A Compact Solar Spectral Irradiance Monitor for Future

A Compact Solar Spectral Irradiance Monitor for Future

Small Satellite and CubeSat Science Opportunities

Erik Richard, Dave Harber, Paul Smith, Joel Rutkowski,

Zach Castleman, and Ginger Drake

Laboratory for Atmospheric and Space Physics (LASP)

University of Colorado, Boulder Colorado USA

Nathan Tomlin, Malcolm Smith, Michele Stephens, and

John Lehman

National Institute of Standards and Technology (NIST)

Boulder, Colorado USA

Challenges & Opportunities in

Solar Observations, 12 Nov. 2015

A Compact Solar Spectral Irradiance Monitor for Future Small

Satellite and CubeSat Science Opportunities

Richard 1

Solar Spectral Irradiance

Global Energy Budget Contributions Stratosph.

Troposphere

Climate Forcing: H

2

O (vap, liq., ice) , CO

2

, aerosol

O

3

Abs.

Loss

O

2

Dissoc.

O

3

Prod.

SORCE SIM SSI

(200 – 2400 nm)

10%

Spectral variability

1%

0.1%

0.01%

Figure adapted from:

Stephens et al ., Nature Geo., 2012

The measurement of SSI is vital for understanding how solar variability impacts climate and for validating climate model sensitivity to spectrally varying solar forcing

“Acquire SSI and TSI time series of measurements of sufficient length, consistency, and continuity to determine climate variability and change”

Climate Data Records from Environmental Satellites: Interim Report (2004)





Richard 2

SSI Measurement Continuity

I. Ermolli, et al., Atmos. Chem. Phys., 13, 3945 –3977, 2013

ASSI

EURECA

SCIAMACHY

GOME

SBUV

SORCE

NOAA-16, 17, 18

NOAA-9, 11

GOME-2

ISS

SPM

PREMOS

AE-C, AE-D,

AE-E

SME UARS

ISS

LYRA

OSO 3,4,6

SEE

Note: For several of the instruments SSI is not their primary product, therefore calibration and long-term stability corrections not well quantified

TSIS

Measurement continuity relates to both temporal AND spectral coverage

• Are there alternatives that can be implemented without sacrificing quality?

• Can short duration - overlap missions provide the necessary ties?

• Is the data quality adequate for Earth-climate research?





Richard 3

Present SSI Measurement Requirements

SSI Measurement Requirements

Specification Requirement Justification

Irradiance Range Limits 10 -4 -10 1 Wm -2 nm -1 Full scale bounds on SSI

200-2400 nm Nearly full spectrum: 96% TSI



Spectral Range (continuous)

Measurement Uncertainty* (k=1)

(SI-traceable in irradiance)

Measurement Repeatability

0.2%

(Absolute)

100 ppm

(Relative)

Climate modeling input

Radiation budget solar attribution

Precision

Std. dev. of repeated measurements

Long-term stability**

≤400 nm

>400 nm

500 ppm/yr

100 ppm/yr

Solar cycle variability

UV:10%-0.1% (Chromospheric)

Vis-IR: ≤0.1% (Photospheric)

Spectral Resolution Limits

≤ 280 nm

> 280 nm – 400 nm

> 400 nm

2 nm

5 nm

45 nm

**Long-term correctable stability limits represent 10-25% of total expected variability

Solar spectral variability

Strong wavelength dependence in UV

Broader wavelength dependence in Vis-IR

*Absolute Uncertainties (evolution):

SORCE SIM 2-8% TSIS SIM 0.2% CSIM 0.2%





Richard 4

Achieving an Accurate SSI Observation



• GOAL #1 – Place the instrument on orbit with the best possible calibration (SIunits) and characterization



• GOAL #2 – Determine on-orbit changes in instrument responsivity, correct solar data (with documented uncertainties)

X

TBD

• GOAL #3 – Establish a solar irradiance

EDR that can be reliably compared to future observations





Richard 5

LASP Spectral Radiometry Facility (SRF)

L1 Cryogenic Radiometer

SIRCUS Laser System

TSIS SIM in SRF Vacuum Tank





Richard 6

Full Spectrum Irradiance Validation (Absolute)

TSIS SIM (210-2400 nm)

3 channels, 25 wavelengths, both polarizations,

8 FOV angles

Channel A

Channel B

Channel C

± 0.2%


Solar Observations, 12 Nov. 2015 wavelength (nm)



Richard 7

Design Evolution

Simple light path: entrance slit-prism-exit slit-detector

Wavelength is scanned by rotating the prism (continuous spectral coverage-no “order sorting” )

TSIS SIM

–

Silicon (UV-Vis) and InGaAs (IR) photodiodes

•

High S/N and fast

•

Used to take two solar spectra per day

–

Miniature electrical substitution radiometer (ESR)

CSIM

•

Carries the absolute calibration

• Provides long-term stability to calibrate the photodiodes

SORCE SIM

Measurement Equation (Units: Wm



-2 nm -1 )

Shutter

Photodiode

Exit slits

Plane Prism

Disperser

(Rotating)



TSIS SIM

Entrance slit

ESR exit slit

(Rotating)

OAP

Collimators

CSIM

Richard 8

Compact SIM – Dual channel SSI

FSS

Prism

Drive

ES based bolometers

Focal Plane • Two identical, full spectral channels

• Titanium flexures interface with instrument structure (thermal isol.)

• Optical black aluminum enclosure for stray light and contamination control

Entrance Slits (NIST Calib.)

Shutter

Mechanisms

Aluminum Optical Bench

280 mm



Off-Axis

Parabolas



Top Section View

Richard 9

CSIM Optical Overview

Dispersion View

Entrance Slit

F =220 mm

Off-Axis Parabola

Collimates and

Focus for

Photodiodes

Photodiodes

Si, InGaAs,

ExInGaAs

Fused Silica

Rotating Prism

Off-Axis

Parabola Focus for ESR ESR

(VACNT Bolometer)

CSIM incorporates two identical channels, stacked on top of each other, to permit tracking of exposure-induced degradation





Richard 10

CSIM Design Attributes

• Reduced pointing sensitivity

• Increased FOV

• Improved encoder design

• Improved stray light rejection

• Simplified configuration with improved manufacturability

• Reduced size

• Modular design





Richard 11

CSIM Prism Rotation Drive

Bearing

76 mm

Prism Carrier

Assys

Prisms

Brushless DC

Motor

Bearing

Encoder

Scale

Hard Stop (1 of 2)

Encoder Read

Head (1 of 2)

Counterweight

Actual CSIM Prism Drive

(mounted to GSE plate)

Bearing Preload Flexure





Richard 12

CSIM prism positional stability

Measurement stability requires wavelength stability

Single encoder control

Dual encoder control

CSIM dual-encoder arrangement

Requirement for 100 ppm repeatability





Richard 13

CSIM ESR Bolometer Design

• Vertically aligned carbon nanotubes

– Extremely “Black”

– Spectrally flat

– Large thermal conductivity

• Silicon substrate

• SiN Thermal Link

– Low thermal conductivity

– Low thermal mass

• Patterned heater and leads

• Bonded thermistor

Well controlled fabrication process

Parameter

Active Area

Bolometer

Thermal Link

Absorber

Thermal Link

Impedance

Heat Capacity

Value

1.2 x 4.5 mm

1.2 x 6.3 x 0.375 mm

Silicon

1.2 x 0.5 x 0.002 mm

Silicon Nitride

VACNT

~5500 K/W

~4.8 mJ/K





Richard 14

Vertically Aligned Carbon Nanotubes (VACNT)





Richard 15

Vertically Aligned Carbon Nanotubes (VACNT)





Richard 16

VACNT ESR Noise Estimate

Noise spectral power density vs. frequency Assembled Prototype ESR

Bolometer Model

•

Measured thermal parameters

Z

0

=5500 K/W, C p

=4.8 mJ/K, tau=19 s

same temperature noise as TSIS

Noise Level for 40s Measurement

•

TSIS ESR ~ 1.6 nW

• CSIM ESR ~ 0.24 nW





19 mm

Richard 17

VACNT ESR Noise Measurement

 Prototype CSIM ESR meets TSIS SIM ESR performance

1000

TSIS SIM ESR

CSIM Prototype ESR

100

200 sec 40 sec

10

40 sec measurement ~ 1.2 nW

1

0.001



0.010

0.100

Frequency [Hz]

1.000



10.000

Richard 18

CSIM CubeSat Package

6U Dimensions: ~ 11 x 22 x 33 cm

Optical Bench Assy

Blue Canyon

S/C Bus (XB1)

Star Tracker #1

Deployment

Switches

Separation connector

Supplemental battery

Fine Sun

Sensor (FSS)

Battery charge connector Coarse Sun Sensor



NanoSat Deployer

I/F Tab



Instrument

Electronics

19

Richard 19

CSIM CubeSat Overview

< 1 m



Planetary Systems Corp.

Canisterized Satellite Dispenser (CSD)



Richard 20

Summary

The CSIM instrument concept will mitigate potential risks associated with large mission delays – resulting in observational data gaps – by developing a cost effective, reduced-size SSI instrument.

• CSIM offers significant implementation flexibility for future alternative flight opportunities – hosted payloads, small sats, &

CubeSats

• CSIM will enable high priority Earth science measurements of SSI and provide an SI-traceable tie to existing and future satellite records, including the SSI record that began with SORCE (2003) and beyond TSIS (2017 )





Richard 21

Acknowledgements

NASA Earth Science Technology Office (ESTO); IIP-13-0036





Richard 22

Backup Slides





Richard 23





Prism Geometry for refraction operation

Richard 24





Prism Geometry for reference operation

Richard 25

A Compact Solar Spectral Irradiance Monitor for Future

Solar Spectral Irradiance

SSI Measurement Continuity

Present SSI Measurement Requirements

Achieving an Accurate SSI Observation

LASP Spectral Radiometry Facility (SRF)

Full Spectrum Irradiance Validation (Absolute)

Design Evolution

Compact SIM – Dual channel SSI

CSIM Optical Overview

CSIM Design Attributes

CSIM Prism Rotation Drive

CSIM prism positional stability

CSIM ESR Bolometer Design

VACNT ESR Noise Estimate

VACNT ESR Noise Measurement

CSIM CubeSat Package

CSIM CubeSat Overview

Summary

Acknowledgements

Backup Slides

Related documents

Products

Support

A Compact Solar Spectral Irradiance Monitor for Future

Solar Spectral Irradiance

SSI Measurement Continuity

Present SSI Measurement Requirements

Achieving an Accurate SSI Observation

LASP Spectral Radiometry Facility (SRF)

Full Spectrum Irradiance Validation (Absolute)

Design Evolution

Compact SIM – Dual channel SSI

CSIM Optical Overview

CSIM Design Attributes

CSIM Prism Rotation Drive

CSIM prism positional stability

CSIM ESR Bolometer Design

VACNT ESR Noise Estimate

VACNT ESR Noise Measurement

CSIM CubeSat Package

CSIM CubeSat Overview

Summary

Acknowledgements

Backup Slides

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