A different kind of spacecraft

The Space Shuttle program was approved in 1972 with the aim of providing reusable transportation to low Earth orbit. Its winged orbiter combined a crew cabin, a large payload bay and engines. It could carry equipment into orbit and return substantial cargo, creating opportunities different from a small returning capsule.

The design also had to satisfy competing demands involving payload, crew, launch performance and operations. A capability is therefore not a promise of effortless service. Carrying wings and return equipment had consequences for the rest of the vehicle and its support infrastructure.

At launch, the system joined an orbiter, an external tank and two solid rocket boosters. The orbiter’s three main engines used liquid hydrogen and oxygen from the external tank. The boosters supplied additional thrust, separated and were recovered for refurbishment. The external tank was discarded rather than recovered for reuse.

“Reusable” described major parts of the system, not every item launched. A clear diagram should distinguish recovered hardware from expendable hardware. It should also distinguish an engine from the tank supplying its propellants; the large tank was not a fourth main engine.

Enterprise performed atmospheric approach-and-landing tests but never flew in orbit. Columbia carried John Young and Robert Crippen on STS-1 in April 1981, the first orbital Shuttle flight. An atmospheric test and an orbital test exposed the vehicle to different environments.

Imagine qualifying a reusable vehicle using only runway landings. That would leave ascent loads, orbital operations and entry heating untested. Good development divides a large claim into experiments while recognizing which combined conditions still need a flight demonstration.