Perched on the end of the space station's robot arm directly below the international lab complex, astronaut Clay Anderson threw a refrigerator-size ammonia tank overboard today, pushing the 1,400-pound early ammonia servicer away behind the station to clear the way for future assembly work.

Credit: NASA TV

"We've got good downlink, we're solid here on the ground, everybody is go," astronaut Chris Cassidy radioed from mission control in Houston. "Jettison on your call."

"All right, let's give her a whirl, shall we?" Anderson replied. "All right, leaning back... here goes forward, jettison! It's (tumbling) about 180 degrees in 10 seconds and it's mostly a negative pitch with a slight right roll bias."

"Nice work," Cassidy said.

Dramatic video from the station showed the ammonia tank, clad in white insulation blankets, slowly tumbling away behind the station as the outpost sailed high above the Atlantic Ocean off the southeast coast of Brazil. Anderson's goal was to impart a departure velocity of about 1 mph.

"We're looking at all the camera views and we think you had a great throw, looks right down the middle," Cassidy reported.

"Well in that case give (Houston Astros pitchers) Brad Lidge and Roy Oswalt a call and tell 'em I just palmed a 17,500-mile-an-hour fast ball."

NASA originally planned to bring the no-longer-needed ammonia tank down on a space shuttle, but a 2004 decision to complete the station and retire the shuttle in 2010 forced NASA to reduce the number of planned flights and to come up with an alternative for getting rid of the EAS.

The ammonia tank was launched in 2001 to provide additional coolant in case of a leak in an interim thermal control system that supported the initial stages of station assembly. The ammonia was never needed and the lab's permanent cooling system is now in operation.

The EAS was mounted on the P6 solar array truss segment. Those solar panels were retracted during the last two shuttle missions so the truss segment can be repositioned on the far left side of the station's main solar array truss in October. But the massive EAS must be removed before P6 can be relocated.

And so Anderson, positioned head down on the end of the fully extended robot arm, sent the ammonia tank on its way.

"It's pretty majestic looking floating out there," Anderson observed as it floated away in the distance.

Flying through the extremely thin atmosphere present in low-Earth orbit, the EAS will slowly lose altitude, but it will take nearly a year for the orbit to "decay" enough to reach the point where the tank will begin burning up. Even so, the structure will not completely burn up and at least some debris is expected to hit the ground.

"We don't know precisely when it will re-enter," lead flight director Bob Dempsey said last week. "The EAS, we do expect that some small parts of it will survive re-entry. We have looked at the risk of that and we believe it's reasonable. ... We will try to provide as much information as possible about the timing and the location of where that re-entry will occur. It likely would be over water, but ... it's too hard to predict exactly at this point."

Concerned about future close encounters between the station and the ammonia tank and a video mast mounting plate that also was jettisoned today, flight controllers are planning a major reboost maneuver this evening to raise the altitude of the lab complex from 207 to 212 statute miles. Along with providing plenty of clearance, the maneuver also will set up the proper rendezvous conditions for a Progress supply ship and the shuttle Endeavour, scheduled for launch Aug. 7.

"It would very likely eventually come back in the same orbital vicinity of the space station," Dempsey said of the ammonia tank. "So to prevent any possibility of recontact, we will be doing a reboost of the entire space station about 10 hours after the jettison. This will ensure that we remain above it. The EAS will slowly decay over time and it should have a lifetime on orbit of about 300, 330 days and it'll eventually re-enter and most of it should burn up."

Today's spacewalk began with Anderson and Expedition 15 commander Fyodor Yurchikhin switching their spacesuits to internal battery power at 6:24 a.m. EDT as they floated in the Quest airlock module.

The spacewalkers installed a video camera support mast on the left side of the space station's solar array truss. Yurchikhin then replaced a faulty remote power control module while Anderson reconfigured cables in the Z1 truss to clear the way for release of the ammonia tank.

Then Anderson, perched on the end of the space station's fully extended robot arm, tossed a 212-pound piece of no-longer-needed flight support hardware overboard as the lab complex sailed 220 miles above the south Atlantic Ocean.

"Pretty amazing," Anderson marveled a few minutes before he released the smaller piece of gear. "Who'd have thought a kid from Nebraska would be doing something like this?"

With the station flying backward to provide plenty of clearance, Oleg Kotov, operating the robot arm from inside the Destiny lab module, positioned Anderson head down directly below the station. Once in position, Anderson rocked back and then forward, pushing the flight support equipment away to the rear of the station with his arms.

"I'm leaning back right now," he narrated. "At least I think I am. All right. I'm going to start rocking forward... (garble) jettison!" he grunted as he shoved the support platform away.

"Good jettison," Yurchikhin confirmed.

Spectacular video from the station showed the flight support equipment platform slowly falling away behind the station against the cloudy Earth below, tumbling end-over-end every few seconds. It was a dress-rehearsal of sorts for the later ammonia tank jettison.

"It looked like a fantastic throw from here," mission control radioed a few minutes later.

"Great, glad to be of service," Anderson replied. "I'll be sending my bill in the mail for trash disposal."

After the ammonia tank was thrown overboard, the spacewalkers cleaned the docking port seals on the lower hatch of the Unity module and accomplished other get-ahead tasks. The EVA ended at 2:06 p.m., completing the 88th spacewalk devoted to station assembly and maintenance since construction began in 1998 and the 11th so far this year.

"I think it's a very important day today because not only are we working together as a good crew on board, but this was the first day and the first time that a Russian cosmonaut operated, in orbit, the robotic manipulator," Anderson said as he was wrapping up arm operations. "And I think Oleg demonstrated to everyone what an outstanding arm operator he is and what an outstanding cosmonaut he and Fyodor both are. So my hat goes off to both of them and I'm very appreciative of their work. Thanks."

"Well said, Clay, we couldn't agree with you more," Cassidy replied from mission control in Houston.

Seventy astronauts, cosmonauts and international station and shuttle fliers have now logged 544 hours and 44 minutes of EVA time building and maintaining the space station. This was the third spacewalk for Yurchikhin, pushing his total to 18 hours and 43 minutes, and the first for Anderson.