Satellites what they do and how they work
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SATELLITES What They Do and How They Work. Michael J. Mackowski Aerospace Engineer October 2013 With Updates from Shawn Shepherd. What Satellites Do. Types of Satellite Missions: Weather Communications Navigation Scientific Planetary Military. Weather Satellites. GOES 10.

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Satellites what they do and how they work

SATELLITESWhat They Do andHow They Work

Michael J. Mackowski

Aerospace Engineer

October 2013

With Updates from Shawn Shepherd


What satellites do

What Satellites Do

  • Types of Satellite Missions:

    • Weather

    • Communications

    • Navigation

    • Scientific

    • Planetary

    • Military

2


Weather satellites

Weather Satellites

GOES 10

3


Science satellites

Science Satellites

Landsat Data Continuity Mission (LDCM)

Gamma Ray Large Area Space Telescope (GLAST or Fermi)

Tropical Rainfall Measuring Mission (TRMM)

4


Science satellites1

Science Satellites

Hubble Space Telescope

Tropical Rainfall Measuring Mission (TRMM)

Hubble Space Telescope

Gamma Ray Large Area Space Telescope (GLAST or Fermi)

5


Military satellites

Military Satellites

Hexagon Photo Reconnaissance Satellite

Defense Support Program

6


Interplanetary satellites

Interplanetary Satellites

Voyager

Mars Exploration Rovers:

Spirit and Opportunity

7


Communications satellites

Communications Satellites

Superbird 6

Tracking and Data Relay Satellite

Hughes/Boeing 376

8


How satellites work

How Satellites Work

  • All satellites have:

    • 1. Bus Structure - This is the platform where all the equipment is mounted.

    • 2. Subsystems - This equipment is required to keep the satellite running.

      Electrical power

      Temperature control

      Commands and Telemetry (data)

      Attitude Control for pointing

      Communication

      Propulsion for moving

9


How satellites work1

How Satellites Work

  • All satellites have:

    • 3. Payloads - Theses are different for each satellite, depending on its mission.

      • Sensors:Video camera

        Thermal camera

        Radar

        Scientific sensors

        Telescopes

      • Other:Telecommunication equipment

        Navigation equipment

        Laser equipment

10


The basic idea is

The Basic Idea is…

  • Satellites collect data and send it back to Earth

    • Collecting data about weather, scientific topics, land use, military interest, etc.

    • Relaying data for communications and navigation

11


Parts of a satellite

Parts of a Satellite

  • All of the different types of spacecraft have certain elements in common.

  • They are implemented in different ways depending on the mission requirements.

  • These elements are:

    • Structure

    • Payload (seen on previous charts)

    • Subsystems (seen on following charts)

      Electrical power

      Temperature control

      Command and data handling

      Attitude control (pointing) and knowledge

      Communication

      Propulsion

12


Structure

Structure

  • A frame, usually aluminum or composite, is used to mount everything

  • Has to be built to withstand the forces of launch

13


Electrical power

Electrical Power

  • Most satellites convert solar energy to electricity via solar panels similar to the ones on houses.

    • Fixed panels

    • Oriented panels (follow the sun)

    • Cylindrical (for spinning satellites)

  • Batteries are needed when the sun is eclipsed.

Nickel hydrogen battery

Solar array

14


Electrical power1

Electrical Power

  • The more power (equipment) you need the bigger the solar arrays have to be.

  • They also get larger the further you travel from the Sun.

  • Nuclear options include:

    • RTG: radioisotope thermal generators

    • Nuclear reactor (very high power)

15


Thermal control

Thermal Control

  • It is cold in space but the electronic equipment on the satellite generates heat.

  • The temperature must be balanced or the equipment will fail.

  • The object is to keep everything at a nice constant temperature.

  • Insulation blankets

  • Heaters

  • Radiators (flat shiny areas to reflect or dump heat)

Heaters

Swift satellite with various types of surfaces

16


Propulsion

Propulsion

  • Once in orbit, you need it for:

    • Changing orbits

    • Leaving Earth orbit

    • Maneuvers at other planets

    • Re-entry

    • Pointing and steering

  • Types of rocket fuel:

    • Liquid oxygen and liquid hydrogen

    • Solid chemicals

    • Hydrazine (single propellant)

Prop tank

17


Pointing

Pointing

  • Most satellites are “3-axis stabilized” satellites

    • Gyroscopic Reaction Wheels are used for fast movement

    • Electromagnetic Torque Rods ‘grab’ the Earth’s magnetic field for tighter control

  • Sensors are needed to determine which way the satellite is pointed.

    • Star trackers look at the stars

    • Sun sensors look at the sun

Reaction wheel

Torque rod

18


Command and data

Command and Data

  • On-board computer is used for:

    • Data collection

    • Command distribution

    • Control of payloads and equipment

    • Memory for programmed sequences

    • Emergency procedures

  • Data recorder

    • Stores data for later playback

Electronics Module

19


Communications

Communications

  • Receiver antennas and transmitters are used to ‘talk’ to the satellite with radio waves from the mission control center

  • Receives commands and transmits data to Earth

S-band antenna

Cassini high gain antenna

X-band antenna

20


Putting it together

Putting It Together

  • Every kind of spacecraft has some combination of these features.

  • How they are organized, and which ones are more critical, largely determines what the spacecraft looks like.

21


Design process

Design Process

MISSION

POINTING

POWER SOURCE

PAYLOAD LOCATION

SUBSYSTEM LOCATION

22


Design process1

Design Process

First you understand the mission: destination, duration, type and quantity of payloads

MISSION

POINTING

POWER SOURCE

PAYLOAD LOCATION

SUBSYSTEM LOCATION

23


Design process2

Design Process

MISSION

The payloads will determine which way the spacecraft points and how accurately you must maintain that pointing.

POINTING

POWER SOURCE

PAYLOAD LOCATION

SUBSYSTEM LOCATION

24


Design process3

Design Process

MISSION

POINTING

That will set where the payloads (instruments) are located relative to the other equipment

POWER SOURCE

PAYLOAD LOCATION

SUBSYSTEM LOCATION

25


Design process4

Design Process

MISSION

The next biggest driver is the power source, typically solar arrays. They are large and must not block the view of the instruments.

POINTING

POWER SOURCE

PAYLOAD LOCATION

SUBSYSTEM LOCATION

26


Design process5

Design Process

MISSION

POINTING

POWER SOURCE

PAYLOAD LOCATION

All of the remaining subsystems are located on the bus structure. This rarely drives the overall layout of the satellite.

SUBSYSTEM LOCATION

27


Satellite features

Satellite Features

  • The end result will vary depending on the type of satellite (mission)

28


Put it all together

Put It All Together

  • Build it, test it, launch it.

29


Put it all together1

Put It All Together

  • Collect data and transmit it back to Earth

Fermi Gamma Ray Observatory

30


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