STUDSAT – An Undergraduate Satellite Initiative
by Divya Shankar
Divya Shankar is a student designer involved with Project Icarus. Divya is doing a Bachelor of Engineering in Electronics and Communication Engineering at Nitte Meenakshi Institute of Technology, Bangalore, India. And will be graduating in June 2012. She is a self-admitted space buff and loves space technology. She has recently been working in a project called STUDSAT (www.teamstudsat.com ), which is a Student satellite project in collaboration with ISRO (Indian Space Research Organization) and has been working on this since her 1st year of her engineering degree. Divya writes about her experience on STUDSAT. STUDSAT is a student satellite built by 30 undergraduate students from across India. It’s a PICO satellite, weighing less than 1 Kg, volume of 1.1 litres, designed to operate in low Earth Orbit (LEO) at an altitude of 680Km. The Payload of the Satellite was a CMOS camera capable of capturing images with a ground resolution of 90 meters approximately, the best achieved by any ‘Pico’ category satellite in the world. The satellite was designed to send the image and telemetry data from the orbit to the ground station. The mission life was estimated as six months.
The Pico-category is the first of its kind in India and it is now the smallest satellite ever launched by an Indian organization. Being an experimental mission, its major objective was to enable students to acquire first hand experience on the designing, fabrication and realization of a space mission at a minimum cost and to perform functions carried out in remote sensing applications. It all began in IAC, 2007 held at Hyderabad, India. Few friends who had attended the conference were inspired by the talk of the scientist from ISRO about building mini-satellites in the universities. Then the group of students joined together approached the respective college managements and ISRO scientists and got the approval of building a satellite with the collaboration of 7 colleges across South India and ISRO. MOU (memorandum of understanding) was signed by all the colleges and ISRO and the project was funded. The satellite building started in 2008 and it took almost 2 and 1/2years for the completion of the project. Satellite!!! Building it!!! These expressions were recipients of our exclamations during the initial days. We were very excited with the whole idea and surely many of us have lost sleep dreaming about it like it was a film star. Lots of thoughts, questions and suggestions were running marathons in our heads. Suddenly in between a class an idea would spring in our heads and our faces would glow like CFL bulbs (trying to be eco-friendly here). Thoughts about how would we build it, the instruments we would be using, making the prototype, testing it and the biggest attraction – to enter ISRO were constantly in our heads. Although some of us did not have a clue about it in the beginning, there was still an element of excitement when we embarked on this journey and for the rest, the feeling cannot be put down on paper. Guess we never knew the maximum extent to which Google could be used until we took up this project. The work started exactly the way the satellites are built in ISRO or any space agency. The Satellite had all the subsystems which are present in the bigger satellites. The subsystems were: 1. Payload 2. Structure 3. Attitude determination and control: 4. Onboard communication 5. Onboard command and data handling 6. Electronic power systems 7. Ground station My role in the project: I worked in the ground station subsystem which is named as NASTRAC (Nitte Amateur Satellite Tracking Centre). NASTRAC: • The main objective of NASTRAC was to track the amateur satellites orbiting in lower earth orbit and to establish a communication link with the satellites. • To test some of the in-house developed software on the data received from the satellites • To process the data received from the satellite to display the health monitoring parameters and the image captured. My work in ground station: 1. LNA: LNA is a low noise amplifier designed to increase the signal strength and cancel the noise component. The design was based on a proper signal to noise ratio with the noise figure and gain of LNA. The signal received is given to LNA, which has a gain of 23dB and a noise figure of 0.6dB 2. Antenna design and simulation: The antenna system used is a quad-stacked array of circularly polarized Yagi-Uda antenna with a gain of 16dbi.Each array has 6 directors,1 driven element and 1 reflector. It can operate in a band-width between 435MHz to 440MHz. The antenna system is mounted on AZ/EL rotor. The azimuth rotor can move from 0 to 360 deg (geographic North is considered as 0 deg and angle measure is done in clockwise direction), the elevation rotor can move from 0 deg to 180 deg. The rotor controller is interfaced to the software. 3. Transceiver and TNC: Transceiver is used to transmit and receive the signal. It is a UHF/VHF transceiver capable of transmission power up to 75 watts at UHF and 100 watts at VHF. The demodulated data will be sent to Terminal Node Controller that acts like a modem and performs the packet radio protocol to retrieve the data sent by the satellite. 4. Tracking system: In a satellite tracking system the control system should be able to command the basic ground station hardware such as the antenna and the radio. The satellite tracking should be autonomous to track the satellites based on some configuration files. Due to predictable condition of the satellite movement in the space, the satellite tracking system can calculate a satellite position can be done based on known orbit parameters such as Two Line Element (TLE). In order to keep the satellite tracking working precisely, the system should provide Doppler correction to update the frequency of the ratio. For these applications two softwares such as NOVA and HRD are used. Establishing a communication link: The RF signal is received by the quad-stacked circularly polarized Yagi-Uda antenna and passed through a LNA. The RF signal is then given to a transceiver which demodulates the frequency modulated signal in the case of image and telemetry downlink and continuous wave demodulation in the case of beacon signal.The image and telemetry is modulated using Frequency Shift Keying at a baud rate of 2400bps and the beacon data transmitted uses continuous wave modulation. The Image and telemetry output of the transceiver which is a FSK data is given to a modem which demodulated the FSK signal and gives a stream of binary data which is then given to a micro-controller to extract the image and telemetry data from the data frame. LAUNCH: The entire team was involved completely in to this, working over nights, staying back in college for days together and finally the day was fixed for the launch. ISRO decided to put the satellite on orbit with ISRO built CARTOSAT-2B. Finally on JULY 12th 2010 the satellite was launched from SHAR-Sathish Dhawan Space Centre, Shriharikota. It was put on orbit by PSLV C15 along with other 4 satellites.
Since there is restriction for the number of people to be allowed for the launch place, the team was divided in to 3 groups. 1 group in the NASTRAC (ground station built by us), 1 group in SHAR (the launch place) and 1 group in ISTRAC (ISRO Satellite Tracking and Commanding centre) I got an opportunity to experience the launch from ISRO’s ISTRAC in the midst of scientists of high rank. The experience is incredible. We received the beacon and the telemetry data from the satellite. This is proved as many HAMS around the world also received it. As a legacy we are started with STUDSAT-2. This time its building of two satellites and establishing inter satellite communication. I have taken up onboard communication to work in the second one. So A long way to go…