Chandrayaan-1: The First Indian Mission to the Moon
Authors: Thyagarajan K. , Annadurai M. 
Published: December 2023

There are numerous reasons for continuing the study of the Moon. Although the Moon is better characterized and more studied than any other planetary body in the solar system, hypothesis of it’s origin is still controversial. Earlier missions were limited in characterizing the moon in the sense that the data were only from samples on representative locations of moon or the observations are not detailed enough to make in depth study. With the advancement in technology and miniaturization, it is now possible to observe moon as close as possible with better resolutions both in spatial and spectral that would provide better insight in the origin and early evolution of the moon based on chemical and mineralogical criteria. Chandrayaan-1 is one such mission.

The primary objectives of the Chandrayaan-1 mission are simultaneous chemical, mineralogical and topographic mapping of the lunar surface. These data should enable us to understand compositional variation of major elements. The major element distribution will be determined using an X-ray fluorescence spectrometer (LEX), sensitive in the energy range of 1-10 keV where Mg, Al, Si, Ca and Fe give their Kα lines. A solar X-ray monitor (SXM) to measure the energy spectrum of solar X-rays, which are responsible for the fluorescent X-rays, is included. Radioactive elements like Th will be measured by its 238.6 KeV line using a low energy gamma ray spectrometer (HEX) operating in 20-250 keV regions. The mineral composition will be determined by a Hyperspectral imaging spectrometer (HySI) sensitive in 400-930 nm range. The wavelength range is further extended to 3000 nm where some spectral features of the abundant lunar minerals and water occur, by using a near infra-red spectrometer (SIR-2) and Moon Mineralogy Mapper (M3). A terrain mapping camera (TMC) in the panchromatic band will provide three dimensional map of the lunar surface with a spatial resolution of about 5 m. Aided by a laser altimeter (LLRI) to determine the altitude of the lunar craft, to correct for spatial coverage by various instruments, TMC should enable us to prepare an elevation map with an accuracy of about 10m.

Five instruments under international cooperation have been accommodated that will complement and supplement the scientific objectives of Chandrayaan-1. These are: a Miniature Imaging Radar Instrument (mini-SAR), Sub keV Atom Reflecting Analyser (SARA), The Moon Mineralogy Mapper (M 3), Infra Red Spectrometer ( SIR-2) and a Radiation Dose Monitor(RADOM). Apart from these scientific payloads, a Moon Impact Probe (MIP) which will be released to impact on the Moon during the Mission is also accommodated as a technology fore runner for future Lunar Landing mission.

Chandrayaan-1 will be launched from SHAR using PSLV-XL a variant of flight proven PSLV. The mission will have two years nominal mission life in 100km lunar polar orbit. ISRO is setting up an Indian Deep Space Network (IDSN) near Bangalore consisting two ground terminals of 18m and 32m diameter. Indian Space Science Data Centre will be suitably located to act as science data repository.