User:VITSAT

SEDS VIT CubeSat Student Satellite Programme is an initiative taken by the SEDS (Students' for Exploration and Development of Space) students' chapter at VIT University, Vellore, India. It aims at building a series of picosatellites under the name of VITSAT.

A CubeSat is a picosatellite of the dimensions 10 x 10 x 10 cm^3 and weighing no more than 1 kilogram. These standards have been specified by the CalPoly Cubesat Programme who have been pioneers in building such satellites.

The current mission under this programme is VITSAT-1. The work on VITSAT-1 started in January 2007, by a group of 20 students. The division of the system is as follows:

1. Attitude Control and Determination Subsystem. (ADC)

2. Command and Data Handling Subsystem. (CDH)

3. Communication Subsystem. (COM)

4. Power Subsystem. (POW)

5. Structure, Mechanisms and Thermal Subsystem. (SMT)

6. Payload Subsystem. (PLD)

The satellite will be placed in polar sun synchronous orbit and its orbital time will be approximately 96 minutes which amounts to 15 revolutions everyday.

The main operational modes of the satellite after the launch vehicle takes off will be as follows:

A. Boot Mode

1. Satellite Deployment from the Launch Vehicle

2. Batteries are switch on using the kill switch

3. On board CDH system boots.

4. ADC de-tumbling mode.

5. End of ADCS de-tumbling mode. Interrupt sent to CDH

6. Deployment of Antennae

7. ADC de-tumbling mode to orient the antennae in proper direction.

8. Wait for the first signal to be received from the ground station. 9. End of initial boot mode.

Note: The above modes occur only once in the lifetime of the satellite. The following modes reoccur as and when the conditions demand so.

B. Battery Charge Mode

10. ADC points the solar cell to the sun.

11. POW is on. COM is off. 12. Batteries are charged.

13. End of this mode is occurs on full battery charging and is identified by an interrupt signal from the POW to CDH.

C. Power Save Mode and Emergency mode

14. ADC, POW and COM are switched off

15. CDH is operated at minimal power

16. Once the batteries are charged as indicated in mode B, mode C also ends. .

D. Camera Shoot Mode

17. ADC points the camera to the earth horizon whose picture has to be taken.

E. Communication Mode

18. ADC points the antennae in the direction in which it can effectively communicate with the earth station.

Note: the satellite enters this mode only when it is in that part of its orbit path which is around the ground station. This occurs 3 times in every 24 hours.

Note: In case the satellite completely shuts down, it has to wait till enough power is generated by the solar cells and the modes begin from number 3 with the rebooting of CDH. The thermal system is independent of the above modes as it is essentially passive and has only one active element the electrical heater for sensitive components like the battery and the camera module .

The primary tasks of each of the above are as follows:

ADC:

1. Measure and Control the orientation of the satellite once it is in orbit.

2. Provide necessary pointing accuracy to the antennae during the communication mode.

3. Face the solar panels towards the sun during the power save mode.

4. Control the angular rotation of the satellite to prevent high spin rates that may damage the satellite structure or decrease its lifetime due to the developed stresses.

It achieves the above mentioned tasks by measuring the orientation of the satellite using sensors (magnetometers) and performing control operations using actuators (magnetorquers).

CDH:

1.Perform command and data handling operations in the satellite and hence control the same while it s out of the range of the ground station.

2. Monitor and maintain the housekeeping data of the other subsystem of the satellite and the general health of the satellite.

3. Provide operation sequences to various subsystems.

4. Perform subsystems control, communication with the ground station, data and software storage in allocated memories, fault detection and management, telemetry stream generation, data uplink and downlink feature etc.

5. Provide interfacing among all the subsystems.

COM:

1. To provide uplink and downlink between the ground station and the satellite by using TNC (terminal node Controller), transceiver, antennae etc.

2. To calculate the link budget, BER (bit error rate) and other parameters based on the frequency chosen.

3. Choose the antennae to be used.

POW:

1. To generate, store, regulate and distribute electrical power supply to all components.

2. To choose solar cells for power generation.

3. To choose batteries for power supply in the eclipse zone.

4. To desing a circuit to connect all components on the power grid.

STM

1. To design a robust and a light weight mechanical structure and arrangement of all components in the satellite.

2. To ensure smooth functioning of mechanisms of satellite deployment from the launch vehicle, power on the satellite by means of a kill switch and deployment of antennae.

3. To maintain overall thermal balance of the satellite and it components within the optimum temperature range.

4. To do the above within the standard specifications of CalPoly CubeSat design specifications

PLD

1. To use a cmos/ccd camera to capture images of the horizon of the earth(blue) in the background of space(black).