US astronauts begin key ISS repair spacewalk

Aug 07, 2010

Two International Space Station astronauts set out Saturday on the first of two spacewalks to fix a cooling pump that dramatically failed last week.

ISS astronauts will need at least two to remove the failed ammonia pump unit and replace it with a new one after the device failed a week ago.

Doug Wheelock and Tracy Caldwell Dyson slept in the Quest airlock module overnight to accommodate their bodies to a different pressure and were awakened at about 2:00 am (0600 GMT) to begin final preparations for their work.

They activated battery power and other life-support systems inside their spacesuits, and opened the hatch at 7:19 am (1119 GMT), a procedure that officially marked the beginning of their seven-hour walk.

The beginning of the walk was slightly delayed because of what was described by US space officials as a "communication problem" inside Caldwell Dyson's helmet. The problem has been successfully resolved, the official said.

The first spacewalk will focus on removing the ammonia pump module that failed last Saturday and putting its replacement in place, according to officials from the National Aeronautics and Space Administration.

A second spacewalk is planned Wednesday to connect fluid ammonia lines to the replacement pump.

Mission managers plan a final review of that plan early next week, incorporating updated information on the station's configuration after the first spacewalk, NASA officials said.

The spacewalks are challenging because the crew will be handling ammonia lines at full operating pressure, which makes the lines stiff during reconnection and mating, experts warned.

The timeline for the spacewalk will require numerous "break-out points" to ensure adequate time to complete decontamination procedures if the crew comes in contact with ammonia.

Once the failed unit has been removed, the two astronauts will have to move a 780-pound (355 kilograms) spare unit around 30 feet (10 meters) from the opposite side of the truss for insertion into the gap left by the defective pump module.

"This is a big, unwieldy object, so maneuvering it around and handing it off to crew members... could take some time and a lot of focus," Courtenay McMillan, the spacewalk flight director for the expedition, told reporters earlier in the week.

But robotics experts have devised procedures that will be used by station crew member Shannon Walker to guide the station's robotic arm, Canadarm2, from the robotics workstation in the Destiny Laboratory.

She will move Wheelock into position to swap the failed unit with the spare unit, stored on an external stowage platform.

That spare parts carrier is attached to the Quest airlock that Wheelock and Caldwell Dyson will use to exit and reenter the station.

The crew faced a very tight lead time for such a tricky spacewalk -- less than a week when NASA usually takes two weeks to prepare for a spacewalk to fix a "Big 14 failure," when a major unit stops working.

If the second of the two ISS cooling units fails -- a highly unlikely scenario, according to NASA -- then the ISS astronauts would no longer be able to cool most of space station components.

The crew would not be in danger however because they could move to the Russian segment of the ISS, which has its own cooling system.

Astronauts tried to reactivate the pump module after Saturday's failure, but the circuit breaker tripped, said.

Explore further: SDO captures images of two mid-level flares

add to favorites email to friend print save as pdf

Related Stories

NASA delays spacewalks to fix ISS cooling pump

Aug 05, 2010

NASA on Thursday pushed back by one day the first of two spacewalks to fix a pump module on the International Space Station's (ISS) cooling system that dramatically failed last week. ...

Space station cooling system suddenly shuts down

Aug 01, 2010

(AP) -- Half of the International Space Station's cooling system suddenly shut down during the weekend, forcing the astronauts to power down equipment and face the likelihood of urgent spacewalking repairs.

NASA schedules four ISS spacewalks

Jan 24, 2007

NASA astronauts are to conduct an unprecedented series of four spacewalks during the next month at the International Space Station.

Recommended for you

SDO captures images of two mid-level flares

Dec 19, 2014

The sun emitted a mid-level flare on Dec. 18, 2014, at 4:58 p.m. EST. NASA's Solar Dynamics Observatory, which watches the sun constantly, captured an image of the event. Solar flares are powerful bursts ...

Why is Venus so horrible?

Dec 19, 2014

Venus sucks. Seriously, it's the worst. The global temperature is as hot as an oven, the atmospheric pressure is 90 times Earth, and it rains sulfuric acid. Every part of the surface of Venus would kill you ...

Image: Christmas wrapping the Sentinel-3A antenna

Dec 19, 2014

The moment a team of technicians, gowned like hospital surgeons, wraps the Sentinel-3A radar altimeter in multilayer insulation to protect it from the temperature extremes found in Earth orbit.

Video: Flying over Becquerel

Dec 19, 2014

This latest release from the camera on ESA's Mars Express is a simulated flight over the Becquerel crater, showing large-scale deposits of sedimentary material.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.