Systematic design of a parachute recovery system for the stratos III student built sounding rocket

In the summer of 2016 a group of students from Delft Aerospace Rocket Engineering (DARE) started a project to reclaim the European altitude record for amateur rocketry currently set at 32.3 km by HyEnD. This project was named Stratos III as a follow-up on Stratos II+. To recover the flight data, video footage, payload and valuable hardware, the nose cone would have to be recovered. The Stratos recovery team, consisting of Bachelor and Master students from the TU Delft, was tasked with this job. During the conceptual phase it was decided to separate the rocket just before it will enter the atmosphere and only recover the nose cone. Removing the mass of the empty tank and engine reduces the difficulty of recovering the flight data, as well as the required mass of the recovery system. Additionally, it would create an aerodynamically unstable nose cone. Upon contact with the atmosphere, the nose cone will enter a flat spin with a frequency of 2 Hz, this bleeds off velocity thus making recovery easier. At an altitude of 4000 meters a Hemisflo ribbon drogue parachute will be deployed. This type of parachute is designed to handle the high dynamic pressures and supersonic conditions encountered during the flight. To be capable of handling the high temperatures which are experienced in supersonic flight, the drogue parachute is made out of aramids. Due to the spin experienced by the nose cone it is required to eject the drogue such that the suspension lines are stretched within half a revolution of the nose cone. This is achieved using a cold gas deployment device. The drogue parachute ensures that the nose cone is stabilized and slowed down to subsonic velocities which assures the main parachute will be deployed in its operating envelope. The main parachute is a cruciform parachute with its corners attached. The aspect ratio of this parachute is 0.7, which ensures a high drag coefficient combined with sufficient oscillatory stability. To determine whether the entire recovery system was capable of handling all possible flight conditions a grid search simulation was done to find the operational limits of the system. It was seen that the inflation load of the drogue parachute was highly sensitive to changes in the altitude and velocity at apogee. These simulations showed that there are possible cases where the inflation loads of the drogue parachute approached the structural limit of 10 kN, however none of the flight cases crossed the maximum loads. This system gives the team confidence that the flight hardware will be recovered.