Chandrayaan-1: Mission Definition and Goal

Chardrayaan-1 is the first Indian Mission to the Moon devoted to high-resolution remote sensing of the lunar surface features in visible, near infrared, X-ray and low energy gamma ray regions. This will be accomplished using several payloads already selected for the mission. In addition a total of about 10 kg payload weight and 10 W power are earmarked for proposals, which are now solicited. The mission is proposed to be a lunar polar orbiter at an altitude of about 100 km and is planned to be launched by 2007-2008 using indigenous spacecraft and launch vehicle of ISRO. The mission is expected to have an operational life of about 2 years.

Mission Objectives

Carry out high resolution mapping of topographic features in 3D, distribution of various minerals and elemental chemical species including radioactive nuclides covering the entire lunar surface using a set of remote sensing payloads. The new set of data would help in unravelling mysteries about the origin and evolution of solar system in general and that of the moon in particular.

Realize the mission goal of harnessing the science payloads, lunar craft and the launch vehicle with suitable ground support system including DSN station, integration and testing, launching and achieving lunar orbit of ~100 km, in-orbit operation of experiments, communication/telecommand, telemetry data reception, quick look data and archival for scientific utilization by identified group of scientists.

Specific areas of study

High resolution mineralogical and chemical imaging of permanently shadowed north and south polar regions

Search for surface or sub-surface water-ice on the moon, specially at lunar pole

Identification of chemical end members of lunar high land rocks

Chemical stratigraphy of lunar crust by remote sensing of central upland of large lunar craters, South Pole Aitken Region (SPAR) etc., where interior material may be expected

To map the height variation of the lunar surface features along the satellite track

Observation of X-ray spectrum greater than 10 keV and stereographic coverage of most of the moon's surface with 5 m resolution, to provide new insights in understanding the moon's origin and evolution

Proposed Scientific Payloads

The scientific payloads selected so far are:

Terrain Mapping stereo Camera (TMC) in the panchromatic band having 5m spatial resolution and 40 km swath, to prepare a high resolution atlas of moon

A Hyper Spectral Imager (HySI) operating in 400-900nm band with a spectral resolution of 15nm and spatial resolution of 80 m with a swath of 40 km, for mineralogical mapping

A Lunar Laser Ranging Instrument (LLRI), for determining accurate altitude of the spacecraft above the lunar surface for topographical mapping

A collimated Low Energy (0.5-10 keV) X-ray spectrometer (LEX) for measuring the fluorescent X-rays emanating from the lunar surface having ground spatial resolution of about 10 km, for elemental mapping of Si, Al, Mg,Ca, Fe,Ti

A Solar X-ray Monitor (SXM) in 2-10 keV energy range, for solar X-ray flux monitoring

A High Energy (10-200keV) X-ray/g-ray spectrometer (HEX) having a ground spatial resolution of approximately 20 km, for measuring 210Pb, 222Rn degassing, U, Th etc.

Brief technical specification of the payloads:

Terrain Mapping Camera (TMC)

The purpose of this instrument is to generate high-resolution 3-D cartographic map of the moon using stereoscopic cameras. The broad specifications of TMC are given below:

Ground resolution 5 m
Swath 40 km
Spectral Band Panchromatic

Hyper Spectral Imager (HySI)

Uses a wedge filter and an area array detector to obtain the full spectrum information of the target by acquiring image data for mineralogical mapping. The broad specification of HySI are given below:

Ground resolution 80 m
Swath 40 km
Spectral range 400-900µm
No of spectral bands 32
Spectral resolution 15 nm

Lunar Laser Ranging Instrument (LLRI)

The LLRI is used for providing ranging data for determining the accurate altitude of the spacecraft above the lunar surface. The broad specification of LLRI are given below:

Pulse repetition rate 1 Hz
Telescope 15 cm dia, reflective
Pulse-width 10 ns
Vertical resolution 10 m

X-ray Fluorescence Spectrometers

This payload consists of three parts: (a) Low Energy X-ray detector (LEX) to map the abundance of light elements like Mg, Al, Si, Ca, Ti and Fe, (b) High Energy X-ray/ gama-ray detector (HEX) to map the distribution of high atomic number elements over the lunar surface such as 210Pb, 222Rn, U, Th and (c) Solar X-ray Monitor (SXM) to continuously measure the flux of solar X-rays.

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Information Courtesy: Indian Space Research Organisation (ISRO)