E-Paper
HT This Day: April 20, 1975 -- India enters space age
India’s first scientific satellite, “Aryabhata” named after the great Indian astronomer and mathematician of the 5th century, today began orbiting the earth at an altitude of about 600 kms after it was launched by a Soviet Intercosmos rocket from a Soviet cosmodrome.
India’s first scientific satellite, “Aryabhata” named after the great Indian astronomer and mathematician of the 5th century, today began orbiting the earth at an altitude of about 600 kms after it was launched by a Soviet Intercosmos rocket from a Soviet cosmodrome.
This significant event in India’s march towards technological self-reliance has earned India the eleventh position among nations which have orbited satellites.
The other countries which have put satellites into orbit so far are the Soviet Union, the United States, Britain, Canada, Australia, Japan, Italy, West Germany, France and China.
The 360-kg satellite, launched at 1 p.m. (IST), is now orbiting at a speed of 96.41 minutes per revolution around the earth.
It is to stay in the orbit for six months and conduct three scientific experiments. The satellite is functioning normally, according to preliminary information obtained from ground tracking stations in Shriharikota near Madras and Bears Lake in the outskirts of Moscow.
Monitoring of the satellite done by sending radio commands from these stations showed that all the instruments on board are functioning normally.
A Tass message from Moscow said that control of the satellite, now jointly done by Indian and Soviet scientists, would be handed over to India after three days.
The satellite, designed by Indian scientists at the Indian Satellite Centre at Bangalore with assistance from Soviet scientists, had undergone tests at the Soviet cosmodrome for a few weeks before it was launched today.
The satellite has been launched into an orbit with the following parameters:
Apogee height 623 km
Perigee 564 km.
Inclination 50.4 degrees.
Orbital period around the earth 96.41 minutes.
The 26-faced blue-and-violet spacecraft is 14 centimetres in diameter and 116 centimetres high.
Spin stabilisation
The three experiments to be conducted by the satellite are: X-ray astronomy for the detection and study of X-ray emission from outer space, study of solar neutron and gamma rays emanating from the sun, and study of aeronomy including ionosphere which is useful for radio communication.
The data obtained from these three experiments is expected to bring in new information on outer space, the sun and the earth’s atmosphere.
The satellite is designed to circle the earth at a speed of about 8 kms per second. At this speed, it will take the satellite slightly over 90 minutes to travel once around the earth.
The satellite is stabilised by means of a spin system which consists of sit onboard spherical titanium containers filled with compressed nitrogen gas, and connected to a pair of nozzles protruding at diametrically opposite ends of the satellite frame.
As soon as the satellite is ejected from the rocket, the first container will release the gas automatically. After a minute, the second container is to repeat the operation.
These powerful jets of gas will set the satellite spinning at 90 revolutions per minute.
The momentum generated by the two gas jets keeps the satellite spinning for about 27 days during which the number of revolutions gradually dwindles.
When the spin rate gets reduced to about ten revolutions per minute, the ground tele-command station at Sriharikota, through remote control, activates the next container, The process will be repeated until all the remaining containers are used up. The satellite will thus be kept spin-stabilised for about six months.
Within these six months, the satellite is expected to complete all the three experiments as planned.
The spinning, besides keeping the satellite vertical or stable, helps the spacecraft to evenly expose all its sides to the rays of the sun. 11, thus avoids overexposure of any one side of its body.
The electrical power needed by the satellite is provided by solar panels composed of 18,500 individual solar cells mounted on the outer side of the satellite.
These cells convert sunlight into electricity, and together they can generate 46 watts of average power while exposed to sunlight.
The power thus obtained is fed to the various electronic sub-systems on the satellite as well as to 20 nickel-cadmium rechargeable batteries.
When the satellite moves into the shadow of the earth during its 90-minute orbits, the solar cells cannot generate power due to lack of sunlight. At this stage, the batteries take over to maintain the power supply to the sub-systems without any break.
The energy lost by the battery at this time will be replenished as soon as the spacecraft emerges into the sunlit side again.
The data collected by the three experiments will be stored instantaneously in a tape-recorder onboard the satellite. These data will be transmitted in codes to the ground receiving station located at ISRO’s Sriharikota range and the two other receiving stations in the Soviet Union and France when the satellite passes over these two stations.
During every orbit, the path of the satellite will be slightly shifted because of earth’s rotation and as result the very high-frequency signals transmitted by the craft -can be monitored by a particular -round station during only four of the 16 daily orbits.
Data transmission
When the satellite passes over Sriharikota and Moscow stations its transmitter can respond to coded ground telecommand and send the taped information to earth at a speed ten times faster than the rate at which it was recorded in the tape.
It means, all the information the tape-recorder collects during a 40-minute recording can be conveyed to ground stations in just four minutes.
The sensitive components of the satellite, except the solar panels, are housed in the temperature controlled belly of the spacecraft. For this purpose, even the metal sheets and the paints used for passive thermal control in the satellite are specially made to resist extremes of temperatures.
This precaution is essential because the spacecraft will be exposed to the searing heat of the unobstructed sunlight in space.
Consequently, when it is on the sunlit side of the earth, the outer section of the satellite gets heated up to about 130 degree centigrade and then the temperature drops to minus 100 degree centigrade when, it enters the shadow side of the earth.
This fluctuation between extreme temperatures can put out the delicate on-board electronic systems unless they are protected by an artificial environment conducive to their working. This is achieved by coating the satellite’s outer surface and electronics boxes with paints of known absorptive and emissive characteristics.
Apart horn the valuable data to be collected from the three experiments, India attaches great significance to the successful working of this satellite.
This scientific satellite is the forerunner of India’s future applications satellites. The sophisticated technology developed to build I the satellite will be used to make India’s future satellites for communication, television broadcast, resources survey and meteorology.
The Soviet Union has launched the satellite from its cosmodrome under an agreement signed on May 10, 1972 between the ISRO and the Academy of Sciences of the Soviet Union.
Balloon Test
The design, fabrication and testing of a satellite is a very complex and elaborate affair. In the first instance, most of the electronics sub-systems were broad boarded and tested using a combination I of Indian and imported components. The sub-systems whim included telemetry, telecommand and communication units were integrated inside a satellite structure roughly half in size of the final version, and tested out on a balloon flown at about 25 km altitude on May 3, 1973 from Hyderabad.
The system also included the X-ray astronomy payload, the magnetometers and the sun sensors. The communication link to a distance of 400 km, the electrical behaviour of the X-ray astronomy package and the altitude sensors were tested by this method.
A mechanical mock-up model comprising the structure and the various subsystems was built next, in order to evaluate the mechanical design. This model was subjected to acceleration shock and vibration tests corresponding to the levels that would be encountered during the launch ‘ phase. These tests were completed in February 1974.
The same model was also taken to the cosmodrome in USSR during April 1974 and mated with the actual Soviet rocket (Launch vehicle) to check the compatibility with the rocket. Simultanuously work on building a pre-prototype model was also completed to understand the problems related to the mechanical assembly and electrical integration.
The pre-prototype version differed from the prototype and the flight models in the use of non-space qualified components, very detailed environmental tests could be carried out on this model. The electrical prototype of the satellite which is a replica of the flight model was fabricated employing knowledge gained from the other models and tested at Peenya during June-November 1974.
The satellite model was carried on a helicopter during January 1973 and the satellite kept almost stationery at various distances and altitude from the ground station. The entire uplink and downlink was checked. The final phase was the fabrication of two flight models – one serving as a standby for any last minute snags.
The complete integration and testing of the flight model were completed during January – march 1975, Detailed testing of the integrated satellite was done using computer-controlled checkout system built around an Indian TDC-12 computer (manufactured by the Electronic Corporation of India Ltd, Hyderabad).
The model was transported to the cosmodrome in the Soviet Union abroad a IAF aircraft on March 17, 1973. The last minute tests of the satellite were made possible by special ground checkout system designed in India.
The primary ground station for receiving data and commanding the satellite is located at Sriharikota (Shar) near Madras. The ground station has an antennae array and complete setup for receiving, displaying and analysing them to determine the state of health of the satellite.
Besides these complete facilities to command the satellite a complete tracking network, consisting a Doppler and inter-foremetry and tone arranges has been installed at Shar. The functions of the entire ground system had been tested with a helicopter bourn satellite model, simulating the maximum range during its orbit.
A second ground station has been built with help of USSR Academy of sciences in Moscow for receiving data. This will increase data coverage from satellite. Telecommand station built by the Indian team has also been installed in Moscow to command and receive data,
The commanding station in Moscow is manned by Indian Personnel. To further increase data coverage, the French national Space Agency (CNES) with whom ISRO has arrangements, has been requested to provide the realtime telemetry reception and tracking of the satellite from the station of the French space network.
