Download Albert Caubet

June 2014
Astronet-II School – Zielona Gora
Advances in spacecraft
autonomy and control
University of Strathclyde, Glasgow
Albert Caubet
[email protected]
www.strath.ac.uk/space
Motivation – Active Debris
Removal (ADR)
J.-C. Liou, An active debris removal parametric study for LEO environment
remediation
June 2014
Albert Caubet
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Motivation – Active Debris
Removal
§  Capture techniques
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• 
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Robotic arm
Net
Harpoon-tether
Tentacles/Clamps
Thruster plume
(contactless)
Astrium
JAXA
Ion-Beam Shepherd, Bombardelli
June 2014
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Attitude Stabilisation
Electromagnetic Module (ASEM)
§  Baseline design
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Compact module carried by chaser S/C
Magnetic torque rods
Primary battery (large energy density, but not rechargeable)
Various avionics subsystems (OBC, power distribution, sensors,
telemetry)
•  Module attached onto target (autonomous propulsive transfer)
§  Rationale
•  Risk reduction for chaser S/C
•  Relaxation of requirements on capture systems
§  Sizing based on Envisat model
June 2014
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Attitude Stabilisation
Electromagnetic Module (ASEM)
1. 
2. 
3. 
4. 
5. 
6. 
Battery
Magnetorquers
Subjection drills
Thrusters
Avionics
Tanks
2.
5.
1.
•  Autonomous approach
•  Multiple attempts possible
•  S/C stays at a safe
distance
6.
3.
4.
40 cm
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System elements
§  Torque rod
•  Solenoid with a ferromagnetic core (Hiperco 50)
•  Two pairs of rods in square configuration
•  Magnetic moment:
•  In terms of wire properties and applied voltage:
March 2014
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Attitude Stabilisation
Electromagnetic Module (ASEM)
§  Control law
•  Affects sizing of torque rods and battery
•  Magnetic control torque:
•  Alternatives:
o 
o 
o 
B-dot:
Commutation (switching, on-off)
Modified B-dot – moment not dependent on angular rate
is the angular distance between the i-th torque rod and the magnetic field vector.
Magnetic moment direction shall be dynamically adjusted so that torque opposes angular velocity
June 2014
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Attitude Stabilisation
Electromagnetic Module (ASEM)
§  Control law
•  Comparison using simplified 2D model
12000
0.12
On-Off law
Modified B-dot
B-dot law
0.08
0.06
0.04
8000
6000
4000
2000
0.02
0
10000
Energy [Wh]
Angular rate (rad/s)
0.1
0
June 2014
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60
80
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Time (days)
120
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Albert Caubet
On-Off law
Modified B-dot
B-dot law
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Attitude Stabilisation
Electromagnetic Module (ASEM)
§  Attitude determination
•  Magnetorquers interfere during magnetometer’s reading of Earth
magnetic field
•  Absolute reference position using computer vision system on-board
chaser – use chaser’s attitude sensors
•  Specially relevant for autonomous propulsive approach – Guidance
and Navigation take place in the chaser
University of Bristol
June 2014
Albert Caubet
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Attitude Stabilisation
Electromagnetic Module (ASEM)
§  System optimization
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Use of simplified 2D model based on Envisat
Analytical estimation of torque rod and battery mass and size
Exhaustive search optimization
Mass minimization
Reasonable detumbling time
§  Design variables
•  Stabilization time
•  Power
•  Torque rod geometry
June 2014
Albert Caubet
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Attitude Stabilisation
Electromagnetic Module (ASEM)
§  Trade-off mass-time
§  Optimal mass at long stabilization time
L = 850 mm; d = 25 mm
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22
Mass (kg)
20
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March 2014
0
20
40
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Settling time (days)
Albert Caubet
80
100
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Attitude Stabilisation
Electromagnetic Module (ASEM)
•  Torque rods 400 Am2
•  Orbit 1000 km alt., 99
deg. Inc.
•  Tumbling rate 1 rpm = 6
deg/s
•  Wet mass: 19.7 kg
•  Stabilisation in 21.5
days
June 2014
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Conclusions & Future Work on
ASEM
§  A 20-kg module would be able to detumble an Envisat-like
satellite in 22 days
§  This system allows the chaser to be less agile, reduces risk
during capture and relaxes requirements (e.g. robotic arms,
GNC)
§  Extensive assessment of potential targets for ADR –orbit,
tumbling rate, moments of inertia, etc
§  Scaling of the system with different targets and angular
momentums
§  Optimal detumbling control method
§  ESA: Intended ITT on debris detumbling
June 2014
Albert Caubet
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Asteroid close proximity flight
§  Overview
•  Aerospace, automation & control, IT, telecom, security
•  Aerospace section: 150+ employees
§  3-month internship
§  Goal: develop a guidance and control algorithm for asteroid
hovering
§  Related missions
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Don Quijote (asteroid deflection)
NEOShield (FP7) (asteroid deflection)
AIDA (ESA + NASA) (asteroid deflection)
Hayabusa (sample return)
MarcoPolo-R (sample return)
OSIRIS-Rex (sample return)
June 2014
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Asteroid close proximity flight
§  Asteroid deflection mission
architecture
•  Orbiter
o 
o 
o 
o 
Arrives months before impact
Performs asteroid characterisation
Can be used as beacon for the
impactor
Observes impact and measures the
deflection
•  Impactor
o 
o 
June 2014
Is guided towards the asteroid at
very high terminal speed
Transfers momentum to asteroid by
inelastic impact and ejecta
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Asteroid close proximity flight
§  Close proximity operations
•  Inertial hovering
o 
o 
o 
Fixed distance, e.g. on the line Sun-Asteroid
For asteroid mapping (as it rotates below S/C)
Centre of brightness navigation
•  Body-fixed hovering
o 
o 
o 
Fixed position w.r.t. asteroid rotating frame, at low altitude
Feature-based navigation (high image processing capability reqd.)
For landing preparation
•  Landing
o 
Transition from body-fixed hovering to touch-down (sample collection)
•  Orbiting
o 
June 2014
Photo-Gravitational Stable Orbit (PGSO) for gravity characterisation
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Asteroid close proximity flight
§  Mission scenario
•  Asteroid: Didymos (binary) – Primary 800 m, secondary 150 m
•  Inertial hovering at 15 km and 100 km
•  Body-fixed hovering at 250 m and 45 deg latitude
§  Potential model for inertial hovering
•  Binary system (2 spheres) à “equivalent ellipsoid”
•  Coefficients of spherical harmonics potential to meet binary’s potential
!
June 2014
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Asteroid close proximity flight
§  Developing appropriate guidance & control
•  Hayabusa & others: control box / dead-band
•  Classic: PID
•  Advanced: Sliding Mode Control, Model Predictive Control, etc.
“Required” vs “Nice To Have”
June 2014
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Thanks for your attention
Questions, comments, suggestions are
welcome
[email protected]