Today's spaceships are probably as safe as they can be, given the technology available. Every time a passenger boards an airplane, the chances of perishing during the flight are about one in 5 million. The risk levels are therefore relatively low. In the case of the Space Shuttle, however, nearly one in sixty flights has killed the entire crew. And yet the Shuttle is considered safe enough to operate, even though the statistical risk of a catastrophic failure is almost a hundred thousand times the level of a commercial airliner. But why are today's spaceships so much more dangerous than today's aircraft? The answer has to do with how they leave the ground (Fig. 2.6).

Fig. 2.6 Ballistic launch of Space Shuttle Columbia on April 12, 1981 (courtesy NASA)

Most spacecraft today, including the Space Shuttle, are launched as ballistic missiles, resulting in very high risk factors. This point is fundamental in understanding the huge difference in safety between rockets and airplanes. Because conventional spaceships are typically launched by nonreusable ballistic missiles, they have undergone far fewer test flights than airplanes, all of which have been through extensive flight test programs. Spaceflight is very difficult, presenting a much greater challenge than the relatively benign speeds and low altitudes of aerodynamic flight. Hence space launches have occurred far less often than flights of airplanes. Another factor exacerbating this situation is an immature market. Since 1957, the only customers for Earth's space launch industry have been a few hundred satellites and, of course, government space programs. Space tourism is about to change all that.

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