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Table of Content

  1. Introduction
  2. Design Challenges
  3. Components of communication subsystem
  4. Reference

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:

  • 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:

  1. Element of Spacecraft design: Charles D. Brown
  2. 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:

  1. CubeSats Antenna Design: Nacer Chahat
  2. Magellan Communication System Example: From Element of Spacecraft chapter 9

NOTE:

  1. Watch Lectures from Nanosat material: Lecture No. 10, 11, 12, 13 for basic of this subsystem.
  2. Link Budget: Lecture-24 and Chapter 9 from Element of Spacecraft last part.