Mobile Launcher Platform

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An MLP being carried by a Crawler-Transporter.

The Mobile Launcher Platform or MLP is a two-story structure used by NASA, along with the Crawler-Transporter, to transport the Space Shuttle stack from the Vehicle Assembly Building (VAB) to either Launch Pad 39-A or 39-B 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 have remained in service to this day, with substantial alterations.

1 Function
2 Evolution
3 References
4 External links

[edit] Function

Each MLP weighs 9.25 million pounds (4,2 Mkg) and measures 160 feet by 135 feet (49 meters by 41 meters), and is 25 feet (7.6 meters) high.

Originally designated the "Mobile Launcher"^[1], 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).

After the launch vehicle is assembled in the Vehicle Assembly Building (VAB), a Crawler-Transporter carries an empty MLP into the VAB and positions it under the vehicle. The vehicle is lowered onto the MLP and affixed to the platform by means of attach posts. The Crawler-Transporter then carries the combined platform and vehicle to the launch site, and deposits them there together. Once the launch has been completed, the Crawler-Transporter retrieves the empty MLP from the pad to be readied for its next use.

[edit] Evolution

The Saturn V "stack" for the Apollo 11 moon landing mission moves up the ramp toward its launch site on the Mobile Launcher, carried by the Crawler-Transporter.

[edit] Apollo

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 launch umbilical tower 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 #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.

[edit] Space Shuttle Program

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.

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 masts contain the feed lines through which liquid hydrogen (LH₂) and liquid oxygen (LOX) are loaded into the shuttle's external fuel tank, as well as electrical hookups and flares that are used to burn off any ambient hydrogen vapors at the launch site immediately prior to Main Engine start.

The Space Shuttle Main Engine (SSME) vents its 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 flank the external fuel tank.

Water is released onto the mobile launcher platform on Launch Pad 39A at the start of a rare sound suppression system test in 2004. During launch, 300,000 gallons (1136 m³) are poured onto the pad in only 20 seconds.

The Space Shuttle assembly is held to the MLP through the use of 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 are 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 260-foot stack, were so much farther away from the engines. Because the shuttle is about half the height of the Saturn, the crew-cabin and payload bay are 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 much of the protective thermal tiles.

NASA's solution to this danger is to cushion the MLP at every launch with a flood of flowing water. Starting 6.6 seconds before engine ignition, a 300,000-gallon water tank at the launch site begins dumping water down a pipeline and into the exhaust vents of the MLP. Next, six 12-foot-high towers known as "rainbirds" begin to spray water over the MLP and into the flame deflector trenches below it. The water absorbs some of the bruising forces of the acoustic waves, and discourages fires that might be caused by the rocket exhaust. This water-dumping mechanism, known as the Sound Suppression System, empties the launch pad tank in around 20 seconds. The giant white clouds that billow around the shuttle at each launch are not smoke, but steam generated as the rocket exhaust boils away huge quantities of water.^[2] The suppression system reduces the acoustic sound level to approx 180 dB.

[edit] Project Constellation

With the announcement by NASA that the agency will replace the Space Shuttle with the Orion spacecraft and the Ares I crew launch vehicle and the Ares V cargo launch vehicle, NASA will construct three new light-weight MLPs that will support the new Ares I rocket and its launch umbilical tower, which altogether will weigh about 9.5 million lbs. This will allow NASA to use the current Crawler-Transporter vehicles until their replacements are constructed to support the heavier Ares V rocket and its launch support tower^{[citation needed]}. The new MLP systems are being designed by ASRC Aerospace under the University-Affiliated Spaceport Technology Development Contract (USTDC) contract. The Ares V rocket will use the existing Shuttle MLPs, but modified and strengthened to support the heavier weight of the vehicle and its support tower.