Moon Satellite

(competitive spotlander)

by CHEDAR-1 (T #087)

A little from the history of the project

Moon Satellite is a model rocket I created together with my son Tom during his Science Fair project (to be WEBized later). Tom's project is dealing with a rocket stability and besides all the others factors that may change the stability, effect of the spin around axial axis was investigated. To see how much stability is added by the spin, Tom suggested to try a very short rocket. Because of the low weight of the rocket we figured, that tumble recovery will be sufficient. To our surprise our rocket did not tumble but autorotated.

How does this rocket work

The effects of the spin around the axial axis are used twice:

During the boost spin stabilizes the rocket. This rocket is very short and without the spin created by the spin tabs on the fins is unstable.
During the descend the spin tabs force the rocket to spin again and resulting autorotation slows down falling rocket. The descend speed is low enough to ensure a safe landing.

Rocket Construction

Almost everything you need to know to put this rocket together is in a simple drawing above. Beside this plan you'll need some parts:

4 1/8'' inches of a BT55 tube (body tube)
2 centering rings from BT55 to BT20 tube
3 inches of a BT20 tube (for a motor mount)
an engine hook for 18 mm motor (optional)
a nosecone of your choice (we think the conical one is the best looking)
a sheet of a 3/16'' balsa

some tools:

razor saw for cutting balsa (or X-Acto knife)
ruler, pencil
Elmer's white or yellow glue, CA glue
small scissors or paper puncher
tape

and finally some dimensions (CAUTION: all numbers are valid but the drawings are not in scale):

fins (cut them with the spin tabs in one piece) are 3 7/8'' wide, 1'' high on the smaller end, 2'' high on the bigger end
spin tabs (after you cut and sand the fins, separate the spin tabs) are 3 7/8'' wide and 1/2'' high
launch lug is 1/8'' in diameter, 1 1/8'' long and its upper end is placed 2 1/8'' from the bottom of the body tube (BT55)
vent holes are 1/4'' in diameter and are placed 2 7/8'' above the bottom of the body tube

Construction is very straightforward:

BT20 tube + 2 centering rings + engine hook + glue + tape = motor mount
Cut and sand the fins (whole fins with tabs together).
Cut the tabs from the fins, sand the bevels and glue the tabs back in the angle.
Insert and glue motor mount into the body tube. End of the motor mount tube and end of the body tube are even.
Mark the fin positions on the tube (fins are 90 degrees apart).
Glue the fins to the body tube (see drawing for correct placement).
Punch four vent holes (the vent holes are in the line with the fins)
Attach the nosecone (use a CA glue for plastic nosecone).
Decorate your rocket with the colors of your choice.

Flying Moon Satellite

Recommended engine is B4-2, B6-2, C5-3 or C6-3. You can secure the engine using engine hook

(in such case make sure you did not forget to make a vent holes) or you can allow the rocket to spit the engine (this makes rocket lighter for the descend). Both configurations work. Rocket boosts straight and spins fast around the axial axis, reaches an apogee, turns the nose down and descends slowed by the autorotation.

Open Spot Landing and Moon Satellite

OSL is competition event when you need a good guess and lots of luck to land as near as possible to the target. Strategies used in OSL usually includes low flying model and small but still sufficient recovery device. Moon Satellite has some features which make it a good model for OSL competition.

It boosts straight even in windy condition, so you do not need to worry about the weathercocking.
It descends straight, so you do not need to worry about the drift.
Its recovery device is fully deployed all the time, so you do need to worry about the "full deployment" rule.
It takes A-C engines giving you the versatility in the strategy.
Engine hook prevents the engine spitting (just do not forget to make the vent holes).

Our competition version of Moon Satellite is equipped with Sidewinder type nosecone because it is more durable and does not look so threatening as the sharply pointed conic nosecone.

Used literature:

Timothy S. Van Milligan: Model Rocket Design and Construction : How to Create and Build Unique and Exciting Model Rockets That Work