December 30, 2013
The six-person International Space Station is headed toward a resumption of normal operations following a pair of unscheduled late-December spacewalks by NASA astronauts to replace a degraded external thermal control system (TCS) pump module.
The astronauts followed the excursions with other measures to restore cooling to all U.S. segment electrical systems deactivated in response to a Dec. 11 flow control valve failure.
The last of the electrical loads – all in the European Space Agency’s Columbus laboratory module – were expected to be restored to the repaired cooling system on Dec. 31, according to Kelly Humphries, a spokesman at NASA’s Johnson Space Center.
Research activities that ramped up as the assembly of the station’s U.S. segment was completed in July 2011 were among the operations interrupted by the balky valve housed within the pump module. So were the anticipated Dec. 18 launching of Orbital Sciences Corp.’s “ORB-1” resupply mission to the ISS and a Russian spacewalk. Launching of the Antares/Cygnus rocket/commercial freighter combination on what is to be the first mission flown under a $1.9 billion, eight-flight Cargo Resupply Services contract between NASA and Orbital Sciences was rescheduled for no earlier than Jan. 7. ORB-1 was postponed to clear the way for the contingency spacewalks on Dec. 21 and 24 by ISS astronauts Rick Mastracchio and Mike Hopkins.
Full ISS thermal control was restored Dec. 24-25. NASA’s Mission Control orchestrated the gradual return of nonessential electrical systems that were shut down in response to the thermal control restrictions in the aftermath. Those included research activities in the U.S. Destiny, Japanese Kibo and Columbus labs as well as connecting U.S. nodes.
A third ISS spacewalk — an unrelated Russian excursion on Dec. 27 to install a pair of Earth observing cameras for UrtheCast, a Vancouver, Canada-based commercial venture in collaboration with the Russian federal space agency Roscosmos — was not so successful. Cosmonauts Oleg Kotov, the ISS commander, and Sergey Ryazanskiy quickly installed but were then forced to retrieve the medium- and high-resolution still and video imagers when ground controllers were unable to establish the desired telemetry links for the planned Internet-based, subscriber service.
The setback pushed the spacewalk to 8 hr., 7 min., a Russian record.
Initially, the Mission Operations Directorate at NASA’s Johnson Space Center responded to an electrical failure of the flow control valve in Loop A of the station’s dual-loop ammonia TCS system with plans for three spacewalks. The successful strategy, accomplished with one fewer spacewalk than envisioned, included measures to avoid a repeat of the worrisome leak that allowed water to flow into the helmet of European Space Agency astronaut Luca Parmitano, who was wearing a U.S. spacesuit, during a July 16 spacewalk.
But Mastracchio had to don a different NASA spacesuit after an inadvertent airlock activation of the sublimator on his protective garment following the Dec. 21 excursion. Both spacewalks included brief but ultimately inconsequential exposures to leaking frozen ammonia, a toxic substance, as Mastracchio and Hopkins detached and reattached coolant lines.