samir rawashdeh space systems laboratory university of

Orbital Environment Simulator

Samir Rawashdeh

Space Systems Laboratory

University of Kentucky

2009 Summer CubeSat Developers' Workshop August 9, 2009

2

Overview

Introduction

Implementation Details

Capabilities

KySat-1: Passive Magnetic Stability

RamSat: Aerodynamic Stability

Future Enhancement

August 9th, 2009 CubeSat Developers' Workshop, Logan, UT

3

Introduction

Passive Stability Systems

Aerodynamic

Passive Magnetic

Gravity Gradient

PuTEMP (concept) - Purdue

Magnet Placement in KySat-1

RamSat (concept) –

Kentucky Space


4

Challenges

Determining Pointing Accuracy

Magnetic Hysteresis Damping Behavior

Uncontrolled Axis of Freedom

Behavior in 6DOF

Effect of Gyroscopic “Stiffness”


5

Orbital Environment Simulator

Adjustable Spacecraft Description and Orbit

Mass and Inertia Matrix

Magnets and Hysteresis Material

Geometry (Aerodynamics)

Orbital Elements

Simulate Effect of Orbital Environment on Satellite Attitude

(in 6DOF):

Gravity Gradient

Magnetic Torques

Magnetic Hysteresis Material

Aerodynamic Torque


6

Simulink® Modeling

Model-based Design

Graphical description of dynamics

Definition of initial state

Solve differential equations and propagate the

systems state over time

Hit “play” and watch events unfold.


7

Attitude Propagator


8

Capabilities

Attitude Propagation (Aerodynamic, Gravity

Gradient, Magnetic, and Hysteresis)

Stability System Design Verification

Plotting and Animation (STK)

Case Studies:

KySat-1

RamSat


9

KySat-1: Magnetic Stability

Align with Magnetic Field

Permanent Magnets

Dampen Motion

Hysteresis Material (HyMu80)


10

KySat-1: Simulation


0 2 4 6 8 10 12 14 16 18 20 22140

30

60

90

120

150

180

Time (hours)

Err

or

Angle

(degre

es)

Simulated Time Response of the KySat-1 Passive Magnetic Stability System

Angle to Magnetic Field

Angle to Nadir

11

KySat-1: Animation

12

RamSat: Aerodynamic Stability

Ram-facing

Maximum altitude

No roll control

Simulation:

20cm full width panels

30° deployment angle


13

RamSat: Simulation

0 1 2 3 4 5 6 7 8 90

20

40

60

80

100

120

140

160

180

Time (hours)

Erro

r Ang

le (d

egre

es)

RamSat Time Response: 20cm Panels at 30 degrees

Angle to Velocity Vector

Angle to Nadir


0 2 4 6 8 10 12 14 16 18 20 22140

30

60

90

120

150

180

Time (hours)

Err

or

Angle

(degre

es)



Angle to Nadir

0 2 4 6 8 10 12 14 16 18 20 22140

30

60

90

120

150

180

Time (hours)

Err

or

Angle

(degre

es)



Angle to Nadir

Simulated Time Response: RamSat with 20cm panels at 30 degrees

14

RamSat: Animation

15

Future Enhancements

Active Attitude Control Systems

Torque Coils

Reaction Wheels

Momentum Wheels

Thrusters

System Design Choices

(e.g. reaction wheel size, torque

coil strength)

Control Logic Development

Danjon (concept) –

Kentucky Space


Reaction Wheels

sinclairinterplanetary.com

16

Active Control

Translational Forces

Angular RotationMoments

Kentucky Space - Orbital Environment Simulator

Control Torque

Disturbance Torque

[P]

[V]

[A]

[V]

[A]

[P]

[DesiredAttitude]

[P]

[CurrentAttitude]

Position (X)

Attitude (DCM)

Velocity (V)

Torque (N.m)

Environmental Effects

Position ECI (X) Gravitational Force (N)

Earth's Gravity

Desired Attitude

Current Attitude

Torque (N.m)

Controller

Fxyz (N) [ECI]

Mxyz (N.m) [Body-fixed]

X (m) [ECI]

V (m/s) [ECI]

DCMbe (Attitude) [ECI to Body]

6DOF Dynamics


17

Samir Rawashdeh

Space Systems LaboratoryElectrical & Computer EngineeringUniversity of [email protected]

Thank You

www.kentuckyspace.com


samir rawashdeh space systems laboratory university of

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