ASP Astrobee D

tjkopena

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Quick build thread on ASP's Astrobee D micro-rocket. Unless I'm mistaken it's a relatively new kit, came out in 2021. It's a scale model built around a T-MM minimum diameter tube and will end up about 7" tall.

All the stuff in the bag:
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ASP's instructions are detailed and clear, and I'm a big sucker for the simple lineart cover drawings.

First note to me is the brightly colored little plastic bits. These get used as anchors for the shock cord. I believe that's a change with this kit, the previous ASP MMX kits I've seen tied directly around sections of coupler tubing.

As usual for ASP's MMX kits there's a generous amount of polystyrene fin material. You could cut at least two, maybe three sets of fins out of it. In this kit one whole 1.5" coupler tube is included solely for pushing in the motor block, so that's another very useful extra bit that will find its way into a scratchbuild at some point. There's also their usual length of polystyrene angle stock used purely for marking the tube. I have to work on something to do with these.

The streamer in this kit, supple mylar that works as well as any material does in MMX tubes, is twice as wide as their usual, I believe, and fairly long.

The decals might be at higher resolution than some of their older kits. I don't know if I'll use the black boxes, as opposed to simply masking & painting those tail sections. But the logo and Astrobee D name label are sharply printed.
 

tjkopena

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Reorganizing steps a bit, I like to get most of the cutting and sanding out of the way up front.

First up is lightly sanding the two sections of body tube, so the glue and paint will adhere better. I used 320 grit sandpaper here.

ASP's MMX nosecones are very nice. They're 3D printed, I believe in ABS-like resin. The only work needed on them is scraping and sanding the bottom rim of the shoulder a bit to remove the last traces of the support structures left from printing.

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I'm cheap & a hoarder, so I cut up and rearrange the fin templates in order to conserve a good length for future use. I simply tape them down to the stock and my cutting board with Scotch tape; I haven't found double sided tape as discussed in the instructions to be necessary. After cutting the fins were sanded as a block in the usual way. I did not bother rounding or tapering them, they're so thin anyway and it'll look plenty good either way.

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Lastly for the prep work, one of the coupler tubes gets cut in half. I usually use a razor saw w/ a miter block for one-off cuts of small paper tubes like this when the cleanliness of the cuts don't matter, in this case because they'll be hidden inside the body tube. That said, with a fine tooth saw and going smoothly, they can be cut pretty cleanly. Here I'm using a Miter-Rite jig I got recently. Jury's still out on this one. It's very cleverly designed and I want to really like it. But there's just a bit too much torsional leeway that the set screws alone can't address. Some thin inserts in the blade holder might address that though.

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tjkopena

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Next up is attaching the fins. I used a simple jig I designed (there are many like it though) & 3D printed for T-MM tubes and ~0.5mm stock. I was sure I'd posted a set of T-MM fin jigs to Thingiverse but now I don't see those versions in my designs. I'll correct that later today or tomorrow. A collection of these jigs for several sizes of stock and fin count are available on Thingiverse.

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I use thick gel cyanoacrylate for the initial glueing of these kinds of thin polystyrene fins so that it doesn't go all over the place. A very thin line or even just tack dots along the fin root are necessary to secure the fin in place. With that little glue it sets almost immediately so you have to move the fins into place quickly & accurately.

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Once they're all set I then strengthened them with a fillet-style bead of thin liquid cyanoacrylate along the roots.

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tjkopena

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These next bits I did a bit out of order and differently from the instructions, but it doesn't matter too much.

All of ASP's MMX kits that I've seen take a similar approach to nosecones. The nosecone is glued into a short segment of body tube, which then gets a coupler to connect to the main segment. The shock cord is usually tied around the coupler, or, like in their Corporal, to a tiny lead weight ahead of the coupler that's secured by the latter and serves as both the tiedown anchor and nose weight. In this kit the Kevlar thread is tied around a small plastic tube that is glued inside one of the pieces of cut coupler, which in turn is then itself glued inside the nosecone tube. The primary knots I've used here are buntline hitches.

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The other half of the coupler section cut in half previously is then used as the motor block. I believe these instructions have you glue that coupler in place, then run the thread through, tie it to the other little plastic piece, and then pull that into & glue inside the motor block. I tied the thread to the plastic piece and glued it inside the motor block, then pushed that assembly backwards through the body tube and out the other end. I then used a small glue applicator to smear wood glue inside the body tube by inserting it up to a mark at 24mm. I am super paranoid about using CA for this step because I've had motor blocks seize before they were inserted as far as intended, and I don't really like using extenders like the instructions suggest. In any event, with the wood glue applied, the motor block is pulled into the body tube and then pushed 20mm in with a spent motor which is then removed.

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tjkopena

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Once that glue set, next up is marking a line for the launch lug with the angle stock included in the kit. The lug was tacked into place with thick gel cyanoacrylate, and then strengthened with micro-fillets of thin liquid cyanoacrylate.

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Last, and probably actually least in terms of its necessity for a micro-rocket, is simply attaching the streamer to the shock cord thread with a piece of Scotch tape.

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tjkopena

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With that this ASP Astrobee D is all assembled! I'd say it's ready to fly, but there's a good chance it'll never fly for fear of losing it.

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Regardless, the next step is to get some prototypical tan paint for the fins and nosecone. One of the things that drew me to this kit is precisely that it's a fairly unusual color scheme, so I definitely want to finish it that way. More to come at some point!
 
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