Chandrayaan-3

Chandrayaan-3 (CHUN-drə-YAHN ) is the third mission in the Chandrayaan programme, a series of lunar-exploration missions developed by ISRO. The mission consists of Vikram, a lunar lander, and Pragyan, a lunar rover, as replacements for the equivalents on Chandrayaan-2, which had crashed on landing in 2019.

The spacecraft was launched on July 14, 2023, at 14:35 IST from the Satish Dhawan Space Centre (SDSC) in Sriharikota, India. It entered lunar orbit on 5 August, and touched down near the lunar south pole, at 69°S, on 23 August 2023 at 18:04 IST (12:33 UTC). With this landing, ISRO became the fourth national space agency to successfully land on the Moon, after the Soviet space program, NASA and CNSA, and the first organization in the recorded human history to achieve a soft landing near the lunar south pole.

The lander was not built to withstand the cold temperatures of the lunar night, so it was shut down at sunset over the landing site, twelve days after landing. The orbiting propulsion module remained operational and was repurposed for scientific observations of Earth; it was shifted from lunar orbit to a high Earth orbit on 22 November 2023, where it remains in service.

History

On 22 July 2019, ISRO launched Chandrayaan-2 on board a Launch Vehicle Mark-3 (LVM3) launch vehicle consisting of an orbiter, a lander and a rover. The lander was scheduled to touch down on the lunar surface on 6 September 2019 to deploy the Pragyan rover. The lander lost contact with mission control, deviated from its intended trajectory while attempting to land near the lunar south pole, and crashed.

The lunar south pole region holds particular interest for scientific exploration. Studies show large amounts of ice there. The ice could contain solid-state compounds that would normally melt under warmer conditions elsewhere on the Moon—compounds which could provide insight into lunar, Earth, and Solar System history. Mountains and craters create unpredictable lighting that protect the ice from melting, but they also make landing there a challenging undertaking for scientific probes. For future crewed missions and outposts, the ice could also be a source of oxygen, of drinking water as well as of fuel due to its hydrogen content.

The European Space Tracking network (ESTRACK), operated by the European Space Agency (ESA), and Deep Space Network operated by Jet Propulsion Laboratory (JPL) of NASA are supporting the mission. Under a new cross-support arrangement, ESA tracking support could be provided for upcoming ISRO missions such as those of India's first human spaceflight programme, Gaganyaan, and the Aditya-L1 solar research mission. In return, future ESA missions will receive similar support from ISRO's own tracking stations.

For the first time on the lunar surface, a laser beam from NASA's Lunar Reconnaissance Orbiter was broadcast on 12 December 2023, and it was reflected back by a tiny NASA retroreflector on board the Vikram lander. The purpose of the experiment was to determine the retroreflector's surface location from the moon's orbit. The Chandrayaan-3 lander's Laser Retroreflector Array (LRA) instrument began acting as a location marker close to the lunar south pole. Through multinational cooperation, the LRA was housed on the Vikram lander. On a hemispherical support framework, it consists of eight corner-cube retroreflectors. This array enables any orbiting spacecraft equipped with appropriate instruments to use lasers ranging from different directions. The 20 gram passive optical instrument is intended to survive for several decades on the lunar surface.

Objectives

ISRO's mission objectives for the Chandrayaan-3 mission are:

1. Engineering and implementing a lander to land safely and softly on the surface of the Moon.
2. Observing and demonstrating the rover's driving capabilities on the Moon.
3. Conducting and observing experiments on the materials available on the lunar surface to better understand the composition of the Moon.

Spacecraft

Design

Chandrayaan-3 comprises three main components: a propulsion module, lander module, and rover.

Propulsion module

The propulsion module carried the lander and rover configuration to a 100-kilometre (62 mi) lunar orbit. It was a box-like structure with a large solar panel mounted on one side and a cylindrical mounting structure for the lander (the Intermodular Adapter Cone) on top.

A few months after the conclusion of the lander portion of the mission, ISRO officials said that the propulsion module was equipped with two radioisotope heating units (RHU), designed and developed by BARC (Bhabha Atomic Research Centre). RHUs keep spacecraft at their operational temperature using the decay of radioactive material, to generate electricity to power heaters. Chandrayaan-3 project director P Veeramuthuvel said ISRO may use nuclear resources to maintain instruments in future rovers. ISRO officials later said the RHUs could not be installed on Chandrayaan-3's Vikram lander and Pragyan rover because it would have increased their mass. This reduced their maximum lifespan to 14 Earth days, or 1 lunar day. This will serve as a precursor test as ISRO is collaborating with the Indian governmental Department of Atomic Energy for development of RHU & RTG payloads for the future Chandrayaan and Deep space exploration missions.

On 4 December 2023, ISRO reported that the propulsion module was reinserted into an orbit around the Earth. The primary objective of the reinsertion was to allow Earth observations by spectral and polarimetric instruments. It remains in operation in a High Earth Orbit.

Vikram lander

The Vikram lander was responsible for the soft landing on the Moon. It is also box-shaped, with four landing legs and four landing thrusters capable of producing 800 newtons of thrust each. It carried the rover and had various scientific instruments to perform on-site analysis. The lander has four variable-thrust engines with slew rate changing capabilities, unlike Chandrayaan-2's lander, which had five, with the fifth one being centrally mounted and capable only of fixed thrust. One of the main reasons for Chandrayaan-2's landing failure was altitude increase during the camera coasting phase. This was removed by allowing the lander to control altitude and thrust during all phases of descent. Altitude correction rate was increased from Chandrayaan-2's 10°/s to 25°/s with Chandrayaan-3. Additionally, the Chandrayaan-3 lander is equipped with a laser Doppler velocimeter (LDV) to allow measuring altitude in three directions. The impact legs were made stronger compared to Chandrayaan-2 and instrumentation redundancy was improved. It targeted a more precise 16 km² (6.2 sq mi) landing region based on images provided by the Orbiter High-Resolution Camera (OHRC) onboard Chandrayaan-2's orbiter. ISRO improved the structural rigidity, increased polling in instruments, increased data frequency and transmission, and added additional multiple contingency systems to improve lander survivability in the event of failure during descent and landing.

Rover pragyan

The Pragyan rover is a six-wheeled vehicle with a mass of 26 kilograms (57 pounds). It is 917 by 750 by 397 millimetres (36.1 in × 29.5 in × 15.6 in) in size. The rover is expected to take multiple measurements to support research into the composition of the lunar surface, the presence of water ice in the lunar soil, the history of lunar impacts, and the evolution of the Moon's atmosphere.