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Nasa engineers have still not fixed the troublesome fuel sensor that stopped an earlier launch attempt but feel they are now getting on top of the issue.
Agency officials said they would start the countdown clock on Saturday for what will be the first shuttle mission since the loss of Columbia in 2003.
Discovery's 12-day venture into orbit will take it to the space station."We
have a great amount of work to do to get us through this but we all agree that this work is doable to take us to a launch on the 26th (of July)," shuttle programme manager Bill Parsons told reporters.
Controlled stop
At issue is the performance a low-level fuel cut-off sensor, which failed to give a correct reading during a routine pre-launch check last week.
SHUTTLE RETURN TO FLIGHT
Shuttle schematic (BBC)
Mission known as STS-114
Discovery's 31st flight
17th orbiter flight to ISS
Payload: Raffaello Multi-Purpose Logistics Module
Lift-off: To be determined
Location: Kennedy Space Center, Launch Pad 39B
Discovery crew: Collins, Kelly, Noguchi, Robinson, Thomas, Lawrence and Camarda
Guide to key shuttle changes
The sensor is one of four that warn the shuttle computers if the external tank is about to run dry.
This allows the computers to shut down Discovery's three main engines and its fuel pumps in an orderly fashion - neither too soon nor too late; both scenarios have potentially disastrous consequences.
Exhaustive work by hundreds of engineers suggests that an electrical grounding problem lurking somewhere inside the spacecraft is the most probable cause of the sensor's faulty behaviour.
Shuttle officials said some further tests still needed to be done but that they felt confident now to proceed to a countdown.
Clear plan
If the sensor worked properly during the final hours before launch, Discovery would fly, Bill Parsons said.
If the problem reoccurred but was well understood, then the go-ahead would likely be given to launch the orbiter anyway, he added.
Nasa workers (AP)
Nasa engineers will continue to work through the sensor problem
"We believe the best way to go through this is to do a countdown," he said "If the sensors work exactly like we think they will, then we'll launch on that day.
"If anything goes not per the plan that we've laid out in front of us, then we'll have a scrub and we'll have to talk about it."
Including the first launch attempt on Tuesday, there are at least four opportunities for Discovery to launch during the current launch window, which extends until 31 July; although Nasa managers are now also looking at the possibility of additional launch opportunities in the first week of August.
It would be a controversial move to fly Discovery with a low-level fuel sensor still malfunctioning.
Nasa used to permit launches with only three of the four sensors working properly but then insisted on a four-out-of-four approach after the 1986 Challenger explosion.
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NASA najavila lansiranje za Utorak
CAPE CANAVERAL, Fla. -
NASA will try to launch Discovery on the first space shuttle mission in more than two years next Tuesday, and may press ahead with liftoff even if there's a repeat of the fuel gauge problem that halted last week's countdown.
State
Mission managers decided Wednesday night to bypass another fueling test of Discovery and go straight for the real thing in an effort to understand and either fix or work around the fuel gauge failure. The most probable cause is an electrical grounding problem lurking inside the spacecraft.
"We believe the best way to go through this is to do a countdown," said shuttle program manager Bill Parsons. "If the sensors (gauges) work exactly like we think they will, then we'll launch on that day. If anything goes not per the plan that we've laid out in front of us, then we'll have a scrub and we'll have to talk about it."
Multiple safety nets are in place "to ensure we don't proceed unless we feel we're safe to go fly," he added.
But in what would be an almost certainly controversial move in the wake of the 2003 Columbia tragedy, NASA might also proceed with the liftoff if the fuel gauge problem recurs but is considered well understood. That would mean revoking a launch rule requiring all four hydrogen fuel gauges at the bottom of Discovery's external tank to be working properly, and instead relying on just three out of four.
That looser three-out-of-four rule was thrown out after the 1986 Challenger launch explosion.
The fuel gauges are intended to keep a shuttle's main engines from shutting down too early or too late after liftoff, both potentially disastrous situations. Only two of the four are needed to ensure safety, but ever since the Challenger accident, NASA has required all four to be operating.
"Right now, we think we have eliminated all the common causes that we believe could do this and we've done everything we possibly could on the vehicle," Parsons said.
The countdown — the first since Columbia's final flight — was halted shortly before the scheduled liftoff July 13 when one of the fuel gauges malfunctioned. The same type of problem marred a fueling test of Discovery back in April with a different external tank; it was written off as an "unexplained anomaly."
Despite a week of exhaustive scrutiny by hundreds of engineers, NASA has been unable to pinpoint the precise cause or location of the fuel gauge failure. An electrical grounding problem is considered the most likely cause, and the space agency is holding out hope that it can trace the problem to interference from shuttle equipment in the next few days.
Among the many shuttle parts suspected of possibly causing electromagnetic interference are newly installed heaters on the external fuel tank. The heaters are meant to prevent the kind of lethal damage suffered by Columbia at liftoff.
"We have a great amount of work in front of us to get us through this and get us ready," Parsons said. "But we've all agreed that this work is doable."
The countdown will begin Saturday for a Tuesday morning launch attempt.
If Discovery and its crew of seven aren't flying by the beginning of August, their trip to the international space station will be bumped to September to ensure a daylight launch and good surveillance photography throughout the shuttle's ascent. NASA wants to see any Columbia-type damage that might occur.
A chunk of fuel-tank foam insulation tore a hole in Columbia's left wing at liftoff and led to its catastrophic re-entry on Feb. 1, 2003. All seven astronauts were killed.
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Cryo Sat,spreman
Engineers are carrying out final checks on the ice monitoring craft CryoSat, in preparation for an autumn launch.
The European Space Agency (Esa) satellite has gone through months of testing in Germany and will be transported to Russia's Plesetsk Cosmodrome next month.
The three-year mission will monitor how the world's ice sheets are changing.
Its main objective is to test the prediction that ice cover is diminishing due to global warming.
Data gathered by submarines suggests that Arctic sea ice is thinning rapidly.
The measurements carried out by the subs, in the 1960s and 1970s, and in the 1990s, by scientific vessels, suggest that Arctic sea ice has shrunk 40% in draught - the difference between the surface of the ocean and the bottom of the ice pack.
But scientists still do not have a full picture of how the polar caps as a whole are responding to climate change because of the paucity of data.
'On tenterhooks'
Dr Seymour Laxon, of the Centre for Polar Observation and Modelling at University College London, UK, said that Cryosat would provide a clear answer to this question.
CryoSat rendition (European Space Agency)
CryoSat will fly as close to the North Pole as possible (Image: European Space Agency
"We are all on tenterhooks, waiting for CryoSat to give us the first view of what has been happening to the thickness of the sea ice around the North Pole since 1998, the last year for which submarine data are available," he told the BBC News website.
"Its amazing to think that something that was just an idea on paper 7 years ago will, in just a few months, actually be a satellite in orbit."
During the last 12 months the satellite has been put through a battery of mechanical and environmental tests at the Space Test Centre at IABG (Industrieanlagen-Betriebsgesellschaft mbH) in Ottobrunn, Germany.
These are nearly complete, and the spacecraft is due to be shipped to the launch site towards the end of August.
"We've still got a few major tests to do over the next couple of weeks. Once that is completed the spacecraft should be in good shape, from our point of view," said CryoSat spacecraft operations manager, Nic Mardle.
Earth Explorer
CryoSat is the first of Esa's Earth Explorer missions, which focus on specific aspects of the planet's environment, in this case polar ice.
Principal Operations Engineer, Kate Adamson, said the radar altimeter on CryoSat would be the most accurate instrument of its type to fly.
"It's essentially a low-cost mission but has a very specialised instrument on it, the SIRAL radar altimeter, that can take very accurate measurements of the height of ice sheets and the sea ice, down to the centimetre level," she said.
A US space agency (Nasa) satellite, IceSat, launched in 2003, is already mapping the Antarctic and Greenland ice sheets, which cover 10% of the Earth's land area, using a laser instrument.
Data from both satellites should give scientists the clearest picture yet of what is happening to the world's total ice mass, and the consequences for climate, ocean currents and global sea levels.
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Posada Discaverija se vratila u Kenedi
The seven astronauts who will crew the Discovery shuttle flew back into Kennedy Space Center on Friday.
Their launch has been reset for Tuesday after engineers said they were getting on top of a fuel sensor problem that scrubbed last week's lift-off attempt.
The STS-114 mission team, led by Eileen Collins, has been continuing with its training in Texas during the delay.
On 13 July, the crew were actually in their seats and ready for launch when they were told to stand down.
Since then, Nasa engineers have been trying to work out why the fuel sensor, which monitors the volume of cryogenic hydrogen in the shuttle's external tank, failed to work properly during a routine pre-launch check.
SHUTTLE RETURN TO FLIGHT
Shuttle schematic (BBC)
Mission known as STS-114
Discovery's 31st flight
17th orbiter flight to ISS
Payload: Raffaello Multi-Purpose Logistics Module
Lift-off: To be determined
Location: Kennedy Space Center, Launch Pad 39B
Discovery crew: Collins, Kelly, Noguchi, Robinson, Thomas, Lawrence and Camarda
Guide to key shuttle changes
They believe an electrical grounding problem somewhere inside the spacecraft is the most probable cause, and hope to have fixed the glitch, or at least fully understood its behaviour, by Tuesday's lift-off.
"We are very proud of the work that the engineers and the managers and the technicians have done over the past week and a half, trying to find out what's going on with this very elusive problem," Commander Collins said on touching down at KSC.
"We hope that we're able to launch on Tuesday, but regardless of when we launch, what's important to us is that we get through this process and that we do it right," she added.
The US space agency has set Tuesday's launch for 1039 EDT (1439 BMT; 1539 BST).
If this is missed because of another technical problem or because of bad weather, there would be three more opportunities to launch before the closure of the current window on 31 July - although Nasa managers are now also looking to see if that cannot be widened into the first week of August.
The time and size of the window is governed by the position of the International Space Station (ISS) in its orbit and the need to launch the orbiter in daylight hours so all aspects of its ascent can be photographed.
Discovery's 12-day mission will deliver parts and supplies to the ISS. It will also give the astronauts a chance to test new safety features on the shuttle brought in following the loss of Columbia in February 2003.
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Jos jednom krece odbrojavanje!
CAPE CANAVERAL, Fla. - The countdown clocks began ticking again Saturday for
NASA's return to space, as shuttle managers voiced optimism — but not certainty — that they had fixed the fuel gauge problem that thwarted the first launch attempt.
"No doubt there is some degree of finger crossing," NASA test director Pete Nickolenko said before the start of the second countdown in two weeks.
"But the other side of the coin is that we have really performed a very thorough troubleshooting analysis to a great degree, an excruciating degree of detail with all the shuttle program experts and the contractors that we can get."
NASA is aiming for a Tuesday morning liftoff of Discovery on the first shuttle mission since Columbia's disastrous re-entry in 2003. The flight was delayed by two weeks after one of four hydrogen fuel gauges in Discovery's big external tank failed a routine test on July 13, just two hours before the initial scheduled liftoff.
In the past few days, NASA has repaired three areas of spotty electrical grounding, sanding the connectors like someone might do with flashlight batteries that haven't been used in a while. They also scoured the spacecraft for any electromagnetic interference that might have exacerbated the fuel gauge problem.
Technicians switched the wiring between the troublesome fuel gauge and another one, in an attempt to better understand the sensor problem if it recurs.
The 14 engineering teams that have been working nonstop on this problem have eliminated more than 300 possible causes, Nickolenko said. What remains in the so-called fault tree are faulty electrical grounding in the shuttle's aft fuselage, which has been fixed, and possible electromagnetic interference, which may still be out there. No interference has been found, but the true test will come when the shuttle is fueled and all its systems are running right before liftoff.
Nickolenko said he and others are confident the system will work the way it's supposed to come Tuesday. But he hastily added, "We were confident that we were going to be in that case for the first launch attempt, too."
Mission managers are considering launching Discovery and its crew of seven even if one of the fuel gauges malfunctions, as long as the problem is reminiscent of what happened two weeks earlier and is thought to be well understood. The same problem spoiled a fueling test back in April.
NASA's own launch rules require that all four fuel gauges be working, even though only two are needed to ensure that the main engines don't shut down too soon or too late, both potentially deadly situations. Any rule change at the last minute, to allow less than four good gauges, would almost certainly raise eyebrows.
Technical issues aside, the weather could end up interfering.
Forecasters are putting the odds of acceptable launch conditions at 60 percent because of the threat of rain and clouds.
NASA has until the beginning of August to launch Discovery to the international space station, or it must wait until September to ensure good lighting throughout the ascent. The space agency is insisting on a daylight liftoff for good camera views in case the shuttle is hit by fuel-tank foam insulation, ice or other debris.
Columbia was brought down by a 1 1/2-pound chunk of foam that pierced the left wing. The gaping hole led to the shuttle's destruction during re-entry on Feb. 1, 2003, and the deaths of all seven astronauts.
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Discovery ce se lansirati i pored problema sa gorivom
CAPE CANAVERAL, United States (AFP) - Discovery's launch could go ahead even if a fuel gauge malfunction reoccurs, but weather might delay the liftoff,NASA said, two days ahead of the first space shuttle flight since the 2003 Columbia disaster.
NASA ran more than 160 tests but has failed to explain what exactly caused the failure of one of the four hydrogen level sensors that prompted the last-minute cancelation of the July 13 launch.
The space agency hopes to detect the root of the problem during last-minute testing while the shuttle's massive external tank is being filled.
If the problem reoccurs on the same sensor or another similar one and engineers have a clear understanding of the problem, the launch would go ahead as planned, said Wayne Hale, deputy manager of the space shuttle program.
But he insisted that if any other low fuel level sensors malfunctioned, the launch would be called off.
The sensors send data on the levels of hydrogen in the tank to determine when the three engines should be shut off during the ascent into orbit.
Failure of the sensors can result in premature shutdown of the orbiter's engines during the shuttle's ascent.
But Hale was optimistic. "We are ready to go launch Tuesday morning," he said at a news conference at the Kennedy Space Center, near Cape Canaveral, Florida.
NASA appeared far more concerned weather could delay the mission.
Weather forecasters said there was a 40 percent chance that cloud cover or rain could scrub Tuesday's planned launch, as NASA wants a clear view of the shuttle as it ascends into orbit.
"We do have some concern for launch," said NASA weather officer Kathy Winters.
The launch also would be called off if there is thunderstorm activity within 20 nautical miles (37 kilometers) of the Kennedy Space Center launch pad, since it could affect an eventual emergency landing. There were also concerns about the weather in alternate emergency landing sites in France and Spain.
The Space Shuttle Discovery, formally known as STS-114, is scheduled to liftoff from its Florida seashore launch pad at 10:39 am (1439 GMT) Tuesday, taking the seven crew -- including a Japanese national -- to a rendezvous with the ISS.
Should Tuesday's launch be called off, NASA will have until the end of the month to send Discovery into orbit so it can hook up with the orbiting ISS. After that, the next window for a daytime launch will be in September.
NASA's decision not to launch at night is among the new safety measures the space agency has adopted after Columbia burst into flames upon re-entering the Earth's atmosphere on February 1, 2003, killing all seven astronauts.
The tragedy was blamed on a small piece of insulation that broke off just after liftoff and struck the orbiter's left wing, causing a razbijac that allowed superheated gases to penetrate the structure just minutes before the planned landing.
Now, more than 100 cameras will be installed on the ground and aboard two airplanes to capture the shuttle's first two minutes of ascent.
Should something go wrong in the first few minutes, the shuttle could return to the Kennedy Space Center, or head to a base on the other side of the Atlantic, either in France or in Spain.
During one of three planned spacewalks, Japanese astronaut Soichi Noguchi and his US counterpart Stephen Robinson will test repair techniques.
The spacecraft will also deliver vital supplies and equipment after docking with the International Space Station, whose crew will photograph Discovery's underside.
If the images show Discovery suffered significant damage during ascent, the seven astronauts will wait for another shuttle to bring them back to Earth from the ISS.
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NASA planira da lansira
CAPE CANAVERAL, Fla. -
NASA will allow the shuttle Discovery to lift off Tuesday, despite not fully understanding its recent fuel tank failure and as long as the problem resurfaces in the same way it did earlier this month.
NASA workers have switched the wiring between the problem sensor and another one after the gauge failure forced the space agency to postpone the space shuttle's launch while astronauts were boarding Discovery on July 13.
NASA's own launch rule — in place since the 1986 Challenger disaster — requires that all four hydrogen fuel gauges in the external tank be working properly. But NASA will go ahead with the rescheduled launch at 10:39 a.m. Tuesday if the problem doesn't recur or if it only is found in the two sensors that have been rewired, Wayne Hale, deputy manager of the shuttle program, said at a Sunday evening news conference.
"If the problem recurs ... we're going to do some more tests just to make sure we understand what is causing this to happen and if we're comfortable that we have a good understanding, then we can go fly," Hale said.
NASA Administrator Michael Griffin said he is comfortable with the decision and even hopes the problem recurs to further pinpoint the source of the trouble. He acknowledged that the public might perceive that the space agency is rushing to launch, but insisted it was the right technical judgment.
"It's not a safety of flight issue," Griffin said.
Although the focus of NASA's attention has been on the sensor, rain and clouds may end up causing more concern on launch day. Forecasters put the odds of good launch weather Tuesday at 60 percent. Additionally, the weather at the overseas emergency landing sites is not looking good at all.
"My observation is that when the weather is good, you have vehicle problems. If the vehicle works, you have weather problems," Hale said. "Since we have some weather concerns, I'm confident the vehicle is going to be OK."
NASA has just one week to launch Discovery and its crew of seven to the international space station, before putting off the mission until September. The space agency is insisting on good lighting in order to see any signs of the type of launch damage that crippled Columbia, the last shuttle launch.
Columbia and its seven astronauts were brought down by a broken section of fuel-tank foam insulation that struck just over a minute after liftoff and proved lethal during descent two weeks later, on Feb. 1, 2003.
Workers last week repaired faulty electrical grounding inside Discovery in hopes that would solve the fuel gauge problem that cropped up during the first launch attempt. The same type of problem occurred back in April during a fueling test, and was written off then as an "unexplained anomaly."
NASA had 14 teams around the country studying the problem. They have eliminated possible explanations one by one, but they have been unable to arrive at a definitive answer.
The fuel gauges are needed to prevent the main engines from shutting down too soon or too late during liftoff, in the event of an extreme problem like a leaking tank. The first scenario could result in a risky, never-attempted emergency landing; the second could cause the engine turbines to rupture and, quite possibly, destroy the spacecraft. Only two fuel gauges are needed to avoid such dangerous situations.
Going with three out of four would result in a "deviation" in the rule, Hale told reporters, but he said NASA engineers' understanding of the problem is vastly improved than it was 10 days ago.
"I wake up every day and I ask myself, 'Are we pushing too hard? Are we doing this thoroughly? Have we done the right technical things?'" Hale said. "I think we're all still struggling a little bit with the ghost of Columbia and therefore we want to make sure we do it right."
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Lansiranje najavljeno za Utorak,uprkos problemima
The Discovery shuttle could lift off on Tuesday even if the sensor problem that prevented the launch on 13 July recurs.
Engineers have raced to isolate the glitch, and have come up with two likely candidates.
The current launch window is open until 31 July, but may be widened into the first week of August.
Discovery's mission 12-mission to the International Space Station marks Nasa's first shuttle launch since the loss of Columbia on 1 February 2003.
"We have literally run every check that we can think of," said Wayne Hale, shuttle deputy programme manager, "and so far, no repeat."
Wiring switch
Dr Mike Griffin, the US space agency's administrator, said he hoped the problem did recur during countdown tests, so engineers could resolve the problem once and for all.
"What you want of Nasa is that we make the right technical decisions, that we do the right thing, to the extent that we can figure that out, which is hard," he explained.
"We can't restrict the range of our options to those things that are going to present well."
The launch attempt on 13 July was scrubbed when one of four identical engine cut-off (Eco) sensors failed a routine countdown check. The sensors act as fuel gauges, monitoring the volume of cryogenic hydrogen in the shuttle's external tank.
For Tuesday, the wiring between sensors number two - which played up last time - and number four has now been switched, to try to isolate the glitch.
If engineers see a failure in either of these sensors, managers say they will understand the problem well enough to fly Discovery.
However, if an unforeseen problem with the other sensors arises, they will have to abort the launch.
A 'huge effort'
Engineers have so far identified and fixed three electrical grounding issues in the sensor wiring system and also suspect electromagnetic interference from other hardware could be the root cause of the problem.
Mr Hale brandished an example of the sensor involved at a news conference here at Kennedy Space Center.
"Just because I brought this, I don't want anyone to go away with the idea we're indicting the sensors," he told journalists.
Though engineers have completed a battery of "ambient" tests on the sensor system, they have to wait until the early hours of Tuesday to check how they perform with a full tank of cryogenic liquid hydrogen.
Mr Hale countered suggestions that Nasa carry out a "tanking" test, in which the external tank is filled up with cryogenic propellants, before attempting launch.
"I think we're all still struggling a bit with the ghosts of Columbia, so we want to make sure we do this right," said Mr Hale.
"Are we taking care enough to do it right? Based on the last 10 days' worth of effort, the huge number of people and the tremendous number of hours that have been spent testing and analysing - I think we're coming to the right place."
At the right time
The sensors at the heart of Nasa's troubleshooting operation ensure the orbiter's three main engines shut down before its fuel runs out, avoiding the potentially catastrophic scenario of the motors running with empty tanks.
But the agency also needs to be sure that the sensor glitch does not lead to the alternative and equally unwelcome scenario in which the engines shut down too early because the system believes wrongly all the tanks are empty.
An engine shutdown before Discovery reached its intended orbit could force the crew to abort the mission and make an emergency landing.
The US space agency has set Tuesday's launch for 1039 EDT (1439 BMT; 1539 BST).
Discovery's 12-day mission will deliver parts and supplies to the ISS. It will also give the astronauts a chance to test new safety features on the shuttle brought in following the loss of Columbia.
If Tuesday's launch goes ahead as planned, the shuttle will return to Earth on the morning of 7 August, landing at Kennedy Space Center.
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