Endeavour's initial launch window opens April 29 and extends through May 4. If the shuttle is not off the ground by then, the team will stand down for three days to reload liquid oxygen and hydrogen fuel cell reactants and to give the Air Force time to launch an Atlas 5 rocket carrying a missile early warning satellite. The shuttle launch window would re-open around May 8 and extend through May 29.

Credit: Justin Ray/Spaceflight Now

NASA had planned to launch Endeavour on April 19, but earlier this month the fight was delayed 10 days because of a conflict with the launch and docking of a Russian Progress supply ship. The delay put the shuttle launch on the same day as the British royal wedding of Prince William and Kate Middleton.

Asked if NASA considered an additional delay to avoid a conflict with the royal wedding, Bill Gerstenmaier, chief of space operations for NASA, said "we work beta (angle) constraints and we work launch range constraints. I haven't yet put on our manifest charts 'wedding constraints.' So we didn't factor that into our thinking."

As with all post-Columbia flights, Endeavour's ascent will be monitored by batteries of launch pad cameras, radar and long-range trackers, on the lookout for any signs of foam insulation falling from the external tank that could damage the shuttle's fragile heat shield.

Debris poses the biggest threat during the first two minutes and 15 seconds of flight when the dense lower atmosphere can cause lightweight insulation to come to a near standstill in a fraction of a second. The accelerating space shuttle can then slam into it at a high relative velocity.

A phenomenon known as "cryo pumping" can cause foam to pop off later in ascent when liquefied air trapped under the foam near the top of the liquid hydrogen tank warms and expands as the fuel level drops during the climb to space. But testing and flight experience show cryopumping typically happens well after the aerodynamically sensitive period.

Given the history of Endeavour's "hurricane tank," mission managers expect to see more foam insulation falling away during the climb to space than usual because not all of the post-Columbia tank improvements were carried out for the repaired tank.

"This tank doesn't have some of the modifications to it that other tanks have had, so we expect to see some foam loss," Gerstenmaier said. "If you remember, we used to lose foam around the LH2 ice frost ramps on the hydrogen tank because there was a little alignment pin that would allow some cryo pumping and ingestion around the ice frost ramps which could cause some foam to come off in those areas.

"We fully expect this to occur on this tank," he said. "It'll again be late losses of foam, but we expect to see some foam losses in that area."

Kelly and company plan to close out their first day in space setting up a computer network, downlinking photos of the external tank, breaking out equipment and testing the ship's robot arm.

The next day, Johnson, Fincke and Vittori will use the robot arm and an instrumented extension boom to carry out a detailed inspection of Endeavour's reinforced carbon carbon nose cap and wing leading edge panels to make sure the most critical elements of the shuttle's heat shield came through the climb to space in good shape. Laser scans and high-resolution photographs will be beamed down to NASA's Damage Assessment Team for detailed analysis.

While the heat shield inspection is underway, Fincke, Feustel and Chamitoff will check out their spacesuits and the tools they'll use during the mission's four spacewalks. The crew also will break out and test the rendezvous tools they will use during final approach to the space station.

The terminal phase of the rendezvous will begin about three hours before docking on fight day three when Kelly and Johnson will fire the ship's maneuvering jets to begin closing the final nine miles between the two spacecraft. Approaching from behind, Kelly will pause at a point 600 feet directly below the space station. He then will oversee a slow computer-assisted back flip maneuver that will expose the orbiter's belly to the station.

As black heat shield tiles on the shuttle's underside come into view, station flight engineer Paolo Nespoli and Catherine "Cady" Coleman, working in the Russian Zvezda command module, will snap hundreds of photographs using cameras equipped with 400-mm and 800-mm telephoto lenses capable of spotting even minor damage and defects.

With the rendezvous pitch maneuver complete, Kelly will manually guide Endeavour up to a point about 400 feet directly in front of the station with the shuttle's nose pointed toward deep space and it's open payload bay facing the lab's forward port. With the two spacecraft flying in formation at more than 5 miles per second, Kelly will carefully move in for a docking.

Joining Nespoli and Coleman to welcome the shuttle crew aboard will be Expedition 27 commander Dmitri Kondratyev, Ronald Garan and Russian cosmonauts Andrey Borisenko and Alexander Samokutyaev.

After a brief "meet and greet" in the forward Harmony module, the shuttle crew will get a routine safety briefing before splitting up and getting to work.

The major item on the post-docking agenda is installation of External Logistics Carrier No. 3 on the upper left side of the station's power truss.

The ELC-3 pallet is moved from Endeavour's payload bay to its home on the space station truss. Credit: NASA

Mounted in Endeavour's cargo bay just in front of the Alpha Magnetic Spectrometer, ELC-3 tips the scales at just over 14,000 pounds, loaded with large components that will become part of the station's extensive spare parts inventory for use down the road, after the shuttle fleet is retired. Three other ELCs were attached to the station during two earlier shuttle missions, two on the right side of the power truss and one on the lower left.

ELC-3 is carrying 10 spare remote power control module circuit breakers, two spare S-band antenna assemblies, an ammonia tank loaded with 600 pounds of coolant, a high-pressure oxygen tank for the station's airlock and a spare arm for a Canadian cargo manipulator that can be attached to the station's main robot arm. It is also carrying a suite of small military experiments.

Fincke and Vittori, operating the shuttle's robot arm, will pull ELC-3 from Endeavour's cargo bay three hours after docking and hand it off to Johnson and Chamitoff, operating the space station's robot arm. From there, the station arm will move ELC-3 to the upper attachment point on the port side of the power truss.

Once in position, a motorized clamp will lock ELC-3 in place and an umbilical will deliver power to component heaters and electronics.

Getting ELC-3 attached is "absolutely critical because there's no other way to get the big spares on board without the orbiter," said space station Flight Director Derek Hassmann. "It's amazing the amount of inventory we have on orbit in terms of critical pump modules, in terms of communications equipment, in terms of high pressure gas tanks for the airlock. I would say we're in an excellent position for shutle retirement. We've made tremendous progress over the past five or six years, first in identifying the plan and getting all the tons of hardware on orbit."

ELC-3 must be unloaded from the shuttle first because of center-of-gravity re-entry and landing constraints. If ELC-3 cannot be unberthed for some reason, the spare parts pallet and the AMS will be returned to Earth.

But no such problems are expected and if all goes well, the astronauts will turn to their primary payload on flight day four.

Feustel and Vittori will pull the Alpha Magnetic Spectrometer out of the shuttle's cargo bay using Endeavour's robot arm. As with ELC-3, the AMS will be handed off to the station arm, operated by Johnson and Chamitoff. They will move the particle detector to the upper right side of the power truss and robotically lock it in place.

Power and data cables will be remotely connected. No other crew interaction is required and data collection will begin almost immediately.

"Not too long ago, Steve Hawking, a very well known physicist, came to spend an afternoon with me at Geneva (where we were) assembling the detector," Ting said. "He asked me a question. He said, why do you do AMS on the station, not with a satellite? I told him it's really not possible to do a very, very precise, very sophisticated state-of-the-art detector to study the origin of the cosmos without the space station. Because space station can provide support of large weight and enormous amount of power. So without a space station, AMS would not have been possible."

Using the same magnet that flew on a shuttle test mission in 1998, the AMS will record subtle shifts in the trajectories of incoming charged particles to look for evidence of antimatter left over from the big bang birth of the cosmos and to search for clues about the nature of mysterious dark matter and evidence for new forms of matter that have been predicted but never seen.

Built at CERN, the European Organization for Nuclear Research, and managed by the U.S. Department of Energy, the $2 billion AMS is an international collaboration between 16 nations, 60 institutes and some 600 physicists. Ting, a soft-spoken Chinese-American physicist who shared the 1976 Nobel Prize in physics, is a tireless advocate.

"The largest accelerator on Earth is 16 miles in circumference, the large Hadron Collider, LHC," he said. "In LHC there are four big experiments. Thousands and thousands of physicists work there trying to understand the beginning of the universe, what is the origin of mass, why different particles have different masses.

"The cost of ISS is about 10 times more than the LHC. The LHC has four experiments. On the space station, to study particle physics, the origin of the universe, (we only have) AMS. And that's why we're very grateful to the United States House of Representatives and the Senate, which passed the resolution to support NASA to have an additional flight to put us in space."

The Large Hadron Collider is capable of generating energies as high as 7 trillion electron volts. To put that in perspective, 1 trillion electron volts is roughly equivalent to the energy of a single flying mosquito. But in particle physics, that energy is concentrated in a single sub-atomic particle and particles from deep space can have energies as high as 100 million trillion electron volts.

"This means that no matter how accelerators are here on Earth, you cannot compete with the cosmos," Ting said.

One of the many mysteries AMS was designed to explore is what happened to the anti-matter that must have been created in the big bang. Scientists believe equal amounts of matter and anti-matter were produced, but a slight imbalance -- or some other factor -- resulted in a universe dominated by normal matter. Or at least a nearby universe made up of normal matter.

"If the universe comes from a big bang, before the big bang it is vacuum," Ting told reporters recently. "Nothing exists in vacuum. So in the beginning, you have (negatively charged) electron, you must have a (positively charged) positron so the charge is balanced. So you have matter, you must have antimatter, otherwise we would not have come from the vacuum.

"So now the universe is 14 billion years old, you have all of us, made out of matter. The question is, where is the universe made out of antimatter? With this experiment, the reason we designed it to such a large size with so many layers of repetitive position detectors is to search for the existence of antimatter to the age of the observable universe, anti-helium, anti-carbon.

"We can distinguish this particle from billions of ordinary particles," he said. "If you think about it, this is not a trivial job. In the city of Houston during the rainy season, you have about 10 billion raindrops per second. If you want to find one that's a different color, it's somewhat difficult. This illustrates the precision this detector is going to achieve."

Dark matter, the mysterious, as-yet-undetected material believed to provide the glue -- gravity -- needed to hold galaxies and clusters of galaxies together, is believed to make up a quarter of the universe compared to the 4 percent made up of the normal matter familiar to human senses. The rest is believed to be in the form of dark energy, a repulsive force that appears to be speeding up the expansion of the universe.

While AMS cannot directly detect dark matter, it can detect the particles that would be produced in dark matter collisions.

AMS is maneuvered to its attachment point on the space station truss. Credit: NASA

AMS also will be on the lookout for so-called "strangelets," sub-atomic particles made up of quarks in different combinations than particles found on Earth. There are six types of quarks -- known as up, down, top, bottom, charm and strange -- but protons and neutrons making up normal matter seen on Earth are made up of just two -- different combinations of up quarks and down quarks.

"The smallest particle are called quarks," Ting said. "We know six quarks exist. But it's very, very strange. All the material on Earth is made up of just two, up and down. We know in the accelerator, six types exist, but on Earth you only see the first two. So the simple question you want to ask is, where's the material made out of three types of quarks? Up, down and strange? It's a very simple question, but a very, very important question."

Whatever AMS discovers, scientists will have plenty of data to work with. Some 25,000 particle detections per second are expected when the instrument is up and running.

"We're gathering data at seven gigabits per second," said Trent Martin, the AMS project manager at the Johnson Space Center in Houston. "We can't send that huge amount of data down through the space station data system, it's just too much.

"So the onboard computers actually go through a process of condensing that data down to just the data that we're truly interested in, compressing it as much as possible. We send down data on average at about six megabits per second, constantly for the entire time that AMS is on. The computers can store up data and we can burst it down at a much higher rate."

Asked to speculate on what AMS might discovery, Ting declined, saying "Most physicists who predict the future normally end up regretting it."

"My responsibility and the responsibility of my senior collaborators is to make sure the instrument is correct," he said. "Because the detector is so sensitive, everything we measure is something new. We want to make sure it's done correctly."

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