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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Chandrayaan programme | 5/7 | https://en.wikipedia.org/wiki/Chandrayaan_programme | reference | science, encyclopedia | 2026-05-05T12:59:47.013443+00:00 | kb-cron |
Chandrayaan-3's Vikram lander had undergone 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. 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. The landing region was unchanged from the previous mission, 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. 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, 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. On 3 September 2023, before putting Vikram to sleep mode, ISRO conducted a hop on the lunar surface by firing its 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.
=== Rovers ===
==== Pragyan (Chandrayaan-2) ====
The Rover named Pragyan carried two scientific payloads that were to be used in determining the elemental composition and its abundance near the landing site. 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. The Chandrayaan-2's Pragyaan was precluded from its operations after the crash landing of its carrier Vikram.
==== Pragyan (Chandrayaan-3) ====
Unlike the lander, there were no changes made in the Pragyan rover except for switching ISRO's logo with Emblem of India on the left and right wheels respectively that would imprint them on the regolith. The scientific objectives too remained unchanged since the previous mission. On 23 August 2023, a few hours after the soft landing, the ramp was deployed for the Pragyan to touch down and begin its operations on the surface. 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. On 3 September 2023, with the lunar night approaching, the rover was shut down and put into 'sleep mode'.
== Science == The Chandrayaan programme has been vastly regarded as successful, especially with the discovery of lunar water. It continues to provide scientific data and high-resolution imagery thanks to Orbiter High Resolution Camera (OHRC) which is the most advanced lunar camera so far with 25 cm (9.8 in) spatial resolution and it is currently operational onboard Chandrayaan-2's orbiter. Chandrayaan-1 lost its contact a year before its intended duration, however, the Chandrayaan-2's orbiter is carrying forward the research from the orbit and is expected to operate until 2026. The first soft landing and on-site science mission of Chandrayaan-3 conducted the first experiments in the lunar south pole region thus contributing to the understanding of the region which holds the potential for a future crewed lunar base.
=== Discovery of water on the Moon ===