Chandrayaan-1

In order to reach its objective, the mission defined these goals:

• High-resolution mineralogical and chemical imaging of the permanently shadowed north- and south-polar regions
• Searching for surface or sub-surface lunar water-ice, especially at the lunar poles
• Identification of chemicals in lunar highland rocks
• Chemical stratigraphy of the lunar crust by remote sensing of the central uplands of large lunar craters, and of the South Pole Aitken Region (SPAR), an expected site of interior material
• Mapping the height variation of features of the lunar surface
• Observation of X-ray spectrum greater than 10 keV and stereographic coverage of most of the Moon's surface with 5 m (16 ft) resolution
• Providing new insights in understanding the Moon's origin and evolution

• TMC or the Terrain Mapping Camera is a CMOS camera with 5 m (16 ft) resolution and a 40 km (25 mi) swath in the panchromatic band and was used to produce a high-resolution map of the Moon.[29] The aim of this instrument was to completely map the topography of the Moon. The camera works in the visible region of the electromagnetic spectrum and captures black and white stereo images. When used in conjunction with data from Lunar Laser Ranging Instrument (LLRI), it can help in better understanding of the lunar gravitational field as well. TMC was built by the ISRO's Space Applications Centre (SAC) at Ahmedabad.[30] The TMC was tested on 29 October 2008 through a set of commands issued from ISTRAC.[31]
• HySI or Hyper Spectral Imager is a CMOS camera, performed mineralogical mapping in the 400–900 nm band with a spectral resolution of 15 nm and a spatial resolution of 80 m (260 ft).
• LLRI or Lunar Laser Ranging Instrument determines the height of the surface topography by sending pulses of infrared laser light towards the lunar surface and detecting the reflected portion of that light. It operated continuously and collected 10 measurements per second on both the day and night sides of the Moon. LLRI was developed by Laboratory for Electro Optics Systems of ISRO, Bangalore.[32] It was tested on 16 November 2008.[32][33]
• HEX is a High Energy aj/gamma x-ray spectrometer for 30–200 keV measurements with ground resolution of 40 km (25 mi), the HEX measured U, Th, ²¹⁰Pb, ²²²Rn degassing, and other radioactive elements.
• MIP or the Moon Impact Probe developed by the ISRO, is an impact probe which consisted of a C-band Radar altimeter for measurement of altitude of the probe, a video imaging system for acquiring images of the lunar surface and a mass spectrometer for measuring the constituents of the lunar atmosphere.[34] It was ejected at 14:30 UTC on 14 November 2008. As planned, the Moon Impact Probe impacted the lunar south pole at 15:01 UTC on 14 November 2008. It carried with it a picture of the Indian flag. India is now the fourth nation to place a flag on the Moon after the Soviet Union, United States and Japan.

Moon Mineralogy Mapper (left)

SIR-2 Logo

• C1XS or X-ray fluorescence spectrometer covering 1–10 keV, mapped the abundance of Mg, Al, Si, Ca, Ti, and Fe at the surface with a ground resolution of 25 km (16 mi), and monitored solar flux.[35] This payload results from collaboration between Rutherford Appleton laboratory, U.K, ESA and ISRO. It was activated on 23 November 2008.[36]
• SARA, the Sub-keV Atom Reflecting Analyser from the ESA mapped mineral composition using low energy neutral atoms emitted from the surface.[37][38]
• M³, the Moon Mineralogy Mapper from Brown University and JPL (funded by NASA) is an imaging spectrometer designed to map the surface mineral composition. It was activated on 17 December 2008.[39]
• SIR-2, a near infrared spectrometer from ESA, built at the Max Planck Institute for Solar System Research, Polish Academy of Science and University of Bergen, also mapped the mineral composition using an infrared grating spectrometer. The instrument is similar to that of the Smart-1 SIR.[40][41] It was activated on 19 November 2008 and scientific observations were started on 20 November 2008.[36]
• Mini-SAR, designed, built and tested for NASA by a large team that includes the Naval Air Warfare Center, Johns Hopkins University Applied Physics Laboratory, Sandia National Laboratories, Raytheon and Northrop Grumman, with outer support from ISRO. Mini-SAR is the active Synthetic Aperture Radar system to search for lunar polar ice, water-ice. The instrument transmitted right polarised radiation with a frequency of 2.5 GHz and monitored scattered left and right polarised radiation. The Fresnel reflectivity and the circular polarisation ratio (CPR) are the key parameters deduced from these measurements. Ice shows the Coherent Backscatter Opposition Effect which results in an enhancement of reflections and CPR, so that water content of the Moon's polar regions can be estimated.[42][43][44]
• RADOM-7, Radiation Dose Monitor Experiment from the Bulgarian Academy of Sciences mapped the radiation environment around the Moon.[45] It was tested on 16 November 2008.[32][33]

First orbit burn

The first orbit-raising manoeuvre of Chandrayaan-1 spacecraft was performed at 03:30 UTC on 23 October 2008 when the spacecraft's 440 Newton liquid engine was fired for about 18 minutes by commanding the spacecraft from Spacecraft Control Centre (SCC) at ISRO Telemetry, Tracking and Command Network (ISTRAC) at Peenya, Bangalore. With this Chandrayaan-1's apogee was raised to 37,900 km (23,500 mi), and its perigee to 305 km (190 mi). In this orbit, Chandrayaan-1 spacecraft took about 11 hours to go around the Earth once.[50]

Second orbit burn

The second orbit-raising manoeuvre of Chandrayaan-1 spacecraft was carried out on 25 October 2008 at 00:18 UTC when the spacecraft's engine was fired for about 16 minutes, raising its apogee to 74,715 km (46,426 mi), and its perigee to 336 km (209 mi), thus completing 20 percent of its journey. In this orbit, Chandrayaan-1 spacecraft took about twenty-five and a half hours to go round the Earth once. This is the first time an Indian spacecraft has gone beyond the 36,000 km (22,000 mi) high geostationary orbit and reached an altitude more than twice that height.[51]

Third orbit burn

The third orbit raising manoeuvre was initiated on 26 October 2008 at 01:38 UTC when the spacecraft's engine was fired for about nine and a half minutes. With this its apogee was raised to 164,600 km (102,300 mi), and the perigee to 348 km (216 mi). In this orbit, Chandrayaan-1 took about 73 hours to go around the Earth once.[52]

Fourth orbit burn

The fourth orbit-raising manoeuvre took place on 29 October 2008 at 02:08 UTC when the spacecraft's engine was fired for about three minutes, raising its apogee to 267,000 km (166,000 mi) and the perigee to 465 km (289 mi). This extended its orbit to a distance more than half the way to the Moon. In this orbit, the spacecraft took about six days to go around the Earth once.[53]

Final orbit burn

The fifth and final orbit raising manoeuvre was carried out on 3 November 2008 at 23:26 UTC when the spacecraft's engine was fired for about two and a half minutes resulting in Chandrayaan-1 entering the Lunar Transfer Trajectory with an apogee of about 380,000 km (240,000 mi).[54]

Chandrayaan-1 completed the lunar orbit insertion operation on 8 November 2008 at 11:21 UTC. This manoeuvre involved firing of the liquid engine for 817 seconds (about thirteen and half minutes) when the spacecraft passed within 500 km (310 mi) from the Moon. The satellite was placed in an elliptical orbit that passed over the polar regions of the Moon, with 7,502 km (4,662 mi) aposelene and 504 km (313 mi) periselene. The orbital period was estimated to be around 11 hours. With the successful completion of this operation, India became the fifth nation to put a vehicle in lunar orbit.[10]

First orbit reduction

First Lunar Orbit Reduction Manoeuvre of Chandrayaan-1 was carried out on 9 November 2008 at 14:33 UTC. During this, the engine of the spacecraft was fired for about 57 seconds. This reduced the periselene to 200 km (124 mi) while aposelene remained unchanged at 7,502 km. In this elliptical orbit, Chandrayaan-1 took about ten and a half hours to circle the Moon once.[55]

Second orbit reduction

This manoeuvre was carried out on 10 November 2008 at 16:28 UTC, resulting in steep decrease in Chandrayaan-1's aposelene to 255 km (158 mi) and its periselene to 187 km (116 mi), During this manoeuvre, the engine was fired for about 866 seconds (about fourteen and a half minutes). Chandrayaan-1 took two hours and 16 minutes to go around the Moon once in this orbit.[56]

Third orbit reduction

Third Lunar Orbit Reduction was carried out by firing the onboard engine for 31 seconds on 11 November 2008 at 13:00 UTC. This reduced the periselene to 101 km (63 mi), while the aposelene remained constant at 255 km. In this orbit Chandrayaan-1 took two hours and 9 minutes to go around the Moon once.[57]

Final orbit

Chandrayaan-1 spacecraft was placed into a mission-specific lunar polar orbit of 100 km (62 mi) above the lunar surface on 12 November 2008.[58][59] In the final orbit reduction manoeuvre, Chandrayaan-1's aposelene and periselene were both reduced to 100 km.[59] In this orbit, Chandrayaan-1 takes about two hours to go around the Moon once. Two of the 11 payloads—the Terrain Mapping Camera (TMC) and the Radiation Dose Monitor (RADOM)—were switched on. The TMC acquired images of both the Earth and the Moon.[59]

The Moon Impact Probe (MIP) crash-landed on the lunar surface on 14 November 2008, 15:01 UTC near the crater Shackleton at the south pole.[58] The MIP was one of eleven scientific instruments (payloads) on board Chandrayaan-1.[60]

The MIP separated from Chandrayaan at 100 km from lunar surface and began its nosedive at 14:36 UTC. going into free fall for thirty minutes.[58] As it fell, it kept sending information back to the mother satellite which, in turn, beamed the information back to Earth. The altimeter then also began recording measurements to prepare for a rover to land on the lunar surface during a second Moon mission.[61]

Following the deployment of the MIP, the other scientific instruments were turned on, starting the next phase of the mission.[60]

After scientific analyses of the received data from the MIP, the Indian Space Research Organisation confirmed the presence of water in the lunar soil and published the finding in a press conference addressed by its then Chairman G. Madhavan Nair.

ISRO had reported on 25 November 2008 that Chandrayaan-1's temperature had risen above normal to 50 °C (122 °F),[62] Scientists said that it was caused by higher than expected temperatures in lunar orbit.[62] The temperature was brought down by about 10 °C (18 °F) by rotating the spacecraft about 20 degrees and switching off some of the instruments.[62] Subsequently, ISRO reported on 27 November 2008 that the spacecraft was operating under normal temperature conditions.[63] In subsequent reports ISRO says, since the spacecraft was still recording higher than normal temperatures, it would be running only one instrument at a time until January 2009 when lunar orbital temperature conditions are said to stabilize.[64] It was initially thought that the spacecraft was experiencing high temperature because of radiation from the Sun and infrared radiation reflected by the Moon.[65] However the rise in spacecraft temperature was later attributed to a batch of DC-DC converters with poor thermal regulation.[66][67]

The mineral content on the lunar surface was mapped with the Moon Mineralogy Mapper (M³), a NASA instrument on board the orbiter. The presence of iron was reiterated and changes in rock and mineral composition have been identified. The Oriental Basin region of the Moon was mapped, and it indicates abundance of iron-bearing minerals such as pyroxene.[68]

In 2018 it was announced that M³ infrared data had been re-analyzed to confirm the existence of water across wide expanses of the Moon's polar regions.[69]

ISRO announced in January 2009 the completion of the mapping of the Apollo Moon missions landing sites by the orbiter, using multiple payloads. Six of the sites have been mapped including landing sites of Apollo 15 and Apollo 17.[70]

The craft completed 3,000 orbits acquiring 70,000 images of the lunar surface,[71][72][73] which is quite a record compared to the lunar flights of other nations. ISRO officials estimated that if more than 40,000 images have been transmitted by Chandrayaan's cameras in 75 days, it worked out to nearly 535 images being sent daily. They were first transmitted to Indian Deep Space Network at Byalalu near Bangalore, from where they were flashed to ISRO's Telemetry Tracking And Command Network (ISTRAC) at Bangalore.

Some of these images have a resolution of down to 5 metres (16 ft), providing a sharp and clear picture of the Moon's surface, while many images sent by some of the other missions had only a 100-metre resolution.[74] For comparison, the Lunar Reconnaissance Orbiter Camera has a 0.5 meter resolution.[75]

On 26 November, the indigenous Terrain Mapping Camera, which was first activated on 29 October 2008, acquired images of peaks and craters. This came as a surprise to ISRO officials because the Moon consists mostly of craters.[76]

The X-ray signatures of aluminium, magnesium and silicon were picked up by the C1XS X-ray camera. The signals were picked up during a solar flare that caused an X-ray fluorescence phenomenon. The flare that caused the fluorescence was within the lowest C1XS sensitivity range.[77][78][79]

On 25 March 2009 Chandrayaan beamed back its first images of the Earth in its entirety. These images were taken with the TMC. Previous imaging was done on only one part of the Earth. The new images show Asia, parts of Africa and Australia with India being in the center.[80][81]

After the completion of all the major mission objectives, the orbit of Chandrayaan-1 spacecraft, which had been at a height of 100 km (62 mi) from the lunar surface since November 2008, was raised to 200 km (124 mi). The orbit raising manoeuvres were carried out between 03:30 and 04:30 UTC on 19 May 2009. The spacecraft in this higher altitude enabled further studies on orbit perturbations, gravitational field variation of the Moon and also enabled imaging lunar surface with a wider swath.[82] It was later revealed that the true reason for the orbit change was that it was an attempt to keep the temperature of the probe down.[83] It was "...assumed that the temperature [of the spacecraft subsystems] at 100 km above the Moon's surface would be around 75 degrees Celsius. However, it was more than 75 degrees and problems started to surface. We had to raise the orbit to 200 km."[84]

The star tracker, a device used for pointing attitude determination (orientation), failed in orbit after nine months of operation. Afterward, the orientation of Chandrayaan was determined using a back-up procedure using a two-axis Sun sensor and taking a bearing from an Earth station. This was used to update three axis gyroscopes which enabled spacecraft operations.[71][72][73] The second failure, detected on 16 May, was attributed to excessive radiation from the Sun.[85]

On 21 August 2009 Chandrayaan-1 along with the Lunar Reconnaissance Orbiter attempted to perform a bistatic radar experiment using their Mini-SAR radars to detect the presence of water ice on the lunar surface.[86][87] The attempt was a failure; it turned out the Chandrayaan-1 radar was not pointed at the Moon during the experiment.[88]

The Mini-SAR has imaged many of the permanently shadowed regions that exist at both poles of the Moon.[89] In March 2010, it was reported that the Mini-SAR on board the Chandrayaan-1 had discovered more than 40 permanently darkened craters near the Moon's north pole which are hypothesized to contain an estimated 600 million metric tonnes of water-ice.[89][90] The radar's high CPR is not uniquely diagnostic of either roughness or ice; the science team must take into account the environment of the occurrences of high CPR signal to interpret its cause. The ice must be relatively pure and at least a couple of meters thick to give this signature.[89] The estimated amount of water ice potentially present is comparable to the quantity estimated from the previous mission of Lunar Prospector's neutron data.[89]

Although the results are consistent with recent findings of other NASA instruments onboard Chandrayaan-1 (the Moon Mineralogy Mapper (MP3) discovered water molecules in the Moon's polar regions, while water vapour was detected by NASA's Lunar Crater Observation and Sensing Satellite, or LCROSS[89]) this observation is not consistent with the presence of thick deposits of nearly pure water ice within a few meters of the lunar surface, but it does not rule out the presence of small (<∼10 cm), discrete pieces of ice mixed in with the regolith.[91]

Direct evidence of lunar water through Chandrayaan-1 Chandra's Altitudinal Composition (CHACE) output profile

These images show a very young lunar crater on the side of the Moon that faces away from Earth, as viewed by Chandrayaan-1's NASA Moon Mineralogy Mapper equipment

On 18 November 2008, the Moon Impact Probe was released from Chandrayaan-1 at a height of 100 km (62 mi). During its 25-minute descent, Chandra's Altitudinal Composition Explorer (CHACE) recorded evidence of water in 650 mass spectra readings gathered during this time.[103] On 24 September 2009 Science journal reported that the Nasa Instrument Moon Mineralogy Mapper (M³) on Chandrayaan-1 had detected water ice on the Moon.[104] But, on 25 September 2009, ISRO announced that the MIP, another instrument on board Chandrayaan-1, had discovered water on the Moon just before impact and had discovered it 3 months before NASA's M³.[105] The announcement of this discovery was not made until NASA confirmed it.[106][107]

M³ detected absorption features near 2.8–3.0 µm on the surface of the Moon. For silicate bodies, such features are typically attributed to hydroxyl- and/or water-bearing materials. On the Moon, the feature is seen as a widely distributed absorption that appears strongest at cooler high latitudes and at several fresh feldspathic craters. The general lack of correlation of this feature in sunlit M³ data with neutron spectrometer H abundance data suggests that the formation and retention of OH and H₂O is an ongoing surficial process. OH/H₂O production processes may feed polar cold traps and make the lunar regolith a candidate source of volatiles for human exploration.

The Moon Mineralogy Mapper (M³), an imaging spectrometer, was one of the 11 instruments on board Chandrayaan-I that came to a premature end on 28 August 2009.[108] M³ was aimed at providing the first mineral map of the entire lunar surface. M³ data were reanalyzed years later and revealed "the most definitive proof to date" of the presence of water in shaded regions of craters near the Moon's north and south poles.[69]

Lunar scientists had discussed the possibility of water repositories for decades. They are now increasingly "confident that the decades-long debate is over" a report says. "The Moon, in fact, has water in all sorts of places; not just locked up in minerals, but scattered throughout the broken-up surface, and, potentially, in blocks or sheets of ice at depth." The results from the Chandrayaan mission are also "offering a wide array of watery signals."[109][110]

According to European Space Agency (ESA) scientists, the lunar regolith (a loose collection of irregular dust grains making up the Moon's surface) absorbs hydrogen nuclei from solar winds. Interaction between the hydrogen nuclei and oxygen present in the dust grains is expected to produce hydroxyl (HO−
) and water (H
2O).[111]

The SARA (Sub keV Atom Reflecting Analyser) instrument developed by ESA and the Indian Space Research Organisation was designed and used to study the Moon's surface composition and solar-wind/surface interactions. SARA's results highlight a mystery: not every hydrogen nucleus is absorbed. One out of every five rebounds into space, combining to form an atom of hydrogen. Hydrogen shoots off at speeds of around 200 kilometres per second (120 mi/s) and escapes without being deflected by the Moon's weak gravity. This knowledge provides timely advice for scientists who are readying ESA's BepiColombo mission to Mercury, as that spacecraft will carry two instruments similar to SARA.

Chandrayaan-1 imaged a lunar rille, formed by an ancient lunar lava flow, with an uncollapsed segment indicating the presence of a lunar lava tube, a type of large cave below the lunar surface.[112] The tunnel, which was discovered near the lunar equator, is an empty volcanic tube, measuring about 2 km (1.2 mi) in length and 360 m (1,180 ft) in width. According to A. S. Arya, scientist SF of Ahmedabad-based Space Application Centre (SAC), this could be a potential site for human settlement on the Moon.[113] Earlier, Japanese Lunar orbiter SELENE (Kaguya) also recorded evidence for other caves on the Moon.[114]

Data from the microwave sensor (Mini-SAR) of Chandrayaan-1 processed using the image analysis software ENVI, has revealed a good amount of past tectonic activity on the lunar surface.[115] The researchers think that the faults and fractures discovered could be features of past interior tectonic activity coupled with meteorite impacts.[115]