Modelling and Preliminary Sizing of a Direct Descent, Spin-Stabilised, Lunar Braking Stage

Capon, Christopher (2012). Modelling and Preliminary Sizing of a Direct Descent, Spin-Stabilised, Lunar Braking Stage B.Sc Thesis, School of Engineering, The University of Queensland.

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Author Capon, Christopher
Thesis Title Modelling and Preliminary Sizing of a Direct Descent, Spin-Stabilised, Lunar Braking Stage
School, Centre or Institute School of Engineering
Institution The University of Queensland
Publication date 2012
Thesis type B.Sc Thesis
Supervisor Russel Boyce
Michael Creagh
Total pages 94
Language eng
Subjects 0901 Aerospace Engineering
0913 Mechanical Engineering
Formatted abstract
This thesis develops a six degree of freedom simulator to model the direct descent trajectory of White Label Space’s spin-stabilised, lunar braking stage for their Google Lunar X-Prize attempt. The simulator is used to size the Spin-up Motors and Yo-Yo de-spin mechanism, as well as model the position in the separation envelope, residual body rates and coning angles. This is achieved through the use of Newtonian and Lagrangian techniques to build equations of motion to model the descent realistically. The response of system is verified against projectile motion datasets from Platus D, Ayoubi M and Fedor J.

It is found that a Spin-up Motor with a burn time of 0.71 s and average thrust of 1.1 kN, will achieve a spin-stabilisation of 55 RPM . Comparison of these values with Alliant Techsystem’s STAR 3 and STAR3A suggests that such a motor would be 80.77mm in diameter and 210 mm long.

The Yo-Yo mechanism is sized to provide a 95% reduction in initial spin rate based on an inextensible, radial release system. A 4.7 m long, 2.938 mm diameter, 4340 high tenile steel tether requires a tip mass of 1.25kg to achieve this degree of spin reduction. The total mass of the Yo-Yo mechanism is 3 kg.

The Solid Rocket Motor is based on a STAR30BP was an average thrust of 35kN. The propellant grain is sized based on the geometer of the STAR30BP with a diameter of 762 mm and length of 990.6 mm . The regression rate of the grain is selected to match the burn time of the STAR30BP as 7.1 mm/s. The resulting Δv supplied by this motor is 1.679 km/s, which proves to be a good compromise between separation velocity and drift distance.

A Monte Carlo analysis using a Normal Gaussian distribution is conducted to determine the coupled effects of various perturbing factors on the separation position. Applying a large mean value on the perturbing factors shows a general drift of separation position away from the maximum separation envelope of 20 km. Moving the centre of the data cluster demonstrates a probability of an optimum separation of 73% and acceptable separation of 99%. Refining the perturbing factors to represent controlled entry conditions increases the optimum separation probability to 100% without moving the position of separation envelope.

Using the control entry condition factors, another Monte Carlo study is conducted on the residual body rates and coning angles. This shows a spin-stabilisation of 55 RPM effectively counters a moderate degree of purtubations, where the standard deviation of the body rates are in the order of 0.05 RPM. The coning angles show instability that is determined to be due to the Yo-Yo release. It demonstrates the sensitivity of the Yo-Yo to initial conditions; however the magnitude of the coning angles is within the ability of the Lander module to re-orient itself after separation using a reaction control system. Therefore it is deemed acceptable.

Finally two primary areas of possible optimisation are identified but are outside the scope of this thesis. The first is the use of a stretch Yo-Yo system, which could provide a larger spin reduction for the same mechanism mass. The second involves optimisation of the trajectory with an increased SRM thrust, while delaying the ignition stage. This could be used to minimise separation velocity and drift time.
Keyword rocket motor

Document type: Thesis
Collection: UQ Theses (non-RHD) - UQ staff and students only
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Created: Wed, 26 Nov 2014, 15:22:53 EST by Ahmed Taha Siddiqui on behalf of Scholarly Communication and Digitisation Service