Space station malfunctions prompt shutdowns

One of two coolant systems
aboard the International Space Station malfunctioned late Saturday, triggering
alarms and extensive power shutdowns to keep critical systems from overheating.

The apparent failure of an
ammonia pump in coolant loop A forced flight controllers to shut down two of
four stabilizing gyroscopes, used to help control the space station’s
orientation, one communications channel and several computer control units. The
astronauts also installed jumpers between the Russian Zarya propulsion module
and the U.S. segment of the lab complex to maintain proper cooling.

“It seems like we’re in a
sim right now,” flight engineer Tracy E. Caldwell Dyson joked with flight
controllers shortly after 1 a.m. Sunday, referring to training simulations.

NASA officials said the
space station was in a safe, reduced-power configuration using coolant loop B.
It took the astronauts several hours to complete the shutdowns, but flight
controllers told them they could sleep late Sunday while analysis continued on
the ground.

“We’re going to be working
hard overnight to figure out what’s going on,” astronaut James M. Kelly radioed
from mission control shortly before the astronauts went back to bed. “By
tomorrow, a little bit later on, hopefully we’ll be able to send you up a
little bit better idea of where we stand on everything.”

The International Space
Station is equipped with two independent coolant loops mounted on the lab’s
main solar power truss that use ammonia circulating through huge radiator
panels to dissipate the heat generated by the station’s electronics.

While the loops are
independent, the station cannot operate at full power with just one coolant
loop. Spare components are on board, including two coolant system pumps, but
installation is considered difficult and two spacewalks would likely be

Caldwell Dyson and Army Col.
Douglas H. Wheelock were already planning to conduct a spacewalk Aug. 5 to
mount a robot arm attachment fixture to the Zarya module and to rig the central
Unity module for attachment of a storage compartment during a shuttle flight in

It is not yet known whether those plans will be affected by
the problems with the coolant system.