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NASA rules out extra EVA for Discovery's spacewalkers
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: April 15, 2010


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Flight controllers have decided not to add a fourth spacewalk to the shuttle Discovery's mission to replace a nitrogen tank in the International Space Station's ammonia coolant system, concluding the system can safely operate for an extended period despite a stuck valve preventing normal pressurization. Astronaut Megan McArthur radioed the news to shuttle commander Alan Poindexter just after the crew woke up around 12:21 a.m. EDT.


Credit: NASA
 
"We have some big picture words for you on the plan this morning," she called from mission control. "The decision has been made to not perform a fourth EVA on this mission. Analysis shows the current ATA (ammonia tank assembly) config is OK for an extended period. Once everybody's awake and you've had some coffee, you can get with the ISS crew and call down on the big loop to the ISS MCC (mission control center) and they'll give you some more detailed words."

"OK, Megan, that sounds great, thanks a lot," Poindexter replied. "Again, we appreciate all the extra effort that went into quickly looking at that option. We're glad the station will be fine without the extra EVA here for a little bit. Thanks a lot."

A fourth spacewalk would have required a one-day mission extension and delayed Discovery's undocking from Saturday to Sunday. As it now stands, the Discovery astronauts will press ahead with their normal flight plan, undock on Saturday and land back at the Kennedy Space Center early Monday.

The major item on the shuttle crew's agenda Thursday was wrapping up equipment transfers between the station and the Leonardo cargo module that was carried up aboard Discovery and attached to the lab complex the day after docking.

The Italian-built module was launched with more than 17,000 pounds of equipment and supplies for the space station. For its return, it will be packed with nearly 11,000 pounds of equipment, trash and no-longer-needed material.

The astronauts plan to leave the cargo module for the last time around 3 a.m. Around 7:30 a.m., astronaut Stephanie Wilson and shuttle pilot James Dutton will grapple the module with the station's robot arm. A little more than an hour later, the common berthing mechanisms will disengage and Wilson will move the cargo module back to the shuttle's cargo bay. The module should be locked in place by around 10 a.m.

The astronauts are scheduled to go to bed around 4:20 p.m., just after President Barack Obama delivers a major space policy speech at the Kennedy Space Center. During an orbital news conference Wednesday, Poindexter said the crew was following news coverage of the president's visit but had not made plans to watch any of the proceedings.

At the Johnson Space Center in Houston Wednesday, engineers spent the day carrying out a detailed analysis to determine whether a fourth spacewalk should be added to Discovery's mission to replace a nitrogen tank in the space station's external cooling system.

One of the primary goals of Discovery's mission was to replace one of two ammonia coolant tanks on the station's main power truss. Before staging the first of three spacewalks to swap out the tanks, flight controllers sent commands to close a nitrogen pressurization vent valve. After the new tank was installed, engineers attempted to reopen the nitrogen valve but it failed to respond and appears to be stuck in the closed position.

The nitrogen is used in a bellows system to maintain the proper pressure when the ammonia coolant expands due to solar heating and contracts due to cooling. Solar heating currently is increasing as the angle between the sun and the plane of the station's orbit changes. Without the nitrogen pressurization system, engineers worried there was a chance coolant loop A could be damaged due to the ammonia's unchecked expansion.

Before that happens, flight controllers could simply shut down electrical systems and deactivate coolant loop A. But that last-resort option would cripple the space station.

As it turned out, an exhaustive analysis showed coolant loop A can handle the expected temperature increases over the next few weeks even without normal pressurization. That will allow the station crew to defer swapping out the nitrogen tank until a quieter period when it will have less impact on station operations.

"We could possibly do a (station crew) spacewalk between space shuttle flights, so maybe we go do a spacewalk before STS-132 (the next flight) that's coming up in May," said Flight Director Ed Van Cise. "Maybe there's enough flexibility for us to do it after STS-132, maybe the engineers and the program managers determine the best thing to do is actually try to do something during the STS-132 mission because there are more people, more resources available."

Additional details will be posted as they become available.

Here is an updated timeline of today's activity (in EDT and mission elapsed time; includes revision J of the NASA television schedule):


EDT........DD...HH...MM...EVENT

04/15
12:21 AM...09...18...00...Crew wakeup
01:51 AM...09...19...30...ISS daily planning conference
02:36 AM...09...20...15...Middeck transfers
02:51 AM...09...20...30...Cargo module (MPLM) egress
03:06 AM...09...20...45...MPLM deactivation
03:26 AM...09...21...05...MPLM vestibule demate
04:56 AM...09...22...35...MPLM vestibule depress
05:21 AM...09...23...00...Education robotics taping (shuttle arm)
05:51 AM...09...23...30...Education robotics taping (station arm)
05:51 AM...09...23...30...EVA transfer to shuttle
06:11 AM...09...23...50...Crew meals begin
07:26 AM...10...01...05...Station arm (SSRMS) grapples MPLM
08:41 AM...10...02...20...MPLM uninstall
09:56 AM...10...03...35...MPLM install in payload bay
10:11 AM...10...03...50...SSRMS ungrapples MPLM
10:30 AM...10...04...09...Mission status briefing on NTV
11:11 AM...10...04...50...Heat shield inspection procedures review
01:30 PM...10...07...09...Presidential visit to KSC; preempts NTV
01:41 PM...10...07...20...Evening planning conference
03:51 PM...10...09...30...ISS crew sleep begins
04:21 PM...10...10...00...STS crew sleep begins
06:15 PM...10...11...54...NTV mission coverage resumes
07:00 PM...10...12...39...Daily highlights on NTV
07:45 PM...10...13...24...Flight director update on NTV

04/16
12:21 AM...10...18...00...Crew wakeup

Spaceflight Now Plus
Additional coverage for subscribers:
VIDEO: NASA RULES OUT EXTRA EVA FOR DISCOVERY CREW PLAY
VIDEO: PREVIEW OF FLIGHT DAY 11 ACTIVITIES PLAY
VIDEO: WEDNESDAY EVENING'S FLIGHT DIRECTOR INTERVIEW PLAY

VIDEO: FLIGHT DAY 10 HIGHLIGHTS MOVIE PLAY
VIDEO: PLANNING UNDERWAY FOR POSSIBLE FOURTH EVA PLAY
VIDEO: EDUCATIONAL EVENT WITH NORTH CAROLINA SCHOOL PLAY
VIDEO: WEDNESDAY MORNING'S MISSION STATUS BRIEFING PLAY
VIDEO: JOINT SHUTTLE AND STATION CREW NEWS CONFERENCE PLAY
VIDEO: TUESDAY EVENING'S FLIGHT DIRECTOR INTERVIEW PLAY

VIDEO: FLIGHT DAY 9 HIGHLIGHTS MOVIE PLAY
VIDEO: CREW'S HOME MOVIES FOR FLIGHT DAY 9 PLAY
VIDEO: TUESDAY MORNING'S MISSION STATUS BRIEFING PLAY
VIDEO: ROBOT ARM MOVES OLD TANK SHUTTLE PAYLOAD BAY PLAY
VIDEO: SPACEWALKERS REMOVE HANDLING BAR FROM OLD TANK PLAY
VIDEO: UMBILICALS HOOKED UP TO NEW AMMONIA TANK PLAY
VIDEO: PREVIEW OF FLIGHT DAY 9 ACTIVITIES PLAY
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
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