SpaceX says it’s ready to launch rockets again
After the explosion in September of one of its rockets, SpaceX is now ready to get back into the business of sending payloads to space, the company announced Monday, with its next rocket headed to orbit as soon as Sunday.
In a statement, SpaceX — or more formally, Space Exploration Technologies Corp. — said an investigation had determined the likely cause: an unexpected interplay of supercold helium and oxygen with carbon fibers and aluminum.
The company said it had devised workarounds to prevent a recurrence.
The explosions on Sept. 1 that destroyed a Falcon 9 rocket on the launchpad at Cape Canaveral Air Force Station in Florida was perplexing and concerning, because it occurred during what is usually regarded as a safer portion of operations — the fueling of propellants — about eight minutes before the ignition of the engines for a planned test.
The trouble appeared to start near the liquid oxygen tank on the second stage of the two-stage rocket, and in less than a tenth of a second, that section was in flames, followed by the destruction of the entire rocket and a $200 million communications satellite.
The investigation narrowed in on three helium containers within the second-stage liquid oxygen tank. The containers consist of an aluminum liner with an outer layer of strong carbon fibers. During launch, as the liquid oxygen is consumed, the helium is heated and released to maintain pressure within the tank.
In December 2015, SpaceX began using an upgraded Falcon 9 design that uses supercooled liquid oxygen at minus 340 degrees, 40 degrees colder than what is typically used for rocket propulsion. The lower temperature makes the oxygen denser, which improves engine thrust.
But the helium was even colder. As the carbon and aluminum cool, they shrink at different rates, opening gaps into which liquid oxygen could flow. In addition, the helium may have been below the temperature at which oxygen freezes, and some of the trapped oxygen may have become solid.