From Apollo to multi-user, the changing yet similar nature of Launch Complex 39

by Ryan Weber

To launch the Shuttle, NASA needed to make modifications to both 39A and 39B, the most visible of which was the addition of a Fixed Service Structure (FSS) and a Rotating Service Structure (RSS) to each pad.  

The FSS — built from sections of the Saturn V’s Launch Umbilical Tower — contained a single swing arm (the Orbiter Access Arm) for crew loading and payload installation to the Orbiter’s crew cabin.  A second structure, the hydrogen vent system, connected a single vent line to the External Tank to vent gaseous hydrogen safely away from the vehicle during fueling and stable replenishment.

The third access arm, the Gaseous Oxygen vent arm, was not part of the original FSS design, and its need was only discovered in the late 1970s with the arm’s design and construction moved along at a fast pace to be readied in time for the first Shuttle mission.

This arm was needed to safely vent gaseous oxygen away from the top of the External Tank to prevent ice build up that could damage the Orbiters’ Thermal Protection System.

Meanwhile, the RSS was added to the permanent pad design to service the Orbiters for fueling, work access, and payload installation/checkouts at the launch pad.  They also provided pad access to the Solid Rocket Booster forward assemblies. The RSS sat on a hinge column with outer support provided by two, eight wheel trucks capable of moving along a twin rail system to allow for a 120 degree rotation between its “Mate” position around the Orbiter and its “Park” position for launch. 

(Credit: NASA)

(Photo caption: Shuttle Enterprise on LC-39A in the summer of 1979 during a sound suppression system test. Note the lack of the gaseous oxygen vent arm on the tower. Its need was not discovered until a tanking test revealed dangerous ice build-up on the top of the External Tank.)

Other large modifications involved replacing the Saturn V flame deflectors with three new ones to serve the Shuttle and the addition of a Sound Suppression System to protect the vehicle at liftoff.  This included the addition of a 88.3 meter tall water tower with a 300,000 gallon (1.1 million liter) capacity.

The water was dumped into the Mobile Launch Platform exhaust holes and around the top of the platform just before and during liftoff.

For stacking and rollout to the pad, the Shuttle used the same system as Apollo by stacking in the VAB (though it only stacked in High Bays 1 and 3, with High Bay 2 available later in the program for hurricane roll-back protection). The three Saturn-era Mobile Launch Platforms were reconfigured and reused for the Shuttle program.

The first Shuttle mission lifted off from LC-39A on April 12, 1981, with the final mission, STS-135, lifting off from the same pad 30 years later on July 8, 2011.  Orbiters Columbia, Challenger, Discovery, and Atlantis all debuted from LC-39A, with Endeavour being the only vehicle to date to debut from 39B.

(Credit: NASA)

(Photo caption: May 11, 2009 — Atlantis launches from LC-39A on the STS-125 mission to the Hubble Space Telescope as Endeavour sits ready to launch on 39B for the STS-400 Launch On Need rescue mission for STS-125. Pad-B can be seen here in a partially reconfigured state for the Constellation Program. This was the 19th and final time two Space Shuttle stacks occupied both launch pads at LC-39; the first was in December 1985 when Columbia was on 39A for STS-61C as Challenger was rolled out to Pad-B for the STS-51L mission.)

STS-51L/Challenger marked the program’s first use of 39B on January 28, 1986.  STS-116/Discovery was the final Shuttle mission to launch from Pad B; however, Endeavour would take up residence on the pad twice for the STS-400 Launch On Need rescue flight for the final Hubble servicing mission in 2008 and 2009, respectively.

Other notable Shuttle-era missions included STS-31 in which Discovery deployed the Hubble Space Telescope, STS-71 in which Atlantis docked with the Russian space station Mir for the first time, STS-88 in which the Endeavour conducted the first International Space Station assembly mission, the five rescue and servicing missions to the Hubble, and the many dozens of scientific missions that bettered life on Earth.

During the Shuttle program, 82 missions launched from 39A while 53 departed from 39B – with the final 39B use during the Shuttle program overlapping with the short-lived Constellation Program.


The troubled Constellation Program, begun in 2005, would overlap in its entirety with the Space Shuttle Program, with only one suborbital test flight occurring in 2009.  Despite this, work began on a new Mobile Launcher as well as the construction of three large lightning protection towers at 39B.

The Ares 1-X rocket was a test version of the crew launch Ares 1 rocket for the Constellation Program and consisted of a single Shuttle Solid Rocket Booster with a dummy fifth segment on top and a boilerplate second stage and Orion capsule.

The Ares I-X was stacked on a Shuttle mobile launch platform and taken to a modified Pad-B. Liftoff occurred on October 28, 2009 with a successful flight.  The entire Constellation program would have used the existing LC-39 site for operational use, but plagued with issues, the program was canceled in 2010.


After the end of the Shuttle program, LC-39A sat fallow — with NASA having no plans to use it.  On April 14, 2014, SpaceX signed a 20 year lease with the US space agency for control of LC-39A with exclusive launch rights.  

The agreement was in part a decision to continue using human-rated launch facilities for SpaceX’s role with NASA’s Commercial Crew Program, as 39A had the needed human-launch equipment already in place.

However, major operational changes would ensue.  While SpaceX launches from 39A are controlled from a Firing Room in the Launch Control Center, none of SpaceX’s rockets utilize the crawlers or the crawlerway, and the VAB is not required for Falcon 9 and Falcon Heavy integration.

In fact, overtop of the crawlerway at 39A, SpaceX constructed a Horizontal Integration Facility for rocket assembly and maintenance.  The Falcon 9s or Falcon Heavies are then rolled up the ramp to the launch stand on 39A via rail and lifted vertically into launch position.

Falcon 9 lifts off from LC-39A carrying Dragon Endeavour with astronauts Doug Hurley and Bob Behnken to the ISS (Credit: Brady Kenniston for NSF)

Other completed changes SpaceX has made to LC-39A include the removal of the RSS, refurbishment of the FSS including removal of most but not all Shuttle-era hardware, a new Crew Access arm for the Crew Dragon capsule, updated plumbing for RP-1 fuel, relocation of the slide wire basket emergency egress system, complete network and data line upgrades, and a rework of the flame trench to send all exhaust out the north end, with the south end now sealed.

The first SpaceX launch from 39A was a NASA mission, CRS-10 on February 19, 2017; it marked the first uncrewed launch from 39A since Skylab in May 1973 and the first-ever commercial launch from the Kennedy Space Center and LC-39 area.

On May 30, 2020, SpaceX launched the Demo-2 mission of their Crew Dragon capsule with Doug Hurley and Bob Behnken aboard, ending the U.S. human launch gap created by the end of the Shuttle program and once again returning 39A to the role it was always built to serve: launching humans into space.

Since leasing Pad-A, other notable SpaceX launches include the debut of the Falcon Heavy, the first Bangladeshi satellite, the first re-use of a Falcon 9 first stage, the Crew-1 and Crew-2 launches of eight international crewmembers to the International Space Station, and the critical In-Flight Abort test of Crew Dragon ahead of human flights on Dragon.

The pad marked its 100th launch since Apollo 4 with the CRS-11 cargo mission to the ISS on June 3, 2017.

In addition to current uses, SpaceX is currently building a Vertical Integration Facility or Mobile Service Platform, which will be used to vertically integrate payloads with Falcon 9s and Falcon Heavies for US Space Force and Defense missions.

Another major modification to 39A is the started-but-stopped Starship launch and recovery area inside the pad’s perimeter but next to the main concrete structure.  To supplement Starship, SpaceX will need to add additional liquid oxygen tanks and a liquid methane storage facility as well as an integration tower for stacking.

Artemis and SLS

While SpaceX took over at Pad-A following Shuttle, NASA retained Pad-B and the other LC-39 area facilities for the SLS and Artemis programs, the successor to Constellation and the Shuttle.

The new Mobile Launcher under construction for Ares I and the Constellation Program was taken and heavily modified for the SLS Block 1 version of NASA’s new rocket for the Artemis program. 

Built largely from Shuttle designs, SLS is far more massive than Saturn V or the Shuttle at rollout, and one of the two crawlers had to be extensively modified to support the new mass requirements.  Upgrades to the other crawler, though not as extensive, were also carried out for the Artemis program.

The SLS Mobile Launcher, a holdover from the Constellation Program, is carried on a modified Apollo-era crawler transporter to LC-39B for testing. (Credit: Stephen Marr for NSF/L2)

While the crawlers are the same, the mobile launch platforms which served Apollo and Shuttle are no longer needed, and with no one currently wanting to use them for a new system, they are currently in different states, with one being used for mass testing runs up and down the crawlerway, one in storage, and one partially converted by Northrop Grumman who was going to use it for their OmegA rocket which was cancelled in 2020.

Pad-B also required extensive modifications not just to remove all Shuttle hardware but also to bring it up to 21st century standards.  All the old 1960s and 70s era tech was removed and upgraded; in essence, NASA transformed Pad-B into a multi-user launch pad optimized for the SLS rocket.

New data and transmission systems were installed, the sound suppression system and flame deflectors were re-worked, and like SpaceX with LC-39A, 39B’s flame trench was modified so that all SLS exhaust will exit the north side of the trench, not the south.

An additional liquid hydrogen sphere for the increased fuel needs of the SLS rocket is also under construction as well.

The three lightning protection towers, originally for Constellation, were kept as part of the Pad-B design for SLS and Artemis, and a small launcher LC-39C pad was built inside the Pad-B perimeter for pad-sharing operations (which no one has contracted for).

Additionally, the crawlerway itself received a major upgrade for Artemis.  Aside from replacing the top layer of river rocks as they were ground down by the crawlers over the years, the crawlerway’s foundation — its crushed stone — has only been upgraded and repaired once, after the conclusion of the Shuttle program.

This work on the path leading to Pad 39B saw the removal of the river rock and the addition of new lime rock to the crawlerway’s foundation.  Afterward, 30,000 tons of new river rocks were re-added to return the crawlerway to its operational configuration.

Multi-user spaceport

In addition to the pad facilities going multi-user, the LC-39 area is also vital to NASA’s vision and operation of the Kennedy Space Center as a multi-user spaceport.

The two most visible customers of LC-39 facilities aside from the launch pads and VAB are Boeing, currently using former Shuttle processing facilities to build and process the Starliner capsules for the Commercial Crew Program, and the US Air Forces, currently using the other two Shuttle processing hangers, formerly called the Orbiter Processing Facility, for their X-37B spaceplane program.

Additionally, hundreds of companies and organizations use the LC-39 site for research operations.

Yet through all the changes and cycling programs… one thing remains true: the initial design for the Apollo Program and what was needed at Kennedy for the Saturn V continue to shape the way the spaceport and its hundreds of daily users operate the facility.

(Lead image: Launch Complex 39. Credit: NASA)

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