Sunday, April 30, 2017

ISS "Power Up!"

The P6 truss was the second truss segment added to the station.  This component is responsible for generation, storage, regulation and distribution of electrical power to the ISS and was initially responsible  for early station internal temperature cooling functions. The truss was delivered to the ISS aboard Space Shuttle Endeavour during STS-97 and was initially installed on top of the Z1 truss on December 3, 2000. The truss resided at that location until it was moved to the far port end of the station truss near the end of the station assembly sequence during STS-120 in late October, 2007.

The P6 truss consists of three main parts (from bottom to top as oriented vertically atop the Z1 truss): the long spacer, the integrated equipment assembly, and the photovoltaic array assembly. The prominent feature of the truss are the solar array wings (SAW) which reside at the top of the component.  Each SAW consists of two bifacial solar panel blankets separated by a center mast. The individual blankets measure 14.5 feet wide and 112 feet long and fold up acordian-style into solar panel blanket boxes measuring a mere 20 inches high by 15 feet long! The total span of the deployed SAW array is 240 feet tip-to-tip. The SAW can generate up to 32.8 kW of DC power and provided the station with a major power capacity boost prior to the addition of the Destiny laboratory via STS-98 on February 10, 2001.

The P6 truss also contains a Photo Voltaic Thermal Control System (PVTCS) with a single Photovoltaic Radiator (PVR) located on the forward side of the truss.  The truss also houses the Early External Thermal Control System (EETCS) which has two Thermal Control Radiators (TCR) located on the starboard (STCR, a.k.a., "sticker") and aft (TTCR, a.k.a., "ticker") sides of the truss. The PVTCS is responsible for dissipating heat from the truss batteries that are charged by the SAW. The EETCS provided early internal temperature cooling operations for the station prior to addition of the main ETCS cooling loop which was added as part of the installation of the P1 and S1 trusses in late 2002.

The P6 component is part of the for-purchase portion of AXM's excellent ISS kit.  Parts consist of 2 pages for the truss portion, one page (actually one page x 3  to build all three radiators) representing the deployed version of the PVR and TCR components, another page ( x 4) for the solar panel blankets, a page ( x 4, 2 for stowed configuration, 2 for deployed configuration) for the solar panel blanket box arm assemblies, and a page (x 2) for the solar panel masts.    The P6 assembly manual is 26 pages and contains numerous reference photos that depict the shuttle payload and ISS versions of the component.  The P6 manual depicts assembly using the original mast canister support parts, whereas the S6 counterpart instructions depict assembly of the mast canister supports using the most recent modified mast canister supports and support covers included on the kit's parts page.

I started on this component during the latter portion of the Z1 truss build back in July of 2016.

I built the long spacer and fabricated magnetic "feet" in order to ensure proper magnet alignment at the Rocketdyne Truss Attachment System (RTAS) mount points on the Z1 truss' zenith face.  This was important to perform at this point in order to alleviate a subsequent unmount the Z1 truss from its target display configuration.

Next, I assembled the integrated equipment assembly portion of the truss and applied layering to the various battery and power conversion components to increase realism.  I then attached the part to the top of the long spacer, paying close attention to proper alignment of the two parts.


I then turned my attention to fabrication of the stowed PVR and TCRs.  The plans prescribed fabrication of a rectangular paper nub as the friction-based attachment point.  I built the first component as directed and fitted it to the main truss body.  However, I had problems getting the nub to fit properly and hold its shape after a few attachment attempts.  I ended up deciding to fabricate nubs using blocks of balsa sanded down to ensure a snug fit that are immune to paper nub crushing from repeated handling to affix and remove the component.

I then cut out components of the zenith side SAW mast canister base plate, applying cutouts and layering in order to achieve depth.

I affixed the completed base plate to the top of the component.

I then proceeded to cut out and assemble the trunnion and keel pin truss support members, including the top trunnion pin "ears".  I applied layering to the ears to increase depth/realism.  I glued magnets to the inside of each ear to provide ceiling hang points for the component. Complimentary magnets were affixed to the exterior of each ear to promote a snug glue point on the inside. I also added the S-band antenna mount point to the starboard side of the forward ear.  I then glued the trunnion ears to the prescribed points, taking special care to ensure proper orientation/alignment.

I then decided to add some more layering to edge areas to increase realism.

Next, I cutout and fabricated the mast cylinder bases, again using layering to achieve depth and detail.

I then turned my attention to fabrication of the Beta Gimbal Assembly (BGA) for each SAW.  The BGA is responsible for automatically adjusting the angle of each SAW relative to the ecliptic as the IIS orbits the Earth during daylight in order to point the solar arrays at the Sun for optimal power generation.  The instructions prescribe gluing each BGA in a static position.  I desired to modify this approach so that each BGA could be rotated in order to accurately depict relative position of the SAW to the mast canister, sequential shunt unit (SSU), electronics control unit (ECU), and BGA. To accomplish this, I first fabricated the BGA axle using a piece of dowel rod covered with the axle parts, and the built up the lip toward the inside edge by lapping paper strips around the edge.  Next, I cut out the mast canister supports and notched the inner edge to a depth matching the width of the BGA axle lip.

I then wrapped the canister support cover around the BGA axle and glued down the lower sides of the cover to the mast cylinder base, making sure that the inner lip of the BGA abutted the edge of the canister support cover's notched area.

I cutout and formed each mast canister.  I then carefully cut out the external mast canister cables and other details from a copy of the parts page and layered the cutouts onto the mast canisters to increase depth and realism.

Next, after careful study of numerous EVA photos of the mast canisters, I determined that the inner edge of the solar panel blanket box arms should abut further up on the outer edge of the mast canister than what is depicted in the assembly instructions.  This change required a portion of the outer side of the mast canisters to be cut off and then affixed to the opposite side of the solar panel blanket box inner segment.  

I proceeded with this modification by first cutting off the prescribed portion from the outer edge of each mast canister.

I then affixed the cut edge from each canister to the inside edge of the solar panel blanket box arms.

This process was repeated for deployed versions of the solar panel blanket box arms (I extracted copies of the cut sections of the canisters from another copy of the parts page).

I then attached the mast canisters to the BGAs and reinforced the axle contact point on the canister side in order to accommodate anticipated strain at this join due to the weight of the SAW assemblies and masts.

I layered the inner side of each solar panel blanket box to make the various blanket cables' pully and tensioner assemblies stand out to provide more detail.  Layering was also performed on the outer sides where handholds are located.

I now turned my attention to building deployed versions of the PVR and two TCRs.  Both look the same visually and are built from the same parts page.  The ISS model requires up to five of these components to be deployed at once.  I decided to go ahead and build all of the deployed radiators now, versus coming back later to build the additional two that are not needed for display of the P6 component.

The actual radiator segment of each component is mostly a simple box cutout sequence, except for the base portion of the component which contains a couple of angle cuts.  However, cutout of the zig-zag braces that are affixed to each edge of the radiator is a bit tedious to perform due to the parts being so narrow and requiring a number of precise angle/edge cuts.  Furthermore, there are two sides to each brace, which doubles the amount of work to extract the parts.  Patience and a slow, methodical approach to cutting out these parts is key (a sharp knife blade doesn't hurt either :-).  I found that cutting out a piece and then walking away from it for a few moments and then returning for the next cut was the best approach for me to ensure accuracy in my cuts.  

My biggest frustration with building these radiators centered around getting the correct bend angle on each panel so that the zig-zag struts would align properly.  Again, patience is key.  Take your time, and, as my wife keeps reminding me "This is a hobby.  There is no timeline to meet/beat."  

Drawing from my success with using balsa for the stowed radiator attachment nubs, I repeated the process on these components and was very pleased with the snug fit - no sagging/drooping!

I now moved onto finishing out the deployed solar panel blanket box arms.  The instructions depict these components with hollow interiors, whereas the numerous ISS photos that I reviewed all show the inside edge of each half almost flush to the top with a copper coloring.  I decided again to modify the parts to better depict my findings.  I determined that balsa strips could be used to build up the inner area of each box, with a copper-colored paper strip glued to the top side.

Next up - the SAW masts.  AXM suggests using transparency film in the assembly instructions for this part in order to achieve a more realistic rendition.  I liked his suggestion and proceeded down that path.  I soon realized that the challenges with using the transparency film would be 1) how to get good, clean folds, and 2) finding a strong glue that won't cloud the transparency and will hold the glued seam.

After a good bit of research, I determined that a form would need to be used to reinforce the fold lines and serve as the foundation for glue clamping.  I found a 5/8" square basswood rod at a local hobby store which very closely matched the inner sidewall dimensions of the mast.  I performed some light sanding of the rod to get the form down to the correct thickness.  During the same hobby store visit I picked up some Testors clear model cement which does not cloud clear plastic, is non-toxic, and cleans up with water.  It can also be used to make clear windows. Awesome stuff!

I proceeded to cut out the mast parts, consisting of two half segments and an inner joiner.  I made sure to leave a lap edge on both segments to be used as the glue point.  Next,  I scored the inside of each half along the line at each each edge.  I then took the scored part and wrapped it around the the forming rod, applying pressure to in order to sharply form the edges to achieve a good box shape.  I then applied the glue to the inner lapping lip and clamped the part down onto the rod using small binder clips.

I let the part dry overnight and removed the clamps. Voila!

After assembling the mast parts I then moved onto determining the method for affixing the deployed solar panel blanket arms to each end of the mast.  I briefly thought about just trying to glue the mast edges to the inside face of each arm's center point, however, I realized that such a join may not be strong enough due to limited surface edge contact.  

I concluded that the best way to attached the arms would be to affix a small block of the basswood rod onto the inside center point of each arm and affix the edge of the mast to the block with glue by inserting the block into the end of the mast.  Still hoping that the mast canister axles could hold up the SAWs on their own, I decided that I would need to reinforce the block connection point on the mast canister side in order to provide strength.  I inserted small wire pins though the block and protruding through the solar panel blanket arm's center point in order to reinforce this connection point. 

I cut off two sections of the basswood rod, making sure that the thickness of the block was slightly less than the thickness of the inner center point cylinder on each solar panel blanket box arm assembly.  Next, I cut the wire pins and formed holes in the basswood block using a small straight pin, and then glued the pins into the block.
I then applied a silver coating to the blocks using a Sharpie and affixed the blocks to their respective inner center points.  Affixing the mast canister-side blocks took a bit more effort, as I had to pierce holes into the canister end-wall so that the embedded pins could be inserted.

I allowed the block assemblies to thoroughly dry overnight and then proceeded to fit the ends to the masts. I applied clear window glue to the edges of each block, slipped the mast edge over the blocks, and allowed the fitted assemblies to dry thoroughly.

I then affixed one of the assembled masts to the mast canister in order to see how well the mast canister axles could support the SAW array weight.  I was disappointed to see that the masts sagged a bit with the weight of just the masts without any solar panel blankets attached. I concluded that some sort of end support would be inevitably necessary when the components are ceiling mounted.

I proceeded with assembly of the four solar panel blankets.  

Based on my prior experience dealing with slight sagging on the Zvezda and Zarya solar panels, I knew for sure that I would have sag issues with these panels due to their ralative size, as each is approximately 18 inches long.  I decided to sandwich wire strands between the panel faces to add some rigidity and to enhance realism, as the actual blankets each contain 5 cables strung across the blanket face to keep them taut.

I wanted the panels to have a little bit of shine to them and was interested to see if Mod Podge would achieve the desired result and perhaps add some stiffness.  I applied a thin coat to each copy of the solar panel parts page and let it dry overnight. I then cut out the panel sections and joined the 2-part sections for each side using a plain paper joiner tab instead of card stock in order to avoid having a thicker center area on the resulting panels' cross section.  I pressed each joined panel side under books to flatten out the part. Next, based on various photos of the actual SAW solar blankets, I determined the correct position for each cable and scored a line for each cable location on the inside of each panel.  I then cut sections of 28 gauge wire and affixed the wire to one panel side along the scored lined using small smears from peel-and-stick fabric adhesive sheets spaced out every one to two inches.  

I have tried a number of techniques and materials to get a good bond between solar panels up to this point in the ISS build.  For Zarya's solar panels I spread a thin layer of tacky glue, which worked OK, but introduced too much moisture which caused some warping and required a bit of pressing under books to eliminate.  For Zvezda's panels I used an Elmer's Extreme School Glue Stick, which avoided the warping behavior, but it didn't spread as evenly as desired. I ended up having to touch up various edges with tacky glue and a straight pin in order to get all join edges properly adhered.  I also used the same school glue stick to join panels for the Soyuz and Progress vehicle builds with better outcome, likely due to their smaller comparative size.

I wanted a better outcome for the SAW panels, since they're much larger and involve more work to assemble with the wire strand sandwiching technique.  I was convinced that a glue stick is the best application technique for this type of application, so I conducted some research to determine which glue stick would work best.  My research pointed to Elmer's CraftBond Extra-Strength Glue Stick as a good candidate based on various customer reviews using it in crafting applications, so I decided to pick a stick up at my local craft store to give it a try.  

I was pleased with the results.  This glue stick spread more evenly than the regular school glue stick and it did not introduce moisture like regular glue application had caused.  I spread the glue to the inside of the panel without the wire strands attached and was able to easily bond both sides of the solar panel together with good contact/adhesion.  I applied book weight on top of each panel assembly and let them sit overnight.  I cut a thin slice of plain paper and layed it across the glue seam at the center on each panel side to re-introduce the white grid line that was omitted by the segment join.

Joining the solar panel blankets to their respective blanket arms proved to be a bit tricky due to my introduction of the wire strands "complication".  AXM's instructions for attaching the panels involves a simple tacking of the edge to the outer arm across the entire edge of the blanket and attachment to the edge to the inner arm using the ribbon tabs located on each end of the arm.  However, my decision to include the wire strands added complication by requiring small holes to be placed across the inside face of each arm so that the wire could be inserted. I had to also ensure that enough wire was left on the inside end of the blanket to ensure that the wire would fully extend into the respective hole on the arm. I chose also to place holes across the inner face of the outer arms for wire insertion.  I cut the wire much shorter on this side, bent each strand in half, and inserted the bend strands with a bit of glue into the holes to attach to the outer side.  I was very pleased with the end result!

Next, I cut out the grapple fixture plates and inserted a piece of wire at their centers to represent the center grapple pin and add detail.

I assembled the four trunnion pins, using layering and small wire sections to achieve realism.

I then proceeded to attach the trunnion and keel strut assemblies, trunnion pins, grapple fixtures, and space target dots at prescribed locations on the truss structure.

I chose to support the outer sides of each SAW using a strands of monofilament (4 lb. test) looped around the mast at the outer end.  Each strand will be attached to the ceiling using a small fishhook.

The build was now complete.  Time to transport the build to my office!

As with prior builds, I initially setup the component on a side desk in my office for a few days to allow my co-workers to take a close look at my handy work before I added it to the ceiling mount configuration.

After a few days of display on my side desk I transferred the truss assembly to its initial ceiling mount location atop the Z1 truss.

I'm now moving onto building the Destiny Lab component.  Stay tuned!

1 comment :

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