NASA Astronaut Joe Acaba, in the broken red striped spacesuit, and Astronaut Ricky Arnold, in the white striped suit, work to relocate Crew and Equipment Translation Aid (CETA) near the Mobile Transporter (MT) during an STS-119 spacewalk in March 2009.
The International Space Station’s mission managers are preparing for a likely unplanned spacewalk by Astronauts Scott Kelly and Tim Kopra no earlier than Monday, Dec. 21.
Late Wednesday, the Mobile Transporter rail car on the station’s truss was being moved by robotic flight controllers at Mission Control, Houston, to a different worksite near the center of the truss for payload operations when it stopped moving. The cause of the stall is being evaluated, but experts believe it may be related to a stuck brake handle, said ISS Mission Integration and Operations Manager Kenny Todd. Flight controllers had planned to move the transporter away from the center of the truss to worksite 2. The cause of the stall that halted its movement just four inches (10 centimeters) away from where it began is still being evaluated. Progress 62 is scheduled to launch at 3:44 a.m. EST Monday, and dock on Wednesday to the Pirs docking compartment at 5:31 a.m. Wednesday.
The ISS Mission Management Team met Friday morning and is targeting Monday for the spacewalk, but will meet again in a readiness review Sunday morning. Managers could elect to press ahead for Monday, or take an extra day and conduct the spacewalk Tuesday.
ISS Expedition 46 Commander Scott Kelly and Flight Engineer Tim Kopra of NASA will conduct the spacewalk. It will be the 191st spacewalk in support of space station assembly and maintenance, the third in Kelly’s career and the second for Kopra. Kelly will be designated Extravehicular Activity crew member 1 (EV1) wearing the suit bearing the red stripes, and Kopra will be Extravehicular Activity crew member 2 (EV2) wearing the suit with no stripes.
A start time for the spacewalk either Monday or Tuesday has not yet been set, but NASA TV coverage will begin 90 minutes prior to the start of the spacewalk.
Station Managers “GO” For Monday Morning Spacewalk
NASA astronauts Scott Kelly and Tim Kopra will conduct a spacewalk Monday morning. Credit: NASA
The International Space Station Mission Management Team met Sunday and gave its approval to proceed with a spacewalk Monday out of the Quest airlock by Expedition 46 Commander Scott Kelly and Flight Engineer Tim Kopra of NASA to assist in moving the Mobile Transporter rail car a few inches to a worksite on the station’s truss where it can be latched in place and electrically mated to the complex. The green light for the unplanned spacewalk to take place Monday came three days after the Mobile Transporter stalled just four inches away from its embarkation point at worksite 4 near the center of the station’s truss as it began to move to another worksite to support robotic payload operations with its attached Canadarm2 robotic arm and the Special Purpose Dexterous Manipulator (Dextre).
Station managers ordered the spacewalk to latch down the transporter as a cautionary measure in advance of the scheduled docking of the new unpiloted ISS Progress 62 cargo ship on Wednesday that will link up to the Pirs Docking Compartment. The Progress is on track for launch from the Site 31 launch pad at the Baikonur Cosmodrome in Kazakhstan Monday at 2:44 a.m. Central time (2:44 p.m. Baikonur time).
The planned 3 to 3 ½ hour spacewalk is scheduled to begin Monday at 7:10 a.m. Central time. The start time for the spacewalk is variable since Kopra will be conducting a fit check of his U.S. spacesuit in parallel with other spacewalk preparations. NASA TV coverage will begin at 5:30 a.m. Central time.
Kelly, who will be making his third spacewalk, will be extravehicular crew member 1 (EV 1) wearing the U.S. spacesuit bearing the red stripes. Kopra, who arrived on the station on Dec. 15, will be making the second spacewalk of his career as extravehicular crew member 2 (EV 2) wearing the suit with no stripes. It will be the 191st spacewalk in support of station assembly and maintenance and the seventh spacewalk of the year by station crew members.
Kelly and Kopra will float out of the Quest airlock to the area where the Mobile Transporter has stalled to check out the position of its brake handles and other mechanisms to make sure the rail car can be commanded to move back to worksite 4 by robotic flight controllers at Mission Control, Houston. It is suspected that a brake handle on an equipment cart attached to the starboard side of the transporter may have inadvertently engaged, which if correct, should easily be released to allow for the transporter to be moved into place for its latching.
If the primary task of moving the transporter to its worksite is completed quickly, Kelly and Kopra may press on to a few get-ahead tasks that include the routing of cables in advance of International Docking Adapter installment work to support U.S. commercial crew vehicles, and opening a door housing power distribution system relay boxes just above the worksite to facilitate the future robotic replacement of modular components.
Update: 21.30 MEZ
EVA successfully frees stuck CETA cart outside ISS
An unplanned spacewalk has been completed on the ISS, successfully fixing a stuck transportation cart outside the station. The hardware was preventing the movement of a robotic transporter along the station’s Truss. While not a critical safety issue, the situation was highly undesirable, hence a quick resolution was required. The EVA lasted three hours and 16 minutes.
The issue in question concerned a piece of hardware known as the Mobile Transporter (MT), which serves to transport components of the station’s robotic Mobile Servicing System (MSS) along the station’s Truss structure.
Along the front side of the station’s Truss structure – specifically the S0, S1, S3, P1, and P3 Truss segments – exists a rail structure, which the MT is able to move along, in order to provide transportation to the station’s robotic arm.
This enables the arm to move from one end of the Truss structure to the other, thus greatly extending its reach.
Attached to the MT is another piece of hardware called the Mobile Base System (MBS), which serves as a supporting structure and interface between robotic hardware such as the Space Station Remote Manipulator System (SSRMS), the Special Purpose Dextrous Manipulator (SPDM), and the MT.
The MBS features four Power & Data Grapple Fixtures (PDGFs) that can each serve as a base point from which the SSRMS can be controlled.
The MBS also features the Payload ORU Accommodation (POA), which is essentially a Latching End Effector (LEE) like that found on the SSRMS, which can hold onto payloads while the MT transports them.
The SSRMS is normally based on either Node 2 or the US Lab, which are both located in the center of the station’s Truss structure.
However, if the SSRMS needs to reach either end of the Truss structure, it can move, or “change its base”, to the MBS, which will then, along with the MT to which the MBS is attached, move along the rails located on the Truss, thus allowing the SSRMS to reach the outer edges of the Truss structure.
The MT can only move at a maximum rate of one inch per second, and is propelled by a piece of hardware called the Linear Drive Unit (LDU). However, the MT cannot stop at any given location along the Truss rails.
Instead, it must stop at any of the ten designated “worksites” located along the Truss rails. These worksites feature mechanical and electrical connections to allow the MT to secure itself to the Truss, and to provide power to the MBS and its attached robotic hardware.
When the MT moves along the Truss, or is stationary in between any of the worksites, it is only lightly attached to the Truss rail structure via wheels known as Roller Suspension Units (RSUs).
Electrical power for MT translation via the LDU is available through the Trailing Umbilical System (TUS), which is a cable reel that extends and retracts as the MT moves. The MBS and attached hardware are unpowered during MT motion or when the MT is not located at a worksite.
However, when located at any one of the ten worksites, the MT securely clamps itself to thicker portions of the Truss rails via Load Transfer Units (LTUs), which take over from the RSUs. Electrical power is available via the Umbilical Mechanism Assembly (UMA), which provides power to the MBS and attached hardware.
Two Crew & Equipment Translation Aid (CETA) carts are also attached to either side of the MT. The CETA carts are transportation aids for spacewalkers, to which EVA hardware can be attached, with the CETA carts then being manually moved along the Truss rails by spacewalkers.
The CETA carts feature two Dynamic Brake handles, two Parking Brake handles, and two Parking Brake Release handles, all of which can be manually operated by spacewalkers in order to arrest the CETA cart’s motion and secure it to a desired location along the rails.
The CETA carts are attached to the Truss rails via four Wheel/Brake Assemblies, with one being located in each of the four corners of their respective CETA cart. The two CETA carts are attached to the MT when not in use, which allows them to translate along the rails along with the MT whenever it moves.
Problem & concerns:
On December 17, while the MT was in the ground-controlled process of translating from Worksite-4 (WS-4) to WS-2, the Translation Drive (TD) Integrated Motor Controller Assembly-A (IMCA-A) experienced an error, resulting in MT motion being stopped shortly after the MT had left WS-4.
Another error was then experienced when the MT attempted to translate back to WS-4.
The MT was effectively “stuck” in this position just short of WS-4, which is located just to the Starboard side of the S0 Truss, very close to the center of the Truss.
As such, the MT was unable to engage the LTUs or the UMA, and as such was only lightly attached to the Truss rail via its RSUs (which are braked).
Electrical power to the MBS is being provided via the Mobile Transporter Relay Assembly (MTRA), which was only recently installed on the ISS in October 2014, with the purpose of providing power to the MSS when the MT has stopped motion between worksites, in order to provide “keep alive” power to the MSS in the event that the MT gets stuck.
After analysis, ground teams believed that the stuck MT was likely caused by a brake being engaged on the Starboard CETA cart, which was preventing the MT from moving as the CETA cart is attached to the MT.
Ahead of the EVA it wasn’t fully known whether the brake handles were responsible for the engaged brake, or whether one of the Wheel/Brake Assemblies had somehow failed.
The Starboard CETA cart brake handles were only recently tied-down by astronaut Scott Kelly during US EVA-33 back in early November, leading to the possibility that they could have somehow inadvertently been engaged at that time.
2015-12-20-235742The concerns with having the MT remain unsecured to a worksite, aside from the fact that robotic operations are greatly impacted as only keep-alive power is available to the MBS and attached hardware, are that the ISS cannot conduct “dynamic” operations, such as attitude changes, as the potential exists for the MT to move around and become damaged as it is not securely latched to the ISS.
This in turn affects dockings of Soyuz and Progress vehicles, which require ISS attitude changes.
Following the successful departure of Progress M-28M (19 December), Progress MS-1 launched (21 December), for a docking two days later. Hence, there was a desire to resolve the stuck CETA cart/MT issue before then.
Following a meeting (20 December), the ISS Mission Management Team (IMMT) gave a GO for an EVA to attempt to free the stuck CETA cart, to occur Monday (21 December).
This EVA was planned to last around 3.5 hours, conducted by NASA astronauts Scott Kelly and Tim Kopra.
The plan was to have the spacewalkers check that all the brake handles on the starboard CETA cart are not engaged, and if they are engaged, to release them.
That proved to be the case, as Kelly worked to put one of the brake handles back into a nominal configuration – allowing the MT to return to action.
The spacewalkers had to go about their work carefully, ensuring the CETA cart did not suddenly “jolt” when the brakes were disengaged, due to stored mechanical energy.
Once the spacewalkers verified that none of the brake handles were no longer engaged, ground controllers moved the MT back to WS-4, which indicated that the problem has been resolved. The MT is now back in a nominal configuration, with electrical power confirmed by the ground controllers.
Alternative options – no longer required – would have included the removal of the CETA cart from the Truss rails completely.
It was also possible to remove and replace each of the four Wheel/Brake Assemblies on the CETA cart.
NASA Astronaut Tim Kopra on Dec. 21 Spacewalk
Expedition 46 Flight Engineer Tim Kopra on a Dec. 21, 2015 spacewalk, in which Kopra and Expedition 46 Commander Scott Kelly successfully moved the International Space Station's mobile transporter rail car ahead of Wednesday's docking of a Russian cargo supply spacecraft. After quickly completing their primary objective for the spacewalk, Kelly and Kopra tackled several additional "get-ahead" tasks. Kelly routed a second pair of cables in preparation for International Docking Adapter installment work to support U.S. commercial crew vehicles. Kopra routed an Ethernet cable that ultimately will connect to a Russian laboratory module. They also retrieved tools that had been in a toolbox on the outside of the station, so they can be used for future work.
The three-hour and 16-minute spacewalk was the second for Kopra, who arrived to the station on Dec. 15, and the third for Kelly, who is nine months into a yearlong mission.
Expedition 46 Commander Scott Kelly on a Dec. 21, 2015 spacewalk, in which Kelly and Flight Engineer Tim Kopra successfully moved the International Space Station's mobile transporter rail car ahead of Wednesday's docking of a Russian cargo supply spacecraft. After quickly completing their primary objective for the spacewalk, Kelly and Kopra tackled several additional tasks. Kelly routed a second pair of cables in preparation for International Docking Adapter installment work to support U.S. commercial crew vehicles. Kopra routed an Ethernet cable that ultimately will connect to a Russian laboratory module. They also retrieved tools that had been in a toolbox on the outside of the station, so they can be used for future work.
The three-hour and 16-minute spacewalk was the third for Kelly, who is nine months into a yearlong mission, and the second for Kopra, who arrived to the station on Dec. 15. Kelly shared this picture with his social media followers after the conclusion of the spacewalk, writing "Fix was pretty easy, but the rest always a challenge. With great team on earth we got it done safely. #YearInSpace"
Tim Peake :
My ringside-seat view of yesterday’s #spacewalk – taken from the cupola