The Compact Infrared Imager and Radiometer

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1 The Compact Infrared Imager and Radiometer Earth System Science from a 6U nanosat? Neil Bowles (Univ. Oxford) On behalf of the CIIR Consortium. 22 April 2015 CEOI-ST Technology 1

2 The Why study a tightly integrated, thermal-ir nano-spacecraft? What science questions are we trying to address? Why do we think it stands a chance of working? Update on the current status of the study. Next steps Study will flow requirements against performance against science requirements for the complete system. If they exist, identify technology/performance gaps. 22 April 2015 CEOI-ST Technology 2

3 Science Rational Temporal variability of stratospheric water vapour from limb sounding. Important for understanding long term temperature trends in the lower stratosphere. Sampling at shorter timescales also important for understanding transport and radiative processes in the lower stratosphere. Preparation for future constellations, high temporal resolution measurements Inputs to chemical models etc. Solomon et al April 2015 CEOI-ST Technology 3

4 Overall CIIR Project Concept The CIIR project concept: Develop a new modular, compact imaging radiometer, the CIIR. Integrate it into a 6U Cubesat with supporting subsystems. Test and calibrate the instrument and integrated spacecraft to flight readiness level. So quite ambitious! But How did we get here, and why do we think this will work? Showing work in progress, so numbers not final. 22 April 2015 CEOI-ST Technology 4

5 Heritage Oxford/RALSpace have a long history in the development of limb and nadir viewing thermal infrared instruments. E.g. There is similar hardware in orbit around: The Earth (e.g. HIRDLS, Compact Modular Sounder) The Moon (Lunar Diviner Radiometer Experiment with NASA/JPL) Saturn (Composite Infrared Spectrometer (CIRS) with NASA/GSFC) Mars (Mars Climate Sounder (MCS) with NASA/JPL). Of these HIRDLS and MCS are limb scanning instruments, designed to measure trace gas and temperature in the upper atmosphere of Mars/Earth. 22 April 2015 CEOI-ST Technology 5

6 Precursors: Mars Climate Sounder Limb Scanning instrument measuring temperature, dust and water vapour profiles for Mars. Uses uncooled thermopile detector arrays and miniature (~0.94 x 0.4 mm) filters close to the focal plane. JPL instrument, Oxford provided focal plane assemblies, integrated Cardiff/Reading filters, assisted with calibration. Successfully working in Mars orbit since ~ 2005 MCS schematic from McCleese et al 2007 MCS Flight instrument. All MCS images and plots from McCleese et al 2007 unless otherwise stated 22 April 2015 CEOI-ST Technology 6

7 Example Mars Climate Souder Retrievals 22 April 2015 CEOI-ST Technology 7

8 Precursor: Compact Modular Sounder Flying on TechDemoSat- 1 Original volume envelope was for a more complex imaging FTIR. 11 channel radiometer, intermediate focus design. 4.5 kg, RAL CDHU, Oxford structure Currently working in orbit. Data analysis effort ongoing. 22 April 2015 CEOI-ST Technology 8

9 CMS Details Figure 1 Optical layout of radiometer Thermopile detector array, 32 x 32 Filter block at intermediate focus, mag factor of ~1.7 between filters and detector array 11 Channels, from previous missions 22 April 2015 CEOI-ST Technology 9

10 Example CMS Data from TDS-1 Broad band ~ 60 mins of data averaged. Red = cold (night), yellow = warm no stretch just raw dn 22 April 2015 CEOI-ST Technology 10

11 Why CIIR? Based on experience with TechDemoSat/CMS it was clear that further optimisation was possible. CEOI-ST 8 th call offered chance to take the CMS instrument concept and combine with: Address timely NERC remit science questions (e.g. stratospheric water vapour). Optimised, more compact design. Improved detector array (e.g. Microbolometer or higher performance thermopile arrays). Integration into Cubesat platform. Re-use of existing CIIR subsystems (e.g. CDHU, parts procurement) Opportunity to test Spacecraft is the instrument concept. Awarded study of instrument, in progress. 22 April 2015 CEOI-ST Technology 11

12 Study Concept Process is iterative, with each stage identifying necessary trades. On going, mission definition review in mid-may Unusual approach, start with what we have and see where it gets us 22 April 2015 CEOI-ST Technology 12

13 Science Traceability Matrix Science question defines the instrument requirements. Usually represented via a traceability matrix that evolves with the project. Populating this with realistic numbers is a key aim of this study. 22 April 2015 CEOI-ST Technology 13

14 CIIR in development Overview of proposed instrument Keeps CMS instrument intermediate focus concept. Simplified on-axis Cassegrain telescope with off axis relay. Includes the option for CMS off-axis optics 60 mm aperture (c.f. CMS 50 mm) ULIS Microbolometer array baseline Integration into 6U cubesat structure. 22 April 2015 CEOI-ST Technology 14

15 Incoming radiance Instrument Concept All reflective design to allow wide wavelength range easily changeable for different science goals. To achieve accurate calibrated observations we need to view a known target and space using the whole optical path. Using a mechanism is unavoidable. To minimise risk we want to use a single mechanism. The layout we use to achieve this requires aligned scan axis and telescope optical axis. The calibration target is mounted perpendicular to this axis leading to a T shaped layout which requires a minimum of a 3x2 cubesat. 22 April 2015 CEOI-ST Technology 15

16 Filters and detectors Filters placed at the focal plane of the primary telescope Refocused onto the detector array with a different f/# to allow use of multiple filters which are large enough to fabricate. This approach greatly reduces problems with light scattered from filters and signals from thermal emission from the filters. 22 April 2015 CEOI-ST Technology 16

17 Accommodation Concept 22 April 2015 CEOI-ST Technology 17

18 Scan Orientations The single mechanism can be used for both limb and nadir measurements. The linear filters will be oriented near vertically to place their field of view across the limb. When rotated to view the nadir the field of view rotation determines the scan direction. If we wish to view both limb and nadir we will see the forward or backward looking limb. The limb isn t at 90 to the nadir so we have to compromise on the field of view orientation. LIMB NADIR SPACECRAFT MOTION For push-broom nadir imaging motion must be perpendicular to scan mechanism axis 22 April 2015 CEOI-ST Technology 18

19 Detector options Preferred option is the current generation ULIS 17 μm pitch detector array. Would be good to use the broadband detector with wavelength coverage 20 μm. Have been working with these detectors since early 2000s Part of BepiColombo, Marco Polo-R and NERC instrument studies. Most comprehensive data from our own test programme plus work on characterising detectors for EarthCARE in the late 2000s with SIRA, now SSTL. Temperature stability requirement under study, previous data indicates OK Critical parameter is drift rate between calibrations. Under final analysis. Blank pixels essential for readout noise decorrelation! With thanks to thermoteknix for window info 22 April 2015 CEOI-ST Technology 19

20 Filters Interference filters below 25µm Custom made by Reading University Heritage from HIRDLS, MCS, Diviner Typically 1mm x 9mm Current study baseline: HIRDLS-derived H 2 O H 2 O O O O Aerosol pt pt pt pt Initial selection, still under optimisation 22 April 2015 CEOI-ST Technology 20

21 Platform performance Temperature variation Minutes 22 April 2015 CEOI-ST Technology 21

22 Orbit and Field of View The field of view corresponding to a single pixel is determined by: the pixel dimension (17 m), the f# at the detector and the telescope size. To maximise the signal available we chose: the f# to be as large as practical for imaging (f#1.7) the telescope as large as can be accommodated in the cubsesat (~6cm diameter) leads to a single pixel field of view (ifov) of 180 rad. For an 800km orbital altitude this corresponds to 0.6km resolution at the limb and 0.15km on the surface. Coincidentally, the surface resolution corresponds almost exactly to the orbital smear cause by the standard 0.02 second integration time of the detector array. In almost all channels we will need on board averaging of the measured values to reduce spatial resolution and increase signal to noise performance. 22 April 2015 CEOI-ST Technology 22

23 Platform Performance Pointing Need knowledge to 0.01 degree/minute Completing analysis of this, but absolute pointing needed to 0.5 degrees (10% limb) 22 April 2015 CEOI-ST Technology 23

24 Pointing Stability 22 April 2015 CEOI-ST Technology 24

25 In-Flight Calibration Based on CMS design. V-groove target with baffle CIIR requirements almost certainly met with much shorter baffle No thermal control. Relies on slow drift due to significant thermal mass Temperature measurement is critical 0.1K probably practical with simple housekeeping electronics Need black body stable over several minutes so a black body stability goals will be something like 0.01K per minute CMS data used to verify, so far OK. 22 April 2015 CEOI-ST Technology 25

26 Current Status Closing out study for final review. Feeding all inputs back into instrument model for synthetic retrievals, error covariance matrix terms etc. Pointing concern from simulations, but will be studied using instrument simulator. Bringing it back to the science limb observations of H 2 O, aerosols etc. 22 April 2015 CEOI-ST Technology 26

27 Instrument Summary Max number of channels = 11 Spectral range 6 16 μm FOV = 6.2 x 4.6 degrees Pixel IFOV = 168 μrad, km at 800 km orbit. Uncooled Micrbolometer array, 640 x μm pixels Mass 6 kg (including cubesat) Power <8W Thanks to the CEOI-ST for supporting the feasibility study Lots and lots of more detail on specific sub-systems, ask me at Coffee! 22 April 2015 CEOI-ST Technology 27