Minor CO₂ issue cuts short ISS spacewalk

Mission specialists Chris Cassidy and Dave Wolf yesterday cut short the third STS-127 International Space Station spacewalk, due to "higher than normal carbon dioxide levels" in the former's spacesuit.

The minor alert, prompted by a "potential problem ... with the carbon dioxide scrubbing device", meant the pair had to return to the ISS half an hour earlier than planned, after five-hours and 59 minutes working outside the orbiting outpost.

The two "removed multilayer insulation from the Kibo module and readied the Japanese Exposed Section payloads for their transfer to the Exposed Facility", but completed just two of six planned battery* replacements on the Port 6 (P6) solar array.

NASA says the remaining four will be swapped during the fourth planned spacewalk on Friday. ®

Bootnote

*NASA explains that each battery comprises "thirty-eight individual pressure vessel (IPV) nickel hydrogen (NiH2) battery cells are connected in series and packaged in a Battery ORU" - an Orbital Replacement Unit "designed to allow simple removal and replacement while in orbit".

It adds: "Two ORUs are connected in series, utilizing a total of 76 cells to form one battery."

Six such batteries are packed into the P6 Integrated Equipment Assembly (IEA), which launched on launched on 30 November 2000. NASA says the batteries have a design life of six-and-a-half years.

In case you're wondering how much juice an ISS battery packs, each is expected "to deliver more than 25 Amps in a low-demand orbit to as high as 75 Amps to meet short peaking load requirements at a battery operating voltage range of 76 to 123 V dc".