From 1967 to 2011, three platforms were used at
Launch Complex 39 to support NASA's launch vehicles at the
Kennedy Space Center. Formerly called
Mobile Launchers (
ML), the mobile launcher platforms were constructed for transporting and launching the
Saturn V rocket for the
Apollo program lunar landing missions of the 1960s and 1970s. Each ML originally had a single
exhaust vent for the Saturn V's engines. The Mobile Launchers also featured a
Launch Umbilical Tower (
LUT) with nine
swing arms that permitted servicing of the vehicle on the launch pad, and swung away from it at launch. The Mobile Launchers were built by
Ingalls Iron Works. The
swing arms were constructed by
Hayes International. After the
Apollo program, the bases of the Mobile Launchers were modified for the
Space Shuttle. The Launch Umbilical Towers from ML-2 and ML-3 were removed. Portions of these tower structures were erected at the two launch pads, 39A and 39B. These permanent structures were known as the
Fixed Service Structures (FSS). The LUT from ML-1 was taken apart and stored in the Kennedy Space Center's industrial area. Efforts to preserve the LUT in the 1990s failed due to a lack of funding, and it was scrapped. In addition to removal of the umbilical towers, each Shuttle-era MLP was extensively reconfigured with the addition of two Tail Service Masts (TSM), one on either side of the
main engine exhaust vent. These masts contained the feed lines through which
liquid hydrogen (LH2) and
liquid oxygen (LOX) were loaded into the
Space Shuttle external tank, as well as electrical hookups and flares that were used to burn off any ambient hydrogen vapors at the launch site immediately prior to Main Engine start. The main engines vented their exhaust through the original opening used for the Saturn rocket exhaust. Two additional exhaust ports were added to vent exhaust from the
Space Shuttle Solid Rocket Boosters (SRBs) that flanked the external fuel tank. The Space Shuttle assembly was held to the MLP at eight holddown points using large
studs, four on the aft skirt of each Solid Rocket Booster. Immediately before SRB ignition,
frangible nuts attached to the top of these studs were detonated, releasing the Shuttle assembly from the platform. Each MLP weighed unloaded and roughly with an unfueled Shuttle aboard, measured , and was high. They were carried by one of two
crawler-transporters (CT), which measure , and high. Each crawler weighs about unloaded, has a maximum speed of about loaded, and has a leveling system designed to keep the launch vehicle vertical while negotiating the 5 percent
grade (slope) leading to the top of the launch pad. Two
Diesel engines power each crawler. The MLPs were designed as part of NASA's strategy for vertical assembly and transport of space vehicles. Vertical assembly allows the preparation of the spacecraft in a ready-for-launch position, and avoids the additional step of lifting or craning a horizontally-assembled vehicle onto the launchpad (as the engineers of the
Soviet space program chose to do), while also occupying the launch pad for shorter amounts of time and allowing for more expansive integration facilities.
Mobile Launcher Platform-1 Construction of the Mobile Launcher Platform-1 (MLP-1) (formerly called the Mobile Launcher-3 or ML-3) began in 1964 and was completed with the installation of the Launch Umbilical Tower
hammerhead crane on March 1, 1965. The
swing arms were added at a later date. The ML-3 was used for five crewed
Apollo launches;
Apollo 10,
Apollo 13,
Apollo 15,
Apollo 16 and
Apollo 17. Following the launch of
Apollo 17, the ML-3 was the first of the Mobile Launchers to be converted for use by the Space Shuttle. The Launch Umbilical Tower was dismantled and later partially reassembled on LC-39A as that pad's Fixed Service Structure (FSS) and the base of the launch platform was modified to accommodate the locations of engines on the Shuttle. The platform was redesignated MLP-1. In total, the MLP-1 was used for 52 Shuttle launches between 1981 and 2009. It was used for the first Space Shuttle launch,
STS-1, in April 1981. Following the launch of
STS-119 in March 2009, it was transferred to the
Constellation program. The platform was used only for the
Ares I-X and the MLP-1 suffered substantial damage. The canceled
Ares I-Y would have used the same MLP. However, the Constellation program was canceled and the MLP was left unused. Following the final Space Shuttle launch,
STS-135, usable parts from the MLP-1 were removed and stored in the
Vehicle Assembly Building, with no plans to use the MLP again. In 2021, NASA began rolling out Mobile Launch Platform-1 on Crawler transporter-2 with a concrete ballast on the top to condition the
crawlerway to handle the combined weight of the Space Launch System and
Orion spacecraft in the future. NASA stated that re-conditioning of the crawlerway will be required periodically in the future, and MLP-1 will be retained for that purpose. MLP-1 will be stored in High Bay 1 of the Vehicle Assembly Building when not in use for crawlerway maintenance.
Mobile Launcher Platform-2 Mobile Launcher Platform-2 (MLP-2) (formerly called the Mobile Launcher-2 or ML-2) was used for the uncrewed
Apollo 6 mission, followed by three crewed
Apollo launches;
Apollo 9,
Apollo 12 and
Apollo 14. It was subsequently used for the launch of
Skylab on a Saturn V in 1973. Following the launch of Skylab, ML-2 was the second of the Mobile Launchers to be converted for use by the Space Shuttle. The Launch Umbilical Tower was dismantled and partially reassembled to become the LC-39B Fixed Service Structure (FSS), and the base of the launch platform was modified to accommodate the locations of engines on the Shuttle. The platform was redesignated MLP-2. In total, MLP-2 was used for 44 Shuttle launches, starting in 1983. All of the
orbiters except made their maiden flights from MLP-2. It was also the launch site for the ill-fated
STS-51L mission, when
disintegrated shortly after launch, killing all seven crew members. Following the
Space Shuttle retirement, NASA kept the MLP-2 for
liquid-propellant rockets,
Mobile Launcher Platform-3 is carried atop the ML-1 in the lead-up to
Apollo 11 The first launch from the Mobile Launcher Platform-3 (MLP-3) (formerly called the Mobile Launcher-1 or ML-1) was the maiden flight of the Saturn V, and the first launch from LC-39,
Apollo 4. Following this, it was used for two crewed
Apollo launches:
Apollo 8 and
Apollo 11. After NASA decided to move Saturn IB launches from
Launch Complex 34 to Launch Complex-39B, the ML-1 was modified by the addition of a structure known as the
Milkstool, which allowed the Saturn IB to use the same Launch Umbilical Tower as the much larger Saturn V. Three crewed flights to
Skylab, and the Apollo launch for the
Apollo–Soyuz Test Project, were conducted from the ML-1 using the
Milkstool. Prior to the scrapping of the LUT in 2004, there was a campaign to rebuild and preserve it as a memorial to Project Apollo. The crew access arm is preserved at the
Kennedy Space Center Visitor Complex on the upper level of the gift shop. Following the launch of Apollo-Soyuz, ML-1 was the last Mobile Launcher to be converted for use by the Space Shuttle. The LUT and
Milkstool were dismantled and placed into storage, and the base of the launch platform was modified to accommodate the locations of engines on the shuttle. The platform was redesignated MLP-3. In total, MLP-3 was used for 29 Shuttle launches, starting in 1990. It was the least used of the three MLPs. Following the
Space Shuttle retirement, NASA kept the MLP-3 for
solid-propellant rockets. and later formalized through a Reimbursable Space Act Agreement in August 2019. Under the Agreement,
Vehicle Assembly Building High Bay 2 would be used to assemble the rocket, while MLP-3 and
crawler-transporter 1 would be used to move the rocket to LC-39B for launch. From 2019 to 2020, the OmegA launch tower was under construction on MLP-3. Following the cancellation of OmegA in September 2020, work began to demolish the half-completed launch tower. As of January 2021, MLP-3 is planned to be placed in storage in High Bay 2 of the Vehicle Assembly Building.
Space Launch System atop ML-1 at Launch Complex 39B in January 2026 Between 2009 and 2010, a mobile launcher platform known as Mobile Launcher-1 (ML-1) was constructed as part of the
Constellation program. Following the program's cancellation in 2010, ML-1 was repurposed for the
Space Launch System (SLS) Block 1 configuration, with modifications carried out between 2013 and 2018. The total cost of ML-1 is estimated at approximately $1 billion. The most significant modification to ML-1 involved the platform’s base, where engineers enlarged a exhaust duct into a rectangular opening measuring and reinforced the surrounding structure. These changes were required, because SLS produces substantially greater thrust than the originally planned
Ares I rocket, featuring two solid rocket boosters and a core stage powered by four
RS-25 engines. The ML-1 base is high, long, and wide. The launcher also includes a Launch Umbilical Tower equipped with multiple swing arms used to service the vehicle prior to launch. configuration, outside the
VAB in October 2010 In June 2019, NASA awarded a contract to
Bechtel for the design and construction of Mobile Launcher-2 (ML-2), intended to support the taller SLS Block 1B and planned Block 2 variants. These configurations incorporated the
Exploration Upper Stage (EUS), requiring a higher crew access arm and redesigned umbilical arms. Construction of ML-2 began in 2020, with an initial completion target of 2023. The project was originally estimated to cost under $500 million; however, costs increased substantially over time, with NASA establishing a baseline of $1.8 billion in 2024 and the NASA Office of Inspector General projecting that total costs could reach as much as $2.7 billion. In February 2026, NASA cancelled the SLS Block 1B and Block 2 variants, eliminating the primary need for ML-2 and rendering it surplus to the Artemis program. Amid continued delays and cost growth, NASA announced in March 2026 that it no longer planned to use the launcher. On March 29, 2026, the agency confirmed that a stop-work order had been issued to Bechtel, halting construction. Components common to ML-1 subsequently began to be removed from ML-2 for use as spares. == Cape Canaveral ==