Following SpaceX’s successful launch of the GovSat-1 satellite, the company found that the Falcon 9 rocket used in the launch had unexpectedly survived the fall to Earth, testing a dangerous ‘three-engine landing burn’ in the process.

The launch involved the GovSat-1 satellite placed atop a Falcon 9 rocket, which takes off in two stages. The first stage, also known as the core, fires, expending the majority of its fuel before returning to Earth; then the second stage rockets fire, completing the journey. The Falcon 9 is the only existing rocket designed to be partially reusable, as many cores are equipped with grid fins and deployable landing legs to land safely back at the launch site, or an autonomous spaceport drone ship. The core involved in the GovSat-1 mission, 1032, was first used in May 2017.

GovSat-1 included a geocommunications satellite commissioned by the government of Luxembourg atop a Falcon 9 rocket. The satellite was built by American company Orbital STK and operated by SES from Luxembourg, and aims to support humanitarian and military operations for the country.

Once the satellite was deployed, the Falcon 9 fell back to Earth and fired all three of its engines to land, which company founder and CEO Elon Musk called a “very high retrograde landing”. Typically, Falcon 9 rockets fire a single engine when landing, generating 3gs of force in the seconds before landing; this landing, involving all of the rocket’s engines, generated close to 27gs of force and burned considerably less fuel as the engines are fired for a very short period of time.

The rocket’s survival is also impressive as many SpaceX rockets have exploded upon landing in water, which the company has shared in a ‘blooper reel’. Contact with water can tear the thin aluminium-lithium alloy that separates fuel and oxidiser, triggering an explosion, although this has not happened following SpaceX’s most recent launch.

NASA reported that SpaceX plans to use the unexpected survival of the rocket to further improve the reusability of the craft. “SpaceX is also aiming to make the Falcon 9’s fairing – which protects the payload as it ascends through the atmosphere – reusable,” the agency said. “To this end, the company has been conducting a series of tests with the fairings following separation on operational missions.”