Mission Chandrayaan-2 (candra-yāna, transl. "mooncraft";^[15][16] pronunciation ) is the second lunar exploration mission developed by the Indian Space Research Organisation (ISRO),^[17][18] after Chandrayaan-1.^[19][20] It consisted of a lunar orbiter, the Vikram lander, and the Pragyan lunar rover, all of which were developed in India.^[21] The main scientific objective is to map and study the variations in lunar surface composition, as well as the location and abundance of lunar water.^[22][23]

The mission was launched on its course to the Moon from the second launch pad at Satish Dhawan Space Centre on 22 July 2019 at 2.43 PM IST (09:13 UTC) by a Geosynchronous Satellite Launch Vehicle Mark III (GSLV Mk III).^[9][10][24] The craft reached the Moon's orbit on 20 August 2019 and began orbital positioning manoeuvres for the landing of the Vikram lander.^[25] Vikram and the rover were scheduled to land on the near side of the Moon, in the south polar region^[26] at a latitude of about 70° south at approximately 20:23 UTC on 6 September 2019 and conduct scientific experiments for one lunar day, which approximates two Earth weeks.

However, the lander deviated from its intended trajectory starting at 2.1 kilometres (1.3 mi) altitude,^[27] and had lost communication when touchdown confirmation was expected.^[28][29] Initial reports suggesting a crash^[30][31] have been confirmed by ISRO chairman K. Sivan, stating that the lander location had been found, and "it must have been a hard landing".^[32]

Both ISRO and NASA tried unsuccessfully to communicate with the lander for two weeks before the lunar night set in.

The orbiter, part of the mission with eight scientific instruments, remains operational and is expected to continue its seven-year mission to study the Moon.

On 12 November 2007, representatives of the Russian Federal Space Agency (Roscosmos) and ISRO signed an agreement for the two agencies to work together on the Chandrayaan-2 project.^[33] ISRO would have the prime responsibility for the orbiter and rover, while Roscosmos was to provide the lander. The Indian government approved the mission in a meeting of the Union Cabinet, held on 18 September 2008 and chaired by Prime Minister Manmohan Singh.^[34] The design of the spacecraft was completed in August 2009, with scientists of both countries conducting a joint review.^[35][36]

Although ISRO finalised the payload for Chandrayaan-2 per schedule,^[37] the mission was postponed in January 2013^[38] and rescheduled to 2016 because Russia was unable to develop the lander on time.^[39][40] Roscosmos later withdrew in wake of the failure of the Fobos-Grunt mission to Mars, since the technical aspects connected with the Fobos-Grunt mission were also used in the lunar projects, which needed to be reviewed.^[39] When Russia cited its inability to provide the lander even by 2015, India decided to develop the lunar mission independently.^[38][41]

The spacecraft's launch had been scheduled for March 2018, but was first delayed to April and then to October to conduct further tests on the vehicle.^[42][43] On 19 June 2018, after the program's fourth Comprehensive Technical Review meeting, a number of changes in configuration and landing sequence were planned for implementation, pushing the launch to the first half of 2019.^[44] Two of the lander's legs got minor damage during one of the tests in February 2019.^[45]

Chandrayaan-2 launch was initially scheduled for 14 July 2019, 21:21 UTC (15 July 2019 at 02:51 IST local time), with the landing expected on 6 September 2019.^[20] However, the launch was aborted due to a technical glitch and was rescheduled.^[46][8][47] The launch occurred on 22 July 2019 at 09:13 UTC (14:43 IST) on the first operational flight of a GSLV MK III M1.^[48]

The primary objectives of the Chandrayaan-2 lander were to demonstrate the ability to soft-land on the lunar surface and operate a robotic rover on the surface. Scientific goals include orbital studies of lunar topography, mineralogy, elemental abundance, the lunar exosphere, and signatures of hydroxyl and water ice.^[49] The orbiter will map the lunar surface and help to prepare 3D maps of it. The onboard radar will also map the surface while studying the water ice in the south polar region and thickness of the lunar regolith on the surface.^[50]

The mission was launched on a Geosynchronous Satellite Launch Vehicle Mark III (GSLV Mk III) with an approximate lift-off mass of 3,850 kg (8,490 lb) from Satish Dhawan Space Centre on Sriharikota Island.^{[3][13][10][51]} As of June 2019, the mission has an allocated cost of ₹978 crore (approximately US$141 million) which includes ₹603 crore for space segment and ₹375 crore as launch costs on GSLV Mk III.^[52][53] Chandrayaan-2 stack was initially put in an Earth parking orbit of 170 km perigee and 40,400 km apogee by the launch vehicle.^[54]

As of September 2019, the Chandrayaan-2 orbiter was orbiting the Moon on a polar orbit at an altitude of 100 km (62 mi).^[55] It carries eight scientific instruments; two of which are improved versions of those flown on Chandrayaan-1. The approximate launch mass was 2,379 kg (5,245 lb).^{[4][5][37][56]} The Orbiter High Resolution Camera (OHRC) conducted high-resolution observations of the landing site prior to separation of the lander from the orbiter.^[55][2] The orbiter's structure was manufactured by Hindustan Aeronautics Limited and delivered to ISRO Satellite Centre on 22 June 2015.^[57][58]

The mission's lander is called Vikram (Sanskrit: विक्रम, lit. 'Valour^[61]') Pronunciation named after Vikram Sarabhai (1919–1971), who is widely regarded as the founder of the Indian space programme.^[62]

The Vikram lander detached from the orbiter and descended to a low lunar orbit of 30 km × 100 km (19 mi × 62 mi) using its 800 N (180 lbf) liquid main engines. It then performed a comprehensive check of all its on-board systems before attempting a soft landing that would have deployed the rover, and perform scientific activities for approximately 14 Earth days. Vikram spacecraft apparently crash-landed.^[30][1] The lander's location was spotted on the surface via thermal imaging, but its condition is unknown.^[32] The approximate combined mass of the lander and rover is 1,471 kg (3,243 lb).^[4][5]

The preliminary configuration study of the lander was completed in 2013 by the Space Applications Centre (SAC) in Ahmedabad.^[38] The lander's propulsion system consists of eight 50 N (11 lbf) thrusters for attitude control and five 800 N (180 lbf) liquid main engines derived from ISRO's 440 N (99 lbf) Liquid Apogee Motor.^[63][64] Initially, the lander design employed four main liquid engines, but a centrally mounted engine was added to handle new requirements of having to orbit the Moon before landing. The additional engine was expected to mitigate upward draft of lunar dust during the soft landing.^[51] Vikram was designed to safely land on slopes up to 12°.^[65][66]

Some associated technologies include a high resolution camera, Laser Altimeter (LASA),^[67] Lander Hazard Detection Avoidance Camera (LHDAC), Lander Position Detection Camera (LPDC),^[68] Lander Horizontal Velocity Camera (LHVC), an 800 N throttleable liquid main engine,^[57] attitude thrusters, Ka band radio altimeters (KaRA),^[69][70] Laser Inertial Reference & Accelerometer Package (LIRAP),^[71] and the software needed to run these components.^[2][55] Engineering models of the lander began undergoing ground and aerial tests in late October 2016, in Challakere in the Chitradurga district of Karnataka. ISRO created roughly 10 craters on the surface to help assess the ability of the lander's sensors to select a landing site.^[72]

The mission's rover is called Pragyan (Sanskrit: प्रज्ञान, lit. 'Wisdom^[73][74]') Pronunciation )^[75][73] with a mass of 27 kg (60 lb), would have operated on solar power.^[4][5] The rover was to move on 6 wheels traversing 500 meters on the lunar surface at the rate of 1 cm per second, perform on-site analyses and send the data to the lander, which would have relayed it to the Mission Control on the Earth.^{[76][77][37][56][52]} For navigation, the rover uses:

The expected operating time of Pragyan rover was one lunar day, or around 14 Earth days, as its electronics were not designed to endure the frigid lunar night. However, its power system has a solar-powered sleep/wake-up cycle implemented, which could have resulted in longer service time than planned.^[81][82] Two aft wheels of the rover have the ISRO logo and the State Emblem of India embossed on them to leave behind patterned tracks on the lunar surface,^[83][84] which is used to measure the exact distance travelled, also called visual odometry.

ISRO selected eight scientific instruments for the orbiter, four for the lander,^[85][3][86] and two for the rover.^[37] While it was initially reported that NASA and ESA would participate in the mission by providing some scientific instruments for the orbiter,^[87] ISRO in 2010 had clarified that due to weight restrictions it will not be carrying foreign payloads on this mission.^[88] However, in an update just a month before launch,^[89] an agreement between NASA and ISRO was signed to include a small laser retroreflector from NASA to the lander's payload to measure the distance between the satellites above and the microreflector on the lunar surface.^[90][91]

Payloads on the orbiter are:^[3][86][1]

The payloads on the Vikram lander are:^[3][86]

Pragyan rover carries two instruments to determine the abundance of elements near the landing site:^[3][86]

Chandrayaan-2 launch was initially scheduled for 14 July 2019, 21:21 UTC (15 July 2019 at 02:51 IST local time).^[20] However, the launch was aborted 56 minutes and 24 seconds before launch due to a technical glitch, so it was rescheduled to 22 July 2019.^[46][8] Unconfirmed reports later cited a leak in the nipple joint of a helium gas bottle as the cause of cancellation.^{[47][117][118]}

Finally Chandrayaan-2 was launched on-board the GSLV MK III M1 launch vehicle on 22 July 2019 at 09:13 UTC (14:43 IST) with better-than-expected apogee as a result of the cryogenic upper stage being burned to depletion, which later eliminated the need for one of the apogee-raising burns during the geocentric phase of mission.^{[48][119][120]} This also resulted in the saving of around 40 kg fuel onboard the spacecraft.^[121]

Immediately after launch, multiple observations of a slow-moving bright object over Australia were made, which could be related to upper stage venting of residual LOX/LH2 propellant after the main burn.^[122][123]

After being placed into a 45,475 × 169 km parking orbit by the launch vehicle,^[48] the Chandrayaan-2 spacecraft stack gradually raised its orbit using on-board propulsion over 22 days. In this phase, one perigee-raising and five apogee-raising burns were performed to reach a highly eccentric orbit of 142,975 × 276 km^[104] followed by trans-lunar injection on 13 August 2019.^[105] Such long Earth-bound phase with multiple orbit-raising manoeuvres exploiting the Oberth effect was required because of the limited lifting capacity of the launch vehicle and thrust of the spacecraft's on-board propulsion system. A similar strategy was used for Chandrayaan-1 and the Mars Orbiter Mission during their Earth-bound phase trajectory.^[124] On 3 August 2019, the first set of Earth images were captured by the LI4 camera on the Vikram lander, showing North American landmass.^[60]

After 29 days from its launch, the Chandrayaan-2 spacecraft stack entered lunar orbit on 20 August 2019 after performing a lunar orbit insertion burn for 28 minutes 57 seconds. The three-spacecraft stack was placed into an elliptical orbit that passes over the polar regions of the Moon, with 18,072 km (11,229 mi) aposelene and 114 km (71 mi) periselene.^[106] By 1 September 2019 this elliptical orbit was made nearly circular with 127 km (79 mi) aposelene and 119 km (74 mi) periselene after four orbit-lowering maneuvers^{[107][108][109][110]} followed by separation of Vikram lander from the orbiter on 7:45 UTC, 2 September 2019.^[111]

Two landing sites were selected, each with a landing ellipse of 32 × 11 km.^[125] The prime landing site (PLS54) is at 70.90267 S 22.78110 E (600 km (370 mi) from the south pole^[126]), and the alternate landing site (ALS01) is at 67.874064 S 18.46947 W. The prime site is on a high plain between the craters Manzinus C and Simpelius N,^[127][26] on the near side of the Moon.

Vikram began its descent at 20:08:03 UTC, 6 September 2019 and was scheduled to land on the Moon at around 20:23 UTC. The descent and soft-landing were to be done by the on-board computers on Vikram, with mission control unable to make corrections.^[128]

The initial descent was considered within mission parameters, passing critical braking procedures as expected, but the lander's trajectory began to deviate at about 2.1 kilometres (1.3 mi; 6,900 ft) above the surface.^[129][130] The final telemetry readings during ISRO's live-stream show that Vikram's final vertical velocity was 58 m/s (210 km/h) at 330 meters above the surface which, according to some experts, is quite fast for a lunar landing.^{[28][114][131]} Initial reports suggesting a crash^[30][31] were confirmed by ISRO chairman K. Sivan, stating that the lander location was found and that "it must have been a hard landing".^{[32][132][133]}

Radio transmissions from the lander were tracked during descent by analysts using a 25-meter radio telescope owned by the Netherlands Institute for Radio Astronomy. Analysis of the doppler data suggests that the loss of signal coincided with the lander impacting the lunar surface at a velocity of nearly 50 metres (160 ft) per second (as opposed to an ideal 2 metres (6.6 ft) per second touchdown velocity).^[3][134]

The powered descent was also observed by NASA's Lunar Reconnaissance Orbiter (LRO) using its Lyman-Alpha Mapping Project (LAMP) instrument to study changes in the lunar exosphere due to exhaust gases from the lander's engines.^[135]

The mission's orbiter used thermal imaging to locate the lander.^[136] Unconfirmed reports, citing an ISRO official, stated that the lander was intact,^[137] but there has been no official announcement by ISRO on the lander's physical condition.^[32][138] ISRO's Chairman, K. Sivan, tasked senior scientist P. S. Goel to head the Failure Analysis Committee to look into the causes of the failure.^[139] Both ISRO and NASA attempted to communicate with the lander for about two weeks before the lunar night set in.^[140][141] while NASA's Lunar Reconnaissance Orbiter (LRO) flew over on 17 September 2019 and acquired some images of the intended landing zone.^[142] However, the location was near dusk, causing poor lighting for optical imaging.^[143][144] NASA's LRO images, showing no sight of the lander, were released on 26 September.^[126] The LRO will fly over again on 14 October under more favorable lighting conditions.^[145]

The lander and rover were primarily engineering tests,^[146] and the lander's success criteria was defined for every phase, scoring 90% to 95%.^[146] The orbiter part of the mission, with eight scientific instruments, remains operational, and will continue its seven-year mission to study the Moon.^[130]

Key scientists and engineers involved in the development of Chandrayaan-2 include:^{[148][149][150]}