How Safe Does a Rocket Have to Be?

SpaceX Falcon 9 Launch

The FAA determined that launches of the Falcon 9/Dragon are more dangerous than allowed under the law, but gave SpaceX a waiver to fly.

Rocket science, rocket artistry, momentum-altering sorcery. Whatever term you apply to it, launching large rockets is serious business with the capacity to do a lot of harm if things go awry. Concerns about launch vehicles and their spacecraft inadvertently falling from the sky and hurting people or property loomed large in the minds of men in the early days of spaceflight. Before the Space Shuttle first flew, international law established that countries are responsible for the damage caused by spacecraft launched from their nation, regardless of where the damage occurred or who launched it.

In order to regulate and monitor the space transportation industry and share the burden of this potential liability, commercial space launch companies must apply for and obtain launch licenses from the FAA. The FAA cannot permit a launch unless the total expected average number of casualties (Ec) for the launch and subsequent mission is less than .00003. In other words, the FAA cannot issue a launch permit through the traditional launch licensing process if there is a better than 30 in a million chance that people will be harmed by a commercial launch. The FAA has outlined the general methods for making Ec calculations, but sometimes launch vehicle operators and the FAA arrive at different Ec values.

An Ec analysis is a statistical calculation which quantifies the risk to the public from debris, blast hazards, and toxic materials from a proposed launch and mission. The FAA recommends combining deductive and inductive analyses of vehicle failure in order to calculate Ec and has provided guidance for calculating Ec. 14 CFR 417.107 prohibits the launch of an expendable launch vehicle if the total expected average number of casualties (Ec) for the launch exceeds 0.00003 (30 x 10-6 or 30 in a million) for risk from debris. It also prohibits a mission involving a reentry vehicle when the Ec for both the launch and the reentry together exceed .00003 for debris. Launch vehicle designers like SpaceX perform risk analyses during the design and testing process and arrive at an Ec value for their vehicles and flight profiles.

The FAA makes their own independent Ec calculation for missions and vehicles. As SpaceX President Gwynne Shotwell put it in an interview with Discovery News, “It’s not like [the government take] our word for what we tell them. They go do their own independent analysis.” Fortunately, the FAA may allow launches, like the upcoming Falcon 9 launch to the International Space Station, where the FAA calculates an Ec that is higher than .00003, if the FAA determines that waiving the Ec requirement will not jeopardize the public, jeopardize national security, and will be in the public interest.

For both the historic 2010 re-entry of the Dragon capsule and SpaceX’s upcoming trip to the ISS, the FAA has calculated an Ec for the missions of more than 30 x 10-6. For its 2010 mission, SpaceX initially calculated the mission Ec to be 21 x 10-6. The FAA, however, calculated an Ec of 47 x 10-6. SpaceX successfully petitioned the FAA for a waiver of the Ec requirement by pointing out some of the vehicle’s safety systems, including Dragon’s ability to monitor its safety-critical systems in real-time and successfully deorbit with the loss of two entire propulsion modules. The FAA approved the waiver application in part because doing so would encourage the growth of the commercial spaceflight industry and further the goals of the COTS program. By law, the FAA shall encourage commercial spaceflight activities. This waiver was issued November 30, 2010, less than two weeks before Dragon C1 flew.

According to the FAA, past Titan IV launches were 2-3 times as likely to cause harm from falling debris than COTS Demo Flight 2.

The FAA has determined that the upcoming COTS Demo Flight 2 has an Ec of between 98 and 121 x 10-6. On April 17, 2012, the FAA notified SpaceX that they will again waive the Ec requirement and allow the COTS Demo Flight 2 and the reentry of a Dragon capsule. In the notice of waiver, the FAA points out that the Air Force has previously approved a government launch of a Titan IV rocket where the risk ranged from 145 to 317 in a million. They also point out that debris risk from the Space Shuttle was routinely higher than the FAA’s current commercial launch requirements, in part because of the significant number of visitors present at the launches.

It is encouraging to see the FAA taking their directive to encourage commercial spaceflight activities seriously by relaxing potentially strenuous safety requirements. The current 30 in a million requirement was instituted before many of the newer entrants to the space transportation industry began operating. In light of SpaceX’s frequent requests to have this requirement relaxed and historic examples of it being waived, such as the previously mentioned Titan launch, perhaps the FAA should relax the base rule, in order to avoid the cost to both company and taxpayer of frequent waiver applications. What do you, dear readers, think?

Happy creating!

5 thoughts on “How Safe Does a Rocket Have to Be?

  1. The range uses a different, more relaxed number for Ec. FAA seems inclined to use the same number but has to go through too much work to do so.

  2. It appears that the rules are bent. It’s probably time to formulate an improved limit, an improved process or both..

  3. Andrews, YOu know your gigi knows little about what you do, but I like to see your pic and name!
    YOu go, gandson!! Love, gigi

  4. Nice post which They also point out that debris risk from the Space Shuttle was routinely higher than the FAA’s current commercial launch requirements, in part because of the significant number of visitors present at the launches. In which It is encouraging to see the FAA taking their directive to encourage commercial spaceflight activities seriously by relaxing potentially strenuous safety requirements. Thanks a lot for posting.

Comments are closed.