Next generation infrared calibration sources Daniel Peters Dave

Next generation infrared calibration sources Daniel Peters, Dave Smith, Tim Nightingale, Robert A. Mc. Pheat, Frauke Izdebski, and Connor Mc. Gurk

Next generation Infrared Sources Background Acknowledgments Theory Next Generation Infrared Sources (flight). Calibration facility Thermometer and electronics calibration and results Temperature traceability results

Acknowledgments RAL Space: Gayatri Patel, Dave Smith, Daniel Peters, Tim Nightingale, Kathryn Ford, Tom Morse, Coraline Dalibot, Robert Hardie, Adam Hughes, Mike Shepherd, Ben Cartwright, Connor Mc. Gurk, Luke Bushnell, Nick Waltham NPL: Jonathan Pearce, Radka Veltcheva SNS: Ben Jenson, Steve Northam 3

Theory: Planck’s law • Everything in thermal equilibrium emits plank radiation. • Sun: 5, 777 K • SLSTR hot BB ~300 K • Thermal radiometers also selfemit (glow!), and this needs correcting as it’s a significant part of the signal. Unless the whole instrument is cooled. 4

Theory: Blackbody • The accuracy of Blackbody emission, εB(T), d depends on: • Emissivity knowledge, ε • Coating • Geometry • Temperature knowledge, T • • Thermometry readout electronics Thermometry sensors Thermometry calibration Thermal gradients • All of these areas must be addressed in any BB design. In this presentation we address the temperature traceability on orbit of the calibration source. 5

Theory: Temperature Traceability • Requirement is to provide traceable measurements of fundamental data records used for climate monitoring to SI units • For temperature this is the International Temperature Scale of 1990, ITS 90 • For (A)ATSR and SLSTR the traceability is achieved via internal BB sources NPL reference • ITS-90 fixed points SPRT Blackbody • ITS-90 • Known temperature • Radiance 6

Theory: Temperature Traceability • Requirement is to provide traceable measurements of fundamental data records used for climate monitoring to SI units Storage In flight • For temperature this is the International (years) Temperature Scale of 1990, ITS 90 • For (A)ATSR and SLSTR the traceability is achieved via internal BB sources NPL reference • ITS-90 fixed points SPRT Blackbody • ITS-90 • Known temperature • Radiance 7

Theory: Temperature Traceability • Requirement is to provide traceable measurements of fundamental data records used for climate monitoring to SI units Storage In flight • For temperature this is the International (years) Temperature Scale of 1990, ITS 90 • For (A)ATSR and SLSTR the traceability is achieved via internal BB sources NPL reference • ITS-90 fixed points SPRT Blackbody • ITS-90 • Known temperature • Radiance Fly intrinsic standard, ITS-90 fixed point 8

Past work: Temperature Traceability, Phase Change Cells • Work is based on existing ideas, CLARREO (NASA) , also use PCC and have developed the TRL including Gallium PCC (CLARREO instrument currently at TRL 6). • • Bruce A. Wielicki, CLARREO Science Team Report 2018, https: //clarreo. larc. nasa. gov/pdf/CLARREO_Science_Team_Report_final. pdf TS Topham et al, “Observational Study: Microgravity testing of a phase-change reference on the International space station”, npj, Microgravity 2015, 2373 -8065/15 • RAL Space Background Development to TRL 3 • 2017 NSTP-3 project with NPL, demonstrated critical function, repeatable transition temperature in miniature cell at the 10 m. K level. • Moving from TRL 3 to TRL 5 • 2018 CEOI-10 project, NGENIRS (Next GENeration Infra. Red Sources) to integrate into a flight cavity (SLSTR like design) demonstration under TVAC to raise TRL to 5/6. FORUM and LSTM are key drivers for this project. 9

CEOI-11 NGen. IRS Project Next Generation Infra. Red Calibration Sources Project Objectives: To build and characterise a fully functional prototype flight blackbody demonstrator whilst advancing key technologies: Critical electronics for lower power and high accuracy thermometry; Phase change cells to allow on-orbit temperature calibration (this presentation); Utilisation of carbon-nano coating process for infrared calibration sources. Demonstration in operational environment to achieve TRL-5/6. Advancement of flight blackbody sources that may be exploited for future Earth Observation and Meteorological missions. Building upon heritage from the SLSTR and 3 successful NSTP pathfinder precursor projects. • Study funded by the Centre for Earth Observation Instrumentation (CEOI). 10

NGen. IRS : Cavity Design – Mechanical Cross section of NGen. IRS blackbody Phase change cell 11

NGen. IRS : Thermal Vacuum Calibration Facility Calibration facility allows independent control of Environment and Mechanical interface temperatures. During Cycling and Calibration, and Calibration Checks environment and mechanical interface are controlled to the same temperature. The chamber is close to isothermal. Thermal characterisation tests and phase change cell tests are done under nonisothermal worst case SLSTR flight-like chamber conditions. 12

NGen. IRS : End-End Calibration and Calibration checks Electronics, new semi-ridged electronics wrapped around cavity and close to sensors. Digital interface from cavity Calibration of thermometers and electronics against an standard platinum resistance thermometer, SPRT during calibration ramp. Calibrations checked against SPRT during static plateaus. 13

NGen. IRS : End-End Calibration - Results 14

NGen. IRS : Phase Change Cell PCC Requirements matrix ID Performance requirement NGENIRS-PR-PC 01 Non-operational range of a typical flight instrument* NGENIRS-PR-PC 02 Operational range of a typical flight instrument* NGENIRS-PR-PC 03 ITS-90 calibration uncertainty to base PRTS shall be <20 m. K Phase change cell cross calibration uncertainty during whole mission (10 years* storage 7. 5 years flight*) shall be <10 m. K NGENIRS-PR-PC 04 NGENIRS-PR-PC 05 Mass of phase change cell shall be <20 g and ideally <5 g 15

NGen. IRS: Phase Change Cell Melts 1 to 3 Wall and base heater used as per SLSTR. 25 C to 30 C cycles Melts 4 to 7 Wall and base heater used as per SLSTR. Cycle from Freeze observation to 30 C to increase number of melts observed. Melts 8 to 11 Only wall heater to reduce cavity gradients. 16

NGen. IRS : PCC – example Freeze No. Node A Calibrated Temperature (°C) 2 3 4 5 6 7 8 9 10 11 27. 7 29. 3 29. 2 29. 3 28. 9 28. 8 28. 7 The cell was repeatedly frozen within a few °C of its melting point – a large undercool was not required. 17

NGen. IRS : PCC – Melt embedded in cavity Melt No. Node A Melting Temperature (°C) 1 2 4 5 6 7 8 9 10 11 Mean of Melts 1 to 11 29. 778 29. 781 29. 789 29. 774 29. 780 29. 776 29. 783 29. 782 29. 780 29. 781 29. 780 ± 0. 008 NPL Calibrated Gallium Melting Temperature * 29. 783 ± 0. 010 The plot shows example plateau. The temperature of a calibrated thermometer mounted on the base of the blackbody next to the phase change cell for a single melt during thermal testing of the prototype. The Red dotted line is the NPL calibrated temperature of the phase change cell, the orange dotted line is the k=2 uncertainties. The table shows the melt temperature as determined by the calibrated thermometer. The repeatability is very good and within the calibrated k=2 uncertainties of the calibrated value from NPL. *Miniature gallium phase-change cells for in situ thermometry calibrations in space, J. V. Pearce, R. I. Veltcheva, D. M. Peters, D. Smith, T. Nightingale, Measurement Science and Technology 30(12) 124003 (2019) https: //doi. org/10. 1088/1361 -6501/ab 38 e 4 18

Phase change cell model demonstrated performance PCC Compliance matrix. ID Performance requirement NGENIRS-PRPC 01 Non-operational range of a typical flight Compliant: instrument* The PCC has been subjected to 5 thermal cycles over the non-operational temperature range of SLSTR under TVAC. Operational range of a typical flight Compliant: instrument* The PCC has been operated at typical SLSTR flight operational temperatures under TVAC. ITS-90 calibration uncertainty to base PRTS Compliant: shall be <20 m. K Melting can be determined to within 10 m. K in full cavity under TVAC. Phase change cell cross calibration uncertainty Compliant: during whole mission (10 years* storage 7. 5 NPL analysis shows no significant sensitivity to expected years flight*) shall be <10 m. K flight radiation. Melting repeatable to within 10 m. K, in TVAC. NGENIRS-PRPC 02 NGENIRS-PRPC 03 NGENIRS-PRPC 04 NGENIRS-PRPC 05 Performance attained Mass of phase change cell shall be <20 g and Compliant: ideally <5 g Phase change cell mass is <15 g 19

Conclusions Integration of the key technologies into a fully functional prototype blackbody cavity, and verification of performance of the critical functions within a flight representative thermal environment to demonstrate TRL-5. In particular thermal vacuum cycling and thermometer calibration demonstrated that thermometry electronics and blackbody could be calibrated as a system. It provided measurements of temperature of each thermometer node with high accuracy over typical operation flight temperatures to meet current and future flight BB performance requirements. The thermal characterisation phase demonstrated the ability to provide an in-flight ITS-90 calibration fixed point in agreement with NPL’s calibrated values. 20