Criticism of the Space Shuttle program stemmed from claims that NASA's Space Shuttle program failed to achieve its promised cost and utility goals, as well as design, cost, management, and safety issues. Fundamentally, it failed in the goal of reducing the cost of space access. Space Shuttle incremental per-pound launch costs ultimately turned out to be considerably higher than those of expendable launchers. By 2011, the incremental cost per flight of the Space Shuttle was estimated at $450 million, or to low Earth orbit (LEO). In contrast, the comparable Proton launch vehicle is said to cost as little as $110 million, or around to LEO, despite not being reusable. When all design and maintenance costs are taken into account, the final cost of the Space Shuttle program, averaged over all missions and adjusted for inflation (2008), was estimated to come out to $1.5 billion per launch, or to LEO. This should be contrasted with the originally envisioned costs of of payload in 1972 dollars (approximately $ per pound adjusting for inflation to 2019). While the shuttle did serve a purpose servicing satellites and space stations in orbit, it failed at its original goal of achieving routine, reliable access to space, partly due to multi-year interruptions in launches following Shuttle failures. It was never as economical as expendable rockets for the task of launching satellites. NASA budget pressures partly caused by the chronically high NASA Space Shuttle program costs have eliminated NASA crewed space flight beyond low earth orbit since Apollo, and severely curtailed use of uncrewed probes. NASA's promotion of and reliance on the Shuttle slowed domestic commercial expendable launch vehicle (ELV) programs until after the 1986 Challenger disaster. Two out of the five spacecraft were destroyed in accidents, killing 14 astronauts, the largest loss of life in space flight. Purpose of the system The "Space Transportation System" (NASA's formal name for the overall Shuttle program) was created to transport crewmembers and payloads into low Earth orbits. It would afford the opportunity to conduct science experiments on board the shuttle to be used to study the effects of space flight on humans, animals and plants. Other experiments would study how things can be manufactured in space. The shuttle would also enable astronauts to launch satellites from the shuttle and even repair satellites already out in space. The Shuttle was also intended for research into the human response to zero-g. The