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Planetary News: Human Spaceflight (2006)Space Shuttle Atlantis Begins Return to ISS Assembly
By A.J.S. Rayl |
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Atlantis Launches
Through a haze of clouds, Space Shuttle Atlantis hurtles toward space for a rendezvous with the International Space Station on mission STS-115. Liftoff was on-time at 11:14:55 a.m. EDT. Mission STS-115 is the 116th space shuttle flight, the 27th flight for Atlantis, and the 19th U.S. flight to the International Space Station. Credit: NASA |
After a series of nerve-wracking postponements, Atlantis – STS-115 -- lifted off today just seconds before 11:15 am Eastern Daylight Time (8:15 am Pacific Daylight Time, 15:15 Greenwich Mean Time) from the Kennedy Space Center, on a 12-day mission to resume building the international space station (ISS).
"It's been a long road with a lot of detours . . . but now it's time to fly," said Commander Brent Jett just before blast-off. The shuttle is scheduled to dock with the ISS on Monday, September 11.
The weather in the area was pleasant and cooperative for the 27th flight of Atlantis, which last flew in October 2002. Temperatures hovered around the upper 70s, and there were light winds, with scattered clouds in the sky. While there were a couple of minor issues on the way up, there was nothing that threatned the flight or crew.
The launch, from pad 39B, couldn't have come soon enough for the astronauts or the agency. This was the last launch opportunity in this launch window or until late September.
Like many shuttle missions, STS-115 has been ready to go, then scrubbed several times – first on August 27 because of lightning hitting the launch pad, and on August 29 when it was rolled off the pad and back inside the protection of the Vehicle Assembly Building, because of what appeared to be an increasing threat from Tropical Storm Ernesto.
As the storm passed, the launch was slated for September 6, but that lift-off was called off at the last minute because of a troublesome fuel cell. NASA engineers determined that any failure of the suspect fuel cell during the mission posed no danger to Atlantis and its crew, and that 2 fuel cells alone would provide the mission with enough power to accomplish the major goals. Despite what was described as a "lively" debate September 7, the decision to fly was nearly unanimous, according to Wayne Hale, space shuttle program director.
Atlantis was powered up for launch again yesterday, September 8, but then powered back down after the launch team reported that one of the four engine cut-off (ECO) sensor systems inside the liquid hydrogen section of the space shuttle's orange external tank failed during a pre-launch check. The sensor system is one of several that protect the shuttle's main engines by triggering their shutdown if fuel runs unexpectedly low.
As the tank's liquid oxygen and liquid hydrogen was drained Friday, engineers monitored and collected data on the liquid hydrogen sensors. According to NASA's launch rules, a preplanned procedure states if a single ECO sensor fails, engineers need to drain the tank and verify all the sensors are working as they go dry. Since the sensors and system worked as expected, Atlantis was cleared to launch with 3 of 4 working sensors.
Commander Jett, Pilot Chris Ferguson, and mission specialists Joe Tanner, Dan Burbank, Heide Stefanyshyn-Piper and Canadian astronaut Steve MacLean spent the down time studying flight plans and spend time with their families.
Getting off the ground is with any shuttle flight just the beginning, but with STS-115, "it's time to hold your breath again," according to NASA mission releases. The test flights of the shuttle's safety improvements -- which were instituted after the disintegration of Columbia in February 2003 -- have gone well. But the space shuttle flight schedule in the final years leading up to its retirement in 2010 is extremely aggressive, calling for 4 to 5 flights a year, and, rather than winding down, these last missions are winding up as some of the most challenging ever confronted by the program.
The crew of Atlantis STS-115
After suiting up, the STS-115 mission crew exits the Operations and Checkout Building to board the Astrovan to Launch Pad 39B. On the left, front to back, are Pilot Christopher Ferguson and Mission Specialists Steven MacLean and Heidemarie Stefanyshyn-Piper. On the right, front to back, are Commander Brent Jett and Mission Specialists Daniel Burbank and Joseph Tanner. Credit: NASA / Kim Shiflett |
On this Return to Assembly mission, NASA gets down to the business of completing the construction of the ISS. The STS-115 astronauts will deliver and install the 17.5-ton, bus-sized P3/P4 integrated, girder-like truss segment on the station. The truss, which includes a set of giant solar arrays, batteries, and associated electronics, will provide one-quarter of the total power-generation capability for the completed station, and, if everything goes according to plans, will be completed in 3 spacewalks. Mission Specialists Stefanyshyn-Piper, Burbank, and MacLean are all slated to make their first spacewalks during this flight.
The mission includes all the safety protocols tested on the past 2 shuttle flights, including improved imagery during launch, heat shield inspections on orbit, and a shuttle backflip as it approaches the station.
Although the crew has trained for this mission for 4 years, there are always things that can go wrong and every astronaut and cosmonaut knows that despite best efforts the nature of a complex mission means problems you never expected have a way of popping up when you least expect them. But on STS-115 the astronauts' schedules are so tight there is little margin for the unexpected. In fact, the crew will be going almost nonstop for seven days straight. “It’s a very busy flight,” Atlantis Commander Brent Jett said in the days leading up to launch. “We’ve never had to fit so many activities back to back on consecutive days.”
The crew must use the shuttle's robotic arm to inspect Atlantis' heat shield on the second day of the mission while en route to the station, a shuttle safety enhancement. As soon as they dock to the ISS on their third day in space, the astronauts are scheduled to unload the school-bus-sized package of solar panels, batteries, and electronics. "Flight day 2, we have a very, very full day with the inspection,” Jett confirmed. “The day before docking is now a full day of robotics work. So we go from launch day, right in to flight day 2 -- inspections, right in to flight day 3 -- docking and unberth, then the first spacewalk, the second spacewalk, solar array deploy, and then another spacewalk. The timeline is a big challenge.”
The ISS before STS-115
With a backdrop of the blackness of space and Earth's horizon, this full view of the International Space Station (ISS) was photographed by a crewmember onboard Discovery following the undocking of the 2 spacecraft. Discovery pulled away from the complex on August 6, 2005. Credit: NASA |
The drama builds with concern about unpacking and installing the solar arrays and the joint that will rotate them. They have been ensconced in their flight package since May 2003 when they were originally scheduled to be delivered. The reason for the concern stems from an incident on STS-97 in November 2000 when a matching set of 240-foot long arrays was deployed and the cables meant to pull them taut came off their pulleys. It could have left the wings slack and vulnerable to tearing and breaking, but the crew was able to fix it.
Atlantis Mission Specialist Heide Stefanyshyn-Piper, who will work with the arrays during 2 spacewalks, said she believes that problem has been fixed and won’t be an issue this time around. But the arrays have been packed away for several years, and b because they’re so large, they have to be folded to fit in the shuttle’s cargo bay. Although the arrays have been checked and rechecked, when it comes time to unfold them, they could stick, the team is prepared, Piper said, and has logged time practicing ways to manually unfold them.
The drama will build still more as Atlantis delivers the station's first Solar Alpha Rotary Joint – a 10-foot wide, wagon-wheel-shaped joint that will allow the arrays to turn toward the Sun. This is a first. Nothing like this joint has ever flown in space -- and there’s no guarantee it will work like it’s supposed to. “We just don’t know,” Piper said. “We think it’s going to work. On paper it works. But you just never know until you get it up on orbit.”
If all goes according to design, the drama will finally reach a kind of crescendo as the 2 array wings are attached, dramatically changing the station's overall appearance – and balance. The responsibility for keeping the station pointed in the right direction falls to Lead Shuttle Flight Director Paul Dye and his team in Mission Control in Houston. The computers should take care of it, but should is always the "operative" word. As Dye put it: “You do the engineering and then you hope the engineering matches the real world when you get up there."
The expanding ISS
This diagram shows how the International Space Station (ISS) will look once the STS-115 crew completes the installation of the P3/P4 truss and the second set of solar arrays. Credit: NASA |
If the station did start to tilt, it can be righted of course. But any problems or hiccups that come up would throw off the mission’s entire timeline. Adjusting the station’s orientation might require firing the shuttle’s engines, and that would use up limited and valuable fuel.
The pressure is on, but the crew is ready and excited. Atlantis Pilot Chris Ferguson, who will help with a lot of the robotic arm work, is confident. He said he’s been studying for four years and he’s ready for his final exam. “They’re high intensity ops, but I think we can do it,” he said. “I think we’ve considered everything we can consider before flight. If we can get through the first seven days, the rest is downhill. After Flight Day 7 – if it goes well – it gives us time, hopefully, to get some sleep.”
The pressure to complete the construction of ISS and retire the shuttle is ever present, and some observers have been criticizing NASA for taking chances with the lives of astronauts and the remaining 3 orbiters. The space agency is pressing on.
The ever-expanding cost of the ISS –- now estimated at around $100 billion dollars for development, assembly, and operating costs for 10 years – has also been a source of controversy internationally. It is shared, however, over a period of almost 30 years between the participants, the United States, Russia, Canada, Japan, and 10 of the 17 European nations who are part of the European Space Agency (ESA).
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