NASA released the December 9, 2015 letter today that Lt. Gen. Tom Stafford (Ret.) sent to Bill Gerstenmaier, who heads NASA’s human spaceflight operation. The letter raises two concerns about SpaceX’s Falcon 9 rocket when it is used to take NASA astronauts to the International Space Station (ISS). Stafford, a former Gemini and Apollo astronaut, chairs NASA’s ISS Advisory Committee and the letter was from the committee as a whole. At a meeting of the committee on Monday, Stafford said he still has not received a reply; the committee again expressed its concerns.

SpaceX currently launches cargo to the ISS using robotic Dragon spacecraft launched by Falcon 9 rockets. The company is developing a version of Dragon that can accommodate people — Crew Dragon — that also will be launched by Falcon 9. It is one of two companies (the other is Boeing) chosen by NASA to develop “commercial crew” vehicles to ferry astronauts to and from ISS under public private partnership arrangements. Falcon 9 is also used for commercial satellites. On September 1, 2016, while fueling a Falcon 9 for a routine pre-launch test two days before a planned launch of the Amos-6 commercial communications satellite, a fire began near the rocket’s second stage, quickly engulfing the rocket and satellite, both of which were destroyed in the ensuing explosion. SpaceX is still trying to identify the root cause of the failure, but the incident raised concerns about crew safety when the rocket is used for astronauts. SpaceX founder and CEO Elon Musk tweeted after the incident that Dragon would have been fine because it has an abort system that would have carried it away from the exploding rocket.

The Stafford letter was written 8 months before that incident after the committee was briefed by NASA commercial crew program manager Kathy Lueders about SpaceX’s plan to fuel the rocket after the crew was strapped into their seats. It raises two issues. First is SpaceX’s proposal to fuel the rocket after the crew is aboard because it uses supercooled oxygen that must be loaded just 30 minutes before launch. The Stafford committee letter said:

“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. 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.”

Indeed, after the September 1 incident, SpaceX said that no one was injured because “per standard operating procedures, all personnel were clear of the pad.”

The second issue raised by the Stafford letter, and which was also discussed at the Monday committee meeting, is that the Falcon 9 design does not include a recirculation pump. “We are concerned that there may be insufficient precooling of the tank and plumbing with the current planned oxidizer fill scenario, and without recirculation there may be stratification of oxidizer temperature that will cause a variation in the input conditions to the oxidizer pump.”

SpaceX said last week that although it has not determined the root cause of the September 1 incident, they believe it is related to helium loading conditions that are “mainly affected by the temperature and pressure of the helium being loaded” into helium tanks inside the Falcon 9’s second stage liquid oxygen (LOX) tank.

At Monday’s meeting, committee member Joe Cuzzapoli asked Stafford whether the committee had ever received a response to the December 2015 letter. Cuzzapoli has decades of experience designing and building rockets dating back to Apollo-Saturn and the space shuttle. Stafford said no, but that he

had phoned Gerstenmaier in August to ask about it and was told the

committee would receive another briefing in two months. As it turned

out, that conversation took place just days before the September 1

incident.

SpacePolicyOnline.com requested a copy of the letter immediately after the committee’s meeting on Monday. Today, NASA notified us that it has posted the letter on the agency’s Freedom of Information Act (FOIA) electronic library website.

In the interim, NASA provided a statement that it continues to evaluate SpaceX’s plans and has a “rigorous review process” to ensure commercial crew vehicles meet safety and technical requirements.

Stafford said at Monday’s meeting that he hopes the committee will receive a briefing on this matter at its December meeting in Houston.