Single-stage-to-orbit - Comparison With The Shuttle

Comparison With The Shuttle

The high cost per launch of the Space Shuttle sparked interest throughout the 1980s in designing a cheaper successor vehicle. Several official design studies were done, but most were basically smaller versions of the existing Shuttle concept.

Most cost analysis studies of the Space Shuttle have shown that workforce is by far the single greatest expense. Early shuttle discussions speculated airliner-type operation, with a two-week turnaround. However, senior NASA planners envisioned no more than 10 to 12 flights per year for the entire shuttle fleet. The absolute maximum flights per year for the entire fleet was limited by external tank manufacturing capacity to 24 per year.

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.

Many in the aerospace community concluded that an entirely self-contained, reusable single-stage vehicle could solve these problems. The idea behind such a vehicle is to reduce the processing requirements from those of the Shuttle.