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Department of Electrical and Electronic Engineering
University of Peradeniya
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Department of Electrical and Electronic Engineering
University of Peradeniya

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Peradeniya Alumnus Is Behind Sri Lanka's First Ever Satellite Launched

 

What is a nanosatellite?

Smarter and greener energy technologies are expected replace the legacy power network in near future. Variety of innovative technologies, system architectures and market models are being investigated in order to significantly reduce the carbon footprint of the energy sector. This project investigates the advantages of active participation of customers in energy market through a customer friendly plug & play system architecture. Where, aggregated Distributed Energy Resources (DER) like solar PV, Electric Vehicles and controllable loads in customer domain are controlled in an optimal fashion to minimize carbon emission while ensuring customer satisfaction. In this project, in addition to developing the required optimization algorithm, the study was extended to model the effects of random communication delays on the aggregated output of DERs using applied probability theory.

A satellite can be viewed as an intelligent robot orbiting the earth. Although the satellites orbit at hundreds of kilo meters from the earth at incredible speeds (Ravana-1 orbits at a speed of 25,200 Km per hour at an altitude of 400 km), they can listen to and instantly act upon commands transmitted from a ground station. For example, an operator at a ground control station can type a command to re-boot the OBS of a satellite orbiting hundreds of km from the earth just as you reboot a computer in front of you!


A good insight into how a satellite functions can be obtained by considering an example. Consider how a satellite records an image. First of all to record an image, the camera on-board the satellite should be facing the side of the earth illuminated by the Sun. How does the satellite find this information? The answer is that every satellite is equipped with a device called “Sun sensor”. Signals from the Sun sensor are interpreted by the OBS and the satellite can verify whether it is in the shadowed region of earth or not. Moreover, to record an image the satellite camera should correctly pointed towards the earth. This means that the satellite should be free of any rotational movements. This is ensured by the ADCS circuitry. The rotations of the satellite are measured by on-board gyroscopes. As nanosatellites do not use any liquid or solid fuel, control of the satellite is done by sending currents through a system of coil which crosses the magnetic field of the earth at very high speeds (25,200 km per hour in the case of Ravana-I). Calculation of currents to the coils to correct any rotations is based on the gyroscope and Sun sensor readings. This is done by the ADCS using a control algorithm.

 


Challenge of Ravana-I

Designing electronic circuits for satellites faces 4 unique challenges.

  1. The circuits should function under extreme temperatures. Nanosatellites are subjected to temperatures as cold as -200 C when under the shadow of the earth and temperatures as high as +1000 C when facing the Sun.
  2. The circuits should withstand extremely high vibrations. The vibrations during the launch of a satellite usually range around 10 times the gravitational acceleration.
  3. The ordinary electronic circuits use heat sinks which rely on thermal convection to carry excess heat generated in electronic components. As nanosatellites operate in a near vacuum, special techniques are needed for the thermal management.
  4. Radiation issues. This is less of an issue for nanosatellites and these satellites operate at low altitudes.

Therefore, development of a satellite demands not only unique design approaches but also test procedures to confirm performance prior to launch.


Impact of the project

Ravana-I marks the successful completion of the 1st sage of a long term project of the Aruthur C Clarke Institute for Modern Technology (ACCIMT), Sri Lanka. This project has been carried out in collaboration with the Kyushu Institute of Technology, Japan which has resulted in a direct technology transfer. Although technically advanced, design of nanosatellites provides a low cost path to acquire space technology. At present, the cost of a nanosatellite stands around US$ 50,000/= which is within the reach of a developing country. However, the benefits of designing a nanosatellites are many. Few of the potential benefits are listed below.

  • The level of advanced training received by the design team can be utilized to improve the quality of products developed in Sri Lanka which will have a direct impact on our local and export markets. For example, the technical know-how acquired in designing satellite circuitry to withstand extreme conditions can be used to produce robust products.
  • Products of a country capable of producing space qualified products has more acceptance in international markets.
  • Nanosatellites can be used to monitor activities such as deforestation.
  • Nanosatellites provide a reliable communication link that can be used for telemetry applications. For example, nanosatellites can be combined with ground based sensors to monitor and control floods. 
 

 

Professional Organizition

PHES IEEE IESL IET

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