Page "Single-stage-to-orbit" Paragraph 81

Very efficient ( hence complex and sophisticated ) main engines were required to fit within the available vehicle space.

Likewise the only known suitable lightweight thermal protection was delicate, maintenance-intensive silica tiles.

These and other design decisions resulted in a vehicle that requires great maintenance after every mission.

The engines are removed and inspected, and prior to the new " block II " main engines, the turbopumps were removed, disassembled and rebuilt.

While Space Shuttle Atlantis was refurbished and relaunched in 53 days between missions STS-51-J and STS-61-B, generally months were required to repair an orbiter for a new mission.

Given that there were 25, 000 people working on Shuttle operations, the payroll alone was the Shuttle's single biggest operating cost.