NASAfacts

National Aeronautics and Space Administration

Mobile Launcher Tower 

Umbilicals and Accessories

NASA’s Space Launch System rocket, or SLS, will 

be the most powerful rocket in the world, with the 

capability to launch humans beyond Earth’s orbit 

on Artemis missions. The SLS rocket, powered by 

four RS-25 core stage engines and two solid rocket 

boosters, along with an RL10 in-space propulsion 

engine, provides the energy necessary to launch the 

Orion spacecraft to the Moon or beyond. 

Prior to rollout and launch, teams stack the Orion 

spacecraft atop the SLS rocket and process it on 

the mobile launcher inside High Bay 3 of the Vehicle 

Assembly Building (VAB) at NASA’s Kennedy Space 

Center in Florida. The tower on the mobile launcher is 

equipped with several connections, called launch accessories and umbilicals, which attach to the SLS’s 

core stage and twin solid rocket boosters, as well as 

the interim cryogenic propulsion stage (ICPS) and the 

Orion spacecraft. 

These umbilicals provide power, communications, 

coolant, and fuel. Additional accessories provide access and stabilize the rocket and spacecraft. During 

launch, each accessory releases from its connection 

point, allowing the rocket and spacecraft to lift off 

safely from the launch pad.

Aft Skirt Electrical Umbilicals 

Two aft skirt electrical umbilicals connect to the SLS 

rocket at the bottom outer edge of each booster and 

provide electrical power and data connections to the 

SLS rocket until it lifts off from the launch pad. These 

umbilicals act like a telephone line, carrying a signal 

to another subsystem on the mobile launcher called 

the Launch Release System. This system distributes 

the launch signal to the rest of the launch accessories and the SLS boosters, and it initiates the launch 

release command.

Aft Skirt Purge Umbilicals 

Two aft skirt purge umbilicals also connect to the SLS 

rocket at the bottom outer edge of each booster to 

remove potentially hazardous gases and maintain 

components within acceptable temperature ranges 

An artist illustration of the mobile launcher with umbilical lines 

installed on the tower and attached to NASA’s Space Launch 

System rocket and Orion spacecraft. Image credit: NASA
National Aeronautics and Space Administration

John F. Kennedy Space Center

Kennedy Space Center, FL 32899

www.nasa.gov

FS-2021-08-727-KSC

through a heated gaseous nitrogen purge to the cavity of each 

booster’s aft skirt. Teams connect these umbilicals during pad 

operations, and they remain connected until released during 

liftoff.

Tail Service Mast Umbilicals 

Two tail service mast umbilicals connect from the zero-level 

deck on the mobile launcher to the SLS rocket core stage aft 

section. These umbilicals are about 33 feet tall. They provide 

liquid oxygen and liquid hydrogen fluid lines and electrical cable connections to the SLS core stage engine section to support propellant handling during prelaunch operations. The umbilicals tilt back before launch to ensure all hardware safely and 

reliably disconnects and retracts from the rocket during liftoff. 

Core Stage Intertank Umbilical 

The core stage intertank umbilical is a swing arm umbilical that 

connects to the SLS core stage intertank, which sits between 

the rocket’s liquid hydrogen and liquid oxygen tanks. The intertank umbilical’s main function is to vent gaseous hydrogen, 

which is boil off from the extremely cold liquid hydrogen fuel, 

from the core stage. The arm also provides conditioned air, 

pressurized gases, and power and data connections to the 

core stage. This umbilical, located at the 140-foot level on the 

mobile launcher tower, swings away at launch. 

Core Stage Forward Skirt Umbilical 

The core stage forward skirt umbilical is located at the 180-foot 

level on the mobile launcher tower, above the liquid oxygen 

tank. This umbilical connects to the core stage forward skirt of 

the SLS rocket and then swings away at launch. Its main purpose is to provide conditioned air and nitrogen gas to the SLS 

core stage forward skirt cavity. 

Orion Service Module Umbilical 

The Orion service module umbilical connects from the mobile 

launcher tower to the Orion service module. The umbilical is 

located at the 280-foot level of the tower and, prior to launch, 

transfers liquid coolant and air for the electronics, as well as 

purge air and nitrogen gas for the environmental control system to support the spacecraft and the Launch Abort System. 

The umbilical tilts back at launch. 

Interim Cryogenic Propulsion Stage 

Umbilical 

The interim cryogenic propulsion stage umbilical is located at 

about the 240-foot level on the mobile launcher tower. This umbilical supplies fuel, oxidizer, purge air, gaseous nitrogen and 

helium, and electrical connections to the interim cryogenic propulsion stage of the SLS rocket. The engine, just like the core 

stage engines, uses fuel (hydrogen) and oxidizer (oxygen) to 

create thrust. The umbilical also provides hazardous gas leak 

detection and swings away at launch. 

Launch Accessories

Crew Access Arm 

The crew access arm is located at the 274-foot level on the 

mobile launcher tower. The arm rotates from its retracted position and interfaces with the SLS rocket at the Orion crew hatch 

location to provide entry and exit for the Orion crew module 

during operations in the VAB and at the launch pad. The access arm provides a clean and controlled work area for people and equipment entering the crew module, an emergency 

egress path during emergency conditions, and access to servicing panels for the Orion crew module and service module. 

On human missions, the access arm also provides entry and 

exit for astronauts. The arm retracts from the Orion spacecraft 

before launch. 

Vehicle Stabilizer System 

The vehicle stabilizer system is located at the 200-foot level of 

the mobile launcher tower, and provides a structural interface 

to the SLS core stage. The system helps reduce core stage 

motion during rollout to the launch pad, processing operations, 

high wind events at the pad, and the launch countdown. The 

stabilizer drops down and away from the SLS at launch. 

Vehicle Support Posts 

Eight posts support the load of the solid rocket boosters, 

with four posts for each booster. The support posts, made 

of cast steel, are five feet tall and each weigh about 10,000 

pounds. They are located on the deck of the mobile launcher 

and are instrumented with strain gauges to measure loads 

during stacking, integration, rollout, and launch operations. 

The posts will structurally support the SLS rocket through T-0 

and liftoff.

The center’s Engineering Directorate and Exploration Ground 

Systems tested the launch umbilicals and accessories at Kennedy’s Launch Equipment Test Facility. After testing, teams 

transported the launch accessories to the Launch Complex 

39B area and installed them on the mobile launcher tower. The 

umbilicals will be mated to the SLS for testing to ensure proper 

release and retract from the rocket. Following this test, the umbilicals will be remated for launch.