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25 September, 2018 00:00 00 AM

Satellite for mankind

Satellites that face toward space collect data from the solar system and universe
M. Zahidul Islam
Satellite for mankind

The launching of Bangabandhu satellite-1 is not just a thrill or an excitement it is an essential element of our thriving futures to move forward along with the fast marchingworld. It appears to be a reflection of one of the prudential policies of the government. Many of us have still questions in our mind: what itis, how it works, are we ready to have it, shall we continue to maintain it, and how it helps to improve our social, cultural and economic life? It is an enormous inspiration to our striving efforts to build-up a happy and prosperous nation along with our grim pictures ofendemic corruption, anarchy in transport sector, leaking of question papers, questionable standard of education, irregularities and mismanagement in land sector, lack of efficiency and sincerity in administrative system etc. Our PM says it is a milestone on our way to progress. It offers opportunities as well as challenges and we must have to explorethe. According to the space-scientists satellite isan object in space that orbits or circles around a bigger object. It is a moon, planet or machine that orbits a planet or star. Generally‘satellite’ means a machine that is launched into space and moves around Earth or another body in space. There are two types of satellites: 1) Natural satellites: such as Earth which orbits the sun,and Moon which orbits the Earth. There are a large number of natural satellites in the solar system with almost every planet having at least one moon. 2) Artificial satellites: such asSputnik, International Space Station etc. are orbiting the Earth. Presently thousands of artificial satellites orbit the Earth. Artificial Satellite starts its journey in the mid-20th century when Soviet Union first launched the ‘Sputnik’ on 04 Oct 1957.  

A satellite consists of a number of parts having sub-systems depending on its expected use, functions and purposes. The sub-systems are the groups of devices that help the instruments to work together. The most common components include:

1.    The structure subsystem (Body or structure): It holds everything and can take the forces of a rocket launch and keep the components together in space. It provides a stable framework to keep the satellite pointed at the right place on Earth’s surface. The body is like a telescope, whenit is deployed, an outer cylinder is driven down by tiny electric motors to expose the inner cylinder and locks into place. The outside of the body is made of solar cells, which convert the sun's energy to electricity.

2.    The propulsion subsystem (Propeller):It launches the space craft to its permanent position includes small thrusters (motors) that help to keep it in the assigned place in orbit. Sometimes the satellites drift out of position due to the solar wind, gravitational or magnetic forces, then the thrusters are fired to move it back into its right position in the orbit.

3.    The power subsystem(Solar panel and batteries): It provides electricity to run the satellite. It generates electricity from the solar panels and store electricity in storage batteries to ensure the constant supply of electricity. It includes a power supply and distribution system, telemetry, communications and navigation system, on-board intelligence, and thermal management equipment.

4.    The communication subsystem: handles all the transmitting and receiving functions. It receives signals from the Earth, amplifies them, and transmits (send) them to another satellite or to a ground station.

5.    The thermal control subsystem:keeps the active parts of the satellite cool enough to work properly. In space as there is no air,so a special type of thermal control system is provided to drive out the heat into the space.

6.    The attitude control subsystem: It helps to keep the satellite in the right position in orbit. The forces on a satellite in orbit are in balance, but there are some disturbing forces such as the gravitational effect of the sun and moon etc. cause a satellite to drift out of its position slowly over time and increase the Satellite Orbital Inclination that cause an east-west libration or back and forth movement, when the attitude system tells the propulsion system to fire a thruster to move the satellite back where it belongs to.

7.    The ground station monitoring subsystem: It transmitscommands to the satellite and monitors its health. The telemetry and command system provides a way for people at the ground stations to communicate with the satellite. It involves computers that gather and process data from the instruments and execute commands from Earth.

8.    The Command and Control subsystem: Includes Antenna which is used mainly for two reasons: 1) to receive and transmit the telecommunication signals to provide services to its users and if it disrupts the users may experience a delay in services; 2) to provide Tracking, Telemetry, and Command (TTC) functions to maintain the operation of the satellite in orbit; and if it disrupts, there is a risk of losing control of the satellite.The TTC systems are used for monitoring all the vital operating parameters of the satellite.A radiois also usedto talk to the satellite, both to send it commands and get back information from it. On board computers get the command executed and monitor the performances of the satellite.Usually satellite emits a beacon that sends out a signal which enables it to be tracked by a ground station.

9.    Payload subsystem: It consists of sensors or radios or particle detectors or cameras or anything else that required in performing the tasks of a particular mission of the satellite. It can be a weapons system, optics, communication system or scientific instruments.   

10.    Transponders: A transponder is a device that shifts the frequency of an uplink signal and amplifies it for transmission to the earth in a downlink.Each transponder handles a particular frequency range ("bandwidth"). There are multiple transponders on a satellite, each capable of supporting one or more communication channels.

A satellite needs to be placed into precisely controlled orbits directly over the equator, with an orbital period equal to the Earth's rotational period of one sidereal day and following the direction as the earth's rotation at an altitude of 22,236.47 miles (35,786.13 kms) above the Earth. The velocity of a satellite orbiting at this altitude is 6,877.82 mph (11,068.78.kph) and this velocity must be precisely maintained. Since the satellite rotates over the equator in the same direction as the rotation of the Earth with the same angular velocity as the Earth, it remains in the same position relative to the Earth. The time required for one rotation is 23 hours 56 minutes and 04 seconds is known as a sidereal day. Though a single geostationary satellite can see approximately 42% of the Earth's surface but it can cover actually 34% of it. The path length of such a satellite is a minimum of 22300 miles and a response in a conversation can take half a second only. Sometimes we can see this delay when news reporters use a satellite link.

The artificial satellites have been used for many purposes by different countries of the world.

The Bangabandhu Satellite-1 (a 3.7 ton geostationary communication satellite) was made by France company Thales Alenia Space and launched by SpaceX with Falcon 9 rocketfrom the Kennedy Space Centre, Florida,USA on 12 May 2018 and was placed into the orbital slot on 119.1 degree east longitude with a lifespan of 15 years. Bangladesh bought this slot from Russian satellite company ‘Intersputnik’ for $28 million. It has a payload of 40 transponders of which 26 Ku-Band and 14 C-Band, to deliver focused telecommunications coverage to Bangladesh. One transponder is equivalent to 36 MHz.For domestic purpose 20 transponders will be used, while the remaining will be sold in international market. The Ku-band will cover Bangladesh and its territorial water bodies of the Bay of Bengal, India, Pakistan, Nepal, Bhutan, Sri Lanka, Indonesia and the Philippines. The C-band will cover Bangladesh, India, Indonesia, the Philippines, Myanmar, Bhutan, Nepal, Sri Lanka, Afghanistan, Pakistan, Tajikistan, Kyrgyzstan, Uzbekistan, Turkmenistan, and parts of Kazakhstan.  The total project cost was Tk 2,902 crore, of which HSBC Bank provided €155 million (approximately over Tk 1,585 crore) and the rest was from the government.Bangladesh has entered the Elite Space Club of 57 nations.

1.    It would immensely contribute to the digital advancement with the expansion of internet and telecommunication services throughout the country including theremote and rugged areassuch as forests, haors, coastal areas, deep-sea zones etc.

2.    Currently, Bangladesh meets its demand for satellite connectivity by renting bandwidth from foreign operators which costs about $14 million a year. Now we can save this money, and moreover we can earn huge amount of foreign currency by selling the satellite's transponder to other countries, while the local TV channels huge viewership particularly in the Middle East countries are expected to be increased.

3.    In the event of unexpected disasters like cyclone or tornado, when traditional telecommunication system may collapse then satellite network can provide uninterrupted telecommunication services throughout the country. It helps in rescue operations after natural disasters.

4.    It is helpful for distance learning, treatment, telemedicine, and improvement of weather forecast facilities.

5.    The satellite will also provide broadband connectivity to rural areas throughout the country. It will be able to count holdings as well as measure population density.

6.    It will improve the Direct to Home (D2H) services, making people's access to worldwide TV entertainment faster and easier, including video services, e-learning, family planning, farming, disaster recovery, research etc.

7.    The satellite will have VSAT private networks consisting of voice, data, video and internet services to the banks, corporate offices etc. In can also provide the voice service to cellular backhaul and data service for internet, SCADA, SOHO etc.

8.    It will act as acrucial tool for the surveillance and ensuring national security.

9.    The satellite will make video distribution easier as well enabling broadcasters to effortlessly distribute their content to intermediaries like cable TV network operators or re-broadcasters like DTH operators.

10.    It will give opportunities for the learners of new generation to know the universe and space, nuclear technology, marine science and other areas of science, culture, nature etc.

People with much appreciation expected the successful implementation of this satellite project which can greatly improve our social, cultural and economic life. The government should take effective measures to face the ensuing challenges to achieve the target.

This sincere effort will increase confidence and enrich our insight on the challenges and opportunities for the future space exploration and enable us to contribute a lot for the benefit and welfare of our people as well as for mankind and advance humanity.

The writer is former Editor, Journal of the Institution of Engineers, Bangladesh



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Editor : M. Shamsur Rahman

Published by the Editor on behalf of Independent Publications Limited at Media Printers, 446/H, Tejgaon I/A, Dhaka-1215.
Editorial, News & Commercial Offices : Beximco Media Complex, 149-150 Tejgaon I/A, Dhaka-1208, Bangladesh. GPO Box No. 934, Dhaka-1000.

Editor : M. Shamsur Rahman
Published by the Editor on behalf of Independent Publications Limited at Media Printers, 446/H, Tejgaon I/A, Dhaka-1215.
Editorial, News & Commercial Offices : Beximco Media Complex, 149-150 Tejgaon I/A, Dhaka-1208, Bangladesh. GPO Box No. 934, Dhaka-1000.

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