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U.S.
The FREND Robotic Arm ICRA 2012 Workshop on Robotic Satellite Servicing
Sean Dougherty - Monday, May14th
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U.S.
“Astrotug” Stations in Space.
Donald Cox (1960)
DARPA Phoenix Mission Concept
NASA Servicing Mission Concept
On-orbit Servicing A long time coming
Credit: DARPA
Credit: NASA
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U.S.
2007: Orbital Express 2008-present: FREND
Great Strides Recently
2012: RRM
Credit: NRL
Credit: NASA Credit: DARPA
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U.S. SUMO/FREND Program
• Demonstrate the capability of autonomously executing unaided grapple of a variety of S/C interfaces Proximity Operation Testbed with dual platform motion simulator
7+ DOF Robotic Arm
Scanning LiDAR with 6DOF Pose Algorithm
Grapple Feature Tracking Algorithm
Trajectory Planner, Compliance Algorithm
NRL On-Orbit Demonstration Testbed – Photo Courtesy of NRL
FREND Arm
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U.S. FREND Arm Overview
• 7DOF
• 2m
• 78Kg
• 10 Kg Payload
• 15 cm/s Tip Velocity
• ± 1mm Accuracy
• 5.2 Hz Natural
Frequency
• F/T Sensing
• Tool Drive EE
• Custom MCBs
• 1g Testable
• Operate in GEO
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U.S. FREND Robotic Arm System Elements
Spacecraft Simulator
Joint Level Electronics
Robotic Manipulator
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U.S. Arm Optimized for Mission Success
Mass
Launch
Locks
Accuracy
Stiffness
Amplifier
Current
Capabilities
Available
Bus VoltagePower
Capabilities
Length
Thermal
Control
Requirements
Coatings,
Blankets
Payload/
EE
Flex
Speed,
Torque
Workspace
Power
Required
Agility
Avionics
Design
S/C
Interface
Sensors
Motor
Selection
EE
Interface
F/T Sensor
Loads
Kinematics
Phoenix IDD FREND
DOF 4 5 7
Length (m) 2 1 2
Mass (Kg) 9 4.2 78
Accuracy (+/- cm) 1.8 0.5 0.1
Payload (Kg) 2.5 2 10
Tip Speed (cm/s) 3.5 1 15
Natural Frequency (Hz) 2 3 5.2
Power (W) 15 10 180
Phoenix IDD FREND Phoenix
MSL
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U.S. FREND Arm Driving Requirements
1. Allow grappling of a cup-cone interface located 3” away from satellite
structure
2. The arm must maximize dexterity
3. The arm must minimize its stowed volume
4. The arm must achieve a 15cm/s (6cm/s) velocity along its end-
effector axis in 75% (95%) of its dexterous workspace
5. The arm must weigh less than 80Kg
6. The arm must support its own weight as well as a 5 Kg payload
7. The arm is required to position a tool tip with a tip linear accuracy of
+/- 2mm and an angular accuracy of +/- 0.4 deg
8. The arm must achieve at least a 1Hz closed-loop bandwidth
9. The arm must survive launch loads
10.The arm must be able to operate in GEO
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U.S. Good Tools Enable Rapid Iteration
RESTOR
May 13, 2012
Page 9
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U.S.
May 13, 2012
Page 10
Flexibility & Stability Analysis
Gravity Sag Analysis
Good Tools Enable Rapid Iteration
Launch Loads Analysis
Combined Stack Analysis
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U.S.
RESTOR
May 13, 2012
Page 11
4
Testing & Validation
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U.S. Testing & Validation
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of MDA Information Systems, Inc. is strictly prohibited by law. PRIVILEGED & CONFIDENTIAL.
U.S. Testing & Validation
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U.S. Performance – Natural Frequency
2.5 3 3.5 4 4.5-4
-3
-2
-1
0
1
2
3
4x 10
-3
Measured vs. Simulated Responses
Time (sec)
Am
plit
ud
e X
-dir
(m
)
Experimental Data
Estimated Data
5.2 Hz Natural Frequency in Extended Pose 6.4 Hz Natural Frequency in Nominal Pose
5.2 Hz Natural Frequency
1.7% Damping Ratio
7.2s Settling Time (2%)
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U.S. Performance – Arm Relative Accuracy
• Seven-Part Trajectory 1. Self-Motion 2. Wrist Yaw Motion 3. Fast Approach 4. Lateral Traverse 5. Slow Plunge 6. Wrist Elevation 7. Combine Wrist Yaw-Roll
0 20 40 60 80 100 120 140 160 1800
0.01
0.02
0.03
0.04
0.05
0.06
Time (s)
Tip
Velo
city M
ag
nitu
de(m
/s)
1 5 76432
0 100 2000
50
100
Time (s)
Join
t P
ositio
n (
de
g) Shoulder Yaw
0 100 200-100
-50
0
Time (s)
Join
t P
ositio
n (
de
g) Shoulder Pitch
0 100 200-100
-50
0
50
Time (s)
Join
t P
ositio
n (
de
g) Shoulder Roll
0 100 20050
100
150
Time (s)
Join
t P
ositio
n (
de
g) Elbow Pitch
0 100 200-200
-100
0
100
Time (s)
Join
t P
ositio
n (
de
g) Wrist Roll
0 100 200-100
-50
0
Time (s)
Join
t P
ositio
n (
de
g) Wrist Pitch
0 100 200-200
-100
0
Time (s)
Join
t P
ositio
n (
de
g) Wrist Yaw
Augmented Trapezoidal Motion Planner Continuous Velocity
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U.S. Tracking Error
• In Track Error ≤ ±1mm
• Cross Track Error ≤ ± 0.5 mm
0 20 40 60 80 100 120 140 160 180-1
-0.5
0
0.5
1x 10
-3
Time (s)
X-T
ip E
rror
(m)
0 20 40 60 80 100 120 140 160 180-5
0
5
10
15x 10
-4
Time (s)
Y-T
ip E
rror
(m)
0 20 40 60 80 100 120 140 160 180-15
-10
-5
0
5x 10
-4
Time (s)
Z-T
ip E
rror
(m)
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U.S. Conclusions
The FREND robotic arm is a new
benchmark for space technology High dexterity
High accuracy, absolute position
High stiffness, high bandwidth
Novel set of electronics
Integral FTS, thermal, cabling
Flight ready
1-g testable
Photo Courtesy of NRL
Additional Thoughts/Considerations: Multi-arm systems are worth the mass
• If we adopt long-term, multi-target view
• Arms are a reusable asset – only need to pay to get to orbit once
• Refueling and high ISP propulsion worth considering
Autonomous vision still a big challenge
• Accuracy & bandwidth effect arm design
• Getting better all the time but still computationally intensive and lighting conditions still challenging
• Level of target preparedness worth considering
