The Mars Lander model rocket was introduced by Estes in 1969. Designed by Wayne Kellner, it featured shock-absorbing landing gear that allowed it to land upright
...Plus without damage (usually). When Estes stopped making the kit, Semroc began offering a nearly identical replacement kit that is still available today.
This 3D-printable reproduction has the advantage of allowing easy replacement of the springs/rubber bands used on the landing gear - something that was difficult to do on the original. Most parts connect via twist-lock fittings. Only the landing pads (feet) need to be super-glued together and glued onto the landing gear (legs). The landing gear shown are red PLA and everything else is white PLA, with the pads spray-painted silver.
The finished model is about 12 inches or 30 cm tall.
I have not flown this model, but I have included features that should make it possible. There is a shock-cord attachment lug inside the rocket, just below the nose cone base. There is a launch lug tube that runs the entire length of the rocket that should accept a 1/8" launch rod. The ejection baffle should protect the parachute somewhat, although, depending on the material used, it may need replacing after one or more flights.
The nose cone base has a compartment that is the same diameter as U.S. copper pennies, so that nose weight can be added as necessary. Wadded paper can be used to fill out the remaining space in the compartment.
An engine mount tube with centering rings would need to be built, with rings spaced so the entire mount is held in place between the ejection baffle and the flange on the bottom of the lower core tube. If standard model rocket materials like wooden centering rings and paper tube are used for the engine mount, it would ensure that it could withstand the heat of the engine. You could design and print an engine mount if you select material that can stand the heat, or be prepared to replace it if it warps.
Note that the price you pay for easy assembly/disassembly is a heavier rocket. Even though it is 1:1 scale, the PLA-printed one came out to 6 oz compared to 3 oz for the balsa/paper model. If you fly it, you will need to adjust engine rating accordingly, and check the CG/CP relationship. The site linked below has some RockSim info to help with that.
The embossed patterns on the ascent stage should be deep enough to survive sanding and painting. The embossing on the cardstock wraps on the original kit was fairly shallow.
A warning about the decals: If you use water-slide decals on raw printed plastic, they go on nicely, but after they dry they will come off easily if disturbed since the layer lines make for minimal contact with the decal. You might want to either sand and paint the model before applying them.
Update: 12/19/2017: Added file "Full Landing Pad.stl" - This combines upper and lower parts for people who want to print them together as one and use some infill to support
