Space station gets the last of its wings

When Canadian astronaut Robert Thirsk joins the crew of the International Space Station for an extended six-month stay in May, he'll be part of the first six-person crew in the orbiting station's 11-year history. But before he and his crewmates get there, the station is going to need a power boost.
The above image illustrates Discovery conducting the Rendezvous Pitch Manoeuvre before docking at the space station. ((NASA))
When Canadian astronaut Robert Thirsk joins the crew of the International Space Station for an extended six-month stay in May, he'll be part of the first six-person crew in the orbiting station's 11-year history. But before he and his crewmates get there, the station is going to need a power boost.

That's the focus of the next NASA mission to the space station, as the space shuttle Discovery is set to deliver the station's fourth and final set of solar panels.

U.S. Air Force Col. Lee Archambault will lead the seven-man Discovery crew on the mission, which is scheduled to take place on Wednesday, March 11, 2009. Also scheduled to fly aboard the shuttle are pilot Tony Antonelli and mission specialists Joseph Acaba, John Phillips, Steve Swanson and Richard Arnold, all American, and Koichi Wakata from the Japan Aerospace Exploration Agency.

The addition of the S6 truss structure, which carries two solar arrays spanning 73 metres when fully extended, will be one of the last major enhancements to the station before NASA retires the shuttle fleet in 2010, and certainly one of the most noticeable changes.

The installation of solar arrays has been a tricky job for NASA in the past, so the station and shuttle crews will focus most of the 11 days the shuttle will spend at the station during its 15-day mission on getting the job done right.

Discovery is also scheduled to deliver a replacement part for the station's new water recycling system. That part failed after the space shuttle Endeavour departed in December.

One of its crew members, Japanese taikonaut Wakata, will also replace U.S. astronaut Sandra Magnus as a member of the station's three-person crew, joining American astronaut Michael Finke and Russian cosmonaut Yury Lonchakov.

And there will be four spacewalks during the mission, one to install the solar array and the other three dedicated to station maintenance.

Solar arrays finally arrive

You need only look at the name of the latest shuttle mission — STS-119 — to appreciate how long the space station has been awaiting its fourth and final pair of solar arrays, particularly since the previous flight carried the mission title STS-126. The mission was originally scheduled for 2004, but the delivery of the final solar panels was pushed back repeatedly as NASA juggled its shuttle launch timetable after the Columbia disaster in 2003 and delays to other flights.

With its arrival and installation, NASA and its partners hope the station will be able to generate 84 to 120 kilowatts of electricity, or enough to provide power to more than 40 average homes. That power will come in handy as the station adds to its crew in May and more experiments are delivered to the station.

"More crew means that we'll have to run more life support equipment, more crew support equipment — toilet facilities, water processing equipment and all of that stuff," said Kwatsi Alibaruho, the lead space station flight director for the mission, in a statement. "We'll have to run more of all of that, so we need additional power."

The process of unloading and attaching the arrays will begin on day four of the mission, a day after the shuttle docks with the station and the two crews meet.

Using the space station's Canadarm 2, the astronauts will grab the 14-tonne truss structure from the cargo bay of the shuttle and then hand it to the shuttle's Canadarm robotic arm. The Canadarm will then hand it back to Canadarm 2, which will move it into position on the far starboard side of the station.

The actual installation will take place on day five, when Swanson and Arnold leave the station in their spacesuits and help the operator of the robotic arm connect to the existing starboard-side structure.

The actual unfurling of the solar arrays could happen on day six of the mission or day eight if the crews need to spend some time inspecting the shuttle for damage that may have occurred during takeoff. But they might end up needing both days if past experience is any guide. In particular, the space station and shuttle crews have had difficulty with the solar arrays in the past.

During Discovery's October 2007 mission, one of the port-side array's solar wings tore when the wires that guide the solar panels got snagged as it was being unfurled. That problem came as a result of earlier difficulties folding the array when it was moved from one part of the station to its current location on the port side of the station.

In the Space Station Processing Facility at NASA's Kennedy Space Center, Boeing workers stand ready as the starboard integrated truss, known as S6, is rotated in order to remove and replace lower deck batteries. ((NASA))

To keep a better eye on the arrays as they unfurl, NASA said the process would happen in two stages, with a break in between to assess how the extension of the solar wings is progressing.

Urine recycling system fix

The other major delivery to the station is a replacement distillation assembly for the station's water recycling system, which converts urine into drinking water for the station's astronauts.

The space shuttle Endeavour delivered the recycling system to the station in November 2008, but the distillation assembly, which removes impurities from the urine in the early stages of the recycling process — failed not long after the shuttle departed and returned to Earth.

Three other spacewalks are scheduled for the mission on the seventh, ninth and 11th days of the mission in which pairs of astronauts will perform a variety of tasks, including preparing batteries on the P6 truss for replacement and performing maintenance on the Canadian-made Dextre robot and the station's Canadarm 2.

Discovery is scheduled to depart on Day 12 of the mission and return to Earth three days later.

Future missions

After its departure, NASA has planned for seven more shuttle missions to the station.

The next shuttle to visit the station is scheduled to be Endeavour, with Canadian astronaut Julie Payette among its crew. It will be delivering the final piece of Japan's Kibo laboratory, a kind of back porch to the main structure where experiments dependent on exposure to the outer space environment will be housed.

But the timing of that mission is up in the air, as NASA currently has it slated for May 15, just three days before Atlantis is set to lift off for the Hubble Space Telescope. NASA is unable to launch two shuttles in a span of three days, so one or both of the missions will likely have a change in schedule.

The timing won't affect Thirsk, however, as he will be travelling to the station aboard a Russian Soyuz rocket.

Three more shuttle missions are scheduled for 2009. The first two involve the delivery of experiments and spare equipment and the final mission of the year, slated for December, will deliver an advanced living space called Node 3, along with an ESA-built observatory module called Cupola. The shuttles will then have three more scheduled missions in 2010 before the fleet is scheduled to be retired.