Posted on 12/18/2006 7:38:17 AM PST by NormsRevenge
HOUSTON - The space shuttle Discovery crew was awakened by the Beach Boys hit "Good Vibrations" on Monday to get them ready for a day of work trying to shake loose a jammed solar energy array.
Two spacewalking astronauts were scheduled to work on the stuck solar wing, with instructions from their counterparts inside the international space station and in Mission Control.
It was to be the fourth spacewalk of this now 13-day mission. NASA added it to the schedule on Saturday after several attempts to fully fold the solar array were unsuccessful.
U.S. astronaut Robert Curbeam was poised to set a new record for the most spacewalks completed on a mission by a single crew member, this being his fourth. Swedish astronaut Christer Fuglesang, who paired up with Curbeam on two earlier spacewalks, will assist as Curbeam attempts to loosen stuck grommets on the 115-foot array.
The planned activity inspired the "Good Vibrations" wake-up music.
"Good morning, Discovery," Mission Control astronaut Shannon Lucid radioed up. "We sort of thought that the wakeup music this morning summed up our hopes for the day."
NASA began retracting the accordion-like structure on Wednesday to make room for some new solar arrays that must rotate to face the sun in order to generate electricity. The new arrays would kick in after astronauts rewired the station over two spacewalks.
Reconfiguring the orbiting space lab's interim power system to a permanent electricity grid was a primary goal of the Discovery mission. But the old array, part of the interim system, retracted only halfway before stalling. That was enough to allow the new arrays to rotate but NASA needs it to fold fully into a box so it can be moved to a permanent position on a later shuttle flight.
On the last scheduled spacewalk, which took place Saturday, Curbeam and Sunita Williams went to the array after completing their main tasks, and spent about two hours shaking the array, trying to coax apart the problem grommets. They partially succeeded and other astronauts were able to command the array to retract several degrees more. But more grommets got stuck and the spacewalking duo's time was up.
Asked by a reporter how important is it to get the arrays retracted, crew member Joan Higginbotham, who will be operating a crane-like robotic arm during the spacewalk, offered this assessment: "It's very important from a personal standpoint," she said. "I think we're all very Type A personalities — I think my crew would agree with me there — so we always like to accomplish the task that we are given."
The array could safely be left in its current configuration for a couple of months, but NASA managers decided to take advantage of the extra hands on deck and the flexibility in their time schedule to try and resolve the problem now.
"Of course it's a little more challenging because we haven't done the training on the ground for it, but we did have a lot of generic training for solar array wing deploy and retract," Curbeam said in an interview Sunday evening. "I have a pretty good feeling that we've got a good chance for success."
The robotic arm will take Curbeam to the trouble spots on the array, and he'll have a variety of tools with which to pry the grommets — and a guide wire that runs through them — free.
Curbeam said he'll treat the spacewalk like any other, but added, "Probably the most important thing is for us to keep in mind that since it's my fourth — and you tend to get more and more comfortable as you go along — just to make sure we don't make any mistakes."
Discovery is set to land on Friday, having left the space station with a 2-ton, $11 million addition installed and a new power system. They'll leave Williams on the space station as its newest resident and bring back her predecessor, German astronaut Thomas Reiter.
So damn cool. They earned their pay today, no doubt about it. In March, there will be revised flight rules out the wazoo.
With it half folded, they could have just plucked it off and put it on P5.
Nope. The CG would exceed the SSRMS loading abilities, and too bulky to manuever into position.
Maybe...not sure I am convinced. What is the mass of P6?
I don't have that number, but I know you can't manipulate P6 without the arrays furled or jettisoned. The Robotics ops are untenable, if only because the geometry leaves you with hardware collisions.
Trust me - an the retract had to occur, or a jettison.
hmmmm.
Mass of P6 = 15,824 Kg = 16 Metric tons
Wha?
NASA has a geometric model of the ISS, but I can't get it from here - my primary PC is in for repairs, so I am freeping from my "dust box." So I will have to wait, until I can go look. Darn.
I see that the SSRMS is capable of handling large payloads of up to 116,000 kg, so the mass is not a major factor.
No, but the geometry may well be - can't tell from here. Also, torque likely is - it has to be translated 90 degrees, then rotated 90, then translated 90 again, while being moved out to the end of P5.
The arrays themselves have movement constraints, as well, and there is risk (or certainty!) of breaking them if in their extended state during assembly.
Imagine carrying two flat pieces of thin cardboard each longer than your body and trying to walk through the rooms of your house. Imagine the cardboard was very expensive and your house was full of expensive items adorning every countertop and table. Would you hold the boards straight out to your sides, or would you try to tuck them under your arms?
SSRMS may still be able to take the torque, if rotated exceedingly slowly.
Well, depends on how likely it was that the cardboard wuold never be usable again, and what it would cost to get replacement cardboard into orbit, if such were even possible, and what, on the space station, will be unusable, if the P6 panels can never be extended again (or are the panel assemblies replaceable in orbit?) (I imagine that is fun). Clearly, the bulk of the mass is the truss, not the panels, so if they are replacable, that changes things.
P6 Panel extension - pretty likely, though no guarantees.
P6 Replacement - We have a spare, so we can jettison the current ones if need be and replace.
Speaking of jettison, it's easier to drop the arrays fron the port side of ISS than from the nadir (top) position, where they are now. Everyone is much happier with the prospect of jettison if we get P6 installed on P5.
Oh, as for ISS reuasability without P6 panels, we just gained 50% more power with P4, so losing P6 is a static situation for now.
"reuasability" should be "usability"
Is the half of P6 that is still extended, still in use?
Nope. Powered down for the moment.
I gotta run, y'all have a good night.
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