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Technology that orbits our planet
THE WORD “satellite” has become part of our everyday vocabulary, as we encounter it frequently in phrases like “satellite broadcasting”, “satellite navigation” and “satellite television”. It is, therefore, worthwhile to explore what satellites are and how they operate? It is important also to look into the myriad applications of satellite technology and to ascertain why this technology is of paramount importance to Pakistan?
By definition a satellite is a man-made object placed in an orbit around the Earth or another planet in order to collect information or for communications. This is a very basic definition of an artificial satellite and can further be expanded upon for each type.
Following are the nine types of satellites that are in use today:
— Astronomical satellites;
— Atmospheric studies satellites;
— Communication satellites
— Navigation satellites;
— Reconnaissance satellites;
— Remote sensing satellites;
— Search and rescue satellites;
— Space exploration satellites, and;
— Weather satellites.
Astronomical satellites are basically big telescopes floating around in space and are used for studying various astronomical phenomena and planetary surfaces. Atmospheric studies satellites are deployed to study the Earth’s atmosphere and they relay data related to ionospheric activities to the ground stations.
Communications satellites are commonly used for broadcasting television footage etc but are also used for telecommunications links like the internet and fax. A navigation satellite, as the name suggests, provides real-time location information to users and is heavily used in aviation, defence and maritime activities.
Reconnaissance satellites are used for spying and are usually the most advanced in terms of technology. In terms of applications, the most useful breed of satellites is called remote sensing satellites. They use electromagnetic radiations to measure different properties of a target from a distance and have a very wide range of applications.
Search and rescue satellites receive distress calls that are relayed to the Local User Terminal (LUT), which forwards it to the rescue coordination centres (RCC) via mission control centres (MCC). Space exploration satellites probe deep into the space and relay important data and images back to the Earth, where scientists use them for carrying out research in different disciplines.
Weather satellites measure the all-important variables relating to meteorology. They can also study clouds and predict storms and hurricanes.
All satellite systems have certain things in common. They all have sophisticated electronic equipment, sensors, antennas and a stand-alone power source — such as solar panels — on board. Another common characteristic of all satellite systems is that they have ground control stations, which are used to control satellite missions around the world or in space.
The satellite system equipment in space is called Space Segment (SS) and the equipment on the Earth is called Ground Segment (GS) or Control Segment. In certain systems, there is an additional User Segment or user terminal. Apart from these, there are also ground stations for certain satellites that may receive and process satellite data.
At the heart of all satellite systems is their “payload”. Payload is defined as the combination of hardware and software on the spacecraft that interact with the “subject”. Subject means the portion of the outside world under observation by the satellite in question.
Satellite payload could be as simple as a camera mounted for imaging targets on the ground, or could be a complex Directed Energy Weapon (DEW), such as high-powered laser to eliminate targets on the ground. Payload type depends on the mission objectives of a satellite system.
Apart from payload, the rest of the hardware and software on board a satellite are designed to perform supporting functions. A typical satellite Space Segment may consist of the following subsystems besides the payload:
— Telemetry, Tracking and Command (TT&C);
— Command and Data Handling (C&DH);
— Electrical Power Subsystem (EPS);
— Thermal Control Subsystem (TCS);
— Structures and Mechanisms;
— Orbit Determination and Control Subsystem (ODCS), and;
— Attitude Determination and Control (ADCS).
Telemetry, Tracking and Command (TT&C) is also known as the communications subsystem and is basically responsible for communications link between the satellite and ground stations or between the satellite and other satellites that relay data to the Earth.
The payload mission data is transmitted to the ground stations via TT&C. Moreover, the operator commands, which originate at the ground control station to control the satellite mission, are also received by this subsystem.
The command and data handling subsystem receives the operator commands from the TT&C subsystem, validates them, decodes them and eventually distributes them to the other satellite subsystems. It is also responsible for gathering, processing and formatting data from other subsystems to be sent to the ground station.
Electrical Power Subsystem (EPS) converts solar (the Sun), chemical (batteries) or nuclear energy to electrical energy and distributes it to all satellite subsystems. The power regulation and control and energy storage functions are part of EPS responsibility domain.
In space, a satellite is vulnerable to many heat sources, including the Sun, the Earth, and onboard electronics. However, the electronic and mechanical components of a satellite subsystem function reliably only if they operate in a specific temperature range. It is, therefore, important to maintain a temperature range for these components and this is achieved by using the Thermal Control Subsystem, also known as TCS.
The mechanical structures carrying all other satellite subsystems need to be designed carefully, keeping in view factors like the space environment, satellite mission objectives and payload characteristics. These structures are designed and developed by the Structures and Mechanisms team.
During all phases of a satellite mission lifecycle, it is important to know the position and velocity of the satellite. It is equally important to be able to control the satellite orbit around the Earth. The Orbit Determination and Control Subsystem (ODCS) is responsible for these operations.
A similar subsystem known as Attitude Determination and Control Subsystem (ADCS) stabilizes the satellite and orients and maintains it in the desired direction even in the presence of external disturbance torques.
When a satellite is developed and tested on ground, the last stage of the mission prior to the normal operation is to deploy it into its orbit around the Earth, using a space propulsion system. A space launch vehicle is used to deploy the satellite into its orbit.
Orbits are of many types, but the most commonly used orbits are polar, Sun synchronous and geosynchronous orbits. Orbits at lower altitudes above the Earth are called Lower Earth Orbits (LEO). Lower Earth Orbit satellites are 300 to 1,000kms above the Earth, whereas the Medium Earth Orbit (MEO) satellites have higher altitudes, of about 10,000kms. Geosynchronous satellites, also known as geostationary satellites, stay fixed relative to the Earth and are normally at an altitude of 35,786kms.
Some satellites operate independently, while others operate in a group called constellation. Navigation satellites usually operate in groups. However, there are some remote sensing satellites that work in groups, for instance those produced in Italy — called COSMO — shall operate in a constellation.
The most important satellites for the developing nations are communications and remote sensing satellites. While benefits of a communications satellite are quite obvious, remote sensing satellites have more applications than any other breed of satellites. These satellites use electromagnetic radiation in different bands to retrieve information about targets on the Earth.
Remote sensing satellites have both civilian and military applications. Civilian applications include those in agriculture, forestry, geology, surveying, oceanography, natural hazard monitoring, disaster mitigation, environmental monitoring and sea-ice mapping. In agriculture, remote sensing data can be used for crop health monitoring, yield estimation and predicting drought.
In geology, these satellites can help map important natural resources of a country through geological mapping. In order to minimize the damage due to certain calamities, remote sensing satellites can provide critical data to the authorities. In case of earthquakes, this data can be used for damage assessment and can also be used to prioritize rescue missions depending on the severity of damage.
In hydrology, flood delineation and determining soil moisture content are two common applications. For city and regional planning authorities, remote sensing can be used to detect change in urban land cover and to make topographic maps.
Military applications of remote sensing satellites include determination of the layout of the enemy’s military facilities, locating military equipment of the enemy, monitoring a military build-up or movement, detecting ballistic missiles, differentiating camouflaged enemy tanks from their surroundings and detecting ships on the sea.
Some of these remote sensing satellites can provide high resolution images of critical locations on the ground. In an article titled “US national security and government regulations of commercial remote sensing from outer space” — published in Air Force Law Review in 2001 — it was disclosed that high resolution satellite images of nuclear reactors and missile bases of some Asian countries were available in the market.
Remote sensing satellites with radars on board, also called Active Microwave Sensors, can even image important locations at night under all weather conditions. Some famous remote sensing satellites are Landsat, SPOT, IKONOS, Quickbird, CHRIS and Canadian RADARSAT.
In Global Navigation Satellite System (GNSS), the most famous technology in use is called Global Positioning System (GPS); a constellation of 24 American satellites that can provide real-time location information to any user on the Earth with a GPS receiver. GPS is a technology that has numerous applications, but is mainly used by the army, air force and navy for navigational operations and surveying.
However, there are civilian applications too, such as Location Based Services (LBS), surveying, and cartographic applications. The European Union, along with some other participating countries, is launching its own constellation of navigation satellites called Galileo. The Galileo project after completion will consist of 30 satellites.
GPS has a feature called “selective availability”, which when turned on limits the positional accuracy determined by a receiver. Most countries, therefore, are looking forward to Galileo as an alternative.
India, which relies heavily on navigation satellites for network-centric-warfare — such as in the Brahmos Cruise Missile — has entered into a contract with Russia, whereby it can use Glonass, a Russian version of GPS technology.
In South Asia, India is vigorously pursuing a space race and is competing with some developed countries. The Indian Space Research Organization (ISRO) has launched about 30 satellites to date and intends to launch 12 new ones in the next few years.
The ISRO has not only successfully built satellites but also has developed satellite launch vehicles, which are rockets used to put satellites in their orbits. Its satellite launch vehicle PSLV can launch satellites in polar orbits and for geosynchronous satellites, it is developing the GSLV project.
Its satellites include INSAT and GSAT series of satellites for communications, IRS and Resource-Sat for remote sensing, Cartosat for cartographic mapping, besides a microwave remote sensing satellite.
The Pakistan Space and Upper Atmosphere Research Commission (Suparco) is currently working on the Paksat-1R Satellite, following the Badar series. In the meantime an American satellite HGS-3 has been named Paksat-1 and is presently in use.
A project called SAINT (Satellite Assembly, Integration and Test) has been launched to promote indigenous development of satellite subsystems, their integration and testing. Pakistan also has built some ground receiving stations to receive data from certain commercial satellites.
The importance of search and rescue satellites has not been ignored by Suparco and ground receiving stations for Local User Terminal (LUT) and a Mission Control Centre (MCC) have been established in Lahore. Pakistani engineers and scientists, specifically the Satellite Research and Development Centre team, are working diligently to foster the indigenous development of satellites.
Nonetheless, it would be a grave mistake not to realize that we are lagging behind many other developing nations in this technology and we need to redouble our efforts. It is imperative for Pakistan to own and operate satellites specifically developed to meet its national defence and civilian needs.
Satellite technology, like nuclear capability, is no longer a luxury. It has become a necessity and a more proactive approach is needed to cope with the challenges associated with this field. The following are some of the recommendations that may boost our space programme:
— There should be an effective coordination between Suparco and the leading engineering universities. Final year students in electrical engineering, mechanical engineering, computer engineering, metallurgy and physics should be assigned at least one project each in satellite technology;
— Small groups of three universities each, based on their geographical proximity, should be formed and they should be assigned joint projects, with the Satellite Research and Development Centre acting as the central administrative hub;
— A new magazine for satellite technology must be launched that gathers research papers from all the universities and research institutions working on projects related to satellite and space technology. This will help form a common information pool;
— An annual competition be instituted for research publications, undertaken by students as well as researchers. The winners be given due recognition, making it desirable for individuals to participate in the competition;
— The Higher Education Commission (HEC) should grant more PhD scholarships to the students who wish to pursue research in space sciences and related fields;
— The ministry of defence should set up a defence remote sensing centre to probe into the different applications of satellite remote sensing, specifically focusing on Satellite Microwave Remote Sensing technologies, such as the Synthetic Aperture Radar (SAR). A research study should also be conducted for devising techniques to protect sensitive sites from foreign remote sensing satellites;
— The curricula for certain degrees should be amended to add important subjects, such as astrodynamics, satellite geodesy, satellite navigation and satellite communications engineering, and;
— Leading businessmen may also play an active role in developing satellite programmes by providing university students and faculty members with the funds required to carry out research projects.
The development and deployment of satellite systems require an immense amount of research, besides the expensive electronic and mechanical equipment needed to build one. On top of that, there is a launching cost as well. Even the most modest satellites can cost millions of dollars.
However, this enormous cost is well justified, keeping in view the benefits the technology offers. It is important to realize that indigenous satellite technology development programme in Pakistan is currently in its primitive stages and needs a major impetus.
The Satellite Research and Development Centre (SRDC), besides the other wings of Suparco, is already doing a highly commendable job. Nevertheless, it would be a mistake to ignore the challenges of the long journey that lies ahead.
The writer is a research assistant at the University of New South Wales in Australia
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