduled for September 2026. NASA announced earlier this year a nearly one-year delay from its previous date December 2025.

During a budget hearing with the Senate Appropriations Committee earlier this week, NASA Administrator Bill Nelson said they are closely monitoring Starship development as Flight 4 approaches.

“Artemis 3, if you compare it to the Apollo program, is a combination of Apollo 9, 10 and 11, which was the moon landing, and part of Apollo 8, which orbited the moon ten times,” Nelson said. “It is a difficult task and if we land, it depends on SpaceX having its lander ready.”

“Now they have reached all their milestones and in a couple of weeks they will launch that huge rocket that has 33 Raptor engines in its tail and they will do more to demonstrate their space capabilities. Nelson added. “I'm hopeful that SpaceX is ready with its lander.”

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