A milestone mission, long delayed, awaited the STS-117 crew.
The International Space Station would finally extend its wings fully with the installation of the first of two solar arrays to the end of the starboard truss, forming the station’s planned “H”-shaped configuration.
But weather at Cape Canaveral would present one more delay.
Thunderstorms are normal and frequent in Florida. With Atlantis on the pad, a storm rolled through on February 26, 2007, about three weeks before her scheduled launch. The storm dropped golf-ball sized hail, pummeling the upper External Tank and causing minor damage to 26 of the Orbiter’s tiles. Most of the Orbiter’s critical tiles were covered by the Rotating Service Structure and saved from impacts.
The stack had to be rolled back to inspect and repair the ET foam insulation. The repair was vital not only to keep the launch vehicle’s cryogenic propellants from evaporating rapidly during fueling but, after the loss of Shuttle Columbia, no opportunity for foam loosened by the hailstorm would be tolerated.
Repairs took three months. By May 15, the stack was returned to the pad, now sporting a distinctive spotted appearance on the External Tank from the hailstones, where minor impacts made there were not considered a vehicle threat.
STS-117 delays pushed back much of the year’s flight schedule. STS-118 was to fly in March, but now had a June 8 launch date.
Without the S3-S4 truss on 117, the planned STS-118 launch could not happen, nor could two later flights, all related to truss and solar array installations and moves.
STS-117’s launch on June 8, 2006 was thankfully uneventful as launches go.
The S3-S4 truss also carried a new solar array with its Solar Alpha Rotary Joint (SARJ). Like its counterpart on the P3-P4 truss, added on STS-115, the SARJ would allow the first starboard array to rotate, angling itself to the sun for maximum power production.
Atlantis carried the heaviest station assembly payload ever at 16,183 kilograms (35,677 lb).
Included in the crew was a replacement for outgoing Expedition 15 member Sunita Williams: Clayton C. Anderson, on his first spaceflight.
Once in orbit, Atlantis began a standard check of its thermal protection system using the Orbiter Boom Sensor System (OBSS), which detected a minor but concerning problem.
Over the years, most of the Orbiter fleet’s low-temperature silica TPS tiles located on the upper fuselage were replaced by thermal protection blankets. These larger, flexible blankets greatly reduced post-flight servicing time and effort.
Discovered by the crew on one of the Orbiter’s orbital maneuvering system (OMS) pods, a corner of a thermal blanket had separated from the tiles nearby on ascent.
Thankfully, the blanket issue was not in a critical heat location. Plans for repair of the blanket after docking with the station began with NASA’s mission management team as they cleared Atlantis to continue the rendezvous. If the pitch-roll maneuver procedure in inspecting the Orbiter by station crews revealed any additional or severe TPS damage, Atlantis would have the option of safe haven mode if the need arose.
Atlantis arrived at the station two days later on June 10. The now-routine roll pitch maneuver began, with additional TPS inspection by station crews ultimately revealing no further issues.
Flight day 4 began the first of three scheduled spacewalks by James Reilly and John Olivas. Before the EVA could start, a significant issue developed when the station’s attitude control system, the Control Moment Gyroscopes, went offline. The station was free-drifting as a result for about an hour before control was returned.
Before EVA 1, the new S3/S4 truss was released from its payload bay launch restraints, lifted up with the Orbiter’s manipulator arm and mated to the station. Canisters that held the new arrays were moved into their deployment position for activation on the following day.
Atlantis was notified that their mission would gain an extra two days and a fourth spacewalk. The extra time would make up for any assembly catch-up while also allotting time for a repair of the port OMS thermal blanket.
The crews would need that extra time. The station had more surprises in store that would slow down additional assemblies.
Flight day 5 began a slow, careful deployment of the new solar arrays.
Again, the station itself fought the mission. The Russian Segment, with computers in the Zvesda module that controlled station attitude, went offline, leaving the station adrift again as the control-moment gyroscopes stopped working properly. Work began to restore some station attitude control to the gyroscopes, which was completed by the end of the day. But more work on the computers would be required.
Patrick Forrester and Steven Swanson began EVA 2 on Flight Day 6 to tend to the Solar Array Rotary Joint (SARJ) on the S3/S4 truss which allowed the full array to rotate with the sun. However, a control mechanism was wired backwards. As a cautionary measure, one of the locking mechanisms used to safe the array on ascent was left in place.
On Flight Day 7, the ISS control computers failed again. As work began to get these computers operating, Shuttle crews began retraction of the P6 array, no longer needed with the S3/S4 in place. As with a previous mission, array retraction was slow because of folding issues. They managed to get half of the array folded away so that EVA 3 could proceed the following day. Atlantis was pressed into service to use its maneuvering thrusters to keep the station at a suitable orientation while the ISS attitude issues were worked out.
Things finally were going the crews’ way by Flight Day 8. Astronauts Reilly and Olivas set out on EVA 3 on initially separate tasks. As Reilly installed a hydrogen vent to aid the Destiny module’s oxygen generation system, Olivas was connected to the Shuttle robotic arm and maneuvered in place to fix the damaged OMS thermal blanket. Reilly was also tasked to disconnect some electrical cables as part of the station attitude control issues, hoping that any interference believed coming from the connectors would no longer affect the station computers. Isolating the computer issues were enough to keep the station oriented, but secondary systems were still not trusted.
Together, the two astronauts with others in the station succeeded in completing the S6 array retraction. The S6 truss would be moved on a later mission.
Flight Day 9 was left to supplies transfer and light work duties as the crews caught their breath and prepared for the final EVA. Russian engineers on the ground with the crews were finally able to stabilize the ISS attitude control computers and systems on that day.
Flight Day 10 brought the fourth bonus EVA. Spacewalkers Swanson and Forrester completed the SARJ work, removing interlocks to allow the new truss to fully rotate. Work on a new camera for viewing the exterior of the Quest airlock was done, along with many get-ahead tasks that would make later EVA assembly work easier on following missions.
With a day off for the crews on Flight Day 11, Atlantis said goodbye once more to the ISS, departing the station on June 19.
A parting shot of the station showed it finally appearing more like its final form, the “H” shape bright in the sky.
Atlantis was to deorbit and touchdown on June 21, but, as with their launch attempts, the Kennedy Space Center’s weather would fight the Orbiter’s return, with unacceptable winds. Landing was scrubbed and rescheduled to June 22, but again, Florida’s weather conspired against the crew with thundershowers in the area. Ideal landing conditions existed at Edwards Air Force Base, so the crews made their touchdown there.
The next mission for the ISS assembly would provide a replacement station gyroscope and a truss extension for S5.
But STS-118 would also bond memories of what could have been, with echoes of NASA’s most tragic losses in Space Shuttle history reverberating throughout the mission.
Next mission: Assembly 13A.1.