This week's EVA

[steve82]

Looks like there was a little bit of excitement during the EVA the other night. Suits were ok, the crew finished all of the tasks (I'm getting a little worried now that these 2-man EVA's outside an empty ISS are getting "routine") but they had a couple of problems. The ISS attitude drifted to a point to where the CMG's were getting close to saturation. This was not totally unexpected, and is believed to be caused by a characteristic of the suits (more on that later). So they put the ISS in free drift for a while. But in free drift, the solar panels aren't as well aligned with the sun so they have to command a "load shed" and turn off various non-critical electrical systems on the ISS in response to the reduced electric power availability. The load sheds are in big data tables and this time around, one of the tables was wrong so the automated load shed command just kept on down the line turning things off until it had reduced enough power. It took out the S-Band com system AND one of the CMG's. Oh Oh. Not good to lose S-Band while you have your 2-man crew floating outside an empty station, although the Russians seem to have a lot of experience doing EVAs without comm, it makes us a little nervous on the US side. Finally they moved the guys away from the SM to a safe location and were able to pop thrusters to restore attitude. Here's the press release:<br />http://www.spaceref.com/news/viewsr.html?pid=13557<br /><br />And what caused the attitude disturbance? The prevailing theory is that the sublimators used to remove heat from the Orlon suits are outgassing enough to produce about a Newton of force. Ordinarily not enough to cause a problem but, with the crew back on the SM, considerably away from the C.G., it's enough to result in a real disturbance torque. First rule of nonpropulsive vents: ANY nonpropulsive vent can, in the right circumstances, be propulsive!<br />

 

[bobw]

Thanks for posting about the suits. That's wierd. <div class="Discussion_UserSignature"> </div>

 

[nacnud]

Where does this port vent from, if it comes out of the suit normal to the astronauts back then to negate any force the astronauts would have to work back to back or face to face. If it vents from the side head to head or feet to feet working should help. Do astronauts try to share a common up down orientation to mitigate disorientation during spacewalks? Interesting problem anyway, would it be possible to vent to a bag or something as any force could be a problem that far from the centre of gravity of the station.<br />