How They Work Michael J Mackowski Aerospace Engineer October 2013 With Updates from Shawn Shepherd 2 What Satellites Do Types of Satellite Missions Weather Communications Navigation Scientific ID: 631570
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SATELLITES
What They Do andHow They Work
Michael J. Mackowski
Aerospace Engineer
October 2013
With Updates from Shawn ShepherdSlide2
2
What Satellites Do
Types of Satellite Missions:
Weather
Communications
Navigation
Scientific
Planetary
MilitarySlide3
3
Weather Satellites
GOES 10Slide4
4
Science Satellites
Tropical Rainfall Measuring Mission (TRMM)
Gamma Ray Large Area Space Telescope (GLAST or Fermi)
Landsat Data Continuity Mission (LDCM)Slide5
5
Science Satellites
Tropical Rainfall Measuring Mission (TRMM)
Gamma Ray Large Area Space Telescope (GLAST or Fermi)
Hubble Space Telescope
Hubble Space TelescopeSlide6
6
Military Satellites
Defense Support Program
Hexagon Photo Reconnaissance SatelliteSlide7
7
Interplanetary Satellites
Voyager
Mars Exploration Rovers:
Spirit and OpportunitySlide8
8
Communications Satellites
Tracking and Data Relay Satellite
Superbird 6
Hughes/Boeing 376Slide9
9
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 movingSlide10
10
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 equipmentSlide11
11The Basic Idea is…
Satellites collect data and send it back to EarthCollecting data about weather, scientific topics, land use, military interest, etc.Relaying data for communications and navigationSlide12
12Parts 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:StructurePayload (seen on previous charts)Subsystems (seen on following charts)
Electrical power
Temperature control Command and data handling Attitude control (pointing) and knowledge Communication PropulsionSlide13
13
Structure
A frame, usually aluminum or composite, is used to mount everything
Has to be built to withstand the forces of launchSlide14
14
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 arraySlide15
15Electrical PowerThe 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 generatorsNuclear reactor (very high power)Slide16
16
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)
Swift satellite with various types of surfaces
HeatersSlide17
17
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 hydrogenSolid chemicalsHydrazine (single propellant)
Prop tankSlide18
18
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 rodSlide19
19
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 recorderStores data for later playback
Electronics ModuleSlide20
20
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 antennaSlide21
21Putting It TogetherEvery 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.Slide22
22Design Process
MISSION
POINTING
POWER SOURCE
PAYLOAD LOCATION
SUBSYSTEM LOCATIONSlide23
23Design Process
MISSION
POINTING
POWER SOURCE
PAYLOAD LOCATION
SUBSYSTEM LOCATION
First you understand the mission: destination, duration, type and quantity of payloadsSlide24
24Design 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.Slide25
25Design Process
MISSION
POINTING
POWER SOURCE
PAYLOAD LOCATION
SUBSYSTEM LOCATION
That will set where the payloads (instruments) are located relative to the other equipmentSlide26
26Design 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.Slide27
27Design 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.Slide28
28Satellite Features
MISSION
WEATHER
COMM
SCIENCE
PLANETARY
MILITARY
Points
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)Slide29
29
Put It All Together
Build it, test it, launch it.Slide30
30
Put It All Together
Collect data and transmit it back to Earth
Fermi Gamma Ray Observatory