baby come back (please)

From tip to toe:

  • Machined 6061 tip

  • 3D printed + annealed PETG Ogive nosecone

  • Egg timer Quark Avionics

  • DIY Fiberglass body tubes

  • G10 + Tip2Tip reinforced fiberglass fins (Later carbon fiber)

  • CNC Machined 6061 Motor plate

The build

Baby Come Back was a rocket I built in an attempt to get my Level 2 certification. This requires successfully launching and recovering a rocket motor with a total impulse of 640Ns - 5120Ns.

However, the certification was only an excuse to build this rocket.

What I really wanted was to demonstrate my ability to learn a new skill and use it to build a rocket from scratch, all in a month.

I began with OpenRocket, a tool that allows quick design and simulation of a rocket. I then proceeded to purchase fiberglass cloth and resin from Lowe’s, rolling it on a mandrel to create the body tubes. Although this process seems simple, it caused the most headache and frustration. The optimum working temperature for the resin was 75°F, however, summer heat caused temperatures inside the building to rise to 85°F causing the resin to cure much faster than usual, reducing my working time from 20 minutes down to 7. Subsequent headaches arose when it came time to remove the mandrel. I tried various methods with mold release, parchment paper, grease, and packing tape only to come to the conclusion that it just comes down to luck with the way the resin cures. Out of 5 layups, I managed to yield 3 successful tubes.

Fortunately, everything else was smooth sailing.

SIMULATIONS

OpenRocket model for version 2 (post-CATO). Note the stability margin calibers (2.19cal)

This rocket is designed with a “dual deployment” in mind. At apogee, the lower booster section (right side body tube) will eject via blackpowder charges, deploying a drogue parachute. At 500ft AGL, the upper bodytube and nosecone will be ejected, deploying the main parachute.

The reasoning behind using a drogue parachute is to 1) slow the vehicle down for main deployment, and 2) to prevent the rocket from drifting with the wind for miles

Verifying camera mounts won’t kill the flight

This is the same plot as the one on the left but without the camera mounts on the nose. Drag coefficient is ~0.625

Here is the simulated flight with stability variables plotted. The drag coefficient from this rocket design with the camera mounts on the nose is ~0.657

Comparing the plot on the left (with camera mounts) and right (without camera mounts), we can see the left plot has less stability margin calibers during the course of the flight. This makes sense as the camera mounts add drag toward the front, shifting the center of pressure up. However, the 2cal - 3.5cal range is actually more preferable. The more calibers, the more stable the rocket is, but it is also more likely to “wind cock” - when the rocket turns and flies into the wind, wasting acceleration and thus lowering the apogee.

The basic altitude, velocity, and acceleration vs time plot.

This is a good plot to check the velocity off the launch rod and the coasting phase.

From the plot we can see the velocity at “Launch Rod Clearance” is 50ft/s, a velocity to ensure there is enough air over the fins to provide aerodynamic stability. We can further check this by identifying 0.65 calibers of stability at the same event on the stability plots above.

MANUFACTURING

LAUNCH 1

The launch was less than ideal. Shortly after takeoff, the seal on the bottom of the motor failed and the exhaust blew out the side causing the rocket to begin “coning” or “spiraling” due to the sudden sideways thrust.

This was a manufacturer’s defect unfortunately, so there wasn’t much I could learn from.