Scientific Objectives of IRSIS :

• To exploit the crucial gap in astronomical spectroscopic

capability in the wavelength range 2 - 6 µm

(between HST-NICMOS cut-off & SPITZER-IRS cut-on)

• Spectroscopic Survey at 1.7-6.4 µm covering > 50% of

the full sky (within 2 years) including the Galactic plane

(M-L-T & brown dwarfs, PAH mapping, minor bodies, AGBs,

RGBs, ULIRGs, ToO, etc)

Summary of the IRSIS instrument

Wavelength coverage : 1.7- 6.4 mm [2 channels]

SW (1.7-3.4 mm) ; LW (3.2-6.4 mm)

Angular resolution : 18″

Spectral resolution, R = (l/Dl) ~ 100

Cassegrain [RC] telescope : ~ 30 cm primary dia., f/12

@ ~100K by Passive cooling

Micro-lenses + Infrared fibre-bundles to couple Focal Plane to

multiple slits of 2-channel spectrometer

Optical components for dispersion: Grating

Cooled (~ 80 deg. K by Passive cooling) detector arrays : HgCdTe

(2K x 2K for Lab Model) (1K x 1K for Engineering and Flight Models)

Spectroscopic Imaging : Topology

Telescope focal plane IFU Slit Collimator Unit

NIR Detector Array Camera Unit Grating

Simultaneous spectra from all sub-areas (fibres) of sky !

Major Sub-systems of IRSIS

Telescope

Spectrograph

Integral Field Unit (IFU)

H1RG Detector & Data Handling Unit

Passive cooling units

Interfaces with space craft (science data,

telemetry, tele-command, power etc.)

IRSIS Telescope Test Collimator Spectrograph parts

Zemax Raytrace and Solidworks model of the Spectrograph of Lab Model

Telescope and Spectrograph Mechanical Assemblies

fabricated at TIFR Central Workshop

Collimator Unit with Grating Camera Unit

Laser Pointer (635nm)

Webcam with Graph Paper Screen

Spectrograph Test - Experimental Set-Up

Comparison of Zemax and Lab test Images

Assembled Telescope with Alt-Azimuth Mount

Star trail Image from the Telescope without Tracking

IRSIS Telescope test within Laboratory with test Collimator

Optical Materials: Lenses: BaF2,SF57,Fused Silica

• Grating-Fused Silica • Filter-Silicon • Window-Sapphire

DESIGN AND FABRICATION OF IFU

Measured Plate Scale: 0.39 “ / pixel

Design, Fabrication & Assembly of the Telescope,

Spectrograph, IFU and their end-to-end

performance verification test with H2RG at

cryogenic temperatures have been completed.

‘Laboratory model’ has been presented to the

ISRO and work for the ‘Engineering model’ has

been initiated.

Procurement of detector array, design of the

readout electronics, passive cooling using V-V

grove, installing the Cryogenic Thermovac

chamber, understanding the satellite bus interface

etc. are under progress.

CURRENT STATUS OF THE IRSIS MODELS

OPTICAL AND MECHANICAL DESIGNS THERMAL DESIGNS

PERFORMANCE VERIFICATION TESTS IN IR LAB AT DAA, TIFR

FUTURE PLANS

Lenses, grating and fibres for the

Engineering model have been identified

and will be procured.

Customized readout electronics for the

H1RG detector is being designed.

Passive cooling design (using V-V groove)

is in the advance stage and it is under

experts supervision.

Preliminary Design Review (PDR) will be

held with ISRO sometime in July 2019 for

the detailed discussions with their experts.

Thermovac chamber has been designed

and it will be installed at Balloon Facility,

Hyderabad in near future, for IRSIS tests

at cryogenic temperatures.

INFRARED SPECTROSCOPIC IMAGING SURVEY (IRSIS) PAYLOAD

FOR AN INDIAN SMALL SATELLITE MISSION S.K. Ghosh, D.K. Ojha, P. Manoj, B. Mookerjea, S.S. Poojary, S.L. D’Costa, M.B. Naik, P.R. Sandimani, H. Shah,

G.S. Meshram, R.B. Jadhav, S.B. Bhagat, S.M. Gharat, C.B. Bakalkar, B.G. Bagade

PLATE WITH MICROHOLES POLISHED FIBERS

IFU FABRICATED IN LAB

Engineering Model Long Wavelength (LW) specifications:

Wavelength: 3.2 – 6.4 µm

Lens, Grating, Fiber optics have been identified.

Basic Zemax model of LW Engineering Model

Major inputs from ISRO for Flight Model

IMS-2 satellite bus will not have any restrictions

on size and mass of the payload.

ISRO has an expertise in designing a passive

cooling system, which can be used for IRSIS.

X-band can be used for higher Telemetry data

rate.

Spectrometer End-to-End testing with IFU

500 Deg C BLACKBODY SOURCE, K FILTER

DAIM -2019

DAIM -2019

Modelling for the Passive Cooling using V-V groove

Cryogenic Thermovac Chamber Design Typical Presentation of the Chamber