Updates-
• The orbiter and lander modules will be stacked as an integrated module and accommodated inside an advanced GSLV MK-III launch vehicle
- The journey from the earth to the moon will take around 45-50 days.
NEW DELHI: India’s highly ambitious Rs 800-crore Chandrayaan-2 mission will be launched between July 9 and July 16. The spacecraft, involving an orbiter, a lander called Vikram and a rover named Pragyan, is expected to land on the moon on September 6.
The orbiter and lander modules will be stacked as an integrated module and accommodated inside an advanced GSLV MK-III launch vehicle. The rover will be housed inside the lander. After the launch from Sriharikota into the earth-bound orbit by GSLV MK-III between July 9 and 16, the integrated module will reach the moon orbit using an orbiter propulsion module, a statement from Indian Space Research Organisation (Isro) said. The journey from the earth to the moon will take around 45-50 days.
CHANDRAYAAN-2 LAUNCH, LUNAR TRANSFER, AND LANDING TRAJECTORY
Modified from a presentation given by ISRO director M. Annadurai to the United Nations Committee on the Peaceful Uses of Outer Space in June 2017.
Once Chandrayaan-2 spacecraft reaches the lunar orbit, Vikram will separate from the orbiter and soft-land at the predetermined site close to the south pole, which had not been explored by other countries.
Talking to TOI, Isro chairman K Sivan said, “Once Vikram lands on the lunar surface on September 6, rover Prayan will come out of it and roll out on the lunar surface for 300-400 metre. It will spend 14 earth days on the moon for carrying out different scientific experiments.”
Sivan said, “Altogether, there will be 13 payloads in the spacecraft. Three payloads in rover Pragyan and rest 10 payloads in lander Vikram and orbiter." The rover will analyse the content of the lunar surface and send data and images back to the Earth through the orbiter within 15 minutes, he said.
The launch of India’s second lunar mission was initially planned in April last year but Isro kept deferring it because of the complexities involved in the mission. In fact, the four-legged Vikram lander suffered a fracture in one of its legs during a test earlier this year. India had also almost lost the race to
Israel
to become the fourth country in the world after
, US and China to land the spacecraft on the moon. However, with Israel’s Beresheet failing to land on the moon on April 12 this year, Chandrayaan-2’s moon-landing on September 6, if successful, will make India the fourth country in the world to land on the moon.
The landing of 3,290-kg Chandrayaan-2 craft will be much more difficult than Israel’s Beresheet. While Beresheet tried to touch down on a plain of solidified lava, known as the Sea of Serenity, which has a flattened surface and more exposure to the sun, Chandrayaan-2 will explore the south pole, an uncharted territory. Only China’s Chang’e 4 spacecraft had recently in January landed on the moon’s far side, also known as the dark side because it faces away from the Earth and remains comparatively unknown.
India had first launched its moon mission Chandrayaan-1, which involved only an orbiter, on October 22, 2008. The spacecraft made more than 3,400 orbits around the moon during which it took hundreds of images of the moon. The Rs 386-crore mission concluded when the communication with the spacecraft was lost on August 29, 2009. Chandrayaan operated for 312 days as opposed to the intended two years but the mission achieved 95% of its planned objectives.
CHANDRAYAAN-2 LANDING TRAJECTORY
From M. Annadurai et al. presentation to the 10th IAA Symposium on the Future of Space Exploration, Torino, Italy, 27-29 June, 2017.
Orbiter
The orbiter is physically similar to Chandrayaan-1. It is three-axis stabilized with reaction wheels. The orbiter carries five science instruments and two supporting instruments.
- Terrain Mapping Camera 2 (TMC-2) is based upon TMC (a predecessor on Chandrayaan-1) and will perform 3D mapping of the lunar surface using two cameras.
- Collimated Large Array Soft X-ray Spectrometer (CLASS) is based upon C1XS (a predecessor on Chandrayaan-1) and will map abundance of major rock-forming elements on the Moon including Mg, Al, Si, Ca, Ti, and Fe. Assisting it is the Solar X-ray Monitor (XSM), which measures solar x-ray emission.
- Chandra's Atmospheric Composition Explorer(ChACE-2) is a neutral mass spectrometer that is based upon CHACE (a predecessor on Chandrayaan-1's Moon Impact Probe).
- Synthetic Aperture Radar (SAR) will perform radar mapping of the surface in both L and S bands of the radio spectrum. It has heritage from MiniSAR on Chandrayaan-1 but will be the first L-band radar mapper to orbit the Moon.
- Imaging Infra-Red Spectrometer (IIRS) is sensitive to light with wavelengths between 0.8 and 5 microns and has the specific goal of mapping the abundance of hydroxl ions and molecular water.
- Finally, the Orbiter High Resolution Camera (OHRC) will perform high-resolution imaging of the landing site prior to the lander mission.
CAD MODEL OF CHANDRAYAAN-2, LAUNCH CONFIGURATION
Chandrayaan-2 consists of an orbiter, lander, and small rover. Here, the spacecraft is shown in its launch configuration.
Lander
Physically, the lander is shaped like a truncated square-based pyramid, built around a cylinder that houses the substantial propellant tank. It will perform inertial navigation throughout the descent using its Laser-gyro-based inertial reference unit and accelerometer package, LIRAP. The propulsion system includes four throttleable engines that can each provide 800 newtons of thrust, and 8 attitude rockets of 50 newtons each. The lander will communicate direct to Earth using a steerable, dual-gimbal, S-band radio antenna.
The lander has multiple cameras in its Hazard Detection and Avoidance (HDA) system, which it will use to determine horizontal velocity from feature tracking and identify the landing site using pattern matching. HDA also contains microwave and laser altimeters and a laser Doppler velocimiter. The HDA system collects data and instructs the rockets to fire to steer the lander to the landing site. I didn't find any reference that indicated whether the lander has the ability to photograph the landscape it's sitting on. Surely it must, but I don't know.
Once on the ground, the lander will deploy its science payload:
- Instrument for Lunar Seismic Activity (ILSA) will study moonquakes. Large enough quakes could allow it to study the Moon's deep interior, potentially from a polar position not accessible to the Apollo seismometers, which would be cool. This experiment will be a lot cooler if the lander is capable of surviving multiple lunar days.
- Chandra’s Surface Thermophysical Experiment (ChaSTE) will measure thermal properties of the lunar surface.
- Radio Anatomy of Moon Bound Hypersensitive ionosphere and Atmosphere (RAMBHA-Langmuir Probe) will measure near surface plasma density and how it changes over the course of the lunar daytime. According to a recent Nature article, lunar plasma is thought to participate in the levitation of lunar dust, a problem for future human exploration.
And, of course, the lander will carry a rover. The rover is very small, roughly Sojourner-sized, at 20 kilograms. Like NASA's Mars rovers, the Chandrayaan-2 rover uses a rocker-bogie suspension system supporting six independently motorized wheels, but unlike NASA's rovers its corner wheels do not steer. Therefore, it steers by rotating the wheels at different rates, like a tank. This is a perfectly fine method for a lightweight rover as long as the net effect of steering isn't to sink the rover into the soil.
To make sure the rover could move and steer on the Moon without embedding, ISRO developed a big sandbox filled with crushed anorthosite to test rover mobility in. When NASA does this with Mars rovers, they build full-size mobility system mockups with tiny bodies so the whole vehicle weighs on Earth what the real rover weighs on Mars, where gravity is a third of Earth's. But that wouldn't work for the already-small Chandrayaan-2 rover trying to simulate lunar gravity at a sixth of Earth's. So ISRO developed a different solution that I just love: attaching a giant helium-filled balloon to a duplicate test rover to counterbalance 5/6 of its weight. These tests succeeded, evidently.
MOBILITY TESTING OF THE CHANDRAYAAN-2 ROVER
ISRO employs a balloon to counteract 5/6 of the weight of a duplicate of the Chandrayaan-2 rover in order to test its mobility on simulated lunar soil at lunar gravity. From M. Annadurai et al. presentation to the 10th IAA Symposium on the Future of Space Exploration, Torino, Italy, 27-29 June, 2017.
Because of its small size, the rover instrumentation is fairly limited, much like Sojourner's was. It has two navigation cameras for stereo path planning and an inclinometer for safety (drives will stop if the rover's inclination or motor current gets too high). It has no rear-facing cameras. It will use a small radio antenna for communication with the lander, which will relay rover data to Earth. The radio antenna is atop its vertically-mounted solar panel. Its solar panel is mounted vertically because of the near-polar landing site. That suggests the rover will need to turn in place after traverses to align the panel for good power production.
The rover is equipped with two science instruments for elemental composition, both of which point downward, beneath the rover: a Laser-Induced Breakdown Spectroscope (LIBS) and an Alpha Particle X-Ray Spectrometer. In general, LIBS will get you lower-mass elements and APXS will get you higher-mass elements, with substantial overlap between them. LIBS is faster, APXS more sensitive to trace elements if you can give it long enough integration time. Perhaps they will be using LIBS along traverses, and APXS at stops.
Interestingly, a paper I read about the LIBS instrument suggested it was designed for a one-year primary mission. Officially, the lander mission has an expected lifetime of 14 days, but maybe there is hope that it will survive a lunar night to do science on a second lunar day. That would be awesome. But any successful landing at all would be an enormous accomplishment for India; I don't want to get greedy.
CHANDRAYAAN-2 LANDER DEPLOYING ROVER
CAD MODEL OF CHANDRAYAAN-2 ROVER FROM BELOW
Looking Ahead
Originally, Chandrayaan-2 was supposed to be a collaboration with the Russian space agency, but budget problems made Russia drop out, and India decided to go it alone. If Chandrayaan-2 succeeds, India's next step will be lunar sample return. They'd be following exactly the same path China has at the Moon, going quickly from a successful orbiter, to a lander/rover, to autonomous sample return. Unlike China, however, India is using international collaboration to increase its chances for success; Indian prime minister Narendra Modi and his Japanese counterpart Shinzo Abe signed an agreement a couple of weeks ago to collaborate on a future joint lunar sample return mission.
A lot of people are trying to make the separate Chinese and Japanese/Indian lunar efforts into a race. To be sure, there is some national pride riding on successes in space, and reaching milestones first. But races have only one winner. We all win when more organizations launch scientific missions into space. All of these countries have shared the data they gathered during past missions with scientists and the public. India's mission landing near the south pole, and China's landing on farside, will only enhance global understanding of the Moon, regardless of who gets there first. India or China may yet be defeated by physics -- deep-space exploration is challenging -- but they won't be defeated by each other's success.
Good luck, saubhaagy to ISRO and India on the upcoming launch of Chandrayaan-2!
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