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Space Forum / Shuttle / January 2008Spacewalks Variations
It is not clear to me why not performing EVA-5 ahead of a EVA-4 now dedicated to repair the solar array blanket. The both spacewalks are preplanned with different spacewalkers and different independent tasks. EVA-5 is well planned and important for the upcoming timline, and the multiple changed EVA-4 could gain an addtional day of planning. Albert I think the current thinking is that the array can be fixed, but the longer its left, the more danger of the damage getting worse. The rotary joint look and see is not going to get worse if the joint is not moved, and thus can be delayed. I'm sure much of the rest can be fitted in as and when. I myself wonder if the obss could be employed toget access to the array without running the snagging risk implicit in retracting to get at the damaged section. I find it hard visualising the array folding and deployed mechanics, but seems to me, its got to be under some tension to be rigid enough o not wobble about as its moved in normal use, so whatever they need to use may need to be quite strong. Brian  SignatureBrian Gaff - briang1@blueyonder.co.uk Note:- In order to reduce spam, any email without 'Brian Gaff' in the display name may be lost. Blind user, so no pictures please! > It is not clear to me why not performing EVA-5 ahead of a EVA-4 now > dedicated to repair the solar array blanket. [quoted text clipped - 4 lines] > > Albert > wobble about as its moved in normal use, so whatever they need to use may > need to be quite strong. And most likely non-conductive, and not mind UV in the sunlight. And be something a spacesuited astronaut can successfully work with. Maybe glue s sheet of something over the tear once it's tied down with some tie-raps? What sort of glue would work in vacuum? Epoxy? And have on hand up there, or it would have to wait for a supply mission? I'm sure people on the ground are on it, trying various solutions... > What sort of glue would work in vacuum? Epoxy? And have on > hand up there, Tile cement -- that being one of the Mission Objectives that may be omitted this time around due to the joint and tear problems. /dps [...] > I myself wonder if the obss could be employed toget access to the array > without running the snagging risk implicit in retracting to get at the > damaged section. Sounds like the new pole in the cargo bay: -- this from AP via Yahoo <http://news.yahoo.com/s/ap/20071031/ ap_on_sc/space_shuttle;> <quote> The torn section of the wing cannot be reached with the space station's 58-foot robot arm. So NASA plans to attach the shuttle inspection boom to the station's robot arm, and put Scott Parazynski on the boom to free the snagged part of the wing. It helps that Parazynski is tall - 6-foot-2 - and has long arms. NASA doesn't want him bumping the wing or touching its sunlight-collecting blankets. There would be no need to mend the tears </quote> /dps Well, I wrote my bit before I learned that they were indeed going to use the OBSS, but I feel that as nobody is really sure about the snag that caused the tear yet, a range of options will be needed to be on hand. Considring the array seems to have holes in various places, sounds like some form of strap could be used. Obviously you want the panel to be as near to flat and as it was as you can to ensure it gets the sun when in the right attitude. However, the structural loading is what worries me. If you elect to cut a snagged wire you may make things worse unless you really know the stress distribution of a fully deployed array in zero g. Brian SignatureBrian Gaff....Note, this account does not accept Bcc: email. graphics are great, but the blind can't hear them Email: briang1@blueyonder.co.uk ______________________________________________________________________________________________________________ > [...] >> I myself wonder if the obss could be employed toget access to the array [quoted text clipped - 17 lines] > > /dps [...] > However, the structural loading is what worries me. If you elect to cut a > snagged wire you may make things worse unless you really know the stress > distribution of a fully deployed array in zero g. Well, at the time I clipped that quote, the plan was to only inspect on this spacewalk and to decide on repairs only after analyzing the results. /dps Reading Scott Parazynski describing the spacewalk in an interview to opinia. co.uk and the prep leading up to it it makes you realise just what an incredible team effort went in to ensure the repair was succesful. Truly inspirational >[...] >> I myself wonder if the obss could be employed toget access to the array [quoted text clipped - 17 lines] > >/dps Reading Scott Parazynski describing the spacewalk in an interview to opinia. co.uk and the prep leading up to it it makes you realise just what an incredible team effort went in to ensure the repair was succesful. Truly inspirational >[...] >> I myself wonder if the obss could be employed toget access to the array [quoted text clipped - 17 lines] > >/dps [...] > I find it hard visualising the array folding and deployed mechanics, but > seems to me, its got to be under some tension to be rigid enough o not > wobble about as its moved in normal use, so whatever they need to use may > need to be quite strong. Here's an attempt at a verbal picture: imagine a stack of punch cards (playing cards have too wide an aspect ratio -- the "cards" are long and skinny). Add hinges to opposite long sides so you have a Z-fold (or fan-fold if you prefer). The "first" long side gets attached to a curtain rod, and the "last" long side gets anchored in the box. I can't tell from <http://www.nasa.gov/images/content/ 195515main_iss016e007399_hires.jpg> if the narrow sides are attached to the scissors jack or not -- perhaps Jorge or Jim can fill in that detail. The scissors jack is parallel to the narrow sides, and pushes the curtain rod out, and the panels ("punch cards") follow along, pulled by the hinges. This is highly over-simpllified, of course, and may contain errors, so I'll keep an eye out for those people updating the verbal picture. /dps >This is highly over-simpllified, of course, and may contain errors, so >I'll keep an eye out for those people updating the verbal picture. ...No, you just might have explained what went wrong up there: chads :-) OM Signature]=====================================[ ] OMBlog - http://www.io.com/~o_m/omworld [ ] Let's face it: Sometimes you *need* [ ] an obnoxious opinion in your day! [ ]=====================================[ > ...No, you just might have explained what went wrong up there: chads > :-) <vbg> /dps [...] > Here's an attempt at a verbal picture: imagine a stack of punch cards > (playing cards have too wide an aspect ratio -- the "cards" are long [quoted text clipped - 3 lines] > you prefer). The "first" long side gets attached to a curtain rod, > and the "last" long side gets anchored in the box. Looking at pictures like <http://www.nasa.gov/images/content/ 196032main_iss016e009207_hires.jpg>, I'm amazed by how much flimsier these are than I was thinking -- being used to consumer-grade PVs, with lots of substrate and lots of support material. Imagine the punch cards being shaved to at least 1/2 their original thickness. In fact, looking in the vicinity of the tear, it makes me think of the woven/plastic tarp material at the auto supply or camping store. And the repairs look a lot like a cable ties joined end-to-end to make a 6-10 foot reach (2-3 meters). /dps >[...] >> Here's an attempt at a verbal picture: imagine a stack of punch cards [quoted text clipped - 20 lines] > >/dps Oh yeah. These are not Earth-grade solar panels with thick tempered glass and aluminum frames. That Kapton is thinner than Scotch tape... (although there are at least several layers of it). Keep in mind that these have been highly optimized, mostly for performance *per pound*. Durability, size, output power, cost, etc. Everything is a tradeoff in space. The amazing thing is that they are streched with, what, 70 lbs of tension, when fully furled. Given that P6 had other problems after being retracted after several years, including the frayed retraction cable, I am rather surprised that they didn't have more problems than they did. SignatureBob the Tomato |
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