Chandrayaan-1 spacecraft carrying 11 scientific instruments weighs about 1400 kg at the time of its launch and is shaped like a cuboid with a solar panel projecting from one of its sides. The state of the art subsystems of the spacecraft, some of them miniaturised, facilitate the safe and efficient functioning of its 11 scientific instruments.
The spacecraft structure has been mainly built using composites and Aluminium honeycomb material. The Thermal subsystem consisting of paints, tapes, multi layer insulation blanket, optical solar reflectors, heat pipes, heaters and temperature controllers, ensures the proper functioning of the spacecraft by keeping its temperature within acceptable limits. The Mechanisms subsystem of Chandrayaan-1 spacecraft takes care of the deployment of its solar panel and the steering of the dual gimballed antenna.
The spacecraft is powered by a single solar panel generating a maximum of 700 W. A 36 Ampere-Hour (Ah) Lithium ion battery supplies power when the solar panel is not illuminated by the sun. The Telemetry, Tracking and Command subsystem of Chandrayaan-1 working in S-band takes care of radioing the detailed spacecraft health information, facilitating the knowledge about spacecraft's position in space and allows the reception and execution of commands coming from earth by the spacecraft.
Sun and star sensors as well as gyroscopes provide the orientation reference for spacecraft in space. The Attitude and Orbit Control subsystem, essentially the brain of Chandrayaan-1, consisting of a Bus Management Unit (BMU), reaction wheels and thrusters, ensures the proper orientation and stability of the spacecraft as well as in changing its orbit during different phases of its flight.
To make Chandrayaan-1 spacecraft to escape from orbiting Earth and to travel towards the moon, its liquid apogee motor (LAM) is used. Liquid propellants needed for LAM as well as thrusters are stored onboard the spacecraft.
Chandrayaan-1 spacecraft's Communications subsystem transmits the precious information gathered by its eleven scientific instruments to Earth in 'X-band' through its Dual Gimballed Antenna.
Chandrayaan-1 spacecraft is built at ISRO Satellite Centre, Bangalore with contributions from ISRO/Department of Space (DOS) establishments like Vikram Sarabhai Space Centre (VSSC), Liquid Propulsion Systems Centre (LPSC) and ISRO Inertial Systems Unit (IISU) of Tiruvananthapuram, Space Applications Centre (SAC) and Physical Research Laboratory (PRL) of Ahmedabad and Laboratory forElectro-optic Systems (LEOS) of Bangalore.
Chandrayaan-1: The Goals
The primary objectives of Chandrayaan-1 are:
The primary objectives of Chandrayaan-1 are:
1. To expand scientific knowledge about the moon
2. To upgrade India's technological capability
3. To provide challenging opportunities for planetaryresearch to the younger generation of Indian scientists
Chandrayaan-1 aims to achieve these well defined objectives through high resolution remote sensing of the moon in the visible, near infrared, microwave and X-ray regions of the electromagnetic spectrum. With this, preparation of a 3-dimensional atlas of the lunar surface and chemical mapping of entire lunar surface is envisaged.
Chandrayaan-1: The Payloads
There are 11 payloads (scientific instruments) through which Chandrayaan-1 intends to achieve its objectives. The instruments were carefully chosen on the basis of many scientific and technical considerations as well as their complementary /supplementary nature. They include five instruments entirely designed and developed in India, three instruments from European Space Agency (one of which is developed jointly with India and the other with Indian contribution), one from Bulgaria and two from the United States. Thus, Chandrayaan-1 is a classic example of international cooperation that has characterised the global space exploration programmes of the postcold war era.
The Indian payloads are:
1. Terrain Mapping Camera (TMC): The aim of this instrument is to completely map the topography of the moon. The camera works in the visible region of the electromagnetic spectrum and captures black and white stereo images. It can image a strip of lunar surface which is 20 km wide and resolution of this CCD camera is 5 m. Such high resolution imaging helps in better understanding of the lunar evolution process as well as in the detailed study of the regions of scientific interest. When used in conjunction with data from Lunar Laser Ranging Instrument (LLRI), it can help in better understanding of the lunar gravitational field as well. TMC is built by ISRO's Space Applications Centre (SAC) of Ahmedabad.
2. Hyperspectral Imager (HySI): This CCD camera is designed to obtain the spectroscopic data for mapping of minerals on the surface of the moon as well as for understanding the mineralogical composition of the moon's interior. Operating in the visible and near infrared region of the electromagnetic spectrum, it will image a strip of lunar surface which is 20 km wide with a resolution of 80 m. It will split the incident radiation into 64 contiguous bands of 15 nanometer (nm) width. HySI will help in improving the already available information on mineral composition of the lunar surface. HySI is also built by SAC.
3. Lunar Laser Ranging Instrument (LLRI): This instrument aims to provide necessary data for determining the accurate altitude of Chandrayaan-1 spacecraft above the lunar surface.It also helps in determining the global topographical field of the Moon as well as in generating an improved model for the lunar gravity field. Data from LLRI will enable understanding of the internal structure of the moon and the way large surface features of the moon have changed with time. The infrared laser source used for LLRI is Nd-YAG laser wherein Neodimium atoms are doped into a Yittrium Aluminium Garnet crystal. The wavelength of the light emitted by LLRI is 1064 nm. LLRI is built by ISRO's Laboratory for Electro Optic Systems (LEOS) of Bangalore.
4. High Energy X-ray Spectrometer (HEX): This is the first planetary experiment to carry out spectral studies at 'hard' X-ray energies using good energy resolution detectors. HEX is designed to help explore the possibility of identifying polar regions covered by thick water-ice deposits as well as in identifying regions of high Uranium and Thorium concentrations. Knowledge of the chemical composition of the various solar system objects such as planets, satellites and asteroids provides important clues towards understanding their origin and evolution. HEX uses Cadmium Zinc Telluride (CZT) detectors and is designed to detect hard X-rays in the energy range of 20 kilo electron Volts (keV) to about 250 keV. HEX is built jointly by Physical Research Laboratory (PRL) of Ahmedabad and ISRO Satellite Centre of Bangalore.
5. Moon Impact Probe (MIP): The primary objective of MIP is to demonstrate the technologies required for landing a probe at the desired location on the moon. Through this probe, it is also intended to qualify some of the technologies related to future soft landing missions. This apart, scientific exploration of the moon at close distance is also intended using MIP.
The 29 kg Moon Impact Probe consists of a C-band Radar Altimeter for continuous measurement of altitude of the Probe above lunar surface and to qualify technologies for future landing missions, a Video Imaging System for acquiring images of the surface of moon from the descending probe and a Mass Spectrometer for measuring the constituents of extremely thin lunar atmosphere during its 20 minute descent to the lunar surface. MIP is developed by Vikram Sarabhai Space Centre of Thiruvananthapuram.
Chandrayaan-1: The Payloads
Of the six payloads from abroad in Chandrayaan-1, three are from the European Space Agency (ESA). They are:
1. Chandrayaan-1 Imaging X-ray Spectrometer (C1XS): This instrument intends to carry out high quality mapping of the moon using X-ray fluorescence technique for measuring elemental abundance of Magnesium, Aluminium, Silicon, Iron and Titanium distributed over the surface of the moon. This will help in finding answers to key questions about the origin and evolution of the moon. The instrument is sensitive to X-rays in the energy range of 0.5—10 keV. C1XS is jointly developed by Rutherford Appleton Laboratory of England and ISRO Satellite Centre, Bangalore.
2. Smart Near Infrared Spectrometer (SIR-2): This instrument aims to study the lunar surface to explore the mineral resources, the formation of its surface features, the way different layers of the moon's crust lie over one another and the way materials are altered in space. It has the ability to detect and record near Infrared radiation coming from the moon. Since this is the radiation band through which various minerals and ices reveal their existence, SIR-2 is well suited for making an inventory of various minerals on the lunar surface. It can detect the radiation in the range of 0.93-2.4 micron. SIR-2 is developed by Max Plank Institute of Germany.
3. Sub keV Atom Reflecting Analyser (SARA): The aim of this instrument is to study the surface composition of the moon, the way in which moon's surface reacts with solar wind, the way in which surface materials on the surface of the moon change and the magnetic anomalies associated with the surface of the moon. SARA will be sensitive to neutral atoms that have escaped from the surface of the moon and having energy in the range of 10 eV—2 keV (kilo-electron-Volt). The instrument has been developed by the Swedish Institute of Space Physics and Space Physics Laboratory (SPL) of ISRO's Vikram Sarabhai Space Centre built its processing electronics.
The Bulgarian Payload onboard Chandrayaan-1 is:
4. Radiation Dose Monitor (RADOM): This instrument aims to qualitatively and quantitatively characterise the radiation environment in space around the moon’s vicinity. It will help study the radiation dose map of space near the moon at various latitudes and altitudes. Besides, the instrument helps in investigating whether the space near the moon shields it from cosmic rays coming from distant cosmic sources as well as those from the sun. Such studies and investigations will be helpful in the important task of finding out the shielding requirements of future manned missions to the moon. RADOM is developed by the Bulgarian Academy of Sciences.
The NASA instruments carried by Chandrayaan-1 are:
5. Mini Syntheic Aperture Radar (MiniSAR): This is one of the two scientific instruments of the United States flown in Chandrayaan-1 mission. MiniSAR is from Johns Hopkins University's Applied Physics Laboratory and Naval Air Warfare Centre, USA through NASA. Working in S-band, MiniSAR is mainly intended for the important task of detecting water ice in the permanently shadowed regions of the Lunar poles up to a depth of a few meters. It can optimally distinguish water ice from the dry lunar surface. MiniSAR has a spatial resolution of about 75 metres.
6. Moon Mineralogy Mapper (M3): This is an imaging spectrometer which is intended to assess and map lunar mineral resources at high spatial and spectral resolution to support planning for future targeted missions. It will help in characterising and mapping lunar minerals in the context of the moon's early geological evolution. M3 is from Brown University and Jet Propulsion Laboratory through NASA. M3 may also help in identifying water ice in the lunar polar areas. Its operating range is 0.7 to 3 micrometre. The instrument has a spatial resolution of 70 m.
The launch of Chandrayaan-1 takes place from the Second Launch Pad at Satish Dhawan Space Centre, SHAR, Sriharikota in the Nellore district of Andhra Pradesh state. Sriharikota is situated at a distance of about 80 km to the North of Chennai.
Chandrayaan-1
spacecraft begins its journey from earth onboard India's Polar Satellite Launch Vehicle (PSLV-C11) and first will reach a highly elliptical Initial Orbit (IO). In the Initial Orbit, the perigee (nearest point to earth) is about 250 km and apogee (farthest point from the earth) is about 23,000 km.After circling the Earth in its Initial Orbit for a while, Chandrayaan-1 spacecraft is taken into two more elliptical orbits whose apogees lie still higher at 37,000 km and 73,000 km respectively. This is done at opportune moments by firing the spacecraft's Liquid Apogee Motor (LAM) when the spacecraft is near perigee.
Subsequently, LAM is fired again to take Chandrayaan-1 spacecraft to an extremely high elliptical orbit whose apogee lies at about 387,000 km.
In this orbit, the spacecraft makes one complete revolution around the Earth in about 11 days. During its second revolution around the Earth in this orbit, the spacecraft will approach the Moon's North pole at a safe distance of about a few hundred kilometers since the Moon would have arrived there in its journey round the Earth.
Once the Chandrayaan-1 reaches the vicinity of the Moon, the spacecraft is oriented in a particular way and its LAM is again fired. This slows down the spacecraft sufficiently to enable the gravity of the moon to capture it into an elliptical orbit.
Following this, the height of the spacecraft's orbit around the moon is reduced in steps. After a careful and detailed observation of perturbations in its intermediate orbits around the moon, the height of Chandrayaan-1 spacecraft's orbit will be finally lowered to its intended 100 km height from the lunar surface.
Later, the Moon Impact Probe will be ejected from Chandrayaan-1 spacecraft at the earliest opportunity to hit the lunar surface in a chosen area. Following this, cameras and other scientific instruments are turned ON and thoroughly tested. This leads to the operational phase of the mission. This phase lasts about two years during which Chandrayaan-1 spacecraft explores the lunar surface with its array of instruments that includes cameras, spectrometers and SAR.
The Ground Segment
32m DSN Antenna
18m Antenna
During the various phases of its flight, Chandrayaan-1 spacecraft will send detailed information about its health to Earth through its transmitter. At the same time, the spacecraft will be ready to receive radio commands sent from Chandrayaan-1Spacecraft Control Centre instructing it to perform various tasks. Besides, the spacecraft receives, modifies and retransmits the radio waves sent by ground antennas in a precise way. This plays a crucial role in knowing its position and orbit at a particular instant of time. All these happen at 'S-band' frequencies in the microwave region of the electromagnetic spectrum.
Additionally, as it orbits the Moon, the spacecraft sends valuable imagery and other scientific information to Earth through X-band (at a higher frequency compared to S-band), which also lies in the microwave region.
But, such information is transmitted through radio at a very low power of a few watts. Thus, radio signals carrying that precious information become extremely feeble by the time they travel 400,000 km from the Moon and reach the earth. The Ground Segment of Chandrayaan-1 performs the crucial task of receiving the radio signals sent by spacecraft. It also transmits the radio commands to be sent to the spacecraft during different phases of its mission. Besides, it processes and safe keeps the scientific information sent by Chandrayaan-1 spacecraft.
ISRO Telemetry, Tracking and Command Network (ISTRAC) had a lead role in establishing the Ground Segment facility of Chandrayaan-1 along with ISRO Satellite Centre (ISAC) and Space Applications Centre (SAC). The Ground Segment of Chandrayaan-1 consists of:1. Indian Deep Space Network (IDSN)2. Spacecraft Control Centre (SCC) 3. Indian Space Science Data Centre (ISSDC)
The Indian Deep Space Network performs the important task of receiving the radio signals transmitted by Chandrayaan-1 spacecraft that become incredibly feeble by the time they reach the earth. Besides, it can send commands to the spacecraft at a power level of up to 20 kilowatts. IDSN consists of two large parabolic antennas, one with 18 m and the other 32 m diameter at Byalalu, situated at a distance of about 35 km from Bangalore. Of these, the 32 m antenna with its 'seven mirror beam waveguide system' is indigenously designed, developed, built, installed, tested and qualified. The 18 m antenna can support Chandrayaan-1 mission, but the 32m antenna can support Chandrayaan-1 and any spacecraft mission further deep into space.
During the initial phase of the mission, besides these two antennas, other ground stations of ISTRAC Network at Lucknow, Sriharikota, Bangalore, Thiruvananthapuram, Port Blair, Mauritius, Brunei, Biak (Indonesia) and Bearslake (Russia) as well as external network stations at Goldstone, Applied Physics Laboratory in Maryland, Hawaii (all three in USA), Brazil and Russia support the mission.
The Spacecraft Control Centre, located near ISTRAC campus at Peenya, North of Bangalore, is the focal point of all the operational activities of Chandrayaan-1 during all the phases of the mission. Commands to be transmitted to Chandrayaan-1 spacecraft to maintain its health as well as to make it perform various tasks originate from here. Experts specialising in various spacecraft subsystems as well as spacecraft mission operations personnel will be available at SCC.
The Indian Space Science Data Centre forms the third element of the Chandrayaan-1 ground segment. ISSDC receives (from IDSN as well as other external stations that support Chandrayaan-1), stores, processes, systematically archieves, retrieves and distributes the precious scientific information sent by Chandrayaan-1 cameras, spectrometers and other scientific instruments from the lunar orbit. It has state-of -the- art computers and data storage devices. ISSDC is also located at Byalalu.
32m DSN Antenna
18m Antenna
During the various phases of its flight, Chandrayaan-1 spacecraft will send detailed information about its health to Earth through its transmitter. At the same time, the spacecraft will be ready to receive radio commands sent from Chandrayaan-1Spacecraft Control Centre instructing it to perform various tasks. Besides, the spacecraft receives, modifies and retransmits the radio waves sent by ground antennas in a precise way. This plays a crucial role in knowing its position and orbit at a particular instant of time. All these happen at 'S-band' frequencies in the microwave region of the electromagnetic spectrum.
Additionally, as it orbits the Moon, the spacecraft sends valuable imagery and other scientific information to Earth through X-band (at a higher frequency compared to S-band), which also lies in the microwave region.
But, such information is transmitted through radio at a very low power of a few watts. Thus, radio signals carrying that precious information become extremely feeble by the time they travel 400,000 km from the Moon and reach the earth. The Ground Segment of Chandrayaan-1 performs the crucial task of receiving the radio signals sent by spacecraft. It also transmits the radio commands to be sent to the spacecraft during different phases of its mission. Besides, it processes and safe keeps the scientific information sent by Chandrayaan-1 spacecraft.
ISRO Telemetry, Tracking and Command Network (ISTRAC) had a lead role in establishing the Ground Segment facility of Chandrayaan-1 along with ISRO Satellite Centre (ISAC) and Space Applications Centre (SAC). The Ground Segment of Chandrayaan-1 consists of:1. Indian Deep Space Network (IDSN)2. Spacecraft Control Centre (SCC) 3. Indian Space Science Data Centre (ISSDC)
The Indian Deep Space Network performs the important task of receiving the radio signals transmitted by Chandrayaan-1 spacecraft that become incredibly feeble by the time they reach the earth. Besides, it can send commands to the spacecraft at a power level of up to 20 kilowatts. IDSN consists of two large parabolic antennas, one with 18 m and the other 32 m diameter at Byalalu, situated at a distance of about 35 km from Bangalore. Of these, the 32 m antenna with its 'seven mirror beam waveguide system' is indigenously designed, developed, built, installed, tested and qualified. The 18 m antenna can support Chandrayaan-1 mission, but the 32m antenna can support Chandrayaan-1 and any spacecraft mission further deep into space.
During the initial phase of the mission, besides these two antennas, other ground stations of ISTRAC Network at Lucknow, Sriharikota, Bangalore, Thiruvananthapuram, Port Blair, Mauritius, Brunei, Biak (Indonesia) and Bearslake (Russia) as well as external network stations at Goldstone, Applied Physics Laboratory in Maryland, Hawaii (all three in USA), Brazil and Russia support the mission.
The Spacecraft Control Centre, located near ISTRAC campus at Peenya, North of Bangalore, is the focal point of all the operational activities of Chandrayaan-1 during all the phases of the mission. Commands to be transmitted to Chandrayaan-1 spacecraft to maintain its health as well as to make it perform various tasks originate from here. Experts specialising in various spacecraft subsystems as well as spacecraft mission operations personnel will be available at SCC.
The Indian Space Science Data Centre forms the third element of the Chandrayaan-1 ground segment. ISSDC receives (from IDSN as well as other external stations that support Chandrayaan-1), stores, processes, systematically archieves, retrieves and distributes the precious scientific information sent by Chandrayaan-1 cameras, spectrometers and other scientific instruments from the lunar orbit. It has state-of -the- art computers and data storage devices. ISSDC is also located at Byalalu.
The Future.
Chandrayaan-1 is the first spacecraft mission of ISRO beyond Earth orbit. Chandrayaan-1 will be followed by Chandrayaan-2 which features a lander and a rover. India and Russia will jointly participate in this project. However, there may be a provision to accommodate payloads from other space agencies as happened in Chandrayaan-1. This apart, studies are being conducted by ISRO on sending unmanned spacecraft to planet Mars as well as to asteroids and comets. Through such programmes, ISRO intends to undertake the exploration of space besides its primary mission of developing and utilising space technology for the overall development of the country.
