 An artist's rendering of SLS Block 1 with Orion spacecraft on the pad before launch. | |
| Function | Super heavy-lift launch vehicle |
|---|---|
| Country of origin | United States |
| Project cost | US$18.6 billion (as of 2020) |
| Cost per launch | Over US$2 billion excluding development (estimate) |
| Cost per year | US$2.5 billion for 2020 |
| Size | |
| Height | 111.25 m (365.0 ft), Block 2 Cargo |
| Diameter | 8.4 m (28 ft), core stage |
| Stages | 2 |
| Capacity | |
| Payload to LEO | |
| Mass |
|
| Payload to trans-lunar injection | |
| Mass |
|
| Associated rockets | |
| Comparable | |
| Launch history | |
| Status | Active |
| Launch sites | Kennedy Space Center, LC-39B |
| First flight | NET 22 November 2021 |
| Notable payloads | Artemis 1, Orion |
| Boosters (Block 1, 1B) | |
| No. boosters | 2 five-segment Solid Rocket Boosters |
| Length | 54 m (177 ft) |
| Gross mass | 730 t (1,610,000 lb) |
| Thrust | 14.6 MN (1,490 tf; 3,300,000 lbf) sea level 16 MN (1,600 tf; 3,600,000 lbf) vacuum |
| Total thrust | 29.2 MN (2,980 tf; 6,600,000 lbf) sea level 32 MN (3,300 tf; 7,200,000 lbf) vacuum |
| Specific impulse | 269 s (2.64 km/s) |
| Burn time | 126 seconds |
| Propellant | PBAN, APCP |
| First stage (Block 1, 1B, 2) – Core stage | |
| Length | 65 m (212 ft) |
| Diameter | 8.4 m (27.6 ft) |
| Empty mass | 85 t (187,990 lb) |
| Gross mass | 979 t (2,159,322 lb) |
| Engines | 4 RS-25D/E |
| Thrust | 9.1 MN (930 tf) vacuum |
| Specific impulse | 366 s (3.59 km/s) (sea level) 452 s (4.43 km/s) |
| Burn time | 480 seconds |
| Propellant | LH2 / LOX |
| Second stage (Block 1) – ICPS | |
| Length | 13.7 m (45 ft) |
| Diameter | 5 m (16 ft) |
| Empty mass | 3.5 t (7,690 lb) |
| Gross mass | 30.7 t (67,700 lb) |
| Engines | 1 RL10B-2 |
| Thrust | 110.1 kN (11.23 tf; 24,800 lbf) |
| Specific impulse | 465.5 s (4.565 km/s) |
| Burn time | 1125 seconds |
| Propellant | LH2 / LOX |
| Second stage (Block 1B, Block 2) – Exploration Upper Stage | |
| Length | 17.6 m (58 ft) |
| Diameter | 8.4 m (28 ft) |
| Engines | 4 RL10C-3, later 4 RL10C-X |
| Thrust | 440 kN (45 tf; 99,000 lbf) |
| Propellant | LH2 / LOX |
The Space Launch System (SLS) is an American super heavy-lift expendable launch vehicle, which has been under development by NASA since its announcement in 2011. It replaced the Ares I, Ares V, and Jupiter planned launch vehicles, which all never left the development phase. Like those proposals, it is a design derived from the components and technology of the earlier Space Shuttle.
It had been planned to become the primary launch vehicle of NASA's deep space exploration plans throughout the 2010s (now 2020s), including the planned crewed lunar flights of the Artemis program and a possible follow-on human mission to Mars. SLS is intended to replace the retired Space Shuttle as NASA's flagship vehicle. Following the cancellation of the Constellation program, the NASA Authorization Act of 2010 envisioned a single launch vehicle usable for both crew and cargo. In 2013, SLS was projected to be the most capable super-heavy lift launch vehicle ever built.
The initial variant of SLS, Block 1, was required by the U.S. Congress to lift a payload of 70 t (69 long tons; 77 short tons) to low Earth orbit (LEO), but it was later planned to exceed that requirement with a rated payload capacity of 95 t (93 long tons; 105 short tons). As of 22 December 2019, this variant is planned to launch Artemis 1, Artemis 2, and Artemis 3. The later Block 1B is intended to debut the Exploration Upper Stage and launch the notional Artemis 4 through Artemis 7. Block 2 is planned to replace the initial Shuttle-derived boosters with advanced boosters and would have a LEO capability of more than 130 t (130 long tons; 140 short tons), again as required by Congress. Block 2 is intended to enable crewed launches to Mars.
As of 2018, SLS was planned to have the world's highest-ever total LEO payload capability, but not the world's highest ever injection mass. The SLS is planned to launch the Orion spacecraft and use the ground operations and launch facilities at NASA's Kennedy Space Center in Florida. The rocket will use the Launch Complex 39B at the Kennedy Space Center. The first launch is currently scheduled for 4 November 2021.
Vehicle description
The SLS is a Space Shuttle-derived launch vehicle, with the first stage of the rocket being powered by one central core stage and two outboard boosters. The upper stage is being developed from the Block 1 variant to a Block 1B and 2 variant, the Exploration Upper Stage.
Core stage
The Space Launch System's core stage contains the Main Propulsion System (MPS) of the launch vehicle. It is 65 m (212 ft) long by 8.4 m (27.6 ft) in diameter and fuels the four RS-25 rocket engines at its base. The core stage is structurally and visually similar to the Space Shuttle external tank, containing the liquid hydrogen fuel and liquid oxygen oxidizer. Flights 1 through 4 are planned to use modified RS-25D engines left over from the Space Shuttle program. However, the RS-25 engines were designed with reuse in mind for the Space Shuttle, so later flights are planned to switch to a expendable optimized RS-25 variant, lowering per engine costs over 30%.
The core stage is fabricated at NASA's Michoud Assembly Facility and is common across all currently planned evolutions of the SLS to avoid the need for redesigns to meet varying requirements.
Boosters
Block 1 and 1B boosters
Blocks 1 and 1B of the SLS are planned to use two five-segment Solid Rocket Boosters (SRBs). These new SRBs are derived from the four-segment Space Shuttle Solid Rocket Boosters, with the addition of a center booster segment, new avionics, and lighter insulation. The five-segment SRBs provide approximately 25% more total impulse than the Shuttle SRB, but will no longer be recovered after use.
Booster Obsolescence and Life Extension program
The stock of SLS boosters is limited by the number of casings left over from the Shuttle program, since they modify flown boosters to add an additional segment. There are enough to last through eight flights of the SLS, but a replacement will be required for further flights. On 2 March 2019, the Booster Obsolescence and Life Extension (BOLE) program was announced. This program will use new solid rocket boosters built by Northrop Grumman Innovation Systems for further SLS flights. These boosters would be derived from the composite-casing SRBs in development for the OmegA launch vehicle before it was canceled, and are projected to increase Block 1B's payload to TLI by 3–4 metric tons, which is still 1 ton below the payload capacity of Block 2.
Block 2 – advanced boosters
Block 2 will have special advanced boosters which will enable Block 2 to carry 130 metric tons (130 long tons; 140 short tons) to LEO and at least 46 metric tons (45 long tons; 51 short tons) to TLI.
Upper stage
ICPS – Block 1
The Interim Cryogenic Propulsion Stage (ICPS) is planned to fly on Artemis 1. It is a stretched and human-rated Delta IV 5-meter (16 ft) Delta Cryogenic Second Stage (DCSS) powered by a single RL10B-2 engine. Block 1 is intended to be capable of lifting 95 tonnes to low Earth orbit (LEO) in this configuration if the ICPS is considered part of the payload. Artemis 1 is to be launched into an initial 1,800 by −93 km (1,118 by −58 mi) suborbital trajectory to ensure safe disposal of the core stage. ICPS will then perform an orbital insertion burn at apogee and a subsequent translunar injection burn to send Orion towards the Moon. The ICPS for Artemis 1 was delivered by ULA to NASA about July 2017, and was housed at Kennedy Space Centre as of November 2018. As of February 2020, ICPS (not EUS) is planned for Artemis 1, 2, and 3. ICPS will be human-rated for the crewed Artemis 2 flight.
EUS – Block 1B and 2
The Exploration Upper Stage (EUS) is planned to fly on Artemis 4. Similar to the S-IVB, the EUS will complete the SLS ascent phase and then re-ignite to send its payload to destinations beyond LEO. It is expected to be used by Block 1B and Block 2, share the core stage diameter of 8.4 meters, and be powered by four RL10C-3 engines. It will eventually be upgraded to use four RL10C-X engines instead.
Payload carrying capacity
Resilience
The SLS is planned to have the ability to tolerate 23 tanking cycles, 13 are reserved for launch attempts on Artemis 1. The assembled rocket is to be able to remain at the launch pad for at least 180 days and can remain in a stacked configuration for at least 200 days.
Development history
Program history
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 US$10 billion for the SLS rocket, US$6 billion for the Orion spacecraft and US$2 billion for upgrades to the launch pad and other facilities at Kennedy Space Center. These costs and schedule 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 95-tonne launches (1 uncrewed, 3 crewed), with the 130-tonne version ready no earlier than 2030.
The Human Exploration Framework Team (HEFT) estimated unit costs for Block 0 at US$1.6 billion and Block 1 at US$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 September 2012, an SLS deputy project manager stated that US$500 million per launch is a reasonable target cost for SLS.
In 2013, the Space Review estimated the cost per launch at US$5 billion, depending on the rate of launches. NASA announced in 2013 that the European Space Agency (ESA) will build the Orion service module.
In 2011, NASA announced an "Advanced Booster Competition", to be decided in 2015, which would select whose boosters would be used for Block 2 of the SLS.
Several companies proposed boosters for this competition:
- Aerojet, in partnership with Teledyne Brown, offered a booster powered by three new AJ1E6 LOX/RP-1 oxidizer-rich staged combustion engines, each producing 4,900 kN (1,100,000 lbf) thrust using a single turbopump to supply dual combustion chambers. On 14 February 2013, Aerojet was awarded a US$23.3 million, 30-month contract to build a 2,400 kN (550,000 lbf) main injector and thrust chamber.
- Alliant Techsystems
(ATK) proposed an advanced SRB nicknamed "Dark Knight", which would
switch to a lighter composite case, use a more energetic propellant, and
reduce the number of segments from five to four.
- Some comparable launch vehicles
- Pratt & Whitney Rocketdyne and Dynetics proposed a liquid-fueled booster named Pyrios.
In 2013, the manager of NASA's SLS advanced development office indicated that all three approaches were viable.
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. Due to this cancellation, it was reported in February 2015 that SLS is expected to fly with the original five-segment SRB until at least the late 2020s. This decision was vindicated as a later study found that the advanced booster would have resulted in unsuitably high acceleration. The overly powerful booster would need modifications to Launch Pad 39B (LC-39B), its flame trench, and Mobile Launcher, which are being evaluated.
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 US$7.021 billion. Ground systems modifications and construction would require an additional US$1.8 billion over the same time period.
In October 2018, NASA's inspector general reported that the Boeing core stage contract had made up 40% of the US$11.9 billion spent on SLS as of August 2018. By 2021, core stages were expected to have cost a total of US$8.9 billion, which is twice the initially planned amount.
In December 2018, NASA estimated that yearly budgets for SLS will range from US$2.1 to US$2.3 billion between 2019 and 2023.
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. Several launches previously planned for the SLS Block 1B are now expected to fly on commercial launcher vehicles such as Falcon Heavy, New Glenn and Vulcan. However, the request for a budget increase of US$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. The 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.
Blue Origin submitted a proposal to replace the Exploration Upper Stage with an 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, unsuitability of the proposal to current ground infrastructure, and unacceptable acceleration in regards to Orion components.
On March 18th 2021, CS-1 successfully completed its 8 minute Green Run test.
Funding history
For fiscal years 2011 through 2020, the SLS program had expended funding totaling US$18.648 billion in nominal dollars. This is equivalent to US$20.314 billion in 2020 dollars using the NASA New Start Inflation Indices.
For fiscal year 2021, US$2.257 billion.
| Fiscal year | Funding (millions) | Status | |
|---|---|---|---|
| Nominal | In US$2020 | ||
| 2011 | US$1,536.1 | US$1,819.9 | Actual (Formal SLS Program reporting excludes the Fiscal 2011 budget.) |
| 2012 | US$1,497.5 | US$1,755.5 | Actual |
| 2013 | US$1,414.9 | US$1,634.1 | Actual |
| 2014 | US$1,600.0 | US$1,812.3 | Actual |
| 2015 | US$1,678.6 | US$1,863.8 | Actual |
| 2016 | US$1,971.9 | US$2,159.6 | Actual |
| 2017 | US$2,127.1 | US$2,286.8 | Actual |
| 2018 | US$2,150.0 | US$2,256.6 | Actual |
| 2019 | US$2,144.0 | US$2,199.9 | Actual |
| 2020 | US$2,525.8 | US$2,525.8 | Enacted |
| 2021 | US$2,585.9 | US$2,585.9 | Enacted |
| 2011–2020 | Total: US$18,648 | Total: US$20,314 |
|
On top of this, the costs to assemble, integrate, prepare and launch the SLS and its payloads are funded separately under Exploration Ground Systems, currently about US$600 million per year.
Excluded from the above SLS costs are:
- Costs of payloads for the SLS (such as Orion crew capsule)
- Costs of the predecessor Ares V / Cargo Launch Vehicle (funded from 2008 to 2010)
- Costs for the Ares I / Crew Launch Vehicle (funded from 2006 to 2010, a total of US$4.8 billion in development that included the 5-segment Solid Rocket Boosters that will be used on the SLS)
Included in the above SLS costs are:
- Costs of the interim Upper Stage for the SLS, the Interim Cryogenic Propulsion Stage (ICPS) for SLS, which includes a US$412 million contract
- Costs of the future Upper Stage for the SLS, the Exploration Upper Stage (EUS) (funded at US$85 million in 2016, US$300 million in 2017, US$300 million in 2018, and US$150 million in 2019)
Per launch costs
The per launch costs for 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 (for example, a marginal cost per one additional launch, which ignores development and annual recurring fixed costs vs. total cost per launch, including recurring costs but excluding development); but also based on differing purposes for which the cost estimates were developed.
There are no official NASA estimates for how much 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. For example, similarly, the Space Shuttle was estimated (in 2012 dollars) to cost US$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 US$252 million of marginal cost. However, at the rate that it actually flew, the cost in the end was US$1.64 billion per Space Shuttle launch, including development.
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 SLS. 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 was advised by NASA HQ in 2019 to budget US$500 million for an SLS launch in 2035. Another study in 2019 also proposing a space telescope assumed a budget for their launch of US$650 million in current day dollars, or US$925 million for when the launch would occur, which is also in the "mid-2030s".
Europa Clipper is a NASA scientific mission that was 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 that stated Europa Clipper would need to give up US$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 actually save over US$1 billion. (Although this savings may have included a portion of costs related to the delay in launch schedule; a commercial alternative could launch sooner than SLS) A JCL (Joint Cost and Schedule Confidence Level) analysis cited in that letter put the cost savings at US$700 million, with SLS at US$1.05 billion per launch and the commercial alternative at US$350 million.
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 US$2 billion" per launch after development is complete (program development has cost US$20 billion to date in 2020 dollars). The letter urged Congress to remove this requirement, in agreement with the NASA Inspector General, adding that using a commercial launch vehicle for Europa Clipper instead of SLS would save US$1.5 billion overall. NASA did not deny this US$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". This OMB figure is dependent on the rate of construction, so building more SLS rockets faster could decrease the per-unit cost. For example, Exploration Ground Systems – whose only role is to support, assemble, integrate, and launch SLS – has separately budgeted fixed costs of US$600 million per year on facilities, spread across however many rockets launch that year. Then NASA Administrator Jim Bridenstine shared informally that he disagrees with the US$2 billion figure since the marginal cost of an SLS launch should decrease after the first few, and is expected to end up around US$800 million to US$900 million, although contract negotiations were only just beginning for those later cores.
On 1 May 2020, NASA awarded a contract extension to Aerojet Rocketdyne to manufacture 18 additional RS-25 engines with associated services for US$1.79 billion, bringing the total RS-25 contract value to almost US$3.5 billion.
Constellation
From 2009 to 2011, three full-duration static fire tests of five-segment SRBs were conducted under the Constellation Program, including tests at low and high core temperatures, to validate performance at extreme temperatures. The 5-segment SRB would be carried over to SLS.
Early SLS
During the early development of the SLS a number of configurations were considered, including a Block 0 variant with three main engines, a Block 1A variant with upgraded boosters instead of the improved second stage, and a Block 2 with five main engines and the Earth Departure Stage, with up to three J-2X engines. In February 2015, it was determined that these concepts would exceed the congressionally mandated Block 1 and Block 1B baseline payloads.
On 14 September 2011, NASA announced the new launch system, which is intended to take the agency's astronauts farther into space than ever before and provide the cornerstone for future U.S. human space exploration efforts in combination with the Orion spacecraft.
On 31 July 2013, the SLS passed the Preliminary Design Review (PDR). The review included not only the rocket and boosters but also ground support and logistical arrangements. 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.
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.
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 lower cost.
Northrop Grumman Innovation Systems has completed full-duration static fire tests of the five-segment SRBs. Qualification Motor 1 (QM-1) was tested on 10 March 2015. Qualification Motor 2 (QM-2) was successfully tested on 28 June 2016.
SLS History
As of 2020, three SLS versions are planned: Block 1, Block 1B, and Block 2. Each will use the same core stage with four main engines, but Block 1B will feature the Exploration Upper Stage (EUS), and Block 2 will combine the EUS with upgraded boosters.
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. Between 2015 and 2017, NASA test fired RS-25 engines in preparation for use on SLS.
As of late 2015, the SLS program was stated to have a 70% confidence level for the first crewed Orion flight by 2023, and as of 2020, NASA is continuing to project a 2023 launch.
A test article build for the core stage began on 5 January 2016 and was expected to be completed in late January 2016. Once completed the test article was to be sent to ensure structural integrity at Marshall Space Flight Center. A structural test article of the ICPS was delivered in 2015. the core stage for Artemis 1 completed assembly in November 2019.
The first core stage left Michoud for comprehensive testing at Stennis in January 2020. The static firing test program at Stennis Space Center, known as the Green Run, will operate 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 hot fire (test 8) took place on 16 January 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 hot fire test was successfully completed March 18, with all 4 engines igniting, throttling down as expected to simulate in-flight conditions, and gimballing profiles. The core stage was shipped down 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. It was refurbished there in preparation for stacking. 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 later in 2021.
The intended uncrewed first flight of SLS has slipped multiple times: originally from late 2016 to October 2017, then to November 2018, then to 2019, then to June 2020, then to April 2021, and most recently to November 2021.
Criticism
The SLS has been criticized on the basis of program cost, lack of commercial involvement, and the non-competitive nature of a vehicle legislated to use Space Shuttle components.
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.
In 2011–2012, the Space Access Society, Space Frontier Foundation and The Planetary Society called for the cancellation of the project, arguing that SLS will consume the funds for other projects from the NASA budget. U.S. Representative Dana Rohrabacher and others proposed that an orbital propellant depot should be developed and the Commercial Crew Development program accelerated instead. A NASA study that was not publicly released and another from the Georgia Institute of Technology showed this option to be possibly cheaper. 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. 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 SLS and blocked further investment in it.
In 2011, Mars Society/Mars Direct founder Robert Zubrin suggested that a heavy lift vehicle could be developed for US$5 billion on fixed-price requests for proposal.
In 2010, SpaceX's CEO Elon Musk claimed that his company could build a launch vehicle in the 140- to 150-tonne payload range for US$2.5 billion, or US$300 million (in 2010 dollars) per launch, not including a potential upper-stage upgrade. In the early 2010s, SpaceX went on to start development of SpaceX Starship, a planned fully reusable super-heavy launch system. Reusability is claimed to allow the lowest-cost super-heavy launcher ever made. If the price per launch and payload capabilities for the Starship are anywhere near Musk's claimed capabilities, the rocket will be substantially cheaper than the SLS.
In 2011, Rep. Tom McClintock and other groups called on the Government Accountability Office (GAO) to investigate possible violations of the Competition in Contracting Act (CICA), arguing that Congressional mandates forcing NASA to use Space Shuttle components for SLS are de facto non-competitive, single source requirements assuring contracts to existing Shuttle suppliers. 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". Opponents of the heavy launch vehicle have critically used the name "Senate launch system", 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."
In 2013, Chris Kraft, the NASA mission control leader from the Apollo era, expressed his criticism of the system as well. Lori Garver, former NASA Deputy Administrator, has called for canceling the launch vehicle alongside the Mars 2020 rover. Phil Plait has voiced his criticism of SLS in light of ongoing budget tradeoffs between the Commercial Crew Development and SLS budgets, also referring to earlier critiques by Garver.
In 2019, the Government Accountability Office found that NASA had awarded Boeing over US$200 million for service with ratings of good to excellent despite cost overruns and delays. As of 2019, the maiden launch of SLS was expected in 2021. NASA continued to expect that the first orbital launch would be in 2021 as late as May 2020.
On 1 May 2020, NASA awarded a US$1.79 billion contract extension for the manufacture of 18 additional RS-25 engines. Ars Technica, in an article published on the same day, highlighted that over the entire RS-25 contract the price of each engine works out to US$146 million and that the total price for the four expendable engines used in each SLS launch will be more than US$580 million. They critically commented 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.
Former NASA Administrator Charlie Bolden, who oversaw the initial design and development of the SLS, also voiced 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".
