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STS-115 Mission Overview

Boosting the Space Station's Power: Canadian Astronaut Flexes Canadarm2 and Walks in Space

It was back to work building the International Space Station (ISS) for the flight of the Space Shuttle, and once again Canadian talent and technology were front and centre. The crew of six, including veteran Canadian astronaut Steve MacLean, left Earth onboard Atlantis on August 27, 2006, to continue constructing the world's largest and most complex space project.

As NASA's third Shuttle mission after its two return-to-flight demonstrations, STS-115 was to deliver new truss segments and solar arrays to the ISS. Installing these new components had MacLean performing some of the most challenging tasks ever done by any Canadian astronaut. Over the course of the mission, he choreographed a series of complex robotic manoeuvres using Canadarm2 to perform assembly tasks-a first for a Canadian astronaut-and performed a 6.5-hour spacewalk
to install the power generating panels.

The 12-day mission was the 19th Shuttle trip to the orbiting laboratory and the 27th flight for Atlantis. Steve MacLean was joined on STS-115 by commander Brent Jett (veteran of three Shuttle missions and five spacewalks), pilot Chris Ferguson, and mission specialists Joseph Tanner (veteran of three Shuttle missions and five spacewalks), Dan Burbank (veteran of one Shuttle mission to the ISS), and Heidemarie Stefanyshyn-Piper. MacLean was a Shuttle mission veteran as well, having served as a payload specialist in 1992 on STS-52.

Safety inspection, Canadian style

The day after the Shuttle thundered out of the atmosphere and reached orbit, every inch of the spacecraft began to be examined for possible signs of damage from the launch, using a unique remote-sensing system: a Canadian-made 15-metre extension to the Space Shuttle's Canadarm.

The Orbiter Boom Sensor System is an extension of the Space Shuttle's Canadarm. (Credit: NASA)

Like a dentist's mirror, the Orbiter Boom Sensor System (OBSS) gives the astronauts the extra reach needed to survey the hard-to-see areas of the Shuttle while in space, including its thermal tiled underbelly, as well as the leading edges of the wings. The boom extension builds on the experience Brampton, Ontario's MDA has gained in developing several generations of space-borne robotic manipulators, such as the Shuttle's Canadarm, the Space Station's Canadarm2, and the two-armed robot known as Dextre, installed on the ISS in mid-March 2008.

The end of the boom is outfitted with high-tech digital cameras and laser ranging sensors that can inspect every single Shuttle tile for cracks and holes while in orbit. Designed by Ottawa-based space vision technology developer NEPTEC, one of these Laser Camera Systems consists of a wide-angle, high-speed, high-precision instrument that uses a state-of-the-art scanning technique to generate three-dimensional images. The crew used the same system to give the Shuttle a second inspection later on in the mission, on flight day nine while still docked to the station, to look for possible micrometeorite damage.

View of the Space Shuttle's nose when docking with the International Space Station 
on Mission STS-114 in 2005. (Credit: NASA)

Coming into port

In the final hour before rendezvous with the station on day three, MacLean briefly took the Shuttle pilot's seat to support the docking procedures with the ISS. Once moored to the station and settled onboard, preparations began for the next historic chapter in the assembly of the ISS. Over the next eight days, Atlantis astronauts conducted a series of intricate robotic manoeuvres using the two Canadarms and perform three spacewalks to set up a new truss system, or structure, on which the second of four pairs of solar arrays were unfurled. These solar arrays form the largest power system ever constructed in space, generating a total of 128 kilowatts.

Cosmic handshake

For Canadians, the action-packed assembly phase of the mission began soon after docking, when MacLean and Burbank prepared for a hand-off manoeuvre involving two generations of Canadian robotic arms. Late on day three, using the Shuttle arm, Burbank delicately plucked the truss assembly out of the Shuttle's cargo bay and handed it off to Canadarm2, operated by MacLean inside the station. This was the first time in history that Canadarm2 assisted in ISS construction under the control of a Canadian astronaut. After this intricate two-hour operation, MacLean parked the robotic arm and its massive payload above the Shuttle cargo bay overnight in preparation for next day's busy construction activities.

On the morning of flight day four, using the Canadian-built robotic workstation located inside the station's U.S Laboratory module Destiny, MacLean began the first part of the multi-day installation sequence to attach the new truss assembly to the port side of the space station. Gingerly controlling Canadarm2, MacLean moved the P3/P4 truss, which weighed 15.9-tonnes at launch, toward the station and positions it so that claw-like capture latched securely to the orbiting outpost's existing P1truss system. Once the truss was firmly attached, MacLean commanded Canadarm2 to release its grip.

MacLean also used the Canadian-developed Space Vision System in these operations. The system provides critical images to the robotic workstation. Cameras at the end of the Shuttle arm send images of the installation taken at various angles to an onboard screen, producing a three-dimensional view. This gave MacLean a sense of the exact location, movement, and orientation of the payload Canadarm2 was grappling. This information is critical to accurate alignment of the truss for its installation on the station.

The Space Vision System (Credit: CSA)

Follow the Sun

On day four, as MacLean positioned Canadarm2 to grapple the newly delivered P3/P4 truss segment at the installation site, Tanner and Stefanyshyn-Piper stepped outside and conducted the first seven-hour spacewalk of the mission, plugging in connectors so the truss segments could be powered up by ground controllers once installations would be completed a few days later. The spacewalkers also released the restraints that protected the solar arrays during launch, and prepared the Solar Alpha Rotary Joint, or SARJ, and removed its locks for initial rotation of the solar arrays. With this special joint, the panels were able to rotate and follow the Sun for the first time, maximizing the power generating capability of the station.

Canadian spacewalk

On day five, MacLean donned his spacesuit and stepped out into the vacuum of space for the first time with fellow crewmate Burbank. Their job was to remove thermal covers, install braces and struts, and remove the numerous locks and restraints that immobilized the SARJ during the launch. The astronauts worked in close contact with ground controllers who powered down systems as connections were made. During the overnight hours, while the astronauts slept, ground controllers powered up and tested the SARJ, setting the stage for the activation of the solar panels.

Excitement and tension both in space and on the ground reached its peak on flight day six, when all eyes focused on the solar panels as they unfurled. For launch, the two 34-by-12-metre panels were folded origami-style and loaded into Atlantis' cargo bay. As they slowly opened out to their full length, MacLean supported the deployment by positioning Canadarm2 next to the newly installed truss system, using its cameras for a close-up view. Meanwhile, Ferguson was in Atlantis using the Shuttle arm video system to offer secondary camera angles during the operation. Ground controllers turned on the solar arrays overnight. MacLean then walked Canadarm2 off its Mobile Base System to Destiny, the American Laboratory module in preparation for future arm operations.

Canadarm2 (Credit: NASA)

Overseeing all the delicate operations using the robotic arms were the Canadian flight controllers who made sure things went smoothly and by the book. Based at the Johnson Space Centre in Houston and Canadian Space Agency headquarters in Longueuil, Quebec, the Canadian engineers worked jointly with their American counterparts. Like a ballet sequence, the complex robotic arm manoeuvres performed during the assembly phase of the mission had been choreographed years in advance by the robotics flight control team.

Day seven saw the third and final EVA of the mission, when Tanner and Stefanyshyn-Piper went outside the station and prepared the orbiting facility for the next assembly mission, STS-116, which was scheduled for December 2006. They installed a new transponder antenna and cleared away a section of the railway track on the new truss, so that it could be used by the Canadian-built Mobile Base System. This railcar construction platform transports Canadarm2 and other equipment across the length of the ISS truss.

Close-up view of a portion of the thermal protection tiles on Space Shuttle Discovery's during STS-114 in 2005 (Credit: NASA)

MacLean rounded out his mission by participating in an innovative Earth-observation project that could only be done from a unique platform in space like the ISS. From this 400-km-high vantage point, MacLean snapped hundreds of digital images of Canadian geological features. Scientists matched his snapshots with satellite data to shed some light on the impact of deforestation and global warming on environmental conditions in the country.

Once the remaining maintenance work and all the preparations for the next assembly mission were completed, the crew undocked on day nine and began preparing the Shuttle for their return flight home three days later.

On day ten, MacLean controlled Canadarm to pluck the boom extension out of Atlantis' cargo bay. The crew then conducted a final visual check-up for any possible on-orbit thermal tile damage to the vehicle, and beamed images back to ground control for inspection.

A Canadian space milestone

Circling over 400 km above our planet, the ISS is the most ambitious engineering project ever undertaken and represents an unprecedented international effort between the partner nations.

Right from the start, Canada has had a leading role in this great endeavour. MacLean and his crewmates built on the extensive heritage of Canadian know-how and innovation already contributed, and STS-115 is a milestone for Canada's space program in that it showcases the most Canadian involvement in ISS assembly to date. Canada's first spacewalker, Chris Hadfield, helped attach the newly completed Canadarm2 onto the station in 2001, while the first set of solar panels were delivered by Canadian veteran astronaut Marc Garneau in his third flight to space in 2000.

Chris Hadfield is the first Canadian to have walked in space (Credit: NASA)

This was the first mission dedicated to ISS assembly since the Columbia disaster in 2003, which temporarily grounded the remaining orbiters and suspended construction.