NASA astronaut Chris Cassidy and Italian astronaut Luca Parmitano were hard at work outside the International Space Station (ISS) for the second time in only a week. However, the EVA was terminated, when water started to leak into Parmitano’s space suit helmet, immediately resulting in the duo heading back to the Quest Airlock.
US EVA-22, performed exactly one week ago on July 9, was a resounding success with all primary objectives completed, and some objectives previously planned for EVA-23 completed also – namely the inspection of the Functional Cargo Block (FGB) Power & Data Grapple Fixture (PDGF) for grounding wires, and the partial routing of the FGB PDGF 1553 data cable.
One of the main objectives of the EVA – the Removal & Replacement (R&R) of the Space to Ground Transmitter Receiver Controller-2 (SGTRC-2) – successfully resulted in that piece of hardware being recovered after a failure six months ago, per L2’s rolling ISS Updates section:
“Ku Band String 2 Recovery – Yesterday, the SGTRC that was replaced during EVA-22 was powered and checked out. The checkout was good and Ku Band String 2 was transitioned to operational. Ku Band String 2 is planned to be primary for 6 months, then String 1 will be made primary.”
The successful R&R of SGTRC-2 means that, for the first time ever, ISS flight controllers can now remotely swap between using the two ISS Ku-band antennas, with no manual reconfiguration needed by the crew.
The SGTRC controls the pointing of the Space to Ground Antenna (SGANT), which is responsible for transmitting high-rate Ku-band data (such as video and payload data) from the ISS to Earth. There are two SGANTs on ISS, the first of which was installed on STS-92 in 2000, and the second on STS-132 in 2010.
Previously, in order to swap between using one SGANT and the other, the ISS crew had to manually swap cables over inside the ISS to plug the station’s data downlink control system into a different SGANT, i.e. unplug SGANT-1 from the downlink system and plug SGANT-2 in its place.
However, in April this year the ISS Ku system was overhauled to provide vastly increased downlink rates via modern electronics, and during this the legacy Ku systems were replaced with a single Integrated Communications Unit (ICU).
Two ICUs were installed, a primary and a back-up, with ISS ground controllers being able to remotely swap between which was prime and which was back-up, i.e. swapping “strings” between ICU-1/Ku string 1 and ICU-2/Ku string 2.
However, with SGTRC-2 failed (rendering SGANT-2 unusable), even if ground controllers had swapped strings remotely, the ISS crew would still have needed to perform the manual cable reconfigurations to plug SGANT-1 into whichever ICU was prime (as only one SGANT can be connected to a single ICU at any one time).
With SGANT-2 now recovered however, ICU-2 can be permanently connected to SGANT-2 (with ICU-1 being permanently connected to SGANT-1), meaning that ISS ground controllers can now remotely string swap between using ICU-1/SGANT-1 and ICU-2/SGANT-2, with the result being that for the first time ever, SGANT redundancy has been achieved without the need for any manual cable reconfigurations by the crew.
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US EVA-23 began at 11:57 PM GMT, when Cassidy and Parmitano exited the station’s Quest Airlock after performing the now routine In Suit Light Exercise (ISLE) regime to purge nitrogen from their bloodstreams.
The first order of business for EV-1 Chris Cassidy once he exited the Airlock was to translate up to the Z1 Truss to begin the second part of the Z1 Y-bypass jumper task, the first part of which was completed on last week’s EVA.
The purpose of this task is to use a Y-shaped cable to provide a Z1 Secondary Power Distribution Assembly (SPDA), essentially a bank of circuit breakers to which electrical loads are connected, with two alternate sources of power, so that they could still remain powered even if one of their sources should go down at a future date.
Luca Parmitano proceeded to the FGB PDGF worksite to finish routing the 1553 data cable started during last week’s EVA.
This task will finally allow the FGB PDGF to become fully operational and give the SSRMS a base point on the Russian Segment (RS) of the station, a task that was originally planned to be conducted almost three years ago in August 2010, but which was pushed back multiple times due to more pressing failures outside the station.
Parmitano also got started on routing an Ethernet cable between the US segment of the station and the future Russian Multipurpose Laboratory Module (MLM), which is now looking likely to be delayed into at least the second quarter of 2014.
However, once Cassidy had completed the Z1 Y-bypass jumper task, and Parmitano had completed the FGB PDGF 1553 cable task and was deep into the MLM Ethernet cable task, Parmitano started reporting a quickly rising amount of water in his helmet, from an unknown source.
The significant quantity of water quickly became a concern as it was entering Parmitano’s eyes, nose, and mouth, and as such ISS flight controllers made the decision to terminate the EVA early.
Parmitano headed straight back to the A/L, while Cassidy grabbed the EVA bags and headed back to the A/L himself to begin the repress, with Luca no longer able to hear any communications due to the amount of water in his helmet.
Repress was started and the EVA was terminated after a duration of 1 hour 32 minutes.
Once repress was completed and the hatch was opened, Luca was removed for the A/L straight away and his helmet removed immediately, with water floating away in the process.
After the water bag – used for drinking water – in Luca’s EMU was classed as a suspect for the leak, this was later ruled out as the source.
Engineers are still evaluating root cause, but noted the potential for what Luca classed as “funny tasting” water was because it may have mixed with the anti-fogging material on his visor. However, where the water came from is still unknown.
The next opportunity to complete the remaining EVA-23 tasks is not yet known.
(Images: L2’s ISS Section and NASA)
(L2 Members refer to the L2 ISS Section for Updates, Images and Presentations relating to this situation on the ISS).
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