by Douglas Messier
Even as SpaceX prepares to make its first Crew Dragon flight test to the International Space Station (ISS) next month, challenges remain for certifying the vehicle to carry NASA astronauts, according to a new safety report.
In its annual report released last week, NASA’s Aerospace Safety Advisory Panel (ASAP) identified two inter-related safety concerns with SpaceX’s system: the redesign of helium composite overwrap pressure vessels (COPVs) used in the Falcon 9 rocket, and the company’s desire to load astronauts aboard Crew Dragon before fueling the booster.
ASAP’s report also expressed concerns about the certification of parachute systems for Crew Dragon and Boeing’s Starliner spacecraft. Starliner is also scheduled to make two flight tests to the space station this year in advance of providing transportation on a commercial basis.
On Sept. 1, 2017, a Falcon 9 rocket exploded on the launch pad at Cape Canaveral while it was being fueled for a pre-flight engine test. An Israeli communications satellite was lost and the launch pad severely damaged in the resulting fireball, which began in the booster’s second stage.
At the time of the explosion, the rocket was being loaded with super cold, densified propellants. SpaceX traced the explosion to one of the helium COPVs located on the inside of the second stage liquid oxygen (LOX) tank. The company said frozen LOX became trapped between the composite over wrap and the liner, setting off a spark that caused the explosion.
Although no similar accidents have occurred on subsequent Falcon 9 flights, SpaceX has been designing and testing an updated helium vessel known as COPV 2.0 to eliminate the possibility of another explosion.
“Testing to date has identified a potential ignition source related to fiber breakage, but the impact of this ignition source has yet to be determined,” ASAP said in its report. “Consequently, while NASA and SpaceX have made significant progress in understanding the COPV 2.0 behavior in its environment, we believe that the team has yet to arrive at a clear definition of the risk posture or mitigation strategies related to operations with the redesigned COPV….
“It is imperative that the Program understands the potential hazards, the controls of those hazards, and the margins involved, and also ensures that the operating environment stays within those margins if the redesigned COPV tanks are to be implemented for crewed flights,” the report added.
SpaceX’s “load-and-go” plan to place astronauts aboard Crew Dragon and then fuel the Falcon 9 booster has caused a significant amount of concern. In past programs, the rocket was fueled and allowed to settle first, then a small team placed the crew aboard.
NASA’s International Space Station Advisory Committee has unanimously opposed the new procedure. In December 2015, Committee Chairman and former NASA astronaut Tom Stafford laid out the panel’s concerns in a December 2015 letter to Associate Administrator William Gerstenmaier.
“There is a unanimous, and strong, feeling by the committee that scheduling the crew to be on board the Dragon spacecraft prior to loading oxidizer into the rocket is contrary to booster safety criteria that has been in place for over 50 years, both in this country and internationally,” Stafford wrote. “Historically, neither the crew nor any other personnel have ever been allowed in or near the booster during fueling. Only after the booster is fully fueled and stabilized are the few essential people allowed near it.”
The densified, super cold propellants provide the Falcon 9 with performance, allowing it to carry heavier payloads. For maximum effectiveness, the propellants need to be loaded just prior to launch so that they do not start warming up. Thus, it makes sense to place the crew aboard first.
The ASAP report said the NASA Engineering and Safety Center (NESC) has determined that load-and-go plan is feasible with proper precautions. (Emphasis mine)
“The NESC has independently studied the load and go procedure and provided a thorough report that identifies the hazards and available controls,” the ASAP report stated. “Based on the NESC report, the CCP has decided that the load and go concept is viable if subsequent analysis is adequate and if verifiable controls are identified and implemented for all the credible hazard causes that could potentially result in an emergency situation or worse.”
The panel said the risk of load-and-go could be acceptable if the steps stipulated by NESC are implemented. However, ASAP is primarily concerned that the COPV issues be resolved before any astronauts are loaded aboard a Crew Dragon.
“Upon gaining a greater understanding of the margins related to operating with the redesigned COPV, NASA should re-assess the adequacy of the controls associated with the load and go procedure to ensure that the operating environment dictated by this process is within the acceptable safety limits of not only the COPV 2.0 tanks, but all other identified hazards as well,” the report stated.
ASAP also expressed concerns about the parachute systems on both SpaceX’s Crew Dragon and Boeing’s Starliner.
“The ASAP firmly believes that before the crewed missions are conducted, each provider’s parachute systems must be fully qualified, including successful completion of the reliability testing with a consistent design,” the report stated.
“Qualification tests, which are tests designed to prove that the final design meets requirements, should not be confused with design and flight testing, the purpose of which is to collect data to establish the final parachute configuration. We encourage the Program to continue to look carefully at the parachute qualification process for both providers,” the document added.
NASA has stipulated that Crew Dragon and Starliner meet a 1-in-240 number for loss of crew (LOC). ASAP’s report said that while the LOC numbers are important, they should not distract NASA and the two providers from mitigating high-risk areas through design or operational procedures.
“It is important for NASA to evaluate the many other parameters available—including redundancy in designs, reliability, identified hazards and their controls, as well as the certification process—in addition to understanding the data behind the LOC calculations, in order to determine the resultant risk posture for the commercial vehicles….Relying on only the LOC number to describe program risk moving forward is insufficient and misleading,” the report stated.
ASAP said it appears that NASA has been prioritizing safety over schedule.
“To date, we still see no direct evidence across NASA that schedule pressure is driving decisions that will adversely impact safety, but important testing remains,” the report stated. “As with all testing of complex space hardware, inevitable discoveries will likely necessitate the careful weighing of all the technical and operational aspects of risk-benefit trades.”
The panel also stressed clear communications when it comes to certifying components and systems.
“A clear set of guidelines for how to proceed when a certification condition is inadequate, and what defines ‘inadequate,’ needs to be specified and communicated to the workforce,” the report stated. “In addition, it should be recognized by all parties, both internal and external to NASA, that the certification process is not merely a ‘paperwork’ process; it involves considerable detailed technical activity by both NASA and the partners.”
The panel made two recommendations to NASA concerning commercial crew.
Required Actions for Crewed Flight Test Risk Reduction: NASA should confirm and then clearly communicate the required content and configuration for the upcoming CCP test flights-Demo-1 and Orbital Flight Test (OFT)-specifically, those items that must be successfully demonstrated prior to the first crewed flights.
Action to Ensure U.S. Access to the International Space Station Given Commercial Crew Program Schedule Risk: Due to the potential for delays in the schedule for the first Commercial Crew Program (CCP) flights with crew, senior NASA leadership should work with the Administration and the Congress to guarantee continuing access to ISS for U.S. crew members until such time that U.S. capability to deliver crew to ISS is established.
NASA had not responded to either recommendation by the time the annual report was printed.