Most powerful rocket ever built, the Starship, destroyed and severely damaged the entire SpaceX launch site during last week’s test flight. The 120-meter-tall combination of booster and spacecraft performed well during the test. The vehicle reached an altitude of 39 kilometers before several issues forced SpaceX to order its destruction above the Gulf of Mexico. But why was the Starbase launch site completely devastated after the dust settled?
Absence of a flame deflector
Enormous power of the 33 Raptor engines on the booster (first stage) of the spacecraft created a crater in the reinforced concrete beneath the Orbital Launch Pad (OLP). The pieces that flew off hit nearby infrastructure and are believed to have damaged the same Raptor engines that shut down during the flight.
The reason is said to be the lack of a flame trench (flame deflector) in the Starbase’s orbital launch pad. These massive structures are carefully designed to divert the engine exhaust, which reaches maximum power during liftoff, away from the platform.
Flame trenches are very common features in platforms that host launches of powerful rockets. For example, NASA recently built a new one (ref.) at Kennedy Space Center‘s Pad 39B, so that the site can support the launches of its new gigantic rocket. Space Launch System (SLS) made its first flight last November, departing from Pad 39B to kick off the Artemis 1 lunar mission. The pad hardware suffered minor damage but withstood the 4 million kilograms of thrust generated during liftoff.
Absence of a flame deflector, a serious mistake?
Artemis 1 mission made the SLS the most powerful rocket ever successfully flown. But the Starship’s Booster is in a different category of power. The 33 Raptor engines produce approximately 7.5 million kilograms of thrust at maximum power, nearly double that of the SLS, which destroyed the entire launch site. SpaceX had considered the idea of digging a flame trench on the nearby Boca Chica beach during the construction of the site, but ultimately decided against it.
“Aiming to not have a flame deflector at Boca, but this could be a mistake” said the company’s founder and CEO Elon Musk on Twitter in October 2020 (ref.). This doesn’t mean Musk was right. In fact, it appears that the company still has an ace up its sleeve that doesn’t involve building a flame trench. But it’s highly likely that this is the reason why the Starship destroyed the launch site.
On Friday, April 21, Musk tweeted (ref.) that SpaceX had begun building “a huge water-cooled steel plate to put under the launch mount” three months ago. The plate was not ready in time for the Starship’s debut, but SpaceX went ahead with the test anyway. According to some rather optimistic estimates, the heat-resistant concrete underneath the OLP called Fondag was supposed to survive liftoff.
Data and image analysis
The company based this assumption on data from the first static fire, when 31 out of the 33 first-stage Raptors were ignited for a few seconds while the vehicle remained anchored to the ground. But the February static fire didn’t generate the full power of an actual launch, Musk noted in a tweet on Saturday (ref.). “We are early in the analysis, but the force of the engines when they throttled up [on April 20] may have shattered the concrete rather than just eroded it. The engines were only at half thrust for the static fire test” he wrote.
Soon we will know what SpaceX has decided and whether the new steel plate will provide adequate protection to the orbital launch pad in the future. In the same Friday tweet, Musk stated that SpaceX should be ready to attempt another Starship launch in 1 or 2 months.