The Space Launch System Explained: A Guide to NASA’s Moon Rocket

The Space Launch System Explained: A Guide to NASA’s Moon Rocket

SLS continues on its journey to the launchpad. Photo” Michael Galindo/Cosmic Chicago

NASA’s Space Launch System, or SLS, is the most powerful rocket NASAs ever built, designed to get us back to the Moon. SLS will launch astronauts in the Orion spacecraft, and NASA will use the SLS to lay the groundwork for Artemis missions that will pave the way to deep space exploration.

This new rocket consists of several major elements and systems designed in cooperation with companies from all over the United States and international partners. The maiden flight of SLS, Artemis 1, is set to take place no earlier than August 29th, 2022.

SLS on the launch pad at Kennedy Space Center. Photo: Michael Galindo/Cosmic Chicago

Until then, use this guide to get to know the Space Launch System, NASA’s Moon rocket.

Space Launch System

The Space Launch System (SLS) rocket stands 344.2 ft tall and will weigh 5.74 million pounds when fully fueled. Two solid rocket boosters provide propulsion, and four Space Shuttle-era RS-25 engines, which together will provide a maximum thrust of 8.8 million pounds, accelerate the rocket to 22,600 mph.

The SLS Rocket. Credit Michael Galindo

Core Stage

The Core Stage of the SLS is the backbone of the rocket, supporting the upper stages, including the Orion spacecraft, the four RS-25 main engines, and both Solid Rocket boosters. At 212 ft tall, the Core Stage comes in at 27.6 ft in diameter without the insulating foam.

SLS Core Stage. Credit Michael Galindo

The Core Stage contains the propellant that powers the RS-25 engines, Liquid Oxygen (LOX), and Liquid Hydrogen (LH2). When fully fueled with propellant, it will weigh 2.4 million pounds and contain 733,000 gallons. The core stage will operate from liftoff to Earth orbit for approximately 480 seconds, reaching a top speed faster than 17,500 mph, 23 times the speed of sound.

RS-25 Engines

Four previously flown Space Shuttle engines will power SLS to orbit; they successfully flew 135 Shuttle missions before being upgraded for SLS. Each RS-25 stands 14 ft tall and has a maximum diameter of 8 ft. Powered by LOX and LH2 the engines produce approximately 500,000 pounds of thrust. That is enough thrust to keep eight Boeing 747’s in the air and propel the SLS 73 times faster than an IndyCar at the Indianapolis Motor Speedway.

RS-25 Engine on display at Space Center Houston. Credit Michael Galindo

Due to the high speed and altitude of the rocket at main engine cutoff, the RS-25 engines are no longer reusable.

Solid Rocket Boosters

During the first two minutes of flight, the Solid Rocket Boosters (SRB) provide more than 75 percent of the total thrust for SLS. Each booster stands 177 ft tall and are the most powerful solid propellant boosters ever built for flight.

Solid Rocket Boosters during SLS Rollout to the Launch Pad. Credit Michael Galindo

Each booster generates 3.6 million pounds of thrust and burns for approximately 2 minutes and 12 seconds when they jettison from the rocket. Unlike the Shuttle program, the SRB’s used for SLS are not going to be recovered. Northrop Grumman, the prime contractor for the SRB, is currently developing new boosters for future Artemis flights.

Photogrammetric Markings

Distributed all over the SLS are black and white squares and checkerboards. These are Photogrammetric Markings.

Photogrammetric Markings seen on the SRB’s and Core Stage of SLS. (Red Circles and Squares) Credit Michael Galindo

These markings serve as references for engineering cameras positioned around the launch pad and on the rocket itself. The markings help characterize the movement of the rocket, and its stages during launch and separation events.

More Photogrammetric Marking shown in red circles at the base of the SLS rocket and on the Mobile Launch Platform. Credit NASA

Interim Cryogenic Propulsion Stage (ICPS)

After the Core Stage has separated, the ICPS will take over. Based on the cryogenic stage from the Delta IV rocket, the ICPS was modified and upgraded for use on SLS.

ICPS being stacked with SLS. Credit NASA

The stage is 45 ft tall and 16.7 ft in diameter with a single Aerojet Rocketdyne RL10B-2 engine. The RL10 is a proven engine with over 500 flights over 50 years. The ICPS will circularize Orion’s orbit around earth and the Trans Lunar Injection (TLI) burn that will send Orion to the Moon.

Orion Crew Module

The Orion Crew Module is where future astronauts will live and work during Artemis missions. The crew module is able to sustain up to four astronauts for 21 days without needing to dock with another spacecraft for resupply, providing a safe habitat during launch, reentry, and recovery. The crew module is the only part of SLS that is recoverable and will return.

Orion Service Module

The service module, built by Airbus, is provided by the European Space Agency (ESA). It provides fuel, power, and propulsion to the spacecraft, and potable water, nitrogen, and oxygen to the crew.

Orion Crew and Service Module during testing. Credit NASA

Just before reentering Earth’s atmosphere, the service module will be separated and burn up in the atmosphere.

Launch Abort System (LAS)

In the event of an emergency during launch, the LAS will activate and pull the Orion spacecraft safely away from the SLS. The LAS also works to keep Orion safe from aerodynamic and acoustic forces during launch and abort environments.

The Orion Launch Abort System seen during the AA-2 launch in 2019. Credit Michael Galindo

Within milliseconds of an emergency, the LAS activates its abort motors, and Orion accelerates from 0-500 mph in two seconds. Once the abort motors finish firing, the LAS attitude control motor will fire and orient Orion for separation from the LAS. Once separated, Orion’s parachutes will deploy and allow for a safe water recovery.

Sophie Sanchez contributed to this piece.


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Sophie Sanchez

I’ve turned a lifetime fascination for space exploration and astronomy into a career writing, speaking, and creating STEM programming about all things space. Until I get the chance to experience space for myself I’ll share the stories of every mission of a lifetime I have the opportunity to witness.

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