Some Glitches Arise, Requiring Fourth Spacewalk, Longer Mission

Crew members from Space Shuttle Discovery (STS-116) installed a large component on the International Space Station (ISS) and set about rewiring it from the temporary circuitry that the ISS has used for years, moving to a permanent wiring arrangement.

The work at first was parceled out among three scheduled extravehicular activities, or spacewalks, by astronauts.

But a glitch where a solar array electrical generating unit refused to retract fully compelled crew members to make a fourth spacewalk at 1:47 p.m. ET today.

Mission specialists Robert Curbeam, on his fourth spacewalk of the mission, and European astronaut Christer Fuglesang, on his third, will execute the EVA. They’ll work on balky grommets and perhaps try shaking the partially-folded solar array to persuade it to close completely into the blanket box.

Engineers investigating difficulties with fully retracting the port-side solar array wing of the ISS P6 Truss believe a guide wire may be snagged in a swiveling grommet on one of the array’s panels.

The solar array has been fully extended for six years in the harsh environment of space, with its alternating sizzling heat and frigid cold, and it came as no surprise that the array wouldn’t fold easily.

The array remained almost halfway retracted as it has been since Wednesday.

Station flight controllers commanded the array through a series of “wiggle” tests, swiveling the kinked wing 10 degrees at a time repeatedly to see if that would help the situation by getting guide wires to move freely.

Curbeam and Fuglesang spent last night in the Quest airlock for the pre-spacewalk campout. During the campout, the pressure is lowered in the airlock to the pressure normally found on at Earth 10,000 feet above sea level. The procedure protects against decompression sickness as Curbeam and Fuglesang go to the even lower pressure of spacesuits on Monday.

With the added spacewalk, the STS-116 crew’s stay at the station has been extended to Tuesday. Undocking is now set for 5:09 p.m ET. Landing is now targeted for 3:55 p.m. Friday at Kennedy Space Center, Fla., where the mission originated.

To begin the tasks, Curbeam and Fuglesang walked into the void of space last week. They moved to install a new component of the ISS girder-like truss.

The component, called the P5 spacer, weighs two tons down in the gravity on Earth, and is the fifth truss segment added to the port side of the station.

The addition of the P5 sets the stage for relocation of the P6 truss and its set of solar arrays. The P6 will be moved from its current location on the top of the Destiny Laboratory to the P5 during a future mission.

From inside the space station, Mission Specialist Joan Higginbotham was given the task of using the ISS robotic arm to move the new segment with only inches of clearance into its installation position. Outside, the spacewalkers’ job was to guide Higginbotham with visual cues.

Following the choreographed script, with the segment in place, Curbeam and Fuglesang got the job of bolting it to its permanent position, finalizing installation with power, data and heater cable connections. Pilot Bill Oefelein coordinated the spacewalk. All the spacewalks are emanating from the ISS Quest Airlock.

Also, the STS-116 and Expedition 14 crews continue joint operations.

Some other glitches arose, but nothing to endanger the crew or mission completion.

For example, no damage was found on the orbiter vehicle after its ascent from Kennedy Space Center Dec. 9. (Please see Space & Missile Defense Report, Monday, Dec. 11, 2006, page 1.)

After docking with the ISS, Discovery continued to maintain the orientation of both the station and shuttle using the shuttle steering jets, a function it began performing during preparations for the spacewalk on Thursday.

Originally, control of the station’s orientation was to be transferred back to the space station gyroscopes late Thursday after the spacewalk tasks were completed and station systems powered up. However, problems were experienced as that transfer was attempted.

Flight controllers believe the problems were due to a higher-than-usual amount of atmospheric drag currently experienced by the station due to recent solar activity.

This is all part of a tricky electrical ballet during which part of the space station power circuitry has to be shut down, temporarily leaving the station dependent only upon the remaining systems.

The space station has grown gradually over many years, as the huge space shuttles truck gargantuan components into space, and they are bolted together as the ISS streaks along at 17,500 miles an hour hundreds of miles above Earth.

Thus far, the total weight of the ISS if it were on Earth as of September was 454,240 pounds.