Lecture 2, Space Segment

Presentation / Lecture 2, Space Segment

Date Submitted: 06 June 2001

Written by RPC Telecommunications Ltd.. Website: http://www.rpctelecom.com

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This is the second in the series of general satcom tutorial lectures submitted by RPC Telecommunications.

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-Section 1
Orbit Theory: Kepler's Laws.
-Section 2
Orbit Theory: Formulae.
-Section 3
The Real World.
-Section 4
Types & Implications of Orbit.
-Section 5
Satellite Hardware.
-Section 6
Launch Vehicles.
-Section 7
Flight Plan & Maintaining Satellite In Orbit.
-Section 8
Stationkeeping & Stabilisation.

Sensor Technology

Sun Sensors
  • Cosine Detector

  • Digital Sensor

Spinning Earth Sensor (Earth Horizon Telescope)

Reaction Devices
Gas Thrusters
  • provides stabilisation, stationkeeping and attitude control
  • single or bi-propellant fuel (hydrazine + catalyst, monomethyl hydrazine + oxidiser - nitrogen tetroxide)
  • significant impulses may be generated for major orbit manoeuvres, also suitable for small impulse attitude control
  • but, quantity of fuel is limited by launch mass - more fuel means less payload

Momentum Wheels

  • primarily for stabilisation/attitude control
  • one, two or three axis stabilisation

Reaction Wheels (e.g. Olympus)

  • need gas thrusters for "momentum dumping"

Spin Stabilisation

  • alternative method to provide stabilisation/attitude control
  • antennas must be despun through BAPTA which is a possible single point failure mechanism
  • only provides stabilisation in one axis so other devices (usually gas thrusters) are still required

Ion Thrusters

  • of increasing interest - no on-board fuel
  • only provide low impulse thrust but over an extended period
  • technology not yet proven for space use

Other Approaches

  • solar sails
  • magnetic coils
  • gravity gradient
Gas Thrusters
Mono-propellant system:

Rubber diaphragm or capillary action used to ensure fuel is expelled from output pipe. Heaters are used to increate specific impulse.

Bi-propellant system:

Commonly used for both apogee motor and stationkeeping. Tanks commonly oversized and fuel added until satellite has specified wet mass.


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