Chandrayaan-2

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The Chandrayaan-2 mission was successfully launched on 22nd July 2019 at 14:43 hrs by GSLV MkIII-M1 from Satish Dhawan Space Centre (SDSC), Sriharikota. After a series of Earth bound manoeuvres, the spacecraft entered into Lunar Transfer Trajectory (LTT) on August 14th. Lunar Orbit Insertion (LOI) manoeuvre was performed on August 20th, thereby Chandrayaan-2 was successfully inserted into the elliptical orbit around the Moon. This was followed by a series of Lunar bound orbit maneuvers for reducing the orbit to circular polar orbit around the Moon.

Chandrayaan-2 Orbiter is currently in a 100 km x 100 km orbit around the Moon On September 2nd, Vikram lander separated from the Orbiter and de-orbiting maneuver was performed to reduce the orbit to 35 km x 101 km. Vikram landing was attempted on 7th September and it followed the planned descent trajectory from its orbit of 35 km to around 2 km above the surface. Communication with lander and ground station was lost. All the systems and sensors of the Lander functioned excellently until this point and proved many new technologies such as variable thrust propulsion technology used in the Lander. However, the Orbiter is healthy and all the payloads are operational.

Chandrayaan-2 carried eight experiment payload on board for studying surface geology, composition and exospheric measurements of Moon. These measurements will continue to enhance upon the understanding built from previous lunar missions.

Handbook of Chandrayaan 2 Payloads Data & Science. PDF 12 MB

Chandrayaan-2 Large Area Soft X-ray Spectrometer (CLASS)

CLASS measures the Moon’s X-ray Fluorescence (XRF) spectra to examine the presence of major elements such as Magnesium, Aluminium, Silicon, Calcium, Titanium, Iron, and Sodium. The XRF technique will detect these elements by measuring the characteristic X-rays they emit when excited by solar X-ray emission. CLASS is a non-imaging spectrometer with gold coated copper collimators defining the field of view of each detector as 7 deg X 7 deg Full Width at Half Maximum (FWHM). This translates to a 12.5 km X 12.5 km footprint at the 100 km altitude of the spacecraft. Aluminium door to protect the sensors from the high energy particle flux in the radiation belts en-route to the Moon also houses radioactive isotopes with a Titanium foil for calibration onboard.
Solar X-ray Monitor (XSM)

XSM detects X-rays emitted by the Sun and its corona, measures its intensity, and supports the CLASS payload. It provides the solar X-ray spectrum in the energy range of 1-15 keV incident on the lunar surface. XSM provides high energy resolution and high-cadence measurements (full spectrum every second) as input for analysis of data from CLASS. The XSM is operating in the lunar orbit from 12th September 2019. The XSM provides disk integrated solar spectra in the energy range of 1 – 15 keV with a spectral resolution of better than 180 eV at 5.9 keV, which is the best available among similar instruments that carried out such measurements till now. The XSM also offers the highest time cadence for such instruments: full spectrum every second and light curves in three energy bands every 100 ms. The unique design features of the XSM allows observations over a wide dynamic range of X-ray fluxes from the quiet Sun to X-class flares. Presently, the XSM is the only instrument operational providing soft X-ray spectral measurements of the Sun over a broad energy range.
CHandra’s Atmospheric Compositional Explorer 2 (CHACE 2)

CHACE 2 will expand upon the CHACE experiment on Chandrayaan-1. It is a Quadrupole Mass Spectrometer (QMA) capable of studies of the lunar neutral exosphere in the mass range of 1 to 300 amu with the mass resolution of ~0.5 amu. CHACE 2’s primary objective is to carry out an in-situ study of the composition and distribution of the lunar neutral exosphere and its variability. The CHACE-2 instrument consists of the sensor probe (cylindrical in shape) and the electronics. The sensor probe consists of a built-in electron impact ionizer along with a Bayard-Alpert collector to measure the total pressure; a set of four quadrupole rods and a detector assembly. The detector assembly consists of a Faraday Cup (FC) and a Channel Electron Multiplier (CEM).
Dual Frequency Synthetic Aperture Radar (DFSAR)
The dual frequency (L and S) SAR will provide enhanced capabilities compared to Chandrayaan-1’s S-band mini SAR in areas such as:
- L-band for greater depth of penetration (About 5m — twice that of S-band)
- Circular and full polarimetry — with a range of resolution options (2-75 m) and incident angles (9°-35°) — for understanding scattering properties of permanently shadowed regions
- The main scientific objectives of this payload are:
  - Quantitative estimation of water-ice in the polar regions
  - High-resolution lunar mapping in the polar regions
  - Estimation of regolith thickness and its distribution
The Dual Frequency Synthetic Aperture Radar (DFSAR) on board Chandrayaan-2 Orbiter is a microwave imaging instrument in L- and S-band frequencies and the first fully-polarimetric SAR to study the Moon. L-band frequency enables double the surface penetration capability with respect to what is obtained using S-band. The instrument is basically two SAR systems (for L & S bands) sharing a common antenna aperture with wide bandwidth.

Various instrument features like high-efficiency transmitter, low-noise high-gain receiver, onboard range-compression (first for any ISRO SAR mission) have enabled a highly sensitive instrument with polarimetric capability. Its best resolution (2m in slant-range) is one order better than the previously flown SARs to the Moon. The backscattered signals from the targets are coherently measured by the DFSAR in different polarizations to enable studies of physical and dielectric properties of the lunar surface/ shallow-subsurface. With these polarimetric measurements, the instrument primarily aims to unambiguously address the presence of water-ice in permanently shadowed regions (PSRs), characterizing the physical and dielectric properties of lunar surface, volcanic features, impact craters and their associated ejecta.
Imaging Infra-Red Spectrometer (IIRS)
Imaging Infra-Red Spectrometer (IIRS) is a hyper-spectral optical imaging instrument. This instrument maps geomorphology and mineralogy of lunar surface. The mission is intended to cover the Moon surface. The prime objectives of IIRS are:
- Global mineralogical and volatile mapping of the Moon in the spectral range of ~0.8-5.0 μm for the first time, at the high resolution of ~20 nm
- Complete characterization of water/hydroxyl feature near 3.0 μm for the first time at high spatial (~80 m) and spectral (~20 nm) resolutions
IIRS measures the reflected solar radiation along with the emissions from the lunar surface at an altitude of 100 km on a polar circular orbit at a spatial resolution of ~80 m and spectral resolution of ~20-25 nm across the spectral range of 0.8-5.0 μm in ~250 spectrally contiguous bands. The diagnostic absorption features of major and minor lunar minerals are found to occur in the spectral domain of ~0.75-2.5 μm that fall well within the spectral range of IIRS thereby making their detection possible by the spectrometer. On the other hand, the spectral range of ~2.5-3.3 μm is being dedicatedly used to detect the presence of lunar OH/H2O features having fundamental absorptions around 3.0 μm.
Terrain Mapping Camera (TMC 2)

TMC 2 is a miniature version of the Terrain Mapping Camera on Chandrayaan-1 mission. Its primary objective is to map the lunar surface in the panchromatic spectral band (0.5-0.8 microns) with a high spatial resolution of 5 m and a swath of 20 km from 100 km lunar polar orbit. The data collected by TMC 2 will give us clues about the Moon’s evolution and help us prepare 3D maps of the lunar surface. This camera enables in preparing global high resolution image mosaic and Digital Elevation Model (DEM).
Orbiter High Resolution Camera (OHRC)

OHRC provides high-resolution images of the landing site which ensure the Lander’s safe touchdown by detecting any craters or boulders, prior to separation. The images it captures, taken from two different look angles, serve dual purposes. First, these images are used to generate DEMs (Digital Elevation Models) of the landing site. Second, they are used for scientific research after its initial role in the landing phase. OHRC’s images can capture the same area on the lunar surface from two different orbits. The coverage area in this case is of 12 km x 3 km with ground resolution of 0.32 m. OHRC is an optical camera system based on Time Delay Integration (TDI) imaging sensors with 12000 detectors. It has 4 TDI settings and 7 different integration times.
Dual Frequency Radio Science (DFRS) Experiment

To study the temporal evolution of electron density in the Lunar ionosphere. Two coherent signals at X (8496 MHz), and S (2240 MHz) band are transmitted simultaneously from satellite, and received at ground-based receivers. DFRS is a radio science experiment used to analyze the planetary/lunar atmosphere ionosphere. It uses two highly correlated radio frequencies in X- and S-bands. Since there is no need for any specific data to be sent for the DFRS experiment, the signals allocated for tele-command and ranging can also be used to carry out the said experiment.

Major results from Chandrayaan-2

Science results from Chandrayaan-2 payloads were documented and released to public on the occasion of two-year completion of the mission. In addition to this, few science results from payloads are provided below.

CHandra’s Atmospheric Composition Explorer-2 (CHACE-2) onboard Chandrayaan-2 orbiter is a quadrupole based neutral mass spectrometer aimed at observing the tenuous Lunar exospheric composition from spacecraft altitude. Argon-40 (Ar-40) is a noble gas in the lunar exosphere, understood to be originated from the radiogenic potassimum-40 and it had been detected by several previous missions, mostly covering the equatorial and low-latitude regions of Moon. The CHACE-2 not only made observations over the low-latitude regions, but also covered the other latitude regions as well, in-situ from a polar orbit, for the first time. Figure 2 shows the map of the surface densities of Ar-40 estimated from CHACE-2 observations. The Ar-40 distribution is depicted both in terms of Solar longitudes (Fig. 1a) and Selenographic longitudes (Fig. 1b), covering both low- and mid-latitude regions. The observations show that the diurnal trend agrees with LACE/Apollo observations from the low latitude region on the lunar surface. In addition, CHACE-2 observations show for the first time that these features extend to the mid-latitude regions. Further, the number density of Ar-40 is seen to exhibit significant spatial heterogeneity. CHACE-2 observations showed Ar-40 enhancements over certain longitude sectors including KREEP (Potassium, Rare Earth Elements and Phosphorous rich region on the Moon) region and the South Pole Aitken (SPA) terrain. These observations call for a deeper understanding of the surface-exosphere interactions and source distribution.

Lunar lobate scarps are relatively small-scale tectonic landforms that are interpreted to be the surface expression of low angle thrust faults. Lobate scarps are believed to be young lunar landforms and are observed both in the mare and highland regions. A plausible lobate scarp (Length is 1416 m and average relief across this scarp is 24 m) was mapped by the Terrain Mapping Camera (TMC-2). This NW-SE oriented scarp is located between Dorsa Geike and Dorsa Mawson. It is estimated that this lobate scarp could have been formed in the Copernican period. Image acquisition at low Sun elevation angle provides opportunity to map the features having smaller dimensions such as lobate scarps.

Ortho image of TMC-2 of lobate scarp region. The plausible Lobate scarp (yellow colored line), craters (red colored circles) used for surface age estimation and Hanging Wall (HW), Foot Wall (FW) are indicated by blue polygons. Profiles P1-P4 are shown in the red colored lines.
Topographic cross-sections along the profiles P1-P4.

XSM is carrying out broadband spectroscopy of the Sun from lunar orbit. Currently XSM is the only X-ray spectrometer in the world which regularly measures the soft X-ray spectrum of the Sun with the highest time cadence. This has yielded very interesting observations of the microflares occurring outside active region as well as elemental abundances in the quiet Sun corona. XSM has also observed number of B-class flares and their analysis has yielded unprecedented observations of variation of the elemental abundances during such flares

XSM observed nine B-class flares ranging from B1.3 to B4.5 during the minimum phase of Solar Cycle 24. The evolution of temperature, emission measure, and absolute elemental abundances of four elements Mg, Al, Si, and S are examined. These are the first measurements of absolute abundances during such small flares and this study offers a unique insight into the evolution of absolute abundances as the flares evolve. The results demonstrate that the abundances of these four elements decrease towards their photospheric values during the peak phase of the flares. During the decay phase, the abundances are observed to quickly return to their pre-flare coronal values as shown in below figure.

The six panels show the results of the time resolved X-ray spectroscopy for a representative flare. Panels a-b show the variation of temperature and emission measure, respectively, during flare activity, whereas panels c-f show the variation of elemental abundances of Mg (c), Al (d), Si (e), S (f) in logarithmic scale.