calibration of on-orbit ir sensors by off-board illumination from neighboring satellites

8/7/2019 Calibration of on-orbit IR sensors by off-board illumination from neighboring satellites

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Calibration of on-orbit IR sensors by off-boardillumination from neighboring satellites

Lorraine E. Ryan, Munson A. Kwok, Randy M. Villahermosa, The AerospaceCorporation (United States); Joseph L. Cox, Missile Defense Agency (United States)

April 14, 2009

Approved for Public Release 08-MDA-4308 (13 MAR 09)DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited .


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2Approved for Public Release 08-MDA-4308 (13 MAR 09)DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited .

INTRODUCTION

Performance Validation

- Post-launch performance validation for infrared (ONIR)sensors requires time-intensive multi-method approaches Ground Truth: cold and warm homogeneous surfaces Ground Sources: Plumes, Calibrated lasers

Transfer functions must be applied Celestial Bodies: stars, moon and others

In band characteristics uncertainties established bymultiple sources

Infrared Sensor Bands

Near infrared (NIR): from 0.7 to 1.0

Short-wave infrared (SWIR): 1.0 to 3 micrometersMid-wave infrared (MWIR): 3 to 5 micrometers

Mid-Long-to Long wave infrared (LWIR): 7 to 10 or 8 to14

Very-long wave infrared (VLWIR): 12 to about 30micrometers,

Source Atmosphere Sensor System


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Application Concept

High utility for in-flight, all-Space periodic calibration check of On-orbit Non-Imaging (Non-focusing) Infrared (ONIR) sensors

- Verify end-to-end operability, from sensor to analog amp to A/Dto on-board processing to digital output to ground

- Verify selected pixel performance of focal plane array

- Verify line-of-sight performance of space vehicle/payload- Account for BOL to EOL changes quantitatively

Cooperative target by use of buddy constellation satellite

- Well-established target orbit allows track verification

Dual use possible as space vehicle radiator Require minimal impact on size, weight, electric power, data

handling, complexity

Improvement over star-calibration: controllable targetcharacteristics


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Generic LEO Constellation

Assume a LEO circular ring at altitude A with N satellitesevenly spaced

- A = 800 km, 1000 km, 1200 km- N= 6, 9, 12

Assume Earth coverage viewing in longitude- Minimal field of regard (FOR) of sensor is thus defined on

azimuthal (AZ) axis of payload Assume similar defined coverage viewing in latitude

- Minimal FOR of sensor on elevation (EL) axis is defined Assume sensors are normally near-nadir pointing, toward

Earth


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Constellation View

Earth

N=6Earth radius 6378 km

BA

x y

z

B as target

AZ-EL

A as sensor

CONOPS

B on position or rotate tocalibration board about Z

A points to B within FORexcursion about X (AZ) and Y(EL)

Calibration conducted on Asensor


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Satellite Assumptions

Satellite orbit velocity is 7.5 km/sec.

Sun angle will be mostly behind the sensor view in daylight with solar arraysto be deployed, away from calibration board LOS

Albedo is negligible for MW and LW regimes

Satellite at 30 C (waste heat, Earth, solar radiation)

Calibration/Target Board guidelines

- Simple, flat geometry for easier analysis

Sized to simulate real targets (cross section) at range- Surface finish: Lambertian, high emissivity, low solar abs. (Perfect uniformity with

high thermal conductivity)- Meet SWaP: i.e.: no active illumination or similar complexity

- Thermistor (array) to verify board radiance

- Optional: heater for more than one temperature setting

- Assessment as a radiator


7/187Approved for Public Release 08-MDA-4308 (13 MAR 09)DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited .

Proposed Calibration Board Features

Calibration board shall be rectangular: 1 x 2.5-m

Board shall be mounted on surface orthogonal to solar panels

One or two boards, opposite each other, can be considered

Since calibration board probably replaces MLI in an area

- Board solar absorbance -MLI in same area- Board emissivity -MLI, for MW, LWIR

Two types of surfaces to be traded

- Graphite epoxy part, rough finish, thermally conductive

- Space qualified white paint (low solar absorbance, high MW,LW emittance) Single thermistor diagnostic, around centroid of board, v. array

Structural support TBD, but also GR-EX for CTE* match andthermal isolation. *Coefficient of thermal Expansion)



Space Sensor Range to Vehiclewith Calibration Board

N = 6zen= 30

or N = 12alt. satellites

N=9zen= 20

N=12zen= 15

A = 800 km --- km 4910 km 3716 kmA = 1000 km 7378 km 5047 km 3819 kmA= 1200 km 7578 km 5184 km 3923 km zen

Range: Target to Sensor

Range Rate = 0 km/sec.

and = 0 /secCondition A=800 km and N=6 does not clear limb of Earth

With ring N = 12, one can calibrate at two ranges

Condition A=1000 km and N=6, board is viewed throughthe atmosphere Geometric Example of ranges



Earth Limb Interference?

ONIR sensors are focal plane arrays

- Assume a sensor A with telescope and LWIRFPA with 256 x 256 pixels (SOA)

- Assume pixel IFOV of 25 rad.- FOV is 6.4 millirad (1/2FOV=3.2 millirad)

- Seek limb angle 3.2 millirad for LOS-centered pixel A

N = 6zen= 30

or N = 12

alt. satellites

N=9zen= 20

N=12zen= 15

A = 800 km --- 140 280A = 1000 km 0 (12 km) 209 365A= 1200 km 43.5 (185 km) 277 439

Limb radius = Earth radius + atmospherer-Limb = 6378 km + 20 km

Limb angle , (milliradians )

(Earth limb to LOS distance)

Conclude:Limb is not on

FPA sensor inpractical cases

FPA

Object plane



Radiometric Estimate

Estimate the number of LWIR photoelectrons (pes)on pixel for Radiometric Feasibility

1) T= in ambient eclipse 0C or 2) T 2 = 20 C

pes/sec. on one pixel emitted from calibration board

- P = QE A tb [ ( ) f ( )f co( ) N BB( , T)]d is receiver throughput, vignetted, transmitted QE is quantum efficiency of receiver pixel (TIS) f co is LWIR cutoff of pixel material (TIS data) f are receiver bandpass filters (1, 0.2 band) is solid angle (ster.) defined by receiver

aperture D and range R to calibration board(D=0.3m)

A tb is projected area of calibration board (m 2) uniform, isotropic unpolarized, Lambertian

is emissivity of board (assume constant)

NBB is the blackbody radiance of board

QE

fco

f

MCT

1

1



LWIR Radiometric Analysis

N = 6zen= 30

or N = 12alt. satellites

N=9zen= 20

N=12zen= 15

A = 800 km --- 4.7 x 10 5 8.2 x 10 5

A = 1000 km --- 4.4 x 10 5 7.8 x 10 5

A= 1200 km 2.0 x 10 5 4.2 x 10 5 7.4 x 10 5

Estimated Number of Photoelectrons/sec. Generated at Pixelby Calibrator

(no multiplication layers on sensing layer)

Conclude: good pixel S/N for SCA for all cases checked

Model assumes an 8 cut-on filter and flat filter through LWIR. MCT Sensing layer spectral data typical of FPAsdeveloped by government. Sensor telescope aperture is 30 cm with effective magnification of 10 4. Board T=0 C.

For A=1200 km, N =6, increasing T by 20 C raises number to only 2.8 x 10 5.



Radiometric Signal Interferences

Spacecraft cross section in view (MLI wrapped)

- Side profile assumed 1.25 m x 3.0 m; 33% not calibration board

- Surface temperature about the same T (30 C) ~ operational ambient

- Strategies for calibrator

Calibration board area to dominate side panel Heat board (or cool spacecraft) surface relative to backing

Appendages (i.e. solar arrays) in profile

- Notional design: 2 deployed arrays of 5 panels at side panel size

- Strategies for calibrator

Measure in the eclipse to cool appendages (reach -70 C) Ref.: Aerospace Spacecraft Thermal Control Handbook, 2008-09-24

Turn arrays toward edge as needed

Calibration Board on SV



Space Vehicle Radiant Background

Situation Key Parameter Interfering RadianceFraction

(fraction of Board Radiance) A/A B T( C)

Spacecraft background 0.45 0.5 0 0.25

Solar panels: full view 0.45 12 -70 1.83Solar panels: 45 view 0.45 8 -70 1.29

Solar panels on edge, 5 cm-thick 0.45 0.2 -70 0.03

Baseline Board Radiance is 787 Watts, = 0.9, A B = 2.5 m 2, T = 0 C.

A sufficient large Calibration Board must cover the S/C side

Solar panels must be positioned to be nearly on edge



Calibration Board as Radiator

Blackbody sizing indicates that 1.0 x 2.5 m 2 board will radiate in anhemisphere

- 787 watts at 0 C, = 0.9- 1077 watts at 30 C, = 0.9- 1390 watts at 50 C, = 0.9

Environmental heat loads (direct solar, albedo, Earthshine)

- None, in eclipse Board as Radiator: capacity = BB environmental loads

- 1077 watts at 30 C; 1390 watts at 50 C

- Max. kilowatt- level heat lift possible with the board - Equilibrium radiator T is TBD depending on S/C heat flux

A task for the concept design phase



Heater Trade

Heat balance at 0 C on Calibration Board, eclipse:

- Heat flux makeup = Radiant power Dissipation power- If makeup efficiency = 1 and S/C dissipation is 500 W

287 watts-makeup = 787 watts 500 watts Requires 300 watt type of heater and DC power

Board may require distributed heater, a complexity to assureuniformity

- Board thickness (mass vs. heater)- Heater (electrical vs. heat pipe vs. capillary pump loop)

Heat Pipe Configuration near board surface


16/1816Approved for Public Release 08-MDA-4308 (13 MAR 09)

DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited .

Calibration Board Material Trade(still open-matrix identified)

Trade Criteria

- BOL vs. EOL performance (emissivity change)

- Thermal performance (slow time constant)

- Weight (low)

- Contamination issue

- Surface uniformity, texture and thermal conductivity- Ease of integration - heater/spreader, thermistor diagnostic, thermal isolation

s s

Kapton (bare) 0.315 0.44

Ge-Kapton

Aeroglaze Z306 (black paint)

Silvered Teflon < 0.09 < 0.4

Z93 (white paint)

"Nusil silicone-based coating"

Graphite-epoxy composite

Aluminum (bare)

Az-93 (white paint)

MaterialBOL EOL (LEO) Contamination

Susceptibilityg/cm3



DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited .

Calibration Board MaterialTrade Space Criteria

Analysis assumptions: high emissivity, low solar absorptance

Trade Criteria- Solar absorptance (minimize solar loading)

- BOL vs. EOL degradation ( increase from space environment, contamination)

- Thermal performance (impact to spacecraft hardware)

- Surface uniformity, texture, and thermal conductivity

Typical thermal materials/coatings can meet analysis assumptions- Material down-select a task for the design concept phase

Thermal Material/CoatingBOL* EOL*

Comment

Al-Kapton (baseline) 0.39 0.73 0.67 0.73 2 mil thick; EOL is 5 years; baseline forcomparison

AZ93 0.15 0.91 0.15 0.90Ref: AZ Technology Corp.; 5 mil thick;EOL for is 4 years, space station orbit; EOLfor is based on lab testing

Graphite Epoxy 0.93 0.85 0.93 0.85 Generic material for composites

Z306 Black Paint 0.95 0.87 0.92 0.87 3 mil thick; EOL is 5 years in GEO*Unless otherwise noted, taken from Gilmore, D. G. Satellite Thermal Control Handbook 1994. Kapton is registered trademark of DuPont



Summary and Next Steps

Calibration board for Infrared Sensors at the System Level (Telescope) to the FPA pixels

appears feasible for ONIR operational constellation

Adds only slight complexity and a little SWaP (Size, Weight and Power) impact

- Size is important and may cover most one equipment compartment side

- Power to maintain (vary) board temperature, mostly passive

- May require heat spreader for surface uniformity

- Thermistor data handling and control system

- Less weight and size impact if Calibration Board is also radiator

- CONOPS for calibration will require little additional motion capability over that

required by main missions

Compatible material solution possible

Next Steps

- Develop several design concepts

- Conduct detailed trades

calibration of on-orbit ir sensors by off-board illumination from neighboring satellites

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