Shaping SHAPE - A spectro-polarimeter onboard Chandrayaan-3 to observe Earth as an Exoplanet

Anuj Nandi; Swapnil Singh; Bhavesh Jaiswal; Anand Jain; Smrati Verma; Reenu Palawat; Ravishankar B. T.; Brajpal Singh; Priyanka Das; Supratik Bose; Supriya Verma; Waghmare Rahul Gautam; Yogesh Prasad K. R.; Bijoy Raha; Bhavesh Mendhekar; Sathyanaryana Raju K.; Srinivasa Rao Kondapi V.; Sumit Kumar; Mukund Kumar Thakur; Vinti Bhatia; Nidhi Sharma; Govinda Rao Yenni; Neeraj Kumar Satya; Venkata Raghavendra; Vivechana M. S.; Evangelin Leeja Justin; Praloy Karmakar; Naga Manjusha J.; Motamarri Srikanth; Abhishek Singh; Prabakaran B.; Honey Gupta; Priyanka Mishra; Chinmay Kumar Rajhans; Kalpana K.; Veeramuthuvel P

arXiv · 2608.19371

Shaping SHAPE - A spectro-polarimeter onboard Chandrayaan-3 to observe Earth as an Exoplanet

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Abstract

Spectro-polarimetry of HAbitable Planet Earth (SHAPE) is an experimental instrument onboard the Propulsion Module (Orbiter) of the Chandrayaan-3 mission, designed to perform disc-integrated spectro-polarimetric observations of Earth from lunar and highly elliptical Earth orbits. SHAPE is a compact, lightweight spectro-polarimeter comprising three subsystems: the Electro-Optical Detector System (EODS)-Optics, EODS-Electronics, and Radio Frequency Source (RFS). An Acousto-Optic Tunable Filter (AOTF), driven by an in-house-developed 80$-$135 MHz RF source, provides spectral filtering in the near-infrared (NIR) wavelength range of 1.0$-$1.7 $\mu$m and produces two narrow-band beams with mutually perpendicular linear polarization states. The instrument optics, with a field of view of approximately 2.6{\deg}, focus the two beams onto InGaAs detectors. A spectral resolution of 2$-$4 nm is achieved using in-house-designed low-noise front-end electronics. The instrument also incorporates processing and power electronics for signal processing, detector biasing, and subsystem control. We present the overall instrument design, results from pre-launch ground-based testing, and in-orbit operational performance. The current configuration enables SHAPE to measure disc-integrated signatures of Earth over a range of phase angles, providing a test bed for characterizing Earth-like exoplanets and benchmarking future exoplanet observations.

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Anuj Nandi, Swapnil Singh, Bhavesh Jaiswal, Anand Jain, Smrati Verma, Reenu Palawat, Ravishankar B. T., Brajpal Singh, Priyanka Das, Supratik Bose, Supriya Verma, Waghmare Rahul Gautam, Yogesh Prasad K. R., Bijoy Raha, Bhavesh Mendhekar, Sathyanaryana Raju K., Srinivasa Rao Kondapi V., Sumit Kumar, Mukund Kumar Thakur, Vinti Bhatia, Nidhi Sharma, Govinda Rao Yenni, Neeraj Kumar Satya, Venkata Raghavendra, Vivechana M. S., Evangelin Leeja Justin, Praloy Karmakar, Naga Manjusha J., Motamarri Srikanth, Abhishek Singh, Prabakaran B., Honey Gupta, Priyanka Mishra, Chinmay Kumar Rajhans, Kalpana K., Veeramuthuvel P. 2026-08-19. Shaping SHAPE - A spectro-polarimeter onboard Chandrayaan-3 to observe Earth as an Exoplanet. https://arxiv.org/abs/2608.19371

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