LADAR Measurements of the
International Space Station
LADAR Guidance for Autonomous
Rendezvous and Docking
Colin L. Smithpeter (csmithp@sandia.gov ), Robert
O. Nellums, Steve M. Lebien, George Studor*,
George James*
Sandia National Laboratories
*NASA Johnson Space Center
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
Laser Radar
• Laser Radar provides angle, angle, range images
•
of target
Potential for small, standalone sensor in AR&C
– Range & bearing with each image, day or night, uncooperative
targets
– 6 DOF velocities from sequential images
– Target vehicle orientation from 3D images
X:+2 Y:-2 Z:+20
DX:-0.2 DY:0.0 DZ:+2
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
Key Points
• Laser Radar is accurate, rapid, and small
– What are the issues?
• Scanning Versus Scannerless
– Virtually all existing ladar capabilities utilize scanning
– A unique, scannerless laser radar has been developed by
Sandia National Laboratories.
• Laser Dynamic Range Imager (LDRI) Overview
– Scannerless demonstration on STS 97 Mission in 2001.
• AR&C LADAR concept
• Next Generation micro LADAR
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
Laser Radar Issues
• Optical energy per pixel measurement
– Minimum signal requirement depends upon ladar architecture, including
quantum efficiency, noise, and background. Typical to require 100s of
photons, but a single photon is potentially feasible.
– Required illumination, given required signal, tends to vary directly with
number of pixels, range2 and FOV2. Energy can become prohibitive at
long range.
– Temporal and spectral filtering required to reduce solar background
• Target Albedo
– Specular materials, such as Mylar, can be very difficult to detect
– Diffuse materials, such as brushed metal or beta-cloth, provide reliable
returns
– Retro-reflective cubes or tapes greatly enhance return from range
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
Scanning Versus Scannerless
• Why Scanning
– Single-channel EO can incorporate sophisticated readout
of return waveform
– Single axis can incorporate spatial filter: IFOV can be
much smaller than pixel spacing, to reduce solar
background
– Variable FOV, pointing, and pixel spacing
• Why Scannerless
– Focal plane eliminates bulk and reliability issue of
scanning mechanism
– Focal plane enables fast image acquisition. Single flash
feasibility.
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
LADAR Sensor
• Challenge: Measure laser pulse return time in each pixel
with nanosecond accuracy
– Nyquist indicates 2 GHz bandwidth, thousands of samples
• Sandia Approach: Detect laser time of flight by sampling
waveform with limited number of frequencies
– Heterodyne laser return with AM receiver
– Reduce complexity and bandwidth, improve resolution and sensitivity
– 10 MHz BW for nanosecond accuracy
Example: Simulated return through obscuration
Obscuration
Return
Target
Return
Detected Laser Return
Unclassified
Processed Sensor Output
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
Scannerless Range Imaging
Sin(w)
Intensity
tJ
Pulse Launch
Unclassified
1/w
tT
Time
Range Encoded
Image
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
Example: M60 tank at 250m in daylight
Intensity
Phase
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
Laser Dynamic Range Imager
• Motivation: Structural Dynamics of ISS
• Assembly, control, and operation of large,
flexible ISS structure requires validated
structural models
– High density of structural modes
– Limited instrumentation for on-orbit validation
– Supplement with non-contact measurement
Image vibration motion with LADAR sensor
• Secondary applications: Inspection, proximity
operations navigation
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
LDRI Mission Requirements
• Image natural mode frequency and amplitude
– Induce vibration with Shuttle thruster firing
• Replace Intensified Video Camera Illuminator
– Weight 4.4 lbs, Size 5(w)x3.5(h)x9(l) inches
– Eye safe laser illumination, 40 degree field of view
• Dynamic range accuracy of 0.1 inch, frequencies to
7 Hz
ITVC/LDRI Assembly
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
On-Orbit Images
Intensity
Intensity
Hi-Frequency Range
Unclassified
Absolute
Surface Rendering
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
Solar Array Measurements
Planar Relief (Inches Away
from Observer)
IntensityTwo Transverse SAW Cross-Sections Range
4
3
2
Bus Tab Toward Observer
Bus Tab Away from Observer
1
0
-1 0
50
100
150
-2
-3
Uncalibrated Units (Upper Right to Lower Left)
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
ISS Range Movie
Grayscale cycles every 107 cm of range
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
On-Orbit Vibration Data
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
On-Orbit Vibration Data
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
LDRI Summary
• Developed a space qualified LADAR
– 5 lbs, Size ~ 10x5x4 inches
– 0.1 inch range resolution, 640x480 pixels
– Eye safe laser illumination, 40 degree field of view
– Capturing 30 fps for vibration data to 7.5 Hz
• Flown on STS 97
– Measured vibration amplitudes of 0.1 inches
– Demonstrated inspection/characterization of structures
• Funded by JSC engineering division and
HEDS Shuttle upgrades office.
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
AR&C Concept
• Acquisition of target vehicle
– Target: 1km range, 3m diameter, non-cooperative
– Sensor: 10nm SBW, 10cm aperture, 400ns gate
– Worst case Radiometry: at edge of 20 deg FOV, 5% albedo
ET TA2 D 2T R cos( v ) cos( H )
ER 
R2
– Require 500 photons per pixel for reliable detection
– Required laser energy is 10mJ per pulse
– Solar background drives required laser energy to 80mJ/pulse
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
AR&C Concept
• Rendezvous
– Continuous updates on range, bearing, and 6 DOF rates
– Bearing resolution improves with decreasing range
 5 arc min at 250m
 Sub-meter range accuracy
– Update rates to 30 Hz
• Docking
– Increase FOV to 90 deg
– Determine 6 DOF orientation from 3D image
 Extract features and correlate with known features
 Correlated current 3D image with reference model
– 100 pixels across target at 10m separation, sub-cm range
accuracy, 0.2 deg rotational accuracy
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
Required LDRI development
• Daylight Illuminator
– Q-SW doubled YAG laser
• Electronics Upgrade
– Processor and digital interface
– Digital camera
• Autonomous Algorithms
– Range, bearing, and rates
Sandia Micro Laser
– Orientation
• Issues
– Specular surfaces
– Motion artifacts
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
Future LADAR Technology
• Current Issues
– Motion distortion
– Eye safety & stealth
– Required laser energy
– Complexity and cost
– Multiple returns
• Solution:
– Miniaturize receiver to focal plane array chip
– New algorithms utilizing multiple frequencies
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
Near-term Flash LADAR
• Completed prototype
• Size: 7x10x10 inches, 15 lbs
Electronics
4 cameras
Optical block
Top down view
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
Micro LADAR
• Focal plane array of detectors
• Instant 2 frequency sampling by parallel mixers
– Range and passive image sensor
– Bond visible, NIR, or IR detectors
Detector
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
Micro LADAR
2x128 Prototype
• Objective: Develop IC detector array
for instantaneous range imaging
•
Sandia Technology: Sample laser
return with selected frequencies
– Increase resolution by 10x
– Eliminate threshold detection
 Reduce false returns
 Enhance sensitivity & dynamic range
• Status:
FPA Impact
• Instantaneous imaging  Freeze motion
• 2x128 prototype fabricated by JPL
with NASA & DARPA funding
• Integrated FPA  Low-cost and compact
• Enhanced sensitivity  Long Range ( >2km) • Alternate Sandia approach 1x128 array
• IR operation  Eye-safety and stealth
• Demonstrated basic function (TRL 3)
• Dual IR & 3D  Enhanced ATR capability
• Foliage penetration  Enhanced operability
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
FPA Sensor
• Laser return sampled
instantly with parallel
mixers
– Hybrid array architecture
for operation in IR and
dual mode passive and
active imaging
– Store heterodyne product
in pixel for readout
– Single pulse (flash)
imaging avoids motion
artifact
– Currently at TRL 3
8x16 FPA Prototype
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
First Device Testing
• Measure laser response
• Sweep laser time of flight
2x128 Prototype
– Detected modulation indicates
basic operation
– Gating working at 1 ms
Capacitor output (V)
1.780
1.770
1.760
1.750
1.740
1.730
1.720
400.00
500.00
600.00
700.00
800.00
900.00
1000.00
Laser delay (ns)
Typical timing and output
Unclassified
Range sweep at 3 MHz modulation
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.
Micro LADAR AR&C Impact
• Single pulse illumination – no motion artifact
• Near IR operation for eye safety on manned
mission
• Reduce size and complexity
– System dominated by laser size
• Background rejection
– Reduce laser energy
– Enable CW diode laser illumination
Unclassified
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energy under contract DE-AC04-94AL85000.