Space Launch System

This article is about the NASA rocket family. For the similarly-named US Air Force project of the 1960s, see Space Launcher System.
Space Launch System

Artist's rendering of the SLS Block 1 launching with Orion.
Function Launch vehicle
Country of origin United States
Project cost US$7 billion (2014-2018, 2014 estimate),[1] to
35 billion (until 2025, 2011 estimate)[2][3]
Cost per launch US$500 million (2012, planned)[4] to
5 billion[5][6]
Size
Diameter 27 ft 7 in (8.4 m) (core stage)
Stages 2
Capacity
Payload to
LEO 		150,000 to 290,000 lb (70,000 to 130,000 kg)
Associated rockets
Family Shuttle-Derived Launch Vehicles
Launch history
Status Undergoing development
Launch sites LC-39B, Kennedy Space Center
First flight No later than November 2018[7]
Notable payloads Orion MPCV
Boosters (Block 1)
No boosters 2 Five-segment Solid Rocket Boosters
Thrust 3,600,000 lbf (16,000 kN)
Total thrust 7,200,000 lbf (32,000 kN)
Specific impulse 269 seconds (2.64 km/s) (vacuum)
Burn time 124 seconds
Fuel PBAN, APCP
First Stage (Block 1, 1B, 2) - Core Stage
Diameter 27 ft 7 in (8.4 m)
Empty mass 187,990 lb (85,270 kg)
Gross mass 2,159,322 lb (979,452 kg)
Engines 4 RS-25D/E[8]
Thrust 1,670,000 lbf (7,440 kN)
Specific impulse 363 seconds (3.56 km/s) (sea level), 452 seconds (4.43 km/s) (vacuum)
Fuel LH2/LOX
Second Stage (Block 1) - ICPS
Length 44 ft 11 in (13.7 m)
Diameter 16 ft 5 in (5 m)
Empty mass 7,690 lb (3,490 kg)
Gross mass 67,700 lb (30,710 kg)
Engines 1 RL10B-2
Thrust 24,800 lbf (110.1 kN)
Specific impulse 462 seconds (4.53 km/s)
Burn time 1125 seconds
Fuel LH2/LOX
Second Stage (Block 1B, Block 2) - Exploration Upper Stage
Diameter 27 ft 7 in (8.4 m)
Engines 4 RL10
Thrust 99,000 lbf (440 kN)
Fuel LH2/LOX

The Space Launch System (SLS) is a United States Space Shuttle-derived heavy expendable launch vehicle being designed by NASA. It 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.

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 70 metric tons to low Earth orbit (LEO), which will be increased with the debut of Block 1B and the Exploration Upper Stage.[9] 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;[10] this would make the SLS the most capable heavy lift vehicle ever built.[11][12]

These upgrades will allow the SLS to lift astronauts and hardware to various beyond-LEO destinations: on a circumlunar trajectory as part of Exploration Mission 1 with Block 1, to a near-Earth asteroid in Exploration Mission 2 with Block 1B, and to Mars with Block 2. 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.

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 $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.[13][14]

Design and development

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,[15] would take the agency's astronauts farther into space than ever before and provide the cornerstone for future US human space exploration efforts.[16][17][18]

Three versions of the 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 70 metric tons (77 short tons) and Block 1B has a baseline of 105 metric tons (116 short tons). The proposed Block 2 will have similar lift capacity and height to the original Saturn V.[19] It was reported in February 2015 that NASA evaluations showed "over performance" versus the baseline payload for Block 1 and Block 1B.[20]

During the development of the SLS a number of different configurations were considered, including a Block 0 with three main engines,[21] a Block 1A variant which would have upgraded the vehicle's boosters instead of its second stage,[21] and a Block 2 with five main engines and a different second stage, the Earth Departure Stage, with up to three J-2X engines.[22]

On July 31, 2013 the SLS passed the Preliminary Design Review (PDR). The review encompassed all aspects of the SLS' design, not only the rocket and boosters but also ground support and logistical arrangements.[23] On August 7, 2014 the SLS passed a milestone known as Key Decision Point C and entered full-scale development, with an estimated launch date of November 2018.[24]

Vehicle description

Rendering of the SLS Block 1 showing the large core stage, two 5-segment SRBs, and the smaller upper stage.

Core stage

The core stage will be 8.4 meters (28 ft) in diameter and utilize four RS-25 engines.[8][21] Initial flights will use modified RS-25D engines left over from the Space Shuttle program,[25] later flights are expected to switch to a cheaper version of the engine not intended for reuse.[26] 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.[11][27] It will be fabricated at the Michoud Assembly Facility.[28]

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,[29][30] which was eliminated to avoid the need to substantially redesign the core stage for more powerful variants.[21] Likewise, while early Block 2 plans included five RS-25 engines on the core,[22] it was later baselined with four engines.[20]

Boosters

Artist's rendering of a Block 1 SLS.
Comparison of the Saturn V, Space Shuttle, and SLS Block I

Shuttle-derived solid rocket 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.[31][32]

Orbital ATK (formerly Alliant Techsystems) has completed four full-scale, full-duration static fire tests of the five-segment SRB. Development Motor 1 (DM-1) was tested on September 10, 2009; DM-2 was tested on August 31, 2010, and DM-3 on September 8, 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). These tests validated motor performance at extreme temperatures.[33][34][35] Qualification Motor 1 (QM-1) was tested on March 10, 2015.[36]

Advanced boosters

For Block 2, NASA plans to switch from Shuttle-derived five-segment SRBs to advanced boosters.[37] 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.[8][38] Several companies proposed boosters for this competition:

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."[46]

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.[47] In 2014, NASA confirmed the development of Block 1B instead of Block 1A and called off the 2015 booster competition.[20][48] 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.[20]

Upper stage

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) by November 2018,[7] will use a the Interim Cryogenic Propulsion Stage (ICPS). This stage will be a modified Delta IV 5-meter Delta Cryogenic Second Stage (DCSS),[49] and will be powered by a single RL10B-2. Block 1 will be capable of lifting 70 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.[50]

Exploration Upper Stage

The Exploration Upper Stage (EUS) is scheduled to debut on Exploration Mission 2 (EM-2). It is expected to be used by Block 1B and Block 2 and, like the core stage, will be 8.4 meters in diameter. The EUS would be powered by four RL10 engines,[51] and would 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.[52]

Other upper stages

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 crew capsule is docked on the right.

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.[67]

Fabrication

In mid-November 2014, construction of the first SLS began using the new welding system at NASA's Michoud Assembly Facility, where major rocket parts will be assembled.[68]

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.[69]

In January 2015, NASA began test firing RS-25 engines in preparation for use on SLS.[26]

Program costs

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.[24] 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.[70]

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.[13] These costs and schedule were considered optimistic in an independent 2011 cost assessment report by Booz Allen Hamilton for NASA.[71] An unofficial 2011 NASA document estimated the cost of the program through 2025 to total at least $41bn for four 70 t launches (1 unmanned, 3 manned),[2][3] with the 130 t version ready no earlier than 2030.[72]

The Human Exploration Framework Team (HEFT) estimated unit costs for Block 0 at $1.6bn and Block 1 at $1.86bn in 2010.[73] However, since these estimates were made the Block 0 SLS vehicle was dropped in late 2011, and the design was not completed;[74] NASA announced in 2013 that the European Space Agency will build the Orion Service Module.[75]

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.[4] By comparison, the cost for a Saturn V launch was US$185 million in 1969 dollars,[76] which is roughly US$1.2 billion in 2014 dollars.

On July 24, 2014, Government Accountability Office audit predicted that SLS will not launch by the end of 2017 as originally planned since NASA is not receiving sufficient funding.[77]

Alternatives

The Space Access Society, Space Frontier Foundation and the Planetary Society called for cancellation of the project, arguing that SLS will consume the funds for other projects from the NASA budget and will not reduce launch costs;[78][79][80] some estimate this cost for the SLS to be about $8,500 per pound lifted to low earth orbit (LEO).[81] U.S. Representative Dana Rohrabacher and others added that instead, a propellant depot should be developed and the Commercial Crew Development program accelerated.[78][82][83][84][85] Two studies, one not publicly released from NASA[86][87] and another from the Georgia Institute of Technology, show this option to be a possibly cheaper alternative.[88][89]

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.[90][91][92][93][94] 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.[95]

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.[96] Based upon extrapolations of increased payload lift capabilities from past experience with SpaceX's Falcon launch vehicles, SpaceX CEO Elon Musk stated in 2010 that he would "personally guarantee" that his company could build the conceptual Falcon XX, a 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.[97][98] SpaceX's privately-funded MCT launch vehicle, powered by nine Raptor engines, has also been proposed for lofting very large payloads from Earth in the 2020s.[99]

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).[79][100][101] Opponents of the heavy launch vehicle have critically used the name "Senate launch system".[49] 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".[78]

Schedule

Planned SLS missions (as of 2014)
Mission Targeted date Variant Notes
SLS-1/EM-1 By November 2018[7] Block 1[22] Send uncrewed Orion/MPCV on trip around the Moon.
SLS-2/EM-2 c. 2025[102][103] Block 1B[51] Send the Orion (spacecraft) with four crew members to an asteroid that had been robotically captured and placed in lunar orbit two years in advance.[104]

Proposed missions

Some of the currently proposed NASA Design Reference Missions (DRM) and others include:[22][63][105][106][107]

An astronaut, possibly part of Exploration Mission 2, performing a tethering asteroid capture maneuver at a near-earth object (NEO). The Space Exploration Vehicle is close by, with the Orion Multi-Purpose Crew Vehicle (MPCV) docked to the Deep Space Habitat in the background.
Artist's rendering of the proposed Mars Transfer Vehicle (MTV) "Copernicus" that would incorporate NTR propulsion and inflatable habitat technology. A five-meter-diameter crewed Orion MPCV is docked on the far left.
Artist's rendering of Design Reference Mission 5.0, a manned mission to Mars with the Descent/Ascent Vehicle on the far left, and the habitat and crewed commuter vehicle, the Small Pressurized Rover (SPR),[110] on the right. The oxygen producing In-Situ Resource Utilization factory would be emplaced about 1 km away.[111]
One section of the Skylab II Habitat would be made from the SLS Block 2 upper-stage hydrogen tank, similar to but larger than Skylab. A unique use for the SLS as no other vehicle is presently being designed with an 8-meter-diameter upper stage tank.
One proposed ATLAST concept, a design based on an 8-meter monolithic mirror. The Hubble Space Telescope by comparison is equipped with a 2.5 m main mirror. A telescope with an 8-meter monolithic mirror is possible only with a payload fairing bigger than 8 meters in diameter.

Funding

In 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.[122]

See also

Videos

References

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  75. ↑ NASA Signs Agreement for a European-Provided Orion Service Module
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