Mobile Launcher Platform
The Mobile Launcher Platform (MLP) was one of three two-story structures used by NASA to support the Space Shuttle stack during its transportation from the Vehicle Assembly Building (VAB) to Launch Pad 39A at the Kennedy Space Center, as well as serve as the vehicle's launch platform. NASA's three MLPs were originally constructed for the Apollo Program to launch the Saturn V rockets in the 1960s and 1970s, and remained in service through the end of the shuttle program in 2011 with alterations.
Each MLP weighs 8,230,000 pounds (3,730,000 kg) unloaded and roughly 11,000,000 pounds (5,000,000 kg) with an unfueled Shuttle aboard, measures 160 feet (49 m) by 135 feet (41 m), and is 25 feet (7.6 m) high. It was carried by a crawler-transporter, which measures 131 feet (40 m) by 114 feet (35 m), and is 20 feet (6.1 m) high. Each crawler weighs about 6,000,000 pounds (3,000,000 kg) unloaded, has a maximum speed of about 1 mile (1.6 km) per hour loaded, and has a leveling system designed to keep the launch vehicle vertical while negotiating the 5 percent grade leading to the top of the launch pad. Two 2,750-horsepower (2,050 kW) diesel engines power each crawler.
Originally designated the "Mobile Launcher", the MLP was 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).
The Mobile Launcher Platform was set atop six legs inside the massive Vehicle Assembly building. The Solid Rocket Boosters were mounted on top of the MLP. The External Tank was then lowered between the two boosters and attached to them. After that, the orbiter was lowered into position and attached to the External Tank. The Crawler-Transporter then carried the combined platform and vehicle to the launch site, and deposited them there together. Once the launch was completed, the crawler-transporter retrieved the empty MLP from the pad to be readied for its next use.
The MLP was originally constructed for the use of transporting and launching the Saturn V rocket for the Apollo program lunar landing missions of the 1960s and 1970s. Each MLP originally had a single exhaust vent for the Saturn V's motors. The MLPs also featured the distinctive 400-foot (120 m) launch umbilical tower (LUT) with arms that permitted the servicing of the rocket on the launch pad. The arms swung away from the Saturn V at launch. For Skylab and Apollo-Soyuz, MLP No. 1 was modified with a so-called "milkstool" pedestal that allowed the shorter Saturn IB rocket to use the Saturn V tower and service arms, and Saturn V Ground Support Equipment (GSE) was removed or de-activated and Saturn IB GSE equipment was installed.
Space Shuttle 
In the post-Apollo years, the umbilical towers from Mobile Launchers 2 and 3 were removed. Portions of these tower structures were erected at the two Space Shuttle (or STS, for Space Transport System) launch pads, Pads 39 A and B. These permanent structures are now known as the "Fixed Service Structure" or in NASA's language of acronyms, FSS. The umbilical tower from Mobile Launcher 1 (which was the platform used for the most significant Apollo missions) was taken apart and stored in the Kennedy Space Center's industrial area. Efforts to preserve it in the 1990s failed, however, for 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, one on either side of the Main Engine exhaust vent. These 31-foot (9.4 m) masts contained the feed lines through which liquid hydrogen (LH2) and liquid oxygen (LOX) were loaded into the shuttle's external fuel 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 Space Shuttle Main Engines (SSMEs) vented their exhaust through the original opening used for the Saturn rocket exhaust. Two additional holes were added to vent exhaust from the Solid Rocket Boosters that flanked the external fuel tank.
The Space Shuttle assembly was held to the MLP through eight attach posts, also called "hold-down bolts", four on the aft skirt of each Solid Rocket Booster. Immediately before SRB ignition, frangible nuts attached to the top of these bolts were detonated, releasing the assembly from the platform.
When NASA began launching shuttle missions, it became clear that the MLP might inadvertently pose a danger to the crew or the vehicle: massive acoustic shock waves and rocket exhaust can bounce off the platform and hit the shuttle as it lifts off. This was true for the Saturn V launches as well, but there was less risk because the Apollo modules, atop the 363-foot (111 m) stack, were much farther away from the engines. Because the shuttle was about half the height of the Saturn, the crew-cabin and payload bay were much closer to the platform and much more vulnerable to the tremendous forces bouncing back off the MLP - on the first mission, STS-1, the shock waves damaged many of the protective thermal tiles.
NASA's solution to this danger was to cushion the MLP at every launch with a flood of flowing water. Starting 6.6 seconds before engine ignition, a 300,000-US-gallon (1,100 m3) water tank at the launch site began dumping water down a pipeline and into the exhaust vents of the MLP. Next, six 12-foot (3.7 m)-high towers known as "rainbirds" began to spray water over the MLP and into the flame deflector trenches below it. The water absorbed some of the bruising forces of the acoustic waves, and discouraged fires that might be caused by the rocket exhaust. This water-dumping mechanism, known as the Sound Suppression System, emptied the launch pad tank in around 41 seconds. The giant white clouds that billowed around the shuttle at each launch were not smoke, but water vapor generated as the rocket exhaust boiled away huge quantities of water. The suppression system reduced the acoustic sound level to approx 142 dB.
With the retirement of the Shuttle in 2011 and its planned replacement Orion spacecraft and launcher in the design and test phase, NASA converted LC-39B from Shuttle operations to support Orion launches. The Ares I-X suborbital mission utilized MLP 1, the same MLP used for Apollo 11, to support the stacking and launch operations. The cancelled Ares I-Y would have used the same MLP.
Starting with Orion 1, NASA would have utilized one of three new MLPs, designed by ASRC Aerospace (under the University-Affiliated Spaceport Technology Development Contract [USTDC]) that would have supported the "stick-like" Orion-Ares I configuration, its launch umbilical tower, and escape equipment. At a weight of about 9,500,000 pounds (4,300 t), the new MLPs would have allowed NASA to utilize the crawler-transporters in their current configuration.
The existing Apollo and Shuttle MLPs, after the retirement of the Shuttle, were to be overhauled and modified, along with LC-39A, for support of the canceled Ares V rocket, the Altair spacecraft, and its launch umbilical tower. The three exhaust ports, in a triangular arrangement (due to the "piggyback" nature of the Shuttle stack) would have been modified for the in-line nature of the Ares V, and the compartments would have been strengthened to support the heavier weight of the launch vehicle. At the same time, NASA would have either modified the existing crawler-transporters or constructed replacements, that would have allowed them to carry both an Orion-Ares I and Altair-Ares V stack from the Vehicle Assembly Building to their respective launch pads had lunar landing missions begun.
Space Launch System 
The same Mobile Launcher that was designed to launch the Ares I Rocket will be modified to launch the Space Launch System. The mobile launcher will have to be altered in order to support the heavier weight and additional thrust of the heavy lift rocket. The biggest changes to modifying the ML will be on the platform's base, where engineers will increase the size of a 22 square feet (2.0 m2) exhaust duct to a rectangle stretching 60 by 30 feet (18 m × 9.1 m) and strengthen the surrounding structure. The SLS will weigh more than twice as much as the planned Ares I rocket. The Ares 1 rocket would have featured a single solid-fueled first stage, while the Space Launch System will include two large strap-on boosters (SRB'S) and a powerful core with up to five Space Shuttle Main Engine (SSME). The modifications are expected be complete by 2016.
- Kennedy Space Center Website, at http://science.ksc.nasa.gov/facilities/mlp.html
- "Sound Suppression Test Unleashes a Flood". NASA. 2004-05-10. Retrieved 2009-03-06.
- Sound Suppression Water System page at NASA's http://www-pao.ksc.nasa.gov/nasafact/count4ssws.htm
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