Space Shuttle liftoff "scrubbed"
- Thread starter Qwickdraw
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Qwickdraw said:
Well with the last disaster it is better safe then sorry.
I also thought I heard something about possible delays due to weather this morning.
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Fuel gauge foils shuttle launch
Liftoff timing depends on the complexity of the sensor repairs
By MARK CARREAU
Copyright 2005 Houston Chronicle
CAPE CANAVERAL, FLA. - A puzzling problem with a fuel gauge forced NASA to scrub efforts to launch Discovery and a crew of seven Wednesday on the first shuttle mission since the Columbia disaster.
A second attempt to begin the landmark mission to the international space station was possible on Saturday, but a much longer delay could not be ruled out, NASA Administrator Michael Griffin said.
The problem surfaced during a test of the four low-level hydrogen propellant sensors in Discovery's external fuel tank — about 2 1/2 hours before the planned afternoon liftoff.
The sensors are designed to signal the shuttle's three rocket engines to shut off when the hydrogen supply has been nearly exhausted and lower the risk that the engines would churn without fuel, triggering an explosion.
The test revealed that one sensor would fail to detect an almost empty tank and would tell the engines to keep running, said NASA's Wayne Hale, the mission management team chief.
Even without the fuel gauge problem, the thunderstorms that popped up around Kennedy Space Center as the astronauts were boarding Discovery would have prevented a liftoff, said NASA shuttle program spokesman Kyle Herring.
Astronauts Eileen Collins, James Kelly, Stephen Robinson, Andrew Thomas, Wendy Lawrence, Charles Camarda and Soichi Noguchi of Japan were in the process of strapping into Discovery when informed of the scrub.
"All I can say is shucks," Hale said. "We came out all set to go today, and we incurred a problem."
The space agency's shuttle fleet has been grounded since Columbia's fatal breakup over East Texas on Feb. 1, 2003.
Engineers immediately initiated a series of assessments they hoped would determine whether the cause of the fuel-gauge problem lies with the sensors themselves or with the easier-to-fix electronics in Discovery's tail section, said Steve Poulis, the shuttle orbiter project manager.
The outcome of their investigation, which might be evident today, will determine whether Discovery can be scheduled for a second liftoff attempt during the launch window that ends July 31 or whether the repairs will force a postponement until September.
The sensor issue has puzzled shuttle managers since it surfaced during an April 14 launchpad test when the fuel tank, which underwent safety modifications after the Columbia tragedy, was filled with chilled propellants for the first time.
Two of the four hydrogen sensors performed erratically, an outcome that engineers were unable to explain.
The test was repeated on May 20 after electronics cabling and other shuttle components were replaced. All four sensors worked, leading engineers to believe that the electrical work had solved the problem.
Meanwhile, Discovery was equipped with another fuel tank fitted with a new electrical heater to address concerns about ice formation. The fuel-gauge test was not repeated after the new tank was installed.
However, engineers continued to study the issue, and mission managers decided to hold a final sensor check during the countdown.
"We did the test, found something, and we stopped," Hale said.
The four sensors are designed to back up each other, lowering the likelihood of an explosion.
But, Hale said, "we are not flying with this. We took no risk."
The most rapid repair — fixing a loose cable or connector in Discovery's tail section — could permit a second launch attempt on Saturday.
But engineers believe the problem could be linked to eight transistors in a larger component called a "point sensor box," also in the shuttle's tail compartment.
If the problem is traced to the box, a second launch attempt might be possible on Monday, Poulis said.
Clustered in the bottom of the shuttle's fuel tank, the fuel gauges would be difficult to replace on the launchpad, possibly forcing NASA managers to move Discovery to a hangar and leading to a longer delay.
If a solution to the problem proves elusive, shuttle managers might have to postpone the mission until September.
Wednesday's scrub proved disappointing for the thousands of people, including a bipartisan group of 45 senators and congressmen, who had traveled to Florida to witness the liftoff.
"NASA is doing the right thing by putting safety first," said U.S. Sen. Kay Bailey Hutchison, R-Texas, who chairs a space agency oversight subcommittee. "He's not going to take any chances, and that is the way it should be."
mark.carreau@chron.com
http://www.chron.com/cs/CDA/ssistory.mpl/topstory/3265649
Liftoff timing depends on the complexity of the sensor repairs
By MARK CARREAU
Copyright 2005 Houston Chronicle
CAPE CANAVERAL, FLA. - A puzzling problem with a fuel gauge forced NASA to scrub efforts to launch Discovery and a crew of seven Wednesday on the first shuttle mission since the Columbia disaster.
A second attempt to begin the landmark mission to the international space station was possible on Saturday, but a much longer delay could not be ruled out, NASA Administrator Michael Griffin said.
The problem surfaced during a test of the four low-level hydrogen propellant sensors in Discovery's external fuel tank — about 2 1/2 hours before the planned afternoon liftoff.
The sensors are designed to signal the shuttle's three rocket engines to shut off when the hydrogen supply has been nearly exhausted and lower the risk that the engines would churn without fuel, triggering an explosion.
The test revealed that one sensor would fail to detect an almost empty tank and would tell the engines to keep running, said NASA's Wayne Hale, the mission management team chief.
Even without the fuel gauge problem, the thunderstorms that popped up around Kennedy Space Center as the astronauts were boarding Discovery would have prevented a liftoff, said NASA shuttle program spokesman Kyle Herring.
Astronauts Eileen Collins, James Kelly, Stephen Robinson, Andrew Thomas, Wendy Lawrence, Charles Camarda and Soichi Noguchi of Japan were in the process of strapping into Discovery when informed of the scrub.
"All I can say is shucks," Hale said. "We came out all set to go today, and we incurred a problem."
The space agency's shuttle fleet has been grounded since Columbia's fatal breakup over East Texas on Feb. 1, 2003.
Engineers immediately initiated a series of assessments they hoped would determine whether the cause of the fuel-gauge problem lies with the sensors themselves or with the easier-to-fix electronics in Discovery's tail section, said Steve Poulis, the shuttle orbiter project manager.
The outcome of their investigation, which might be evident today, will determine whether Discovery can be scheduled for a second liftoff attempt during the launch window that ends July 31 or whether the repairs will force a postponement until September.
The sensor issue has puzzled shuttle managers since it surfaced during an April 14 launchpad test when the fuel tank, which underwent safety modifications after the Columbia tragedy, was filled with chilled propellants for the first time.
Two of the four hydrogen sensors performed erratically, an outcome that engineers were unable to explain.
The test was repeated on May 20 after electronics cabling and other shuttle components were replaced. All four sensors worked, leading engineers to believe that the electrical work had solved the problem.
Meanwhile, Discovery was equipped with another fuel tank fitted with a new electrical heater to address concerns about ice formation. The fuel-gauge test was not repeated after the new tank was installed.
However, engineers continued to study the issue, and mission managers decided to hold a final sensor check during the countdown.
"We did the test, found something, and we stopped," Hale said.
The four sensors are designed to back up each other, lowering the likelihood of an explosion.
But, Hale said, "we are not flying with this. We took no risk."
The most rapid repair — fixing a loose cable or connector in Discovery's tail section — could permit a second launch attempt on Saturday.
But engineers believe the problem could be linked to eight transistors in a larger component called a "point sensor box," also in the shuttle's tail compartment.
If the problem is traced to the box, a second launch attempt might be possible on Monday, Poulis said.
Clustered in the bottom of the shuttle's fuel tank, the fuel gauges would be difficult to replace on the launchpad, possibly forcing NASA managers to move Discovery to a hangar and leading to a longer delay.
If a solution to the problem proves elusive, shuttle managers might have to postpone the mission until September.
Wednesday's scrub proved disappointing for the thousands of people, including a bipartisan group of 45 senators and congressmen, who had traveled to Florida to witness the liftoff.
"NASA is doing the right thing by putting safety first," said U.S. Sen. Kay Bailey Hutchison, R-Texas, who chairs a space agency oversight subcommittee. "He's not going to take any chances, and that is the way it should be."
mark.carreau@chron.com
http://www.chron.com/cs/CDA/ssistory.mpl/topstory/3265649
adbutcher
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When they discovered the problem they had already missed their launch window. They Suppose to try again Saturday but it must be clear here in Houston as well as in Florida in order for NASA to get the green light. Somehow, I don't think they will be able to launch Saturday because it has been raining mooses and elks all day today.
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Welcome to Houston...adbutcher said:
:
GTaylor
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Sorry to sorta change the subject but if you ever get a chance, you need to see a launch live. Words cannot describe the experience, it is truly amazing.
Back to the subject, I agree with BP - considering what's at stake it's better safe than sorry
Back to the subject, I agree with BP - considering what's at stake it's better safe than sorry
Cajuncowboy
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Qwickdraw said:
Just curious. How many fuel gauges do you have to have before one is considered redundant?
adbutcher
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It depends on the MTBF (Mean Time Between Failures). When the number is high for a component/system then you usually add another if it is feasible. Then you do another calculation to determine the 'new' MTBF. If it is acceptable then that is your level of redundancy. If not than you start a new iteration until you reach an acceptable threshold.cajuncowboy said:[/B]
Just curious. How many fuel gauges do you have to have before one is considered redundant?