10.1 PUBLIC SAFETY

¶Shortly after the breakup of Columbia over Texas, dramatic images of the Orbiterʼs debris surfaced: an intact spherical tank in an empty parking lot, an obliterated office rooftop, mangled metal along roadsides, charred chunks of material in fields. These images, combined with the large number of debris fragments that were recovered, compelled many to proclaim it was a "miracle" that no one on the ground had been hurt.1

¶The Columbia accident raises some important questions about public safety. What were the chances that the general public could have been hurt by a breakup of an Orbiter? How safe are Shuttle flights compared with those of conventional aircraft? How much public risk from space flight is acceptable? Who is responsible for public safety during space flight operations?

¶Public Risk from Columbiaʼs Breakup

¶The Board commissioned a study to determine if the lack of reported injuries on the ground was a predictable outcome or simply exceptionally good fortune (see Appendix D.16). The study extrapolated from an array of data, including census figures for the debris impact area, the Orbiterʼs last reported

¶position and velocity, the impact locations (latitude and longitude), and the total weight of all recovered debris, as well as the composition and dimensions of many debris pieces.2

¶Based on the best available evidence on Columbiaʼs disintegration and ground impact, the lack of serious injuries on the ground was the expected outcome for the location and time at which the breakup occurred.3

¶NASA and others have developed sophisticated computer tools to predict the trajectory and survivability of spacecraft debris during re-entry.4 Such tools have been used to assess the risk of serious injuries to the public due to spacecraft re-entry, including debris impacts from launch vehicle malfunctions.5 However, it is impossible to be certain about what fraction of Columbia survived to impact the ground. Some 38 percent of Columbiaʼs dry (empty) weight was recovered, but there is no way to determine how much still lies on the ground. Accounting for the inherent uncertainties associated with the amount of ground debris and the number of people outdoors,6 there was about a 9- to 24-percent chance of at least one person being seriously injured by the disintegration of the Orbiter.7

¶Debris fell on a relatively sparsely populated area of the United States, with an average of about 85 inhabitants per square mile. Orbiter re-entry flight paths often pass over much more populated areas, including major cities that average more than 1,000 inhabitants per square mile. For example, the STS-107 re-entry profile passed over Sacramento, California, and Albuquerque, New Mexico. The Board-sponsored study concluded that, given the unlikely event of a similar Orbiter breakup over a densely populated area such as Houston, the most likely outcome would be one or two ground casualties.

¶Space Flight Risk Compared to Aircraft Operations

¶A recent study of U.S. civil aviation accidents found that between 1964 and 1999, falling aircraft debris killed an average of eight people per year.8 In comparison, the National Center for Health Statistics reports that between 1992 and 1994, an average of 65 people in the United States were killed each year by lightning strikes. The aviation accident study revealed a decreasing trend in the annual number of "groundling" fatalities, so that an average of about four fatalities per year are predicted in the near future.9 The probability of a U.S. resident being killed by aircraft debris is now less than one in a million over a 70-year lifetime.10

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¶The history of U.S. space flight has a flawless public safety record. Since the 1950s, there have been hundreds of U.S. space launches without a single member of the public being injured. Comparisons between the risk to the public from space flight and aviation operations are limited by two factors: the absence of public injuries resulting from U.S. space flight operations, and the relatively small number of space flights (hundreds) compared to aircraft flights (billions).11 Nonetheless, it is unlikely that U.S. space flights will produce many, if any, public injuries in the coming years based on (1) the low number of space flight operations per year, (2) the flawless public safety record of past U.S. space launches, (3) government-adopted space flight safety standards,12 and (4) the risk assessment result that, even in the unlikely event of a similar Orbiter breakup over a major city, less than two ground casualties would be expected. In short, the risk posed to people on the ground by U.S. space flight operations is small compared to the risk from civil aircraft operations.

¶The government has sought to limit public risk from space flight to levels comparable to the risk produced by aircraft. U.S. space launch range commanders have agreed that the public should face no more than a one-in-a-million chance of fatality from launch vehicle and unmanned aircraft operations.13 This aligns with Federal Aviation Administration (FAA) regulations that individuals be exposed to no more than a one-in-a-million chance of serious injury due to commercial space launch and re-entry operations.14

¶NASA has not actively followed public risk acceptability standards used by other government agencies during past Orbiter re-entry operations. However, in the aftermath of the Columbia accident, the agency has attempted to adopt similar rules to protect the public. It has also developed computer tools to predict the survivability of spacecraft debris during re-entry. Such tools have been used to assess the risk of public casualties attributable to spacecraft re-entry, including debris impacts from commercial launch vehicle malfunctions.15

¶Responsibility for Public Safety

¶The Director of the Kennedy Space Center is responsible for the ground and flight safety of Kennedy Space Center people and property for all launches.16 The Air Force provides the Director with written notification of launch area risk estimates for Shuttle ascents. The Air Force routinely computes the risk that Shuttle ascents17 pose to people on and off Kennedy grounds from potential debris impacts, toxic exposures, and explosions.18

¶However, no equivalent collaboration exists between NASA and the Air Force for re-entry risk. FAA rules on commercial

¶space launch activities do not apply "where the Government is so substantially involved that it is effectively directing or controlling the launch." Based on the lack of a response, in tandem with NASAʼs public statements and informal replies to Board questions, the Board determined that NASA made no documented effort to assess public risk from Orbiter reentry operations prior to the Columbia accident. The Board believes that NASA should be legally responsible for public safety during all phases of Shuttle operations, including reentry.

¶Findings:

¶F10.1-1 The Columbia accident demonstrated that Orbiter

breakup during re-entry has the potential to cause casualties among the general public.

¶F10.1-2 Given the best information available to date,

a formal risk analysis sponsored by the Board found that the lack of general-public casualties from Columbiaʼs break-up was the expected outcome.

¶F10.1-3 The history of U.S. space flight has a flawless

public safety record. Since the 1950s, hundreds of space flights have occurred without a single public injury.

¶F10.1-4 The FAA and U.S. space launch ranges have safe-

ty standards designed to ensure that the general public is exposed to less than a one-in-a-million chance of serious injury from the operation of space launch vehicles and unmanned aircraft.

¶F10.1-5 NASA did not demonstrably follow public risk

acceptability standards during past Orbiter re-entries. NASA efforts are underway to define a national policy for the protection of public safety during all operations involving space launch vehicles.

¶Observations:

¶O10.1-1 NASA should develop and implement a public

risk acceptability policy for launch and re-entry of space vehicles and unmanned aircraft.

¶O10.1-2 NASA should develop and implement a plan to

mitigate the risk that Shuttle flights pose to the general public.

¶O10.1-3 NASA should study the debris recovered from

Columbia to facilitate realistic estimates of the risk to the public during Orbiter re-entry.