Chandrayaan Programme
CHANDRAYAAN PROGRAMME
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First mission
Soon after the proposals by the Indian Academy of Sciences in 1999 and by the Astronautical Society of India in 2000, a National Lunar Mission Task Force (NLMTF) was set up which constituted ISRO and leading Indian scientists and technologists across the nation to conduct the feasibility study. The study report was then reviewed by a peer group of 100 scientists from various fields.[6] The recommendations put forward were as follows:
- The Indian Moon Mission assumes significance in the context of the international scientific community considering several exciting missions in planetary exploration, in the new millennium.
- ISRO has the necessary expertise to develop and launch the Moon Mission with imaginative features and it would be different from the past missions. Hence ISRO should go ahead with the project approval and implementation.
- Apart from technological and scientific gains, it would provide the needed thrust to basic science and engineering research in the country. The project would help return young talents to the arena of fundamental research.
- The Academia, in particular, the university scientists would find participation in such a project intellectually rewarding. In this context, the scientific objectives would need further refinement to include other innovative ideas from a broader scientific community through Announcement of Opportunity, etc.
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Chandrayaan-1 was launched on 22 October 2008 aboard PSLV-XL. The solar-powered cuboid orbiter along with the Moon Impact Probe (MIP) weighed 1,380 kg (3,042 lb). It was powered by a single-sided solar array during the day and was supported by lithium-ion batteries during night time. The attitude of the spacecraft was controlled by three-axis stabilization method using two star sensors, gyroscopes and four reaction wheels. The scientific data transmission was conducted in X band frequencies while telemetry tracking was done in S band frequencies. To store these data, two solid-state recorders (SSR) were used with SSR-1 carrying 32 GB dedicated capacity for scientific data while SSR-2 carrying 8 GB capacity for the rest of the scientific data and attitude information. Moon Mineralogy Mapper, an American scientific payload onboard carried its own SSR with 10 GB capacity.[53] The MIP weighed 35 kg (77 lb) with 25 minutes of expected operating duration. It carried a Radar altimeter to record the altitude data which would be used in qualifying technologies for future soft landing missions, a Video imaging system to acquire close-range pictures of the lunar surface, and a Mass spectrometer to study the tenuous atmosphere of the Moon.[54]
The orbiter-impactor composite entered the lunar sphere of gravitational influence on 8 November 2008 and after orbital reduction maneuvers, it attained an elliptical polar orbit of 100 km (62 mi), upon which, two of the eleven scientific payloads, the Terrain Mapping Camera (TMC) which had a spatial resolution of 5 m (16 ft)[55] and Radiation Dose Monitor (RADOM) were switched on for operations.[14][56] On 12 November 2008, the MIP separated from the orbiter and impacted near the lunar south pole's Shackleton crater.[15] While descending, the probe's Chandra's Altitudinal Composition Explorer (CHACE) instrument detected the presence of water.[16] Post deployment of MIP, rest of the nine scientific instruments began operations.[57]
On 25 November 2008, just a couple of weeks after entering lunar orbit, the orbiter's temperature rose to 50 °C (122 °F) after receiving equal amounts of heat from the sun as well as the moon (due to its Albedo). Efforts such as rotating the craft by 20 degrees, shutting down the mission computers, and increasing its orbit to 200 km (120 mi) were made to bring its temperature down and to avoid damaging the onboard instruments.[58] A year later, the overheating problem was responsible for ending the mission as it damaged the star sensors which maintained the orientation of craft. The orientation was then barely maintained with the help of gyroscopes as a temporary measure before losing contact on 28 August 2009, which ended the mission a year before its intended duration. However, the mission was analyzed to be 95% successful with its intended operations.[59][60]
Phase II: Soft landers and rovers
The second phase involved the technical demonstration of the lunar soft landing and operation of a rover. The preparations were already underway before the launch of the first mission. An agreement was signed in 2007 with Russia that included India's contribution in providing a launch vehicle, orbiter, and rover while Russia provided the lander. However, it was later canceled in 2013 after the Russian lander was delayed and after its request to accept the risk.[26]Later in 2017, India signed a deal with Japan's JAXA to conduct a feasibility study for a joint lunar roving mission named Lunar Polar Exploration Mission (LUPEX). For which a technical demonstration of soft landing was required to be conducted.
Chandrayaan-2
Chandrayaan-2 was the second mission under the programme and it included an orbiter, lander, and rover. After the failure of the Chandrayaan-1 orbiter, the Chandrayaan-2 orbiter enabled ISRO to conduct science with modern cameras and instruments. The primary objectives of this mission were to soft land on the surface and operate a rover, to study the lunar surface, its exosphere, minerals and water ice.[63][64]
The orbiter, lander, and rover composite weighed 3,850 kg (8,490 lb), with the orbiter alone weighing 2,379 kg (5,245 lb). The orbiter carried eight scientific instruments with two of the instruments; the Terrain Mapping Camera 2 and Chandrayaan-2 Atmospheric Compositional Explorer 2 (ChACE-2) being upgraded versions of Terrain Mapping camera (TMC) onboard Chandrayaan-1 orbiter and Chandra's Atmospheric Compositional Explorer (CHACE) onboard Moon Impact Probe respectively.[65] The lander named Vikram weighed 1,471 kg (3,243 lb) including the 27 kg (60 lb) rover named Pragyan that it housed inside.[66] Vikram had eight 58 N (13 lbf) thrusters for attitude control and five 800 N (180 lbf) liquid main engines that were derived from ISRO's 400 N (90 lbf) liquid apogee motors[67] and it was designed to safely land on slopes up to 12°.[68] It carried four payloads to study lunar seismic activity, measure the lunar sub-surface temperatures and to measure density and variation of lunar surface plasma (using a langmuir probe). Rover Pragyan carried two scientific payloads that were to be used in determining the elemental composition and its abundance near the landing site.[65] It was designed to travel at a speed of 1 cm/s (0.39 in/s) and could drive up to 500 m (1,600 ft) in its lifetime. Both the lander and rover were expected to operate for one lunar day as they lacked any Radioisotope heater unit (RHU) and were entirely dependent on solar power for operations.[69]
The Chandrayaan-2 was launched on 14 July 2019[33] and it attained the lunar orbit on 20 August 2019.[70] After five orbital reduction manoeuvres, the composite attained a near circular orbit of 127 km × 119 km (79 mi × 74 mi),[71] which was followed by the separation of Vikram on 2 September 2019.[72] After two de-orbiting manoeuvers, Vikram attained a final orbit of 95 km × 119 km (59 mi × 74 mi) after which the powered descent phase began on 7 September 2019. During the descent and landing, the onboard computers had complete control over the lander.[73] The initial descent and critical braking procedures underwent as intended but upon reaching 2.1 km (1.3 mi) altitude, the lander began deviating and lost its contact with the mission control after subsequent crash landing.[74] Upon analysis, it was found that the main engines had higher thrust than normal which led to errors being accumulated over time and this meant the lander could not change its attitude at such a fast pace due to safety constraints in the onboard computer that had a limit on the maximum rate with which it can change its attitude. Coarse throttling of main engines, error in computing the remaining time in the mission and a small landing site of 500 x 500 m were the other reasons attributed to the failure.[75][76]
However, the orbiter remained the sole successful part of the mission with its new mission duration being extended from one year to seven and a half years. The Orbiter High-Resolution Camera (OHRC) during the time remained the most advanced camera in the lunar orbit with a spatial resolution of 25 cm (9.8 in), four times higher than Chandrayaan-1 orbiter's 1 m (3 ft 3 in) resolution. The orbiter is also studying the lava tubes and caves which were previously spotted by the Chandrayaan-1 orbiter.[77][78]
Chandrayaan-3
Two months after the failure of Chandrayaan-2's lander, fresh proposals were made for the third mission named Chandrayaan-3, which was a re-attempt to demonstrate the landing capabilities needed for the LUPEX mission, a proposed partnership with Japan that was planned for 2025-26 time frame.[79] With the Chandrayaan-2 orbiter already operational, the mission was primarily a soft landing and roving demonstration mission, with the propulsion module carrying a single payload in Spectro-polarimetry of Habitable Planet Earth (SHAPE). The SHAPE instrument would study Earth's atmosphere from distance and it would aid in the study of Exoplanets' atmospheres, which employs a similar technique.[80] The landing region was unchanged from the previous mission,[81] with the area of new site being expanded to 4 km × 2.5 km (2.5 mi × 1.6 mi) from previous 500 m × 500 m (1,600 ft × 1,600 ft). Other major changes in the new 'failure-based' approach included the removal of the fifth engine, an increase in fuel capacity, an increase in vertical velocity component, and other software changes.[82]
Vikram lander had undergone some major changes after its predecessor crash landed. There were now four instead of five main engines that provided 800 N (180 lbf) of thrust and had slew rate changing capabilities, unlike previously when the centrally mounted fifth engine lacked the capability. This enabled the lander to control the attitude and thrust during all phases of descent. The attitude correction rate was also increased from Chandrayaan-2's 10°/s to 25°/s with Chandrayaan-3. An additional laser Doppler velocimeter (LDV) was equipped that allowed attitude measurements in all three directions.[83][84] The impact legs were made larger and stronger relative to Chandrayaan-2. The OHRC onboard Chandrayaan-2 enabled the mission to have an expanded landing site with 10 km2 (3.9 sq mi) landing area. The lander underwent several tests including a helicopter drop test that helped in improving the structural rigidity. In the event of a failure during descent and landing, multiple contingency systems were added to improve the survivability chances of the lander. However, there were no changes made in the Pragyan rover and the scientific objectives remained unchanged since the previous mission.[85][84]
Chandrayaan-3 was launched on 14 July 2023 aboard LVM3[86] and on 16 August 2023, the composite attained a final lunar orbit of 113 km × 157 km (70 mi × 98 mi). [87] A day later, the Propulsion Module separated from the lander.[88] On 23 August 2023, the lander that had previously reduced its orbit to 25 km × 134 km (16 mi × 83 mi) via de-orbit burns,[89] began descending using all of its four engines after it reached near its Periselene at 30 km (19 mi). Roughly after eleven minutes of powered descent, the lander maintained the altitude of 7.5 km (4.7 mi) for 10 seconds before changing its attitude to vertical position for the final vertical descent phase. It then used two of its four engines to slow its descent to 150 m (490 ft) and then hovered twice for about thirty seconds before touching down on the chosen optimal spot.[90]
A few hours after the soft landing, the ramp was deployed for the Pragyan rover to touch down and begin its operations on the surface.[91] A few days later, the instruments were turned on and the rover moved 8 m (26 ft) on the surface, thus achieving the primary goal of the mission.[92] On 3 September 2023, with the lunar night approaching, the rover was shut down and put into 'sleep mode'. On the same day, before putting Vikram to sleep, ISRO conducted a hop on the lunar surface by firing Vikram's engines that moved it 40 cm (16 in) vertically as well as laterally before touching down again. The hop experiment proved to be the most significant test conducted by ISRO as the data would aid in future sample return missions under the programme. ISRO also attained a unique record of conducting its first vertical take-off and landing on an extraterrestrial surface before Earth; that was planned to be conducted under its Reusable technology demonstration programme.[93][94][95]
Phase III: On-site sampling
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