Criticism of the Space Shuttle program
Criticism of the Space Shuttle program stems from claims that NASA's Shuttle program has failed to achieve its promised cost and utility goals, as well as design, cost, management, and safety issues. More specifically, it has 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 $18,000 per kilogram (approximately $40000 per pound) to low Earth orbit (LEO). By comparison, Russian Proton expendable launchers, still largely based on the design that dates back to 1965, are said to cost as little as $110 million, or around $5,000/kg (approximately $11,000 per pound) to LEO. 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, was estimated to come out to $1.5 billion per launch, or $60,000/kg (approximately $130,000 per pound) to LEO. This should be contrasted with the originally envisioned costs of $118 per pound (approximately $53 per kilogram) of payload in 1972 dollars ($1,400/kg, [approximately $3086 per pound] adjusting for inflation to 2011).
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 more productive space science using 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.
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 Shuttle was originally billed as a space vehicle that would be able to launch once a week and give low launch costs through amortization. Development costs were expected to be recouped through frequent access to space. These claims were made in an effort to obtain budgetary funding from the United States Congress. Beginning in 1981, the space shuttle began to be used for space travel. However, by the mid-1980s the concept of flying that many shuttle missions proved unrealistic and scheduled launch expectations were reduced 50%. Following the Challenger accident in 1986, missions were halted pending safety review. This hiatus became lengthy and ultimately lasted almost three years as arguments over funding and the safety of the program continued. Eventually the military resumed the use of expendable launch vehicles instead. Missions were put on hold again after the loss of Columbia in 2003. Overall, 135 missions were launched during the 30 years after the first orbital flight of Columbia, averaging approximately one every 3 months.
Some reasons for the higher-than-expected operational costs are:
- The final design differs from the original concept, causing, among other things, the shuttle orbiter to be almost 20% over its specified weight - resulting in it being unable to boost the US Air Force's payloads into polar orbits.
- Maintenance of the thermal protection tiles is a very labor-intensive and costly process, with some 35,000 tiles needing to be inspected individually and with each tile specifically manufactured for one specific slot on the shuttle.
- The Space Shuttle Main Engines (SSMEs) were highly complex and maintenance-intensive, necessitating removal and extensive inspection after each flight. Before the "Block II" engines, the turbopumps (a primary engine component) had to be removed, disassembled, and totally overhauled after each flight.
- The toxic propellants used for the OMS/RCS thrusters required special handling, during which time no other activities could be performed in areas sharing the same ventilation system. This increased turn-around time.
- The launch rate was significantly lower than initially expected. While not reducing absolute operating costs, more launches per year gives a lower cost per launch. Some early hypothetical studies examined 55 launches per year (see above), but the maximum possible launch rate was limited to 24 per year based on manufacturing capacity of the Michoud facility that constructs the external tank. Early in shuttle development, the expected launch rate was about 12 per year. Launch rates reached a peak of 9 per year in 1985 but averaged fewer thereafter.
- When the decision was made on the main shuttle contractors in 1972, work was spread among companies to make the program more attractive to Congress, such as the contract for the Solid Rocket Boosters to Morton Thiokol in Utah. Over the course of the program, this raised operational costs, though the consolidation of the US aerospace industry in the 1990s means the majority of the Shuttle was now with one company: the United Space Alliance, a joint venture of Boeing and Lockheed Martin.
Cultural issues and problems 
For a successful technology, reality must take precedence over public relations, for nature cannot be fooled.
Some researchers have criticized a pervasive shift in NASA culture away from safety in order to ensure that launches took place in a timely fashion. Allegedly, NASA upper-level management embraced this decreased safety focus in the 1980s while some engineers remained wary. According to Vaughan, the aggressive launch schedules arose in the Reagan years as a way to rehabilitate America's post-Vietnam prestige.
The physicist Richard Feynman, who was appointed to the official inquiry on the Challenger disaster, estimated the risk to be "on the order of a percent" in his report, adding, "Official management, on the other hand, claims to believe the probability of failure is a thousand times less. One reason for this may be an attempt to assure the government of NASA perfection and success in order to ensure the supply of funds. The other may be that they sincerely believed it to be true, demonstrating an almost incredible lack of communication between themselves and their working engineers."
Despite Feynman's warnings, and despite the fact that Vaughan served on safety boards and committees at NASA, the subsequent press coverage has found some evidence that NASA's relative disregard for safety might persist to this day. For example, NASA discounted the risk from small foam chunk breakage at launch and assumed that the lack of damage from prior foam collisions suggested the future risk was low.
Shuttle operations 
The Shuttle was originally conceived to operate somewhat like an airliner. After landing, the orbiter would be checked out and start "mating" to the rest of the system (the ET and SRBs), and be ready for launch in as little as two weeks. Instead, this turnaround process usually takes months; Atlantis set the pre-Challenger record by launching twice within 54 days, while Columbia set the post-Challenger record of 88 days. Naturally, the Shuttle program's goal of returning its crew to Earth safely conflicts with the goal of a rapid and inexpensive payload launch. Furthermore, because in many cases there are no survivable abort modes, many pieces of hardware simply must function perfectly and so must be carefully inspected before each flight. The result is high labor cost, with around 25,000 workers in Shuttle operations and labor costs of about $1 billion per year.
Some shuttle features initially presented as important to Space Station support have proved superfluous:
- As the Russians demonstrated, capsules and unmanned supply rockets are sufficient to supply a space station.
- NASA's initial policy of using the Shuttle to launch all unmanned payloads declined in practice, and eventually was discontinued. Expendable Launch Vehicles (ELVs) proved much cheaper and more flexible.
- Following the Challenger disaster, use of the Shuttle to carry the powerful liquid fueled Centaur upper stages planned for interplanetary probes was ruled out for Shuttle safety reasons.
- The Shuttle's history of unexpected delays also makes it liable to miss narrow launch windows.
- Advances in technology over the last decade have made probes smaller and lighter. As a result, robotic probes and communications satellites can now use expendable launch vehicles, such as the Delta and Atlas V, which are less expensive and perceived to be more reliable than the Shuttle.
While the technical details of the Challenger and Columbia accidents are different, the organizational problems show similarities. In both cases events happened that were not planned for nor anticipated. Flight engineers' concerns about possible problems were not properly communicated to or understood by senior NASA managers. The vehicle gave ample warning beforehand of abnormal problems. A heavily layered, procedure-oriented bureaucratic structure inhibited necessary communication and action.
With Challenger, an O-ring that should not have eroded at all did erode on earlier shuttle launches. Yet managers felt that because it had previously eroded by no more than 30%, this was not a hazard as there was "a factor of three safety margin". Morton-Thiokol designed and manufactured the SRBs, and during a pre-launch conference call with NASA, Roger Boisjoly, the Thiokol engineer most experienced with the O-rings, pleaded with management repeatedly to cancel or reschedule the launch. He raised concerns that the unusually low temperatures would stiffen the O-rings, preventing a complete seal, which was exactly what happened on the fatal flight. However, Thiokol's senior managers overruled him, dismissing his safety concerns and allowed the launch to proceed. Challenger's O-rings eroded completely through as predicted, resulting in the complete destruction of the spacecraft and the loss of all seven astronauts on board.
Columbia was destroyed because of damaged thermal protection from foam debris that broke off from the external tank during ascent. The foam had not been designed or expected to break off, but had been observed in the past to do so without incident. The original shuttle operational specification said the orbiter thermal protection tiles were not designed to withstand any debris hits at all. Over time NASA managers gradually accepted more tile damage, similar to how O-ring damage was accepted. The Columbia Accident Investigation Board called this tendency the "normalization of deviance" — a gradual acceptance of events outside the design tolerances of the craft simply because they had not been catastrophic to date.
The subject of missing or damaged thermal tiles on the Shuttle fleet only became an issue following the loss of Columbia in 2003, as it broke up on re-entry. In fact, Shuttles had previously come back missing as many as 20 tiles without any problem. STS-1 and STS-41 had all flown with missing thermal tiles from the orbital maneuvering system pods (visible to the crew). This image from the NASA archives shows many missing tiles on the STS-1 OMS pods. The problem on Columbia was that the damage was sustained from a foam strike to the reinforced carbon-carbon leading edge panel of the wing, not the heat tiles. The first Shuttle mission, STS-1, had a protruding gap filler that diverted hot gas into the right wheel well on re-entry, resulting in a buckling of the right main landing gear door.
While the system was developed within the original cost and time estimates given to President Richard M. Nixon in 1971, the operational costs, flight rate, payload capacity, and reliability have been much worse than anticipated. A year before STS-1's April 1981 launch, The Washington Monthly accurately forecast many of the Shuttle's issues, including an overambitious launch schedule and the consequent higher-than-expected marginal cost per flight; the risks of depending on the Shuttle for all payloads, civilian and military; the lack of a survivable abort scenario if a Solid Rocket Booster were to fail; and the fragility of the Shuttle's thermal protection system.
In order to get the Shuttle approved, NASA over-promised its economies and utility. To justify its very large fixed operational program cost, NASA initially forced all domestic, internal, and Department of Defense payloads to the shuttle. When that proved impossible (after the Challenger disaster), NASA used the International Space Station (ISS) as a justification for the shuttle. Some speculate that, had NASA avoided the Shuttle program and instead continued to use Saturn and commercially available boosters, costs might have been lower, freeing funds for manned exploration and more unmanned space science. In particular, NASA administrator Michael D. Griffin argued in a 2007 paper that the Saturn program, if continued, could have provided six manned launches per year — two of them to the moon — at the same cost as the Shuttle program, with an additional ability to loft infrastructure for further missions:
If we had done all this, we would be on Mars today, not writing about it as a subject for “the next 50 years.” We would have decades of experience operating long-duration space systems in Earth orbit, and similar decades of experience in exploring and learning to utilize the Moon.
Some had argued that the shuttle program was flawed. Achieving a reusable vehicle with early 1970s technology forced design decisions that compromised operational reliability and safety. Reusable main engines were made a priority. This necessitated that they not burn up upon atmospheric reentry, which in turn made mounting them on the orbiter itself (the one part of the shuttle system where reuse was paramount) a seemingly logical decision. However, this had the following consequences:
- a more expensive 'clean sheet' engine design was needed, using more expensive materials, as opposed to existing and proven off-the-shelf alternatives (such as the Saturn V mains);
- increased ongoing maintenance costs related to keeping the reusable SSMEs in flying condition after each launch, costs which in total may have exceeded that of building disposable main engines for each launch;
- less absolute tonnage available to be lifted into space, since the mass of the SSMEs attached to the orbiter necessarily cut into the craft's 'payload budget' (more payload launched at any one time, by definition, reduces launch costs per pound).
A concern expressed by the 1990 Augustine Commission was that, "the civil space program is overly dependent upon the Space Shuttle for access to space." The committee pointed out, "that it was, for example, inappropriate in the case of Challenger to risk the lives of seven astronauts and nearly one-fourth of NASA's launch assets to place in orbit a communications satellite."
Designers look to more economical and reliable launch systems for the future, with lower maintenance and operational costs. One approach is Single Stage To Orbit (SSTO), which would be 100% reusable and use a single stage. NASA evaluated several concepts in the 1990s, and selected the X-33, which would eventually have been the VentureStar. During design that program increased in complexity and development cost, encountered problems and was finally cancelled.
A variant of SSTO is a hypersonic, scramjet-powered, airbreathing vehicle. This would be launched and landed horizontally like an airliner. It would achieve much of orbital velocity while still within the upper atmosphere. It was originally investigated by the U.S. Department of Defense, but passenger-carrying civilian versions were planned. The official name was the Rockwell X-30. Like the X-33, the X-30 development encountered major technical difficulties, primarily due to the system complexity and materials required for hypersonic flight, and was also canceled.
Another approach is lower-cost expendable launch vehicles. NASA currently uses commercial ELVs for unmanned launches, and could use commercial ELVs for future manned launches. This would fit with NASA's mandate to promote commercial access to and use of space. The Commercial Orbital Transportation Services program began in 2006 with the purpose of creating commercially operated unmanned cargo vehicles to service the ISS. The SpaceX Dragon became operational upon launching and docking with the ISS in May 2012. The Orbital Sciences' Cygnus is expected to become operational in 2012. The Commercial Crew Development (CCDev) program was initiated in 2010 with the purpose of creating commercially operated manned spacecraft capable of delivering at least four crew members to the ISS, to stay docked for 180 days and then return them back to Earth. These spacecraft are expected to become fully operational in the mid-2010s. In August 2012, NASA announced funding agreements with three firms, SpaceX, Boeing and Sierra Nevada Corporation, for development of crew delivery capability.
See also 
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