Hydrogen leak scrubs launch of space shuttle Atlantis
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: April 4, 2002
Update for 6:20 p.m. EST: Officials decided late today to press ahead with the repair option that calls for a clamshell-like sleeve to be welded around the line break. Mission managers will meet on Friday morning to select a new target launch date. A Sunday attempt is now considered highly unlikely. Below is the full story as posted at 4:20 p.m.:
The leak occurred shortly after 9 a.m., about an hour and five minutes or so after engineers began fueling Atlantis for a 5:13 p.m. launch attempt. A few moments after switching from slow fill to fast fill, an alert engineer monitoring video cameras focused on the pad saw a cloud of vapor erupt from a hydrogen vent line.
The 16-inch aluminum line is one of two that carry excess hydrogen gas from the shuttle's external tank to a "flare stack" near the pad where the gas is released into the atmosphere in a controlled burn. The line only carries gas, not supercold liquid hydrogen.
"It was during fast fill on the hydrogen side that a facility vent line leaked," Leinbach said. "This was on the side of the mobile launcher, it's a pipe external to the mobile launcher. All leaking gaseous hydrogen was vented to atmosphere, there was no problem with the vehicle itself, there were no leaks inside the mobile launcher."
Video from remotely operated cameras on the east side of the pad showed a cloud of vapor spewing around the circumference of the double-jacketed vent line, presumably due to a cracked weld. The weld in question dates back more than 20 years and is a veteran of more than 80 shuttle fueling operations.
Hydrogen gas can spontaneously ignite in the atmosphere in concentrations greater than about 4 percent due to interactions with other components of the air. While the vapor leaking from the vent line appeared to be fairly dense, Leinbach said there were no sensors nearby to determine the actual concentration.
In any case, no fires broke out and Leinbach downplayed the danger posed by the leak.
"We didn't ever consider this a threat to the vehicle," he said. "Of course, during external tank load there's no one at the pad so there was never any safety issue with people. We just really don't feel it was an issue."
He confirmed that engineers are studying three options for repairing the line. If enough room is available, technicians will grind down the crack, re-weld it and use X-rays or penetrating dyes to confirm the integrity of the seal. That's the best-case scenario, one that would result in a launch attempt as early as Sunday.
A second, more complex, option calls for welding a clamshell-like sleeve around the crack. But that would add a day or two to the repair timeline. The worst-case scenario would require engineers to detach a 60-foot-long section of the vent line and lower it to the pad surface for repairs. The line then would have to be reattached and retested. When another launch attempt could be scheduled under that option is not yet clear.
Under NASA's post Sept. 11 security plan, the agency will not announce a target launch time for Sunday or any other day, saying only that Atlantis will take off, if the pad can be repaired in time, between 2 p.m. and 6 p.m. The exact launch time will be revealed 24 hours before takeoff.
As reported here earlier, however, satellite tracking software shows a Sunday launch would be targeted for around 5:02 p.m. EDT. The launch time moves about 24 minutes earlier each day in accord with the space station's orbit.
Assuming Atlantis gets off the ground Sunday, here's a rough timeline of major mission events (in EDT and mission elapsed time):
DATE/EDT...DD...HH...MM...EVENT 04/07/02 05:02 PM...00...00...00...STS-110 launch 04/09/02 11:38 AM...01...18...36...Station docking 12:47 PM...01...19...45...Hatch opening 04/10/02 11:22 AM...02...18...20...Spacewalk No. 1 begins to attach truss to station 04/12/02 10:52 AM...04...17...50...Spacewalk No. 2 begins 04/13/02 10:52 AM...05...17...50...Spacewalk No. 3 begins 04/15/02 10:52 AM...07...17...50...Spacewalk No. 4 begins 04/16/02 12:22 PM...08...19...20...Farewell ceremony 12:42 PM...08...19...40...Hatches closed 03:22 PM...08...22...20...Station undocking 04/18/02 06:52 AM...10...13...50...Begin deorbit timeline 10:54 AM...10...17...52...Deorbit rocket firing 11:59 AM...10...18...57...Landing
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Launch pad cameras capture this dramatic video of the ruptured hydrogen vent line on the east side of the mobile launch platform and the resulting cloud of vapors. (1min 06sec file)
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NASA Launch Director Mike Leinbach briefs reporters on the hydrogen vent line leak and repair options at the post-scrub press conference at Kennedy Space Center. (26min 31sec file)
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