By all appearances to most anyone outside of SpaceX, the flight of Starlink 12-20 last week was nominal, and afterwards, the landing of Booster B1086 was normal. The booster completed that landing successfully when it touched down aboard ASDS ‘Just Read The Instructions’ about 8.3 minutes after launching. Unfortunately during its ascent, a lot was going wrong inside the vehicle, leading to its loss shortly after it landed when a fire started 45 seconds after touchdown.

In early reports, SpaceX said the following:

“The first stage booster returned to Earth and landed on the Just Read the Instructions droneship, which was stationed in the Atlantic Ocean ~250 nautical miles off the coast of Florida. Following the successful landing, an off-nominal fire in the aft end of the rocket damaged one of the booster’s landing legs which resulted in it tipping over. While disappointing to lose a rocket after a successful mission, the team will use the data to make Falcon even more reliable on ascent and landing.”

A Deeper Explanation

Bill Gerstenmaier, Vice President of Build and Flight Reliability at SpaceX, outlined the events which led to the loss late last week in the Crew 10 pre-flight teleconference hosted by NASA. “Last week on Starlink G12-20, after a successful landing, an off-nominal fire broke out and flared into the rocket. It damaged one of the landing legs, which resulted in the rocket tipping over,” he began.

“We got a chance to see how the hardware really performs in an extremely off-nominal environment, and that’s a pretty rare instance to get a chance to see that,” Gerstenmaier continued. “The engine [on fire] was fully contained in the compartment like it was designed to be. The fire was pretty extensive, did a lot of damage, but the damage is what we’ve expected, what is accounted for in all our procedures and processes.”

Failure Was During Ascent, But Mission Was Safe To Continue

Gerstenmaier continued, saying, “It turns out there was a fuel leak during ascent. It showed up about 85 seconds into ascent. It essentially sprayed some rocket propellant, essentially kerosene, onto a hot component of the engine. It vaporized and created a flammable environment. But on the way up, there was no oxygen to interact with. With the fuel, so there was no problem at all during ascent. And it was perfectly fine. The mission was accomplished.”

In the mission profile, at 85 seconds into the ascent Starlink 12-20 and Booster 1086 was roughly 17.5 kilometers high, and about 38.8 km downrange. It had a little more than another minute of powered flight left prior to MECO, or Main Engine Cutoff, the point at which the first stage has concluded its boosting phase and the staging and landing events begin.

Starlink 12-20 Would Have Been Successful Even If The Fire Started Earlier

“Even if we would have had a problem [a fire] during ascent, this shows that the fire and the damage would be contained to just a single engine out, which still allows us to accomplish the entire mission,” Gerstenmaier stated, underscoring the booster’s resilience despite the anomaly.

Detailing the sequence of events, he explained that while the fire did not compromise the mission itself, it reignited after landing due to a combination of residual oxygen, fuel, and a hot engine component.

“Then coming back after we landed, about 45 seconds after we landed, enough oxygen came into the compartment where it interacted with the fuel and a hot portion of the engine, which was known to be hot. And then we had a fire, and subsequently, it blew out the barrel panel on the side of the rocket just like it was designed to. The fire was all contained,” he elaborated.

Gerstenmaier emphasized that SpaceX is rigorously investigating the incident to pinpoint the exact cause of the fuel leak that led to the post-landing fire.

“So we developed a risk. We put all the rationale through that. We’re double-checking. We’re trying to see if we can understand what occurred that actually caused the fuel leak. It’s pretty difficult to determine what was cause and what was effect from the fire,” he said.

He acknowledged the complexity of the forensic analysis due to the extent of the fire damage.

“The fire was pretty extensive. It melted a lot of aluminum components. So it’s difficult to see. But we’re going through the forensics,” Gerstenmaier noted.

Despite the setback, SpaceX successfully recovered most of the burned booster, which remained aboard the autonomous spaceport drone ship ASDS Just Read The Instructions. The ship and booster remains returned to Port Canaveral over the weekend, allowing teams to conduct further inspections.

“It’s available at the Cape. We’ll continue to keep looking [for the root cause.] We’ll continue to keep briefing NASA [on our findings.] And we’ll be ready as we move forward. So, again, I think we’re in good shape with that. We have a good understanding, and we’ll improve our knowledge, and ultimately, we’ll be safer because of what occurred on this flight,” Gerstenmaier concluded.