1. Thermal Design and Modeling for Infra Red Spectroscopic Imaging Survey Payload (IRSIS) S. L. D’Costa

2. Goals to be achieved 1. Detector temperature to be at 77 K 2. Filter and grating temperature to be at 77 K 3. Optic fibre coupling at 100 K 4. Primary and Secondary mirrors to be at 100 K 5. Electronics temperature ~ 290 K

3. Parameters involved in Thermal Modeling 1. Orbital Parameters 2. Payload geometry 3. Total allowed size and weight of the Payload 4. Configuration of optics 5. Placement of Electronics 6. Total power dissipation in the entire electronics 7. Materials to be used in construction

4. Orbital Parameters Orbit : Sun synchronous Polar orbit of ~800 km. Source : Cooling Technology for Large Space Telescopes – Keith Walyus (NASA Science Technology Conference 2007) Preferred Orbit : Dawn / Dusk Sun Synchronous ~ 800 km., ~ 96 min/orbit ~ 98 degrees inclination

5. Environmental Heat Loads Source : Thermal Performance of the CrIS passive cryocooler – B. Ghaffarian et al – Cryogenics 46 (2006) 158-163 SunAlbedoEarthTotal Noon orbit3.143 Watts0.628 Watts4.290 Watts7.961 Watts 13:30 orbit0.128 Watts0.553 Watts4.290 Watts5.001 Watts 17:30 orbit0.000 Watts0.211 Watts4.290 Watts4.491 Watts 21:30 orbit0.033 Watts0.466 Watts4.290 Watts4.759 Watts Heat loads for different Sun Synchronous orbits in Watts

6. ISRO Launch Capability In 2001, ISRO launched PSLV-C3 with the following Satellites put into orbit 1. TES (Technology Experiment Satellite) 1108 kg. 568 km. Sun Synchronous Polar Orbit 2. PROBA (PRoject for On Board Autonomy) of Belgium, 94 kg., Elliptical orbit 568 x 638 km. 3. BIRD (Bispectral and Infrared Remote Detector of Germany, 92 kg., 568 km. SSO

7. 1. Telescope optics always pointing in the Anti – Sun direction 2. Sun Shield with multiple layers to be deployed after reaching orbit 3. Separate enclosure for Spectrometer with radiation shields and one side facing deep space 4. Detector and spectrometer components cooled by Stirling Cooler 5. Low thermal conductivity struts for mounting telescope and spectrometer on satellite deck Payload Geometry

8. Telescope Optics 1. Cassegrain configuration for telescope 2. High conductivity, high strength (Beryllium?) mount for secondary mirror 3. Open configuration for telescope 4. Type of baffling to be used 5. Fibre coupling to spectrometer enclosure

9. Strategy for Thermal design 1. Firming up basic satellite, telescope and orbit parameters 2. Interacting with ISRO engineers for inputs on thermal insulation and shield design 3. In-house thermal modeling using software like Radtherm 4. Final thermal modeling to be outsourced with inputs from ISRO 5. Testing strategy and facilities