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Space Launch System

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This article is about the NASA rocket family. For the similarly-named US Air Force project of the 1960s, see Space Launching System. For Turkey's UFS satellite launcher, see Space Launch System (Turkey).

Space Launch System
A launch vehicle beside a tower on pad
An artist's rendering of SLS Block 1 with Orion spacecraft on the pad before launch.
FunctionSuper heavy-lift launch vehicle
Country of originUnited States
Project costUS$23.011 billion (inflation adjusted, through 2021) [note 1]
Cost per launchOver US$2 billion excluding development (estimate) [note 2][2][3]
Cost per yearUS$2.555 billion for FY 2021[4]
Size
Height111.25 m (365.0 ft), Block 2 Cargo
Diameter8.4 m (28 ft), Core stage
Stages2
Capacity
Payload to LEO [altitude and inclination needed]
Mass
  • Block 1: 95 t (209,000 lb)[5]
  • Block 1B: 105 t (231,000 lb)[6][7]
  • Block 2: 130 t (290,000 lb)[8]
Payload to trans-lunar injection
Mass
  • Block 1: > 27 t (59,500 lb)[9][10]
  • Block 1B Crew: 38 t (83,700 lb)
  • Block 1B Cargo: 42 t (92,500 lb)
  • Block 2 Crew: > 43 t (94,700 lb)
  • Block 2 Cargo: > 46 t (101,400 lb)
Associated rockets
Comparable
Launch history
StatusAwaiting first launch
Launch sitesKennedy Space Center, LC-39B
First flightNET January 2022[11]
Type of passengers/cargoOrion
Stage info
Boosters (Block 1, 1B)
No. boosters2 five-segment Solid Rocket Boosters
Height54 m (177 ft)[12]
Gross mass730 t (1,610,000 lb)[12]
Powered byoff
Maximum thrust14.6 MN (3,300,000 lbf) sea level
16 MN (1,600 tf; 3,600,000 lbf) vacuum[13]
Total thrust29.2 MN (6,600,000 lbf) sea level
32 MN (3,300 tf; 7,200,000 lbf) vacuum
Specific impulse269 s (2.64 km/s)
Burn time126 seconds
PropellantPBAN, APCP
First stage (Block 1, 1B, 2) – Core stage
Height65 m (212 ft)[14]
Diameter8.4 m (27.6 ft)
Empty mass85 t (187,990 lb)
Gross mass1,073 t (2,365,000 lb)
Powered by4 RS-25D/E
Maximum thrust9.1 MN (2,000,000 lbf) vacuum[15]
Specific impulse366 s (3.59 km/s) (sea level)
452 s (4.43 km/s)
Burn time480 seconds
PropellantLH2 / LOX
Second stage (Block 1) – ICPS
Height13.7 m (45 ft)[16]
Diameter5 m (16 ft)
Empty mass3,490 kg (7,690 lb)[17]
Gross mass32,066 kg (70,693 lb)
Powered by1 RL10B-2/C-2
Maximum thrust110.1 kN (24,800 lbf)
Specific impulse465.5 s (4.565 km/s)[18]
Burn time1125 seconds
PropellantLH2 / LOX
Second stage (Block 1B, Block 2) – Exploration Upper Stage
Height17.3 m (57 ft)[17]
Diameter8.4 m (28 ft)
Powered by4 RL10C-3, later 4 RL10C-X
Maximum thrust407.2 kN (91,500 lbf)
Burn time
  • 350 seconds (LEO ascent)
  • 925 seconds (TLI burn)
PropellantLH2 / LOX
[edit on Wikidata]

The Space Launch System (abbreviated as SLS) is an American super heavy-lift expendable launch vehicle under development by NASA since 2011. It replaces the Ares I and Ares V launch vehicles, which were cancelled along with the rest of the Constellation program.[19][20][21] The SLS is intended to become the successor to the retired Space Shuttle as the primary launch vehicle of NASA's deep space exploration plans through the 2020s and beyond.[22][23][24] Crewed lunar flights are planned as part of the Artemis program, leading to a possible human mission to Mars.[25][26] The SLS is being developed in three major phases with increasing capabilities: Block 1, Block 1B, and Block 2.[5] As of 22 December 2019, SLS Block 1 launch vehicles are to launch the first three Artemis missions.[27] Five subsequent SLS flights are planned to use Block 1B, after which all flights will use Block 2.[28][26][29]

The SLS is planned to launch the Orion spacecraft as part of the Artemis program, making use of the ground operations and launch facilities at NASA's Kennedy Space Center in Florida. Artemis will use one SLS each year until at least 2030.[30] SLS will launch from LC-39B at the Kennedy Space Center. The first launch was originally scheduled for 2016,[31] but it has been delayed at least eight times, adding more than five years to the original six-year schedule.[note 3] As of September 2021, the first launch is scheduled for no earlier than January 2022.[11][32]

Description

See also: Super heavy-lift launch vehicle § Comparison

The SLS is a Space Shuttle-derived launch vehicle. The first stage of the rocket is powered by one central core stage and two outboard solid rocket boosters. All SLS Blocks share a common core stage design, while they differ in their upper stages and boosters.[33][34][35][36]

Core stage

The SLS core stage rolling out of the Michoud Facility for shipping to Stennis.

The core stage is responsible for propelling the upper stage and payload out of the atmosphere and accelerating up to almost orbital velocity, aided by the solid rocket boosters. It contains the liquid hydrogen fuel and liquid oxygen oxidizer tanks for the ascent phase, the forward and aft solid rocket booster attach points, avionics, and the Main Propulsion System (MPS). The MPS is responsible for supplying the four RS-25 engines[33] with fuel and oxidizer, gimballing the engines using hydraulic actuators, and pressurizing the propellant tanks via autogenous pressurization. The core stage provides approximately 25% of the vehicle's thrust at liftoff.[37][38] The stage is 65 m (213 ft) long by 8.4 m (28 ft) in diameter and is both structurally and visually similar to the Space Shuttle external tank.[20][39] The first four flights will each use and expend four of the remaining sixteen RS-25D engines previously flown on Space Shuttle missions.[40][41][42] Aerojet Rocketdyne modifies these engines with modernized engine controllers, higher throttle limits, as well as insulation for the high temperatures the engine section will experience due to their position adjacent to the solid rocket boosters.[43] Later flights will switch to a RS-25 variant optimized for expended use, the RS-25E, which will lower per-engine costs by over 30%.[44][45] The thrust of each RS-25D engine has been increased from 2,188 kN (492,000 lbf), as on the Space Shuttle, to 2,281 kN (513,000 lbf) on the sixteen modernized engines. The RS-25E will further increase per-engine thrust to 2,321 kN (522,000 lbf).[46][47]

Boosters

Blocks 1 and 1B of the SLS are planned to use two five-segment solid rocket boosters. These solid rocket boosters use casing segments that were flown on Shuttle missions as parts of the four-segment Space Shuttle Solid Rocket Boosters. They possess an additional center segment, new avionics, lighter insulation, but lack a parachute recovery system.[48] The five-segment solid rocket boosters provide approximately 25% more total impulse than the Shuttle Solid Rocket Boosters, but will not be recovered after use.[49][50]

The stock of SLS Block 1 to 1B boosters is limited by the number of casings left over from the Shuttle program, which allows for eight flights of the SLS.[51] On the 2nd of March 2019, the Booster Obsolescence and Life Extension program were announced. This program will develop new solid rocket boosters, to be built by Northrop Grumman Space Systems, for further SLS flights, marking the beginning of Block 2. These boosters will be derived from the composite-casing solid rocket boosters then in development for the canceled OmegA launch vehicle, and are projected to increase Block 2's payload to 130 t (130 long tons; 140 short tons) to LEO and at least 46 t (45 long tons; 51 short tons) to trans-lunar injection.[52][53][54]

Upper stages

The Interim Cryogenic Propulsion Stage (ICPS) is planned to fly on Artemis 1, 2, and 3 as the upper stage of SLS Block 1.[55] It is a stretched and human-rated Delta IV 5 m (16 ft) Delta Cryogenic Second Stage powered by a single RL10 engine. The first ICPS will use the RL10B-2 variant, while the second and third ICPS will use the RL10C-2 variant.[56][57][58] Block 1 is intended to be capable of lifting 95 t (93 long tons; 105 short tons) to low Earth orbit (LEO) in this configuration, including the weight of the ICPS as part of the payload.[5] The ICPS will launch Artemis 1 into an initial 1,806 by 30 km (1,122 by 19 mi) suborbital trajectory to ensure safe disposal of the core stage.[59] ICPS will then perform orbital insertion and a subsequent translunar injection burn to send Orion towards the Moon.[60] The ICPS will be human-rated for the crewed Artemis 2 and 3 flights.[55]

The Exploration Upper Stage (EUS) is planned to fly on Artemis 4. The EUS will complete the SLS ascent phase and then re-ignite to send its payload to destinations beyond LEO.[61] It is expected to be used by Block 1B and Block 2. The EUS shares the core stage diameter of 8.4 meters, and will be powered by four RL10C-3 engines.[62] It will eventually be upgraded to use four improved RL10C-X engines.[63] The improved upper stage was originally named the Dual Use Upper Stage (DUUS, pronounced "duce")[61] but was later renamed the Exploration Upper Stage (EUS) due to DUUS sounding like a profanity in Japanese.[64]

Block variants

SLS Vehicle Differences
Flight # Block Core stage engines Boosters Upper stage Payload mass to...
Low Earth orbit (LEO) Trans-lunar injection (TLI) Heliocentric orbit (HCO)
1 1 RS-25D[40] 5-segment Shuttle-derived boosters Interim Cryogenic Propulsion Stage (ICPS) with RL10B-2[58] 95 metric tons (209,000 lb)[5] >27 metric tons (59,500 lb)[65][9][10] Not known
2,3 Interim Cryogenic Propulsion Stage (ICPS) with RL10C-2[56]
4 1B Exploration Upper Stage (EUS) 105 metric tons (231,000 lb)[6] 42 metric tons (92,500 lb)[65][9][10]
5,6,7,8 RS-25E[45]
9, ... 2 Booster Obsolescence and Life Extension (BOLE)[51] 130 metric tons (290,000 lb)[8] >46 metric tons (101,400 lb)[65][9][10] 45 metric tons (99,000 lb)[5]
  • Block 1 configuration
    Block 1 configuration
  • Block 1B configuration
    Block 1B configuration
  • Block 2 configuration
    Block 2 configuration

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.[66][67] These costs and schedules were considered optimistic in an independent 2011 cost assessment report by Booz Allen Hamilton for NASA.[68] An internal 2011 NASA document estimated the cost of the program through 2025 to total at least $41 billion for four 95 t (93 long tons; 105 short tons) launches (1 uncrewed, 3 crewed),[69][70] with the 130 t (130 long tons; 140 short tons) version ready no earlier than 2030.[71] The Human Exploration Framework Team estimated unit costs for Block 0 at $1.6 billion and Block 1 at $1.86 billion in 2010.[72] However, since these estimates were made the Block 0 SLS vehicle was dropped in late 2011, and the design was not completed.[33]

In September 2012, an SLS deputy project manager stated that $500 million is a reasonable target average cost per flight for the SLS program.[73] In 2013, the Space Review estimated the cost per launch at $5 billion, depending on the rate of launches.[74][75] NASA announced in 2013 that the European Space Agency will build the Orion service module.[76] In August 2014, as the SLS program passed its Key Decision Point C review and entered full development, costs from February 2014 until its planned launch in September 2018 were estimated at $7.021 billion.[77] Ground systems modifications and construction would require an additional $1.8 billion over the same time.[78]

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, core stages were expected to have cost $8.9 billion, twice the initially planned amount.[79] In December 2018, NASA estimated that yearly budgets for the SLS will range from $2.1 to $2.3 billion between 2019 and 2023.[80]

In March 2019, the Trump Administration released its Fiscal Year 2020 Budget Request for NASA. This budget did not include any money for the Block 1B and Block 2 variants of SLS. It was therefore uncertain whether these future variants of SLS will be developed, but congressional action restored this funding in the passed budget.[81] Several launches previously planned for the SLS Block 1B are expected to fly on commercial launcher vehicles such as Falcon Heavy, New Glenn, and Vulcan.[82] However, the request for a budget increase of $1.6 billion towards SLS, Orion, and crewed landers along with the launch manifest seem to indicate support of the development of Block 1B, debuting Artemis 3. Block 1B will be used mainly for co-manifested crew transfers and logistical needs rather than constructing the Gateway. An uncrewed Block 1B is planned to launch the Lunar Surface Asset in 2028, the first lunar outpost of the Artemis program. Block 2 development will most likely start in the late 2020s after NASA is regularly visiting the lunar surface and shifts focus towards Mars.[83]

Budget

For fiscal years 2011 through 2021, the SLS program had expended funding totaling $21.209 billion in nominal dollars. This is equivalent to $23.011 billion in 2021 dollars using the NASA New Start Inflation Indices.[84]

Fiscal year Funding Status
Nominal
(millions) 		In $2021[84]
(millions)
2011 $1,536.1 $1,829.5 Actual[85]
(Formal SLS Program reporting excludes the Fiscal 2011 budget.)[86]
2012 $1,497.5 $1,765.6 Actual[87]
2013 $1,414.9 $1,642.7 Actual[88]
2014 $1,600.0 $1,822.4 Actual[89]
2015 $1,678.6 $1,873.3 Actual[90]
2016 $1,971.9 $2,171.7 Actual[91]
2017 $2,127.1 $2,299.4 Actual[92]
2018 $2,150.0 $2,268.3 Actual[93]
2019 $2,150.0 $2,233.1 Actual[94]
2020 $2,528.1 $2,561.0 Actual[95]
2021 $2,555.0 $2,555.0 Enacted[4]
Total: 2011–2021 $21,209.2 $23,011.2

On top of this, the costs to assemble, integrate, prepare and launch the SLS and its payloads are funded separately under Exploration Ground Systems about $600 million per year.[96][97] Payloads that launch on SLS, such as the Orion crew capsule, are similarly accounted separately from SLS. Predecessor programs contributed development to SLS, such as the Ares V Cargo Launch Vehicle, funded from 2008 to 2010, a total of $70 million,[98] and Ares I Crew Launch Vehicle, funded from 2006 to 2010, a total of $4.8 billion[98][99] in development that included the 5-segment Solid Rocket Boosters that will be used on the SLS.[100]

Programs that are included under the above SLS cost table include the interim Upper Stage for the SLS, the Interim Cryogenic Propulsion Stage (ICPS), which includes a $412 million contract.[101]

Also included in the above SLS cost table are the costs of developing the Exploration Upper Stage:

Fiscal year Funding for EUS development
Nominal
(millions) 		In 2021[84]
(millions)
2016 $77.0[91] $84.8
2017 $300.0[102][92] $324.3
2018 $300.0[103][93] $316.5
2019 $150.0[104][94] $155.1
2020 $300.0[95] $303.9
2021 $400.0[4][note 4] $400.0
Total: 2016–2021 $1,527.0 $1,584.6

Launch costs

Estimates of the per launch costs for the SLS have varied widely, partly due to uncertainty over how much the program will expend during development and testing before the operational launches begin, and partly due to various agencies using differing cost measures; but also based on differing purposes for which the cost estimates were developed. For example, a marginal cost per one additional launch ignores the development and annual recurring fixed costs, whereas a total cost per launch includes recurring costs but excludes development.

There are no official NASA estimates for how much the SLS will cost per launch, nor for the SLS program annual recurring costs once operational. Cost per launch is not a straightforward figure to estimate as it depends heavily on how many launches occur per year.[1] For example, similarly, the Space Shuttle was estimated, in 2012 dollars, to cost $576 million per launch had it been able to achieve 7 launches per year, while the marginal cost of adding a single additional launch in a given year was estimated to be less than half of that, at just $252 million of marginal cost. However, at the rate that it flew, the cost, in the end, was $1.64 billion per Space Shuttle launch, including development.[105]: III−490 

NASA associate administrator William H. Gerstenmaier said in 2017 that there would be no official per flight cost estimates of any variety provided by NASA for the SLS.[106] Other bodies, such as the Government Accountability Office (GAO), the NASA Office of Inspector General, the Senate Appropriations Committee, and the White House Office of Management and Budget have put out cost per launch figures, however. Several internal NASA programs and project concept study reports have released proposed budgets that include future SLS launches. For example, a concept study report for a space telescope stated it was advised by NASA HQ in 2019 to budget $500 million for an SLS launch in 2035.[107] Another study in 2019 also proposing a space telescope assumed a budget for their launch of $650 million in current-day dollars, or $925 million for when the launch would occur, also in the "mid-2030s".[108]

Europa Clipper is a NASA scientific mission that was initially required by Congress to launch on the SLS. Oversight bodies both internal and external to NASA disagreed with this requirement. First, NASA's Inspector General office published a report in May 2019[109][110] that stated Europa Clipper would need to give up $876 million for the "marginal cost" of its SLS launch. Then, an addendum to the letter published in August 2019 increased the estimate and stated that switching to a commercial rocket would save over $1 billion. However, those savings may have included a portion of costs related to the delay in launch schedule; a commercial alternative could launch earlier than SLS. A JCL (Joint Cost and Schedule Confidence Level) analysis cited in that letter put the cost savings at $700 million, with the SLS at $1.05 billion per launch and the commercial alternative at $350 million.[111][112] In July 2021, NASA announced that instead of SLS, a SpaceX Falcon Heavy would be used to launch Europa Clipper.[113] This was done for technical reasons unrelated to cost, and the total cost savings was estimated at US$2 billion.[114][115][116]

Finally, a letter from the White House Office of Management and Budget (OMB) to the Senate Appropriations Committee in October 2019 revealed that SLS's total cost to the taxpayer was estimated at "over $2 billion" per launch after development is complete; said development has cost $20 billion in 2020 dollars.[2] The letter suggested Congress remove this requirement, agreeing the NASA Inspector General, adding that using a commercial launch vehicle for Europa Clipper instead of the SLS would save $1.5 billion overall. NASA did not deny this $2 billion cost of launch and an agency spokesperson stated it "is working to bring down the cost of a single SLS launch in a given year as the agency continues negotiations with Boeing on the long-term production contract and efforts to finalize contracts and costs for other elements of the rocket".[1] This OMB figure is dependent on the rate of construction, so building more SLS rockets faster could decrease the per-unit cost.[1] For example, Exploration Ground Systems – whose only role is to support, assemble, integrate, and launch SLS – has separately budgeted fixed costs of $600 million per year on facilities, spread across however many rockets launch that year.[96] Then NASA Administrator Jim Bridenstine shared informally that he disagrees with the $2 billion figure since the marginal cost of an SLS launch should decrease after the first few, and is expected to end up around $800 million to $900 million, although contract negotiations were only just beginning for those later cores.[117]

Early plans

Diagram of four versions of the Space Launch System rocket
Planned evolution of the SLS, 2018
SLS Booster test at Orbital ATK's desert facility northwest of Ogden, Utah, March 2015
Exploration Ground Systems and Jacobs prepare to lift and place the core stage of the SLS rocket, June 2021

The SLS was created by an act of Congress, in which NASA was directed to create a system for launching payloads and crew into space that would replace the capabilities lost with the retirement of the Space Shuttle.[31] The act set out certain goals, such as being able to lift a certain mass into low earth orbit, a target date for the system being operational, and a directive to use "to the extent practicable" existing components, hardware, and workforce from the Space Shuttle and from Ares I.[31]: 12  On 14 September 2011, NASA announced their plan to meet these requirements: the design for the SLS, with the Orion spacecraft as payload.[118][119][120][121]

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.[100] Many options, all of which just needed to meet the congressionally mandated payload minimums,[100] were considered, including a Block 0 variant with three main engines,[33] a variant with five main engines,[100] a Block 1A variant with upgraded boosters instead of the improved second stage,[33] and a Block 2 with five main engines plus the Earth Departure Stage, with up to three J-2X engines.[36]

In the initial announcement of the design of the SLS, NASA also announced an "Advanced Booster Competition", to select which boosters would be used on Block 2 of the SLS.[118][122][38][123] Several companies proposed boosters for this competition, all of which were indicated as viable[124]: Aerojet and Teledyne Brown proposed three booster engines each with dual combustion chambers,[125] Alliant Techsystems proposed a modified solid rocket booster with lighter casing, more energetic propellant, and four segments instead of five,[126] and Pratt & Whitney Rocketdyne and Dynetics proposed a liquid-fueled booster named Pyrios.[127] 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.[100][128] The overly powerful advanced booster would have resulted in unsuitably high acceleration, and would need modifications to LC-39B, its flame trench, and Mobile Launcher.[129][100]

On 31 July 2013, the SLS passed Preliminary Design Review. The review included not only the rocket and boosters but also ground support and logistical arrangements.[130] On 7 August 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.[77][131] In 2013, NASA and Boeing analyzed the performance of several 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.[132] In 2014, NASA also considered using the European Vinci instead of the RL10. The Vinci offers the same specific impulse but with 64% greater thrust, which would allow for the same performance at a lower cost.[133][134]

Blue Origin submitted a proposal to replace the Exploration Upper Stage 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 390 feet, and unacceptable acceleration of Orion components such as its solar panels.[135][136]: 8 

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.[137][138][139] The 5-segment solid rocket booster would be carried over to SLS.[100] Northrop Grumman Innovation Systems has completed full-duration static fire tests of the five-segment solid rocket boosters. Qualification Motor 1 was tested on 10 March 2015.[140] Qualification Motor 2 was successfully tested on 28 June 2016.[141]

Operation

Construction

Liquid hydrogen tank for Artemis 2 under construction, as of August 2020
"Boat-tail" for Artemis 2 under construction, as of June 2021
Engine section shroud structure for Artemis 3 under construction, as of April 2021

As of 2020, three SLS versions are planned: Block 1, Block 1B, and Block 2. Each will 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.[142][6][143] In mid-November 2014, construction of the first Core Stage hardware began using a new welding system in the South Vertical Assembly Building at NASA's Michoud Assembly Facility.[144] Between 2015 and 2017, NASA test fired RS-25 engines in preparation for use on SLS.[44] The ICPS for Artemis 1 was delivered by ULA to NASA about July 2017[145] and was housed at Kennedy Space Centre as of November 2018.[146]

The core stage for the first SLS, built at Michoud Assembly Facility by Boeing,[147] had all four engines attached in November 2019,[148] and it was declared finished by NASA in December 2019.[149]

The first core stage left Michoud Assembly Facility for comprehensive testing at Stennis Space Center in January 2020.[150] 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.[151][152] Test 7 (of 8), the wet dress rehearsal, was carried out in December 2020 and the fire (test 8) took place on 16 January 2021, but shut down earlier than expected,[153] 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.[154] The second fire test was completed on 18 March 2021, with all 4 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 1. It left Stennis on April 24 and arrived at Kennedy on April 27.[155] It was refurbished there in preparation for stacking.[156] On 12 June 2021, NASA announced the assembly of the first SLS rocket was completed at the Kennedy Space Center. The assembled SLS is planned to be used for the unmanned Artemis 1 mission in 2022.[11]

While the first SLS for Artemis 1 is being prepared for launch, NASA and Boeing are constructing the next three, for Artemis 2, Artemis 3, and Artemis 4.[157] Boeing stated in July 2021 that while the COVID-19 pandemic has affected their suppliers and schedules, such as delaying parts needed for hydraulics, they still will be able to provide the Artemis 2 SLS Core stage per NASA's schedule, with months to spare.[157] The spray-on foam insulation process for Artemis 2 has been automated since Artemis 1 for most sections of the Core stage, saving 12 days in the schedule.[158][157] The Artemis 2 forward skirt, which is the foremost component of the Core stage, was affixed on the liquid oxygen tank in late May 2021.[157] For Artemis 3, assembly elements of the thrust structure began at Michoud Assembly Facility in early 2021.[157] The liquid hydrogen tank that is to be used on Artemis 3 was originally planned to be the Artemis 1 tank, but it was set aside as the welds were found to be faulty.[159]: 2  Repair techniques were developed, and the tank has reentered production and will be proof tested for strength, for use on Artemis 3.[159]: 2  As of July 2021, Boeing is also preparing to begin construction of the Exploration Upper Stage (EUS), which is planned to debut on Artemis 4.[157]

Planned launches

Main article: List of Space Launch System launches

Originally planned for late 2016, the intended uncrewed first flight of SLS has slipped more than eight times and more than five years.[note 3] NASA plans to announce a specific projected first launch date after Orion is stacked on Artemis 1.[170] NASA limits the amount of time the solid rocket boosters can remain stacked to "about a year" from the time two segments are joined.[171] The first and second segments of the Artemis 1 boosters were joined on 7 January 2021.[172] NASA can choose to extend the time limit based on an engineering review.[173] On 29 September 2021, Northrup Grumman indicated that the limit can be extended to eighteen months for Artemis 1, based on an analysis of the data collected when the boosters were being stacked.[11] As of 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, by 2023,[174][175][176] and as of 2020, NASA is continuing to project a 2023 launch.[177]

Flight No. Date, time (UTC) Configuration Payload Orbit Outcome
1 16 November 2022, 06:47[178] Block 1 Artemis I (Orion and ESM) TLI Success
Uncrewed maiden flight of the SLS, first operational flight of the Orion capsule. Carrying cubesats for ten missions in the CubeSat Launch Initiative (CSLI), and three missions in the Cube Quest Challenge: ArgoMoon, BioSentinel, CuSP, EQUULEUS, LunaH-Map, Lunar IceCube, LunIR, NEA Scout, OMOTENASHI and Team Miles.[179][180] The payloads were sent on a trans-lunar injection trajectory.[181][182]
2 April 2026[183] Block 1 Crew
TLI Planned
Crewed lunar flyby.
3 Mid-2027[183] Block 1 Crew
Selenocentric Planned
Crewed lunar rendezvous and landing.[184]
4 September 2028[185] Block 1B Crew[186]
Selenocentric (NRHO) Planned
Crewed mission to the Lunar Gateway. Delivery and integration of the International Habitation Module (I-HAB) to the Gateway, following by a crewed lunar landing.[187]
5 March 2030[188] Block 1B Crew[186]
Selenocentric (NRHO) Planned
Crewed mission to the Lunar Gateway, rendezvousing with the first Lunar Exploration Transportation Services (LETS) lander for a lunar landing. Delivery and integration of the ESPRIT module to the Gateway.[189]

Usage beyond Artemis

Main article: List of Space Launch System launches § Proposed launches

While the SLS is only confirmed for use on the first few Artemis missions, many other upcoming proposed NASA missions intend to launch on the SLS, such as: Neptune Odyssey,[190][191] Europa Lander,[192][193][194] Persephone,[195] HabEx,[108] Origins Space Telescope,[107] LUVOIR,[196] Lynx,[197] and Interstellar probe.[198] LUVOIR, for example, developed two possible telescope designs: the larger "LUVOIR-A" for an SLS launch, and "LUVOIR-B" with a smaller mirror and lower resolution, if another launch vehicle must be used.[199]

Criticism

The SLS has been criticized based on program cost, lack of commercial involvement, and the non-competitive nature of a vehicle legislated to use Space Shuttle components.

Funding

In 2011, Rep. Tom McClintock and other groups called on the Government Accountability Office to investigate possible violations of the Competition in Contracting Act, arguing that Congressional mandates forcing NASA to use Space Shuttle components for the SLS are de facto non-competitive, single-source requirements assuring contracts to existing Shuttle suppliers.[200][201][202] The Competitive Space Task Force, in September 2011, said that the new government launcher directly violates NASA's charter, the Space Act, and the 1998 Commercial Space Act requirements for NASA to pursue the "fullest possible engagement of commercial providers" and to "seek and encourage, to the maximum extent possible, the fullest commercial use of space".[203][202] Opponents of the heavy launch vehicle have critically used the name "Senate launch system",[57][202][204]a name that was still being used by opponents to criticize the program in 2021, as "the NASA Inspector General said the total cost of the rocket would reach $27 billion through 2025".[205]

Lori Garver, then NASA Deputy Administrator, called for canceling the launch vehicle alongside the Mars 2020 rover.[206] Phil Plait shared his criticism of the SLS in light of ongoing budget tradeoffs between the Commercial Crew Development and SLS budgets, also referring to earlier critiques by Garver.[207] In 2019, the Government Accountability Office found that NASA had awarded Boeing over $200 million for service with ratings of good to excellent despite cost overruns and delays. As of 2019, the maiden launch of the SLS was expected in 2021.[208][209] NASA continued to expect that the first orbital launch would be in 2021 as late as May 2021.[167]

A diagram showing two bars on both sides
Visual from the March 2020 Inspector General report, showing how NASA used accounting to "mask"[210]: iv  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.[210]: 22 

NASA moved out $889 million of costs relating to SLS boosters, but did not update the SLS budget to match, a March 2020 Inspector General report found. This kept the budget overrun to 15% by FY 2019.[210]: 22  At 30%, NASA would have to notify Congress and stop funding unless Congress reapproves and provides additional funding.[210]: 21–23  The Inspector General report found that were it not for this "masking" of cost, the overrun would be 33% by FY 2019.[210]: iv, 23  The GAO separately stated "NASA's current approach for reporting cost growth misrepresents the cost performance of the program".[211]: 19–20 

On 1 May 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.[212][45] Ars Technica commented that the average cost of each RS-25 therefore rose to $146 million, so each SLS launch uses $580 million for its four engines. Ars noted that for the cost of just one engine, six more powerful RD-180 engines could be purchased, or nearly an entire Falcon Heavy launch with two-thirds of the SLS lift capacity.[212][213] Former NASA Administrator Charlie Bolden, who oversaw the initial design and development of the SLS, also shared his criticism of the program in an interview with Politico in September 2020. Bolden said that the "SLS will go away because at some point commercial entities are going to catch up". Bolden further stated, "commercial entities are really going to build a heavy-lift launch vehicle sort of like SLS that they will be able to fly for a much cheaper price than NASA can do SLS".[214]

Proposed alternatives

In 2009, the Augustine commission proposed a commercial 75 t (74 long tons; 83 short tons) launcher with lower operating costs and noted that a 40–60 t (39–59 long tons; 44–66 short tons) launcher was the minimum required to support lunar exploration.[215] In 2011–2012, the Space Access Society, Space Frontier Foundation, and The Planetary Society called for the cancellation of the project, arguing that the SLS will consume the funds for other projects from the NASA budget.[203][200][216] U.S. Representative Dana Rohrabacher and others proposed that an orbital propellant depot should be developed and the Commercial Crew Development program accelerated instead.[203][217][218][219][220]

A NASA study that was not publicly released[221][222] and another from the Georgia Institute of Technology showed this option to be possibly cheaper.[223][224] In 2012, the United Launch Alliance also suggested using existing rockets with on-orbit assembly and propellant depots as needed. The lack of competition in the SLS design was highlighted.[225][226][227][204][228] In the summer of 2019, a former ULA employee claimed that Boeing, NASA's prime contractor for SLS, viewed orbital refueling technology as a threat to the SLS and blocked further investment in it.[229] In 2011, Robert Zubrin, founder of Mars Society and Mars Direct, suggested that a heavy lift vehicle could be developed for $5 billion on fixed-price requests for proposal.[230] In 2010, SpaceX's CEO Elon Musk claimed that his company could build a launch vehicle in the 140–150 t (310,000–330,000 lb) payload range for $2.5 billion, or $300 million (in 2010 dollars) per launch, not including a potential upper-stage upgrade.[231][232]

  • RS-25D engine testing at Stennis Space Center.
    RS-25D engine testing at Stennis Space Center.
  • SLS Mobile Launcher
    SLS Mobile Launcher
  • The core stage for the SLS rocket for Artemis I
    The core stage for the SLS rocket for Artemis I
  • The SLS core stage rolling out of the Michoud Facility for shipping to Stennis.
    The SLS core stage rolling out of the Michoud Facility for shipping to Stennis.
  • Solid rocket boosters segment
    Solid rocket boosters segment
  • ICPS on the move
    ICPS on the move
  • Engine shot of the 4 RS-25 engines during the first Green Run hotfire test of the SLS core stage on January 16, 2021
    Engine shot of the 4 RS-25 engines during the first Green Run hotfire test of the SLS core stage on January 16, 2021
  • The first Green Run hotfire test of the SLS core stage on January 16, 2021
    The first Green Run hotfire test of the SLS core stage on January 16, 2021
  • Stacking of the SLS solid rocket boosters for Artemis 1 in the VAB
    Stacking of the SLS solid rocket boosters for Artemis 1 in the VAB
  • The Artemis 1 SLS core stage being loaded onto the Pegasus barge
    The Artemis 1 SLS core stage being loaded onto the Pegasus barge
  • The Green Run testing was the first top-to-bottom integrated testing of the stage's systems prior to its maiden flight
    The Green Run testing was the first top-to-bottom integrated testing of the stage's systems prior to its maiden flight
  • Artemis I core stage going into the Vehicle Assembly Building
    Artemis I core stage going into the Vehicle Assembly Building
  • Artemis I in the Vehicle Assembly Building
    Artemis I in the Vehicle Assembly Building

See also

Notes

  1. ^ See the budget table for yearly inflation adjusted figures.
  2. ^ This is for the Block 1 launch vehicle alone and does not include the Orion capsule or service module costs.[1]
  3. ^ a b NASA has announced at least seven schedule slips: December 2016,[31][19][160] October 2017,[161] November 2018,[162] 2019,[163] June 2020,[164] April 2021,[165] November 2021,[166][167] December 2021,[32] and then to some time between January 2022 and March 2022.[168][169][11]
  4. ^ The FY2021 spending plan indicates that this is for "Block 1B (non-add) (including EUS)"


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