SpaceX has concluded its investigation into why one of its Falcon 9 rockets exploded on the launch pad four months ago and is ready to return to flight as early as Sunday.
The company, owned and operated by technology entrepreneur Elon Musk, is opting for a short-term solution to fix the problem, which was traced to super-cold liquid oxygen, known as LOX, getting trapped between layers of a canister holding helium. Three canisters of helium are inside the oxygen tank to maintain pressure.
The extreme cold likely caused one of the canisters to burst, triggering a catastrophic explosion on Sept 1 as a rocket was being fueled for a routine prelaunch engine test at Cape Canaveral Air Force Station in Florida. The accident destroyed the rocket and a $200 million Israeli communications satellite that it was due to send into orbit two days later.
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Engineers at SpaceX have begun designing a new helium canister, but in the meantime the company plans to change its fueling procedures and fill the canisters with warmer temperature helium to avoid what it calls "friction ignition."
The helium canisters, known as composite overwrapped pressure vessels, or COPVs, consist of an aluminum inner liner with a carbon overwrap.
"The recovered COPVs showed buckles in their liners. Although buckles were not shown to burst a COPV on their own, investigators concluded that super chilled LOX can pool in these buckles under the overwrap. When pressurized, oxygen pooled in this buckle can become trapped; in turn, breaking fibers or friction can ignite the oxygen in the overwrap, causing the COPV to fail," SpaceX said in a statement.
Investigators also determined that the loading temperature of the helium was cold enough to create solid oxygen, SpaceX noted, exacerbating the possibility of oxygen becoming trapped, as well as the likelihood of friction ignition.
The short-term solution to the problem is to change the COPV configuration to allow warmer temperature helium to be loaded and to load the helium at a slower pace, SpaceX said "In the long term, SpaceX will implement design changes to the COPVs to prevent buckles altogether, which will allow for faster loading operations," the company said.
Neither change is expected to impact SpaceX's plans to return the rocket's first-stage after launch so it can be refurbished and flown again.
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SpaceX will implement the new protocols during an engine test firing and launch of a Falcon 9 rocket that is slated to fly Sunday from Vandenberg Air Force Base in California. The rocket will be carrying 10 satellites for Iridium Communications.
The company has not said how much damage the Sept 1 accident caused to its primary launch site in Florida, nor when the repaired pad will be ready to support launches.
In the meantime, SpaceX is working to finish its second launch site in Florida, located at NASA's Kennedy Space Center, and plans to fly in the first quarter of 2017.
The Federal Aviation Administration, which oversees commercial U.S. launches, said it had received SpaceX's accident report and was reviewing it.
"The FAA has not yet issued a license to SpaceX for a launch in January," the agency said in an email to Seeker.
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