Spaceflight Insider

Space station crew prepares for contingency spacewalk on Monday

Integrated Truss Assembly

The International Space Station’s truss assembly has rails that run 354 feet (108 meters) along it allowing the Mobile Transporter (MT) to move equipment, crew, and the robotic arms to multiple sites along its length. (Click to view full image.) Photo Credit: NASA

International Space Station (ISS) crew members Scott Kelly and Timothy Kopra are preparing to conduct a contingency spacewalk on Monday, Dec. 21, to fix the Mobile Transporter (MT) after it had got stuck between work sites.

On Wednesday night, Dec. 16, ground teams commanded the MT to move from Work Site 4 (WS4) to WS2. It moves on rails and is able to move 354 feet (108 meters) along the space station’s truss assembly.

“The Translation Drive (TD) Integrated Motor Controller Assembly (IMCA)-A experienced an error shortly after the MT left WS4 which caused motion to stop,” stated the ISS Daily Summary Report for Dec. 17.

STS-119 spacewalk

The Crew Equipment Translation Aid (CETA) cart is thought to have a parking brake engaged. The ISS has two such carts that can be stand-alone or attached to the Mobile Transporter (MT). Photo Credit: NASA

According to the report, several attempts in different configurations were performed to move the MT back to WS4 but were unsuccessful. The teams then powered down the MT and powered up the Mobile Servicing System (MSS) to a mode known as “Keep Alive” using power from the Mobile Transporter Relay Assembly (MTRA). The MT is currently braked, but it is not latched in a safe position.

The cause of the stall was believed to be a stuck brake handle on the starboard Crew Equipment and Translation Aid (CETA) cart, currently attached to the MT, halting its movement just four inches (10 centimeters) from where it began moving.

ISS mission management teams met Friday morning to discuss the issue. The space station cannot be re-oriented since the MT is not in a latched position. The urgency stems from the upcoming launch of Progress MS-1 on Monday – scheduled for 2:44 p.m. Kazakh time (8:44 GMT) – and subsequent rendezvous two days later. The Progress will dock to the Pirs docking compartment at 4:31 a.m. CST (10:31 GMT) on Wednesday. In order for the laboratory to be in the right position for docking, the station must orient itself to a position favorable for the automatic docking sequence.

To clear up the docking port, Progress M28M undocked from the station on Dec. 19 at 1:35 a.m. CST (7:35 GMT). The ISS didn’t need to be reoriented for this event as the outpost was already in an ideal position.

For the Monday spacewalk, Kelly and Kopra will venture out of the Quest airlock for about three-and-a-half hours. Kelly will be the lead spacewalker (EV1) and wear red stripes on his suit, while Kopra will be designated EV2 with no strips. The two will translate over to the CETA cart to examine the brake handles before making the necessary fixes to bring the MT back to an operational state. The 191st spacewalk in support of space station assembly and maintenance is scheduled to start at 7:10 a.m. CST (13:10 GMT). The spacewalk will be shown live on NASA TV starting at 5:30 a.m. CST (11:30 GMT).


The Mobile Transporter (MT) is part of the outpost’s Mobile Servicing System (MSS) which includes systems such as the Space Station Remote Manipulator System (SSRMS), called Canadarm2, and the Special Purpose Dexterous Manipulator (SPDM), called Dextre. Photo Credit: NASA


Derek Richardson is a student studying mass media with an emphasis in contemporary journalism at Washburn University in Topeka, Kansas. He is currently the managing editor of the student run newspaper, the Washburn Review. He also writes a blog, called Orbital Velocity, about the space station. His passion for space ignited when he watched space shuttle Discovery leap to space on Oct. 29, 1998. He saw his first in-person launch on July 8, 2011 when the space shuttle launched for the final time. Today, this fervor has accelerated toward orbit and shows no signs of slowing down. After dabbling in math and engineering courses in college, he soon realized that his true calling was communicating to others about space exploration and spreading that passion.

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