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Space Shuttle Atlantis welcome home ceremony after last mission
Space Shuttle Atlantis begins the last mission of the Space Shuttle program.
Space Shuttle Atlantis touches down for the final time, July 21, 2011, at the end of STS-135.
Empty status board in the Vehicle Assembly Building

The retirement of NASA's Space Shuttle fleet took place from March to July 2011. Discovery was the first of the three active Space Shuttles to be retired, completing its final mission on March 9, 2011; Endeavour did so on June 1. The final shuttle mission was completed with the landing of Atlantis on July 21, 2011, closing the 30-year Space Shuttle program.

The Shuttle was presented to the public in 1972 as a "space truck" which would, among other things, be used to build a United States space station in low Earth orbit in the early 1990s and then be replaced by a new vehicle.[1][2] When the concept of the U.S. space station evolved into that of the International Space Station, which suffered from long delays and design changes before it could be completed, the service life of the Space Shuttle fleet was extended several times until 2011 when it was finally retired.

After the Columbia loss in 2003, the Columbia Accident Investigation Board report showed that the Space Transportation System (STS) was risky and unsafe. In 2004, President George W. Bush announced (along with the VSE policy) that the Shuttles would be retired in 2010 (after completing the ISS assembly).

In/by 2010 the Shuttle was formally scheduled for retirement with Atlantis being taken out of service first after STS-132 in May of that year, but the program was once again extended when the two final planned missions were delayed until 2011.[3] Later, one additional mission was added for Atlantis for July 2011, extending the program further. Counter-proposals to the shuttle's retirement were considered by Congress[4] and the prime contractor United Space Alliance as late as Spring 2010.[5]

Hardware developed for the Space Shuttle met various ends with conclusion of the program, including donation, disuse and/or disposal, or reuse. An example of reuse is that one of the three Multi-Purpose Logistics Module (MPLM) was converted to a permanent module for the International Space Station.[6]

Fate of surviving STS program hardware

[edit]

Space Shuttle Orbiters

[edit]

More than twenty organizations submitted proposals for the display of an orbiter in their museums.[7][8] On April 12, 2011, NASA announced that the 4 remaining Space Shuttle orbiters will be displayed permanently at these locations:[9][10][11]

Shuttle
Name 		Shuttle
Designation 		Retirement Destination
Enterprise* OV-101 Intrepid Museum

New York City, New York

Discovery OV-103 Steven F. Udvar-Hazy Center

Chantilly, Virginia

Atlantis OV-104 Kennedy Space Center Visitor Complex

Merritt Island, Florida

Endeavour OV-105 California Science Center

Los Angeles, California

*Prior to its move to Intrepid Museum, Enterprise was originally displayed in the Steven F. Udvar-Hazy Center, from 2003 to 2011.

Space Shuttle Atlantis towed back to the Orbiter Processing Facility for the last time at the end of the Shuttle program

Museums and other facilities not selected to receive an orbiter were disappointed. Elected officials representing Houston, Texas, location of the Johnson Space Center; and Dayton, Ohio, location of the National Museum of the United States Air Force, called for Congressional investigations into the selection process, though no such action was taken.[12] While local and Congressional politicians in Texas questioned if partisan politics played a role in the selection, former JSC Director Wayne Hale wrote, "Houston didn't get an orbiter because Houston didn't deserve it", pointing to weak support from area politicians, media and residents, describing a "sense of entitlement".[13][14]

Chicago media questioned the decision not to include the Adler Planetarium in the list of facilities receiving orbiters, pointing to Chicago's 3rd-largest population in the United States. The chair of the NASA committee that made the selections pointed to the guidance from Congress that the orbiters go to facilities where the most people could see them, and the ties to the space program of Southern California (home to Edwards Air Force Base, where nearly half of shuttle flights have ended and home to the plants which manufactured the orbiters and the RS-25 engines), the Smithsonian (curator of the nation's air and space artifacts), the Kennedy Space Center Visitor Complex (where all Shuttle launches originated, and a large tourist draw) and the Intrepid Museum (Intrepid also served as a recovery ship for Project Mercury and Project Gemini).[15] The Adler Planetarium was awarded the Fixed Base Shuttle Mission Simulator, however it remained in storage off-display at the planetarium until 2016, when it was transferred to the Stafford Air and Space Museum in Weatherford, Oklahoma.[16]

In August 2011 the NASA Inspector General released an audit of the display selection process; it highlighted issues which led to the final decision. The Museum of Flight in Seattle, Washington, March Field Air Museum, Riverside, California, Evergreen Aviation and Space Museum, McMinnville, Oregon, National Museum of the U.S. Air Force, Dayton, Ohio, San Diego Air and Space Museum, San Diego, Space Center Houston, Houston, Texas, Tulsa Air and Space Museum & Planetarium, Tulsa, Oklahoma and U.S. Space and Rocket Center, Huntsville, Alabama scored poorly on international access. Additionally, Brazos Valley Museum of Natural History and the Bush Library at Texas A&M, in College Station, Texas scored poorly on museum attendance, regional population and was the only facility found to pose a significant risk in transporting an orbiter there. Overall, the California Science Center scored first and Brazos Valley Museum of Natural History scored last. The two most controversial locations which were not awarded an orbiter, Space Center Houston and National Museum of the U.S. Air Force, finished 2nd to last and near the middle of the list respectively. The report noted a scoring error, which if corrected would have placed the National Museum of the U.S. Air Force in a tie with the Intrepid Museum and Kennedy Visitor Complex (just below the California Science Center), although due to funding concerns the same decisions would have been made.[17]

The Museum of Flight in Seattle, Washington was not selected to receive an orbiter but instead received the three–story Full Fuselage Trainer from the Space Vehicle Mockup Facility at Johnson Space Center in Houston, Texas.[18] Museum officials, though disappointed, were able to allow the public to go inside the trainer, something not possible with an actual orbiter.[19]

Space Shuttle Discovery on display at the Udvar-Hazy Center for restorations

In addition to the challenge of transporting the large vehicles to the display site, placing the units on permanent display required considerable effort and cost. An article in the February 2012 issue of Smithsonian magazine discussed the work performed on Discovery. It involved removing the three main engines (they were slated to be reused on NASA's Space Launch System); the windows were given to project engineers for analysis of how materials and systems fared after repeated space exposure; the communications modules were removed due to national–security concerns; and hazardous materials such as traces of propellants were thoroughly flushed from the plumbing. The total cost of preparation and delivery via a modified Boeing 747 was estimated at $26.5 million in 2011 dollars.[20]

Payload hardware

[edit]
  • Spacelab Pallet Elvis – handed over to the Swiss Museum of Transport, Switzerland, in March 2010.[21]
  • One of the two Spacelabs—on display at Bremen Airport, Germany.[21]
  • Another Spacelab is on display at the Udvar-Hazy center behind Discovery
  • MPLM Leonardo: converted to the ISS Permanent Multipurpose Module, currently on-orbit[6]
  • MPLM Raffaello: removed from the bay of Atlantis, stored at KSC, transferred in 2023 to Axiom Space for reuse.
  • MPLM Donatello: the unused MPLM, some parts were cannibalized for Leonardo. The remainder is mothballed in the ISS processing facility at KSC.
  • Various space pallets used since STS-1: the fates of these objects range from space center storage to scrap to museum pieces

Tiles

[edit]

NASA ran a program to donate thermal protection system tiles to schools and universities for US$23.40 each (the fee for shipping and handling). About 7000 tiles were available on a first-come, first-served basis, but limited to one per institution.[22] Each orbiter incorporated over 21,000 tiles.[23]

RS-25

[edit]
Six rocket engines, consisting of a large bell-shaped nozzle with working parts mounted to the top, stored in a large warehouse with white walls decorated with flags. Each engine has several pieces of red protective equipment attached to it and is mounted on a yellow wheeled pallet-like structure.
6 RS-25Ds engines used during STS-134 and STS-135 in storage at Kennedy Space Center

About 42 reusable RS-25 engines have been part of the STS program, with three used per orbiter per mission.[24] NASA decided to retain sixteen engines with plans to make use of them on the Space Launch System, where they will be expended. The first flight of the Space Launch System took place in 2022. The remaining engines were donated to the Kennedy Space Center Visitor Complex, Johnson Space Center Space Center Houston, the National Air and Space Museum, and other exhibits around the country.

RS-25 nozzles

[edit]

Worn out engine nozzles are typically considered scrap, although nine nozzles were refurbished for display on the donated orbiters, so the actual engines can be retained by NASA.[25]

Canadarm (SRMS) and OBSS

[edit]
Boom in use on STS-120

Three Shuttle arms were used by NASA; the arms of both Discovery and Atlantis will be left in place for their museum display. Endeavour's arm is to be removed from the orbiter for separate display in Canada.[26] The OBSS extension of Endeavour's arm was left on the International Space Station, for use with the station's robotic arm.[26]

Information technology

[edit]

In December 2010, as NASA prepared for the STS program ending, an audit by the NASA Office of Inspector General (OIG) found that information technology had been sold or prepared for sale that still contained sensitive information. NASA OIG recommended NASA be more careful in the future.[27]

Other shuttle hardware

[edit]
Atlantis about 30 minutes after final touchdown
Feed through connector for the main tank: one of many thousands of Shuttle parts
Each Shuttle tile had a specific location on an orbiter and was numbered (in yellow on this tile)

KSC Launch Complex 39

[edit]
Main article: Kennedy Space Center Launch Complex 39

The twin pads originally built for the Apollo program were deactivated. LC-39B was deactivated first on January 1, 2007. Three lightning towers were added to the pad and it was temporarily "re-activated" in April 2009 when Endeavour was placed on standby to rescue the STS-125 crew (the STS-125 mission was the last to visit the Hubble Space Telescope, which meant that the ISS was out of range) if needed; Endeavour was then moved over to LC-39A for STS-126. In October 2009 the prototype Ares I-X rocket was launched from 39B. The pad was then permanently deactivated and has since been dismantled and has been modified for the Space Launch System program, and possibly other launch vehicles. Like the Apollo structures before them, the shuttle structures were scrapped. The first launch from 39B since Ares I-X was Artemis 1 on November 16th 2022, being the first lunar bound launch from the pad since Apollo 10. 39A was deactivated in July 2011 after STS-135 was launched.

By 2012, NASA came to the conclusion that it would incur material cost to maintain LC-39A even in an inactive state and decided to seek interest of others to lease the pad for their use. NASA solicited and SpaceX won the competition for use of LC-39A.[28] Blue Origin protested the decision to the General Accounting Office (GAO) generating uncertainty of the intent of NASA in the event that a commercial user or users could not be acquired.[29] On January 16, 2013, one or more news outlets erroneously reported that NASA planned to abandon the pad; NASA was quick to clarify and identify that the actual plan was to, like pad B, convert it for other rockets without dismantling it.[30] If NASA did plan to permanently decommission the pads, they would have to restore them to their original Apollo-era appearance, as both pads are on the National Historic Register.[31]

SpaceX has since converted the pad to launch Falcon Heavy and crewed Crew Dragon Falcon 9 flights. Following the destruction of Space Launch Complex 40 in an on-pad explosion in September 2016, SpaceX had to move all east coast launches to 39A while SLC-40 was being rebuilt. The first launch, Dragon resupply vehicle carried by a Falcon 9, occurred February 12, 2017.[32][33] This flight was the first uncrewed launch from Complex 39 since Skylab was launched in 1973. Once SLC-40 was reactivated, SpaceX finished modifying the pad for Falcon Heavy. Due to SLC-40s destruction, 39A had to be rushed into service, and activities such as dismantling the RSS were put on hold. For the first few missions from 39A, even after SLC-40 was reactivated, SpaceX dismantled the RSS between launches and added black cladding to the fixed service structure.

Vehicle Assembly Building

[edit]
Main article: Vehicle Assembly Building

After STS-135, the VAB was used as a storage shed for the decommissioned shuttles before they were sent to museums. NASA awarded a contract in March 2014 for design and build/delivery of VAB High Bay 3 modifications to support the SLS program. In February 2017, the contractor team completed platform installation to enable SLS stacking.[34][35] SLS/Artemis 1 mission processed through VAB Bay 3 prior to its launch in November 2022.[36] Other VAB bays, such as High Bay 2, are being made available by NASA for other programs.[35]

Mobile Launcher Platform

[edit]
Main article: Mobile launcher platform

Three mobile launcher platforms used to support the Space Shuttle will be used for commercial launch vehicles.

The Mobile Launcher Platform-1 (MLP-1) was used for 62 Shuttle launches, starting in 1981. It was the most used of the three MLPs.

The Ares I-X suborbital mission utilized the MLP-1 to support the stacking and launch operations. The canceled Ares I-Y would have used the same MLP.[37][38] Following the STS-135, usable parts from MLP-1 were removed and stored in the Vehicle Assembly Building, with no plans to use the MLP again.[39] Eventually the MLP was weighed down with concrete blocks and used for conditioning the crawlerway for SLS as of September 2021.

Mobile Launcher Platform-2 (MLP-2) was used for 44 Shuttle launches, starting in 1983. All of the orbiters except Columbia made their maiden flights from MLP-2. It was also the launch site for the ill-fated STS-51L mission, when Space Shuttle Challenger disintegrated shortly after launch, killing all seven crew members.[40] in January 2021 MLP-2 was scrapped, as with 2 more MLPs for SLS under construction, NASA was running out of places to store the launch platforms.[41]

Mobile Launcher Platform-3 (MLP-3) was used for 29 Shuttle launches, starting in 1990. It was the least used of the three MLPs.

The MLP-3 was acquired by Orbital ATK (who was later bought out by Northrop Grumman) to launch their future OmegA rocket. They planned to use the Vehicle Assembly Building High Bay 2 to assemble the rocket, and crawler-transporter 1 to move the rocket to LC-39B for launch. Unfortunately, due to a lack of Federal Funds, Omega was cancelled in September 2020, leaving MLP-3 without a tenant.[42]

Crawler-Transporter

[edit]
Main article: Crawler-transporter

The Crawler-Transporters were used as the mobile part of the pad with the Shuttles; the two vehicles were deactivated and are being upgraded for the Space Launch System. The crawlerways used for transporting launch vehicles from the VAB to the twin pads of KSC are also being extensively renovated for the Artemis program.[43]

Shuttle Carrier Aircraft

[edit]
Main article: Shuttle Carrier Aircraft

Two modified Boeing 747s were used to fly the shuttles back to KSC when they landed at Edwards AFB. N911NA was retired on February 8, 2012, and became a parts hulk for the former Stratospheric Observatory for Infrared Astronomy. Beginning in September 2014, N911NA was loaned out to the Joe Davies Heritage Airpark, in Palmdale, California, where it is on outdoor display next to a B-52. The other aircraft, N905NA was used to send Discovery, Endeavour and Enterprise to their museums and in September 2012 was found to have few parts for SOFIA. It is currently a museum piece at the Johnson Space Center, displayed carrying a full-scale replica of an orbiter.[44]

NASA recovery ships

[edit]

Used to retrieve the SRBs, MV Liberty Star and Freedom Star are now separated. Liberty Star was renamed as TV Kings Pointer and was transferred to the Merchant Marine Academy in New York for use as a training vessel.[45] It will remain on call in case NASA needs it for further missions. Freedom Star was transferred to the James River Reserve Fleet on September 28, 2012, and placed under ownership of the U.S. Maritime Administration (MARAD).[46] In November 2016, MV Freedom Star was re-purposed as a training vessel to the Paul Hall Center for Maritime Training and Education, on loan from MARAD.[47]

Orbiter Processing Facility

[edit]
Main article: Orbiter Processing Facility

The buildings used to process the shuttles after each mission were decommissioned. OPF-1 was leased to Boeing in January 2014 for processing the X-37B spaceplane.[48] Once the agreement for use was signed between NASA and the U.S. Air Force and made public, use of both OPF-1 and OPF-2 for X-37B was confirmed.[49] OPF-3 was leased as well to Boeing for 15 years to use in the manufacture and test of the CST-100 spacecraft.[50]

Shuttle Landing Facility

[edit]
Main article: Shuttle Landing Facility

The runway at KSC is evolving as a Launch and Landing Facility (LLF) to support multiple users including a group of F-104 aircraft, use by launch providers for delivery of rocket stages by aircraft, availability for spaceflight horizontal launch and landing, and for other uses supporting both Kennedy Space Center and adjacent Cape Canaveral Space Force Station.[51] It is used to land the X-37B and will be for Sierra Nevada Dream Chaser spaceplanes. The LLF received its first landing from space since Atlantis when the USAF X-37B landed on it at the end of almost two years in orbit in June 2017.[52]

Former planned Space Shuttle successors

[edit]

There were a number of proposals for space access systems in the 1970s also, such as the Rockwell Star-raker.[53] Star-raker was a large single-stage to orbit (SSTO) design that used both rockets and ramjet for propulsion.[53] It was a contemporary to the Boeing Reusable Aerodynamic Space Vehicle, which was an all-rocket propulsion SSTO design.[54]

Some programs from the early 1980s were the Future Space Transportation System program and the later NASA Advanced Manned Launch System program.[55][56]

In the late 1980s, a planned successor to STS was called "Shuttle II", which encompassed a number of different ideas including smaller tanks over the wings and a detachable crew cabin for emergencies, and was influenced by the Challenger disaster.[57] At one point before retirement, extension of the Space Shuttle program for an additional five years, while a replacement could be developed, was considered by the U.S. government.[4] Some programs proposed to provide access to space after the shuttle were the Lockheed Martin X-33, VentureStar, the Orbital Space Plane Program, and Ares I launcher.

For comparison to an earlier retirement, when the Saturn IB was last flown in 1975 for the Apollo-Soyuz Test Project, the Shuttle development program was already well underway. However, the Shuttle did not fly until 1981, which left a six-year gap in U.S. human spaceflight. Because of this and other reasons, in particular, higher than expected Solar activity that caused Skylab's orbit to decay faster than hoped, the U.S. space station Skylab burned up in the atmosphere.[58]

The Ares I was going to be NASA's crewed spacecraft after STS, with Congress attempting to accelerate its development so it would be ready as early as 2016 for the ISS, in addition they attempted to delay retirement of the shuttle to reduce the time gap.[59] However, Ares I was cancelled along with the rest of Constellation in 2010.[60] The successor to the Space Shuttle after the cancellation would be commercial crew spacecraft, such as the Dragon 2 from SpaceX which first launched crew on May 30, 2020, as the SpaceX Demo-2 mission,[61] and the Starliner from Boeing which first launched crew on June 5, 2024, as the Boeing CFT mission, while NASA's flagship in-house crewed missions will be aboard Orion on the SLS.

Constellation Program

[edit]
Main article: Constellation program
Artist's rendition of the docking of Orion (at right) to the ISS.

Following the Space Shuttle Columbia disaster, in early 2003 President George W. Bush, announced his Vision for Space Exploration which called for the completion of the American portion of the International Space Station by 2010 (due to delays this would not happen until 2011), the retirement of the Space Shuttle fleet following its completion, to return to the Moon by 2020 and one day to Mars.[62] A new vehicle would need to be developed, it eventually was named the Orion spacecraft, a six-person variant would have serviced the ISS and a four-person variant would have traveled to the Moon. The Ares I would have launched Orion, and the Ares V heavy-lift vehicle (HLV) would have launched all other hardware. The Altair lunar lander would have landed crew and cargo onto the Moon. The Constellation program experienced many cost overruns and schedule delays, and was openly criticized by the subsequent U.S. President, Barack Obama.[60][63]

In February 2010, the Obama administration proposed eliminating public funds for the Constellation program and shifting greater responsibility of servicing the ISS to private companies.[64] During a speech at the Kennedy Space Center on April 15, 2010, President Obama proposed the design selection of the new HLV that would replace the Ares-V but would not occur until 2015.[65] The U.S. Congress drafted the NASA Authorization Act of 2010 and President Obama signed it into law on October 11 of that year.[66] The authorization act officially cancelled the Constellation program.[66]

The development of the combination of Ares I and Orion was predicted to cost about US$50 billion.[67] One of the issues with Ares I was the criticism of the second stage, which the post-cancellation Liberty proposal attempted to address by using a second stage from an Ariane 5.[68] The Liberty proposal applied for but was not chosen for commercial crew.[68] The other ongoing complaint was that it made more sense to make a man-rated version of the Atlas or Delta.[67] The first crewed flight for Ares I was scheduled for March 2015, and one of its priorities was crew safety.[69] One reason for the emphasis on safety was that it was envisioned in the aftermath of the Columbia disaster.[69]

Current and future Space Shuttle successors

[edit]
NASA's first direct action with the Soyuz was in 1975, as part of the Apollo-Soyuz Test Project (pictured). As the ISS lifeboat spacecraft all participants needed to train on it in the event of an emergency, if they stayed after the Shuttle left. NASA used the Soyuz concurrently with STS system as far back as 2000, and many other ISS participants have also used this spacecraft to access the space station

Soyuz

[edit]

U.S. astronauts have continued to access the ISS aboard the Russian Soyuz spacecraft.[70] The Soyuz was chosen as the ISS lifeboat during the development of the International Space Station.[71] The first NASA astronaut to launch on a Soyuz rocket was Norman Thagard, as part of the Shuttle-Mir program.[72] Launching on March 14, 1995, on Soyuz TM-21, he visited the Mir however he returned to Earth on the Space Shuttle mission STS-71.[72] The start of regular use of the Soyuz began as part of the International Space Station program, with William Shepherd launching on Soyuz TM-31 in October 2000.[72] NASA has continued to take regular flights in the following two decades.[72] NASA was contracted to use Soyuz seats until at least 2018.[73]

The consideration of Soyuz as a lifeboat began in the aftermath of the dissolution of the Soviet Union.[72] Russia proposed using the Soyuz as a lifeboat for what was still Space Station Freedom in late 1991, leading to further analysis of this concept in the early 1990s.[72] One of the milestones was in 1992, when after three months of negotiations the heads of the two Space Agencies agreed to study applications of the Soyuz spacecraft.[72]

In March 1992, Russian and US space officials discussed the possibility of cooperation in manned space program, including ACRV. On June 18, 1992, after three months of negotiations, NASA Administrator Daniel S. Goldin and Director General of the Russian Space Agency Yuri Nikolayevich Koptev, "ratified" a contract between NASA and NPO-Energia to study possible application of the Soyuz spacecraft and Russian docking port in the Freedom project

— NASA Astronauts on Soyuz: Experience and Lessons for the Future, 2010[72]

Since the first NASA use of Soyuz in 1995, NASA astronauts have flown on the following Soyuz versions: Soyuz-TM, Soyuz-TMA (and Soyuz TMA-M), Soyuz MS (which had its first flight in 2016).[74]

NASA also purchased several space modules from Russia including Spektr, Docking Module (Mir), Priroda, and Zarya.

Orion and the SLS

[edit]
See also: Artemis program
Orion test launches on a Delta IV Heavy, 2014
Artemis 1 mission

The NASA Authorization Act of 2010 required a new heavy–lift vehicle design to be chosen within 90 days of its passing.[75] The authorization act called this new HLV the Space Launch System (SLS). The Orion spacecraft was left virtually unchanged from its previous design. The Space Launch System will launch both Orion and other necessary hardware.[76] The SLS is to be upgraded over time with more powerful versions. The initial version of SLS will be capable of lifting 70 tonnes into low Earth orbit. It is then planned to be upgraded in various ways to lift 105 tonnes, and then, eventually, 130 tonnes.[77][78]

Exploration Flight Test 1 (EFT-1), an uncrewed test flight of Orion's crew module, launched on December 5, 2014, on a Delta IV Heavy rocket.[78]

Artemis 1 is the first flight of the SLS and was launched in November 2022 as a test of the completed Orion and SLS system.[79] Artemis 2, the first crewed mission of the program, will launch four astronauts no earlier than 2026, since all Artemis 1 flight objectives have been met.[80] The second mission will launch on a free-return flyby of the Moon at a distance of 8,520 kilometers (4,600 nmi).[81] After Artemis 2, the Power and Propulsion Element of the Lunar Gateway and three components of an expendable lunar lander are planned to be delivered on multiple launches from commercial launch service providers.[82]

Artemis 3 is planned to launch in 2027[83] aboard a SLS Block 1 rocket and will use the minimalist Gateway and expendable lander to achieve the first crewed lunar landing of the program. The flight is planned to touch down on the lunar south pole region, with two astronauts staying there for about one week.[82][84][85][86]

ISS crew and cargo resupply

[edit]
Main articles: Commercial Crew Program and Commercial Resupply Services
The International Space Station as seen by STS-134
Crew poster for Expedition 50, with text saying "Off the Earth, For the Earth"

The ISS is planned to be funded until at least 2020.[needs update][87] There has been discussion to extend it to 2028 or beyond.[88] Until another U.S. crew vehicle was ready, crews accessed the ISS exclusively aboard the Russian Soyuz spacecraft.[70] The Soyuz was chosen as the ISS lifeboat during the development of the International Space Station, and has been one of the space taxis used by the international participants to this program.[71] A Soyuz took Expedition 1, which included one U.S. astronaut in the year 2000.[71] Previously the United States and Russia had collaborated on extended the Mir space station with the Shuttle-Mir program in the 1990s.[71]

Although the Orion spacecraft is oriented towards deep-space missions such as NEO visitation, it can also be used to retrieve crew or supplies from the ISS if that task is needed.[89] However, the Commercial Crew Program (CCP) produced a functioning crewed space vehicle starting operations in 2020, providing an alternative to Orion or Soyuz.[61] The delay was longer than expected because the Ares I was cancelled in 2010, leaving little time before the STS retired for something new to be ready for flight.[59] U.S. Congress was aware a spaceflight gap could occur and accelerated funding in 2008 and 2009 in preparation for the retirement of the Shuttle.[59] At that time the first crewed flight of the planned Ares I launcher would not have occurred until 2015, and its first use at ISS until 2016.[59] Another option that has been analyzed is to adapt Orion to a human-rated heavy launch vehicle like the Delta IV Heavy.[67] (see also Evolved Expendable Launch Vehicle) Another spacecraft evaluated by NASA, and also for commercial crew, is the OmegA rocket, which will look similar to Ares I and will be based on the Space Shuttle Solid Rocket Booster.[68]

Commercial Resupply Services

[edit]
Main article: Commercial Resupply Services

The Commercial Orbital Transportation Services (COTS) development program began in 2006 with the purpose of creating commercially operated automated cargo spacecraft to service the ISS.[90] The program is a fixed–price milestone-based development program, meaning that each company that received a funded award had to have a list of milestones with a dollar value attached to them that they would not receive until after achieving the milestone.[91] Private companies are also required to have some "skin in the game" which refers to raising additional private investment for their proposal.[92]

On December 23, 2008, NASA awarded Commercial Resupply Services contracts to SpaceX and Orbital Sciences Corporation (with corporate mergers and acquisitions now Northrop Grumman).[93][94] SpaceX is using its Falcon 9 rocket and Dragon spacecraft and Orbital Sciences (now Northrop Grumman) is using its Antares rocket and Cygnus spacecraft.[95] The first Dragon resupply mission occurred in May 2012.[96][97] The first Cygnus resupply mission completed on 23 Oct 2013 after a flight that included remaining attached to the ISS for 23 days.[98] The CRS program provides for all the projected U.S. cargo-transportation needs to the ISS, with the exception of a few vehicle–specific payloads to be delivered on the European ATV and the Japanese HTV.[99]

Commercial Crew Program

[edit]
Main article: Commercial Crew Program

The Commercial Crew Program (CCP) was initiated in 2010 with the purpose of creating commercially operated crew vehicles capable of delivering at least four astronauts to the ISS, staying docked for 180 days and then returning them to Earth.[100] Like COTS, CCP is a fixed–price milestone-based developmental program that requires some private investment.[91]

In the first phase of the program, NASA provided a total of $50 million divided among five U.S. companies, intended to foster research and development into human spaceflight concepts and technologies in the private sector. In 2011, during the second phase of the program, NASA provided $270 million divided among four companies.[101] During the third phase of the program, NASA provided $1.1 billion divided among three companies.[102] This phase of the CCP was expected to last from June 3, 2012, to May 31, 2014.[102] The winners of that round were SpaceX Dragon 2 (derived from the Dragon cargo vehicle), Boeing's CST-100 and Sierra Nevada's Dream Chaser.[103] The United Launch Alliance worked on human-rating their Atlas V rocket as part of the latter two proposals. Ultimately NASA selected the Crew Dragon and CST-100 Starliner with the Dream Chaser only receiving a cargo contract. The Crew Dragon began delivering crew in 2020,[61] with the CST-100, who began delivering crew in 2024.[104][105][106]

On May 30, 2020, SpaceX launched Crew Dragon on the Crew Dragon Demo-2 mission to the International Space Station. It carried a crew of two NASA astronauts, Doug Hurley and Bob Behnken, for a 62-day mission, which was incorporated as part of Expedition 63.[61] This was the first crewed launch of a US-built capsule since the Apollo-Soyuz Test project on July 15, 1975. Hurley, who was the pilot for Atlantis on the final Shuttle mission, STS-135, commanded the Demo-2 mission. Operational use of the Crew Dragon began with the launch of SpaceX Crew-1, carrying four astronauts, on November 16, 2020. The crew joined Expedition 64. Of the crew, only Japanese astronaut Soichi Noguchi had previously flown on the Space Shuttle.[107]

On the other hand on June 5, 2024, Boeing launched Starliner on the CFT mission to the International Space Station.[108] It carried a crew of two NASA astronauts, Barry E. Wilmore and Sunita Williams, for a 8-day short mission, albeit extended to more than a month in length due to propulsion issues. Wilmore, who was the pilot for Atlantis on the 129th Shuttle mission, STS-129, commanded the CFT mission.[109]

[edit]
Space Shuttles in Retirement
  • Atlantis at Kennedy Space Center Visitor Center
    Atlantis at Kennedy Space Center Visitor Center
  • Enterprise moving up the Hudson River to the Intrepid Museum
    Enterprise moving up the Hudson River to the Intrepid Museum
  • Endeavour arriving in Los Angeles (LAX)
    Endeavour arriving in Los Angeles (LAX)
  • Discovery arriving at Washington Dulles
    Discovery arriving at Washington Dulles
  • Discovery on display at Udvar-Hazy Center in Virginia
    Discovery on display at Udvar-Hazy Center in Virginia

See also

[edit]

References

[edit]
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Space Shuttle retirement

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![Space Shuttle Atlantis begins takeoff on STS-135, the final mission][float-right] The retirement of the ended 's 30-year operation of reusable manned spacecraft, culminating in the 135th and final mission, , which launched aboard on July 8, 2011, and landed on July 21, 2011, after delivering supplies to the . The decision to retire the fleet stemmed from the 2004 policy, which mandated completion of ISS assembly followed by program termination to redirect resources toward new exploration architectures. Key factors included persistent safety risks, highlighted by the loss of Challenger in 1986 and Columbia in 2003, which exposed vulnerabilities in the shuttle's design such as thermal protection system failures and external tank debris issues, alongside escalating operational costs exceeding initial projections due to maintenance complexities and limited reusability gains. Politically, the retirement aligned with budget constraints and a shift to commercial crew partnerships and heavy-lift vehicles like the , though it created a multi-year gap in U.S. human spaceflight capability, necessitating reliance on Russian Soyuz vehicles for ISS access until 2020. Following retirement, the four surviving orbiters—Discovery, Atlantis, Endeavour, and Enterprise—were allocated to museums: Discovery to the Steven F. Udvar-Hazy Center in Virginia, Atlantis to the Kennedy Space Center Visitor Complex in Florida, Endeavour to the California Science Center in Los Angeles, and Enterprise to the Intrepid Sea, Air & Space Museum in New York. This transition preserved the vehicles for public display while NASA decommissioned infrastructure, transferred assets, and captured lessons learned to inform future programs, amid debates over the program's legacy of technological achievements versus its economic inefficiencies and human costs.

Decision Process and Timeline

Announcement under Vision for Space Exploration

On January 14, 2004, President announced the (VSE) during a speech at , outlining a strategic shift in U.S. civil space policy that included the retirement of the upon completion of the (ISS). The VSE directed to retire the Shuttle by 2010, after fulfilling commitments to assemble the ISS, thereby freeing budgetary resources—estimated at approximately $4 billion annually from Shuttle operations—for development of successor systems like the aimed at returning humans to the Moon by 2020 and eventual Mars missions. This decision prioritized sustainable deep-space exploration over continued low-Earth orbit (LEO) operations, reflecting empirical assessments of the Shuttle's limitations in achieving broader solar system goals. The announcement was heavily influenced by the (CAIB) report, released on August 26, 2003, following the destruction of Shuttle Columbia on February 1, 2003, which killed all seven crew members due to foam debris impact and systemic organizational failures at . While the CAIB focused on immediate safety reforms—such as eliminating external tank foam shedding risks and improving debris inspection capabilities—it also recommended a fundamental reorientation of 's priorities toward long-term sustainability beyond LEO, critiquing the Shuttle's design as inherently risky for routine operations and advocating for new vehicles to replace aging infrastructure. These findings underscored causal factors like recurring technical vulnerabilities and cultural barriers to , providing empirical justification for phasing out the Shuttle to mitigate ongoing safety hazards and enable resource reallocation. Under the VSE timeline, NASA planned 16 to 19 Shuttle missions following return-to-flight certification in 2005 to complete ISS assembly, targeting retirement by the end of 2010; this schedule was later extended to 2011 due to technical delays and additional logistics requirements. The policy emphasized completing U.S. obligations to 15 international partners on the ISS while transitioning to exploration-focused architecture, with the Shuttle's final role confined to heavy-lift assembly tasks unsuited for indefinite extension given its per-flight costs exceeding $450 million and launch cadence limitations.

Final Missions and Program Closure

STS-134, flown by from May 16 to June 1, 2011, served as the penultimate mission of the , delivering the Alpha Magnetic Spectrometer-02 (AMS-02) particle physics detector to the (ISS). This installation marked the completion of the ULF6 assembly flight, with the crew performing three spacewalks to outfit the station and prepare for future operations. The final mission, , launched aboard on July 8, 2011, and concluded with a landing at on July 21, 2011, after a 12-day, 18-hour, 28-minute flight. delivered the Raffaello containing supplies, scientific experiments, and spare parts to the ISS, ensuring extended station functionality in the absence of routine shuttle resupply. The mission included one spacewalk to stow a failed and transfer cargo, underscoring the program's logistical closure. Atlantis's touchdown on July 21, 2011, concluded the program's 135 missions spanning 30 years from April 12, 1981, to that date, during which 355 unique astronauts from 16 nations were launched into . The fleet had cumulatively orbited over 130,000 times and traveled approximately 542 million miles. Post-landing, entered immediate decommissioning in the Kennedy Space Center's , involving the safeing of propulsion systems, removal of the three Main Engines for preservation and potential , draining of hypergolic fuels, and deactivation of onboard and . This process, spanning months, prepared the orbiter for static museum display while transitioning thousands of program personnel to other roles or commercial initiatives. marked the program's official closure with ceremonies across its centers on August 31, 2011, transitioning shuttle-era infrastructure toward support for the and emerging commercial crew capabilities.

Key Milestones from 2004 to 2011

In January 2004, President George W. Bush announced the Vision for Space Exploration, which directed NASA to retire the Space Shuttle program by 2010 upon completion of International Space Station assembly, redirecting resources toward lunar and Mars missions via the Constellation program. This policy established a fixed timeline for program closure, with NASA's fiscal year 2005 budget request allocating initial funds—approximately $1 billion—for Constellation development while sustaining Shuttle operations. Implementation of Columbia Accident Investigation Board recommendations, including external tank redesigns to mitigate foam debris risks, enabled the Shuttle's return to flight with mission aboard Discovery on July 26, 2005, following a 907-day grounding. The mission tested in-orbit repair techniques and thermal protection system inspections, but post-launch analysis revealed persistent foam shedding from the external tank, prompting further modifications. In November 2005, engineers identified hairline cracks in the tank's foam insulation during pre-launch checks for , delaying that flight until July 4, 2006, and requiring reinforced foam application processes. Between 2006 and 2009, annual appropriations progressively reduced Shuttle funding—from $4.3 billion in FY2006 to planned phase-out levels—while increasing allocations for hardware, adjusting the flight manifest from 18 missions in 2006 to fewer and assembly flights as ISS extended. Technical hurdles, including external foam shedding fixes and bipod ramp redesigns validated in , contributed to manifest compressions, with requesting supplemental Shuttle funding of $5 billion through 2010 to address overruns. By 2010, unresolved issues such as aluminum-lithium tank stringer cracks—discovered in Discovery's external tank during preparations—necessitated repairs and delayed final missions, shifting retirement to September 2011. Congress authorized $2.5 billion in FY2010 for two additional flights ( and ) to complete ISS commitments, culminating in Atlantis's launch on July 8, 2011, and landing on July 21, marking the program's end after 135 missions.

Rationales for Retirement

Safety Risks and Accident Lessons

The Space Shuttle program's safety record was marred by two catastrophic accidents that resulted in the loss of 14 crew members and highlighted inherent design vulnerabilities tied to its partially reusable architecture. On January 28, 1986, during the mission, Challenger disintegrated 73 seconds after liftoff due to the failure of seals in the right solid rocket booster's field joint, exacerbated by unusually low temperatures that reduced the seals' elasticity, allowing hot combustion gases to erode the joint and breach the external tank, triggering a chain of structural failures. The Rogers Commission investigation attributed the root cause to this mechanical failure but also faulted NASA's , including the normalization of prior erosion incidents observed on previous flights and pressures from manifest schedules that overrode engineering cautions against launch in sub-freezing conditions. Nearly 17 years later, on February 1, 2003, Columbia broke apart during reentry on when a insulation segment from the external tank's bipod ramp detached at 81.7 seconds after launch and struck reinforced carbon-carbon panel 8 on the left leading edge, creating a breach that permitted superheated plasma intrusion during atmospheric reentry, leading to aerodynamic disintegration at approximately Mach 18. The (CAIB) confirmed the strike as the physical cause, noting that external tank shedding had occurred on prior missions without consequence due to luck or non-critical impact locations, but criticized 's persistent underestimation of risks, inadequate in-orbit repair capabilities, and fragmented engineering oversight that treated such anomalies as acceptable rather than systemic flaws in the thermal protection system's fragility to low-velocity impacts. These incidents yielded a cumulative catastrophic failure rate of 2 losses in 135 missions (approximately 1.5%), with all 14 fatalities occurring during ascent or reentry phases where the vehicle's complexity amplified single-point failures. In contrast, the Russian Soyuz capsule, relying on simpler expendable boosters and a more robust, non-reusable heat shield, recorded no in-flight crew fatalities after 1971 across over 1,900 launches, achieving a lower per-mission loss probability through design redundancy and avoidance of reuse-induced wear. The Shuttle's pursuit of reusability for the orbiter, solid rocket boosters, and main engines—intended to enable rapid turnaround—compromised safety margins by necessitating field joints, ablative coatings, and tile systems prone to cumulative damage, inspection gaps, and probabilistic rather than deterministic failure modes, as reuse cycles eroded material integrity without fully redundant backups akin to expendable rockets. Post-accident return-to-flight efforts implemented redesigns, such as SRB fillet redesigns after Challenger and external tank foam application modifications plus laser imaging inspections after Columbia, yet empirical data revealed persistent vulnerabilities: foam debris shedding was documented on 21 of the 22 missions flown from STS-114 (2005) through program end, underscoring that while mitigations reduced severity, the underlying causal mechanisms—adhesive inconsistencies, cryogenic stresses, and aerodynamic shear—remained uneliminated in the integrated stack design. These lessons from causal analysis emphasized that the Shuttle's hybrid reusability, by prioritizing payload fraction and turnaround over fault-tolerant simplicity, normalized elevated risks incompatible with sustained human spaceflight, informing the retirement to transition toward vehicles with enhanced redundancy and lower exposure cycles.

Economic Inefficiencies and Cost Overruns

The Space Shuttle program's economic inefficiencies stemmed primarily from optimistic initial cost projections that assumed rapid reusability and high flight rates, which failed to materialize due to the inherent complexities of refurbishing a complex, human-rated orbital vehicle after exposure to extreme environments. In 1971, and contractor estimates projected an operational cost per flight of approximately $10.5 million in then-year dollars, predicated on achieving 50 or more flights annually to amortize fixed costs effectively. These figures represented marginal costs excluding development, but even adjusted for to 2020 dollars, they equated to roughly $20 million per flight—orders of magnitude below actual expenditures. Actual flight rates averaged under five per year across the program's 135 missions from 1981 to 2011, exacerbating per-flight costs as fixed and expenses were spread over fewer operations. Total lifecycle costs for the program, encompassing development, operations, and sustainment from 1972 through 2010, reached approximately $209 billion in 2010 dollars according to NASA estimates. Operational costs alone—excluding initial development—averaged $413.5 million per flight in fiscal year 1993 dollars, as reported by the U.S. Government Accountability Office (GAO), incorporating expenses for payload integration, ground operations, and vehicle turnaround. Later analyses of the operational phase through 1992 pegged average costs at about $1 billion per flight when isolating post-development expenditures. These overruns arose from the program's partial reusability, which promised amortized savings but delivered high recurring expenses; for instance, the fixed annual budget for shuttle operations consumed roughly 40-50% of NASA's overall funding during peak years, limiting diversification into expendable alternatives. A major driver of inefficiencies was the extensive post-flight refurbishment required for each orbiter, which typically spanned 3-6 months between missions and involved meticulous inspections and repairs to ensure structural integrity and thermal resilience. The thermal protection system (TPS), comprising over 20,000 silica tiles, demanded particular attention, with ascent debris impacts and reentry heating damaging 100-250 tiles per flight on average, necessitating replacement of about 75 tiles per mission. Labor and materials for TPS refurbishment alone generated projections of millions in costs per orbiter turnaround, as early NASA studies identified inspection, repair, and replacement as labor-intensive processes unsuitable for quick reuse. Manufacturing and installing a single square foot of TPS tile cost $10,000, compounding expenses across the vehicle's surface area. This refurbishment cycle, far from the envisioned weeks-long turnaround, contributed to launch delays and elevated per-mission overhead, undermining the program's core economic rationale of cost-effective, routine space access.
Cost CategoryInitial Projection (1971 Dollars)Actual Average (1990s Dollars, Operational)
Per-Flight Operational Cost~$10.5 million$413.5 million (, FY1993)
TPS Refurbishment (Per Mission)Minimal (assumed high reusability)Millions (tile replacements and labor)
Annual Flight Rate Assumption50+<5 (program average)
These inefficiencies manifested in opportunity costs, as shuttle sustainment absorbed funds that could have supported development of simpler, expendable ; post-retirement analyses noted the program's dominance redirected resources away from next-generation systems, though quantifiable diversions remain debated in budgetary reviews. The consistently highlighted how underestimated refurbishment needs and flight rate shortfalls inflated life-cycle expenses, rendering the shuttle less competitive than projected against expendable options for routine payload delivery.

Operational Limitations and Aging Infrastructure

The Space Shuttle's operational efficiency was fundamentally limited by protracted refurbishment cycles, which far exceeded initial projections. Early program concepts anticipated turnaround times of as little as two weeks per orbiter, enabling flight rates approaching 100 annually across the fleet to amortize development costs through high reuse. In practice, post-flight processing, including disassembly, inspection, and reassembly of reusable components like the solid rocket boosters and main engines, averaged 87 days, constraining the program to 4-5 missions per year after resuming operations following . This logistical bottleneck stemmed from the vehicle's complex hybrid architecture, where recovered boosters required extensive disassembly and requalification, while integration of a new expendable external tank added preparation delays without achieving the full reusability benefits envisioned in fully reusable designs. Payload performance further highlighted design constraints, as the orbiter's 24-metric-ton capacity to was frequently underutilized due to geometric and integration limitations in the 4.6 by 18-meter payload bay. Missions often prioritized volume-constrained payloads, such as satellites or modules, resulting in mass fractions below maximum ratings; for instance, the bay's fixed dimensions and attachment points restricted denser configurations, compelling operators to forgo full loading to meet stability and requirements. The partial reusability model—retaining the orbiter and boosters but discarding the tank—imposed recurring assembly demands that compounded these inefficiencies, as each flight necessitated custom tank outfitting and booster segmentation, diverting resources from flight cadence improvements. By 2011, the orbiters exhibited pronounced aging effects, having exceeded their original design parameters through cumulative stress rather than raw mission counts. Each vehicle was engineered for a 100-mission lifespan over 10 years, yet cumulative exposure to thermal, acoustic, and induced fatigue in aluminum-lithium airframes, wing carry-through structures, and lines; for example, completed 39 missions, with inspections revealing microcracks and corrosion necessitating hyperbaric weld repairs and reinforced struts. obsolescence compounded structural wear, as 1970s-era computers and wiring harnesses required frequent upgrades to mitigate radiation-induced failures, while the thermal protection system demanded tile-by-tile replacements after each reentry, escalating complexity and risking further delays in an already strained infrastructure.

Controversies and Alternative Perspectives

Debates on Premature Retirement and Capability Gaps

Critics of the Space Shuttle program's retirement argued that it was premature, as post-Columbia safety upgrades, including redesigned Solid Rocket Boosters (SRBs) with improved joints and filtration systems implemented after , had enhanced reliability, allowing for potential further extensions through advanced SRB filament-wound cases and lighter External Tank (ET) variants like the Super LightWeight ET introduced in 1998, which reduced mass by over 7,500 pounds per tank. These modifications, combined with ongoing ET aluminum-lithium alloy transitions in Block II designs, could have sustained operations beyond the (ISS) completion in 2011 without immediately ceding U.S. leadership, preserving institutional expertise and avoiding skill atrophy among the workforce. Proponents of extension, including some former astronauts and engineers, contended that the program's halt disrupted momentum just as ISS assembly peaked, leading to a foreseeable erosion of capabilities unique to the Shuttle, such as heavy-lift delivery up to 55,000 pounds to . The retirement precipitated a nine-year gap in U.S. crewed launches from the final mission on July 21, 2011, to SpaceX's on May 30, 2020, forcing to procure Soyuz seats at escalating costs averaging $80-90 million per by the late 2010s, far exceeding initial 2006 agreements of around $20-30 million. This dependency exposed vulnerabilities during geopolitical tensions, such as Russia's 2014 annexation of and subsequent threats to curtail Soyuz access amid Ukraine-related sanctions, which prompted price hikes and heightened U.S. concerns over supply reliability for ISS crew rotations. Opponents of the timeline highlighted how the gap not only inflated expenditures—totaling over $4 billion for Soyuz seats from 2011-2020—but also risked mission delays if Russian cooperation faltered, underscoring a strategic capability shortfall absent from pre-retirement planning. Counterarguments emphasized that extension would have been uneconomical given the program's systemic flaws, with per-launch costs exceeding $450 million by the due to protracted refurbishments averaging 4-6 months per orbiter turnaround, far from the original 55-day goal, and cumulative expenses surpassing $200 billion over 30 years. The (CAIB) in 2003 identified inherent design risks, such as foam debris shedding from the ET—a persistent issue despite mitigations—and brittle SRB O-rings, rendering long-term sustainment untenable without fundamental redesigns costing billions more. Reliability data reflected this: while the Shuttle achieved 133 successes in 135 flights (98.5% rate), post-2003 operations showed elevated maintenance demands on aging orbiters, with flight rates declining to 4-5 annually due to escalating anomaly resolutions, supporting the view that retirement aligned with of rather than overreaction.

Political Decision-Making and Policy Reversals

The retirement of the Space Shuttle originated in President George W. Bush's , publicly announced on January 14, 2004, at . This initiative explicitly planned for the Shuttle program's end after completing assembly, aiming to reallocate budgetary resources from routine missions—characterized as inefficient "taxi service"—toward sustained human exploration of the Moon and Mars. The policy reflected post-9/11 fiscal pressures, including ballooning deficits from ongoing wars in and , which underscored the need for pragmatic prioritization of strategic national goals over indefinite maintenance of aging orbital infrastructure. Under President , a notable policy reversal occurred with the cancellation of the , the Bush-era successor intended to replace the Shuttle with new crewed vehicles for exploration. Detailed in the fiscal year 2011 budget request unveiled on February 1, 2010, this decision eliminated Constellation's rockets and Orion capsule development, redirecting emphasis toward commercial partnerships for crew transport to the ISS. While framed as fostering innovation through private industry, the move drew bipartisan criticism for introducing uncertainty, lacking firm timelines or destinations, and effectively postponing deeper space objectives like Mars missions in favor of near-term reliance. Congressional Democrats, such as Senator , explicitly deemed it a strategic error that risked eroding U.S. leadership. Detractors attributed the shift to ideological preferences for market-driven solutions, which overlooked the causal risks of disrupting established government expertise in manned systems. Bipartisan congressional dynamics produced additional reversals, notably through the emergence of the as a legislatively mandated heavy-lift vehicle. Enacted via the Authorization Act of 2010 and reinforced in subsequent appropriations, SLS repurposed Shuttle-era components to ensure continuity in and , driven by lawmakers' efforts to safeguard employment in politically sensitive regions including , , , and . This approach, while securing short-term industrial stability, has been critiqued as pork-barrel allocation that entrenched inefficient government monopolies, diverting funds from agile private alternatives and perpetuating dependency on legacy contractors rather than incentivizing competitive innovation. Such interventions highlight how parochial district interests often override first-principles efficiency in space policy formulation.

Long-Term Impacts on US Space Leadership and Budget Allocation

Following the Space Shuttle's retirement in July 2011, 's annual budget, which stood at $18.45 billion for (FY) 2011, gradually increased to approximately $24.9 billion by FY2024 and an estimated $24.9 billion for FY2025, reflecting stabilization rather than expansion amid competing federal priorities. The program's operational costs, which had absorbed roughly $3-5 billion annually or up to 30% of 's pre-retirement budget in peak years like 2005, were redirected toward successors such as the (SLS) and commercial initiatives, but allocation proved uneven due to overruns in government-managed projects. SLS development, initiated in 2011 under the Authorization Act, has incurred $23.8 billion in costs from FY2012 through 2023, with per-launch expenses projected at $4.2 billion for early missions, diverting funds that could have supported broader exploration or efficiency gains elsewhere. This budgetary shift contributed to critiques of diminished U.S. in heavy-lift capabilities, as the nine-year gap in domestic crewed orbital access post-2011 ceded initiative to international competitors and necessitated $3.9 billion in payments to for Soyuz seats through 2019, underscoring temporary vulnerabilities in assured access. However, the retirement catalyzed private-sector innovation, with firms like achieving reusable launch breakthroughs that reduced costs dramatically— launches dropped to under $100 million by the mid-2010s—elevating U.S. commercial dominance and enabling to leverage fixed-price contracts for cost predictability. 's valuation, for instance, escalated from $1 billion in 2010 to $12 billion by 2015 and $350 billion by December 2024, reflecting investor confidence in scalable alternatives to legacy systems like SLS, which reports highlight for persistent overruns exceeding 140% of initial estimates in some components. Workforce transitions further illustrate long-term adaptation, with approximately 7,000 direct Shuttle-related jobs lost by 2012, primarily among contractors at centers like , yet this disruption incentivized retraining and migration to emerging commercial ecosystems. NASA's post-transition surveys indicated over 70% of affected civil servants remained or relocated within the agency, while private hiring surges— alone expanding to over 10,000 employees by 2020—diversified the industrial base away from sole reliance on federal procurement, fostering resilience against program-specific cancellations. Recent proposals, such as FY2026 budget outlines emphasizing commercial heavy-lift over SLS sustainment, signal ongoing recalibration toward cost-effective models that prioritize scalability over inherited infrastructure.

Disposition of Surviving Hardware

Orbiters: Museums and Preservation

Following the retirement of the Space Shuttle program in 2011, NASA allocated its surviving orbiters to museums for public display, emphasizing preservation of historical artifacts while prioritizing institutions with strong educational missions. The five orbiters—Enterprise, Discovery, Atlantis, Challenger, and Columbia—met varied fates, with only Enterprise and the three flight veterans (Discovery, Atlantis, Endeavour) intact for exhibition; Challenger and Columbia were destroyed in accidents in 1986 and 2003, respectively, leaving remnants preserved in memorials rather than full vehicles. Enterprise, the prototype orbiter used for in , was transferred to the Intrepid Sea, Air & Space Museum in , where it entered public display in a dedicated pavilion on July 19, 2012. Discovery, the most flown orbiter with 39 missions, arrived at the National Air and Space Museum's in , on April 19, 2012, and is exhibited horizontally in its James S. McDonnell Space Hangar. Atlantis, completing 33 missions, was installed vertically at the in Florida, opening in the Space Shuttle Atlantis exhibit on June 29, 2013, simulating a post-landing configuration with open. Endeavour, with 25 missions, reached the in on October 13, 2012, initially displayed horizontally; in 2024, it was stacked vertically atop an external tank and solid rocket boosters replica for the Samuel Oschin Air and Space Center exhibit, the only such full-stack display. Prior to transfer, each orbiter underwent a comprehensive decommissioning process at NASA's Kennedy or Johnson Space Centers, including draining of all fluids, removal of hazardous materials such as hypergolic propellants from the , extraction of critical components like , computers, and Space Shuttle Main Engines (which were refurbished for successor programs), and replacement of engines with non-functional replicas for aesthetic purposes. Additional items, including crew lockers, tools, and waste management systems, were removed to ensure public safety and prevent deterioration. This "safing" rendered the orbiters incapable of reactivation, as obsolete systems lacked modern support infrastructure, and key hardware was repurposed or disposed of per federal property guidelines. NASA's allocation process, initiated in , involved evaluating proposals from 21 museums and educational institutions based on criteria such as facility suitability for climate-controlled indoor display, commitment to STEM education and public outreach, preservation expertise, and geographic diversity to maximize national accessibility. Administrator announced selections on April 11, 2011, favoring non-federal entities with demonstrated capacity to inspire future generations over operational reuse, despite congressional debates on alternatives like Houston's . For Challenger and Columbia, recovered debris exceeding 80,000 and 84,000 pieces respectively underwent analysis for accident causation before archival storage at NASA centers, with select artifacts incorporated into memorials like the Challenger Center or Columbia Memorial at .

Engines and Propulsion Components: Refurbishment for New Programs

Following the Space Shuttle program's retirement in 2011, NASA initiated refurbishment of its high-value propulsion components for integration into successor vehicles, particularly the Space Launch System (SLS) under the Artemis program. The RS-25 engines, originally designed as reusable Space Shuttle Main Engines (SSMEs), formed a core part of this effort. Aerojet Rocketdyne, under NASA's Adaptation contract, refurbished and upgraded 16 RS-25 engines from the Shuttle inventory for SLS Block 1 core stages used in Artemis missions I through IV. These engines underwent modifications including new controller avionics, improved sensors, and enhanced nozzle durability to meet SLS expendable flight requirements, leveraging the proven performance heritage to accelerate development timelines. The refurbishment approach capitalized on existing hardware to mitigate costs associated with full-scale new production. While new RS-25 engines entered production via a separate 2015 contract valued at approximately $1.16 billion for up to 20 units, the refurbished engines for initial SLS flights avoided the higher expenses of restarting dormant manufacturing lines from scratch. This strategy enabled SLS's maiden flight, Artemis I, on November 16, 2022, utilizing four refurbished RS-25s that delivered over 1.6 million pounds of thrust at liftoff. Subsequent missions continued this reuse, with the engines' high specific impulse—around 452 seconds in vacuum—providing efficiency advantages over alternative expendable engines, despite criticisms of overall SLS program costs. Solid Rocket Booster (SRB) components from the Shuttle era also saw repurposing for SLS. incorporated steel cases from retired Shuttle SRBs into the five-segment boosters for SLS, manufactured by , enhancing structural reliability through flight-proven materials. These cases, originally designed for refurbishment and reuse across multiple Shuttle missions, were adapted for SLS's higher-thrust configuration, contributing to the boosters' role in generating about 75% of SLS liftoff thrust. Unlike the Shuttle's recoverable SRBs, SLS boosters are expended, but the repurposed cases reduced development risks and costs by building on verified hardware. Nozzles and other propulsion subcomponents were similarly inspected and integrated where feasible, extending Shuttle technology transfer to while archiving non-reusable elements like External Tank tooling for potential future reference.

Ground Facilities and Infrastructure: Repurposing and Decommissioning

Following the Space Shuttle program's retirement in 2011, NASA repurposed key ground facilities at Kennedy Space Center (KSC) to support the Space Launch System (SLS) and commercial launch providers, while decommissioning obsolete infrastructure to reduce maintenance costs and enable multi-user operations. This transition involved leasing pads, modifying assembly structures, and upgrading transport systems, with some Shuttle-era components dismantled or mothballed between 2011 and 2025 to facilitate private sector integration. Launch Complex 39A (LC-39A) was leased to under a 20-year agreement finalized in April 2014, allowing the company to modify the pad for and Heavy launches, with initial operations resuming in February 2016. LC-39B remained under control for SLS preparations, including tower reinforcements and infrastructure upgrades completed by 2020 to handle the taller SLS stack. At LC-39A, Shuttle-era fixed service structures were dismantled piece-by-piece starting in to accommodate 's approach, exemplifying targeted decommissioning to support commercial reusability. The (VAB) underwent extensive modifications beginning in 2013, including removal of Shuttle-specific platforms in High Bay 3 and installation of 10 new adjustable work platforms by 2016 to enable SLS core stage stacking and Orion integration on Mobile Launcher platforms. These upgrades, costing millions and involving structural reinforcements, restored the VAB's role in heavy-lift assembly while preserving its Apollo-era footprint. The two Crawler-Transporters (CT-1 and CT-2), originally built in 1965, received upgrades starting in 2013 to increase load capacity to 18 million pounds for SLS, including new roller bearings, propulsion enhancements with additional generators, and jacking system improvements tested in February 2015. CT-2 completed its modifications by February 2016, enabling transport of SLS elements along the 4.2-mile crawlerway to LC-39B, with further refinements for missions by 2023. Orbiter Processing Facilities (OPFs) were repurposed for commercial and military uses: OPF-1 leased to in 2013 for X-37B processing, OPF-3 converted by Space Florida into the Commercial Crew and Cargo Processing Facility by April 2013, and OPFs 1 and 2 modified for U.S. operations by 2024, including new air handling and electrical systems. The Shuttle (SLF), a 15,000-foot , was transferred to Space Florida on June 22, 2015, under a 30-year agreement for , drone testing, and horizontal launches, reducing 's upkeep burden. By 2025, these efforts had decommissioned redundant Shuttle support towers and utilities, mothballing select structures while demolishing others to clear space for private pads, enabling over 100 commercial launches from KSC since 2011 and sustaining U.S. launch cadence without full government funding.

Auxiliary Systems and Integration Hardware

The Space Shuttle's auxiliary systems encompassed the Shuttle Remote Manipulator System (SRMS), commonly known as the , and the Orbiter Boom Sensor System (OBSS), which facilitated payload deployment, capture, and thermal protection inspections. Following the program's retirement in 2011, Canadarms installed on orbiters such as Discovery and Endeavour were removed and repatriated to for display. For instance, Endeavour's Canadarm was designated for return to the Canadian Space Agency, while components from Discovery were exhibited at the alongside the orbiter. These systems, having supported 90 missions over three decades, saw no operational reuse due to their custom design for shuttle-specific interfaces, though their technology informed subsequent developments like Canadarm2 on the . The OBSS, a 50-foot boom extension equipped with cameras and lasers for wing leading edge inspections post-Columbia disaster in 2003, met varied fates. One unit was permanently attached to the during in May 2011 to extend Canadarm2's reach, despite non-functional sensors. Others remained installed on retired orbiters for museum displays, such as the OBSS on Endeavour at the , reopened with the boom in place by February 2023 to preserve historical configuration. Limited archival value beyond exhibits stemmed from the OBSS's specialized, non-reusable nature tied to shuttle avionics. Thermal protection system (TPS) tiles and related payload integration hardware, including bay liners and interfaces, faced obsolescence challenges post-retirement. Comprising over 20,000 fragile silica-based tiles per orbiter, many originals persisted through the program's end, but the material's brittleness and labor-intensive application precluded adaptation for modern vehicles like the . Surplus tiles entered storage or educational donation programs, with no significant due to discontinuities and limitations in reusable contexts. Payload adapters and integration fixtures, designed for shuttle-specific bays, were largely decommissioned or archived, yielding minimal transferable components amid the shift to modular standards. Onboard information technology systems, including the five general-purpose computers running custom flight software, were preserved within retired orbiters to maintain authentic displays, with software code archived for historical analysis. These AP-101S systems, upgraded incrementally but rooted in architecture, offered no viable reuse owing to outdated processing capabilities—equivalent to less than a modern —and lack of compatibility with contemporary networks. Recovery assets like the two (SCAs), modified 747s used for orbiter ferrying, were retired by after final deliveries; 905 relocated to the for potential training, while 911 supported disassembly for parts or static display.

Post-Retirement Transition and Successors

Interim Manned Access: Dependence on Soyuz and Geopolitical Risks

Following the final Space Shuttle mission, , on July 21, 2011, lacked an operational domestic crewed vehicle for (ISS) access, necessitating contracts with for Soyuz seats to transport U.S. s. Between 2011 and , this arrangement ensured continuity of U.S. presence on the ISS but imposed escalating financial burdens, with per-seat costs rising from approximately $50-60 million in the early post-Shuttle years to $90.2 million by for training, launch, and return services. Overall, expended nearly $4 billion on Soyuz transportation during this period, funding dozens of U.S. flights amid the absence of alternatives. This dependence exposed to geopolitical vulnerabilities, as held a monopoly on crewed access to the ISS, leveraging the situation amid deteriorating U.S.- relations. In March 2014, following 's annexation of , chief Oleg Ostapenko publicly threatened to withdraw from ISS cooperation or hike prices further, prompting U.S. congressional concerns over risks tied to reliance on foreign launch services potentially subject to controls or sanctions. Although did not ultimately sever access—continuing flights under barter agreements for ISS module usage—the episode underscored causal risks from policy decisions prioritizing Shuttle retirement without certified backups, amplifying U.S. exposure to bilateral tensions without domestic redundancy. Delays in restoring U.S. crewed capabilities stemmed from the Commercial Crew Program's developmental timeline, initiated under the NASA Authorization Act but protracted by stringent certification requirements for human-rating, including abort system validations and integrated vehicle testing. SpaceX's Crew Dragon achieved its first crewed demonstration flight, Demo-2, on May 30, 2020—nine years after Shuttle retirement—after overcoming hurdles such as redesigns and in-flight abort tests, while Boeing's Starliner faced parallel software and issues deferring its crewed debut. These setbacks, rooted in rigorous safety standards absent in Soyuz operations, highlighted planning shortfalls: the transition from early Commercial Crew Development awards in to operational certification required iterative fixes, during which Soyuz filled the void but at premium costs exceeding initial projections. While the Soyuz reliance provided interim stability, enabling ISS operations and buying development time for private vehicles, it revealed systemic failures in government forecasting, as pre-retirement assessments underestimated certification complexities and over-relied on international partnerships susceptible to geopolitical shifts. Critics, including reports, noted that earlier investments in parallel capabilities could have mitigated vulnerabilities, yet the approach ultimately transitioned U.S. access away from without permanent rupture in station access.

Commercial Resupply and Crew Programs: Achievements and Private Sector Role

The Commercial Resupply Services (CRS) program, initiated through contracts awarded in December 2008 to and (later acquired by ), aimed to develop and operate private vehicles for (ISS) logistics following the Space Shuttle's retirement. The first operational CRS missions occurred in 2012 with 's and 2013 with Orbital's Cygnus, marking the transition from government-operated to fixed-price commercial deliveries. By October 2025, had completed 33 missions, while had executed 21 Cygnus flights, totaling over 50 missions that delivered more than 159,000 pounds of supplies, experiments, and equipment to the ISS. These missions restored U.S. independent access, with uniquely enabling the return of up to 6,000 pounds of per flight, unlike one-way alternatives. CRS achieved significant cost efficiencies through fixed-price contracts, with NASA investing approximately $3 billion across initial phases for multiple missions, compared to the Space Shuttle's marginal cost exceeding $450 million per flight in its later years (equivalent to over $600 million including amortized infrastructure). Private developers absorbed development risks, leading to per-kilogram delivery costs under CRS averaging $20,000–$30,000, a fraction of Shuttle-era figures when adjusted for inflation and payload capacity, as detailed in NASA cost assessments. This model demonstrated empirical advantages of privatization: rapid iteration, such as SpaceX's reusable Falcon 9 boosters reducing launch expenses by over 90% from traditional expendable rockets, and redundancy via dual providers mitigating single-point failures inherent in monopolistic government programs. Parallel to CRS, the (CCP), funded starting in 2010, sought U.S. crew transport capabilities, awarding contracts to ($2.6 billion) and ($4.2 billion) for spacecraft development. 's Crew Dragon achieved operational certification in May 2020 following the Demo-2 mission, enabling astronaut rotations without foreign dependence. By October 2025, had conducted at least 11 crewed ISS missions under CCP, including Crew-10 (launched March 2025, returned August 2025) and Crew-11 (targeted July 2025), transporting dozens of s with a per-seat cost of approximately $55 million. 's Starliner, however, faced protracted delays; its Crew Flight Test launched June 2024 but encountered propulsion failures, stranding astronauts Butch Wilmore and Suni Williams until their return via in February 2025, with certification and first operational flight postponed to no earlier than 2026, potentially uncrewed. SpaceX's dominance in CCP highlighted private sector efficiencies, with total program savings estimated at $20–$30 billion versus traditional NASA-led development (e.g., Orion's escalating costs exceeding $17 billion pre-first flight), driven by vertical integration, reusability, and competitive fixed pricing that undercut Boeing's overruns exceeding $1.5 billion. These programs collectively restored U.S. orbital access, fostered innovations like autonomous docking and abort systems, and provided data evidencing lower lifecycle costs and faster deployment in commercial models over government-directed efforts, which historically suffered from bureaucratic inertia and cost-plus incentives.

Heavy-Lift Successors: SLS, Orion, and Government-Led Exploration

The Space Launch System (SLS) emerged as NASA's primary heavy-lift vehicle following the 2010 cancellation of the Constellation program, with its architecture mandated by the 2011 NASA Authorization Act to utilize Space Shuttle-derived components for rapid development and job preservation in key congressional districts. The initial Block 1 configuration, featuring a core stage powered by four RS-25 engines and two five-segment solid rocket boosters, successfully debuted with the uncrewed Artemis I mission on November 16, 2022, demonstrating reliable performance in sending the Orion spacecraft on a lunar orbit test flight. This launch validated SLS's capability for deep-space trajectories, though subsequent missions have faced scrutiny for sustaining government-led exploration amid rising private-sector alternatives. Development costs for SLS have escalated significantly, reaching an estimated $27 billion through 2025, driven by technical challenges and contractual inefficiencies inherent in traditional cost-plus procurement models that prioritize distributed employment over streamlined production. The Government Accountability Office (GAO) reported that SLS Block 1 development exceeded baselines by $2.7 billion, while NASA's projected total campaign expenditures, including SLS, at $93 billion from fiscal year 2012 to 2025. These overruns stem causally from political requirements to maintain across multiple states, inflating per-launch costs to over $4 billion, as opposed to reusable commercial systems achieving comparable or superior lift at fractions of the expense. The Orion , built by with Shuttle-era heritage in its abort systems and , integrates as SLS's payload for human-rated missions, having completed its (EFT-1) on December 5, 2014, and Exploration Mission-1 (EM-1) aboard Artemis I in 2022. Artemis II, the first crewed flight targeting a lunar flyby, is scheduled for no earlier than February 5, 2026, following delays from inspections and integration issues, with Orion's capsule stacked atop SLS by October 20, 2025. Critics, including , argue Orion's dual abort engines represent redundant "pork-barrel" engineering, prioritizing congressional earmarks over efficiency in an era where commercial vehicles like offer scalable heavy-lift without such legacy constraints. Future SLS variants, including Block 1B with the Exploration Upper Stage (EUS) for enhanced payload to 46 metric tons and Block 2 with advanced boosters, remain in planning but are hampered by delays; the Mobile Launcher 2 platform for these configurations is not expected until 2029. While SLS/Orion enable sustained government control over lunar and Mars precursor missions—avoiding full reliance on private entities—the architecture's inefficiencies, rooted in mandates for non-competitive contracts, have postponed Moon landings and diverted funds from innovative alternatives, underscoring a tension between assured access and cost-effective progress.

Emerging Low Earth Orbit Platforms: Commercial Stations Post-ISS

The International Space Station (ISS) is slated for deorbit and controlled reentry into the Pacific Ocean in 2030, marking the end of its operational life after over three decades. To ensure continuity in low Earth orbit (LEO) human presence and research capabilities, NASA has initiated the Commercial Low Earth Orbit Destinations (CLD) program, awarding Space Act Agreements totaling $415.6 million in 2021 to three partnerships for preliminary design and risk reduction of free-flying commercial stations. These include Axiom Space ($140 million initial allocation, with separate firm-fixed-price contracts for ISS-attached modules transitioning to standalone operation), Blue Origin's Orbital Reef ($130 million), and Nanoracks' Starlab ($160 million, now under Voyager Space). NASA anticipates further Phase 2 funding of $1-1.5 billion from 2026-2031 to support at least two crew-tended demonstrations, emphasizing private ownership to foster a self-sustaining LEO economy. Independent of initial CLD awards, Vast Space is developing Haven-1, targeting launch as the world's first standalone commercial in May 2026 via , with primary structure completion planned for July 2025. Axiom Station's inaugural module is set for uncrewed launch and ISS attachment in late 2027, followed by crewed habitation and eventual detachment for independent orbit. Blue Origin's advanced to testing in April 2025, incorporating modular habitats for up to 10 occupants and supporting microgravity research, , and . This shift to commercial platforms builds on the proven model of NASA's Commercial Resupply Services and Commercial Crew Program, which reduced costs through competitive private innovation and fixed-price incentives, avoiding the overruns inherent in monolithic government projects like the ISS. Proponents argue it promotes redundancy via multiple operators, enabling tailored capabilities for diverse users while NASA focuses on deep space. Yet, empirical risks persist: historical delays in private ventures, such as Orbital Reef's timeline slipping to late 2020s, combined with dependency on limited launch vehicles and uncertain non-NASA revenue streams, could create multi-year voids in LEO infrastructure post-2030 if fewer than two stations achieve operational maturity. Funding gaps beyond NASA's contributions—estimated at under 20% of total development costs for some projects—underscore the need for robust private investment, with recent leadership changes at Axiom highlighting execution uncertainties.

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