Space Launch System

The SLS is a Space Shuttle-derived launch vehicle. Its first stage consists of a central core stage powered by four engines, flanked by two space shuttle-derived solid rocket boosters. Core stage |left The SLS core stage is built by Boeing at NASA's Michoud Assembly Facility in New Orleans. It measures in length and in diameter, matching the diameter of the Space Shuttle external tank to allow NASA to leverage Shuttle-era experience. The stage is visually similar to the Shuttle tank due to its rust-colored spray-on insulation. Aerojet Rocketdyne refurbished these engines with modernized controllers, expanded throttle capability, and additional insulation to handle the higher thermal environment caused by proximity to the solid rocket boosters. The SLS uses a conical frustum-shaped interstage known as the Launch Vehicle Stage Adapter (LVSA) between the core stage and the narrower diameter upper stage. The LVSA consists of sixteen aluminum-lithium panels made of 2195 aluminum alloy and is built by Teledyne Brown Engineering. The first unit cost approximately $60 million, with the next two costing $85 million combined. Solid rocket boosters Shuttle-derived , with side view showing one of the two boosters The first eight SLS flights are planned to use two five-segment solid rocket boosters derived from the four-segment Space Shuttle Solid Rocket Booster manufactured by Northrop Grumman. The booster for the SLS incorporates casing segments previously flown as part of the Shuttle program, with the addition of a center segment to increase performance. The boosters feature updated avionics and lighter insulation but do not include a parachute recovery system, as they are expended after launch. At liftoff, the two boosters together produce more than 75 percent of the total thrust required to propel SLS. The five-segment configuration provides approximately 25 percent greater total impulse than the Shuttle-era boosters. The BOLE design replaces Shuttle-era steel motor cases with carbon-fiber composite cases, which are lighter and stronger. It also substitutes the hydraulic thrust vector control system with an electronic system and uses a different propellant formulation derived from Northrop Grumman's commercial solid rocket motors. Centaur V (future) In February 2026, NASA announced plans to standardize the SLS on the Block 1 configuration and discontinue development of the Exploration Upper Stage (EUS). With production of the DCSS ended, NASA selected an existing commercially developed upper stage for missions following depletion of the ICPS stock: ULA's Centaur V, which uses a pair of RL10 engines and is expected to provide modestly improved performance over the ICPS. Block variants == Development ==

Funding During the joint Senate-NASA presentation in September 2011, it was stated that the SLS program had a projected development cost of US$18 billion through 2017, with $10 billion for the SLS rocket, $6 billion for the Orion spacecraft, and $2 billion for upgrades to the launch pad and other facilities at Kennedy Space Center. These costs and schedules were considered optimistic in an independent 2011 cost assessment report by Booz Allen Hamilton for NASA. An internal 2011 NASA document estimated the cost of the program through 2025 to total at least $41 billion for four launches (1 uncrewed, 3 crewed), with the version ready no earlier than 2030. The Human Exploration Framework Team estimated unit costs for 'Block 0' at $1.6 billion and Block 1 at $1.86 billion in 2010. However, since these estimates were made, the Block 0 SLS vehicle was dropped in late 2011, and the design was not completed. In 2013, the Space Review estimated the cost per launch at $5 billion, depending on the rate of launches. NASA announced in 2013 that the European Space Agency will build the Orion service module. In August 2014, as the SLS program passed its Key Decision Point C review and was deemed ready to enter full development, costs from February 2014 until its planned launch in September 2018 were estimated at $7.021 billion. In October 2018, NASA's Inspector General reported that the Boeing core stage contract had made up 40% of the $11.9 billion spent on the SLS as of August 2018. By 2021, development of the core stage was expected to have cost $8.9 billion, twice the initially planned amount. In December 2018, NASA estimated that yearly budgets for the SLS will range from $2.1 to $2.3 billion between 2019 and 2023. In March 2019, the Trump administration released its fiscal year 2020 budget request for NASA, which notably proposed dropped funding for the Block 1B and 2 variants of SLS. Congressional action ultimately included the funding in the passed budget. On May 1, 2020, NASA awarded a contract extension to Aerojet Rocketdyne to manufacture 18 additional RS-25 engines with associated services for $1.79 billion, bringing the total RS-25 contract value to almost $3.5 billion. and (2) the costs of developing the Exploration Upper Stage (below). Excluded from the SLS cost above are the costs to assemble, integrate, prepare and launch the SLS and its payloads, funded separately in the NASA Exploration Ground Systems, running at about $600 million per year in 2021, in development, including the 5-segment Solid Rocket Boosters used on the SLS. However, as a compromise, lawmakers suggested eliminating the EUS, and directed NASA to evaluate alternatives such as the Centaur V or New Glenn's GS2 upper stage. In early 2026 this change was implemented with the Centaur V being selected as the future SLS upper stage. for Artemis II lifted into High Bay 2 of the Vehicle Assembly Building shortly after stacking operations began in December 2024 The SLS has considered several future development routes of potential launch configurations, with the planned evolution of the blocks of the rocket having been modified many times. Several companies proposed boosters for this competition, all of which were indicated as viable: Aerojet and Teledyne Brown proposed three booster engines each with dual combustion chambers, Alliant Techsystems proposed a modified solid rocket booster with lighter casing, more energetic propellant, and four segments instead of five, and Pratt & Whitney Rocketdyne and Dynetics proposed a liquid-fueled booster named Pyrios. However, this competition was planned for a development plan in which Block 1A would be followed by Block 2A, with upgraded boosters. NASA canceled Block 1A and the planned competition in April 2014, in favor of simply remaining with the Ares I's five-segment solid rocket boosters, themselves modified from the Space Shuttle's solid rocket boosters, until at least the late 2020s. The overly powerful advanced booster would have resulted in unsuitably high acceleration, and would need modifications to Launch Complex 39B, its flame trench, and Mobile Launcher. On August 7, 2014, the SLS Block 1 passed a milestone known as Key Decision Point C and entered full-scale development, with an estimated launch date of November 2018. EUS options In 2013, NASA and Boeing analyzed the performance of several Exploration Upper Stage (EUS) engine options. The analysis was based on a second-stage usable propellant load of 105 metric tons, and compared stages with four RL10 engines, two MARC-60 engines, or one J-2X engine. In 2014, NASA also considered using the European Vinci instead of the RL10, which offered the same specific impulse but with 64% greater thrust, which would allow for the same performance at a lower cost. In 2018, Blue Origin submitted a proposal to replace the EUS with a cheaper alternative to be designed and fabricated by the company, but it was rejected by NASA in November 2019 on multiple grounds; these included lower performance compared to the existing EUS design, incompatibility of the proposal with the height of the door of the Vehicle Assembly Building being only , and unacceptable acceleration of Orion components such as its solar panels due to the higher thrust of the engines being used for the fuel tank. In February 2026, NASA administrator Jared Isaacman announced the cancellation of EUS. SRB tests From 2009 to 2011, three full-duration static fire tests of five-segment solid rocket boosters were conducted under the Constellation Program, including tests at low and high core temperatures, to validate performance at extreme temperatures. The 5-segment solid rocket booster would be carried over to SLS. Qualification Motor 2 was successfully tested on June 28, 2016. Proposed cancellation On February 7, 2025, Boeing, the primary contractor for the SLS, informed its employees working on the rocket program that they may face layoffs when the company's contract expires in March. The announcement coincided with the anticipated release of the presidential budget, suggesting the Trump administration might propose canceling the SLS program. On May 2, 2025, the Trump administration released its fiscal year 2026 budget proposal for NASA, which calls for terminating the SLS and Orion spacecraft programs after Artemis III. The budget proposal described the SLS as "grossly expensive", noting that it costs $4 billion per launch and has exceeded its budget by 140 percent. The budget allocates funding for a program to transition to "more cost-effective commercial systems", a move projected by the White House Office of Management and Budget to save NASA $879 million. The 2025 One Big Beautiful Bill Act included funding for SLS rockets for the Artemis IV and V missions, but a clause directed NASA to evaluate alternatives to the EUS. == Launch costs ==

NASA has been reluctant to provide an official per-flight cost estimate for the SLS. However, independent agencies, such as the White House Office of Management and Budget and the NASA Office of Inspector General, have offered their own estimates. A White House Office of Management and Budget letter to the Senate Appropriations Committee in October 2019 estimated that SLS's total cost to the taxpayer was estimated at "over $2 billion" per launch. When questioned by a journalist, a NASA spokesperson did not deny this per-flight cost estimate. The NASA Office of Inspector General has conducted several audits of the SLS program. A November 2021 report estimated that, at least for the first four launches of Artemis program, the per-launch production and operating costs would be $2.2 billion for SLS, plus $568 million for Exploration Ground Systems. Additionally, the payload would cost $1 billion for Orion and $300 million for the European Service Module. An October 2023 report found that recurring production costs for SLS, excluding development and integration costs, are estimated to be at least $2.5 billion per launch. In 2025, Sean Duffy, the then acting NASA administrator, said that, "Artemis I, Artemis II, and Artemis III are all $4 billion a launch". NASA has said that it is working with Boeing to bring down the cost of SLS launches and that a higher launch frequency could potentially lead to economies of scale, and would allow fixed costs to be spread out over more launches. However, the NASA Office of Inspector General has called NASA's cost savings goals highly unrealistic and other potential government customers have made it clear they have no interest in using SLS. == Operation ==

Construction tank for Artemis II under construction, August 2020 for Artemis II under construction, June 2021 under construction, April 2021 , three SLS versions were planned: Block 1, Block 1B, and Block 2. Each would use the same core stage with its four main engines, but Block 1B will feature the Exploration Upper Stage (EUS), and Block 2 will combine the EUS with upgraded boosters. The ICPS for Artemis 1 was delivered by ULA to NASA about July 2017 and was housed at Kennedy Space Center as of November 2018. Construction of core stage In mid-November 2014, construction of the first core stage hardware began using a new friction stir welding system in the South Vertical Assembly Building at NASA's Michoud Assembly Facility. and it was declared finished by NASA in December 2019. The first core stage left Michoud Assembly Facility for comprehensive testing at Stennis Space Center in January 2020. The static firing test program at Stennis Space Center, known as the Green Run, operated all the core stage systems simultaneously for the first time. Test 7 (of 8), the wet dress rehearsal, was carried out in December 2020 and the fire (test 8) took place on January 16, 2021, but shut down earlier than expected, about 67 seconds in total rather than the desired eight minutes. The reason for the early shutdown was later reported to be because of conservative test commit criteria on the thrust vector control system, specific only for ground testing and not for flight. If this scenario occurred during a flight, the rocket would have continued to fly normally. There was no sign of damage to the core stage or the engines, contrary to initial concerns. The second fire test was completed on March 18, 2021, with all four engines igniting, throttling down as expected to simulate in-flight conditions, and gimballing profiles. The core stage was shipped to Kennedy Space Center to be mated with the rest of the rocket for Artemis I. It left Stennis on April 24 and arrived at Kennedy on April 27. It was refurbished there in preparation for stacking. On June 12, 2021, NASA announced the assembly of the first SLS rocket was completed at the Kennedy Space Center. The assembled SLS was used for the uncrewed Artemis I mission in 2022. and NASA and Boeing are constructing the next three rockets for Artemis II, Artemis III, and Artemis IV. The complete core stage was set to ship to NASA in late fall 2023, eight months later than was predicted originally. The complete core stage was delivered in July 2024. For Artemis III, assembly of elements of the thrust structure began at Michoud Assembly Facility in early 2021. The liquid hydrogen tank for Artemis III was originally planned to be the Artemis I tank, but it was set aside as the welds were found to be faulty. It was postponed to 2:17 pm EDT (18:17 UTC), September 3, after the launch director called a scrub due to a temperature sensor falsely indicating that an RS-25 engine's hydrogen bleed intake was too warm. NASA originally limited the amount of time the solid rocket boosters can remain stacked to "about a year" from the time two segments are joined. In late 2015, the SLS program was stated to have a 70% confidence level for the first Orion flight that carries crew, the second SLS flight overall, to happen by 2023; however, the flight did not take place until 2026. Usage beyond Artemis Efforts have been made to expand the Artemis missions to launching NASA's robotic space probes and observatories. However, SLS program officials have noted that between the launch cadence of Artemis missions and supply chain constraints, it is unlikely that rockets could be built to support science missions before the late 2020s or early 2030s. Another challenge is that the large solid-rocket boosters produce significant vibrations, which can damage sensitive scientific instruments. During wind-tunnel testing, torsional load values (a measurement of twisting and vibration) were nearly double initial estimates. Although program officials later acknowledged the issue, they expressed confidence in their ability to mitigate it. Europa Lander, Enceladus Orbilander, Persephone, HabEx, Origins Space Telescope, LUVOIR, Lynx, and Interstellar probe. Initially, Congress mandated that NASA use the SLS to launch the Europa Clipper probe. However, concerns about the SLS's availability led NASA to seek congressional approval for competitive launch bids. SpaceX ultimately won the contract, saving the agency an estimated US$2 billion in direct launch costs over SLS, albeit at the cost of a longer flight. After the launch of Artemis IV, NASA plans to transfer production and launch operations of SLS to Deep Space Transport LLC, a joint venture between Boeing and Northrop Grumman. The agency hopes the companies can find more buyers for flights on the rocket to bring costs per flight down to $1 billion. However, finding a market for the large and costly rocket will be difficult. Reuters reported that the US Department of Defense, long considered a potential customer, stated in 2023 that it has no interest in the rocket as other launch vehicles already offer them the capability that they need at an affordable price. == Criticism ==

The SLS has been criticized based on program cost, lack of commercial involvement, and non-competitiveness caused by legislation requiring the use of Space Shuttle components "where possible". Funding report, showing how NASA used accounting to "mask" a cost increase by moving the boosters (which cost $889 million) from the SLS to another cost center, without updating the SLS budget to match Utah Senator Orrin Hatch ensured the new rocket used the Shuttle's solid boosters, which were manufactured in his state. Alabama Senator Richard Shelby insisted that the Marshall Space Flight Center design and test the rocket. Florida Senator Bill Nelson brought home billions of dollars to Kennedy Space Center to modernize its launch facilities. Almost immediately, Representative Tom McClintock called on the Government Accountability Office to investigate possible violations of the Competition in Contracting Act, arguing that the requirement that Shuttle components be used on SLS were non-competitive and assured contracts to existing suppliers. During the First Trump administration, NASA administrator Jim Bridenstine suggested to a Senate committee that the agency was considering using the Falcon Heavy or Delta IV Heavy rocket to launch Orion instead of SLS. Afterward, the administrator was reportedly called into a meeting with Senator Shelby, who told Bridenstine he should resign for making the suggestion in a public meeting. == See also ==