How Propellant Venting Led to Starship Second Failure

The Starship upper stage exploded on its second test flight in November due to a propellant venting issue, according to SpaceX CEO Elon Musk. He said this problem will not affect the next launch, which he expects to reach orbit.

The test flight on Nov. 18 was supposed to put the ship on a long suborbital path, but it lost contact with Mission Control near the end of its engine burn. The SpaceX webcast hosts said it looked like the automated flight termination system (or AFSS) was triggered, but they did not explain why, and the company did not share much information afterwards.

The SpaceX all-hands meeting

Musk revealed the cause of the failure at the recent “all-hands meeting” of the company, held at the Starbase test site in Boca Chica, Texas, on January 11th. SpaceX posted the recording of the event on X the following day.

In 2023, SpaceX completed 96 successful missions, safely flew 12 more astronauts to orbit, launched two flight tests of Starship, and more than doubled the number of people around the world connected by @Starlink.

Watch @elonmusk deliver a company update: pic.twitter.com/7zeTlQLgp9

— SpaceX (@SpaceX) January 12, 2024

He said the ship vented liquid oxygen propellant close to the end of the upper stage burn, because it did not have any payload on board and the propellant was too much.

Musk said that venting caused a fire and ultimately an explosion; this prevented the ship from reaching orbit. “Flight 2 actually almost made it to orbit,” he said. “If it had a payload, it would have made it to orbit.”

In fact, he said the venting would not have been needed if the ship had a payload, since it would have been needed to fuel the ship’s Raptor engines in order to reach orbit. Unfortunately, he did not say how the venting started the fire, or mention the Super Heavy first stage’s explosion shortly after it separated from the ship.

Musk also said that he is confident about the next Starship test flight. “I think we’ve got a really good shot of reaching orbit with Flight 3,” he said.

Onto flight 3, with more tests

The third Starship flight test is tentatively planned for February, according to what SpaceX’s Jessica Jensen said at a NASA Media teleconference on January 9, but in order to launch it still needs an updated launch license from the Federal Aviation Administration (FAA) and, of course, the closing of the formal investigation about flight 2, which is still ongoing.

Musk also said that the upcoming flight will have more tests of Starship’s systems.

He said the flight will include an in-space engine burn from the header tank at the top of the ship, to “prove that we can reliably deorbit”. It will also test transferring propellant from the header tank to the main propellant tank, which is part of a NASA Tipping Point award—inside the Artemis Program milestones—to demonstrate propellant transfer from one Starship to another. He said the first ship-to-ship propellant transfer test is planned for “hopefully by the end of this year, but certainly by next year.”

Musk also said that SpaceX will test the “Pez dispenser” payload door that will deploy the larger “standard” Starlink V2 satellites on future flights, instead of the smaller “V2 mini” satellites that are currently launched on Falcon 9. He said he hopes to launch Starlink V2 satellites by the end of this year.

Other bits of news from the event

The meeting touched other topics regarding SpaceX’s recent milestones and future plans, other than Starship.

Increased launch rate of Falcon 9 and Falcon Heavy has certainly been a central one. The company collected 96 Falcon launches in 2023, and Musk said it plans to do “150 flights or thereabouts” in 2024. We already knew back in 2023 that the company set a goal of 144 launches for 2024, or roughly 12 per month.

Regarding the Falcon launch rate, Musk said that they’re aiming for a turnaround of less than 24 hours between launches from the same launch pad by the end of the year. He added that SpaceX is now working to qualify Falcon 9 boosters for up to 40 flights. To date, the most times the company has re-flown the same booster is 19.

Musk touched other topics, some interesting bits:

• Starlink: 2.3 million customers and counting. More than 9000 lasers across the constellation and sent 1000 to 10,000 times more data over laser links in space than any other system before;
• Fairings: been re-flown more than 300 times, saving each reuse ~$6M;
• Dragon: the fleet “time on orbit” exceeded the Space Shuttle fleet time during 2023, and Dragon has also visited the ISS more times than the Shuttle. SpaceX is targeting seven or eight Dragon launches in 2024, with Polaris Dawn being the first Dragon Mission with an EVA.