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This page is about the NASA rocket family. For the similarly named US Air Force project of the 1960s, see Space Launcher System.
Space Launch System
SLS Block 1 concept art from September 2011
FunctionLaunch vehicle
Country of originUnited States
Size
Diameter8.4 m (core stage)
Stages2
Capacity
Payload to LEO
MassSLS Block I: 70,000 kg (150,000 lb)
SLS Block IA: 105,000 kg (231,000 lb)
SLS Block II: 130,000 kg (290,000 lb)
Associated rockets
FamilyShuttle-Derived Launch Vehicles
Launch history
StatusUndergoing development
Launch sitesLC-39, Kennedy Space Center
First flight17 December 2017[1]
Type of passengers/cargoOrion MPCV
Boosters (Block I)
No. boosters2 Space Shuttle Solid Rocket Boosters
(5-segment)
Powered by1
Maximum thrust16,013.6 kilonewtons (3,600,000 lbf)
Total thrust32,027.2 kilonewtons (7,200,000 lbf)
Specific impulse269 seconds
Burn time124 seconds
PropellantAPCP
First stage (Block I) – Core Stage
Diameter8.4 metres (28 ft)
Powered by4 RS-25D
Maximum thrust7,440 kilonewtons (1,670,000 lbf)
Specific impulse363 seconds (sea level)
PropellantLH2/LOX
First stage (Block IA/II) – Core Stage
Diameter8.4 metres (28 ft)
Powered by5 RS-25E
Maximum thrust9,300 kilonewtons (2,100,000 lbf)
Specific impulse363 seconds (sea level)
PropellantLH2/LOX
Second stage (Block I) – iCPS
Height13.7 metres (45 ft)
Diameter5 metres (16 ft)
Empty mass3,490 kilograms (7,690 lb)
Gross mass30,710 kilograms (67,700 lb)
Powered by1 RL10B-2
Maximum thrust110.1 kilonewtons (24,800 lbf)
Specific impulse462 seconds
Burn time1125 seconds
PropellantLH2/LOX
Second stage (Block II) – Earth Departure Stage
Powered by3 J-2X
Maximum thrust3,930 kilonewtons (880,000 lbf)
Specific impulse448 seconds (vacuum)
PropellantLH2/LOX
[edit on Wikidata]

The Space Launch System, or SLS, is a United States Space Shuttle-derived heavy launch vehicle being designed by NASA. It follows the cancellation of the Constellation Program, and is one of the several successors to the Space Shuttle program. The NASA Authorization Act of 2010 envisions the transformation of the Ares I and Ares V vehicle designs into a single launch vehicle usable for both crew and cargo. It is to be upgraded over time with more powerful versions. Its initial capability of the core elements, without an upper stage, will be between 70 metric tons (for the Block 0 configuration with 3 engines and a partially fueled core) and 100 metric tons (for the Block I configuration with 4 engines and a fully fueled core) to low-Earth orbit (LEO) in preparation for missions beyond low-Earth orbit. With the addition of an integrated upper Earth Departure Stage and a fifth SSME-derived core engine, the total lift capability is to be 130 metric tons which would make it the most powerful rocket ever created.[2][3]

SLS is to take astronauts and hardware to such destinations as near-Earth objects like asteroids, Lagrange points, the Moon, and Mars. SLS may also to support trips to the International Space Station, if necessary. The SLS Program is integrated with NASA's Orion Program, providing a multipurpose crew vehicle. SLS will use the ground operations and launch facilities at NASA's Kennedy Space Center, Florida.

Design and development

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The Space Launch System's planned evolution

On 14 September 2011, NASA announced its design selection for the new launch system, declaring that it would take the agency's astronauts farther into space than ever before and provide the cornerstone for future US human space exploration efforts.[4][5][6] Since the announcement, four versions of the launch vehicle have been revealed – Blocks 0, I, IA and II. Each configuration utilizes different core stages, boosters and upper stages, with some components deriving directly from Space Shuttle hardware and others being developed specifically for the SLS.[7] Later versions will use five RS-25E engines with upgraded boosters and a 8.4-meter diameter upper stage with 3 J-2X engines. The initial Block I two-stage variant will have a similar lift capability to the Saturn INT-20's 60,000 kg, while the proposed Block II final variant will have similar lift capacity and height to the original Saturn V.[8] By November 2011 NASA had selected five rocket configurations for wind tunnel testing, described in three Low Earth Orbit classes; 70 metric tons, 105 metric tons, and 130 metric tons.

On 24 May 2011, NASA announced that development of the Orion spacecraft from the Constellation program will perform the role of the Multi-Purpose Crew Vehicle (MPCV).[9]

Planned evolution

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Block I

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A Delta Cryogenic Second Stage (DCSS), referred to as the Interim Cryogenic Propulsion Stage (iCPS). The core stage would be equipped with four RS-25D engines and strapped to the side of the core stage would be two five segment Solid Rocket Boosters (SRBs). This 70-metric ton configuration currently will only fly two missions, Exploration Mission 1 (EM-1) and Exploration Mission 2 (EM-2).

Block IA

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The core stage would be equipped with four RS-25D or RS-25E engines . strapped to the core stage will be two Advanced Boosters, whether the advanced boosters will utilize a solid or liquid propellant is not yet finalized.

Block II

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The core stage would be equipped with five RS-25E engines. strapped to the core stage will be the two Advanced Boosters from the Block IA configuration. The second stage will be equipped with two J-2X engines.

Misc

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Core stage

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The core stage of the SLS is common to all vehicle configurations, essentially consisting 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.[10][3] The stage will utilise varying numbers and versions of the RS-25 engine depending on the configuration to be used:

  • Block 0 – Unstretched core stage with 3 RS-25D engines.[11][12]
  • Block I – Stretched core stage with 4 RS-25D engines.[7]
  • Block IA & II – Stretched core stage with 5 RS-25E engines.[7]

Boosters

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In addition to the thrust produced by the engines on the core stage, for the first two minutes first stage flight will be aided by two booster rockets mounted either side of the core stage. Early configurations (Blocks 0 and I) of the SLS are set to use modified Space Shuttle Solid Rocket Boosters (SRBs), with either 4 or 5 segments depending on configuration.[7] These boosters will not be recovered and will sink into the Atlantic Ocean downrange.[1] The boosters for Block IA and Block II configurations, however, will be upgraded from the basic boosters, with the selection upgraded booster bids.[13] These boosters may be of either the solid or liquid-fuel type.[7]

ATK, the builder of the Space Shuttle SRBs, has completed three full-scale, full-duration static tests of the five-segment booster that will be used in Blocks 0 & I. Development motor (DM-1) was successfully tested on 10 September 2009; DM-2 on 31 August 2010 and DM-3 on 8 September 2011. For DM-2 the motor was cooled to a core temperature of 40 degrees Fahrenheit (4 degrees Celsius), and for DM-3 it was heated to above 90 degrees Fahrenheit (32 degrees Celsius). In addition to other objectives, these tests validated motor performance at extreme temperatures.[14][15][16]

On 17 June 2011, Aerojet announced a strategic partnership with Teledyne Brown to develop and produce a domestic version of the NK-33 engine, with its thrust increased to 2.2 MN (500,000 lbf) at sea level. This booster is to compete against Shuttle-derived solid rocket boosters for the SLS launch vehicle.[17]

Upper stage

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The SLS will make use of several upper stages in its various configurations:[7][18]

  • Block 0 – No upper stage.
  • Block I – A Delta Cryogenic Second Stage (DCSS), referred to as the Interim Cryogenic Propulsion Stage (iCPS). This 70-metric ton configuration currently will only fly two missions, Exploration Mission 1 (EM-1) and Exploration Mission 2 (EM-2). Although the DCSS is currently the favored upper stage, NASA documentation still lists the kick stage as “TBD”, or to be decided. Atlas V or Delta IV upper stages are noted options.[19]
  • Block IA – A large Cryogenic Propulsion Stage, specifically developed for SLS and powered by liquid hydrogen fuel and liquid oxygen oxidiser. This 105-metric ton rocket will first launch as SLS-3. Currently there are four configurations of this vehicle under analysis by NASA, of which only two will be produced.
  • Block II – A fully-fledged Earth Departure Stage to be powered by three J-2X engines. This 130-metric ton rocket evolution will not debut until the 2030s. As with the Block IA there are also four corresponding configurations of this vehicle under analysis by NASA.

Assembled rocket

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Prior to launch the SLS will have the ability to tolerate a minimum of 13 tanking cycles due to launch scrubs and other launch delays. 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.[20]

Program costs

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During the joint Senate-NASA presentation in September 2011, it was stated that the SLS program has a projected development cost of $18 billion through 2017, with $10B for the SLS rocket, $6B for the Orion Multi-Purpose Crew Vehicle and $2B for upgrades to the launch pad and other facilities at Kennedy Space Center.[21] These costs and schedule are considered optimistic by Booz Allen Hamilton, which conducted an independent cost assessment for NASA.[22] An unofficial NASA document estimated the cost of the program through 2025 to total at least $41B for four 70 metric ton launches (1 unmanned in 2017, 3 manned starting in 2021),[23] with the 130 metric ton version ready no earlier than 2030.[24] HEFT estimate Block 0 unit cost at $1.6 billion.[25]

Criticism

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Criticism of SLS falls in several areas including claims of cannibalization from other areas of the space program. The Space Access Society, Space Frontier Foundation and the Planetary Society called for cancellation arguing that SLS will consume the funds for other projects from the NASA budget and will not reduce per pound launch costs.[26][27][28] Some estimates the cost per pound to LEO at $8,500.[29] Rep. Dana Rohrabacher and other added that instead a propellant depot should be developed and the Commercial Crew Development program accelerated[30][31][32][33][26] Two studies, one not publicly released from NASA,[34][35] and another from Georgia Tech show it as a possible cheaper alternative.[36][37]

Others suggest it will cost less to use an existing rocket (Atlas V, Delta IV, Falcon 9) or proposed derivative (Falcon Heavy), with on-orbit assembly and refuelling as needed, rather than develop a new launch vehicle for space exploration without competition for the whole design.[38][39][40][41][42] Mars Society founder suggested that a heavy lift vehicle should be developed for $5 billion on fixed-price request for proposals,[43] and SpaceX CEO said his company could build one for $2.5 billion.[44][45]

The Augustine commission also proposed option 5b, a commercial 75 metric ton launcher with lower operating costs, and noted than a 40 to 60 metric ton launcher can support exploration.[46]

Congressman 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).[47][48][27]

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".[26]

Proposed missions and schedule

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SLS launch animation

Some of the 14 currently proposed Design Reference Missions include:[49][50][51][18][19][52]

  • ISS Back-Up Crew Delivery – a single launch mission of up to four astronauts via a Block 1 SLS/Orion-MPCV without an Interim Cryogenic Propulsion Stage (iCPS) to the ISS if the Commercial Crew Development program does not come to fruition. This potential mission mandated by the NASA Authorization Act of 2010 is deemed undesirable since the 70mt SLS and BEO Orion would be overpriced and overpowered for said mission requirements. Its current description is “delivers crew members and cargo to ISS if other vehicles are unable to perform that function. Mission length 216 mission days. 6 crewed days. Up to 210 days at the ISS.”
  • Tactical Timeframe DRMs
    • BEO Uncrewed Lunar Fly-by – Exploration Mission −1 (EM-1), a reclassification of SLS-1, is a single launch mission of a Block I SLS with iCPS and lunar Block 1 Orion MPCV with a liftoff mass around 62.2 t with SLS’ Payload Insertion of 50.4 t, which would be a six to ten day test mission with about one day around the Moon. Its current description is “Uncrewed Lunar Flyby: Uncrewed mission Beyond Earth Orbit (BEO) to test critical mission events and demonstrate performance in relevant environments. Expected drivers include: SLS and ICPS performance, MPCV environments, MPCV re-entry speed, and BEO operations,” EM-1 overview as follows; “Notional Mission Event Sequence: 1) SLS lofts Orion to high-apogee orbit, while meeting core disposal constraints,” “2) Kick-stage (TBD) performs burn to raise perigee to safe height. 3)  Kick-stage (TBD) performs TLI burn,” “4)  3–5 day transit time. 5)  Lunar flyby. 6)  3–5 day transit time.”
    • BEO Crewed Lunar Orbit – Exploration Mission −2 (EM-2), a reclassification of SLS-2, is a single launch mission of a Block I SLS with iCPS and lunar Block 1 Orion MPCV with a liftoff mass around 68.8 t with SLS’ Payload Insertion of 50.7 t, which would be a ten to fourteen day mission with a crew of four astronauts who would spend four days in lunar orbit. Its current description is “Crewed mission to enter lunar orbit, test critical mission events, and perform operations in relevant environments,” “Expected drivers include: SLS and ICPS performance, crew support for BEO mission duration, MPCV delta V, MPCV re-entry speed.”
  • Strategic Timeframe DRMs
    • GEO vicinity mission – a dual launch mission separated by 180 days to Geostationary Orbit. The first launch would comprise an SLS with a CPS and cargo hauler, the second an SLS with a CPS and Orion MPCV. Both launches would have a mass of about 110 t.
    • A set of lunar missions enabled in the early 2020s ranging from EML-1 and low lunar orbit to a lunar surface mission. These missions would lead to a lunar base combining commercial and international aspects.
      • The first two missions would be single launches of SLS with a CPM and Orion MPCV to EML-1 or LLO and would have a mass of 90 t and 97.5 t respectively. The LLO mission is a crewed twelve day mission with three in Lunar orbit. Its current description is “Low Lunar Orbit (LLO): Crewed mission to LLO. Expected drivers include: SLS and CPS performance, MPCV re-entry speed, and LLO environment for MPCV,”
      • The lunar surface mission set for the late 2020s would be a dual launch separated by 120 days. This would be a nineteen day mission with seven days on the Moon's surface. The first launch would comprise an SLS with a CPS and lunar lander, the second an SLS with a CPS and Orion MPCV. Both would enter LLO for lunar orbit rendezvous prior to landing at equatorial or polar sites on the moon. Launches would have masses of about 130 t and 108 t, respectively. Its current description is “Lunar Surface Sortie (LSS): Lands four crew members on the surface of the Moon in the equatorial or Polar Regions and returns them to Earth,” “Expected drivers include: MPCV operations in LLO environment, MPCV uncrewed ops phase, MPCV delta V requirements, RPOD (Rendezvous, Proximity Operations and Docking), MPCV number of habitable days.”
    • Five Near Earth Asteroid (NEA) missions ranging from “Minimum” to “Full” capability are being studied.
    • Forward Work Martian Moon Phobos/Deimos, a crewed Flexible Path mission to one of the Martian moons. It would include 40 days in the vicinity of Mars and a return Venus flyby.
    • Forward Work Mars Landing, a crewed mission to spend 500 or more days exploring the surface of the red planet. The ambitious proposal would include the launch of seven SLS HLVs with nuclear propulsion stages, or NTRs (Nuclear Thermal Rocket). The seven payloads would then be assembled in LEO into three separate vehicles for the journey to Mars, the MLV Cargo Vehicle, MLV Habitat Vehicle, and MTV Crew Transfer Vehicle.
  • SLS DoD Missions, the HLV will be made available for Department of Defense and other US Government agencies to launch military or classified missions.
  • Commercial payloads such as the Bigelow Commercial Space Stations have also been referenced.
  • Additionally “Secondary Payloads” mounted on SLS via an Encapsulated Secondary Payload Adapter (ESPA) ring could also be launched in conjunction with a "primary passenger" to maximize payloads.

A very preliminary and unofficial schedule based on a worst case budget has outlined some early SLS flights as:[53]

Mission Targeted date Variant Notes
SLS-1/EM-1 December 2017 Block I[18] Send Orion/MPCV on unmanned trip around the Moon.
SLS-2/EM-2 August 2019[54] Block I[18] Send Orion MPCV with four members into lunar orbit.
SLS-3 August 2022[53] Block IA[18]
SLS-4 August 2023[53] Block IA[18]
SLS-5 August 2024[53] Block IA[53] First launch of SLS Cargo configuration, first flight with RS-25E engines.[18]
SLS-6 August 2025[53] Block IA[53] Manned "Exploration" Mission
SLS-7 August 2026[53] Block IA[53] Cargo launch
SLS-8 August 2027[53] Block IA[53] Manned launch
SLS-9 August 2028[53] Block IA[53] Cargo launch
SLS-10 August 2029[53] Block IA[53] Manned launch
SLS-11 August 2030[53] Block IA[53] New configuration, Cargo launch
SLS-12 August 2031[53] Block IA[53] Manned mission
SLS-13 August 2032[53] Block II[53] New configuration, Cargo launch

See also

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References

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  1. ^ a b "Space Launch System: How to launch NASA's new monster rocket". NASASpaceFlight.com. 20 February 2012. Retrieved 9 April 2012.
  2. ^ "The NASA Authorization Act of 2010". Featured Legislation. Washington DC, USA: United States Senate. 15 July 2010. Retrieved 26 May 2011.
  3. ^ a b Stephen Clark (31 March 2011). "NASA to set exploration architecture this summer". Spaceflight Now. Retrieved 26 May 2011.
  4. ^ "NASA Announces Design For New Deep Space Exploration System". NASA. 14 September 2011. Retrieved 14 September 2011.
  5. ^ "Press Conference on the Future of NASA Space Program". C-Span. 14 September 2011. Retrieved 14 September 2011.
  6. ^ Kenneth Chang (14 September 2011). "NASA Unveils New Rocket Design". New York Times. Retrieved 14 September 2011.
  7. ^ a b c d e f Chris Bergin (4 October 2011). "SLS trades lean towards opening with four RS-25s on the core stage". NASASpaceflight.com. Retrieved 26 January 2012.
  8. ^ Karl Tate (16 September 2011). "Space Launch System: NASA's Giant Rocket Explained". Space.com. Retrieved 26 January 2012.
  9. ^ "NASA Announces Key Decision For Next Deep Space Transportation System". NASA. 24 May 2011. Retrieved 26 January 2012.
  10. ^ Chris Bergin (14 September 2011). "SLS finally announced by NASA – Forward path taking shape". NASASpaceflight.com. Retrieved 26 January 2012.
  11. ^ Chris Bergin (25 April 2011). "SLS planning focuses on dual phase approach opening with SD HLV". NASASpaceflight.com. Retrieved 26 January 2012.
  12. ^ Chris Bergin (16 June 2011). "Managers SLS announcement after SD HLV victory". NASASpaceflight.com. Retrieved 26 January 2012.
  13. ^ Keith Cowing (14 September 2011). "NASA's New Space Launch System Announced – Destination TBD". SpaceRef. Retrieved 26 January 2012.
  14. ^ "NASA and ATK Successfully Test Ares First Stage Motor". NASA. 10 September 2009. Retrieved 30 January 2012.
  15. ^ "NASA and ATK Successfully Test Five-Segment Solid Rocket Motor". NASA. 31 August 2010. Retrieved 30 January 2012.
  16. ^ NASA Successfully Tests Five-Segment Solid Rocket Motor, NASA, 31 August 2010, retrieved 8 September 2011
  17. ^ Frank Morring (17 June 2011). "NASA Will Compete Space Launch System Boosters". Aviation Week. Retrieved 20 June 2011.
  18. ^ a b c d e f g "Acronyms to Ascent – SLS managers create development milestone roadmap". NASASpaceFlight.com. 23 February 2012. Retrieved 9 April 2012.
  19. ^ a b "Exploration Mission 1: SLS and Orion mission to the Moon outlined". NASASpaceFlight.com. 29 February 2012. Retrieved 9 April 2012.
  20. ^ "SLS to be robust in the face of scrubs, launch delays and pad stays". NASASpaceFlight.com. 4 April 2012. Retrieved 9 April 2012.
  21. ^ Marcia Smith (14 September 2011). "New NASA Crew Transportation System to Cost $18 Billion Through 2017". Space Policy Online. Retrieved 15 September 2011. [dead link‍]
  22. ^ "Independent Cost Assessment of the Space Launch System, Multi-purpose Crew Vehicle and 21st Century Ground Systems Programs: Executive Summary of Final Report" (PDF). Booz Allen Hamilton. NASA.gov. 19 August 2011.
  23. ^ "ESD Integration, Budget Availability Scenarios" (PDF). Space Policy Online. 19 August 2011. Retrieved 15 September 2011.
  24. ^ Marcia Smith (9 September 2011). "The NASA Numbers Behind That WSJ Article". Space Policy Online. Retrieved 15 September 2011.
  25. ^ "Human Exploration Framework Team (HEFT) DRM Review – Phase 1 (page 69)" (PDF). nasawatch.com. September 2010.
  26. ^ a b c Henry Vanderbilt (15 September 2011). "Impossibly High NASA Development Costs Are Heart of the Matter". moonandback.com. Retrieved 26 January 2012.
  27. ^ a b Ferris Valyn (15 September 2011). "Monster Rocket Will Eat America's Space Program". Space Frontier Foundation. Retrieved 16 September 2011.
  28. ^ "Statement before the Committee on Science, Space, and Technology US House of Representatives Hearing: A Review of the NASA's Space Launch System" (PDF). The Planetary Society. 12 July 2011. Retrieved 26 January 2012.
  29. ^ "The SLS: too expensive for exploration?". thespacereview.com. 28 November 2011.
  30. ^ Rohrabacher, Dana (14 September 2011). "Nothing New or Innovative, Including It's Astronomical Price Tag". Retrieved 14 Sept 2011. {{cite web}}: Check date values in: |accessdate= (help)
  31. ^ "Rohrabacher calls for "emergency" funding for CCDev". parabolicarc.com. 24 August 2011. Retrieved 15 September 2011.
  32. ^ Jeff Foust (15 September 2011). "A monster rocket, or just a monster?". The Space Review.
  33. ^ Jeff Foust (1 November 2011). "Can NASA develop a heavy-lift rocket?". The Space Review.
  34. ^ Mohney, Doug (21 October 2011). "Did NASA Hide In-space Fuel Depots To Get a Heavy Lift Rocket?". Satellite Spotlight. Retrieved 10 November 2011.
  35. ^ "Propellant Depot Requirements Study" (PDF). HAT Technical Interchange Meeting. 21 July 2011.
  36. ^ Cowing, Keith (12 October 2011). "Internal NASA Studies Show Cheaper and Faster Alternatives to the Space Launch System". SpaceRef.com. Retrieved 10 November 2011.
  37. ^ "Near Term Space Exploration with Commercial Launch Vehicles Plus Propellant Depot" (PDF). Georgia Institute of Technology / National Institute of Aerospace. 2011.
  38. ^ "Affordable Exploration Architecture" (PDF). United Launch Alliance. 2009.
  39. ^ Grant Bonin (6 June 2011). "Human spaceflight for less: the case for smaller launch vehicles, revisited". The Space Review.
  40. ^ Robert Zubrin (14 May 2011). "How We Can Fly to Mars in This Decade—And on the Cheap". Mars Society.
  41. ^ Rick Tumlinson (15 September 2011). l "The Senate Launch System – Destiny, Decision, and Disaster". Huffington Post. {{cite web}}: Check |url= value (help)
  42. ^ Andrew Gasser (24 October 2011). "Propellant depots: the fiscally responsible and feasible alternative to SLS". The Space Review.
  43. ^ Alan Boyle (7 December 2011). "Is the case for Mars facing a crisis?". MSNBC.
  44. ^ "NASA Studies Scaled-Up Falcon, Merlin". Aviation Week. 2 December 2010.
  45. ^ John K. Strickland, Jr. "The SpaceX Falcon Heavy Booster: Why Is It Important?". National Space Society. Retrieved 4 January 2012.
  46. ^ Review of U.S. Human Space Flight Plans Committee. "Seeking A Human Spaceflight Program Worthy of A Great Nation" (PDF). Final Report. NASA. Retrieved 15 April 2010. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  47. ^ "Congressman, Space Frontier Foundation, And Tea Party In Space Call For NASA SLS Investigation". moonandback.com. 4 October 2011. Retrieved 20 October 2011.
  48. ^ "The Senate Launch System". Competitive Space. 4 October 2011. Retrieved 20 October 2011.
  49. ^ Chris Bergin (15 December 2011). "Building the Roadmap for SLS – Con Ops lays out the LEO/Lunar Options". NASASpaceflight.com. Retrieved 26 January 2012.
  50. ^ Chris Bergin (24 January 2012). "SLS Exploration Roadmap evaluations provide clues for human Mars missions". NASASpaceflight.com. Retrieved 26 January 2012.
  51. ^ "SLS interest in DoD launch market and Secondary Payloads potential". NASASpaceFlight.com. 4 February 2012. Retrieved 9 April 2012.
  52. ^ "NASA Exploration Roadmap: A return to the Moon's surface documented". NASASpaceFlight.com. 19 March 2012. Retrieved 9 April 2012.
  53. ^ a b c d e f g h i j k l m n o p q r s t u Chris Bergin (27 July 2011). "Preliminary NASA Plan Shows Evolved SLS Vehicle 21 Years Away". NASASpaceflight.com. Retrieved 28 July 2011.
  54. ^ Chris Bergin (30 September 2011). "SLS mission schedule improving – Crewed Moon mission moving to 2019". NASASpaceflight.com. Retrieved 26 January 2012.
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