As one team of shuttle engineers works to pry NASA's Discovery orbiter from its external tank, another is patiently waiting to fulfill its role as spaceship movers.
Shuttle transport workers rely on a series of specialized vehicles to move orbiters and support hardware from place to place and ultimately to the launch pad at NASA's Kennedy Space Center in Cape Canaveral, Florida.
"We actually have three systems that maintain and operate, the biggest and most notable is the Crawler/Transporter and its [Mobile Launch Platform]," said Ray Trapp, crawler/transporter manager for shuttle contractor United Space Alliance, in a telephone interview. "It's not something that you'd jump in and turn the key and it starts."
Only nine engineers are certified to drive the massive, six-million-pound (2.7-million-kilogram) crawler, which typically takes up to a year of training to operate. More personnel, however, are qualified to handle a pair of vehicles that carry shuttle solid rocket booster motors to NASA's Vehicle Assembly Building (VAB), as well as another carrier reserved solely for delivering orbiters from their processing facilities to the VAB.
It is that last vehicle, the Orbiter Transporter System, to which engineers expect to load Discovery atop this week after shuttle workers remove it from its external tank, USA officials said. The orbiter will be moved to a separate bay inside the VAB and fitted to a new external tank on June 7, before the entire assembly will again board a launch pad-bound crawler, they added.
"You've got a $3 billion spaceship that you're carrying, so you have more of a feeling of responsibility," said Trapp, himself a crawler driver, of hauling Discovery to the pad. "And these guys have a lot of pride in what we do."
NASA's Discovery spacecraft is currently scheduled to launch no earlier than July 13 under the agency's STS-114 mission, its first shuttle flight since the 2003 Columbia disaster that killed seven astronauts and destroyed their orbiter during reentry.
The external tank swap currently underway is designed to maximize launch safety for Discovery's seven-astronaut crew. The new tank, ET-121, is being outfitted with an additional heater to minimize ice debris that could strike Discovery during launch.
Crawling toward launch
Dating back to the Apollo-era, the shuttle's crawler carriers and mobile launch platform were originally built to move the colossal Saturn 5 moon rockets to the launch pad.
Neither of the transport systems was adapted to suite the space shuttle fleet, though several upgrades were performed before the first orbiter flight, Trapp said.
"It's not as complex as a spaceship, but there're a lot of things going on in there," he said of the crawler. "One of the things we're very aware of is that the guys in the 1960's who designed the crawler did a fantastic job."
Standing up to 26 feet (eight meters) high at its tallest, NASA's two crawler vehicles are each 113 feet (34 meters) wide and 131 feet (40 meters) long. They carry a complement 25 engineers and technicians under full operations and weigh up to 18 million pounds when capped with a shuttle launch stack and launch platform. A laser-guided docking system allows drivers position the massive load accurately within a quarter of an inch at the launch pad.
"[That's] one of the things that's always amazed me," Trapp said.
While its one mile an hour speed may seem slow for some, it's fast enough for Discovery.
"When you're walking on the ground, of course, at one mile an hour you can outwalk the crawler in a heartbeat," said Bob Meyers, a systems engineer who drove Discovery out of the VAB during its initial STS-114 rollout earlier this year, in a NASA interview. "But when you have 18 million pounds and you're up in the cab and it's moving a mile an hour, it seems fairly fast."
Last week, the crawler revisited Discovery at Pad 39B and returned it to the VAB for the external tank swap.
While Discovery's rollout and rollback have given crawler operators extra practice at real-time driving, shuttle transports are often driven unloaded to keep them in working order. All three transport systems are required to keep NASA's orbiter fleet flight ready, USA officials said.
"A lot of this equipment doesn't like to jut sit around," Trapp said. "So about every two weeks or so, we'll run the OTS or the crawler just to check them out."
Not bigger, but better
Crawler engineers have used the two years since the Feb. 1, 2003 loss of the Columbia and its crew to upgrade NASA's two crawlers with better electronics, ventilation and control cabs.
All four driver cabs - two per crawler - were replaced with newer versions equipped with safer marine windows to withstand Florida's hurricane season, which began this month.
"In the past, we had to bolt plywood over the windows during hurricanes," Trapp said, adding that the new crawler cabs weather the multiple hurricanes that stuck Florida in 2004 just fine.
Ventilation improvements cleared exhaust from being sucked back into engine and pump compartments, providing a safer, more comfortable environment for engineers and technicians. Adjustments to the exhaust system also softened the crawler's noise levels, and both vehicles received a new set of treads earlier this year.
"We have another big modification coming at the end of this year to the JEL hydraulics systems," Trapp said.
Each crawler carries 16 Jacking, Equalization and Leveling (JEL) bearings to keep the mobile launch platform and shuttle stack level during five percent incline up to the launch pad.
"We've spent a lot of man-hours upgrading and maintaining our equipment with the goal of making that first rollout since Columbia," Trapp said. "It feels really good, and when the time is right we'll launch."
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