Overview

Minerva was Rice Eclipse’s second rocket designed to reach 30,000 feet.

Minerva was designed to compete in the 30,000 foot Commerical-off-the-Shelf division of the 2022 Spaceport America Cup, where it was launched in June 2022. It was also our first-ever dual-separation rocket at this scale.

Minerva had a beautiful flight, and could be seen all the way to a 30,000 foot apogee and beautiful drogue deployment! The rocket slowed down as it disappeared into the clouds. Unfortunately, due to an error on the part of the spaceport volunteers, we were not given the correct GPS coordinates and were therefore unable to retrieve the rocket. Because everything we could see pointed towards a nominal flight for Minerva, we decided to make our next project a dual-stage.

While we have built other rockets in the past, Minerva is incredibly unique. Eclipse designed and manufactured almost every component from scratch, including the carbon fiber tubes that make up Minerva’s airframe. We also designed a brand-new dual-separation recovery system, a new payload attachment mechanism to save space, a 3D printed boattail attachment, and a revised outer airframe manufacturing process based on new data from testing.

Until Minerva, Eclipse had never implemented a dual-separation recovery system on a large-scale rocket. The recovery system is what brings the rocket safely back to the ground, and includes components such as parachutes and a GPS. Minerva’s dual-separation recovery system relies on two parachutes stored in two sections of the rocket’s upper body tube. The 3-foot drogue parachute deploys at apogee, when a barometric altimeter sends a signal to a black powder charge in the drogue compartment of the upper body tube. When the charge goes off, the chamber pressurizes, and the nylon bolts holding the tube coupler to the upper body tube shear, separating the rocket so the parachute can come out and slow the rocket’s descent. Later, when the rocket is at 1,000 feet, the rocket separates again, via another black powder charge, between the nosecone and the upper body tube, where the main parachute is stored. Unlike the drogue, the main parachute is stored in a parachute bag, with a small 1-foot pilot chute above it. The pilot chute comes out first and pulls on the top of the bag so that the 16-foot main parachute opens properly.

When we were first designing Minerva, we wanted to save as much space in the rocket as possible. Our experimental payload was a 3U cubesat, 30cmx30cmx10cm, and as per Spaceport’s rules, it could not be an essential component in the rocket (as in, we need to be able to fly the rocket without the payload). For these two reasons, we decided to attach the payload directly to the top of the motor block, and rather than giving it its own bulkhead on the other end, using the waterjet to make a fiberglass ‘buffer’ to minimize vibrations without taking up any extra space.

The bottom end of Minerva had a boattail, which is a tapered section that starts at the width of the lower body tube and ends at the width of the nozzle. Since there is no overlapping coupler at this point, though, attaching the boattail was a challenging design problem. In the end, we decided to 3D print a pice that fits exactly to the taper of the boattail and then straightens and has threaded holes for bolts to attach to the lower body tube.

Our body tubes, boattail, and fins are made of carbon fiber. To manufacture the body tubes, we wrap layers of carbon fiber around an aluminum mandrel and coat it with epoxy, and then remove it once it’s dry. In previous projects, we used eight layers of carbon fiber, but we did a few tests and found that our tubes were far stronger than we needed them to be––2050lbf. In light of this, we decided to only use seven layers of carbon fiber in our tubes this year. Not only does it make our manufacturing process simpler and cheaper, but it also makes our rocket lighter.

While it shares design heritage with Athena, Minerva features numerous improvements over its predecessor, including a new duel-separation recovery system which allowed us to use only a GPS in the fiberglass nosecone and not create a separate RF transparent belt, a new 8.8 lb scientific payload with a NASA-associated experiment, and mass and size optimizations to the fins, motor assembly, boat tail, and nose cone that allow the design to gain thousands of feet in altitude simulations while considerably reducing the size and mass of the rocket.

Minerva at the 2022 Spaceport America Cup showcase, where teams from all over the world were amazed by our hand-wrapped carbon fiber airframe!