Shuttle Liftoffs Require Precision Launch Pad
The space shuttle is the undisputed star of launch day, with its towering fire and thunderous sound as it soars into the heavens. It gets significant help, though, from a robust supporting actor in the form of a gray launch pad and its weave of wiring, pipes and even a crane.
The pad area is a rough circle more than a mile-and-a-half around. Inside that circle lie huge propellant tanks, banks of high-speed and television cameras, and a water tower that deluges the pad just before liftoff. Baskets anchored beneath high-tension cables stand ready to evacuate astronauts from a shuttle to a protective bunker. The shuttle stack stands in the middle of it all, the ultimate focus of human and hardware attention.
All at a place less than a mile from the ocean that broils in the Florida summer and chills in the winter. As with so many places at NASA's Kennedy Space Center, it's a unique world to work in.
"I kind of feel like I found home," said Kevin Panik, NASA's Pad Facility Integration manager. "I come to work and it's not work. I'm driving in and I'm smiling."
David Sutherland, Pad Operations manager for United Space Alliance, started working at the shuttle launch pads in 1987.
"I'm a lucky guy, no doubt about it," Sutherland said. "I never in my wildest dreams thought I'd have a job like this. Not just being an engineer on shuttle, but being manager of operations. Pretty lucky guy."
Sutherland saw the pad the first time during a job interview.
"I just couldn't imagine that it was this big," he recalled. "It just looked so complicated, that there was so much to it that I'd never understand it, never get it."
About 170 engineers and technicians work at the launch pad to ready a shuttle for liftoff, along with a few dozen more specialists who come and go during the 30-day preparation period at the pad. Those preparations range from the broad tasks of connecting hundreds of wires and cables when the shuttle stack rolls to the pad to the delicate work of moving multi-ton payloads inches at a time into the cargo bay.
"You can't know it all," Panik said. "There's some 50, 75 different systems. You've got to realize you can't know it all."
The crews who work on the launch pad are affectionately called "pad rats" and they average between 16 and 17 years of experience, Sutherland said. Their specialties range from handling extremely toxic chemicals to tying down metal platforms, rails and equipment with rope to prevent it from accidentally impacting the spacecraft. The team also is cross-trained in a number of specialties. Sutherland said it takes about two years to get comfortable with a system.
"I have a high level of confidence in their expertise," Sutherland said. "We're very comfortable with what we do."
Shuttles lifted off two pads during the 30 years of the program, Launch Complex 39A and Launch Complex 39B, or just "pad A" and "pad B" to those who worked on them. Built for the Apollo/Saturn V combination, the pads were identical and each had its own work force during most of the shuttle years. Though shuttles occasionally were on both pads together, the practical benefit of having two pads was to let one be refurbished while launches took place on the other.
A crawler-transporter moves the shuttle stack, mounted on a mobile launcher platform, or MLP, the three miles from the Vehicle Assembly Building to pad A, three-and-a-half miles to pad B. The MLP is anchored to steel columns on the pad surface and connected to the rest of the pad complex.
The MLP holds the shuttle stack with eight bolts that are blown apart at the same time the boosters ignite to allow the shuttle to soar into space.
Also, a pair of connection masts on either side of the shuttle's aft compartment is housed on the MLP. The masts contain a battery of wires, cables and the lines that run propellants into the external tank. At launch, the connectors pull back from the shuttle into the masts where armored doors close over them to protect them from the blast.
The pads are considered by some the most advanced in the world, although straight comparisons are difficult because a pad's structure is a direct reflection of the spacecraft it is hosting. A space shuttle, with its reusable engines, delta wings and 60-foot-long cargo bay, has significantly different needs than a capsule.
"I know that what we do out here is a lot more complicated in that we do the final flight processing, all the propellants are loaded out here," Sutherland said. "The hypergolics are loaded at the pad. I know that at other launch facilities those type tasks are done prior to arrival on the launch pad."
Many of the systems can be operated remotely by launch controllers and computers three miles away with split-second timing to execute a safe launch.
A fence that curves outward makes up the perimeter, providing security and keeping most of the alligators and other wildlife from sneaking in. At the center of the circle stands the 247-foot-tall fixed service structure, or FSS, which is the gantry people see next to the shuttle. A lightning tower at the top reaches another 80 feet or so into the sky.
All the floors on the FSS are grates, which means looking down at shoes means seeing several more levels below. The exception is the 195-foot level, the floor the astronauts get off at to go inside the shuttle. That floor is solid and painted yellow with black chevrons pointing the way from the shuttle to the escape baskets.
Everything at the pad is utilitarian in its design. That can mean large buttons on the elevator that can be felt in the dark or in the watery haze of the fire extinguisher system, or large stickers instead of metal signs that will pull loose in the wake of the launching shuttle.
"When it was designed, it was explosion-proof," Panik said. "Only the mining industry has explosion-proof switches, so we use switches for the lights that are explosion-proof and switches for the fire system that are explosion-proof."
The FSS has three arms that reach out to the shuttle during countdown. The orbiter access arm is a metal bridge that reaches out to the side hatch of an orbiter. Open most of its length, the arm is enclosed at the end in what is known as the White Room. That's where the astronauts get on their last bit of equipment before climbing inside the shuttle and taking their seats. The arm swings into the FSS about seven minutes before launch, but it can be moved back into position in seconds in an emergency.
The Closeout Crew works in the White Room on launch days helping the astronauts and closing the hatch for liftoff. It's also quite a bit smaller than it looks on TV, barely wide enough for two people to stand side-by-side.
The gaseous oxygen vent arm, called the GOX arm by the pad rats, is best known for the "beanie cap" at the end that fits over the nose of the external fuel tank. There is an inflatable band around the base of the cap that seals the area so oxygen inside the tank can be moved from the tank as it boils off during the last few hours of the countdown. Without the cap, super-cold oxygen could condense with air and freeze in ice chunks on the nose of the tank.
The cap swivels up off the tank's nose, and the arm rotates into the launch position two and half minutes before launch.
The third attachment between the shuttle and FSS is the gaseous hydrogen vent arm and it is mostly out of view during the countdown. It does the same thing as the GOX arm, but for the hydrogen boiling out of the tank. Instead of taking the hydrogen gas a few feet and releasing it, the venting system carries the propellant out to a tower away from the shuttle where a propane-based fire burns the excess hydrogen.
The hydrogen vent arm is not much more than a large pipe that stretches to the backside of the tank. It drops away from the tank at the same moment the solid rocket boosters ignite.
The rotating service structure, or RSS, is anchored to the FSS. It has a clean room and lets technicians install payloads into the cargo bay while the shuttle is at the pad.
"You've got six stories of the payload changeout room, that's the bulk of RSS," Sutherland said.
The RSS also houses a hoist to lift the payloads, protected in a canister that looks like the shuttle's cargo bay, into the clean room.
The pad itself is a truncated pyramid of concrete that slopes up 40 feet. The flame trench, lined with flame-resistant bricks and concrete, directs the smoke and exhaust of the three main engines back and away from the shuttle on one side and funnels the solid rocket boosters exhaust toward the ocean. There are pools that hold the contaminated water when it comes off the flame trench so it doesn't go into the neighboring swamps.
Before they get to launch day, the pad rats load chemicals into the shuttle's reaction control system so the array of small thrusters at the shuttle's nose and tail can maneuver the spacecraft in orbit. The chemicals are called "hypergolics" because they burn when they come in contact with each other. Working with them requires careful processes and special equipment, including protective suits.
Liquid hydrogen and liquid oxygen also are pumped into the shuttle's three fuel cells so the shuttle can create electricity while in space. More than 500,000 of the same propellants are pumped into the giant orange external tank on launch day to power the shuttle's three main engines.
The propellants are stored in two spheres on opposite sides of the pad perimeter. Painted white, one storage tank can hold 900,000 gallons of liquid oxygen at minus-297 degrees and the other holds about the same amount of liquid hydrogen at minus-423 degrees.
So what is launch like to someone who has spent more than a month working through every detail of the preparation?
"It's a euphoric feeling," Sutherland said. "It's a feeling of pride and accomplishment."
The work doesn't stop after a launch, either. With the shuttle safely in orbit, the technicians first wash down the pad structure to get rid of the hydrochloric acid residue from the solid rocket booster exhaust. Workers then survey blast damage at the pad.
"It's kind of scorched," Panik said. "It's got an acrid smell, like when you launch model rockets."
They typically spend a few weeks making repairs, re-painting rails and other sections that have been stripped of their coatings by the launch.
Due in part to the proximity of the salty ocean air, the launch pad structures require careful maintenance to keep them from rusting. The last 30 years have seen advances in corrosion treatment, too. Columbia lifted off beside a red launch tower in 1981. By the end of the program, the structures were repainted with a zinc-based coating that gave them a gray look.
The new coating has made a big difference in the pad's appearance following a launch, though.
"Years ago, you'd see snowflakes of rust chips," Sutherland explained.
The pads can still serve surprises, such as when part of the wall of the flame trench gave way during the liftoff of STS-124 in May 2008. The damaged section was sprayed with a fire-resistant concrete and shuttle missions continued.
The shuttle launch pads already are going through changes to adapt to new rockets and spacecraft. Pad B was modified to launch the Ares I-X flight test in October 2009. The orbiter access arm was removed and the GOX arm was modified to hold the rocket in place because it was much taller than the space shuttle stack.
Three lightning towers also were built around the pad, taking the place of the single mast atop the shuttle fixed tower. The FSS and RSS on pad B were taken down as the last shuttle missions were being prepared on pad A, leaving the complex in a "clean concept" look that would be able to host an assortment of rockets in the future.
NASA's John F. Kennedy Space Center