Telecommunication
Table of Content
Introduction:
- This subsystem helps you in setting of connection between Ground station and Satellite.
- It consists of two important links: Uplink and Downlink.
- The communication links are also used for tracking the spacecraft by measuring the angular position of the downlink signal by Doppler measurements and by ranging or two-way Doppler.
Design Challenges:
The telecommunication challenges for Low Earth Orbit (LEO) missions vs. deep space missions are very different.
- In LEO, ground-antenna gain can compensate for limited onboard antenna gain and radio power and CubeSats can manage limitations of power generation and thermal dissipation by duty-cycling high-power components.]
- Most LEO CubeSats rely on UHF and/or S-band radios to receive commands or transmit telemetry back to Earth’s ground station. There are only few radios available at X-band or Ka-band.
- Antenna Design for CubeSats is major challenge.
- X/ Ka band Communication Board design is another challenge to work on.
- Noise and Interference accommodation while designing is major challenge.
Components of Communication Subsystem:
1. Link Budget Design:
- Link Budget is accounting of all the gains and losses from the transmitter, through the medium (free space, cable, waveguide, Fiber, etc.) to the receiver in a telecommunication system.
- It accounts for the attenuation of the transmitted signal due to propagation, as well as the antenna gains, feedline, and miscellaneous losses.
- A simple link budget equation looks like this:
Received Power (dB) = Transmitted Power (dB) + Gains (dB) − Losses (dB)
References:
- Element of Spacecraft design: Charles D. Brown
- CubeSat Antenna Design by Nacer Chahat
2. Communication Board Design:
- It consists of selection of different components for Transmitter and Receiver design.
- Shown below typical ground Receiver schematic.
- Selection of Power Amplifier, IC, Band in which we are going to transmit, etc while designing this board is important step to keep in mind.
- Shown Below UHF board Designed at SSPACE:
3. Antenna Design:
- Existing antenna technologies for CubeSats, we will classify them in the following categories: LGAs (<8dBi)-Low Gain Antennas, MGAs (<25dBi)-Medium Gain Antennas and high-gain antennas (>25 dBi).
- Usually CubeSats mission uses dipole, Microstrip Patch Antennas.
- New concept of Antennas are Foldable antennas based on ORIGAMI concept.
References:
- CubeSats Antenna Design: Nacer Chahat
- Magellan Communication System Example: From Element of Spacecraft chapter 9
NOTE:
- Watch Lectures from Nanosat material: Lecture No. 10, 11, 12, 13 for basic of this subsystem.
- Link Budget: Lecture-24 and Chapter 9 from Element of Spacecraft last part.