Criticism of the Space Shuttle program

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The primary criticisms of the Space Shuttle program are:

• It failed in the goal of greatly reducing the cost of space access (it did not become a 'Space Truck'). Space shuttle incremental per-pound launch costs are not appreciably cheaper than that of expendable launchers.^[1]
• 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.
• The mundane shuttle flights have failed to inspire, excite, or motivate the American public as the previous Mercury, Gemini, and Apollo projects did.

Contents 1 Purpose of the system 2 Design issues 3 Costs 4 Cultural issues and problems 5 Shuttle operations 6 Accidents 7 Looking back 8 Looking ahead 9 References 10 External links

[edit] Purpose of the system

The Shuttle was originally intended to launch once a week and give low launch costs through amortization.^{[citation needed]} Instead it launches 4-6 times per year, and is very expensive. It was also intended for launching satellites, particularly military ones. However, after Challenger, the military began using expendable launch vehicles instead.^[2]

The Shuttle was also intended for research, for example into human response to zero gravity. However the research could have been done on cheaper expendable vehicles, as the Soviets had done.^[2]

[edit] Design issues

All systems as complex as the Space Shuttle inevitably have design issues:

• Positioning of the orbiter on the side of the launch stack - instead of atop it as on all other U.S. multi-stage launch systems - leaves it, the astronauts, and the payload vulnerable to certain in-launch failures and events. For example, the orbiter's heat shield is currently exposed to damage by foam, ice, or other debris falling off the external tank.
• With the orbiter exposed on the side of the fuel tank during launch, the decision to use ceramic tiles as the primary heat shield could appear questionable, as such tiles are fragile, expensive, and time-consuming to replace. However, metallic shielding similar to that developed during the Dyna-Soar program was examined extensively during shuttle development, but would have been too heavy.[1]
• The original O-ring/joint on the SRB was inadequately designed; this in combination with the low ambient temperatures at the time of its final launch led to the loss of Challenger.
• Designers originally contemplated that in the event of a problem, SRB thrust could be terminated. However, later study showed the resultant thrust termination forces would have either destroyed the vehicle or entailed a prohibitive weight penalty for structural reinforcement.
• The Space Shuttle Main Engines SSMEs, while powerful and reusable, are also very maintenance-intensive. An extensive inspection is required after every launch to ensure their operational condition.
• The first iteration of the SSMEs did not use hydrostatic bearings, adding to the maintenance issues.
• Unlike the more conventional capsule approach employed by the Saturn V and Soyuz, the Shuttle lacks independent and immediate crew escape facilities prior to and during much of the initial launch.

[edit] Costs

Some reasons for the higher-than-expected operational costs are:

• The final design differs from the original concept^{[citation needed]}
• Maintenance of thermal protection tiles turned out to be very labor-intensive, averaging about a week's work for one person to replace a tile, with hundreds damaged with each launch.^{[citation needed]}
• The Space Shuttle main engines were highly complex and maintenance-intensive, necessitating removal and extensive inspection after each flight. Before the current "Block II" engines, the turbopumps (a primary engine component) had to be removed, disassembled, and totally overhauled after each flight.^{[citation needed]}
• The launch rate has been significantly lower than initially expected. While this does not reduce actual 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.^[3] Launch rates reached a peak of 9 per year in 1985 but averaged fewer thereafter.
• During the 1970s, the U.S. suffered from high inflation. Between when the program began in 1972 and first flight in April 1981, inflation increased prices over 200%. When evaluating shuttle development costs in later-year dollars, this gives rise to a superficial large cost overrun in the program. In fact, discounting inflation, the shuttle development program was within the initial cost estimate given to President Richard M. Nixon in 1971.^[3]
• 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 and the Senate, 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 is now with one company: Boeing.

[edit] Cultural issues and problems

Some researchers have identified a cultural issue in the design and maintenance of the Space Shuttle in particular and in overall NASA operations in general. Anthropologist Diane Vaughan ("The Challenger Launch Decision: Risky Technology, Culture and Deviance at NASA", University of Chicago press, 1997) examined in detail the engineering and managerial processes used in launching the shuttle.

She found recommendations such as "think like a manager and not an engineer", aired at a videoconference before the 1986 launch of Challenger, a "normalized deviance", which can be best described as a decrease of resources and emphasis given to safety at the expense of ontime launches. Safety-oriented values in the 1980s started to decrease, with full buy-in from NASA upper level managers but some resistance from engineers, relative to their values in the first decade of the Shuttle.

In addition, the late physicist Richard Feynman, appointed to the official inquiry on Challenger, published a personal statement as an appendix to the official report in which Feynman said that in some ways, NASA was trying to repeal the laws of nature in its aggressive launch schedules. [2]

Aggressive launch schedules, according to Vaughan, started in the Reagan years as attention turned to the space program in general and the Shuttle in particular (as America's only manned spaceflight after the final Apollo missions), not so much for scientific reasons but instead as a way to enhance America's prestige post-Vietnam.

Despite Feynman's warnings, and despite the fact that Vaughan served on safety boards and committees at NASA, follow-ups in the general and technical press have found that the NASA culture, described charitably as aggressive, comparatively as smaller concern for safety over ontime launches, and uncharitably as normalized deviance, persists to this day. Evidence for these claims exists in the disregard of small foam chunk breakage and assumptions that the lack of damage from past breakages made a larger and more serious incident less probable.

[edit] 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; Columbia was once launched twice within 56 days. Because loss of crew is unacceptable, the primary focus of the Shuttle program is to return the crew to Earth safely, which can conflict with other goals, namely to launch payloads cheaply. 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.^{[citation needed]}

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.^{[citation needed]}
• 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.^{[citation needed]} 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.

[edit] Accidents

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. In both cases, engineers were greatly concerned about possible problems but these concerns 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. A mindset developed among senior managers that concerns had to be objectively proven rather than simply suspected.^{[citation needed]}

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 not previously eroded by 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, 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 cold 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 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 designed to withstand virtually no 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.^[4]

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 to the reinforced carbon-carbon leading edge panel of the wing, not the heat tiles. On the same subject, a little-publicized detail about the first Shuttle mission, STS-1, was that it had a protruding gap filler that ducted hot gas into the right wheel well on re-entry, resulting in a buckling of the right main landing gear. ^[5]

[edit] Looking back

The neutrality of this section is disputed. Please see the discussion on the talk page.(December 2007) Please do not remove this message until the dispute is resolved.

Opinions differ on the lessons of the Shuttle. While it was developed within the original cost and time estimates given to President Richard M. Nixon in 1971 [3], the operational costs, flight rate, payload capacity, and reliability have been much worse than anticipated. In order to get the Shuttle approved, NASA over-promised its economies and utility. To justify its very large fixed operational program cost, NASA first forced all domestic, internal, and DOD payloads to the shuttle. When that proved impossible (after the Challenger disaster), NASA used the space station 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. The domestic commercial booster industry could have been stimulated, with more resources directed towards lowering the cost of space access.

It can be argued that the general concept of a reusable manned launch vehicle was good, but the shuttle's implementation was flawed. To achieve a reusable vehicle with early 1970s technology entailed several design decisions that compromised operational reliability and safety. For example, an early point in the design phase, reusable main engines became 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), and
• having the orbiter mounted on the side of the launch stack makes it more vulnerable to debris shed from the external tank and solid rocket boosters. In the Columbia disaster, the vehicle and crew were lost because of shed debris damaging the orbiter heat shield.

Some maintain that the Shuttle program advanced the State of the Art, while others say the shuttle program only made incremental advances and pushed the early 1970s technology excessively to build a new capability. Some argue the high costs of the Shuttle program caused the cancellation of worthy manned (X-38, DC-X, X-33, X-34, etc.) and unmanned programs. The shuttle program also caused all other US boosters (ELVs) to be discontinued until the Challenger accident, thereby costing the US initiative in ELV technology.

[edit] Looking ahead

Future designers look to more economical and reliable launch systems 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 canceled.

Another 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, sometimes called the "New Orient Express". The official name was the Rockwell X-30. Like the X-33, the X-30 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. However, NASA plans on rejecting the low-cost commercially available boosters, and instead, designing their own similar but competing boosters using modified shuttle components to build an expendable Shuttle-Derived Launch Vehicle. This technology would be used to develop two separate launchers, one for manned missions and the other for unmanned heavy cargo. This contrasts with the current shuttle where astronauts and heavy cargo are launched in a single vehicle. Unlike the shuttle, this future launcher and associated crew exploration vehicle will have a launch escape system to greatly improve the chances that the crew can be saved in the event of a disaster.

The proposed CEV and CaLV bear a strong resemblance to the Saturn I & V rockets respectively - even to the point of the proposed launchers being numbered in honor of their predecessors: Ares I & V. In terms of flight profile, hardware design concept, and mission capabilities, there is actually little to choose between Ares and Saturn - though the proposed CEV is larger than the Apollo CM. Some critics have seized upon this as a serious indictment of the shuttle program. They argue that if a Saturn-type mission architecture is technically and economically viable for missions currently performed by the shuttle, then the Saturn launchers should never have been abandoned in the first place, and that the shuttle has been a massive waste of time and money.

The reversion of NASA to the capsule/booster technology of Ares/CEV/CaLV must be viewed as a clear rejection of the shuttle concept. Burt Rutan of Scaled Composites, the company that successfully designed, built, and flew the world's only privately-funded reusable spaceplane, SpaceShipOne, has had harsh words for NASA’s Shuttle and CEV programs. Likening the agency's new Moon-shot efforts to "archeology", Rutan contends that the space program must encourage some risk in technological development in order to continue to innovate. He says of NASA's current strategy:

• "They are forcing the [Ares/CEV] program to be done with technology that we already know works. They are not creating an environment where it is possible to have a breakthrough ... It doesn’t make sense." [4]

This echoes other arguments that NASA should utilize commercially available (Off the shelf) boosters where possible, and concentrate on space exploration, space science, and research and development to reduce the cost of space access. These arguments assume that the Shuttle program has run its course, and needs to be retired to make way for a new generation of cost effective and efficient vehicles. Of course, Rutan also boasted after the first successful flight of SpaceShipOne that it must intimidate NASA,[5] so his statements concerning the Shuttle may not be entirely disinterested.

Many feel that the decision by NASA to spurn commercially-available Delta IV and Atlas V boosters, and instead design and develop their own versions, is unwise. They think government should use commercially-available products where available, rather than develop their own, and thereby reduce the cost of access to space. (In fact, the Orion capsule is being developed with off-the-shelf technology, but not the boosters for it.) Many feel that NASA should instead promote private enterprise, and devote national resources to meaningful technology advancements rather than replicating existing ELVs.

[edit] References

[edit] External links

• When Physics, Economics, and Reality Collide: The Challenge of Cheap Orbital Access
• Review of ELV cost-to-orbit per pound
• Space Transportation Costs: Trends in Price Per Pound to Orbit