quarta-feira, 31 de outubro de 2007

Envie uma mensagem aos astronautas da STS-120

Vá a http://spacecenter.org/message.asp, e a sua mensagem será incluída num CD que será entregue aos astronautas da missão STS 120, após o seu regresso.

Ò diabo! Danos graves num painel solar da ISS!

Clique para ver em alta definição.
Infelizmente esta missão de montagem da Estação Espacial Internacional está a sofrer alguns percalços razoavelmente graves. Primeiro foi a descoberta de alguns pedaços de metal numa plataforma que girava os painéis solares de um dos extremos da Estação, e agora, muito mais grave, foi este rasgo impressionante, que ocorreu quando os astronautas estavam a desdobrar um novo painel solar.

A NASA está agora a ponderar possibilidades de reparação deste painel (que continua a gerar electricidade apesar do dano) no próximo Sábado.

Estes problemas são tão mais graves porque afectam os próximos passos da montagem da ISS, durante as próximas missões do Space Shuttle, com prazos apertados - quanto a mim desnecessariamente - pela data marcada para a reforma dos Shuttles em 2010.

Em minha opinião dever-se-ia considerar concluida a montagem da ISS quando esta estiver concluída, e não forçar a NASA a lançar missões a contra-relógio apenas para respeitar uma data arbitrária fixada pelo Presidente George Bush. Claro que isto irá, forçosamente, custar mais dinheiro, mas pelo menos poderemos tentar evitar mais um desastre terrível como os do Challenger e Columbia. Não podemos sucumbir de novo à 'febre de lançar' que condenou 14 astronautas e dois shuttles no passado bem recente.

quarta-feira, 24 de outubro de 2007

Vídeo do lançamento, ontem, do Space Shuttle Discovery

Esta será provavelmente a missão mais complexa de sempre. Será montado um novo módulo na Estação Espacial Internacional, e o tipo de trabalho que terá de ser feito é bastante intenso e complexo.

Durante a contagem decrescente houve vários problemas, e mesmo dúvidas acerca do lançamento, devido nomeadamente ao tempo que estava a piorar bastante próximo do momento do lançamento, e à detecção de gelo numa das condutas que alimentam o Shuttle de combustível - este problema tendo sido considerado MUITO GRAVE pela NASA. No entanto, a análise feita levou os responsáveis a concluir que não haveria perigo para o Shuttle durante o lançamento.

A missão está a correr bem, não tendo havido quase nenhuma queda de gelo a partir do grande tanque externo (côr de laranja), como infelizmente é costume nestas missões.

É a primeira vez que um Shuttle comandado por uma mulher vai ao encontro de uma Estação Espacial também comandada por uma mulher.

Outra curiosidade é a hora do lançamento ter coincidido exactamente com a hora de lançamento da última missão do Challenger.

Shuttle Discovery launched
02:30 PM, 10/23/07, Update:
(UPDATED at 3 p.m. with post-launch news conference; quotes and details; correcting time of docking)

The shuttle Discovery, carrying seven astronauts and a critical connecting module for the international space station, roared to life and rocketed into orbit today, kicking off a high-stakes five-spacewalk mission considered by many the most complex orbital construction work ever attempted.

"I don't think there's ever been an astronaut who doesn't consider their flight the most dramatic, exciting, complex mission ever," lead spacewalker Scott Parazynski said before launch. "But ours is!"

With its three hydrogen-fueled main engines roaring at full throttle, Discovery's twin solid-fuel boosters ignited with a rush of fire and thunder at 11:38:19 a.m., instantly pushing the huge spacecraft away from pad 39A.

Seconds later, Discovery's flight computers sent commands to the booster steering system, rolling the spacecraft about its vertical axis to put the crew in a heads down orientation as the spaceplane arced out over the Atlantic Ocean on a trajectory paralleling the East Coast of the United States.

NASA managers were worried early today about an ice buildup on an umbilical on the lower section of the shuttle's external fuel tank and by threatening weather. But as the morning wore on, the anticipated cloud development held off, engineers decided the ice would most likely shake off at launch and Discovery was cleared for flight.

"OK, Pambo, on behalf of your KSC family, I'd like to wish you good luck, Godspeed, have a little fun up there," Launch Director Mike Leinbach radioed the crew a few minutes before launch.

"Copy that, Mike," replied Melroy, the second woman to command a space shuttle. "We feel a tremendous amount of pride in the 10A and Discovery team and a lot of gratitude for the hard work to get us here. And we're ready to take Harmony to her new home."

Joining Melroy on Discovery's flight deck were Marine Corps pilot George Zamka, flight engineer Stephanie Wilson and Doug Wheelock, an Army helicopter pilot. Strapped in on the orbiter's lower deck were physician-astronaut Parazynski, Italian astronaut Paolo Nespoli and Dan Tani, a space station crew member hitching a ride to the lab complex aboard Discovery. Tani will replace station engineer Clay Anderson, who will return to Earth aboard the shuttle.

Television views from a camera mounted on Discovery's external fuel tank provided spectacular views of the Florida spaceport dropping away and then the limb of the Earth as the ship headed for orbit. Bill Gerstenmaier, chief of space flight operations for NASA, said a quick look at the video indicated about a half-dozen small pieces of foam insulation fell away from the shuttle's external tank during the climb to space.

But in all cases, Gerstenmaier said, the debris separated after Discovery's solid-fuel boosters were jettisoned and well beyond the regime in which the denser lower atmosphere can slow lightweight foam enough to cause impact damage when the shuttle runs into it at a high relative velocity.

"We took a quick look at the video and we saw probably six instances of foam loss off the tank and they were all after solid rocket booster separation," Gerstenmaier said. "So in that sense, they're not a concern from a damage-to-the-orbiter standpoint. ... We'll see when we get some good pictures of the external tank here later today or tomorrow."

While Gerstenmaier was addressing reporters at a post-launch news conference, astronaut Terry Virts in mission control at the Johnson Space Center in Houston, radioed Melroy with a debris update.

"Pam, there were several events noted during ascent," he said. "They occurred after the critical transport mach number. We will continue to look at it. This is just preliminary only, but it did look like a clean ascent. Also there was some ice on the aft LH2 (liquid hydrogen) lines on the tank, we saw that pre launch and it cleared right at T-0 as expected."

The astronauts photographed the tank shortly after it separated from the shuttle in orbit and Parazynski reported "no visible, at least to the naked eye, loss of big pieces of foam."

The crew will carry out a detailed inspection of the shuttle's nose cap and wing leading edge panels using a laser scanner and high-resolution camera on Wednesday while engineers on the ground continue analysis of long-range tracking camera and launch pad footage. In the meantime, NASA managers were thrilled with today 's launching.

"This is a great start to a very challenging mission in front of us," Gerstenmaier said. "If I look at this mission and what's coming up for us, we're combining, effectively, activities we've done on at least four other missions, all into one mission. So this is a pretty exciting mission. We're going to do a solar array deploy, a radiator deploy, a pressurized module addition, just a tremendous series of challenges in front of us.

"I think the teams are ready, really prepared for any eventualilty. ... I can't think of a better start to this mission than what we got today. So again, hats off to the KSC folks and the orbiter folks who gave us a great vehicle and a great ride to start a great mission."

Discovery took off at roughly the moment Earth's rotation carried the launch pad into the plane of the space station's orbit. If all goes well, Melroy will manually guide the shuttle to a linkup with the station around 8:35 a.m. Thursday.

Discovery's docking and the usual welcome aboard ceremony will have an unusual flavor this time around as Expedition 16 commander Peggy Whitson, the station's first female commander, welcomes Melroy, probably the final woman to command a shuttle before the program is retired in 2010. Both women flew together in 2002 when Whitson served as flight engineer of the fifth station expedition and Melroy visited as pilot of the shuttle Atlantis during mission STS-112.

"One of the moments I'm looking forward to the most is when the hatch opens and I see Peggy's face on the other side and we reach through for the traditional handshake," Melroy said in an interview. "That will be a really special moment for me."

Whitson said the timing of their flights was a coincidence, "but I do think it is special, not only special just for Pam and I because, you know, we have flown in space before, but the experience of having two women up there at the same time will hopefully be an inspiration to somebody."

"I was inspired when I was young by the Apollo era astronauts and in particular, I was motivated to become an astronaut when they selected the first female astronauts," she said. "I would hope that we could be a role model like that."

The day after docking, the astronauts will use the station's robot arm to pull the 31,500-pound Harmony module from Discovery's cargo bay as part of the first of the mission's five spacewalks.

Harmony will be temporarily mounted on the left side of the station's central Unity module. After the shuttle departs, Whitson, flight engineer Yuri Malenchenko and Tani will detach the station's main shuttle docking port, known as pressurized mating adapter No. 2, mount it on Harmony and then use the station's robot arm to move both components on the front end of the Destiny laboratory module.

Whitson and Tani plan to stage two spacewalks in November to connect Harmony to the station's cooling system and power grid to clear the way for launch of the European Space Agency's Columbus research lab aboard the shuttle Atlantis in December. Columbus will be attached to Harmony's right-side port while Japan's Kibo lab module will be connected to Harmony's left hatch next year.

"Harmony has six different ports that we can add modules onto to build the station," said Whitson. "So it's, it's our next big connecting piece in our puzzle of putting this huge station together on orbit."

Attaching a new pressurized module would have been the highlight of many past assembly missions. But for Discovery's crew, it is just the beginning. The second major objective of the flight is the disconnection and relocation of a huge set of solar arrays known as P6. Designed as the sixth and final segment of the port, or left, side of the station's main power truss, P6 was mounted at the center of the station in December 2000 to provide power to the U.S. segment during the initial stages of assembly.

Now, with identical solar panels in place on the left and right sides of the main power truss, NASA needs to move P6 to its permanent position on the far left end of the beam. The 35,000-pound segment's huge arrays, stretching 240 feet from tip to tip, were stowed during shuttle missions last December and June. Power and cooling lines were disconnected during an August flight, setting the stage for the massive truss's detachment, relocation and re-extension during Discovery's mission.

The station's robot arm cannot reach far enough on its own to make the move. So the station arm, after handing P6 off to the shuttle's space crane, will be moved by the station's mobile transporter to the far end of the power truss. At that point, the shuttle arm will hand the truss segment back to the station arm and Parazynski and Wheelock, making their third spacewalk by that point, will oversee its attachment to the P5 truss segment.

"Moving the P6 solar array will be a major activity," Melroy said in a NASA interview. "On our second spacewalk - our first spacewalk is all about (Harmony) - we'll be using the robotic arm in one location to actually reach around and pull P6 off ... with the assistance of our spacewalkers.

"Once the P6 has been detached from the space station, then the robotic arm will move it around to the port side of the shuttle, at which point it will be handed off to the shuttle arm. The shuttle robotic arm will take control of the P6 truss while the space station robotic arm is reconfigured and rolled out on the mobile transporter, the mobile platform, all the way to the far end of the port truss. And then, we'll use the station arm to take it back and install it in its final location.

"This is pretty nearly the design-limiting case for the robotic arm of the space station, so it's out at its full extension, trying to get that truss out there," Melroy said. "We'll have the help of the spacewalkers on the third spacewalk to do that. So, all these activities will actually span three days, three full days, two spacewalks with robotics in the middle."

Discovery is scheduled to land back at the Kennedy Space Center on Nov. 6.

quarta-feira, 17 de outubro de 2007

Lançamento do Space Shuttle Discovery aprovado para 23 de Outubro

Apesar de algumas preocupações com telhas de protecção térmica numa das asas do Shuttle, a NASA aprovou o lançamento sem reparar este problema, considerando não ser suficientemente grave para adiar o lançamento.

A terem de ser reparadas, o shuttle teria de ser de novo levado para o Vehicle Assembly Building - VAB - o que implicaria forçosamente um adiamento no lançamento de pelo menos um mês.

Fonte: Email da CBS Space News

Update: Discovery cleared for launch Oct. 23; Hale confident suspect wing panels safe
11:45 PM, 10/16/07

Senior NASA managers today cleared the shuttle Discovery for launch Oct. 23 on a critical space station assembly mission, concluding concern about the integrity of a protective coating on three of 44 wing leading edge panels did not warrant a lengthy delay. While there were no official dissenting opinions, NASA's chief engineer opted to write down his concerns about the decision to proceed with flight and a NASA engineering panel stuck to an earlier recommendation to replace the panels in question.

In a worst-case failure, one in which some unknown mechanism caused the protective coating to somehow come off after the crew's normal heat-shield inspections in orbit and before peak heating during re-entry, the shuttle could suffer a catastrophic leading edge burn through. Replacing the panels in question would eliminate the threat but the work would delay launch for two months or more.

NASA is attempting to complete the international space station and retire the shuttle by the end of fiscal 2010. At a news conference late Tuesday, Hale did not address how the prospect of a long delay might have played into the launch decision. But he made it clear he believes it is safe to proceed with Discovery's flight while testing continues, saying there is no engineering data to support the worst-case scenario.

"We certainly explored it in a great deal of depth," Hale said. "Everybody got to ask questions, everybody got to give their understanding of it down to the working-troop level. And at the end of the day, the flight readiness review board decided we were in an acceptable risk posture to go fly. Which is not to say we completely and perfectly understand the problem that's been laid out. We're going to continue to work very hard on it as the data comes in. We will continually re-evaluate our position from flight to flight and if the risk grows to an unacceptable level, we will take action, whether that's to change some hardware or to delay some flights while we do testing or what have you.

"I really think this was a credit to the lessons that we learned since Challenger and Columbia to be able to listen to all the opinions, to think very clearly about what they mean, apply some critical thought processes and, I trust, come to a good decision that provides us with an acceptable reason to go fly. We have a very important mission ahead of us and the crew is going to have a very intense time on orbit. We need to focus on what they are getting ready to do ... because it's absolutely critical to the next stage of building the international space station which is, after all, the reason for which we're flying the space shuttle."

Discovery's crew - commander Pam Melroy, pilot George Zamka, Scott Parazynski, flight engineer Stephanie Wilson, Doug Wheelock, Italian astronaut Paolo Nespoli and space station crew member Dan Tani - is scheduled to fly to the Kennedy Space Center Friday for the start of the shuttle's countdown Saturday afternoon. Launch is targeted for 11:38 a.m. Tuesday.

Bill Gerstenmaier, NASA's chief of space flight operations, said the crew, represented by the astronaut office at the Johnson Space Center in Houston, agreed with the decision to press ahead with launch. So did NASA's new chief engineer, Michael Ryschkewitsch, although he apparently had reservations. Gerstenmaier said Ryschkewitsch wanted to write down his concerns as part of a process that allows managers to go beyond a simple yes-no vote.

The primary goal of Discovery's mission is to deliver a new multi-hatch module called Harmony that will serve as the connecting point for European and Japanese research modules scheduled for launch in December and early next year. The astronauts also plan to move a stowed set of solar arrays to its permanent mounting point on the far left end of the station's main power truss and stage a recently added spacewalk to test heat shield repair techniques.

Discovery's flight is the first to use a new management approval process, splitting up the traditional flight readiness review into separate program- and headquarters-level meetings. The idea behind the change was to make it easier for mid-level managers and engineers to express their views and opinions, part of NASA's on-going drive to improve communications between engineers and managers.

The program-level review was held Oct. 10 and during that meeting, shuttle project and wing leading edge subsystem engineers recommended launching Discovery on time despite concern raised by the NASA Engineering and Safety Center - NESC - that the coating on three reinforced carbon carbon (RCC) wing leading edge panels might be susceptible to failure.

The issue involves a protective silicon-carbide coating on the shuttle's RCC nose cap and wing leading edge panels. The nose cap and 44 RCC leading edge panels - 22 on each wing - protect the shuttle from the most extreme heating during re-entry when temperatures exceed 3,000 degrees Fahrenheit. A breach in Columbia's left wing leading edge, caused by the impact of foam debris from the ship's external tank, led to the shuttle's destruction in 2003.

Since then, NASA and contractor engineers have paid close attention to the RCC panels and nose cap, devising sophisticated non-destructive tests to assess the health of the critical carbon composite material before each flight. One of those new techniques is called thermography, which measures how heat dissipates in the carbon composite material. The technique can show areas where the protective coating on the panels might be degrading.

"Before Columbia there were two instances where we landed and some of this coating, visibly little amounts ... was off the vehicle when it landed," Hale said. "Nothing bad had happened, the vehicle survived. There was a theory as to why this happened, we developed a screening technique that we thought would detect the problem before it became critical, before it became a safety-of-flight issue."

After the first post-Columbia mission, however, thermography revealed an area of concern on an RCC panel from the shuttle's right wing. The panel - 8R - was removed and returned to the vendor, Lockheed Martin, for refurbishment. In the course of post-flight inspections, Hale said, engineers discovered "there was more sub-surface damage than we would have expected on that panel."

"That kicked off this whole concern and starting in about May, we have been trying to understand do we really have a flight safety concern?" Hale said. "Because we don't know that we do. There are some hypothesized, proposed failure modes that would say you potentially could have a safety-of-flight issue. So we're working through that engineering data.

"Now that's not a simple sound bite," he said. "There is disagreement over the interpretation of results from this panel, which we have now taken and cut little slices of and looked at under a microscope and compared that back with what the thermography readings were before. What does all this mean to us? It's a very complicated problem, it's a very complicated system and we absolutely need to make sure it works right and I can tell you right now, today, there is some question whether or not all these panels will work right. And the question is, do we stop and wait until we completely understand this problem, do we remove three or four or five of these panels and try to replace them with newer and potentially better panels? What do we do? That's what we've been grappling with, that's the issue."

The area of concern is near the apex of the curved RCC panels where they join together with so-called T-seals. Three panels on Discovery - RCC panels 9 right, 13 right and 12 left - were known to have small areas of degraded coating.

Until recently, the leading theory for the cause of such coating degradation was a slow process of oxidation, one that would not be expected to lead to a sudden loss of protection. The areas of concern on the three panels aboard Discovery had not shown any signs of worsening after three flights.

But the NASA Engineering and Safety Center, an independent review group set up after the 2003 Columbia disaster, concluded ongoing analysis of test data did not support the presumed root cause of the coating degradation and that as a result, engineers could not predict how the damage might evolve over time or accurately assess the danger it might pose. The NESC recommended replacing all three panels.

But Hale said there is no actual test or flight data that would suggest a sudden coating failure is a credible scenario. If any such loss did occur during launch or the crew's orbital operations, it would be detected by now-standard post-Columbia heat shield inspections. If any such damage was detected, it could be repaired, in theory at least, by spacewalking astronauts. For severe damage, the crew could take refuge aboard the space station and await rescue by another shuttle.

But if something caused a coating loss after the crew's normal inspections, the shuttle could re-enter with an undetected, potentially catastrophic heat shield defect. The problem for NASA is the recent conclusion that the previously held oxidation explanation may not be valid and as such, engineers do not understand the underlying causes of coating degradation or how that degradation might change over time.

"I would love to be in the position of saying we understand all our problems completely and we have resolved them all and there is nothing that's worrying anybody," Hale said. "The fact of the matter is this is a very complicated vehicle, it's an old vehicle and there are a lot of loose ends out there. We fly every time without having solved every one of our problems, found a root cause of every one of our issues.

"This is an absolutely critical subsystem for the safety of flight and the potential is a catastrophic loss of vehicle. So therefore, we have to pay particularly close attention to it. And we are committed to (finding) a root cause. ... The question you have to ask yourself is do we have sufficient understanding and sufficient mitigation - and in this case, mitigation is things like inspection and repair - to go proceed to fly while we're proceeding to work root cause?"

Gerstenmaier said the question comes down to "where is that line, when is the right time to ... take some remedial action or when is it not a problem? And frankly, we don't know and that's what the teams are struggling with."

"Without an underlying cause mechanism, you can go in one direction that says you ought to (replace the panels) at this value, another direction at a different value. When we thought we had oxidation as a root cause it was clear then we had margin to go fly for an extended period of time. Now, because we don't know what that failure mode is, depending on which failure mode we hypothesize, we may not have as much margin as we like. Then we have to go look at other mitigating circumstances."

Asked how NASA could proceed with flight with major unknowns about a potentially critical failure mode, Hale said "I don't know what else to say other than what we've told you."

"We have a new technique to inspect these panels," he said. "It's showing us some interesting things, we're trying to understand what that means. In the process of understanding, some folks that I highly respect, who are good engineers, have hypothesized this could lead to a very bad situation. We haven't demonstrated that, we have a test program to go out and understand all of that.

"So you ask yourself, should we quit flying? Should we do some minor repairs on these piece parts? What should we do? You look at the mitigations. If it happens during the launch phase, we can detect it on orbit and repair it. And we think if it happens late in entry it won't be a problem. If it happens early in entry, we've done an awful lot of work and calculations and it probably, to a fairly high degree, won't be a problem although it could be. That's the kind of logic we go through."

Said Gerstenmaier: "We would have to lose the coating sometime prior to peak heating to have this potential problem during entry based on our conservative entry tools. So when you factor all those things together, even though you have all these unknowns, even if you extrapolate those unknowns to the worst case, we have enough rationale that says we're OK to continue to fly while we continue to aggressively investigate this."

Novas imagens do Pólo Sul de Titã, tiradas a partir da Sonda Cassini

Novas imagens obtidas por radar, e que mostram mais uma vez o que parecem ser lagos, de metano líquido, à superfície do satélite de Saturno. O Pólo Norte do satélite, recorde-se, também tem o que aparentam ser lagos de metano.

As cores da imagem são geradas por computador, e não são as reais, servem apenas para fins ilustrativos.

Fonte: ESA Portal - recomendo visitar o link, tem um filme que mostra a passagem da Cassini por Titan e a visualização dos lagos.

Anatomia de um Buraco Negro

Um pequeno e simples site interactivo, que nos mostra as principais características dos buracos negros. Recomendado para os que não conseguem visualizar as descrições por escrito, estranhíssimas, nos livros de Stephen Hawking, por exemplo :)

quinta-feira, 4 de outubro de 2007

A Era Espacial faz hoje 50 anos!

Há precisamente 50 anos, a União Soviética surpreendeu o mundo, lançando o primeiro satélite artificial de sempre, o famoso Sputnik - satélite, em russo.

Milhares saíram à rua nessa noite, para ver uma nova estrela, que deslizava rápidamente pelo céu.

Desde esse dia histórico, muitos milhares de missões espaciais foram realizadas. Poucos anos depois de 4 de Outubro de 1957, vendo-se ultrapassado pelos soviéticos em tecnologia espacial, o Presidente Kennedy desafia, em 1961, a URSS a por homens na Lua.

Em 8 escassos anos foram desenvolvidas tecnologias e métodos de trabalho revolucionários, que tornaram o impossível possível! Fomos à Lua.

E enviámos robots a outros planetas.

Hoje fala-se de novo em voltar à Lua, onde não vai nenhum ser humano desde 1972! Mas as primeiras novas missões ocorrerão apenas, na melhor das hipóteses, em 2020. Quase 50 anos depois da Apollo 17.

Mas muito mais nos aguarda nos próximos anos. Novos sistemas de propulsão estão a ser desenvolvidos e testados, que poderão possibilitar missões a Marte em períodos de tempo muito mais curtos do que os actuais.

Não acredito que eu, pessoalmente, venha a ver homens e mulheres a caminhar em Marte, mas espero voltar a vê-los na Lua. Afinal, foi uma das minhas primeiras recordações de infância!

E haverá já gente viva que será, possívelmente, o primeiro homem ou mulher a caminhar sobre Marte!

Parabéns, Sputnik! E a toda a humanidade, por não ter desistido da tarefa mais importante com que se depara nos nossos dias - aprender a trabalhar e a viver no Espaço, para um dia poder estabelecer colónias noutros planetas, e assim ajudar a aumentar as nossas possibilidades de sobrevivência, como espécie!

Actualização - dêem um saltinho à página da Google durante o dia de hoje.

terça-feira, 2 de outubro de 2007

Space Shuttle Discovery pronto para a próxima missão

O Discovery foi colocado na plataforma de lançamento 39-A anteontem, e está a ser preparado para a missão STS 120, que decorrerá a partir de 23 de Outubro, se tudo correr como planeado.

A tripulação da STS-120. Clique para aumentar.
Space shuttle moved to Florida launch pad
Discovery readied for Oct. 23 launch to international space station
By Irene Klotz
Updated: 12:04 p.m. ET Oct. 1, 2007

CAPE CANAVERAL, Florida - Workers at NASA's Kennedy Space Center moved the space shuttle Discovery out to its ocean-side launch pad on Sunday in preparation for a construction mission to the international space station slated to begin in three weeks.

Riding atop an Apollo-era mobile transporter, Discovery was rolled out of the massive Vehicle Assembly Building shortly before 7 a.m. ET for the 3.5-mile (5.6-kilometer) trek to the launch pad. It arrived about six hours later.

NASA is aiming to launch the shuttle on Oct. 23, but the schedule is tight with just two contingency days to spare. Discovery will be carrying a new connecting hub to the station so partner laboratories built by Europe and Japan can be attached to the outpost.

"We'd always like to have more [contingency days]. But we feel comfortable with two and when we're ready to go, we'll go," Discovery launch manager Stephanie Stilson told reporters at the launch site.

Discovery's launch preparations have taken a bit longer than planned. Workers found a leaky seal in the shuttle's right-side landing gear strut that had to be replaced, delaying its move to the launch pad.

If the shuttle crew can successfully install the new connecting node, the space agency should have a good shot at launching Europe's long-delayed Columbus module in December.

NASA needs to fly at least 11 more mission to the station to finish assembly before the shuttle fleet is retired in 2010. The agency also plans two station resupply missions and a final servicing call to the Hubble Space Telescope.

The 16-nation station project is a little more than 60 percent complete.