1:150 Scale Space Shuttle

Jeff Lassahn

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I'm scratch-building a model of Space Shuttle Atlantis. I'm trying for reasonable scale accuracy but I'm not going to be too obsessive about it.

It turns out 1:150 is a really good scale to work at. The external tank is almost exactly a BT-70 (Scale diameter 2.220in, tube diameter 2.217in) and the SRBs are almost exactly BT-50s (Scale diameter 0.975in, tube diameter 0.976in). The Semroc BNC-50C is a close match for the SRB noses. And it will fly on an Estes C5-3 as well as D or E engines.

I've had to make my own ET nose and tail pieces, and the orbiter is going to be a pretty weird construction project no matter what scale it's at. But this is about as easy as a scale shuttle is going to get.

I'm using the pre-release new version of OpenRocket to do a rough mockup, to figure out stability, weight and balance, etc. There's a lot of dirty tricks in the file involving pods that aren't really pods, stages that aren't really stages, and such to get things positioned where I want them. I don't think any of these tricks break either the CP calculations or the boost phase of the flight simulations, so this should be usable as a simulation model. The ET and SRBs are reasonably accurate, if simplified, representations of the final design. The orbiter is not very accurate at all, the only things it's trying to get right in the model are the wing and tail shapes, approximate body cross sectional area, and the mass.

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Jeff Lassahn

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I made my own external tank nose and tail out of balsa.
I don't have a lathe. Any stories you may have heard about how you can shape a nose cone out of balsa using a power drill and some sand paper, I can confirm they're true. It really does work.

I used a 150 grit sanding sponge for most shaping and a 400 grit sponge for final surfacing.

There's already good advice on the forum here about how to do this, like https://www.rocketryforum.com/threads/turning-nose-cone-without-a-lathe.157472/

But here's a quick summary of my experience as a first timer.

First attempt, I used a 3/16 dowel. It felt reasonably strong when I installed it but after a few minutes in the drill it broke, ruining everything.
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I switched to using 1/4" dowels and it worked much better.
In addition to cutting out some paper templates of the profile of the piece, I also found it useful to cut a small length of body tube and keep it on the drill, where I can quickly use it to test fit for the shoulder. Once the shoulder is shaped I slid it onto the piece to both prevent messing up the shoulder and help size the base of the nose.

I can also confirm, too much pressure or removing material too fast results in an out-of-round piece. Shaping the piece with sandpaper works really well. But it produces a LOT of dust. Like really a lot. I worked outside, it's rained a couple of times since I finished this, there's still balsa dust visible on our front walk.

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boomtube-mk2

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If you went 1/144th scale you could use one of the Revell plastic models as the basis for the orbiter.

Actually 1/150th would only be a smidgen smaller than 1/144th so go for it.
 

Jeff Lassahn

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If I used the plastic model it wouldn't be a scratch build anymore. Making an orbiter out of stuff I've got lying around the house seems way easier than figuring out how to move this thread to a different forum category.

The basic construction plan for the orbiter is to make the wings and the bottom of the fuselage out of sheet balsa, then build the main body from cardstock supported by some balsa bulkheads. The nose and OMS pods will be carved from block balsa. I'm going to try to make the engine bells from cardstock, we'll see how that goes.

I want to build the orbiter nearly complete before doing much more with the external tank, because I need an accurate weight for the orbiter to figure out how much to offset the engine mount.

So that means I'm currently fiddling with InkScape to produce full scale drawings for all the balsa and paper orbiter parts. Here's some preliminary mockups of the body panels cut out for initial test fitting.
body_mockup.JPG
 

mjennings

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Awesome work! Are you planning on the orbiter to glide down?
On the old Dr Zooch kit he used 3 fins below the SRBs in a T configuration and had an off center weight in the ET NC. Mine always boosted super straight compared to what I saw of the old Estes stack that has fins similar to your OR plans. Some food for thought excited to see how it comes out!
 

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Very nice concept. Will be interested in how vertical/straight you can get it to fly. My similar build (with motors in the SRBs) likes to pitch over, and I am currently finishing up a rebuild adding some pitch correction to account. What size motor are you planning for? Good luck, will be watching this one.

Posts #4 and #7 in the thread below have some other very detailed info on other shuttle scratch builds, too, which I found helpful.
 

Jeff Lassahn

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I made a bunch of engine bells out of cardstock.
They're all two layer cones, with seams and edges filled with carpenter's wood filler and sanded smooth.
The orbiter main engines then have some details added made from thin strips of card.
The SRB engine bells and the OMS engine bells will remain smooth.
There's also the SRB rear skirts which will eventually have some added details made from balsa sheet and hardwood dowel pieces.
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Jeff Lassahn

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I made some progress on orbiter body construction.

The base and tail are 1/8" balsa, the internal framework is papered 1/16" balsa, and the wings are 1/4" balsa (made by laminating two 1/8" pieces because I don't have any 1/4" stock handy)
Nose and OMS pods are carved from balsa blocks.
There is a central tube that slides out the back with the rear bulkhead and main engines, to give easy access to add nose or tail weight for trimming. I'm using a BT4 with some BT5 coupler pieces as guides because I have that lying around.

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Nose and OMS pods are hand carved based on some templates I printed out, and a lot of eyeballing.
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Jeff Lassahn

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The rear internal structure goes together like this, including the removable rear bulkhead
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The main body is cardstock, preprinted in color. It's supported with some more of the 1/16 balsa pieces, and it's got a first coat of clear to protect it from damage during the rest of the build. I slopped a bit of black paint on the rear support because parts of it will be visible around the OMS pods and there's no way to get in that space later.
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I dry fit the main body while gluing the nose to get the spacing correct, but I'm not installing it permanently yet because I'm not sure it could survive the sanding steps that are coming.
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So far, the top surfaces of the wings and nose are mostly shaped, but I've left the bottoms flat. This is so I can now shape the bottom surfaces as a unit, so the nose contours blend smoothly into the body and wings.
So tonight, more carving and sanding...
 

Jeff Lassahn

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Today I'm feeling a little punchy and will be indulging in some light comedy.
I think it was Michelangelo who said the way to make a space shuttle is start with a block of balsa and a piece of sandpaper, and sand away anything that isn't space shuttle. I might be wrong, it might have been one of the other Ninja Turtles.
Anyway, more sanding to shape the bottom of the nose and the wing leading edges, and now the orbiter is basically properly shaped.
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The next step is to cover everything in carpenter's wood filler. I mean everything, all the balsa pieces, a bunch of random bits of newspaper, the table, whatever clothes I happen to be wearing... the cats have decided they won't benefit from a mirror-smooth surface suitable for painting so they're staying away.

This is the point in the project where I start thinking I'll skip all the tubes and balsa and stuff and just make my next rocket entirely out of CWF.

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Tune in next time for ... MORE SANDING ... but with a finer grit this time.
 

mbeels

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That's looking really good!

I might be wrong, it might have been one of the other Ninja Turtles.

🤣

This is the point in the project where I start thinking I'll skip all the tubes and balsa and stuff and just make my next rocket entirely out of CWF.

Hmm..... I know you jest, but I bet it'd be surprisingly strong mixed as a slurry with chopped fiberglass! Reinforced CWF-crete.
 

Jeff Lassahn

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I'm thinking a mixture of 1/3 CWF, 1/3 CA glue, and 1/3 primer. The Holy Trinity of things to make rockets out of. Only problem is we've got to have a 20 page thread on which brand of primer to use.
 

Jeff Lassahn

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After a certain amount of sanding and filling the revealed defects, I attached the main body piece. This leaves some more seams that need to be filled and sanded.
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After some more mucking about with CWF I've declared it close enough. There's still some places that aren't perfect, but I think I'll live with it.
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Now I just need to figure out what order to do some final assembly and painting.
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Jeff Lassahn

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I painted some stuff.

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Then I put on some "decals" which are actually color printed onto typing paper and glued on
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Then I glued all the bits together and did a little touchup painting
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Then I put a final clearcoat on everything, and now I have a Space Shuttle Atlantis.
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It's not perfect, there's lots of places where the seams are visible on close inspection, and not everything's in perfect alignment. But it feels good to pick it up and think "Space Shuttle!" so I'm pretty happy.

I'll need to balance it for glide, and it needs attachment points for connecting to the rest of the stack, so it isn't really Finished. But it feels like it's reached a milestone.

Next, SRBs, ET and all that stuff.
 
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