Spaceflight Now





Station glitch could prompt spacewalk this week
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: April 13, 2010


Bookmark and Share

Flight controllers have been unable to re-open a jammed valve in a nitrogen tank assembly needed to pressurize one of the International Space Station's two ammonia coolant loops. Faced with increasing temperatures that could force flight controllers to shut down half the station's systems later this month, NASA managers are considering the possibility of extending Discovery's mission by another day and adding a fourth spacewalk to install a spare nitrogen tank assembly. Another option, assuming the valve defies ongoing troubleshooting efforts, would be to defer the replacement work until after Discovery departs, using space station astronauts instead.

"Right now, we are trying to put together the plan, we're looking at work we had done for this on previous flights and trying to put the procedures together," said space station Flight Director Ron Spencer. "The earlier the decision the better. We're still trying to finalize exactly when we have to have that decision. But it's no later than tomorrow."

The current flight plan calls for the Discovery astronauts to move a large cargo module back to the shuttle on Thursday. A final heat shield inspection would be carried out Friday before undocking Saturday and landing back at the Kennedy Space Center Monday.

If a spacewalk is added to the flight, it likely would be carried out Saturday. Under that scenario, undocking would be re-targeted for Sunday and landing would be delayed to Tuesday morning.

Spencer said the astronauts had been informed of the possibility of an additional spacewalk, but he stressed no final decisions had been made.

The space station features two independent coolant loops that use ammonia circulating through huge radiators to dissipate the heat generated by the station's electronic systems. Each loop is fed by a large tank of ammonia that includes an internal bellows pressurized by nitrogen. That pressurization system allows the loops to handle the periodic expansion and contraction of the ammonia coolant due to temperature changes in orbit.

The ammonia tank on the left side of the station's power truss, part of coolant loop B, was replaced by an earlier shuttle crew. The Discovery astronauts replaced the tank on the right side in coolant loop A. Other than alignment problems and trouble getting a few bolts to engage, the tank swap went well and there were no indications of any major issues. But flight controllers were unable to re-open the main nitrogen valve needed to re-pressurize coolant loop A.

Overnight, engineers turned on heaters to warm the valve up, they tried cooling the valve and even adjusting the back pressure in the system. Nothing worked, and the valve remains closed.

"So far, we have been unable to re-open that valve," said Spencer. "We opened that valve on flight day one to get the system to a higher pressure before we took the ammonia tank out and then on flight day four, we closed that valve so we could vent the jumpers for the crew to do the EVA disconnections.

"And since then, we've been unable to re-open that valve, which we first attempted to do after the EVA yesterday. So folks are continuing to troubleshoot that problem on the ground to see if there's other things we can try. In the meantime, we are also pursuing work on EVA options to possibly replace the nitrogen tank assembly. Options we are working on include possibly extending the mission by one day and adding a fourth EVA or to perform a (station crew) EVA if the continued ground troubleshooting is unsuccessful.

"So we'll keep working this problem. We're also working to see how long we can fly station in this configuration before we'd have to do an EVA. So there's a lot of work going on right now to figure out how to fix this problem, figure out what our risk is with this problem and how long we have until we have to correct it."

The issue is pressing because of the changing orientation of the station's orbit with respect to the sun.

Later this month, that so-called "beta-angle" between the sun and the plane of the station's orbit will increase to the point where more sunlight will fall on the station for longer periods. Without pressurization, coolant loop A would not be able to compensate for the expansion of the ammonia coolant and likely would have to be shut down. Shutting down a coolant loop would force flight controllers to shut down half the station's electrical systems.

Complicating the issue for NASA, coolant loop A provides cooling for the electronics associated with the station's robot arm. If coolant loop A is shut down for any reason, a spacewalk using the arm would not be possible, which may increase the pressure to add a spacewalk to Discovery's mission.

Spencer said two spare nitrogen tank assemblies are mounted on the station and available for use if needed, one on the left side of the power truss and one on the right. The hardware making up coolant loop A is on the right side of the truss.

One advantage of adding a nitrogen tank swap out to Discovery's mission is that spacewalkers Rick Mastracchio and Clay Anderson have already trained to do similar tasks with the ammonia tank.

"This task has a lot of similarities associated with the ammonia tank replacement," Spencer said. "The EVA crew on this mission are familiar with the fluid connections, the electrical connections and handling a large (component) in space. The nitrogen tank assembly is not as big as the ammonia tank assembly, but it's still fairly large. So there is an experience base there that we may choose to take advantage of if EVA is necessary."

On the downside, he said, an additional spacewalk would put a certain amount of stress on a crew that already has worked through three grueling spacewalks. The mission already has been extended one day to permit a late heat shield inspection before Discovery's undocking.

"The concerns are, number one, mission length," Spencer said. "We already have a 13-day mission with three EVAs and in this case, it would be the same EVA crew going out to do the fourth EVA. So, we are concerned a little bit about crew fatigue. Normally, if we have four EVAs on a mission, normally it's not the same crew doing all four of them.

"Also, of even bigger concern is procedure shelf life. We spend months developing the procedures for the EVAs we plan to do and we also have procedures canned for certain contingencies. But this is not one of those we had canned as a contingency to do during a shuttle mission. Luckily, we've done these nitrogen tank change outs twice before and so we'll be looking at those procedures. ... We want to make sure we get it right if we're going to go out there."

Spaceflight Now Plus
Additional coverage for subscribers:
VIDEO: MONDAY EVENING'S FLIGHT DIRECTOR INTERVIEW PLAY

VIDEO: FLIGHT DAY 8 HIGHLIGHTS MOVIE PLAY
VIDEO: MONDAY AFTERNOON'S MISSION STATUS UPDATE PLAY
VIDEO: RUSSIAN PRESIDENT CALLS THE SPACE STATION PLAY
VIDEO: SPACE STATION CREW MARKS COSMONAUTICS DAY PLAY
VIDEO: ABC, MSNBC, FOX NEWS AND KUSA-TV INTERVIEWS PLAY
VIDEO: JAXA EVENT WITH JAPANESE ASTRONAUTS PLAY
VIDEO: SUNDAY EVENING'S FLIGHT DIRECTOR INTERVIEW PLAY

HIGH DEFINITION TV DAY 7: MEAL TIME IN ZVEZDA PLAY
HIGH DEFINITION TV DAY 7: GRUELING 7.5-HOUR EVA FINSHES PLAY
HIGH DEFINITION TV DAY 7: VENTURING OUTSIDE THE STATION PLAY
HIGH DEFINITION TV DAY 7: GETTING READY FOR ANOTHER EVA PLAY
HIGH DEFINITION TV DAY 7: OLD CREW SLEEP BUNK REMOVED PLAY
HIGH DEFINITION TV DAY 7: TRANSFERS AND MORE TRANSFERS PLAY

VIDEO: FLIGHT DAY 7 HIGHLIGHTS MOVIE PLAY
VIDEO: CREW'S HOME MOVIES FOR FLIGHT DAY 7 PLAY
VIDEO: SUNDAY MORNING'S MISSION STATUS BRIEFING PLAY
VIDEO: FINALLY WINNING THE BATTLE WITH TANK BOLTS PLAY
VIDEO: NEW COOLANT TANK MANEUVERED INTO POSITION PLAY
VIDEO: DEPLETED AMMONIA TANK REMOVED FROM STATION PLAY
VIDEO: STEP-BY-STEP WALKTHROUGH OF EVA NO. 2 PLAY
VIDEO: PREVIEW OF FLIGHT DAY 7 ACTIVITIES PLAY
VIDEO: SATURDAY EVENING'S FLIGHT DIRECTOR INTERVIEW PLAY

HIGH DEFINITION TV DAY 6: LIFE OF A SHUTTLE ASTRONAUT PLAY
HIGH DEFINITION TV DAY 6: "BUCKET BRIGADE" ON THE STATION PLAY
HIGH DEFINITION TV DAY 6: WORF INSTALLED IN DESTINY LAB PLAY

VIDEO: FLIGHT DAY 6 HIGHLIGHTS MOVIE PLAY
VIDEO: CREW'S HOME MOVIES FOR FLIGHT DAY 6 PLAY
VIDEO: SATURDAY MORNING'S MISSION STATUS BRIEFING PLAY
VIDEO: SCIENCE RACK INSTALLED BY JAPANESE ASTRONAUTS PLAY
VIDEO: NAVAL POSTGRADUATE SCHOOL EDUCATIONAL EVENT PLAY
VIDEO: CBS AND NEBRASKA MEDIA INTERVIEWS WITH CREW PLAY
VIDEO: SMOKE ALARM IN THE ZVEZDA SERVICE MODULE PLAY
VIDEO: PREVIEW OF FLIGHT DAY 6 ACTIVITIES PLAY

VIDEO: MISSION EXTENSION NEWS FROM FLIGHT DIRECTOR PLAY

HIGH DEFINITION TV DAY 5: SPACEWALKERS RETURN TO AIRLOCK PLAY
HIGH DEFINITION TV DAY 5: UNLOADING THE LEONARDO MODULE PLAY
HIGH DEFINITION TV DAY 5: STATION'S NEW EXERCISE MACHINE PLAY
HIGH DEFINITION TV DAY 5: OPERATORS OF THE ROBOTIC ARM PLAY
HIGH DEFINITION TV DAY 5: SPACEWALKERS FREE AMMONIA TANK PLAY

VIDEO: FLIGHT DAY 5 HIGHLIGHTS MOVIE PLAY
VIDEO: CREW'S HOME MOVIES FOR FLIGHT DAY 5 PLAY
VIDEO: STOWAGE RACKS MOVED INTO STATION PLAY
VIDEO: NEW LABORATORY FREEZER FOR KIBO PLAY
VIDEO: FRIDAY MORNING'S MISSION STATUS BRIEFING PLAY
VIDEO: RATE GYRO ASSEMBLY REMOVED FROM STATION PLAY
VIDEO: NEW AMMONIA TANK STOWED IN TEMPORARY SPOT PLAY
VIDEO: ANCHORING FIXTURE ATTACHED TO AMMONIA TANK PLAY
VIDEO: EXPERIMENT RETRIEVED FROM JAPAN'S SCIENCE DECK PLAY
VIDEO: STATION'S ROBOTIC ARM LIFTS TANK FROM SHUTTLE PLAY
VIDEO: NEW AMMONIA COOLANT TANK UNBOLTED FROM CARRIER PLAY
VIDEO: SPACEWALKER PREPS AMMONIA TANK IN SHUTTLE BAY PLAY
VIDEO: THE START OF MISSION'S FIRST SPACEWALK PLAY
VIDEO: STEP-BY-STEP WALKTHROUGH OF EVA NO. 1 PLAY
VIDEO: PREVIEW OF FLIGHT DAY 5 ACTIVITIES PLAY
VIDEO: THURSDAY EVENING'S FLIGHT DIRECTOR INTERVIEW PLAY
VIDEO: THURSDAY AFTERNOON'S MANAGEMENT TEAM UPDATE PLAY

VIDEO: FLIGHT DAY 4 HIGHLIGHTS MOVIE PLAY
VIDEO: RADIO AND TV INTERVIEWS WITH CREW PLAY
VIDEO: THURSDAY MORNING'S MISSION STATUS BRIEFING PLAY
VIDEO: LEONARDO MODULE ATTACHED TO SPACE STATION PLAY
VIDEO: STATION'S ARM GRAPPLES THE LEONARDO MODULE PLAY
VIDEO: NARRATED PREVIEW OF LEONARDO'S INSTALLATION PLAY
VIDEO: WEDNESDAY EVENING'S FLIGHT DIRECTOR INTERVIEW PLAY
VIDEO: WEDNESDAY AFTERNOON'S MANAGEMENT TEAM UPDATE PLAY

VIDEO: FLIGHT DAY 3 HIGHLIGHTS MOVIE PLAY
VIDEO: WEDNESDAY MORNING'S MISSION STATUS BRIEFING PLAY
VIDEO: SHUTTLE CREW WELCOMED ABOARD THE STATION PLAY
VIDEO: POST-DOCKING OF THE SHUTTLE BAY AND TAIL PLAY
VIDEO: DISCOVERY DOCKS TO THE SPACE STATION PLAY
VIDEO: SHUTTLE PERFORMS 360-DEGREE BACKFLIP PLAY
VIDEO: PREVIEW OF RENDEZVOUS AND DOCKING ACTIVITIES PLAY
VIDEO: OBJECT LOST FROM SHUTTLE TAIL DURING LAUNCH PLAY
VIDEO: TUESDAY AFTERNOON'S MANAGEMENT TEAM UPDATE PLAY
VIDEO: THE FULL STS-131 LAUNCH EXPERIENCE PLAY

VIDEO: FLIGHT DAY 2 HIGHLIGHTS MOVIE PLAY
VIDEO: TUESDAY MORNING'S MISSION STATUS BRIEFING PLAY
VIDEO: PREVIEW OF FLIGHT DAY 2 ACTIVITIES PLAY
VIDEO: NARRATED TOUR OF DISCOVERY'S PAYLOAD BAY PLAY
VIDEO: DESCRIPTION OF KU-BAND ANTENNA PROBLEM PLAY

VIDEO: FLIGHT DAY 1 HIGHLIGHTS MOVIE PLAY
VIDEO: SHUTTLE DISCOVERY BLASTS OFF! PLAY | HI-DEF
VIDEO: GO INSIDE MISSION CONTROL DURING LAUNCH PLAY
VIDEO: POST-LAUNCH NEWS CONFERENCE PLAY

VIDEO: LAUNCH REPLAY: VAB ROOF PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: PRESS SITE PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: PATRICK AFB PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: PAD PERIMETER PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: BEACH TRACKER PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: PAD CAMERA 070 PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: PAD CAMERA 071 PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: PLAYALINDA BEACH PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: PAD FRONT CAMERA PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: KSC WEST TOWER PLAY | HI-DEF

VIDEO: ASTRONAUTS LEAVE CREW QUARTERS PLAY | HI-DEF
VIDEO: CREW FINISHES GETTING SUITED UP PLAY | HI-DEF

VIDEO: NARRATED REVIEW OF SHUTTLE'S PREPARATIONS PLAY | HI-DEF
VIDEO: NARRATED REVIEW OF PAYLOADS' PREPARATIONS PLAY | HI-DEF
VIDEO: PREPARING AN EXTERNAL TANK FOR LAUNCH PLAY | HI-DEF

VIDEO: TIME-LAPSE OF GANTRY ROLLING BACK FOR LAUNCH PLAY
VIDEO: LAUNCH PAD'S SERVICE TOWER RETRACTED PLAY | HI-DEF
VIDEO: PAYLOAD BAY DOORS CLOSED FOR LAUNCH PLAY | HI-DEF
VIDEO: ASTRONAUTS INSPECT THE PAYLOAD BAY PLAY | HI-DEF

VIDEO: STS-131 MISSION PREVIEW MOVIE PLAY | HI-DEF
VIDEO: PRE-LAUNCH INTERVIEW WITH COMMANDER POINDEXTER PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH PILOT JIM DUTTON PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH RICK MASTRACCHIOPLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH METCALF-LINDENBURGER PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH STEPHANIE WILSON PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH NAOKO YAMAZAKI PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH CLAY ANDERSON PLAY

VIDEO: PRE-LAUNCH NEWS CONFERENCE PLAY
VIDEO: COUNTDOWN STATUS AND WEATHER OUTLOOK PLAY
VIDEO: PREVIEW OF DISCOVERY'S LAUNCH COUNTDOWN PLAY
VIDEO: ASTRONAUTS ARRIVE FOR LAUNCH PLAY | HI-DEF

VIDEO: FULL FLIGHT READINESS REVIEW NEWS BRIEFING PLAY
VIDEO: RECAP OF THE FLIGHT READINESS REVIEW PLAY | HI-DEF
VIDEO: HELIUM VALVE NO CONSTRAINT TO LAUNCH PLAY | HI-DEF
VIDEO: MANAGERS ASSESS ISSUES BEFORE FLIGHT PLAY | HI-DEF
VIDEO: UPDATE ON PRE-LAUNCH PREPS AT PAD 39A PLAY | HI-DEF

VIDEO: SPACEWALKING SUITS LOADED ABOARD PLAY | HI-DEF
VIDEO: INTERVIEW WITH STS-131 PAYLOAD MANAGER PLAY | HI-DEF
VIDEO: INTERVIEW WITH BOEING PAYLOAD MANAGER PLAY | HI-DEF
VIDEO: PAYLOADS DELIVERED TO LAUNCH PAD 39A PLAY | HI-DEF
VIDEO: TRANSPORT CANISTER ROTATED VERTICALLY PLAY | HI-DEF
VIDEO: LEONARDO PLACED INTO THE TRANSPORTER PLAY | HI-DEF
VIDEO: STATION'S NEW AMMONIA COOLANT TANK PLAY | HI-DEF
VIDEO: LEONARDO HATCH CLOSED FOR FLIGHT PLAY | HI-DEF
VIDEO: FILLING UP ONE OF THE SUPPLY RACKS PLAY | HI-DEF

VIDEO: CAN THE SHUTTLE PROGRAM AVOID LOOMING RETIREMENT? PLAY
VIDEO: WHAT ABOUT ADDING ONE MORE SHUTTLE MISSION? PLAY
VIDEO: FULL BRIEFING BY SHUTTLE AND STATION OFFICIALS PLAY
VIDEO: THE STS-131 MISSION OVERVIEW PRESENTATIONS PLAY
VIDEO: PREVIEW BRIEFING ON MISSION'S SPACEWALKS PLAY
VIDEO: THE ASTRONAUTS' PRE-FLIGHT NEWS BRIEFING PLAY

VIDEO: SHUTTLE EVACUATION PRACTICE PLAY | HI-DEF
VIDEO: CREW MODULE HATCH IS CLOSED PLAY | HI-DEF
VIDEO: ASTRONAUTS BOARD DISCOVERY PLAY | HI-DEF
VIDEO: CREW BRIEFED ON EMERGENCY PROCEDURES PLAY | HI-DEF
VIDEO: TEST-DRIVING AN EMERGENCY ARMORED TANK PLAY | HI-DEF
VIDEO: NIGHTTIME APPROACHES IN TRAINING AIRCRAFT PLAY | HI-DEF
VIDEO: ASTRONAUTS CHAT WITH REPORTERS AT PAD 39A PLAY
VIDEO: CREW ARRIVES FOR PRACTICE COUNTDOWN PLAY | HI-DEF

VIDEO: GANTRY PLACED AROUND DISCOVERY PLAY | HI-DEF
VIDEO: DISCOVERY REACHES PAD 39A PLAY | HI-DEF
VIDEO: OVERNIGHT ROLLOUT BEGINS PLAY | HI-DEF
VIDEO: SHUTTLE HOISTED FOR ATTACHMENT TO TANK PLAY | HI-DEF
VIDEO: CRANE ROTATES THE ORBITER VERTICALLY PLAY | HI-DEF
VIDEO: DISCOVERY MOVES TO ASSEMBLY BUILDING PLAY | HI-DEF

VIDEO: ASTRONAUTS VISIT THEIR SPACECRAFT PLAY | HI-DEF
VIDEO: CREW GOES INSIDE LEONARDO MODULE PLAY | HI-DEF

VIDEO: EXTERNAL TANK ATTACHED TO BOOSTERS PLAY | HI-DEF
VIDEO: FUEL TANK LIFTED INTO CHECKOUT CELL PLAY | HI-DEF
VIDEO: EXTERNAL TANK ARRIVES AT SPACEPORT PLAY | HI-DEF

VIDEO: DISCOVERY'S NOSE POD ATTACHED PLAY | HI-DEF
VIDEO: INSTALLING DISCOVERY'S MAIN ENGINES PLAY | HI-DEF
VIDEO: KSC'S SHUTTLE MAIN ENGINE SHOP PLAY | HI-DEF
VIDEO: GASEOUS NITROGEN TANK REMOVED PLAY | HI-DEF
SUBSCRIBE NOW



MISSION INDEX