This thesis involves the preliminary design of a two-stage rocket, with a primary focus on the development of an inter-stage device. The development of a multi-stage rocket is aimed at further extending the capabilities of the Mechanical Engineering Department into high-altitude, hypersonic flight testing. The upper stage of the rocket is to be based on the Wagtail motor, which is currently under development, while serious development of the booster will be a project for the future.
The preliminary work on the rocket carried out in this thesis included the estimation of the physical size, fin setup, and performance of the booster, as well as possible launch trajectories. The estimates made are expected to allow the rocket to take a 10 kg payload to mach 6 at an altitude of approximately 30 km.
These preliminary estimates formed a basis for the detailed design of the inter-stage device. This included: 1) approximate heating analysis to estimate the temperatures experienced by the module; 2) finite element analysis to ensure sufficient stiffness of the design; 3) materials selection; 4) specification of tolerances in the interlocking mechanism; and 5) experimental testing of a prototype.
The inter-stage device (or, separation module) is bonded to the top of the booster in a similar manner to the bonding between the Wagtail fin canister and motor. The module relies on a drag-induced method of separation as it provides the most reliable solution, and is achieved by ensuring that the deceleration due to drag at burnout, is greater for the booster than it is for the upper stage. This results in the booster being pulled away from the upper stage as soon as it burns out.
The concept chosen for the separation module involves a cylindrical adaptor that slides inside the upper stage fin can, and transmits the thrust of the booster through the aft face of the fin can. It is designed to provide maximum stiffness against bending in order to maintain the “straightness” of the rocket, whilst minimising the resistance to separation.