CAPE CANAVERAL ? NASA ismoving to protect ground crews, astronauts and VIPs from potential disaster,closing shuttle Atlantis' launch pad to all but essential personnel even beforea three-day countdown starts Tuesday.
Noup-close-and-personal tours will take place at Kennedy Space Center's launch pad 39A next week after NASA finishes pressurizing helium and nitrogen tanksaboard the 22-year-old spaceship, which is scheduled to launch at 7:38 p.m.Friday.
Theprecaution is being taken to reduce the risk created by aging pressure vesselsin the orbiter that could burst, triggering a rocket fuel fire or explosionthat might injure or kill workers and seriously damage the launch pad.
The tanks"can explode without warning at normal operating pressures," a safetybulletin sent to workers Friday said. Shrapnel from an exploding tank"would be dangerous to personnel and could potentially puncture adjacenthypergolic fuel systems resulting in fire, explosion and toxic cloudrelease," the bulletin added.
NASArecords obtained by FLORIDA TODAY under the Freedom of Information Act showthat the problem is one of the top risks facing the shuttle program. It is alsoan example of obsolescence issues bound to crop up before NASA retires thethree orbiters in 2010.
"It'sa serious problem, and it is one of a number of problems that I would call 'agingaircraft' issues that we face with these vehicles," shuttle programmanager Wayne Hale said. "So we're trying to understand exactly what thehazard is, and how to accommodate it."
Shuttleorbiters are equipped with 24 helium and nitrogen gas tanks that pressurize theshuttle's main propulsion system, orbital maneuvering engines and nose-and-tailsteering thrusters.
Thespherical tanks provide pressure needed to push rocket propellants into shuttleengines and thrusters at very specific rates required to keep the spaceship onits proper course. Some of the propellants are highly volatile and ignite oncontact.
Ranging indiameter from 19 to 40 inches, the tanks have lightweight titanium or steelshells wrapped with the same type of fabric used to make bulletproof vests --Kevlar -- or carbon graphite. They hold helium and nitrogen gas at extremelyhigh pressures (up to 4,600 pounds per square inch) and are extraordinarilydangerous.
"Youcertainly wouldn't want a 4-foot-diameter helium bottle that's pressurized toabout 4,000 psia to burst on you," Hale said. "That would be a badthing."
A tankrupture on the ground could lead to a fire or explosion that could injure orkill workers in the launch pad area. A failure in flight could lead to the lossof a shuttle and the astronauts inside.
NASAnonetheless is poised to proceed with the launch of Atlantis and sevenastronauts on an International Space Station assembly mission.
"Iwould characterize it as serious but not a showstopper kind of problem,"Hale said. "It's certainly not something somebody has trumped up to getattention. I mean, this is a nontrivial engineering problem. It's quitecomplex."
Built forNASA in the late 1970s and early 1980s, the copper-coloredspheres were designed, developed, manufactured and tested for 10 years ofshuttle fleet operations.
The NASArecords show that proper engineering analyses were done in 1988 to certify thetanks for an additional decade of use. But no subsequent recertification wasdone in 1998 when the agency's extended warranty expired.
NASAengineers raised questions about the tanks, which are named Composite OverwrapPressure Vessels, as the agency was struggling to return the shuttle fleet toservice after the 2003 Columbia accident.
Theaerospace industry already had expressed concern about the structural integrityof similar tanks on satellites and aircraft, and the agency's newly anointedNASA Engineering and Safety Center took up the cause in 2004.
The safetycenter's engineers concluded the orbiter tanks are much more likely to failthan NASA previously thought.
Past NASAanalyses assumed the tanks would leak before they burst. New studies and testsshow that they would explode before they leaked, increasing the hazardconsiderably.
The newtests were done at NASA's White Sands Testing Facility in New Mexico, andanother series aimed at more accurately pinpointing the risk is getting underway.
New tanksare not an option. The original vendor is out of the business and the agencywould not be able to qualify a new producer before the shuttles' retirement. SoNASA is changing the way it operates to reduce the risk.
Pressurewithin the tanks aboard Atlantis will be brought up to 80 percent -- ratherthan 100 percent -- this weekend, a move meant to lessen the amount of timefull pressure is maintained before launch. The launch pad will be cleared ofall but essential personnel when pressure is increased to full flight levelsMonday.
"We gothrough our standard two-stage pressurization trick now and do that as close tolaunch countdown as possible. The principal risk is to the ground crews, and sowe clear the pad when we go through the pressurizations," launch directorMike Leinbach said.
"Thisis an ongoing activity," Hale said. "We believe that we have anadequate level of safety for the upcoming flight, and we have a longer programof engineering tests to try to more specifically indicate what we might do tomitigate those problems."
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