While browsing eBay, I found an old issue of Amazing Stories up for auction. On the cover were three space ships in the classic "Mars Lander" style - bulbous bodies and big landing legs. These images just sorta sat in the back of my mind for a while, and slowly a plan for building one of them came together.
The first thing I did was to go shopping. I needed something for the ball-shaped capsules, something for the fuel tanks, and some means of creating the legs, feet and other struts. I spent a lunch hour prowling the aisles of K-Mart, and found a lot of useful parts, including the parts I needed for this lander.
Next, I drew up some quick plans. These are not to scale, but they're pretty close. Mainly they served to play with a paint scheme, and think through how the motor mount and recovery system would work. Given the size of the parts (the ball capsules are 2" fishing floats), this model would be powered by a 13mm motor. The parts, especially the legs, would be relatively fragile, so I'd need a parachute. I plan to make one from the bag my clothing comes from the dry cleaner's in. An eight inch chute and some shock cord should fit into the top-most ball capsule.
I call this model my "Capsule Lander" for now, but may well come up with a more elegant name. As I mentioned above, the main ball capsules are made from two inch fishing floats. The top capsule was cut in half using a razor saw. Both were bored through with holes top and bottom to snugly accept a piece of BT-5 body tube. Inside the top capsule, the body tube enters and is held in place by a BT20/BT5 centering ring. The bottom part of the Kevlar shock cord is tied to this ring. A BT-5 tube coupler (actually an offcut from a used 13mm engine) is glued into the top of the tube. Another piece of BT-5 tube, epoxied in place with another BT20/BT5 centering ring, is glued into the top half of the capsule. This tube fits over the tube coupler in the bottom half, holding the top half of the capsule in place. The other end of the Kevlar shock cord is tied through the upper centering ring.
The second ball capsule is epoxied in place under the first, and held in place by a third BT20/BT5 centering ring. This ring has been notched on the inside-bottom edge to accept the tops of the landing struts.
The four fuel tanks are each made from two plastic vending machine capsules. The kind you get worthless trinkets in for a quarter in most grocery stores. The two halves are glued together with plastic model cement. A hole is bored in the top of each tank, and two more are bored for the mounting pegs. The mounting pegs are made from 1/8" wooden dowel, and pass through the bored hole and all the way to the other (inside) side of the tank. These are epoxied in place for strength.
Two more centering rings are used to make attachment points for the fuel tank mounting pegs. Each ring is carefully marked using a tube marking jig, so that four holes can be drilled through the rings exactly ninety degree apart. To drill these holes, the rings were slipped over a scrap piece of BT-5, which was slipped over a scrap piece of 1/2" dowel. The holes were drilled with a slow speed cordless drill. Once the holes are finished, the rings are glued onto the main body tube such that they line up with the tank mounting pegs. The tanks are then epoxied to the rocket.
The legs are simply 1/8" wooden dowel. For each leg, a balsa support was carefully sanded to fit between each pair of fuel tanks. Each support is notched with a round file. The landing legs are glued into the notches in the upper-most external centering ring, and into the notches in the supports.
The feet are made from the lids to the vending machine capsules, with corrugated cardboard inserts cut to fit. These inserts are slitted with a small X, and the landing strut pushed through the X with epoxy on the tip.
I need to test the stability of the model, but I fully expect to need to add some clear plastic fins underneath each landing leg. I don't think the drag from the feet will be enough at all. Also, I plan to add a paper shroud at the bottom of the body tube, to simulate an engine nozzle.
My good friend Eduard borrowed by model for a bit, and made these amazing 3D images using a ray tracing tool. Pretty cool!
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