Space Launch System

The Space Launch System (SLS) is an American Space Shuttle-derived super heavy-lift expendable launch vehicle. It is part of NASA's deep space exploration plans[8][9] including a crewed mission to Mars.[10][11][12] SLS follows the cancellation of the Constellation program, and is to replace the retired Space Shuttle. The NASA Authorization Act of 2010 envisions the transformation of the Constellation program's Ares I and Ares V vehicle designs into a single launch vehicle usable for both crew and cargo, similar to the Ares IV concept. The SLS is to be the most powerful rocket ever built[13] with a total thrust greater than that of the Saturn V,[14] although Saturn V could carry a greater payload mass.[N 1][15][16][17]

The SLS launch vehicle is to be upgraded over time with more powerful versions. Its initial Block 1 version is to lift a payload of 95 metric tons to low Earth orbit (LEO), which will be increased with the debut of Block 1B and the Exploration Upper Stage.[18] Block 2 will replace the initial Shuttle-derived boosters with advanced boosters and is planned to have a LEO capability of more than 130 metric tons to meet the congressional requirement.[19] These upgrades will allow the SLS to lift astronauts and hardware to destinations beyond LEO: on a circumlunar trajectory as part of Exploration Mission 1 & 2 with Block 1; to deliver elements of the Lunar Orbital Platform-Gateway (LOP-G) with Block 1B; and to Mars with Block 2.[12] The SLS will launch the Orion Crew and Service Module and may support trips to the International Space Station if necessary. SLS will use the ground operations and launch facilities at NASA's Kennedy Space Center, Florida.

Space Launch System
Sls block1 noeas afterburner engmarkings sm
Artist's rendering of the SLS Block 1 Crew launching with Orion on Exploration Mission 1.
FunctionSuper heavy-lift launch vehicle
ManufacturerBoeing, United Launch Alliance, Northrop Grumman, Aerojet Rocketdyne
Country of originUnited States
Project costUS$7 billion (2014-18, 2014 estimate),[1] to
$35 billion (until 2025, 2011 est.)[2][3]
Height111.25 m (365 ft 0 in), Block 2 Cargo
Diameter8.4 m (27 ft 7 in), Core Stage
Payload to LEO
  • Block 1: 95 t (209,000 lb)[4]
  • Block 2: 130 t (290,000 lb)[5]
Payload to Moon
  • Block 1: 26 t (57,000 lb)[4]
  • Block 1B: 37 t (82,000 lb)[4]
Payload to deep space
  • Block 2: 45 t (99,000 lb)[4]
Associated rockets
FamilyShuttle-Derived Launch Vehicles
ComparableSaturn V, Energia, N-1, Ares V, Falcon Heavy, New Glenn, BFR
Launch history
StatusUnder development
Launch sitesLC-39B, Kennedy Space Center
First flightExploration Mission 1 (2020)[6]
Notable payloadsOrion MPCV, Europa Clipper
Boosters (Block 1, 1B)
No. boosters2 five-segment Solid Rocket Boosters
Thrust3,600,000 lbf (16,000 kN)
Total thrust7,200,000 lbf (32,000 kN)
Specific impulse269 seconds (2.64 km/s) (vacuum)
Burn time124 seconds
First stage (Block 1, 1B, 2) – Core Stage
Length64.6 m (211 ft 11 in)
Diameter8.4 m (27 ft 7 in)
Empty mass85,270 kg (187,990 lb)
Gross mass979,452 kg (2,159,322 lb)
Engines4 RS-25D/E[7]
Thrust7,440 kN (1,670,000 lbf)
Specific impulse363 seconds (3.56 km/s) (sea level), 452 seconds (4.43 km/s) (vacuum)
FuelLH2 / LOX
Second stage (Block 1) – ICPS
Length13.7 m (44 ft 11 in)
Diameter5 m (16 ft 5 in)
Empty mass3,490 kg (7,690 lb)
Gross mass30,710 kg (67,700 lb)
Engines1 RL10B-2
Thrust110.1 kN (24,800 lbf)
Specific impulse462 seconds (4.53 km/s)
Burn time1125 seconds
FuelLH2 / LOX
Second stage (Block 1B, Block 2) – Exploration Upper Stage
Diameter8.4 m (27 ft 7 in)
Engines4 RL10
Thrust99,000 lbf (440 kN)
FuelLH2 / LOX

Design and development

Orange tank SLS evolution - Post CDR
Space Launch System's planned upgrade path

On September 14, 2011, NASA announced its design selection for the new launch system, declaring that it, in combination with the Orion spacecraft,[20] would take the agency's astronauts farther into space than ever before and provide the cornerstone for future US human space exploration efforts.[21][22][23]

During the early development of the SLS a number of configurations were considered, including a Block 0 variant with three main engines,[24] a Block 1A variant that would have upgraded the vehicle's boosters instead of its second stage,[24] and a Block 2 with five main engines and a different second stage, the Earth Departure Stage, with up to three J-2X engines.[25] In February 2015, it was reported that NASA evaluations showed "over performance" versus the baseline payload for Block 1 and Block 1B configurations.[26]

Three versions of the SLS launch vehicle 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 a more powerful second stage called the Exploration Upper Stage (EUS), and Block 2 will combine the EUS with upgraded boosters. Block 1 has a baseline LEO payload capacity of 95 metric tons (105 short tons) and Block 1B has a baseline of 105 metric tons (116 short tons).[27] The proposed Block 2 will have lift capacity of 130 metric tons (140 short tons), which is similar to that of the Saturn V.[19][28] Some sources state this would make the SLS the most capable heavy lift vehicle built;[29][30] although the Saturn V lifted approximately 140 metric tons (150 short tons) to LEO in the Apollo 17 mission.[15][31]

On July 31, 2013, the SLS passed the Preliminary Design Review (PDR). The review encompassed all aspects of the SLS's design, not only the rocket and boosters but also ground support and logistical arrangements.[32] 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.[33][34] In April 2017, NASA announced that the schedule for the maiden flight would slip to 2019.[35] In November 2017, the EM-1 maiden flight slipped further to June 2020.[6]

Vehicle description

Orange tank SLS launch through clouds - Post CDR
Artist's rendering of a SLS Block 1

Core Stage

The Space Launch System's Core Stage will be 8.4 meters (28 ft) in diameter and use four RS-25 engines.[7][24] Initial flights will use modified RS-25D engines left over from the Space Shuttle program;[36] later flights are expected to switch to a cheaper version of the engine not intended for reuse.[37] The stage's structure will consist of a modified Space Shuttle external tank with the aft section adapted to accept the rocket's Main Propulsion System (MPS) and the top converted to host an interstage structure.[29][38] It will be fabricated at the Michoud Assembly Facility.[39]

The core stage will be common across all currently planned evolutions of the SLS. Initial planning included studies of a smaller Block 0 configuration with three RS-25 engines,[40][41] which was eliminated to avoid the need to substantially redesign the core stage for more powerful variants.[24] Likewise, while early Block 2 plans included five RS-25 engines on the core,[25] it was later baselined with four engines.[26]


SLS Booster test in the Utah desert

Shuttle-derived boosters

Blocks 1 and 1B of the SLS will use two five-segment Solid Rocket Boosters (SRBs), which are based on the four-segment Space Shuttle Solid Rocket Boosters. Modifications for the SLS included the addition of a center booster segment, new avionics, and new insulation which eliminates the Shuttle SRB's asbestos and is 860 kg (1,900 lb) lighter. The five-segment SRBs provide approximately 25% more total impulse than the Shuttle SRB and will not be recovered after use.[42][43]

Orbital ATK (formerly Alliant Techsystems, part of Northrop Grumman since mid-2018) has completed full-duration static fire tests of five-segment SRBs. These include successful firings of three developmental motors (DM-1 to DM-3) from 2009 to 2011. The DM-2 motor was cooled to a core temperature of 40 °F (4 °C), and DM-3 was heated to above 90 °F (32 °C) to validate performance at extreme temperatures.[44][45][46] Qualification Motor 1 (QM-1) was tested on March 10, 2015.[47] Qualification Motor 2 was successfully tested on June 28, 2016. It was the final ground test before Exploration Mission 1 (EM-1).

Advanced boosters

For Block 2, NASA plans to switch from Shuttle-derived five-segment SRBs to advanced boosters.[48] This will occur after development of the Exploration Upper Stage for Block 1B. Early plans would have developed advanced boosters before an updated second stage; this configuration was called Block 1A. By 2012 NASA planned to select these new boosters through an Advanced Booster Competition which was to be held in 2015.[7][49] Several companies proposed boosters for this competition:

  • Aerojet, in partnership with Teledyne Brown, offered a booster powered by three AJ1E6 engines, which would be a newly developed LOX / RP-1 oxidizer-rich staged combustion engine. Each AJ1E6 engine would produce 4,900 kN (1,100,000 lbf) thrust using a single turbopump to supply dual combustion chambers.[50] On February 14, 2013, NASA awarded Aerojet a $23.3 million, 30-month contract to build a 2,400 kN (550,000 lbf) main injector and thrust chamber.[51]
  • Alliant Techsystems (ATK) proposed an advanced SRB nicknamed "Dark Knight". This booster would switch from a steel case to one made of lighter composite material, use a more energetic propellant, and reduce the number of segments from five to four.[52] It would deliver over 20,000 kN (4,500,000 lbf) maximum thrust and weigh 790,000 kg (1,750,000 lb) at ignition. According to ATK, the advanced booster would be 40% less expensive than the Shuttle-derived five-segment SRB. It is uncertain if the booster will allow SLS to deliver the mandated 130 t to LEO without the addition of a fifth engine to the core stage,[26] as a 2013 analysis indicated a maximum capacity of 113 t with the baselined four-engine core.[53]
  • Pratt & Whitney Rocketdyne and Dynetics proposed a liquid-fueled booster named "Pyrios".[54] Each booster would use two F-1B engines which together would deliver a maximum thrust of 16,000 kN (3,600,000 lbf) total, and be able to continuously throttle down to a minimum of 12,000 kN (2,600,000 lbf). The F-1B would be derived from the F-1 engine, which powered the first stage of the Saturn V. It would have been easier to assemble, with fewer parts and a simplified design,[55] while providing improved efficiency and a thrust increase of 110 kN (25,000 lbf).[56] Estimates in 2012 indicated that the Pyrios booster could increase Block 2 low-Earth orbit payload to 150 t, 20 t more than the baseline.[57]

Christopher Crumbly, manager of NASA's SLS advanced development office in January 2013 commented on the booster competition, "The F-1 has great advantages because it is a gas generator and has a very simple cycle. The oxygen-rich staged combustion cycle [Aerojet's engine] has great advantages because it has a higher specific impulse. The Russians have been flying ox[ygen]-rich for a long time. Either one can work. The solids [of ATK] can work."[58]

Later analysis showed the Block 1A configuration would result in high acceleration which would be unsuitable for Orion and could require a costly redesign of the Block 1 core.[59] In 2014, NASA confirmed the development of Block 1B instead of Block 1A and called off the 2015 booster competition.[26][60] In February 2015, it was reported that SLS is expected to fly with the five-segment SRB until at least the late 2020s, and modifications to Launch Pad 39B, its flame trench, and SLS's Mobile Launcher Platform were evaluated based on SLS launching with solid-fuel boosters.[26]

Upper Stage

Common Extensible Cryogenic Engine
An RL10 engine, like the one pictured above, will be used as the second stage engine in both the ICPS and EUS upper stages.

Interim Cryogenic Propulsion Stage

Block 1, scheduled to fly Exploration Mission 1 (EM-1) in 2020,[6] will use the Interim Cryogenic Propulsion Stage (ICPS). This stage will be a modified Delta IV 5–meter Delta Cryogenic Second Stage (DCSS),[61] and will be powered by a single RL10B-2. Block 1 will be capable of lifting 95 t in this configuration, however the ICPS will be considered part of the payload and be placed into an initial 1,800 km by -93 km suborbital trajectory to ensure safe disposal of the core stage. ICPS will perform an orbital insertion burn at apogee, and then a translunar injection burn to send the uncrewed Orion on a circumlunar excursion.[62] In May 2018, NASA updated the payload capability of the SLS Block 1 from 70 to 95 metric tons to low Earth orbit.[4]

Exploration Upper Stage

The Exploration Upper Stage (EUS) was scheduled to fly on Exploration Mission 2 (EM-2). It was expected to be used by Block 1B and Block 2 and, like the core stage, have a diameter of 8.4 meters. The EUS is to be powered by four RL10 engines,[63] complete the SLS ascent phase and then re-ignite to send its payload to destinations beyond low-Earth orbit, similar to the role performed by the Saturn V's 3rd stage, the J-2 powered S-IVB.[64] Because of delays in building the mobile launch platform needed to hold the more powerful EUS, the EM-2 flight might launch earlier than planned but it will not use the EUS,[65] it will not carry a module for the Lunar Gateway and it will not orbit the Moon.

Other upper stages

Orion docked to Mars Transfer Vehicle
Artist's impression of the Bimodal Nuclear Thermal Rocket engines on the Mars Transfer Vehicle (MTV). Cold launched, it would be assembled in-orbit by a number of Block 2 SLS payload lifts. The Orion spacecraft is docked on the left.
  • The Earth Departure Stage, powered by J-2X engines,[66][67] was to be the upper stage of the Block 2 SLS had NASA decided to develop Block 1A instead of Block 1B and the EUS.[64]
  • In 2013, NASA and Boeing analyzed the performance of several second stage options. The analysis was based on a second stage usable propellant load of 105 metric tons, except for the Block 1 and ICPS, which will carry 27.1 metric tons. The ICPS upper stage and upper stages using four RL10 engines and two MB60/RL60 engines and one J-2X engine were studied.[68] 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 a reduction of one or two of the four second stage engines for the same performance for a lower cost.[69][70] Robotic exploration missions to Jupiter's water-ice moon Europa are increasingly seen as well suited to the lift capabilities of the Block 1B SLS.[71]
  • An additional beyond-LEO engine for interplanetary travel from Earth orbit to Mars orbit, and back, is being studied as of 2013 at Marshall Space Flight Center with a focus on nuclear thermal rocket (NTR) engines.[72] In historical ground testing, NTRs proved to be at least twice as efficient as the most advanced chemical engines, which would allow quicker transfer time and increased cargo capacity. The shorter flight duration, estimated at 3–4 months with NTR engines,[73] compared to 6–9 months using chemical engines,[74] would reduce crew exposure to potentially harmful and difficult to shield cosmic rays.[75][76][77][78] NTR engines, such as the Pewee of Project Rover, were selected in the Mars Design Reference Architecture (DRA).[76][77][79][80] In 2017 NASA continued research and development on NTRs, designing for space applications with civilian approved materials, with a three-year, $18.8-million contract.[81]

Payload carrying capacity

SLS variant Payload mass to … (metric tons)
low Earth orbit (LEO) trans-lunar injection (TLI) heliocentric orbit (HCO)
Block 1 95 t[4] 26 t[4]
Block 1B 105 t[27] 37 t[4]
Block 2 130 t[5] 45 t[4]

Fabrication and testing

SLS on MLP at night
Rendering of the SLS Block 1 with its older black-and-white paint scheme, showing core stage, two 5-segment SRBs, and the smaller upper stage.
SLS Liquid Oxygen Tank Hardware in Welding
Welding of the SLS liquid oxygen tank in the South Vertical Assembly Building at Michoud Assembly Facility

In mid-November 2014, construction of the first SLS rocket began using the new welding system in the South Vertical Assembly Building at NASA's Michoud Assembly Facility, where the Core Stage will be assembled.[82]

The SLS will have the ability to tolerate a minimum of 13 tanking cycles due to launch scrubs and other launch delays before launch. The assembled rocket is to be able to remain at the launch pad for a minimum of 180 days and can remain in stacked configuration for at least 200 days without destacking.[83]

In January 2015, NASA began test firing RS-25 engines in preparation for use on SLS. Tests continued throughout Spring of 2015. Further testing was conducted in 2016 and 2017.[37]

Multiple facilities throughout the country have started full scale fabrication of different segments of the launch vehicle. Orbital ATK began casting propellant for the solid rocket boosters and manufacturing parts for the boosters in 2016. The company test fired a solid rocket booster in early 2015,[84] and a second booster in June 2016.[85]

Confidence article builds for the core stage began on January 5, 2016 and were expected to be completed in late January of that year. Once completed the test articles will be sent to ensure structural integrity at Marshall Spaceflight Center. The ICPS for EM-1 was slated for assembly in late January 2016, and a structural test article was delivered to NASA in 2015 for confidence testing.[86]

Program costs and funding

During the joint Senate-NASA presentation in September 2011, it was stated that the SLS program had a projected development cost of $18 billion through 2017, with $10 billion for the SLS rocket, $6 billion for the Orion Multi-Purpose Crew Vehicle and $2 billion for upgrades to the launch pad and other facilities at Kennedy Space Center.[87][88] These costs and schedule were considered optimistic in an independent 2011 cost assessment report by Booz Allen Hamilton for NASA.[89] An unofficial 2011 NASA document estimated the cost of the program through 2025 to total at least $41bn for four 95 t launches (1 uncrewed, 3 crewed),[2][3] with the 130 t version ready no earlier than 2030.[90]

The Human Exploration Framework Team (HEFT) estimated unit costs for Block 0 at $1.6bn and Block 1 at $1.86bn in 2010.[91] However, since these estimates were made the Block 0 SLS vehicle was dropped in late 2011, and the design was not completed.[92] The Space Review estimated the cost per launch at $5 billion, depending on the rate of launches.[93][94] NASA announced in 2013 that the European Space Agency will build the Orion Service Module.[95]

NASA SLS deputy project manager Jody Singer at Marshall Space Flight Center, Huntsville, Alabama stated in September 2012 that $500 million per launch is a reasonable target cost for SLS, with a relatively minor dependence of costs on launch capability.[96] By comparison, a Saturn V launch cost US$185 to US$189 million in 1969-1971 dollars or roughly $1.23 billion in 2016 dollars adjusted for inflation.[97][98]

On July 24, 2014, Government Accountability Office audit predicted that SLS would not launch by the end of 2017 as originally planned since NASA had not been receiving sufficient funding.[99]

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.[34] Ground systems modifications and construction would require an additional $1.8 billion over the same time period. As of February 2015 the Orion spacecraft was expected to enter its Key Decision Point C review in the first half of 2015.[100]

For Fiscal Year 2015, NASA received an appropriation of US$1.7 billion from Congress for SLS, an amount that was approximately US$320 million greater than the amount requested by the Obama administration.[101]

In October 2018, NASA's inspector general reported that the Boeing SLS stages contract portion (accounting "for over 40 percent of the $11.9 billion spent on the SLS Program" as of August 2018) is expected to cost a total of US$8.9 billion by 2021, which is twice the initial planned amount.[102]

Funding history and planning

For fiscal years 2011 through 2018, the SLS program had expended funding totaling $13,999 million in nominal dollars. This is equivalent to $15,109 million adjusting to 2018 dollars using the NASA New Start Inflation Indices.[103]

Fiscal Year Funding ($millions) Line Item Name
2011 $1,536.1 Actuals, 2011, Space Launch System[104]
(Formal SLS Program reporting excludes the Fiscal 2011 budget as being before "formulation start" in November 2011,[105] Fiscal Year 2012)
2012 $1,497.5 Actuals, 2012, Space Launch System[106]
2013 $1,414.9 Actuals, 2013, Space Launch System[107]
2014 $1,600.0 Actuals, 2014, Space Launch System[108]
2015 $1,678.6 Actuals, 2015, Space Launch System[109]
2016 $1,971.9 Enacted, 2016, Space Launch System[109]
2017 $2,150.0 Appropriated, 2017, Space Launch System[110]
2018 $2,150.0 Appropriated, 2018, Space Launch System[111]
2011-2018 Total: $13,999M

Excluded from the prior SLS costs are:

  • Costs of the predecessor Ares V / Cargo Launch Vehicle (funded from 2008 to 2010)[112]
  • Costs for the Ares 1 / Crew Launch Vehicle (funded from 2006 to 2010, a total of $4.8 billion[112][113] in development that included the 5-segment Solid Rocket Boosters that will be used on the SLS)
  • Costs to assemble, integrate, prepare and launch the SLS and its payloads such as Orion (funded under the NASA Ground Operations Project,[114] currently about $400M[108] per year)
  • Costs of payloads for the SLS (such as Orion)

Included in the prior SLS costs are:

  • Costs of the interim Upper Stage for the SLS, the Interim Cryogenic Propulsion Stage (ICPS) for SLS, which includes a $412M contract[115]
  • Costs of the final Upper Stage for the SLS, the Exploration Upper Stage (EUS) (funded at $85M in 2016,[116] $300M in 2017[110] and $300M in 2018[111])

For 2019 to 2023, NASA "notional"[117] yearly budgets for SLS range from $2.1 to $2.3B a year. As of late 2015, the SLS program has a 70% confidence level for its "first Orion mission with astronauts by 2023" according to the Associate Administrator for NASA, Robert Lightfoot.[118][119][120]

As of mid-2018, the SLS is scheduling its first test launch, with no crew, for mid-2020.[121]

There are no NASA estimates for the SLS program recurring yearly costs once operational, for a certain flight rate per year, or for the resulting average costs per flight. Bill Hill, NASA manager of exploration systems development has indicated "My top number for Orion, SLS, and the ground systems that support it is $2 billion or less" (annually).[122] NASA associate administrator William H. Gerstenmaier has indicated, "[per mission] costs must be derived from the data and are not directly available. This was done by design to lower NASA's expenditures."[123]


The Space Access Society, Space Frontier Foundation and The Planetary Society called for cancellation of the project in 2011–12, arguing that SLS will consume the funds for other projects from the NASA budget and will not reduce launch costs.[124][125][126] U.S. Representative Dana Rohrabacher and others added that instead, an orbital propellant depot should be developed and the Commercial Crew Development program accelerated.[124][127][128][129][130] Two studies, one not publicly released from NASA[131][132] and another from the Georgia Institute of Technology, show this option to be possibly cheaper.[133][134]

Others suggest it will cost less to use an existing lower payload capacity rocket (Atlas V, Delta IV, Falcon 9, or the derivative Falcon Heavy), with on-orbit assembly and propellant depots as needed, rather than develop a new launch vehicle for space exploration without competition for the whole design.[135][136][137][138][139] The Augustine commission proposed an option for a commercial 75 metric ton launcher with lower operating costs, and noted that a 40 to 60 t launcher can support lunar exploration.[140]

Mars Society founder Robert Zubrin, who co-authored the Mars Direct concept, suggested that a heavy lift vehicle should be developed for $5 billion on fixed-price requests for proposal. Zubrin also disagrees with those that say the U.S. does not need a heavy-lift vehicle.[141] SpaceX's CEO Elon Musk stated in 2010 that he would "personally guarantee" that his company could build a launch vehicle in the 140–150 t payload range, for $2.5 billion, or $300 million per launch, but cautioned that this price tag did not include a potential upper-stage upgrade.[142][143] Musk went on to start development of the fully reusable BFR super-heavy launcher and upper stage Starship in the early 2010s. Because of this reusability, Musk claims that it will be the lowest cost super-heavy launcher ever made.[144] If the price per launch and payload capabilities for the BFR are anywhere near Musk's claimed capabilities, the rocket will be substantially cheaper than the SLS.

Rep. Tom McClintock and other groups argue that the Congressional mandates forcing NASA to use Space Shuttle components for SLS amounts to a de facto non-competitive, single source requirement assuring contracts to existing shuttle suppliers, and calling the Government Accountability Office (GAO) to investigate possible violations of the Competition in Contracting Act (CICA).[125][145][146] Opponents of the heavy launch vehicle have critically used the name "Senate launch system".[61] 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".[124]

In 2013, Chris Kraft, the NASA mission control leader from the Apollo era, expressed his criticism of the system as well.[147] Lori Garver, former NASA Deputy Administrator, has called for cancelling the program.[148] Phil Plait has voiced his criticism of SLS in light of ongoing budget tradeoffs between Commercial Crew Development and SLS budget, also referring to earlier critique by Garver.[149]

Doubts have also been expressed about the utility and cost of depots.[150] "Patrick R. Chai and Alan W. Wilhite of Georgia Tech presented a study early in 2011 estimating that depot tanks would lose about $12 million worth of propellant per month in low Earth orbit if protected only with passive insulation."[151]

The Planetary Society accepted that a Mars mission could be had with existing budgets.[152]


The list below includes only NASA planned missions published in April 2017,[12] and updated in September 2018.[153]

Planned SLS missions
Name Acronym SLS Block Crew Launch date Status Duration Destination Purpose
Exploration Mission 1 EM-1 1 Crew N/A June 2020[6] Scheduled 25.5 days[154] Distant retrograde lunar orbit Send Orion capsule on trip around the Moon, deploy 13 CubeSats.[6][33][155][156][157][158][154]
Exploration Mission 2 EM-2 1 Crew 4 people June 2022[158] Scheduled 9 days[159] Lunar flyby First crewed Orion capsule[160][161][162][163]and Interim Cryogenic Propulsion Stage (ICPS) to be sent on a free-return trajectory around the moon.[159]
Europa Clipper EC 1 Cargo N/A 2023[153] Proposed 6 years Jovian orbit Flagship-class robotic orbiter to explore Europa[164][165]
Exploration Mission 3 EM-3 1B Crew 4 people 2024[153] Planned 30 days[153] L2 Southern Near Rectilinear Halo Orbit (NRHO) Deliver European System Providing Refuelling, Infrastructure and Telecommunications (ESPRIT), the U.S. Utilization Module to LOP-G.[153]
Exploration Mission 4 EM-4 1B Crew 4 people 2025[12] Planned 26-42 days[158] L2 Southern NRHO Deliver International Partner Habitat to LOP-G[12]
Exploration Mission 5 EM-5 1B Crew 4 people 2026[12] Planned 26-42 days[158] L2 Southern NRHO Deliver U.S. Habitat to LOP-G[12]
Exploration Mission 6 EM-6 1B Crew 4 people 2026 Planned 26-42 days[158] L2 Southern NRHO Deliver airlock module to LOP-G[12]
Exploration Mission 7 EM-7 1B Cargo N/A 2027 Planned L2 Southern NRHO Deliver Deep Space Transport (DST) vehicle to LOP-G[12]
Exploration Mission 8 EM-8 1B Crew 4 people 2027 Planned 191–221 days L2 Southern NRHO LOP-G checkout[12]
Exploration Mission 9 EM-9 1B Cargo N/A 2028 Planned L2 Southern NRHO LOP-G Cargo logistics and refueling[12]
Exploration Mission 10 EM-10 2 Crew 4 people 2029 Planned 1 year L2 Southern NRHO LOP-G long-duration test (Shakedown cruise, 300–400 days)[12]
Exploration Mission 11 EM-11 2 Cargo N/A 2030+ Planned L2 Southern NRHO LOP-G Cargo logistics and refueling[12]
Exploration Mission 12 EM-12 2 Crew 4 people 2030+ Planned 2 years Mars orbit Interplanetary flight[12]
Cancelled SLS missions
Name Acronym SLS Block Crew Launch date Status Duration Destination Purpose
Exploration Mission 2 EM-2 1B Crew 4 people Late 2022 Delegated to commercial launcher 16-26 days[158] Lunar halo orbit Deliver Power and Propulsion Element (PPE) as the first module of the Lunar Orbital Platform-Gateway (LOP-G).[12][162]
2026 Cancelled Lunar orbit Send astronauts to return samples from a previously captured asteroid[166][167]
Exploration Mission 6 EM-6 1B Crew 4 people 2024[153] Delegated to commercial launcher[168] 26-42 days[158] L2 Southern NRHO First logistics module supply mission and delivery of the robotic arm to LOP-G.[12]


Space Launch System: Igniting the Boosters

Pathfinder boosters arrived at Kennedy Space Center

Booster segments arriving at the Kennedy Space Center

SLS Engine Test

RS-25D engine testing at Stennis Space Center

Artist concept of the SLS Block 1 configuration

SLS Block 1 configuration

SLS Liquid Oxygen Tank Hardware in Welding

Welding of the SLS liquid oxygen tank in the South VAB of NASA's Michoud Assembly Facility

SLS Liquid Hydrogen Fuel Tank

Welding of the SLS liquid hydrogen tank

Mobile Launcher under modification for SLS (KSC-2014-4886)

MLP under modification for future rockets

Barrel Section of the Space Launch System Core Stage

SLS core stage segment at its I-STIR weld equipment in the North Vertical Assembly Building

Final assembly of SLS liquid hydrogen tank structural test article

Final Assembly of the liquid hydrogen tank structural test article in the South VAB, December 2018

Space Launch System liquid hydrogen tank

The completed SLS liquid hydrogen tank structural test article in the South Vertical Assembly Building, December 2018

See also


  1. ^ SLS has greater thrust than Saturn V but a lower payload capability.


  1. ^ "NASA commits to $7 billion mega rocket, 2018 debut". CBS News. August 27, 2014. Retrieved 2015-03-13.
  2. ^ a b Andy Paszior (September 7, 2011). "White House Experiences Sticker Shock Over NASA's Plans". The Wall Street Journal. Retrieved 2015-02-22.
  3. ^ a b "ESD Integration, Budget Availability Scenarios" (PDF). Space Policy Online. 19 August 2011. Retrieved 15 September 2011.
  4. ^ a b c d e f g h i Harbaugh, Jennifer (9 July 2018). "The Great Escape: SLS Provides Power for Missions to the Moon". NASA. Retrieved 4 September 2018.
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External links

2020s in spaceflight

This article documents expected notable spaceflight events during the 2020s.

In 2020, NASA plans to launch the Mars 2020 rover, as well as carry out the maiden launch of the Space Launch System; in 2022, NASA plans to carry out the first crewed flight of the Space Launch System.

The trend towards cost reduction in access to orbit is expected to continue. In 2020, Blue Origin plans the maiden flight of New Glenn with a reusable first stage. In 2022, SpaceX plans to launch its new fully reusable BFR.NASA plans a return to the Moon sometime in the 2020s, first by assembling a Lunar Orbital Platform-Gateway in lunar orbit. A manned exploration of Mars could follow in the mid 2030s. An unmanned and then a manned trip to Jupiter and Europa have been commonly contemplated, but no space agencies or companies have yet announced definite plans to launch a manned mission further than Mars. SpaceX, a private company, has also announced plans to land humans on Mars in the mid-2020s, with the long-term goal of enabling the colonization of Mars.

India plans first crewed flight with a spacecraft called Gaganyaan for December 2021 on a home-grown GSLV-III rocket. The mission would make India the 4th nation to launch a manned space flight after Russia, US and China.


ArgoMoon is a nanosatellite that will fly on board NASA's Space Launch System during its first mission (Exploration Mission 1) scheduled for 2019. The satellite has the dimensions of a shoe box (12 cm x 24 cm x 36 cm) in CubeSat terms, it is a 6U.

The objective of the ArgoMoon mission is to provide NASA information about the correct launch vehicle operations through photography. At the time the second stage will release the CubeSats, it will not be able to communicate with the ground anymore. Flying ArgoMoon in the EM-1 mission will also be the opportunity to test nanotechnology in the hostile environment of deep space. ArgoMoon will complete its operations using a proprietary software for autonomous navigation.

BAC Mustard

The Multi-Unit Space Transport And Recovery Device or MUSTARD, usually written as Mustard, was a concept explored by the British Aircraft Corporation (BAC) during the mid-1960s for launching payloads weighing as much as 2,300 kg (5,000 lb) into orbit. Operating as a multi-stage rocket for launch, the individual stages were near-identical modules, each flying back to land as a spaceplane.

Baikal (rocket booster)

The Baikal booster (russ. Байкал) was a proposed reusable flyback booster for the Angara rocket family based on the Angara Universal Rocket Module in 2001. It was designed by the Molniya Research and Industrial Corporation (NPO Molniya) for the Khrunichev Space centre, reusing the flyback and control system for the reusable Buran orbiter.

Delta Cryogenic Second Stage

The Delta Cryogenic Second Stage (DCSS) is a family of cryogenic rocket stages used on the Delta III & Delta IV rockets, and which is planned to be used on the Block I Space Launch System. The stage consists of a cylindrical LH2 tank structurally separated from an oblate spheroid LOX tank. The LH2 tank cylinder carries payload launch loads, while the LOX tank and engine are suspended below within the rocket's inter-stage. The stage is powered by a single Pratt & Whitney RL10B-2 engine, which features an extendable carbon-carbon nozzle to improve specific impulse.


EQUULEUS (EQUilibriUm Lunar-Earth point 6U Spacecraft) is a nanosatellite of the 6-Unit CubeSat format that will measure the distribution of plasma that surrounds the Earth (plasmasphere) to help scientists understand the radiation environment in that region. It will also demonstrate low-thrust trajectory control techniques, such as multiple lunar flybys, within the Earth-Moon region using water steam as propellant. The spacecraft was designed and developed jointly by the Japan Aerospace Exploration Agency (JAXA) and the University of Tokyo.EQUULEUS will be one of thirteen CubeSats to be carried with the Orion EM-1 mission into a heliocentric orbit in cislunar space on the maiden flight of the Space Launch System, scheduled to launch in December 2019.

Earth Departure Stage

The Earth Departure Stage (EDS) is the name given to the proposed second stage of the Block 2 Space Launch System. The EDS is intended to boost the rocket's payload into a parking orbit around the Earth and from there send the payload out of low Earth orbit to its destination in a manner similar to that of the S-IVB rocket stage used on the Saturn V rockets that propelled the Apollo spacecraft to the Moon. Its development has been put on hold (though not abandoned) until stages capable of transferring heavy payloads to Mars are required (currently expected in the 2030s).

Exploration Mission-1

Exploration Mission-1 or EM-1 (previously known as Space Launch System 1 or SLS-1) is the uncrewed first planned flight of the Space Launch System and the second flight of the Orion Multi-Purpose Crew Vehicle. The launch is planned for June 2020 from Launch Complex 39B at the Kennedy Space Center. The Orion spacecraft will spend approximately 3 weeks in space, including 6 days in a retrograde orbit around the Moon. It is planned to be followed by Exploration Mission 2 in 2023.

Exploration Mission-2

The Exploration Mission-2, or EM-2, is a scheduled 2023 mission of the Space Launch System and possibly the first crewed mission of NASA's Orion spacecraft.Originally, the crewed mission was intended to collect samples from a captured asteroid in lunar orbit by the now cancelled robotic Asteroid Redirect Mission. The plan is for a crewed Orion spacecraft to perform a lunar flyby test and return to Earth. As of September 2018 the last crewed spacecraft to leave low Earth orbit was Apollo 17 in 1972.

Exploration Mission-3

The Exploration Mission-3, or EM-3, is a planned 2024 mission of the Space Launch System and second crewed mission of NASA's Orion spacecraft. The intended goal of the mission is to deliver the ESPRIT and U.S. Utilization modules to the Lunar Orbital Platform-Gateway (LOP-G).

Exploration Upper Stage

The Exploration Upper Stage (EUS) is being developed as a large second stage for Block 1B of the Space Launch System (SLS), succeeding Block 1's Interim Cryogenic Propulsion Stage. It will be powered by four RL10C-3 engines burning LOX/LH2 to produce a total of 440 kN (99,000 lbf) thrust. As of February 2015 the SLS Block 1B is baselined at 105 metric tons. The EUS is expected to first fly on the Exploration Mission 3 launch of the SLS scheduled for 2023.


The J-2X is a liquid-fueled cryogenic rocket engine that was planned for use on the Ares rockets of NASA's Constellation program, and later the Space Launch System. Built in the United States by Aerojet Rocketdyne (formerly, Pratt & Whitney Rocketdyne), the J-2X burns cryogenic liquid hydrogen and liquid oxygen propellants, with each engine producing 1,307 kN (294,000 lbf) of thrust in vacuum at a specific impulse (Isp) of 448 seconds (4.39 km/s). The engine's mass is approximately 2,470 kg (5,450 Lb), significantly heavier than its predecessors.The J-2X was intended to be based on the J-2 used on the S-II and S-IVB stages of the Saturn rockets used during the Apollo program, but as required thrust for the Ares I increased due to weight problems it became a clean-sheet design. It entered development in 2007 as part of the cancelled Constellation program. Originally planned for use on the upper stages of the Ares I and Ares V rockets, the J-2X was later intended for use in the Earth Departure Stage of the Block II Space Launch System, the successor to the Constellation program. The engine is intended to be more efficient and simpler to build than its J-2 ancestor, and cost less than the RS-25 Space Shuttle Main Engine. Differences in the new engine include the removal of beryllium, a centrifugal turbo pump versus the axial turbo pump of the J-2, different chamber and nozzle expansion ratios, a channel-walled combustion chamber versus the tube-welded chamber of the J-2, a redesign of all the electronics, a gas generator and supersonic main injector based on the RS-68, and the use of 21st-century joining techniques.

Lunar Orbital Platform-Gateway

The Lunar Orbital Platform-Gateway (LOP-G) is a proposal for a lunar-orbit space station intended to serve as an all-in-one solar-powered communications hub, science laboratory, short-term habitation module, and holding area for rovers and other robots.The science disciplines to be studied on the Gateway are expected to include planetary science, astrophysics, Earth observations, heliophysics, fundamental space biology and human health and performance.The Gateway is meant to be developed, serviced, and utilized in collaboration with commercial and international partners. It will also serve as the staging point for crewed and robotic lunar exploration and a staging point for NASA's proposed Deep Space Transport craft to perform a 300-400 day shakedown mission prior to NASA's first crewed Mars mission. Deep Space Transport is a concept of a reusable vehicle that uses electric and chemical propulsion and would be specifically designed for crewed missions to destinations such as Mars.The development is led by the International Space Station partners: ESA, NASA, Roscosmos, JAXA and CSA for construction in the 2020s. The International Space Exploration Coordination Group (ISECG), which comprises 14 space agencies participating with NASA, have concluded that LOP-G will be critical in expanding human presence to the Moon, Mars and deeper into the Solar System. Formerly known as the Deep Space Gateway, the station was renamed in NASA's proposal for the 2019 United States federal budget. The omnibus spending bill passed by Congress in March 2018 provided NASA with $504 million for preliminary studies during the 2019 fiscal year.

Mobile Launcher Platform

The Mobile Launcher Platform (MLP) is one of three two-story steel structures used by NASA at the Kennedy Space Center to support the Space Shuttle stack throughout the build-up and launch process: during assembly at the Vehicle Assembly Building (VAB), while being transported to Launch Pads 39A and B, and as the vehicle's launch platform. NASA's three MLPs were originally constructed for the Apollo program to launch the Saturn V rockets in the 1960s and 1970s, and remained in service through the end of the shuttle program in 2011 with alterations. The Space Launch System rocket will be mounted atop a renovated platform.


OMOTENASHI (Outstanding MOon exploration TEchnologies demonstrated by NAno Semi-Hard Impactor) is a small spacecraft and semi-hard lander of the 6U CubeSat format that will demonstrate low-cost technology to land and explore the lunar surface. The CubeSat will also take measurements of the radiation environment near the Moon as well as on the lunar surface. Omotenashi is a Japanese word for "welcome" or "hospitality".OMOTENASHI will be one of thirteen CubeSats to be carried with the Orion EM-1 mission into a heliocentric orbit in cislunar space on the maiden flight of the Space Launch System, scheduled to launch in December 2019.

Shuttle-Derived Launch Vehicle

Shuttle-Derived Launch Vehicle, or simply Shuttle-Derived Vehicle (SDV), is a term describing one of a wide array of concepts that have been developed for creating space launch vehicles from the components, technology and infrastructure of the Space Shuttle program. SDVs have also been part of NASA's plans several times in the past. In the late 1980s and early 1990s, NASA formally studied a cargo-only vehicle, Shuttle-C, that would have supplemented the crewed Space Shuttle in orbiting payloads.

In 2005, NASA decided to develop the Ares I and Ares V launch vehicles, based in part on highly modified Shuttle components to replace the Space Shuttle, and enable exploration of the Moon and Mars. The agency also studied a third such vehicle, the Ares IV. As of April 2011, NASA's replacement vehicle for the Space Shuttle is an SDV, the Space Launch System and multiple commercial vehicles. Over the course of the 2010 two different commercial vehicles were developed that use man-rated heavy lift launcher. In the meantime NASA has continued to use the Russian Soyuz, which it also used during the Shuttle program as part of the International Space Station program.

SkyFire (spacecraft)

SkyFire is a planned nanosatellite spacecraft that will fly by the Moon and collect surface spectroscopy and thermography. It is scheduled to fly on the Space Launch System, Exploration Mission 1 (EM-1) scheduled to launch in 2020.

Space Launch System (Turkey)

The Space Launch System (Turkish: Uydu Fırlatma Sistemi), shortly UFS, is a project to develop the satellite launch capability of Turkey.

The aim of the project is to support the sustainability of the national satellite programs and to reach the space independently. It consists of the building of a spaceport, the development of satellite launch vehicles as well as the establishment of remote earth stations. Contracted to the national missile manufacturer, Roketsan, on July 17, 2013, the project is currently in the pre-conceptual design phase. The Space Group Command of the Turkish Air Force, which is being formed, will operate the spaceport when it is completed.According to a newspaper report, the UFS will be capable of launching low-Earth-orbiting satellites into an altitude of 500–700 km (310–430 mi). The budget for the launch system's infrastructure is given with US$50 million and for the electronics another US$50 million.

Space Shuttle main engine

The Aerojet Rocketdyne RS-25, otherwise known as the Space Shuttle main engine (SSME), is a liquid-fuel cryogenic rocket engine that was used on NASA's Space Shuttle and is planned to be used on its successor, the Space Launch System.

Designed and manufactured in the United States by Rocketdyne (later known as Pratt & Whitney Rocketdyne and Aerojet Rocketdyne), the RS-25 burns cryogenic liquid hydrogen and liquid oxygen propellants, with each engine producing 1,859 kN (418,000 lbf) of thrust at liftoff. Although the RS-25 can trace its heritage back to the 1960s, concerted development of the engine began in the 1970s, with the first flight, STS-1, occurring on April 12, 1981. The RS-25 has undergone several upgrades over its operational history to improve the engine's reliability, safety, and maintenance load. Subsequently, the RS-25D is the most efficient liquid fuel rocket engine currently in use.The engine produces a specific impulse (Isp) of 452 seconds (4.43 km/s) in a vacuum, or 366 seconds (3.59 km/s) at sea level, has a mass of approximately 3.5 tonnes (7,700 pounds), and is capable of throttling between 67% and 109% of its rated power level in one-percent increments. The RS-25 operates at temperatures ranging from −253 °C (−423 °F) to 3300 °C (6000 °F).The Space Shuttle used a cluster of three RS-25 engines mounted in the stern structure of the orbiter, with fuel being drawn from the external tank. The engines were used for propulsion during the entirety of the spacecraft's ascent, with additional thrust being provided by two solid rocket boosters and the orbiter's two AJ-10 orbital maneuvering system engines. Following each flight, the RS-25 engines were removed from the orbiter, inspected, and refurbished before being reused on another mission.

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