Chandrayaan-1 was launched on 22 October 2008 at 6.22 am IST from Satish Dhawan Space Centre using the ISRO's 44.4 metre tall four-stage PSLV-XL launch rocket. Chandrayaan-1 was sent to the Moon in a series of orbit-increasing manoeuvres around the Earth over a period of 21 days as opposed to launching the craft on a direct trajectory to the Moon. At launch the spacecraft was inserted into geostationary transfer orbit (GTO) with an apogee of 22,860 km and a perigee of 255 km. The apogee was increased with a series of five orbit burns conducted over a period of 13 days after launch.
For the duration of the mission, ISRO's telemetry, tracking and command network (ISTRAC) at Peenya in Bangalore, tracked and controlled Chandrayaan-1. Scientists from India, Europe, and the U.S. conducted a high-level review of Chandrayaan-1 on 29 January 2009 after the spacecraft completed its first 100 days in space.
Earth orbit burns
- First orbit burn: The first orbit-raising manoeuvre of Chandrayaan-1 spacecraft was performed at 09:00 hrs IST 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, and its perigee to 305 km. In this orbit, Chandrayaan-1 spacecraft took about 11 hours to go around the Earth once.
- Second orbit burn: The second orbit-raising manoeuvre of Chandrayaan-1 spacecraft was carried out on 25 October 2008 at 05:48 IST when the spacecraft’s engine was fired for about 16 minutes, raising its apogee to 74,715 km, and its perigee to 336 km, 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 high geostationary orbit and reached an altitude more than twice that height.
- Third orbit burn: The third orbit raising manoeuvre was initiated on 26 October 2008 at 07:08 IST when the spacecraft’s engine was fired for about nine and a half minutes. With this its apogee was raised to 164,600 km, and the perigee to 348 km. In this orbit, Chandrayaan-1 took about 73 hours to go around the Earth once.
- Fourth orbit burn: The fourth orbit raising manoeuvre was carried out on 29 October 2008 at 07:38 IST when the spacecraft’s engine was fired for about three minutes, raising its apogee to 267,000 km and the perigee to 465 km. 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.
- Final orbit burn: he fifth and final orbit raising manoeuvre was carried out on 4 November 2008 04:56 am IST 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.
Lunar orbit insertion
Chandrayaan-1 successfully completed the lunar orbit insertion operation on 8 Nov 2008 at 16:51 IST. This manoeuvre involved firing of the liquid engine for 817 seconds (about thirteen and half minutes) when the spacecraft passed within 500 km from the Moon. The satellite was placed in an elliptical orbit that passed over the polar regions of the Moon, with 7502 km aposelene (point farthest away from the Moon) and 504 km periselene (nearest to the Moon). 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.
- First orbit reduction: First Lunar Orbit Reduction Manoeuvre of Chandrayaan-1 was carried out successfully on 9 November 2008 at 20:03 IST. During this, the engine of the spacecraft was fired for about 57 seconds. This reduced the periselene from 504 km to 200 km 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.
- Second orbit reduction: his manoeuvre, which resulted in steep decrease in Chandrayaan-1’s aposelene from 7,502 km to 255 km and its periselene from 200 km to 187 km, was carried out on 10 November 2008 at 21:58 IST. During this manoeuvre, the engine was fired for about 866 seconds (about fourteen and half minutes). Chandrayaan-1 took two hours and 16 minutes to go around the Moon once in this orbit.
- Third orbit reduction: Third Lunar Orbit Reduction was carried out by firing the on board engine for 31 seconds on 11 November 2008 at 18:30 IST. This reduced the periselene from 187 km to 101 km, 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.
- Final orbit: Chandrayaan-1 spacecraft was successfully placed into a mission-specific lunar polar orbit of 100 km above the lunar surface on 12 November 2008. In the final orbit reduction manoeuvre, Chandrayaan-1’s aposelene was reduced from 255 km to 100 km while the periselene was reduced from 101 km to 100 km. 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) – have already been successfully switched on. The TMC successfully acquired images of both the Earth and the Moon.
Impact of the MIP on the lunar surface
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The Moon Impact Probe (MIP) crash-landed on the lunar surface on 14 November 2008, 15:01 UTC (20:31 Indian Standard Time (IST)) near the crater Shackleton at the south pole. The MIP was one of eleven scientific instruments (payloads) on board Chandrayaan-1. The MIP separated from Chandrayaan at 100 km from lunar surface and began its nosedive at 14:36 UTC (20:06 IST) going into a free fall for thirty minutes. 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 planned for 2013.
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Following the successful deployment of MIP, the other scientific instruments were turned on, starting the next phase of the mission. After scientific analyses of the received data from MIP, Indian Space Research Organisation confirmed presence of Water on Lunar soil and published the finding in a press conference addressed by its then Chairman.
Rise of spacecraft's temperature
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ISRO had reported on 25 November 2008 that Chandrayaan-1's temperature had risen above normal to 50°C, scientists said that it was caused by higher than normal temperatures in lunar orbit. The temperature was brought down by about 10°C by rotating the spacecraft about 20 degrees and switching off some of the instruments. Subsequently ISRO reported on 27 November 2008 that the spacecraft was operating under normal temperature conditions. 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 stabilise. The spacecraft was experiencing high temperature because of radiation from the Sun and infrared radiation reflected by the Moon.
Orbit raised to 200 km due to malfunctions
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After the completion of all the major mission objectives, the orbit of Chandrayaan-1 spacecraft, which was at a height of 100 km from the lunar surface since November 2008, had to be raised to 200 km due to malfunctions. The orbit raising manoeuvres were carried out between 09:00 and 10:00 IST 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. However, 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. The temperature of the spacecraft subsystems at 100km above the Moon's surface would be around 75 degrees Celsius. However, there was more than 75 degrees and problems started to surface. Then ISRO raised the orbit to 200km.
Attitude sensing due to Star Sensor failure
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The star sensor, a device used for direction finding of which the mission carried two, failed in orbit after nine months of operation. Afterward, the direction of Chandrayaan was determined using a back up procedure using a two axis Sun sensor and taking a bearing from a ground station. This was used to update three axis gyroscopes which enabled spacecraft operations, although some failures may have reduced the craft's lifetime. The first of the sensors failed on 26 April. The second failure, detected on 16 May, was attributed to excessive radiation from the Sun.
Bistatic RADAR experiment with LRO
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On 21 August 2009 Chandrayaan-1 along with the Lunar Reconnaissance Orbiter was used to perform a bistatic radar experiment to detect the presence of water ice on the lunar surface. In this experiment, Chandrayaan emanated RADAR pulses which, after reflection from the surface, were picked up by the receivers of both the Chandrayaan and the LRO. Both receivers, Mini-SAR in Chandrayaan and Mini-RF in LRO, were pointed at the Erlanger crater for four minutes during which the observations were made. In March 2010, it was reported that the Mini-Sar experiment onboard the Chandrayaan-1 had discovered cold dark spots which are hypothesized to contain an estimated at least 600 million metric tonnes of water-ice held within northern polar craters.
End of the mission
After suffering from several technical issues including failure of the star sensors and poor thermal shielding, Chandrayaan stopped sending radio signals at 1:30 AM IST on 29 August 2009 shortly after which, the ISRO officially declared the mission over. Chandrayaan operated for 312 days as opposed to the intended two years but the mission achieved 90% of its planned objectives. Among its many achievements was the discovery of the widespread presence of water molecules in lunar soil.
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Chandrayaan