Early design work on the Starchaser Thunderstar system needed to ensure, before committing to cutting metal, that we had an aerodynamically stable vehicle for the mission. Aerodynamic Instability at any mission phase would lead to flight failure. For this field of research to establish aerodynamic status of the Thunderstar structure we elected to select suitable aerodynamic analysis software programs to perform our analysis iteration using the design geometry.

The complete Thunderstar structure consists of;

• The Main launch vehicle.
• The Capsule.
• The Launch Escape System.

The launch mission phase is where the complete structure will be propelled forwards. Aerodynamic stability in this flight mode will be checked by the analysis to follow. To obtain a definition of the model geometry for the aerodynamic analysis, the coordinates of the mid-nodes of the elements that run along the centre-line are recorded.

This capsule is designed to accommodate three men and sustain them safely for the complete mission life. The design of the three-manned capsule has been done in Pro-Engineer software package and is shown below: The above is the FEA model representation of the double skinned Capsule complete with access hatch and windows. The mid-node coordinates of the capsule are recorded and a separate aerodynamic analysis is made.

A possible mission event may be a launch failure situation, whereby the capsule/LES rockets are activated on the ascent and separation from the main launch vehicle occurs. The crew have a means of escape. It is necessary therefore that combined capsule and LES have flight dynamics which are aerodynamically stable. The Finite Element model representation of the combined Capsule/LES are shown opposite. Once again the profile shape is required for aerodynamic analysis Before progressing onto the analytical work we take a brief look at Aerodynamic stability.

Change rocket aerodynamic geometry:
Demands on geometric dimensions have been due to many influences. Considerations have been given to: Manufacturability dimension limitation of the Main fuel tanks; Crew seating arrangement; Safety issues, eg, access and escape etc.; Equipment layout.

Adjust size of fins.
Large fins at the rear of the rocket ensure that the Centre of Pressure is moved towards the rear of the rocket behind the Centre of Mass. The number of fins at the rear of the rocket also increases the aerodynamic forces in this region.

Add nose weight.
Adding mass to the front of the Thunderstar rocket structure will move the Centre of mass forwards.

Fuel.
The major mass component of the rocket is its fuel, the Centre of Mass will change as the fuel is burned.

Other aspects of stabilty.
Engine thrust should always be concentric to avoid imbalances. Other than adjusting Centre of Pressure positions spin stabilisation may be employed - causing the rocket to spin. The angular momentum provides inherent gyroscopic stability.
There are three ways to accomplish a spin like desired;

• Fins can be slightly inclined on the main rocket structure.
• Fins can have a cambered aerodynamic shape.
• Spin tower launches are a possibility.

DETERMINATION OF THE CENTRE OF PRESSURE
Comparison of different centre of pressure software.
The two super-sonic aerodynamic analysis programs were compared:

• HyperCFD, By AeroRocket.com
• SpaceCad. By SpaceCad.com

HyperCFD was chosen for the analysis of the rocket structure under supersonic flight conditions. Ascent mission emergency phase of the Capsule/ LES system. The generic drawing represents this configuration at supersonic speed. This geometry was used in both software packages purely to compare the results. HyperCFD. SpaceCad.

HyperCFD. Mach 3 speed.
HyperCFD results: Centre of Pressure. = 0.566 * 10.413m = 5.894m from nosecone tip.

Spacecad: Mach 3 speed.
SpaceCAD Results: Centre of Pressure is = 5.925m from tip of nosecone tip.

CONCLUSION:
The HyperCFD and SpaceCAD results are very similar for the position of the centre of pressure at mach 3 on the Capsule+LES combination. Further calculations will be done only using HyperCFD.

STARCHASER THUNDERSTAR ROCKET:
The location of the centre of pressure of the Starchaser launch system at various mission phases assisted in establishing the vehicles aerodynamic stability.
Rocket/Capsule/LES system during the following mission phases.
Lift-Off emergency phase.
LES-Capsule ascent.
Capsule ascent.
Capsule descent.

ASCENT PHASE:- Sub-sonic:
Combined Capsule-LES

The top part of the Starchaser Thunderstar houses the Capsule and the Launch Escape System. The analysis here is for the ascent mission emergency phase of the Capsule/ LES. The generic drawing represents this configuration. The dimensions used here are representative of the structures configuration and is shown below (Note data altered to protect research).
AeroCP: Subsonic centre of pressure analysis software. This is based on Barrowman formula. The Visual basic data entry form gives generic images and dimensional requirements. The user selects the correct image and enters the appropriate data.
NOTE: The Centre of Pressure position calculated is measured in metres from the nose cone tip.

Ascent Mission Phase:- Mach 3:
HYPERCFD Capsule + LES.

The geometrical dimensions used in the HyperCFD analysis below are representative to the combined configuration of the Capsule and the LES. Capsule diameter effect on Centre of pressure position. The following analysis is still applicable to the launch emergency mission phase. The previous HyperCFD analysis used the design diameter of the capsule. This following calculation examines the effect on the location of the centre of pressure due to increasing the capsule diameter. Super-sonic flight condition is examined. It was found from the analysis that the larger diameter capsule moves the centre of pressure location further away from the nosetip.

ASCENT PHASE: Capsule only. Mach 3. HyperCFD:
The results indicated that the centre of Pressure was within the capsule structure. As the Mach number increased then the centre of Pressure moved closer to the nose tip.

Capsule descent mission phase:
At lower mach numbers the Centre of Pressure was located near the heat shield. With higher mach number the Centre of Pressure moved more inboard.

Pressure distribution along the Starchaser ThunderStar:
Represented below is the full Rocket launch system. It includes the main structure system, the manned capsule and the Launch escape system (LES). The above was generated in a Nastran Finite Element system. Coordinates of the Central nodal positions were recorded for initial pressure and thermal distribution investigations along the profile and for possible future Computational Fluid Dynamic Analysis. Calculations were done in MS Excel spreadsheet.

The hatch is one of the essential subsystems of any manned rocket and its design is one of the projects being undertaken during the concept design phase for the Thunderstar vehicle.

Most of the research and design has been carried out by Eddie [whilst enrolled on a Master of Science degree at Delft University of Technology in the Netherlands] during a 3 month internship at Starchaser.

The projects objective was to arrive at one or more 'worked out' designs for the hatch and to have one or two physical mock-ups to demonstrate the feasibility of the design.

Quick overview:
The capsule is designed to accommodate three people and sustain them safely for the complete mission life. The design of the three-manned capsule has been carried out in the Pro-Engineer software package - the model represents a double skinned Capsule complete with access / egress hatch and windows.