It failed in the goal of achieving reliable access to space, partly due to multi-year interruptions in launches following Shuttle failures. NASA budget pressures caused by the chronically high NASA Space Shuttle program costs have eliminated NASA manned space flight beyond low earth orbit since Apollo, and severely curtailed use of unmanned probes. NASA's promotion of and reliance on the Shuttle slowed domestic commercial expendable launch vehicle (ELV) programs until after the 1986 "Challenger" disaster.