Expendable launch systems

An expendable launch system is a launch system that uses an expendable launch vehicle (ELV) to carry a payload into space. The vehicles used in expendable launch systems are designed to be used only once (i.e. they are "expended" during a single flight), and their components are not recovered for re-use after launch. The vehicle typically consists of several rocket stages, discarded one by one as the vehicle gains altitude and speed.

The ELV design differs from that of reusable launch systems, where the vehicle is launched and recovered more than once. Reuse might seem to make systems like the Space Shuttle more cost effective than ELVs, but in practice launches using ELVs have been less expensive than Shuttle launches. (See Space Shuttle Program and Criticism of the Space Shuttle program for discussion of Space Shuttle economics.) Most satellites are currently launched using expendable launchers; they are perceived as having a low risk of mission failure, a short time to launch and a relatively low cost.

Many orbital expendable launchers are derivatives of 1950s-era ballistic missiles. As such, cost was not a major consideration in their design. The largest of these is the Titan IV, the second costliest per-flight launch vehicle in history (following the Space Shuttle).

On the other hand, a reusable launcher requires stronger parts and additional parts, thus decreasing payload capacity. The Space Shuttle was a major national asset, used with great and expensive caution. Only five orbiters were built, and the loss of two (Challenger and Columbia) cause great concern and an extended hiatus in Shuttle flights. Expendable launch failures usually caused a much shorter pause, each of which impacted only that model of launcher.

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