pointing determination for a coherent wind lidar mission

32
Pointing Determination for a Coherent Wind Lidar Mission J. Marcos Sirota, Christopher Field Sigma Space Corp. Michael Kavaya NASA LaRC January 2006

Upload: linus-rasmussen

Post on 02-Jan-2016

33 views

Category:

Documents


2 download

DESCRIPTION

Pointing Determination for a Coherent Wind Lidar Mission. J. Marcos Sirota, Christopher Field Sigma Space Corp. Michael Kavaya NASA LaRC January 2006. Outline. Background Information Wind Lidar Mission Concept Pointing Determination in GLAS/ICESat ICESat attitude data - PowerPoint PPT Presentation

TRANSCRIPT

Page 1: Pointing Determination for a Coherent Wind Lidar Mission

Pointing Determination for a Coherent Wind Lidar Mission

J. Marcos Sirota, Christopher Field Sigma Space Corp.

Michael KavayaNASA LaRC

January 2006

Page 2: Pointing Determination for a Coherent Wind Lidar Mission

Outline

• Background Information– Wind Lidar Mission Concept– Pointing Determination in GLAS/ICESat– ICESat attitude data

• Proposed system for coherent wind lidar

• Analysis of pointing control and determination requirements and solutions.

• Summary

Page 3: Pointing Determination for a Coherent Wind Lidar Mission

7.7 km/s

400 km 467 km

233 km

165 km

165 km

30

32.145

180 ns (27 m) FWHM (76%)

6.1 m (86%)

1/10 s = 722 m

Return light: t+3.1 ms, 24 m, 3.5 rad

First Aft Shott + 46 s

120 shots = 12 s = 86 km

90° fore/aft anglein horiz. plane

FOREAFT

Second shot: t+100 ms, 768 m, 103 rad

2 lines LOS wind profiles1 line “horiz” wind profiles

Orbiting Doppler Wind Lidar at 400 km

7.2 km/s

Nadir tilt rate~ 1rad/ms

Page 4: Pointing Determination for a Coherent Wind Lidar Mission

Pointing Geometry - Side View

VL

Lidar BeamDirection

L T

S

R E

ZT

ZL

EARTHATM

SPACE

ATM

RTZL = 400 kmL = 30 deg.ZT = 4 km (example)T = 32.1 deg.VL = 7676 m/sRT = 462 kmR E = 6371 10.7 km

T = arcsin[(RE + ZL) sinL/(RE + ZT)]

T - L

Earth-Orbiting Doppler Wind Lidar

Page 5: Pointing Determination for a Coherent Wind Lidar Mission

2 “Horizontal” Wind Lines, 400 km, 30 deg nadirAzimuths = ±45, ± 135 deg

78 km

330 km

Horiz.Resol.350 km S/C Ground

Track

100 kmTargetSampleVolume

Page 6: Pointing Determination for a Coherent Wind Lidar Mission

Two “Horizontal” Wind Profile “Lines”

Page 7: Pointing Determination for a Coherent Wind Lidar Mission

7LaRC/Kavaya-

400 km orbit, 45 degree nadir angle25, 65, -120, 115, -155, 155, -60, -25 azimuth

pattern. 1.06 sec. to scan

-500

-400

-300

-200

-100

0

100

200

300

400

500

0 1000 2000 3000 4000

Along-Track (km)

Cross-Track (km)

25 deg.

65 deg.115 deg.

155 deg.

- 155 deg.

- 120 deg.

- 25 deg.

- 60 deg.

1

2

3

4

5

6

7

8

90 deg.

45 deg

4 HorizWindLines

Page 8: Pointing Determination for a Coherent Wind Lidar Mission

Four “Horizontal” Wind Profile “Lines”

Page 9: Pointing Determination for a Coherent Wind Lidar Mission

Space-Based Coherent Doppler Wind Lidar System Schematic

Detector

Injection LockingLoop

PZTDriver

Pulsed Laser Oscillator

Recorder

BS

Mirror

MMOptics

Scan Controller

IF Receiver

Detector &Pre-Amplifier

Local OscillatorLaser

A/DData

Command& DataManagementSystem

Laser Controller

BS

BS

FrequencyLocking

FB Control

Transmitter Laser

LO Laser

Data Transmitter

Lens

Polarizing BS

Master Osc.Laser

Isolator

INS/GPS

SignalBeam

TransmitterBeam

AlignmentMirror

Det.

ControlSignal

Nadir AngleCompensator

PowerAmplifier

90/10 BS

2mm

/4

ControlSignal

ScanController

10mm

10mm

Telescope, Scanner, and PointingDetermination System

Nadir AngleCompensator

Page 10: Pointing Determination for a Coherent Wind Lidar Mission

1. Aim scanner to next desired direction [pre-shot pointing control, 2 deg.]2. Tune LO laser to remove predicted gross motion and earth rotation [pre-shot pointing

knowledge, 0.2 deg.]3. Measure LO laser frequency error and tune electronic mixer to compensate4. Fire laser pulse5. Keep receiver axis well aligned for 3 ms [Stability A: 6.6 rad/3 ms]6. Optically mix, electronically mix, and digitize backscattered signal

7. Divide data into time/range/altitude bins [NALT = 22]

8. Combine shots aimed in same direction, if desired [NACC = 60] [Stability B: 0.2 deg./12 sec.]9. Estimate frequency10. Remove residual spacecraft and earth rotation caused frequencies [Final pointing knowledge,

60 rad]11. Assign time, location, altitude, and direction to each LOS velocity

12. Repeat above sequence for other desired cross-track distances [NCT = 4]

13. Repeat above sequence for aft perspectives collocated with fore perspectives [NPER = 2]

On Orbit

LOS Wind Measurement Sequence

On Orbit Or

Ground Processing

Orbiting Doppler Wind Lidar at 400 km

Page 11: Pointing Determination for a Coherent Wind Lidar Mission

• Pre-shot control

• to ensure that Doppler shift is within LO laser tuning range

• a) 2 deg. from -ZLV, scanner fore or aft, if 4000 MHz LO tuning range

• b) 6.7 deg. from -ZLV , scanner fore or aft, if 4500 MHz LO tuning range

• Pre-shot knowledge

• to allow LO to be tuned for sufficiently small heterodyne beat frequency

• 0.2 to 0.5 deg.

• affects receiver bandwidth and data quality

• Stability, t = 0 to 3 ms, for each shot

• 7.1 rad, 1 , for budgeted 3 dB 1 SNR loss

• Stability, while staring for shot accumulation (for 0.3 m/s LOS error)

• nadir 0.2 deg., azimuth 0.3 deg. (beam azimuth at 45 deg. to wind)

• up to 30 sec.

• Final post-mission knowledge (for 0.3 m/s LOS error)

• 60 rad = 0.0034 deg. = 12 arcsec (scanner azimuth angle at 45 deg. to fore or aft)

• Will require use of lidar surface return data for this Shuttle Hitchhiker mission

Pointing Knowledge, Control, and Stability Requirements

Page 12: Pointing Determination for a Coherent Wind Lidar Mission

Background Information:ICESat

• The Geoscience Laser Altimeter System on ICESat carried the first laser pointing determination system in a Lidar space mission.

– It determines the laser pointing direction w.r.t. the stars with an accuracy of 7.5 microradians per axis for every laser shot (40 Hz).

– The system includes star and laser imagers, a high precision gyroscope, and cross-reference optical sources.

Page 13: Pointing Determination for a Coherent Wind Lidar Mission

Surface Altimetry:• Range to ice, land, water, clouds

• Uses time of flight of 1064 nm laser pulse

• Digitizes transmitted & received 1064-nm pulse waveforms

• Laser-beam pointing from star-trackers, laser camera & gyro

• 3 cm single shot range resolution

• 7 urad angular resolution

Atmospheric Lidar:• Laser back-scatter profiles from clouds & aerosols• Uses 1064 nm & 532 nm pulses• 75 m vertical resolution• Analog; photon counting detection • Simultaneous, co-located measurements with altimeter

Geoscience Laser Altimeter System Measurements

Page 14: Pointing Determination for a Coherent Wind Lidar Mission

SRS Functional Block Diagram

Page 15: Pointing Determination for a Coherent Wind Lidar Mission
Page 16: Pointing Determination for a Coherent Wind Lidar Mission

•The ICESat bus was selected based on its pointing accuracy and stability. The Ball Global Imaging System 2000 is an imaging-based platform where the attitude control and determination system were designed for accurate pointing control and stability during image acquisition of high resolution Earth scenes from orbit.

ICESat Bus

Page 17: Pointing Determination for a Coherent Wind Lidar Mission

Predicted Bus Stability

Page 18: Pointing Determination for a Coherent Wind Lidar Mission

1207.5

1208

1208.5

1209

1209.5

1210

0 200 400 600 800 1000 1200 1400 1600

LRS x axis (arcsec)

LRS Y axis (arcsec)

20 urad

Spacecraft motion with Solar Panel Articulation (Case 1)

~ 1 sec

Star Trajectory in LRS

Page 19: Pointing Determination for a Coherent Wind Lidar Mission

140

145

150

155

160

165

170

0 200 400 600 800 1000 1200

LRS X axis (arcsec)

LRS Y axis (arcsec)

~ 200 urad

~ 1 sec

Spacecraft motion with Solar Panel Articulation (Case 2)

Star Trajectory in LRS

Page 20: Pointing Determination for a Coherent Wind Lidar Mission

1200

1210

1220

1230

1240

1250

1260

0 200 400 600 800 1000 1200 1400 1600

LRS X axis (arcsec)

LRS

Yax

is (a

rcse

c)Normal Flight, No Solar Array Articulation

= 1.2 urad

Page 21: Pointing Determination for a Coherent Wind Lidar Mission

SRS

ICESat II Concept

Old system of equal function

Stellar Reference System in ICESat

Page 22: Pointing Determination for a Coherent Wind Lidar Mission

Space-Based Coherent Doppler Wind Lidar System Schematic

Detector

Injection LockingLoop

PZTDriver

Pulsed Laser Oscillator

Recorder

BS

Mirror

MMOptics

Scan Controller

IF Receiver

Detector &Pre-Amplifier

Local OscillatorLaser

A/DData

Command& DataManagementSystem

Laser Controller

BS

BS

FrequencyLocking

FB Control

Transmitter Laser

LO Laser

Data Transmitter

Lens

Polarizing BS

Master Osc.Laser

Isolator

INS/GPS

SignalBeam

TransmitterBeam

AlignmentMirror

Det.

ControlSignal

Nadir AngleCompensator

PowerAmplifier

90/10 BS

2mm

/4

ControlSignal

ScanController

10mm

10mm

Telescope, Scanner, and PointingDetermination System

Nadir AngleCompensator

Page 23: Pointing Determination for a Coherent Wind Lidar Mission

Pointing determination system concept forWind Lidar Mission

Transceiver Telescope

Silicon Wedge

Frame Motor with Absolute Encoder

Laser Camera /Star Tracker

Lateral Transfer Retroreflector

Counter-rotating Ring

Page 24: Pointing Determination for a Coherent Wind Lidar Mission

Star Tracker Errors Per Axis

• Single frame errors for HD-1003 (example)

- 2 arcsec (1) pitch and yaw (ST coordinates)

- 40 arcsec (1) roll

• If at 45 degree to Nadir it translates to:

~ 30 arcsec per axis per frame• Filtered solution (Star tracker plus Inertial Reference

Unit) shall yield about 3 arcsec per axis (1).

Page 25: Pointing Determination for a Coherent Wind Lidar Mission

Pointing knowledge analysis

Telescope/backplane magnification 5LRS laser pointing determination error 1 uradLRS to Star Tracker stability 2 uradAttitude solution error 15 uradTransfer optics (LTR) 5 uradScanner Encoder accuracy 10 urad

Pointing determination error per axis 18.19 urad 34.68 urad

Page 26: Pointing Determination for a Coherent Wind Lidar Mission

Stability analysis

Spacecraft jitter (max) 0.2 urad/msecSpacecraft motion amplitude 200 urad

Shot return time 3.1 msecMisspointing due to jittter for return pulse 0.62 urad 3.5 uradMisspointing due to jittter for 30 sec integration 200 urad

Orbital rate 1.03 urad/msecMisspointing due to orbital rate for 30 sec 30.9 mrad

1.77 degrees 0.2 degrees

• Stability of ICESat-class spacecraft is adequate for round-trip per shot requirement

• Orbital motion compensation with aft-optics mirror is necessary for multi-shot integration

Requirement

Page 27: Pointing Determination for a Coherent Wind Lidar Mission

Requirement Compliance Analysis

• 1. How will we have pre-shot pointing control? To ensure that the gross Doppler (spacecraft and earth motions) is within the tuning range of the tunable LO laser. (+/- 2-7 degrees)

a. Spacecraft slew rates for ICESat-class bus have demonstrated this level of pointing control.

b. Fine pointing can be achieved with the aft-optics beam steering mechanism.

Page 28: Pointing Determination for a Coherent Wind Lidar Mission

• 2. How will we have pre-shot pointing knowledge? To allow the setting of the tunable LO frequency so that the return signal is within the bandwidth of the detector and electronics. (+/- 0.2 degrees, or ~ 3.5 mrad)

• Pointing knowledge will be obtained from the Laser Sensor, Attitude Determination System, and Scanner Encoder to within 20 urad per axis.

Requirement Compliance Analysis

Page 29: Pointing Determination for a Coherent Wind Lidar Mission

• 3. How will we hold the line of sight of the receiver stable while waiting for the laser light to return from the earth? To avoid more SNR lossthan is budgeted. (8 microradians 1 sigma over 7 ms).

• The stability of the spacecraft is sufficient to comply with this requirement. If we wish to compensate for the 3.1 urad from orbital motion then a fixed-angle wedge or tilt mirror can be introduced on the path between fire and return.

Requirement Compliance Analysis

Page 30: Pointing Determination for a Coherent Wind Lidar Mission

• 4. How will we hold the line of sight stable while we are accumulating several shots to make one wind measurement? To avoid smearing the angle at which we probe the atmosphere which will add error to the wind estimate. (+/- 0.2 degrees over 12 seconds).

• The Nadir Compensation Mechanism will provide compensation form shot to shot, holding the line of sight stable until the end of integration.

Requirement Compliance Analysis

Page 31: Pointing Determination for a Coherent Wind Lidar Mission

• 5. How will we achieve the final pointing knowledge for each shot? To allow minimum error in reporting the measured wind's direction to the user. (+/- 60 microradians assuming earth surface is not available to use for reference).

• The Laser Reference Sensor plus the Scanner Encoder shall provide knowledge for every shot fired w.r.t the stars to better than 20 urad per axis.

Requirement Compliance Analysis

Page 32: Pointing Determination for a Coherent Wind Lidar Mission

Summary

• Pointing requirements for a space based coherent wind lidar mission can be met with space proven technology, and some current miniaturization efforts.

• Same design could be used to adapt the system to various platforms, i.e dedicated craft or multi-instrument (NPOESS).