www.strath.ac.uk/spacespace@strath.ac.uk

Single-slew manoeuvres for spin-stabilized spacecraft

29th March 2011

James Biggs

Glasgow

In collaboration with

Nadjim Horri at the Surrey Space Centre

6th International Workshop and Advanced School“Spaceflight Dynamics and Control”

Introduction

Micro and nano spacecraft seen as viable alternatives to larger spacecraft for certain missions e.g. Enable rapid space access.

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Introduction

Motion Planning

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SSTL-150 UKube 1 – Clydespace andStrathclyde University

Attitude Modes

Two vital mission phases:-

• De-tumbling and stabilisation– initial tip-off speeds (worst case scenario for Ukube -5rpm in every axis .) Tumbling motion must be stabilised or mission will fail. B dot control has been demonstrated.

• Re-pointing and stabilisation – reorient spacecraft to target specific point (e.g. point antenna to ground station, point solar cells towards sun for maximum power.) Accurate re-pointing is yet to be realised .

This presentation proposes a method for re-pointing.

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Introduction

Motion Planning

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method

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Stabilization

Two conventional methods:-

• Spin stabilization – passive, re-pointing required.o Early satellites – NASA Pioneer 10/11, Galileo Jupiter orbiter

• Three axis-stabilization – active control.o Thrusters, reaction wheels on conventional spacecraft.

Spin stabilization is attractive for nano-spacecraft Enables temporary GNC switch off.

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Introduction

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method

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Re-pointing spin stabilized spacecraft

Possibility:-

• Spin down, perform an eigen-axis rotation, spin up.

• Computationally easy to plan and track.

• may not be feasible with small torques of micro/nano spacecraft in a specified time.

Requires better planning/design of reference trajectory.

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Introduction

Motion Planning

Reduction

method

Practical

cost function

Example

Conclusion

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Introduction

Motion Planning

Reduction

method

Practical

cost function

Example

Conclusion

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Introduction

Motion Planning

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method

Practical

cost function

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Motion Planning using optimal control

Kinematic constraint:

Subject to the cost function:Introduction

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Introduction

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Sketch of proof – Kinematic constraint

Introduction

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Sketch of proof – Use a Lie group formulation

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Sketch of proof - Construct the left-invariant Hamiltonian (Jurdjevic, V., Geometric Control Theory, 2002)

Introduction

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Sketch of proof - Construct the left-invariant Hamiltonian vector fields and solve:

Solve the differential equations:

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Sketch of proof.Lax Pair Integration:

Solve for a particular initial condition

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PRACTICAL COST FUNCTION 1Minimise the final pointing direction:

Introduction

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PRACTICAL COST FUNCTION 2

Introduction

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Conclusion Minimize J by optimizing available parameters:

Minimize torque requirement amongst reduced kinematic motions:

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EXAMPLE

Introduction

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SSTL-100

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EXAMPLE

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SSTL-100

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Control Torque History (Nm)

Introduction

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Introduction

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Introduction

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CONCLUSION

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• To realise nano-spacecraft as viable platforms for remote sensing precise attitude control is essential.

• Poses research challenges – low-computational methods for generating low-cost (zero fuel) motions.

• The presented method reduces the kinematics to a subset of feasible motions that can be defined analytically.

• Massive reduction in computation – reduced to parameter optimization.

• Can be extended to minimum time problems, three axis re-pointing i.e. No spinning constraint.

Introduction

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Thank You for your attention

Questions?

23