CAPE CANAVERAL, Fla. -- More than 16 months after a Falcon 9 rocket’s spectacular explosion on its Cape Canaveral launch pad, SpaceX continues to redesign the system blamed for the accident as part of preparations to launch NASA astronauts.
An independent NASA safety panel says fully understanding how the helium pressurization system behaves is “an absolutely essential precursor” to declaring the rocket safe for human launches.
The system submerges helium “bottles” called Composite Overwrap Pressure Vessels, or COPVs, in liquid oxygen tanks. Helium gas pressurizes the super-cold oxidizer for flight.
“SpaceX and NASA agreed that a redesign of the COPV was necessary to reduce the risk for missions with crew on board,” NASA’s Aerospace Safety Advisory Panel wrote in an annual report released Thursday.
The report highlights several issues — including establishing the right safety culture — that likely contributed to a four-month slip in SpaceX's planned first launch of a Dragon capsule carrying astronauts to the International Space Station, to no earlier than December.
Boeing, which is developing CST-100 Starliner capsules for the same purpose, is targeting November for its first test flight of a NASA-Boeing crew.
The safety panel made clear that NASA’s Commercial Crew Program faces a “very real possibility of future schedule slips” given the significant work left to certify the capsules’ safety. It warned NASA not to succumb to schedule pressure found to have contributed to fatal accidents in prior programs.
The helium bottle concern dates to the Sept. 1, 2016, explosion that destroyed a Falcon 9 rocket and $200 million commercial satellite during a fueling test at Launch Complex 40.
SpaceX resumed launching four months later and went on to complete its most successful year yet, with 18 launches, a total it hopes to top this year.
Changes in helium loading operations prevented a repeat of the problem believed to have caused the explosion: buckles in helium tanks that trapped slushy liquid oxygen in gaps between the tanks and their composite wraps. Friction "or other mechanisms" ignited oxygen in the upper stage.
While Falcon launches resumed fairly quickly, a redesigned helium bottle has not yet completed testing nor won NASA’s approval for crew launches.
SpaceX said qualification testing of the system is about two-thirds complete. It could begin flying by late in the first quarter of this year, as part of a Falcon 9 upgrade known as Block 5.
If NASA does not certify that redesign, the safety panel said SpaceX was working on an alternate design using heavier bottles. That might require more changes to the rocket, making it a unique vehicle flown only for occasional crew launches.
Overall, the safety panel praised SpaceX and NASA for “working together to solve a very difficult technical issue.”
That isn’t the only issue outstanding from the 2016 explosion, however.
The safety advisers urged continued focus on SpaceX’s “load and go” fueling process, which will have astronauts strapped into a Dragon capsule while the Falcon rocket below them is fueled with kerosene and super-cold liquid oxygen.
“We advise NASA not to discount other potential hazards associated with loading cryogenic propellants — particularly LOX,” the report states.
United Launch Alliance’s Atlas V rocket, in contrast, will be fueled before a crew boards Boeing’s Starliner.
More broadly, the panel expressed some distrust of SpaceX’s safety culture, while acknowledging that “non-traditional approaches” can achieve the same goals.
It left open a recommendation that NASA demand “verifiable evidence” of appropriate engineering practices and controls, and commended NASA for “its acknowledgement of the need for increased surveillance of at least one provider.”
“NASA should expect both providers to exhibit a safety culture appropriate for human spaceflight,” the report says.
Upcoming tests, the panel said, “will provide an opportunity to gauge the progress of this effort at SpaceX.”
