with early 1970s technology forced design decisions that compromised operational reliability and safety. Reusable main engines were made a priority. This necessitated that they not burn up upon atmospheric reentry, which in turn made mounting them on the orbiter itself (the one part of the Shuttle system where reuse was paramount) a seemingly logical decision. However, this had the following consequences: a more expensive "clean sheet" engine design was needed, using more expensive materials, as opposed to existing and proven off-the-shelf alternatives (such as the Saturn V mains); increased ongoing maintenance costs related to keeping the reusable SSMEs in flying condition after each launch, costs which in total may have exceeded that of building disposable main engines for each launch. A concern expressed by the 1990 Augustine Commission was that "the civil space program is overly dependent upon the Space Shuttle for access to space." The committee pointed out, "that it was, for example, inappropriate in the case of Challenger to risk the lives of seven astronauts and nearly one-fourth of NASA's launch assets to place in orbit a communications satellite." There are some NASA spin-off technologies related to the Space Shuttle program which have been successfully developed into commercial products, such as using heat-resistant materials developed to protect the Shuttle on reentry in suits for municipal and aircraft rescue firefighters. See also Buran (spacecraft) Skylab 4 References External links When Physics, Economics, and Reality Collide: The Challenge of Cheap Orbital Access Review of ELV cost-to-orbit per pound Space Transportation Costs: Trends in Price Per Pound to Orbit Popular Science November 1974, "Reusable space shuttle" by Wernher von Braun Space Shuttle Crewed spacecraft Space Shuttle program Space Shuttle program