Dr. Zooch - Vostok Build - FINISHED!

[Mushtang]

It took a while to get all the straps in place. I held them up to each other in the order that they'll be on the rocket, and the heights of the straps all match whenever I line up the tops of the tubes.

Before I started marking the locations of the straps I considered measuring from the top instead of the bottom, because I'm expecting to line up all the tubes onto the body tube with the top of the boosters right on the edge of the reduction. If the booster tubes were different lengths and I measured the straps from the bottom of the boosters, the straps wouldn't line up.

But I checked the boosters against each other and they're all the same length. I sure hope I didn't look at them wrong somehow and when I go to put the boosters in place the straps don't line up.

Here's all four boosters with their straps, witches hats, and balsa discs glued in place.

The next step is to paint these suckers before gluing them onto the rocket. What could possibly go wrong?

 

[luke strawwalker]

The instructions then say to cut the fins out of the balsa sheet using the template provided. It was easy enough to cut the triangle out of the card stock and then trace 4 fins onto the balsa. From reading other threads, and from the note on the template, I knew to keep the edge of the fin that was to be the leading edge parallel to the wood grain. .

This is a very handy thing the Doc does on his templates... even draws mock "grain" on the pattern along with arrows and the words "grain direction" or something to that effect... kinda hard to miss...

The triangle was a small right triangle with the hypotenuse being the leading edge. As I was tracing the triangle onto the balsa I started to attempt to reduce the cutting by having 2 fins share an edge, but since there was plenty of balsa I decided against it and spaced them out a little. I still have room to cut out a few more if I mess up the fins..

That's usually how I do it... (cutting them so they share edges if possible). It works but it requires more careful cutting so they all end up the same size. If you have the room and want to take a little extra time cutting them out, the way you did it is probably better... I always "stack sand" my fins to ensure that they are all EXACTLY the same size and that the edges are square after cutting them out...

After cutting them I rounded over the leading edge with sandpaper. I couldn't tell if the instructions intended them to be rounded over or pointed. It said something similar to, "Sand the leading edge to a sharp aerodynamic shape", but I opted for rounded over.

Most rockets and missiles have either wedge-shaped or double-wedge fins... they're the most efficient shapes at supersonic/hypersonic velocities... (and the most aerodynamically effective at those speeds). Now, IIRC, the fins on the R-7 are virtually "diamond shaped" and the wedge shape extends FAR back along the length of the fin... which of course is VERY difficult to sand. (Much like the fins of the Saturn V which basically the front 3/4 of the fin would have to be sanded away to get the "correct" profile...) On the Zooch Saturn V, (and probably this kit too) it would look "more correct" to have the front edge of the fins sanded into a "wedge" shape... say about a 45 degree angle or so, just to give an "indication" that they're wedge shaped... That's what I did on my Saturn V, and it looks pretty good IMHO.

That said, on my Zooch Discoverer Thor, which is the first Zooch kit I build, I rounded over the leading edges of the fins and it looks fine... it's not a biggie...

Also, one other idea to throw out for ya... these fins are IDEAL candidates for PAPERING!!! First fins I ever papered (well, not EVER but that's another story) were on my Zooch Discoverer Thor... they came out TERRIFIC! REALLY strengthens up those balsa triangles!

You're doing a great job so far! KUTGW!!! OL JR

 

[Mushtang]

I'm thinking ahead and planning to attach the fins and spray primer tonight. I'm wondering how the heck I'm going to hold/support these boosters in order to spray them.

The best I have come up with is to loop some tape around and tape the bottom to a board to paint them as they stand up (the tape is to keep the spray from knocking them over), and then after it dries spray the bottoms while holding the top.

I can't think of any way to paint a booster all at once.

 

[Daddyisabar]

I would attach the fins after you attach the boosters, much easier and you can make sure the fins are straight. To paint the boosters separate I would just ball up some tape and then tape the ball to the end of a dowel and stick the base of the booster on top of the tape ball - easier again if you have not yet glued the balsa base on.

 

[Astro-Baby]

I dont suppose any of the booster bases has a hole in or somewhere you could make a hole that will have something covering it up later (booster nozzle or something) - if you could get a small hole in somewhere you could put something like a bit of wire in to hold it while its painted.

Its really a hellish kit you have there.

 

[Mushtang]

I would attach the fins after you attach the boosters, much easier and you can make sure the fins are straight.

Good advice, I'll do that for sure.

I dont suppose any of the booster bases has a hole in or somewhere you could make a hole that will have something covering it up later (booster nozzle or something) - if you could get a small hole in somewhere you could put something like a bit of wire in to hold it while its painted.

Its really a hellish kit you have there.

Good thinking!!! Even if it's not covered with a nozzle a small hole to fit a coat hanger into the very center of the balsa disc would probably go unnoticed once the nozzles are in place - and would be easy to fill if it's a problem.

That's the answer!!! Thanks Astro-Baby!!!

This is one of the reasons I like forums for hobbies. Good ideas from other folks to help!

 

[gdjsky01]

Or you could use a small screw eye... then fix the hole.

 

[luke strawwalker]

I'm thinking ahead and planning to attach the fins and spray primer tonight. I'm wondering how the heck I'm going to hold/support these boosters in order to spray them.

The best I have come up with is to loop some tape around and tape the bottom to a board to paint them as they stand up (the tape is to keep the spray from knocking them over), and then after it dries spray the bottoms while holding the top.

I can't think of any way to paint a booster all at once.

I usually finish the build and then I have a burned out motor casing glued onto an old curtain rod that works great as a paint stick... slide the model over the old motor into the motor mount and paint away...

You're planning to paint the boosters individually before gluing them onto the main rocket body??

If I were doing that, I think I'd tape some string to the bottom of the boosters and suspend them from a couple old coat hangers...

I will paint nosecones and transitions by taping them down to cardboard "paint sticks" (the best thing for this purpose is some foot-long paint sticks from the lumberyard though...)

Later! OL JR

 

[Mushtang]

I usually finish the build and then I have a burned out motor casing glued onto an old curtain rod that works great as a paint stick... slide the model over the old motor into the motor mount and paint away...

You're planning to paint the boosters individually before gluing them onto the main rocket body??

The problem with waiting until I was done on this build is all the spaces behind the boosters that would need paint, but wouldn't be easy to get to. I'd have to get too close with the spray paint cans and I'd have drips everywhere.

Or at least that's what I would expect ME to do. I'm sure most people here would be able to paint it after it was done without a problem, and that is very impressive to me. I don't have enough experience to be able to paint this when it was all put together, so I'll try and paint it first.

 

[Mushtang]

I dont suppose any of the booster bases has a hole in or somewhere you could make a hole that will have something covering it up later (booster nozzle or something) - if you could get a small hole in somewhere you could put something like a bit of wire in to hold it while its painted.

Its really a hellish kit you have there.

This is what I did last night and it worked great! Thanks again for the suggestion. I feel I should name the method after you to make sure you get proper credit. At first I thought I'd call it Astro-Baby's Hole, but that just didn't seem right (just now I accidentally typed Astro's Baby Hole and that would be even worse!), so I'll call it Astro's Wire Paint Holder Method.

I looked in the instructions to see how the nozzles would fit on the bottom of the boosters to pick the best place for the hole and saw that if I put the hole in the exact center it would probably be covered by nozzles if I didn't try and fill it.

(Image of instructions used with permission of Dr. Zooch)

Finding the center of the balsa disc was fairly easy using the tic marks on a circle template and a scrap piece of card stock cut to fit the bottom. Pushing the pencil tip through the center gave me a small pilot hole in the balsa, and then using a tiny drill bit I embiggened the hole to fit a coat hanger I clipped in half. There was no need to use a drill on this soft wood, simply spinning the drill bit in my fingers was enough. It's like buttah.

Now that I had all the elements of Astro's Wire Paint Holder Method in place I put one of the boosters on the wire and sprayed it with gray primer.

Each booster got a coat of primer, then I sanded each one, followed by another coat of primer. After the first coat I was surprised to see discoloration where the CA glue had been used. I was even more surprised to see it after the second coat. I thought primer was supposed to cover up stuff like this and give a uniform painting surface. Is there something I need to do before trying to spray the boosters with a couple coats of gray paint?

 

[luke strawwalker]

The problem with waiting until I was done on this build is all the spaces behind the boosters that would need paint, but wouldn't be easy to get to. I'd have to get too close with the spray paint cans and I'd have drips everywhere.

Or at least that's what I would expect ME to do. I'm sure most people here would be able to paint it after it was done without a problem, and that is very impressive to me. I don't have enough experience to be able to paint this when it was all put together, so I'll try and paint it first.

Yeah, I see your point... probably would be hard to get good coverage down in all those valleys between boosters and core...

Good thinking! KUTGW! OL JR

 

[luke strawwalker]

Each booster got a coat of primer, then I sanded each one, followed by another coat of primer. After the first coat I was surprised to see discoloration where the CA glue had been used. I was even more surprised to see it after the second coat. I thought primer was supposed to cover up stuff like this and give a uniform painting surface. Is there something I need to do before trying to spray the boosters with a couple coats of gray paint?

That's weird... what primer are you using??

Never had that happen before!

Yeah, primer SHOULD cover it up! CA typically turns paper sorta "clearish" but the primer should go over that and give a uniform color... almost sounds like the CA is reacting with the paint in some way... NOT good...

I dunno... you may not have any other choice but to paint one and see how it comes out... I'm at a loss on this one...

Later and good luck! OL JR

 

[Daddyisabar]

CA Soaked/sealed paper will be a different shade/color that regular unsealed paper when hit with primer - don't worry about it, your paint will cover it all up. Sand the primer off until it is really ugly, that means you are filling in all the small bumps, making a good flat surface.

 

[gdjsky01]

CA Soaked/sealed paper will be a different shade/color that regular unsealed paper when hit with primer - don't worry about it, your paint will cover it all up. Sand the primer off until it is really ugly, that means you are filling in all the small bumps, making a good flat surface.

Daddyisabar (or as I call him, Pappy, :wink is correct. Look at Chris M's (hcmbanjo) build's on his web site. He sands down the grey primer until it looks like a camo job for a planet that is grey and white.

 

[Mushtang]

I stopped by my local hobby shop to pick up Testor's EURO GRAY and Sea Gray as specified in the instruction's Paint Scheme #2. This is listed as the rocket's actual color, while a Paint Scheme #1 gives you colors to use to match the appearance of the rocket in most photographs. The difference apparently coming from the Russian's crappy photography techniques.

The hobby shop, didn't have those particular colors in their Testor's selection, but had them in Model Masters brand. I'm color blind anyway, so if the two weren't exactly the same what did I care? So I bought what they had, along with a small bottle of brush on copper paint for the engine bells.

When I got home I begin by painting the first of the boosters in EURO GRAY, again using Astro's Wire Paint Holder Method. I intended to put on a light coat and come back to do another, but the paint came out faster than expected and I was putting on a normal coat. No biggie, the booster wasn't entirely covered and will still need a second coat, but that may wait until the boosters are glued to the rocket. The main point here being to get the boosters painted so that the final paint job isn't so tough. Here's the first booster drying while the Astro's Wire Paint Holder Method sits on a roll top desk in my kitchen.

I also grabbed a big dowel rod and gave my Tamponski rocket a coat of EURO GRAY. We have an old step stool in our kitchen that my mother used to have in her kitchen 40+ years ago when I was a kid, that has proven to be VERY useful when standing rocket parts on their dowel rods to dry!!!

 

[Mushtang]

While the boosters were drying I kept myself busy with the engine bells. These were cut out from the copy I made of the template provided. It was easier to cut these out since the diameters weren't critical and didn't have to match anything exactly, such as the top of another tube or some mating part like that. So I'd cut some, glue them, paint another booster, cut more engine bells, glue them, paint another booster, etc.

The first few bells I created ended up being flat on the side where the glue tab was. So I took another tip from Chris Michielssen and created a form to use. This was simply about 5 inches cut from a large dowel, that I whittled and sanded to the approximate shape of the engine bells.

I'd form the bell with my hands, rolling a smaller dowel across the paper to start the curve, get the bell completely curved to shape, put on the glue, spread it with my finger to wipe off the excess, put the tab in place until it set up enough not to come apart, and then I'd put it onto the dowel form and press hard onto the tab area to make sure the glue completely set up curved instead of flat. It worked GREAT! Thanks Chris!!!

Here's a picture showing my bells in various stages of cutting them out, the small dowel for rolling the curve in my hand, the larger dowel form, and a growing stack of engine bells.

 

[Mushtang]

During the creation of the boosters and main body I have been very careful to keep each booster labeled as to which section of the spider beams they would attach to. The sanding of the spider beams and positioning of the witches hats are unique to each booster and position and I'm sure if I mix them up they won't look as good.

As I was painting each booster and the main rocket I discovered that I was painting over my designations and was risking getting them messed up. After each booster was painted I replaced the penciled on number again near the booster's seam. On one of the boosters I forgot which made me a little nervous for a moment but was able to figure it out easy enough, but it made me want to come up with an additional way to keep track.

It's silly, but I'm sure it will work. I created a place where each booster will be set until it's time to glue it onto the rocket (which should be the next step anyway). Whenever I pick up a booster to paint, sand, inspect, or anything else I'll try and put it back on it's circle before I pick up another.

I'm starting to feel like I'm making this more difficult than it should be.

 

[Mushtang]

Now it's time to paint the outside of the engine bells silver. I didn't want to do these one at a time so I took yet another tip from Chris Michielssen and taped a few pieces of tape upside down to a scrap piece of wood so the tiny bells would stay in place. Luckily I happened to tape them down in a way that was easy for me to see I had an odd number instead of even. There was supposed to be 16, not 15!! A quick search over the table turned up the missing template that I had to finish cutting out and glue together to complete the set.

Here are the bells glued down, ready for paint.


And then after spraying with silver.


When they dry I'll have a choice to make. Do I hand paint the copper before gluing them to the bottoms of the boosters, or after?

 

[Daddyisabar]

Daddyisabar (or as I call him, Pappy, :wink is correct. Look at Chris M's (hcmbanjo) build's on his web site. He sands down the grey primer until it looks like a camo job for a planet that is grey and white.

Pappy Boyington was only in his early thirties and was considered an old pilot. I guess I have a decade and a half on that so "Pappy" ain't so bad.

"Do I hand paint the copper before gluing them to the bottoms of the boosters, or after?"
After - I hand painted the copper in the nozzles as the last step in the painting process. You don't want any clear coats to get on the bright silver-chrome or metalic copper brush paint.

 

[[POW]Eagle159]

I stopped by my local hobby shop to pick up Testor's EURO GRAY and Sea Gray as specified in the instruction's Paint Scheme #2. This is listed as the rocket's actual color, while a Paint Scheme #1 gives you colors to use to match the appearance of the rocket in most photographs. The difference apparently coming from the Russian's crappy photography techniques.

The hobby shop, didn't have those particular colors in their Testor's selection, but had them in Model Masters brand. I'm color blind anyway, so if the two weren't exactly the same what did I care? So I bought what they had, along with a small bottle of brush on copper paint for the engine bells.

When I got home I begin by painting the first of the boosters in EURO GRAY, again using Astro's Wire Paint Holder Method. I intended to put on a light coat and come back to do another, but the paint came out faster than expected and I was putting on a normal coat. No biggie, the booster wasn't entirely covered and will still need a second coat, but that may wait until the boosters are glued to the rocket. The main point here being to get the boosters painted so that the final paint job isn't so tough. Here's the first booster drying while the Astro's Wire Paint Holder Method sits on a roll top desk in my kitchen.

I also grabbed a big dowel rod and gave my Tamponski rocket a coat of EURO GRAY. We have an old step stool in our kitchen that my mother used to have in her kitchen 40+ years ago when I was a kid, that has proven to be VERY useful when standing rocket parts on their dowel rods to dry!!!

Looks really NICE!

Just as an FYI, the Master Modeler paints are made by Testors, so they are like the same!

 

[Mushtang]

Looks really NICE!

Just as an FYI, the Master Modeler paints are made by Testors, so they are like the same!

Thanks!

And thanks for the info on the paint. Makes sense.

 

[Mushtang]

I was now at the point where I could glue on the boosters to the main rocket body. The instructions explain how to build a little table out of the alignment guide to make sure the rockets are lined up properly around the rocket. I tried to figure out how making the thing would be more helpful than just being careful and making a few measurements.

Perhaps it's just because I haven't done enough of these before, but I must have been misunderstanding something, so I skipped the alignment guide and just tried to be careful. I'll definitely use the alignment guide when it comes time to put the fins on.

When I was dry fitting the boosters and sanding the spider beams to make sure they all fit I tried to be as careful as I could to make sure each booster was straight and the spider beams held it in the right position.

I glued on opposite boosters and using painters tape held them in place while I went to see a movie. When I got back I glued on the other two boosters and using more painters tape held them in place while I slept. This morning the tape was removed and as far as I can tell the boosters are in line.

It won't surprise me if later on in this build I realize, "Oooh, THAT is why the alignment was so critical. Oops."

 

[Mushtang]

Somewhere in the past few days I read ahead and prepared some items for this step. The large balsa plug was sanded to fit the small section of tube that was cut off early in the build, and then glued in place. After that I cut the small dowel stick into 1/2" lengths. This was easy to do with the hobby knife just by rolling the blade along the top of the dowel as it rolled across the cutting mat. About 4 or 5 revolutions and it was cut cleanly.

After they're cut I was instructed to sand the ends to angles for gluing, which was easy enough to do. Luckily the angle here wasn't critical so I could just hold the tiny pieces in my fingers.

Here's the finished plug and dowels.


There is an alignment guide for gluing two dowels together to form a V shape. Once you get 5 of these glued you stand them up onto the plug and glue them in place to form the structure under the capsule section.

Very carefully I used the double glue method to get two dowels to stick together, and then I laid them down on the guide to slightly move them into the correct angle. I wasn't concerned that the guide seemed a little off with the lengths, I just used it to make sure the angle was the same.


When all 5 Vs were glued and drying I decided to go ahead and glue them onto the top of the plug. Boy, I was glad I tried this before they dried. I had about 3 of the Vs in place when it became obvious that they weren't going to go all the way around. Something was wrong!


I quickly pulled the Vs out and decided that I was going to have to pull them all apart, sand off the glue, and try again. Dangit.

 

[Mushtang]

As I pulled the Vs off of the plug I realized why they didn't fit. I'd matched the angle of the Vs to the alignment guide instead of the width of the bottom of the Vs. The width of the bottom is the key dimension, and it doesn't really matter what the angle turns out to be.

Because I was doing all this before the Vs had time to completely set, I was able to spread them apart slightly without breaking the glue bond. So no further sanding. Yay!!

Here is a V sitting on the alignment guide with the correct width at the bottom (or close to the correct width anyway).


After I spread each V to fit the alignment width I replaced them onto the plug and got a MUCH better fit all the way around.


When I was happy with the positions I put a dab of glue on the top of each V and left it to dry. When all the Vs are set up I'll put CA on each joint, and when that dries add a lot of glue to the bottom of the Vs, per the instructions. Before the capsule gets glued to the tops of the Vs I'll have to sand them to make sure they're level. They're pretty much level now but sanding will also give more surface area at the tops of the Vs for gluing.

 

[luke strawwalker]

I was now at the point where I could glue on the boosters to the main rocket body. The instructions explain how to build a little table out of the alignment guide to make sure the rockets are lined up properly around the rocket. I tried to figure out how making the thing would be more helpful than just being careful and making a few measurements.

Perhaps it's just because I haven't done enough of these before, but I must have been misunderstanding something, so I skipped the alignment guide and just tried to be careful. I'll definitely use the alignment guide when it comes time to put the fins on.

When I was dry fitting the boosters and sanding the spider beams to make sure they all fit I tried to be as careful as I could to make sure each booster was straight and the spider beams held it in the right position.

I glued on opposite boosters and using painters tape held them in place while I went to see a movie. When I got back I glued on the other two boosters and using more painters tape held them in place while I slept. This morning the tape was removed and as far as I can tell the boosters are in line.

It won't surprise me if later on in this build I realize, "Oooh, THAT is why the alignment was so critical. Oops."

]

Looks good to me!

Are you painting it with frost on the tanks or without?? (gray overall). The boosters and core tanks are frosted a good ways down and doing it later would seem to be a BIG PITA...

Just curious! OL JR

 

[luke strawwalker]

As I pulled the Vs off of the plug I realized why they didn't fit. I'd matched the angle of the Vs to the alignment guide instead of the width of the bottom of the Vs. The width of the bottom is the key dimension, and it doesn't really matter what the angle turns out to be.

Because I was doing all this before the Vs had time to completely set, I was able to spread them apart slightly without breaking the glue bond. So no further sanding. Yay!!

Here is a V sitting on the alignment guide with the correct width at the bottom (or close to the correct width anyway).

After I spread each V to fit the alignment width I replaced them onto the plug and got a MUCH better fit all the way around.

When I was happy with the positions I put a dab of glue on the top of each V and left it to dry. When all the Vs are set up I'll put CA on each joint, and when that dries add a lot of glue to the bottom of the Vs, per the instructions. Before the capsule gets glued to the tops of the Vs I'll have to sand them to make sure they're level. They're pretty much level now but sanding will also give more surface area at the tops of the Vs for gluing.

Just a thought... but the CA really doesn't buy you ANYTHING... If it were me, I'd just go over them again with another layer of white glue... it will bond to the glue already there and make a much stronger bond... the dissimilar CA won't really do that very well, and it won't add NEARLY as much strength! The strongest bond you'd likely get here would have been with yellow wood glue, but the white glue should be adequate to the task... I'd just go over the joints again with another healthy "fillet" of white glue down into any gaps around the joints and then put the healthy layer of wood or white glue down into the tube to join them all together solidly like the instructions suggest...

Looks REALLY good! Coming along VERY nicely and a great first build thread!

OL JR

PS... GREAT tip about the patterns... that's a "gotcha" that would have tripped me up for sure! Nice tip!

 

[Mushtang]

Looks good to me!

Are you painting it with frost on the tanks or without?? (gray overall). The boosters and core tanks are frosted a good ways down and doing it later would seem to be a BIG PITA...

Just curious! OL JR

I'm guessing without, since the instructions just call for EURO GRAY all over the tanks. I had no idea there was frosting, or even what that means.

 

[Mushtang]

Just a thought... but the CA really doesn't buy you ANYTHING... If it were me, I'd just go over them again with another layer of white glue...

Dangit!! Where the hell were you this afternoon while I was putting the CA on???

It's dried and painted the lighter colored Gray now, so too late to do anything about it. I had to sand off the tops of the Vs and was putting a bit of pressure on them to do so, so I'm not at all worried about the strength of the glue. They're not going anywhere unless the rocket is completely destroyed.

I'm about to glue the silver nozzle onto the bottom of the capsule, paint the inside of it copper, then glue the tops of the Vs to the bottom of the capsule (around the nozzle).

 

[luke strawwalker]

I'm guessing without, since the instructions just call for EURO GRAY all over the tanks. I had no idea there was frosting, or even what that means.

The R-7/Soyuz, same as the Atlas, uses kerosene for fuel, which of course is a room temp/atmospheric pressure liquid... BUT they use LIQUID OXYGEN for oxidizer... which at 297 degrees below zero (or thereabouts IIRC) is DEFINITELY cryogenic!

It causes the moisture in the air to freeze to the sides of the rocket on the LOX tank... as the frigid liquid inside absorbs heat from the air, through the metal tank wall, causing the LO2 to boil... (same idea as refrigeration-- the GOX (gaseous oxygen) boiled off has to be vented to the atmosphere through a pressure regulator to maintain the correct pressure in the tank, and the boiled off LO2 has to be replenished to keep the tanks "topped off" at the proper level prior to ignition and liftoff.

That's why when you see the Soyuz, Atlas, and especially the Saturn V, during ignition and liftoff, there's a virtual SNOWSTORM on the launch pad-- because the layer of frost and ice that builds up several inches thick is shaken loose and rains down the sides of the rocket onto the launch pad because of the acoustic vibrations and physical vibration of the vehicle from the turbopumps and engines when the rocket fires up. This can amount to TONS of ice and frost clinging to the sides of the rocket that come raining down like a hailstorm...

Now, Liquid hydrogen is 423 degree below zero, in fact only about 7 degrees or so above absolute zero (again IIRC). This is below the temperature at which AIR ITSELF liquifies... liquid air dribbling off the sides of the tanks and into the machinery is an explosion hazard, because liquid air may be 70-odd percent liquid nitrogen, but it's also 23 percent liquid OXYGEN, which is INCREDIBLY reactive (and bursts into flames when in contact with anything flammable if you just LOOK AT IT HARD ENOUGH! SO, special precautions were used to insulate the LH2 tanks to prevent the formation of liquid air... The original plan was to line the LH2 tanks of the Saturn V with balsa wood planking several inches thick... this evolved into special "insulation tiles" applied to the interior surfaces of the LH2 tanks, and spray-on foam insulation being used on the outside of the Saturn V S-II stage LH2 tank. Of course this also minimized boiloff of the volatile highly flammable LH2, which has to be replenished with additional liquid hydrogen before liftoff and also the GH2 has to be carried off by a vent umbilical and safely burned off, which at KSC is a "burn pond" where it is bubbled to the surface from underwater pipes, ignited, and burned off on the surface of the water as it bubbles up. (Hydrogen burns perfectly clear in air-- you cannot see the flames-- had a buddy in the police academy who got bad 3rd degree burns when he was a chemical plant fireman-- they were fighting a refinery fire and a hydrogen fireball shot straight out toward them and burned them all badly...) And of course GH2 mixed with air is somewhat explosive-- if you've ever had a car battery explode like a hand grenade right in front of you (I have, in a farm tractor) you'll know what I mean!

When the Space Shuttle came along, it was realized that it would be necessary to prevent the "ice storm" raining down the sides of the rocket that had been acceptable with Atlas and the Saturns... because the shuttle's VERY BRITTLE and easily damaged (about like sheetrock, maybe a little softer actually) thermal protection tiles were adjacent and a couple feet away from the side of the External Tank, which would be filled with LOX (in the front 'nosecone' above the SRB's) and LH2 (from the orbiter nosecap tip to the rear dome of the tank). SO, they perfected the spray-on insulation and laid it up in layers sufficient to prevent the formation of ice on the sides of the ET, so no ice could flake off at ignition and pulverize the tiles as it fell... It's still not EXACTLY perfect-- the shuttle had to have it's foam applied VERY CAREFULLY to avoid large bubbles or voids in the foam... these bubbles of trapped air on the hydrogen tank would, once the tank was full of ultra-cold LH2, the air inside the bubbles would LIQUIFY, which then created a vaccuum in the large "bubble" which the outer atmospheric pressure would then "crush" the foam down around the now much smaller volume of liquified air... which weakened the foam, it's bond to itself, and bond to the tank wall... at liftoff the liquid air would also tend to try to push out the bottom of the bubble or void, further weakening the foam, and as the ET's surface would heat to about 400 degrees F due to aerodynamic heating effects, the liquid air would then boil off from the heat and expand greatly in the thinner upper atmosphere, nearly devoid of outside pressure, which would cause the foam to break off the external tank.

As spraying on massive amounts of foam on the outside of the tank is much cheaper and easier than gluing thousands of custom-made insulation tiles to the insides of the fuel tanks, it's the same method used on other LH2 rockets like Delta IV, and the proposed SLS rocket.

SO, now ya know... OL JR

 

[Spacepirate R]

...which would cause the foam to break off the external tank.

And when a chunk fell off and hit Columbia's wing at a few hundred miles an hour it seald it's fate.