SATELLITESWhat They Do and

How They Work

Michael J. MackowskiAerospace Engineer

October 2013

With Updates from Shawn Shepherd

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What Satellites Do

• Types of Satellite Missions: Weather Communications Navigation Scientific Planetary Military

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Weather Satellites

GOES 10

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Science Satellites

Tropical Rainfall Measuring Mission (TRMM)Gamma Ray Large Area Space Telescope (GLAST or Fermi)

Landsat Data Continuity Mission (LDCM)

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Science Satellites

Tropical Rainfall Measuring Mission (TRMM)

Gamma Ray Large Area Space Telescope (GLAST or Fermi)

Hubble Space Telescope

Hubble Space Telescope

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Military Satellites

Defense Support Program

Hexagon Photo Reconnaissance Satellite

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Interplanetary Satellites

Voyager Mars Exploration Rovers: Spirit and Opportunity

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Communications Satellites

Tracking and Data Relay Satellite

Superbird 6

Hughes/Boeing 376

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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 powerTemperature controlCommands and Telemetry (data)Attitude Control for pointingCommunicationPropulsion for moving

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How Satellites Work• All satellites have:

3. Payloads - Theses are different for each satellite, depending on its mission. Sensors: Video camera

Thermal cameraRadarScientific sensorsTelescopes

Other: Telecommunication equipmentNavigation equipmentLaser equipment

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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

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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 powerTemperature controlCommand and data handlingAttitude control (pointing) and knowledgeCommunicationPropulsion

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Structure

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

• Has to be built to withstand the forces of launch

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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 batterySolar array

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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)

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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 blanketsHeatersRadiators (flat shiny

areas to reflect or dump heat) Swift satellite with various

types of surfaces

Heaters

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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

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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 wheelTorque rod

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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

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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

Cassini high gain antenna

X-band antenna

S-band antenna

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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.

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Design Process

MISSION

POINTING

POWER SOURCE PAYLOAD

LOCATION

SUBSYSTEM

LOCATION

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Design Process

MISSION

POINTING

POWER SOURCE PAYLOAD

LOCATION

SUBSYSTEM

LOCATION

First you understand the mission: destination,

duration, type and quantity of payloads

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Design Process

MISSION

POINTING

POWER SOURCE PAYLOAD

LOCATION

SUBSYSTEM

LOCATION

The payloads will determine which way the spacecraft points

and how accurately you must maintain that

pointing.

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Design Process

MISSION

POINTING

POWER SOURCE PAYLOAD

LOCATION

SUBSYSTEM

LOCATION

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

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Design Process

MISSION

POINTING

POWER SOURCE PAYLOAD

LOCATION

SUBSYSTEM

LOCATION

The next biggest driver is the power source,

typically solar arrays. They are large and must not block the view of the

instruments.

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Design Process

MISSION

POINTING

POWER SOURCE PAYLOAD

LOCATION

SUBSYSTEM

LOCATION

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

satellite.

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Satellite Features

MISSION WEATHER COMM SCIENCE PLANETARY MILITARYPoints Down Down Anywhere At the planet Down

How long? Always Always Various Most of the time

Always

Spinner OK OK Not usually Not usually Not usually

Stabilized OK OK Better Better Better

Orbit Polar Equatorial Various Interplanetary

Polar, usually

Life > 7 years > 7 years 3-5 years 3 - 10 years 3 -7 years

Payloads Cameras Transmitters,Receivers,Data recorder

Sensors, Cameras,Telescopes

Sensors, Cameras,Telescopes

Sensors, cameras, listening electronics

Special Long life Stability Long cruise Hardening

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

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Put It All Together• Build it, test it,

launch it.

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Put It All Together

• Collect data and transmit it back to Earth

Fermi Gamma Ray Observatory