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ES
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AT
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AT
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EN T OF TH
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STAR II
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Modulating Retro-reflectors for Space Tracking,
Acquisition and Ranging using
Multiple Quantum Well Technology
G. Charmaine Gilbreath, N. Glenn Creamer, W. S. Rabinovich,
Timothy J. Meehan, Michael J. Vilcheck,
John Vasquez, Rita Mahon, Peter Goetz, and Eun Oh
U. S. Naval Research Laboratory,
Washington DC 20375
http:mrr.nrl.navy.mil
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Objectives:
Provide a compact, lightweight, low power method for inter-satellite acquisition,
communications and navigation.
Approach:
Use frequency-tagged corner-cube Multiple Quantum Well (MQW) retromodulators to provide line-of-sight relative position and orientation between two
spacecraft and demonstrate technique in the NRL Dynamic Motion Simulator
Facility.
Impact:
Method is potentially applicable for long (multiple km) to short (10’s of meters)
inter-platform ranges and can significantly reduce parasitic payload requirements
of the onboard communications, acquisition, and navigation subsystems.
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CONCEPT
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Gimballed
Laser Source
MRR
Pursuer
Spacecraft
PhotoDetector
MQW Modulator with
Corner-Cube Retro
MQW
Retro
On/Off
Signal Driver
Target
Spacecraft
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CONCEPT
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Inter-Spacecraft Geometry
t̂ 3
t̂ 1
Target S/C
Relative Position Vector:

R  R (cos El cos Az pˆ 1  cos El sin Az pˆ 2  sin El pˆ 3 )
Az, El from laser gimbal angles
t̂ 2

R
Relative Attitude (Pointing) Matrix:
p̂ 1
p̂ 3
CT / P
Az
Pursuer S/C
p̂ 2
cos  0  sin   cos  sin  0
  0
1
0   sin  cos  0
 sin  0 cos    0
0
1
Y = yaw
 = pitch
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DEVICE :
0.5
0.4
1
3
2
5
Absorbance
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MQW Retromodulator
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R
0.3
0.2
V=0
V=10
V=20
0.1
4
0.0
1. Interrogation beam; 2. Modulated beam;
3. Electronic driver; 4. Transmissive MQW
modulator; 5. Solid retroreflector
-
1.05
0.95
1.00
1.10
Wavelength (microns)
Picture of Video Payload
Multiple Quantum Well “shutter” requires mW;
is radiation-hard; and cm-class supports
10+ Mbps with standard corner cube.
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• Laser beam divergence illuminates entire array
MRR (8)
o
+/- 30 FOV
• Laser gimbal motion equalizes signal returns of
MRRs 6-8 to provide relative position vector
6
• Signal returns of MRRs 1-5 provide two-axis relative
target attitude (pitch, yaw)
Central
umbrella
array
Central
umbrella
array
2
5 1 3
4
• Combined with pulse TOF measurement, sensor provides
relative navigation of ~1 cm in position and
~0.3 deg in attitude
150
8
7
Signal Return (mV)
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EN T OF TH
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NA V
MRR Array For Target Pose
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R
o
20 cant
0
-30
0
30
Angle Off Boresight (deg)
30 cm
Sensitivity of MRR to laser beam angle
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R
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EN T OF TH
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TM
A
NA V
A
NA V
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Determination of Target Attitude
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6
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Fundamental Signals
Si  S0  a i
Si = signal return from ith MRR
i = laser angle to ith MRR boresight
 = fixed cant angle of MRRs 2-5
Center of
beam
2
5
1
3
Relative Yaw & Pitch Estimation
4
8
7
Diverged laser
interrogator beam
If S3 > S5 :  
else :

If S2 > S4 :  
else :
1 S3  S5

2 S1  S5
1 S5  S3

2 S1  S3
1 S2  S4

2 S1  S4

1 S4  S2

2 S1  S2
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STAR II: MQW Retromodulator Array
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Eight element retromodulator array is shown. Each unit is driven with a different code
for device discrimination.
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TOF
8
7
6
MRR
Array
Laser
Tracker
R
Relative
Position
Estimator
x, y, z
1/s

V
Divert
Control
Logic
Az, El
5
4
3
2
1
Relative
Attitude
Estimator
, 
Attitude
Control
Logic
Accel
Forces
Torques


Gyro
Divert Control Logic:
Target
Motion
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AT
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EN T OF TH
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TM
A
NA V
Pursuer Control Block Diagram
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R

 

F  k P (R  R command )  k D VPursuer
u 
 

Attitude Control Logic:  2   k P    k D  2 
 
u 3 
3 Pursuer
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Acceleration
Pursuer
Dynamics
Rate
Attitude
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NRL Robotics Laboratory
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Upper
Target
Platform
Control
Room
Lower
Servicer
Platform
National testbed for testing and verification of autonomous rendezvous and capture
technologies. This dual platform facility offers 6 degrees of freedom per platform.
Space environmental conditions can be programmed into the simulations. Facility
workspace dimensions: 30 m x 13 m x 5 m
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Target
In play
Pursuer
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6
2
5
Center of
Laser Beam
1
3
4
8
7
Simulation
Actual from GUI
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MRR Code Sequences
8
7
6
Code #
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STAR II
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EN T OF TH
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R
5
4
3
2
1
Each MQW modulator is driven by a unique code which is detected, demodulated and
translated into a level which is sent to the tracking and acquisition algorithm .
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OR Y
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EN T OF TH
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NA V
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NA V
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STAR II
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Sampled Data detected by APD
All Signals
Sampled Data out of
Matched Filter
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8200000
Chaser aligns with Target
8190000
8180000
Signal level
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AT
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R
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R
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L
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EN T OF TH
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TM
A
NA V
A
NA V
ES
STAR II
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EN T OF TH
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TM
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8170000
8160000
8150000
Acquisition and centering
Dynamic Target motion
8140000
8130000
Data point
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8200000
Returns from 3 outer MRR’s
equalized
8190000
8180000
Signal Levels
8170000
Centered
Search
8160000
8150000
Centering
8140000
125
121
117
113
109
105
101
97
93
89
85
Time
Data point
81
77
73
69
65
61
57
53
49
45
41
37
33
29
25
21
17
13
9
5
Overshoot correction
1
Signal level
Detection
8130000
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EN T OF TH
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STAR II
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EN T OF TH
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STAR II Test Demonstrations
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Alignment to a Stationary Target
Tracking a Moving Target
T
T
Commanded
Alignment Offset
P
Commanded
Slew Angle
P
P
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1000
800
600
400
1s = 1 cm
200
0
Attitude Error (deg)
Position Error (cm)
Alignment to a Stationary Target
Gimbal Angles (deg)
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NA V
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STAR II Test Results
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R
0
1
2
3
4
5
6
7
6
4
1s = 0.3 deg
2
0
0
1
2
3
1
2
3
4
5
6
7
4
5
6
7
10
EL
0
-10
AZ
-20
0
Time (min)
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Position Error (cm)
Tracking a Moving Target
50
40
30
20
1s = 1 cm
10
0
Attitude Error (deg)
0
Gimbal Angles (deg)
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B
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AT
OR Y
AT
L
L
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EN T OF TH
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TM
A
NA V
A
NA V
ES
DE
PA
STAR II Test Results
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EN T OF TH
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TM
VY
NA
R
1
2
3
4
5
6
7
8
9
10
6
4
1s = 0.3 deg
2
0
0
1
2
3
4
2
3
4
5
6
7
8
9
10
5
6
7
8
9
10
4
2
EL
0
AZ
-2
-4
0
1
Time (min)
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R
R
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Attitude Estimation Error from a Static Test
0.06
1s = 0.015 deg
0.05
Two-Axis RSS Attitude Error (deg)
R
B
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AT
OR Y
AT
L
L
EA
EN T OF TH
E
TM
A
NA V
A
NA V
ES
DE
PA
STAR II Test Results
R
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NA
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PA
EN T OF TH
E
TM
VY
NA
R
0.04
0.03
0.02
0.01
0
0
1
2
3
4
5
Time (min)
6
7
8
9
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R
R
R
B
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OR Y
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L
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EA
EN T OF TH
E
TM
A
NA V
A
NA V
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Summary
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Results:
MQW retromodulators can provide simultaneous spacecraft-to-spacecraft
optical communication and navigation. The navigation solution potentially
provides about 1 cm in positioning and 0.3 degrees in orientation.
TRL 5 for device and concept
Payload:
Weight:
Retromodulators: .35 oz (10 g) per mounted device so 2.8 oz for 8
Electronics (FPGA + drivers): 8 oz
Mechanical Structure: 6 oz (will vary with function)
Size: ~2.5 cm x 1.5 cm for a .5 cm mounted device
Power: At 1 MHz data rate: 80 mW each device; 740 mW total (incl. Driver)
O