Detumbling and Capturing Strategies with Eddy Current Brake System on Orbital Space Robot

Satoko AbikoDept. of Electrical Engineering,Shibaura Institute of Technology, Japansince April 2015

The Next Generation of Space Robotic Servicing TechnologiesIEEE International Conference on Robotics and Automation

May 26, 2015

Outline of the Talk

1. Background of the Research2. Detumbling Strategies with Eddy Current

Brake3. Performance Evaluation of Eddy Current

Brake System4. Detumbling Experiments with Dual-arm

System5. Conclusions

Introduction

Active Debris Removal (ADR)

Recovery mission of WESTAR‐VI(STS‐41‐B) (NASA).

Recovery mission of INTELSAT6 (NASA).

1. To avoid collisional cascading (Kessler Syndrome)2. To sustainably use space in future

Robotic technology is required to achieve it.

Past Activities for Grasping a Target

ETS‐VII Mission in Japan, Rendezvous‐Docking1997

Active Discussion in Japan for Debris Removal

2007

2009 International workshop for Active Debris Removal

Orbital Express in USA, Rendezvous‐Docking

ETS‐VII (JAXA)

Orbital Express (Boeing)

Many researches have been executed for ADR

DEOS (DLR) Space Infrastructure Servicing (MDA)

Various concepts have been proposed for grasping non‐cooperative target. But…

Scope of This Study

Contactless Detumlbing System

Eddy Current Brakeon the EE

Free Rotational Motion of Space Debris

[1] A. Nakajima, et. al  “Space debris observation by ground‐based optical telescopes,” 2000.[2] D. Mehrholz, et. al “Detecting, tracking and imaging space debris,” 2002.

Observation data of ADEOS [2]

e.g. Second stage of Zenit rocket

• Spin velocity 8.8[°/s]• Nutation angle30 [°]• Nutation velocity 0.2 [°/s]

ADEOS-earth observing satellite• Rotational speed around base

body ：0.1[°/s]• Rotational speed around a

boom：0.4[°/s]

Nutational Motion of a Target

Nutational motion.

Spin axis rotates around H with maintaining a certain angle: nutational angle θ

Grasping a Target by a Robot Arm

The Problem

How to detumble a large attitude change of the target

The approach only with robot manipulator system,  Joint limitation of the robot arm Singularity  Workspace constraints of the robot arm

The serial link manipulators have a limited capability to follow large attitude change of the tumbling target.

Before grasping a non‐coorprative target …, 

The Approach of the Study

Distinguish translational motion and rotational motion of the end‐effector

Robot manipulator system • Mainly used to keep a distance 

between the EE and the target

Eddy Current Brake (ECB)  • Attached on the EE• Used to brake rotational motion

What is Eddy Current Brake (ECB) System ?

Principle of an eddy current brake.

When the rotating conductive object exposed to a magnetic field,

Detumbling method without physical contact

Eddy current is applied to disturb changing of magnetic field.

Force is applied to rotating object to brake a spinning motion.

Detumbling Operation with ECB• Detumbling nutational motion by changing H direction• Eddy current brake exerts f to the target

⇒Nutation angle changes with

Precession by an eddy current brake.

1. Space robot detumbles the target with ECBs on the EE of the robotic arms.

2. The ECB reduces a spinning rate.

3. Space robot captures the target by two arms.

Detumbling Strategy with ECB

Detumbling Simulation

Simulating detumblingoperation for more realistic targets.

Simulation model: Himawari 5（GMS-5） Initial condition

• Spinning rate: 10⺎/3[rad/s]• Nutational angle: 30 [°]• Angular momentum: along Z axis

GMS‐5 (JAXA).

Diameter: 2.15 [m]Height: 3.54 [m]Mass: 345 [kg]

Detumbling Simulation

Detumbling Strategy: One ECB case

Trajectory of spin axis and angular momentum (using one coil).

Detumbling Strategy: One ECB case

• Due to the reaction of the braking force, the space robot move away.

• To keep relative position with the target, the space robot consumes propellent.

Position.

• Problem: reaction force• Use two ECB and place

them opposite to each other

• Reaction forces are canceled

• Only getting reaction torque

• Angular momentum changes around initial direction in X axis

⇒ Two ECBs have to move in order to keep the distance

Detumbling Strategy with ECB

Trajectory of spin axis and angular momentum(using two coils).

Detumbling Strategy

• Position Change：O(10-7) [m]

• Impulse：O(10-2) [Ns] ⇒ 速度はO(10-5)[m/s]

Compared to the case with one ECB, the case with two ECB systems could cancel out the effect of the reaction force.

Impulse.

Position.

Design and Development of ECB

1st developed ECB 2nd Developed ECB

1. approx. 1.02[N] 2. Distributed Winding3. Magnetic saturation happened in the 

yoke4. Eddy current loss happened

1. approx. 3.3‐4.0[N]2. Concentrated Winding3. Design the size of yoke with the 

consideration of magnetic saturation4. Layered structure of yoke to avoid 

eddy current loss

Field Oriented Control of ECB

ECB was developed based on Linear Inductance Motor.

CBF

With Relative Angular Velocity → Constant Braking Force (CBF)

Total braking force is constant.

Field Oriented Control of ECB

ECB was developed based on Linear Inductance Motor.

MBF

W/o Target Angular Velocity → Maximized Braking Force (MBF)

Maximum velocity of the magnetic field is used.

Performance Evaluation of ECB

1st developed ECB 2nd Developed ECB

Performance Evaluation of ECB

2nd developed ECBIn general, MBF approach generates larger braking force than that in the CBF approach

CBF: Constant Braking Force• Maintain constant braking force

despite changing angular velocity of the target

MBF: Maximized Braking Force• Braking force becomes larger

when angular velocity becomes larger

Slowing down with ECB

Mock of the Target

Mechanism 3 axis gimbal mechanism

Material Aluminum columnDiameter 296 [mm]Mass 18 [kg]Moment of Inertia Ratio ≧1

Maximum angle ±20 [deg.]

Detumbling Experiments with Robot Arms

Experimental Results

• Detumbling operation was achieved.

• Nutation angle converges to zero.

Spin angular velocity.

Spin axis trajectory.

Nutation angle.

• Active debris removal mission is required for sustainable space missions.

• Space robotic technology is one approach for the active debris removal.

• Grasping and detumbling operation is a key to achieve the above mission.

• Eddy current brake system is one promising technology to detumble the target.

Conclusions