Chandrayaan-1

• 1. Introduction

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  Chandrayaan-1, India's first lunar probe, lifted off on the 22nd of October 2008 at 00:52 UTC from a launch pad on the coast of Andhra Pradesh, and within months it would settle one of the longest-running debates in planetary science. The name itself carries the mission inside it: in Sanskrit, "Chandra" means Moon and "yāna" means craft or vehicle. A moon vehicle, built by a nation that had only recently set up the task force to decide whether such a thing was even possible.

  The questions driving Chandrayaan-1 were deceptively simple. Was there water on the Moon? What minerals lay across its surface? Could India build and operate the hardware to find out? The answers arrived faster than anyone expected, and one of them rewrote what humanity understood about its nearest neighbor. What follows is the story of how that happened, and what it cost to get there.

• 2. From Idea to Launchpad

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  The idea of an Indian Moon mission first came up at a gathering of the Indian Academy of Sciences in 1999. The Astronautical Society of India began formal planning a year later in 2000, and the Indian Space Research Organisation followed by establishing the National Lunar Mission Task Force. That body concluded ISRO already had the technical expertise to carry out such a mission on its own.

  In April 2003, more than 100 Indian scientists drawn from planetary science, astrophysics, chemistry, engineering, and communication sciences met and formally endorsed the Task Force recommendation. Six months later, in November of that year, the Vajpayee government gave the project its official approval. Former Prime Minister Atal Bihari Vajpayee is credited with announcing the mission publicly. The project gathered further momentum during the tenure of Prime Minister Manmohan Singh, whose government saw the mission through to launch.

  The rocket chosen was the PSLV-XL variant, designated C11, standing 44.4 metres tall and built in four stages. Rather than send Chandrayaan-1 on a direct path to the Moon, ISRO engineers planned a series of five orbit-raising burns around Earth across 21 days. This approach, more energy-efficient than a direct lunar trajectory, would become one of the technical signatures of the mission.

• 3. The Long Road to Lunar Orbit

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  At launch on the 22nd of October 2008, Chandrayaan-1 entered a geostationary transfer orbit with an apogee of 22,860 km and a perigee of 255 km. The first orbit burn, performed the following day at 03:30 UTC, fired the spacecraft's 440 Newton liquid engine for about 18 minutes and pushed the apogee out to 37,900 km. That single burn already marked the beginning of a journey through five distinct orbital shells.

  The second burn on the 25th of October raised the apogee to 74,715 km. This was the first time an Indian spacecraft had ever climbed past the 36,000 km geostationary ring and reached an altitude more than twice that height. By the fourth burn on the 29th of October the apogee had extended to 267,000 km, more than halfway to the Moon. The fifth and final burn on the 3rd of November sent Chandrayaan-1 into its lunar transfer trajectory with an apogee of roughly 380,000 km.

  Lunar orbit insertion came on the 8th of November. The liquid engine fired for 817 seconds as the spacecraft passed within 500 km of the Moon, placing it in an elliptical orbit with an aposelene of 7,502 km and a periselene of 504 km. Four further burns over the next four days brought the craft down to a circular polar orbit of 100 km above the lunar surface, reached on the 12th of November 2008. With that, India became the fifth nation to place a vehicle in lunar orbit.

• 4. Eleven Instruments, Six Nations

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  Chandrayaan-1 carried eleven scientific instruments with a combined mass of 90 kg, five built in India and six contributed by international partners. The payload reflected a deliberate strategy: the mission's science would carry more weight if independent instruments from multiple agencies confirmed the same findings.

  ISRO's own Terrain Mapping Camera, built at the Space Applications Centre in Ahmedabad, had a resolution of 5 metres and a 40 km swath. It was first tested on the 29th of October 2008 through commands issued from ISTRAC. The Lunar Laser Ranging Instrument, developed at ISRO's Laboratory for Electro-Optics Systems in Bangalore, fired infrared pulses at the surface and collected 10 measurements per second continuously on both the day and night sides of the Moon. The Moon Impact Probe carried a C-band radar altimeter, a video imaging system, and a mass spectrometer.

  Among the foreign contributions, the Moon Mineralogy Mapper, known as M3, came from Brown University and the Jet Propulsion Laboratory and was funded by NASA. It was activated on the 17th of December 2008. The C1XS X-ray fluorescence spectrometer, covering the 1-10 keV range and mapping elements including magnesium, aluminium, silicon, calcium, titanium, and iron, was a joint product of the Rutherford Appleton Laboratory in the United Kingdom, the European Space Agency, and ISRO. Mini-SAR, the synthetic aperture radar designed to hunt for polar ice, was built by a team that included the Naval Air Warfare Center, Johns Hopkins University Applied Physics Laboratory, Sandia National Laboratories, Raytheon, and Northrop Grumman. The International Lunar Exploration Working Group later gave the Chandrayaan-1 team its International Co-operation Award in 2008 for hosting what it called the most international lunar payload ever assembled, drawing instruments from 20 countries.

• 5. The Impact Probe and Water

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  On the 14th of November 2008, at 14:36 UTC, the Moon Impact Probe separated from Chandrayaan-1 at an altitude of 100 km and began a 30-minute nosedive toward the lunar south pole. As it fell, it transmitted data back to the orbiter, which relayed the signals to Earth. At 15:01 UTC, the probe struck near the crater Shackleton. ISRO named the impact site Jawahar Point.

  During that 25-minute descent, the probe's Chandra's Altitudinal Composition Explorer, known as CHACE, recorded 650 mass spectra readings and found evidence of water molecules in the lunar soil. The ISRO Chairman at the time, G. Madhavan Nair, confirmed the discovery in a press conference. On the 25th of September 2009, ISRO announced publicly that MIP had detected water just before impact, and that it had done so three months before the M3 instrument's own confirmation. The announcement had been held back until NASA verified the finding independently.

  The M3 detection, published in the journal Science on the 24th of September 2009, identified absorption features near 2.8-3.0 micrometres on the lunar surface. For silicate bodies, those features point to hydroxyl or water-bearing materials. The signal appeared strongest at cooler high latitudes and near fresh feldspathic craters. Years later, M3 data were reanalyzed and yielded what scientists described as "the most definitive proof to date" of water in shaded regions of craters near both poles. Lunar scientists had debated the possibility of water repositories for decades, and the Chandrayaan findings moved the field toward confidence that those deposits were real.

• 6. Heat, Failure, and Silence

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  On the 25th of November 2008, ISRO reported that Chandrayaan-1's temperature had climbed above normal to 50 degrees Celsius. Scientists initially attributed this to higher-than-expected temperatures in lunar orbit, a mix of solar radiation and infrared reflected from the Moon's surface. Engineers responded by rotating the spacecraft about 20 degrees and switching off some instruments, which brought the temperature down by roughly 10 degrees. By the 27th of November ISRO reported normal conditions, though the spacecraft was subsequently limited to running one instrument at a time until January 2009, when lunar orbital temperatures were expected to stabilize.

  The true cause was eventually traced to a batch of DC-DC converters with poor thermal regulation. To manage the heat, engineers later raised the orbit from 100 km to 200 km in a manoeuvre carried out between 03:30 and 04:30 UTC on the 19th of May 2009. The higher altitude also widened the imaging swath and enabled further study of the Moon's gravitational field.

  The star tracker, used for pointing attitude determination, failed after nine months of operation. A second failure detected on the 16th of May was attributed to excessive solar radiation. Orientation was maintained through a backup procedure using a two-axis Sun sensor cross-referenced with gyroscopes. At around 20:00 UTC on the 28th of August 2009, contact with Chandrayaan-1 was suddenly lost. The ISRO Chairman stated that very high radiation had caused the power-supply units controlling both onboard computer systems to fail. Information released later pointed specifically to overheating in the power supply unit made by MDI. The probe had operated for 312 days against an intended two years.

• 7. What the Mission Left Behind

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  A review by scientists found that Chandrayaan-1 had completed 95 percent of its primary scientific objectives despite running for less than half its planned duration. The Terrain Mapping Camera produced more than 70,000 three-dimensional images, including images of the Apollo 15 landing site. ISRO announced in January 2009 that six Apollo landing sites had been mapped in total, including Apollo 15 and Apollo 17. The TMC and HySI payloads together covered about 70 percent of the lunar surface, while M3 covered more than 95 percent.

  The Mini-SAR reported in March 2010 the discovery of more than 40 permanently darkened craters near the Moon's north pole, hypothesized to contain an estimated 600 million metric tonnes of water ice. The C1XS spectrometer detected more than two dozen weak solar flares during the mission and gathered what were described as the most accurate measurements yet of magnesium, aluminium, and iron on the lunar surface, while also confirming the presence of titanium and calcium. The M3 data also confirmed the magma ocean hypothesis, indicating the Moon was once completely molten.

  Chandrayaan-1 also imaged a lunar lava tube near the equator: an empty volcanic tunnel measuring about 2 km in length and 360 m in width. Scientist A. S. Arya of the Space Application Centre in Ahmedabad suggested the structure could be a potential site for human settlement on the Moon.

  On the 2nd of July 2016, NASA used ground-based radar to relocate Chandrayaan-1 in its lunar orbit, almost seven years after contact was lost. Repeated observations over the next three months showed its orbit varying between 150 and 270 km in altitude on a two-year cycle. The mission's public data release was completed by mid-2011, and the data gathered by the SARA instrument also provided direct input for the design of ESA's BepiColombo mission to Mercury, which carried two instruments built on SARA's findings about hydrogen rebound at the lunar surface.