Spaceflight Insider

The Hangar / Space Launch System

SLS Artist's Rendering

Image Credit: Nathan Koga / SpaceFlight Insider

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The Space Launch System (SLS) is a Space Shuttle-derived “super-heavy-lift” launch vehicle that NASA began developing in 2011 in conjunction with the Orion Multipurpose Crew Vehicle to support human space exploration beyond Earth orbit. It was born out of resistance in the U.S. Senate to President Obama’s decision to cancel the Constellation Program in 2010. Unlike Constellation, which envisioned separate crew- and cargo-launch vehicles (Ares I and Ares V), the SLS is designed to be human rated and to carry crew and cargo beyond Earth orbit.

Vehicle Capability/Description

The vehicle’s initial payload mass capability (Block 1) to low-Earth orbit (LEO) is slated to be 154,323 pounds (70,000 kg), which is approximately 20 percent more than the Saturn V rocket. Subsequent Block 1B and Block 2 versions of the SLS are slated to carry 231,485 pounds (105,000 kg) and 286,601 pounds (130,000 kg), respectively.

The SLS consists of a 27.6-foot-diameter (8.4-meter) core stage powered by four Aerojet Rocketdyne RS-25 (Space Shuttle) Main Engines as well as two Orbital ATK five-segment Reusable Solid Rocket Motors (RSRMVs). The RSRMVs have a slightly higher specific impulse and longer burn time compared to the four-segment Solid Rocket Boosters used by the Space Shuttle.

The Block 1 upper stage is a repurposed United Launch Alliance Delta Cryogenic Second Stage, called the Interim Cryogenic Propulsion Stage (ICPS), powered by a single Aerojet Rocketdyne RL10 engine. The ICPS is “interim” because NASA hopes to eventually replace it with a more capable Exploration Upper Stage (EUS) powered by four RL-10 engines.

Like the Saturn and Ares rockets before it, the SLS is designed with crew safety in mind, as the Orion spacecraft is positioned atop the rocket and will have launch abort system to pull it away from the launch vehicle in the event of an emergency.

Mission Profile

The SLS will be stacked in the Vehicle Assembly Building and launched from the Kennedy Space Center Launch Complex 39B. The first flight payload of the SLS will be an unmanned Orion Multipurpose Crew Vehicle, currently scheduled for no later than the end of 2018. The KSC Ground Systems Development Directorate is pursuing a “clean pad” approach to SLS operations, with most of the stacking and servicing occurring in the VAB before rolling out the vehicle on the Mobile Launcher out to the pad.

Like the Space Shuttle, the core stage engines will ignite and come to full thrust before the boosters are activated. Once the engines and boosters are ignited, the vehicle lifts off and the RS-25 engines vector to perform a pitch and roll maneuver the turns the vehicle toward the Atlantic Ocean. The RSRMVs burn for just over two minutes and are then jettisoned. Unlike Shuttle operations, they will not be recovered, refurbished, and reused.

Following booster jettison, the Core Stage burns for another 4.5 minutes. The Core Stage is then jettisoned and the ICPS ignites to bring Orion to its initial orbit. Once all ICPS and Orion systems are evaluated and determined to be nominal, the ICPS ignites again for a trans-lunar injection (TLI) burn. Once the TLI burn is completed, the ICPS is jettisoned and Orion continues toward the Moon.

Vehicle Progress

NASA continues to develop and build test hardware at Marshall Space Flight Center (Core Stage, stage adapters), at Stennis Space Center (RS-25), and at Orbital ATK’s property in Utah (RSRMV). NASA successfully completed a Critical Design Review (CDR) for the SLS in October 2015.

The first flight of the SLS, Exploration Mission One (EM-1), is scheduled for the end of 2018 when it will launch an unmanned Orion spacecraft to lunar orbit, though this date has moved from a projected flight in late 2017.


The first payload the SLS will carry will be the Orion multipurpose crew vehicle. A 2014 NASA briefing has suggested that the SLS could be used to support science missions, including a mission to Jupiter’s moon Europa, a Mars Sample Return mission, large space telescopes, an advanced solar probe, missions to the outer Solar System, or even an interstellar mission.

The vehicle has been promoted to the science community for facilitating more ambitious science missions due to its mass lift capacity, large payload shrouds (8.4 or 10 meters), and high departure energy, avoiding the need for gravitational assist maneuvers.

Block 1
Payload to LEO 70,000 kg
Height 98.1 m
Diameter (Core Stage) 8.4 m
Mass 2.6 million kg
Block 1B Crew
Payload to LEO 105,000 kg
Height 111.4 m
Diameter (Core Stage) 8.4 m
Mass 2.7 million kg
Block 1B Cargo
Payload to LEO 105,000 kg
Height 99.9 m
Diameter (Core Stage) 8.4 m
Diameter (Payload Fairing) 8.4 m, 10 m
Mass 2.7 million kg
Block 2
Payload to LEO 130,000 kg
Height 111.3 m
Diameter (Core Stage) 8.4 m
Mass 2.95 million kg
Diameter (Core Stage) 8.4 m
Diameter (Payload Fairing) 8.4 m, 10 m
Solid Rocket Boosters
Manufacturer Orbital ATK
Engine Reusable Solid Rocket Motors-Five-Segment (RSRMV)
No. Engines 2
Length 53.9 m
Diameter 3.7 m
Gross Mass 725,747.8 kg
Thrust 1,632,932.5 kg (Each)
Specific Impulse (Sea Level) 269 sec.
Burn Time 126 sec.
Core Stage - SLS Block 1
Manufacturer Boeing
Length 64.6 m
Diameter 8.4 m
Empty mass 85,275 kg
Propellant mass 952,543.9 kg
No. Engines 4
Engine RS-25E
Engine Manufacturer Aerojet Rocketdyne
Thrust 1,859.4 kN (Sea Level)
2,277.5 kN (Vacuum)
Specific impulse 366 seconds (Sea Level)
452 seconds (Vacuum)
Burn time 510 seconds
Propellant Liquid Hydrogen / Liquid Oxygen
Interim Cryogenic Propulsion Stage (ICPS)
Manufacturer United Launch Alliance
Length 12 m
Diameter 5 m
Empty mass 3,490 kilograms
Propellant mass 28,576 kg
Engines RL-10B2
Thrust 110.1 kN (RL10A)
Specific impulse 465.5 seconds (Vacuum)
Burn time 1,125 seconds
Propellant Liquid Hydrogen / Liquid Oxygen
Exploration Upper Stage (EUS)
Manufacturer Boeing
Length 17.3 m
Diameter 8.4 m
Propellant mass 129,000 kg
Engines RL10-C
Thrust 101.8 kN
Specific impulse 449.7 seconds
Burn time 350 seconds (LEO ascent) 925 s (TLI burn)
Propellant Liquid Hydrogen / Liquid Oxygen