SPEXone polarimeter instrument thermal design

49th International Conference on Environmental Systems ICES-2019-184 7-11 July 2019, Boston, Massachusetts

Copyright © 2019 SPEXone consortium (Airbus Defence and Space Netherlands BV and SRON Netherlands Institute

for Space Research)

SPEXone polarimeter instrument thermal design

Rob van Brakel1, Marc Oort2 and Jan Doornink3

Airbus Defence and Space Netherlands, Leiden, Netherlands

Jeroen Rietjens4 and Aaldert van Amerongen5

SRON Netherlands Institute for Space Research, Utrecht, Netherlands

SPEXone is a 6u narrow angle, compact spectropolarimeter used to measure the characteristics

of aerosols in the earth’s atmosphere. SPEXone is developed in a partnership between SRON

Netherlands Institute for Space Research and Airbus Defence and Space Netherlands with support

from the Netherlands Organization for Applied Scientific Research (TNO) as a Dutch contribution

to the NASA PACE observatory launching in 2022. SPEXone is a design to cost instrument which

implies there is a fixed budget which shall not be exceeded. The SPEXone polarimeter consists of

an aluminium housing with a radiant cooler and contains one detector module, a reflective

telescope, a transmissive PMO and a reflective grating spectrometer. This paper presents the

thermal design approach. The primary goal of the thermal design is to provide a stable thermal

environment needed for mechanical and optical stability and performance. There were several

design challenges. First, to create a stable thermal environment, temperature fluctuations and

gradients need to be reduced. The temperature level of the detector will be controlled at 293K with

an allowed narrow accuracy range of 0.15K (RMS). In addition, the instrument thermo mechanical

design should be insensitive for thermo elastic loads in order to ensure a stable optical alignment.

Special attention has been put into the control of thermomechanical effects by means of a

Structural, Thermal and Optical Performance (STOP) analysis. Important part of the verification

is to assess the spot size and spot position accuracy (allowed variation 11µm +/-5%). Second, the

implementation of the design-to-cost principle led to the use of a COTS detector module. Some of

the common design practices for narrow range active temperature controlled components could

not be established. Special attention has been put in the design and verification of the detector

temperature control. Analysis has shown that the design is fully compliant to all requirements. The

instrument is approaching the final integration and test phase including a dedicated thermal

balance test planned for the first half of 2020.

Nomenclature

1 Technical Specialist, Engineering Department, [email protected] 2 SPEXone Systems Engineer, Instruments and Services Department, [email protected] 3 Systems Engineer, Technology Department, [email protected] 4 Instrument Scientist, [email protected] 5 SPEXone project manager, [email protected]

ADSN = AIRBUS Defence & Space Netherland BV

ACT = Across Track

ALT = Along Track

ATC = Active Temperature Control

COTS = Commercial Off The Shelf

DEM = Detector Module

DTC = Design To Cost

FOV = Field of View

HARP = Hyper Angular Rainbow Polarimeter

ICU = Internal Computer Unit

I-gain = integration gain factor for heater control

MLI = Multi-Layer Isolation

OCI = Ocean Color Instrument

PACE = Plankton, Aerosol, Cloud and ocean Ecosystem

PFM = Proto Flight Model

P-gain = proportional gain factor for heater control

PMO = Polarization Module

PWM = Pulse Width Modulation

RC = Radiant Cooler

RMS = Root Mean Square

SC = Spacecraft

SPEX = Spectro-Polarimeter for Planetary Exploration

SPM = Spectrometer

TB = Thermal Balance

TBTV = Thermal Balance and Thermal Vacuum

TCS = Thermal Control System

2

International Conference on Environmental Systems

I. Introduction

PEXone is a 6u6 five-angle spectropolarimeter instrument developed as a contributed payload for the NASA

Plankton, Aerosol, Cloud and ocean Ecosystem (PACE) observatory, to be launched in 2022. Making use of the

spectral modulation method to provide measurements of radiance and state of polarization in a continuous wavelength

spectrum and to achieve very high polarimetric accuracy, SPEXone will enable detailed characterization of aerosols

(e.g. absorption, composition, size, height). Figure 1 shows the scanning concept of SPEXone on board of the PACE

spacecraft [3].

The PACE mission will make unique, comprehensive, global, atmosphere and ocean surface measurements with

the goal to understand and quantify global biogeochemical cycling and ecosystem function in response to

anthropogenic and natural environmental variability and change. The PACE observatory includes three instruments:

as a primary instrument the Ocean Color Instrument (OCI), supported by two polarimeters HARP-2 and SPEXone.

SPEXone, in synergy with the other instruments, will allow the PACE mission to perform atmospheric correction, and

provide observations of aerosols and clouds

and the interaction between aerosols and

clouds. Figure 2 shows the PACE

observatory including SPEXone. A more

detailed view on performance aspects of

SPEXone can be found in [1].

A. Design to cost

The SPEXone instrument is contributed by

the Dutch government. The budget for the

development of the instrument is fixed. The

SPEXone instrument development and

governance are organized to reach optimal

performance within the boundaries of a

Design To Cost (DTC) process. All elements

of the instrument, other than the cost, are in

the DTC trade space. The SPEXone project

management practice is aimed to remain

within the DTC trade space while

maximizing science capabilities.

6 One u is defined as a 10x10x10cm3 cube

S

Figure 1. SPEXone instrument on board of the PACE SC 5 angle footprint in orbit.

Dec 17 2018

SPEXOne Pre-CDR Engineering Peer Review

4

Multi-angle spectropolarimetry

between 385-770nm using

spectral modulation

Figure 2. Plankton Aerosol and Cloud Ecosystem (PACE) satellite

configuration. The PACE satellite with the Ocean Color Instrument

(OCI) as prime instrument and the HARP-2 and SPEXone instruments

as secondary payload mounted on the radiator deck.

3


Implementation of the design to cost principle to achieve a high performance to cost ratio is visible in both the design

and AIT process. The detector module and the thermal flexible link are both commercial-of-the-shelf (COTS) items.

Also, to reduce cost of the calibration campaign, the majority of the calibration activities is performed under ambient

conditions.

B. Instrument configuration

The SPEXone instrument consists of a

single optical assembly and contains one

detector. It contains a telescope which looks

into 5 different along-track (ALT) directions

simultaneously. The telescope combines the

images from 5 ALT viewing directions onto

an input slit of the spectro-polarimeter. The

spectro-polarimeter consists of a polarization

modulation optics, which introduces a known

wavelength dependent polarization

modulation on the incoming light using a

chromatic modulator. A polarization beam

splitter in combination with linear wire grid

polarizers acts as an analyser and splits the

light into s & p-polarization states. A

spectrometer creates a spectrum of the

incoming light of two orthogonal

polarizations and images it on the detector.

The SPEXone instrument is built on

heritage with both technology and science.

The newly invented telescope (SRON patent)

specifications are based on mirror manufacturing technology of single point diamond turning on aluminium, as

available in the Netherlands. The polarization modulation optics module is based on an airborne proven unit as

developed in the SPEX airborne program. The spectrometer is a fully reflective design employing free-form

aluminium mirrors as proven in airborne test environment, in the Dutch Tropolite breadboard project (TNO/ADSN).

Manufacturability of the telescope was assessed in a breadboard. Pre-qualification of the polarization modulation unit

was done in a dedicated PMO breadboard work package.

Pre-development of some critical optical coatings in the design has been done in a dedicated coating breadboard

work package.

SPEXone uses spectral polarization

modulation to accurately measure the

state of linear polarization of the incident

light, as well as the absolute radiance

level in the spectral range from 385 to

770 nm. SPEXone has a swath of about

100 km and a spatial sampling distance

of 2.7 km along the swath in each of its

five viewing angles. SPEXone acquires

push-broom spectral images at a rate of 3

Hz, which corresponds to an along track

sampling distance of 2.3 km on-ground.

The optical quality at the slit and in the

spectrometer, in combination with

motion smear during the exposure time

of a single image, is tailored to achieve

Nyquist sampling of an image with a

spatial resolution of 4.6 x 5.4 km (ALT x

ACT).

Figure 3. Close up of the SPEXone instrument to PACE

sidewall. SPEXone consists of the main instrument including the

detector (not shown) and a radiant cooler (RC). The prime Internal

Computer Unit (ICU) is located next to the instrument.

radiator MLI

SPEXone instrument

ICU

MLI

Figure 4. CAD impression of the SPEXone instrument.

radiator

apertures

Titanium bipods

20cm

13cm

4


SPEXone uses a detector module from 3Dplus [4] that is equipped with a CMOSIS CMV4000 image sensor, an

FPGA, SDRAM and flash memory. Dedicated firmware has been developed for the FPGA that allows image

acquisition at 15 Hz while performing 2x2 binning, co-adding and special binning in order to reduce the data.

The ICU is a separate unit that powers and commands the SPEXone detector module, performs thermal control of

the detector module and instrument opto-mechanics, handles the science and housekeeping data acquisition and

communicates with the satellite.

C. Spacecraft Platform and Orbit

The SPEXone instrument carried by the PACE satellite will take place in a sun-synchronous near polar orbit with

an inclination of approximately 98[°] and an altitude of 654[km]. The instrument is placed on the radiant cooler deck

of the spacecraft receiving a minimum amount of sun heat input. The orbital equator crossing times span from 12:50

to 13:10 local time ascending in daylight. The sun to orbit beta angle will range from 6-25[°]. The orbital parameters

are summarized below.

Table 1 orbital parameters

Orbit parameter unit Qty

Semi-major axis [km] 7054.640

Eccentricity [-] 0.001

Inclination [°] 98.0618

Argument of perigee [°] 90

LTAN [hh:mm] 12:50-13:10

Beta Angle [°] 6-25

D. Industrial workshare

SPEXone is developed in a partnership between SRON Netherlands Institute for Space Research and Airbus

Defence and Space in the Netherlands with support from the Netherlands Organisation for Applied Scientific Research

(TNO) as a Dutch contribution to the NASA PACE observatory launching in 2022.

II. SPEXone driving Thermal Design Requirements

The design driving requirements include controlling the temperature of the CMOS detector located within the

detector module to a fixed set point in the temperature range of 291-295[K]. The maximum allowed RMS temperature

variation for the detector is 0.16[K] and for the housing 1[K]. Note that this need to be maintained through the entire

orbit in any season during the entire lifetime. The maximum allowed gradient across the whole instrument housing

including optics is 1[K]. This excludes the titanium bipods and flexures and excludes the thermal links to the radiant

cooler. The heater power budget for operating mode is limited to 10.5[W]. During non-operational mode, the

instrument design temperature limits are 243-323[K]. The orbit averaged heater power budget is 9.7[W].

III. Instrument Thermal Design

A schematic overview of the SPEXone thermal design and interfaces is shown in Figure 5. The generated heat

inside the instrument and the incoming environmental fluxes are rejected to space by a single radiant cooler (RC). The

RC provides a stable sink for both the instrument housing and the detector. The single detector module located inside

the instrument is the only dissipative unit inside the instrument (apart from a low output power LED) with a maximum

power consumption of 2.5[W] in the processing unit PCB and 0.5[W] inside the CMOS detector.

5


The expected interface temperature range that is defined in the SPEXone technical specification is 253 to 313[K].

The specified range envelopes the PACE environment. The SPEXone instrument is mounted directly to the spacecraft

interface deck. To minimize interface heat load variations the instrument is thermally decoupled from PACE by three

titanium struts which combine both strength and thermal insulation. The isostatic nature of the mounts will reduce

thermo-mechanical stresses inside the instrument because of temperature variations of the PACE spacecraft interface

deck.

The instrument is temperature controlled by two separate heater control lines (each equipped with main and

redundant heater and sensors). Each of them equipped with a thermistor (YSI- type) and heater pair (etched foil type)

connected in a feedback loop. The temperatures of the detector and the housing (both controlled at 293K during

nominal operation) are PI controlled.

Although the detector and the instrument will be controlled to the same temperature, titanium struts thermally

decouple them in order to prevent cross coupling of the control lines. In addition, the PCB and the CMOS detector are

integrated into a single unit and they share a single thermal interface. The integrated detector module is shown in

Figure 6.

Figure 5. Thermal control system architecture of the SPEXone instrument. SPEXone consists of the main

instrument including the detector (not shown) and a radiant cooler. The prime Internal Computer Unit (ICU) is

located next to the instrument.

Instrument structure

Radiator

Detector module

ICU

Apertures (5x)

PACE S/C sidewall

ICU to PACE Cable harness

Radiator to instrument cable harness

Cable harness insulators

Instrument to ICU and instrument to PACE cable harness

Non isolating conductive mount

unterface

Isolating conductive interface

MLI PACE

Internal SLI

SPEXone main MLI

Camera to instrument cable harness

Stand offs

6


All the heat generated inside the detector module (2W processing unit + 0.5W CMOS) is conducted via the shared

thermal interface to the interface plate. There is a sensor located close to the CMOS sensor (see right hand side Figure

6). The sensor is a ring oscillator and is processed by the processing unit of the detector module together with the data

signal received from the CMOS. The combined processing has an impact on the read out accuracy of the thermal

sensor inside the CMOS detector which is dependent on the read out frequency of the detector module. This

dependency leads to inaccurate temperature monitoring of the CMOS which is not acceptable due to the tight CMOS

temperature stability requirement of 0.16K rms. Therefore a separate control sensor is used with higher read out

accuracy. The location of the thermal sensor used for thermal control is shown in the right hand side of Figure 7. The

impact of the sensor being located a little further away from the CMOS is verified by a dedicated heater control

analysis, which is presented in section IV.

Figure 6. Detector module of the SPEXone instrument. The 3D-plus standardized detector module consists of an

integrated processing unit and a CMOS sensor.

Thermal interface

CMOS detector

Processing electronics

Thermal interface

Thermal interface

Processing electronics

Ring oscillator thermal sensor

Figure 7. CAD impression of the thermal interfaces of the instrument housing and the detector module to the

radiator. The right hand side of the figure shows the thermal sensor locations.

camera

Titanium flexure

thermal link (IF instrument housing to radiator)

HiPeRflexible thermal link (IF detector to radiator)

Survival heaters

camera heater

thermostats

camera electrical harness

Radiator (rear)

Camera TC IF(see side image)

Camera TC IF

camera heater

TC sensor locationCamera support(3x Ti struts)

7


The detector module interface plate connects the detector module to the flexible thermal link, which conducts the

excess heat to the RC. The thermal link is an ADSN in house developed pyrolytic graphite (PG) thermal strap and is

a standardized catalog item (more details about HiPeR thermal straps in [2]). The conductivity therefore is slightly

over dimensioned. The available heater power budget is not abundant so demanding more heater power than strictly

needed can lead to an exceedance of the available

heater power budget. To meet a specified

conductivity an additional conductive barrier is

placed in between the thermal link and the radiant

cooler. The conductive barrier is a titanium shim.

The actual sizing of the shim shall be determined

by a separate test that includes the PG HiPeR

strap.

An MLI blanket covers the instrument. In

addition, an MLI blanket is installed in between

the instrument and the PACE mounting deck to

reduce radiative heat leak to the spacecraft. In

between the radiant cooler and the instrument a

VDA coated kapton SLI blanket will prevent cold

spots at the side of the instrument. The ICU has a

separate MLI blanket.

The RC will be pointed to deep space and no

direct sun can hit the RC during nominal attitude.

Still, some albedo and planet flux will be received

by the RC surface. During off mode attitude it is

possible that the RC receives sun for a long

duration of time (up to 30 minutes). To minimize

the heat-up when the RC is sunlit, a white

(SolarWhite developed by ENBIO) coating is

applied.

Table 2 thermo optical properties of the radiant cooler

item Surface Finish Emissivity Absorptivity

Main radiant cooler surface SolarWhite 0.8 (BOL)/0.85 (EOL) 0.17(BOL)/0.24(EOL)

Trimming foil VDA coated kapton SLI 0.035 0.14

As previously mentioned the heater power budget is not abundant which requires minimizing the waste heat

extraction. Margins to cover model inaccuracies and systematic margins are kept to a minimum. In addition, the

amount of subcomponent thermal testing prior to instrument thermal balance test is kept to a minimum. This means

that the final power demand and the available margins will become clear at instrument level thermal balance test,

which is planned at the end of phase D. It is obvious that after TB test design changes cannot be implemented without

excessive increase of expenses. In order to be robust but still keeping the heater power to a minimum the radiant cooler

capability is extended and reversely trimmed back by applying low emittance VDA coated kapton foil. If TB test

results show that more radiant cooler capability is needed the radiant cooler area will be increased by reducing the

area covered by the VDA coated kapton foil. The radiant cooler including the VDA coated kapton foil is shown in

Figure 8. Thermo-optical properties of the radiator are presented in Table 2. EOL values are considered for a relatively

short lifetime of three years in orbit.

Survival heating is provided by a single separate power line equipped with main and redundant heaters. The heaters

are controlled by thermostats (also main and redundant) and are located at the radiant cooler. This way both the

instrument housing and the detector are heated simultaneously.

After launch the instrument is decontaminated by raising the temperature of the entire instrument. In the

decontamination case the detector and the instrument are both controlled at 303[K] by elevating the set points of the

operational heater lines.

The internal computer unit (ICU) is a 140x100x70[mm] box that is located next to the SPEXone instrument

mounted to the same spacecraft interface deck. The ICU dissipates 3.7[W] of heat and should be kept within the design

Figure 8. CAD impression of the radiator including the

VDA kapton SLI foil used to reduce the effective radiator

area

radiator

VDA kapton foil

8


limits of 253-318[K] during operation. The dissipated heat inside the ICU is conducted to the spacecraft interface

plane.

IV. Thermal and Thermo-Mechanical Analysis

A detailed thermal model was used to predict heater power consumption during the critical phases. In addition the

thermal analysis is used to produce inputs for a STOP analysis to predict the thermo-elastical behavior. Lastly based

on the thermal model a separate Matlab model is built to model heater control parameters.

A. Thermal Analysis

The thermal model and analysis was performed using ESATAN-TMS. The heater power consumption during

operational and off-modes are presented in Table 3. The temperature predictions together with a description of the

thermal environment is presented in Table 4.

Table 3 predicted heater power consumption SPEXone heaters

Heater line minimum

hotcase

maximum

coldcase

maximum

decontamination

survival

[W] [W] [W] [W]

Detector 0.5 2.5 6.2 0.0

Instrument 0.4 6.9 7.8 0.0

Combined ATC heaters 1.0 9.3 14.0 0.0

Radiant cooler 0.0 0.0 0.0 8.0

Budget 10.5 10.5 16.0 9.7

Note that the sum of the maximum detector and instrument heater power is not necessarily equal to the total

maximum heater power due to the cross-coupling via the radiant cooler.

Table 4 description of the environment and predicted temperatures of SPEXone

heater line unit hotcase coldcase Operational

requirement

decont. survival Allowed

range

Planet temperature [K] 261.5 246.1 n/a 246.1 246.1 n/a

Sun flux [W/m2] 1420 1315 n/a 1315 1315 n/a

Albedo [%] 35 25 n/a 25 25 n/a

Detector thermal sensor [K] 291.5 291.5 n/a 303.0 267.2 243-323

CMOS detector [K] 293.0 293.0 293 +/- 0.15 302.8 267.1 243-323

Instrument sensor [K] 293.0 293.0 293 +/- 1.0 303.0 262.2 243-323

Gradient SPEXone [dK] 0.3 1.6 <1.0 2.0 0.6 n/a

Radiant cooler average

temperature

[K] 274.7 275.9 n/a 283.5 269.7 243-323

PACE interface panel [K] 313.0 253.0 n/a 243.0 243.0 243-323

ICU [K] 313.5 253.5 n/a 243.5 243.0 243-323

Note that the gradient in cold case exceeds the required 1[K]. The impact of the thermo-elastical deformations

caused by the gradient are validated by a STOP analysis.

B. STOP analysis

One of the prime functions of the instrument structure and the thermal design is to provide a stable environment

for the optics to meet the performance requirements. The requirements that are related to the dimensional stability of

the instrument are spot size and spot position (allowed variation 11µm +/-5%). The spot size determines the focus of

the image and the spot position provides spatial and spectral information. Potential sources of disturbance are thermo-

elastical effects induced by temperature variations and gradients, misalignment due to manufacturing tolerances and

gravity release effects. To verify the integrity of the design with respect to these effects a coupled Structural Thermal

Optical Performance (STOP) analysis has been performed.

9


A FEM model has been built to analyze

the deformations caused by the effects

mentioned above. The goal of the analysis

is to find the displacements of all individual

optical elements. The deformations within

the mirrors itself are not considered. The

impact of not taking into account internal

deformation is expected to be relatively

small. All mirrors are monolithic

aluminium parts which are relatively small

compared to the housing. The dominant

effect is expected from deformations within

the aluminium housing. These rigid body

movements are calculated by the method

used by TNO on their STOP analysis used for the Sentinel 5 precursor instrument TROPOMI UVN spectrometer [5]

and the Sentinel 5 instrument UV1 spectrometer optics (UV1 SO) and the telescope beam splitter optical assembly

(TSBOA). A more extensive description of the STOP approach by TNO is presented in [6]. Figure 9 shows the

principle behind the rigid body displacements. For each rigid body representing an optical element, a rotational matrix

R and a translation vector t can be established that describes the displacement of the rigid body. These rigid body

movements will be applied to the optical model build in ZEMAX to calculate the resulting spot sizes and

displacements on the detector. Data set A and dataset B are the nodal grid and displacements of the FEM model.

Table 5 provides an overview of all the cases that have been considered to potentially degrade the performance by

misaligning the optical elements. The cases can but do not necessarily occur simultaneously. The on-ground cases, in

which effects that are already present during on-ground calibration, include orientation with respect to gravity,

manufacturing tolerances, ambient temperature during calibration that can be different from the absolute controlled

level during control, temperature control during on-ground calibration and mechanical loads. Second, the ground to

orbit cases consider the difference between on-ground and in-orbit average misalignments. These are the gravity

release cases, the difference in temperature gradient between on-ground and orbit average gradients and mechanical

loads during launch. Finally cases that represent in orbit variations are micro vibrations induced by reaction wheels,

in orbit thermal distortions, lifetime thermal distortions and reproducibility of the initial state after exposure to survival

and decontamination temperatures.

From the nodal deformations calculated by FEM rigid body movements have been determined of all optical

elements (total of 27 elements). The mean increase in ACT rms spot half width due to AIT (tolerances), gravity case,

enforced displacement (thermal expansion spacecraft interface plane) and worst cold case (temperature gradients and

uniform heating) together is acceptable and within the budget of ~1 μm. Contribution of all individual cases is of the

same order.

Figure 9. The displacement of a rigid body is described by a rotation

R and a translation t

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Table 5 Overview of cases considered for the STOP analysis

C. Heater control analysis

As described earlier the temperature sensor inside the CMOS sensor could not be used. Note that this is a direct

result of the fact that the detector module is an off the shelf item hence not specifically designed for the purpose of

SPEXone. An additional sensor with sufficient accuracy has been applied located close to the CMOS (location

highlighted in section III Figure 7). A dedicated Matlab model has been built to properly model all aspects that affect

the control stability.

The following aspects have been modelled: conversion to digital domain, time delay between ICU and heater

control, non-linearity in ICU and thermistor characteristics, quantization in the analogue-digital-conversion of the

ICU, supply voltage variations in orbit, temperature sensitivity of the ADC reference resistor and physical location of

the heater with respect to the sensor and the controlled part.

The goal of the control analysis is to the find the optimum P and I control gains. The following results have been

obtained. For the on chip CMOS detector sensor, the worst case error is 7.4 mK which is a factor 21 better than the

requirement and a factor 41 better than the resolution. This relies on the assumption that even though the resolution

steps are very large the transitions between the steps are very accurate. Because it is likely that there will be a drift on

the location of the transition, the additional (main) sensor was introduced. For the additional (main) sensor the worst

case error is 8.4 mK which is a factor 19 better than the requirement. the worst case bandwidth for the on-chip sensor

Applicability Name Remark Detailed description disturbance sources

On-ground cases Orientation w.r.t.

gravity

Impacts only

calibration

2g acceleration on x, y, z axis as a result of

changes in orientation with respect to gravity

vector during integration and calibration

AIT cases Impact both calibration

and flight

Manufacturing tolerances.

Ambient temperature

or temperature delta

Impact both calibration

and flight

Uniform temperature offset to account for set

point deviations and sensor absolute temperature

inaccuracies

Temperature control

during on-ground

calibration

Impact only calibration Gradient induced by temperature control during

on-ground calibration

Qualification to

temperature limits


and flight

Degradation after exposure to qualification

temperature limits

On-ground

mechanical load cases


and flight

Mechanical loads:

Transportation loads

Quasi static loads

Sine vibration

Random vibration

Ground to orbit Gravity release cases 1g acceleration on x, y, z axis

Delta gradient

integration/calibration

temperature to steady

state BOL

Gradient induced by temperature control during in

flight temperature control

Mechanical launch

loads

Mechanical loads experienced during launch

In orbit case Micro vibrations Vibrations induced by moving parts within

spacecraft for instance reaction wheels

In orbit thermal load

variations

In orbit temperature variations while operational

as a result of environmental variations during one

orbit

Lifetime temperature

variations

Lifetime temperature variations while operational

as a result of environmental variations over life

Degradation after non-

operational cases

Recovery after exposure to survival and

decontamination temperature levels

11


is 1.2 mHz and for the additional (main) sensor 3.4 mHz. This is because the additional (main) sensor is closer to the

heaters than the main sensor.

For the housing heater the worst case error is 9.1 mK which is a factor 109 better than the requirement. For the

redundant heater the worst case error is 0.7 mK which is a factor 1490 better than the requirement and a factor 15

better than the resolution. The worst case bandwidth for the main heater is 0.7 mHz and for the redundant heater 3.7

mHz. This is because the redundant heater is closer to the sensor.

V. Conclusion

The thermal design of the SPEXone instrument is presented. The thermal modelling results indicates that the

thermal control system of the SPEXone module will be able to obtain operational temperatures within limits and

provide stability for optimal performance. Additional STOP analysis confirms that the deformations of the optical

elements remain within limits.

VI. Acknowledgements

The authors would like to acknowledge the Netherlands Space Office (NSO) and the Ministry of Education Culture

and Science (OCW), the Dutch organization of Scientific Research (NWO), the Netherlands Institute for Space

Research (SRON) and Airbus Defence and Space Netherlands for funding the SPEXone project. We thank the NASA

PACE team for advice and guidance. In addition, we would like to thank 3Dplus for their cooperation in the SPEXone

project.

References

[1] Hasekamp, O.P. et al, “Aerosol measurements by SPEXone on the NASA PACE mission: expected retrieval capabilities”,

Journal of Quantitative Spectroscopy & Radiative Transfer, 2019, pp. 170-184

[2] Maas, A., “Development of Pyrolytic Graphite Applications in Spacecraft Thermal Control Systems”, proceedings 47th

international Conference on Environmental Systems, 16-20 July 2017, Charleston, SC

[3] van Amerongen A , Rietjens J.H.H. , Campo J , Dogan E , Dingjan J , Nalla R , et al. “Spexone: a compact multi-angle

spectro-polarimeter.” Proceedings International Conference on Space Optics 2018 .

[4] Virmontois et al. "Dose and Single-Event Effects on a Color CMOS Camera for Space Exploration" IEEE

TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 66, NO. 1, JANUARY 2019

[5] te Voert M, Witvoet G and van Brakel R, "Thermo-Mechanical stability of TROPOMI", MIKRONIEK Professional Journal

on Precision Engineering, p 5-10 issue 3 2014

[6] Verlaan, A. et al, ”ITER Upper Port Wide Angle Viewing System Optical Design and Performance Analysis”, Fusion

Engineering and Design, Vol. 136 Part B, November 2018 p936-944

Documents

SPEXone polarimeter instrument thermal design