ASAP Report Targets Concerns Over SpaceX Propellant Loading

Credit: USLaunchReport.com
Credit: USLaunchReport.com

A new NASA reports says that while Boeing and SpaceX are making progress on their commercial crew spacecraft, but a number of key technical challenges remain and there is “a very real possibility” of “a substantial slip in the schedule” in the already delayed programs.

In its 2016 Annual Report, NASA Aerospace Safety Advisory Panel (ASAP) said it was concerned about SpaceX’s “load and go” approach of placing the load aboard the Crew Dragon spacecraft prior to loading the Falcon 9 booster with propellants, particularly in the wake of the loss of a booster in September while it was being fueled.

“A number of systems have not yet finalized design or completed testing. Challenges remain in several key systems, such as abort and parachute-related systems, in anchoring the analysis required to certify those systems for human flight,” the report states. “Additionally, there are issues and concerns surrounding the launch systems of both providers, such as the Centaur fault tolerance for Boeing and the ‘load and go’ approach for SpaceX.”

Boeing will be flying its Starliner spacecraft on a modified United Launch Alliance Atlas V, which uses the Centaur upper stage. The Centaur is being upgraded with dual engine capability from the single-engine configuration that ULA uses to launch satellites.

SpaceX’s “load and go” approach is a reversal of procedures that have been used in human spaceflight since the first missions in 1961. The standard practice is to load the launch vehicle first with no personnel at the launch pad, let the rocket settle and its fuel settle, and then place the crew on board with a minimum number of support staff.

SpaceX is using densified (super cold) liquid oxygen (LOX) in the Falcon 9 booster that will launch the Crew Dragon spacecraft. The densified LOX gives the rocket extra payload capacity, but it must be loaded just prior to launch to keep it from warming up. As a result, the company wants to load the crew first.

SpaceX began flying with densified propellant in late 2015 as part of an effort to recover the Falcon 9 first stage for later reuse.  The densified propellant helped offset the performance hit from adding landing legs and other systems to the booster.

NASA’s International Space Station Advisory Committee raised concerns over load and go in 2015. Those concerns were heightened on Sept. 1 when a Falcon 9 caught fire and exploded while it was being fueled on the launch pad for a pre-flight first-stage engine test. The accident destroyed the booster and a $195 million communications satellite.

“One complicating factor for the ‘load and go’ issue is the potential uncertainty in hazard identification and control,”the ASAP report states. “Identification of the hazards is dependent on many factors, which include understanding the environment in which the system will operate.

“In this regard, the Panel is concerned that the dynamic thermal effects on the system associated with loading densified propellants may not be adequately understood, which results in a higher level of uncertainty that must be factored into the risk determination,” the report adds.

SpaceX has said its investigation pointed to a breach of a helium tank located inside of the second stage liquid oxygen (LOX) tank. Investigators concluded that oxygen pooled and froze inside buckle (gap) between the helium tank’s aluminum tank and a layer of carbon composite material that surrounded it. This caused friction or the fibers to break, igniting the composite material.

SpaceX plans to return to flight on Saturday using warmer helium, which it believes will prevent a recurrence of the explosion. The company also plans to change how it manufactures its helium tanks to eliminate buckles between the aluminum and carbon composite shell.

Whether those changes will be enough to satisfy NASA is unclear. Losing a communications satellite or space station resupply ship is one thing; crew safety standards are a lot stricter.

The ASAP report was completed before the investigation into the accident was completed, so it does not comment on SpaceX’s proposed fixes. The panel did have advice for NASA about how to evaluate the risks involved in the load and go approach with regards to Crew Dragon flights.  (Emphasis mine)

We believe that the focus of the investigation must not be solely to identify and fix the specific cause of this mishap. It must focus also on improving the understanding of how the system functions in the dynamic thermal environment associated with “load and go” so that other previously unidentified hazards can be discovered.

This is not a trivial effort. Despite testing at the component and subassembly level, systems often display “emergent” behavior once they are used in the actual operational environment. We are concerned that any determination of risk associated with “load and go” would have significant uncertainty.

For these reasons, we strongly encourage NASA top management to scrutinize this issue and ensure that any decision to accept additional risk or novel risk controls with large uncertainties is justified by the value that will be gained. The decision should not be unduly influenced by other secondary factors such as schedule and budget concerns.

In short, the panel is saying that NASA need to make sure the benefits of using densified propellants are really worth the risk. The rewards are basically an increase in payload to the International Space Station.  ASAP is also telling NASA not to let schedule and budget concerns override safety.

As for schedule, ASAP has some serious concerns about that for both SpaceX and Boeing.

“Although progress is being made, there is still much left to do from a technical perspective,” the report states. “Whether the needed work can be accomplished without a substantial slip in the schedule remains to be seen.”

Each company must conduct two demonstration flights to the International Space Station and then have their systems certified to carry astronauts on a commercial basis. The current flight test schedule is:

  • SpaceX Demonstration Mission 1 (No Crew): November 2017
  • Boeing Orbital Flight Test (No Crew): June 2018
  • SpaceX Demonstration Mission 2 (Crew): May 2018
  • Boeing Crew Flight Test (Crew): August 2018

Whether the schedule will hold is uncertain. The ASAP report notes that “the designs of proposed spacecraft systems are not fully mature and are still in a state of flux.”

Boeing is running 16 months behind schedule on the flight test without a crew and 15 months behind on the crew flight compared with the schedule laid out in the  Commercial Crew Transportation Capability (CCtCap) contact it was awarded in 2014. SpaceX is running 20 months and 19 months behind schedule on its two flights.

A report issued by the NASA Office of Inspector General (IG) in September indicated that neither company was likely to fly astronauts to ISS on a commercial basis before the end of 2018. This is key for NASA because its contract to fly U.S. astronauts on Russian Soyuz spacecraft expires at the end of that year.

The NASA IG report attributed the CCtCap delays to technical challenges faced by Boeing and SpaceX and bureaucratic delays at NASA in reviewing documentation submitted by the two companies.

There are two main review processes under way. One involves standards for systems and equipment proposed by the companies that they feel are comparable to requirements laid down by NASA. The other involves hazard reports on how the companies plan to address specific dangers to the vehicles and their crews.

The ASAP report said NASA and the companies have been making progress in dealing within both areas, but it added that the amount of work remaining to be completed could cause additional delays.

“Virtually all requests for alternate standards have been received, and some 95 percent have been adjudicated and approved by NASA,” the report states. “The approval of these standards is basic to allowing the designs to proceed to completion. In addition to alternate standards, between 65 and 75 percent of all requested variances and Phase II Hazard Reports (HRs) have been reviewed by NASA and dispositioned.”

Another area of concern for ASAP are the calculations for loss of crew (LOC), which appears unlikely to meet NASA’s original goal.

“The ASAP was informed that the LOC goal of 1 in 270 may not be able to be met without additional spacecraft mitigations due to Micrometeoroid and Orbital Debris (MMOD)-associated risks, which are a dominant factor in the LOC calculation,” the report states. “Since the designs of proposed spacecraft systems are not fully mature and are still in a state of flux, it is impossible to determine what the final configurations will yield with respect to LOC.”

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