SATELLITES What They Do and 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  Planetary  Military

3 Weather Satellites GOES 10

4 Science Satellites Tropical Rainfall Measuring Mission (TRMM) Gamma Ray Large Area Space Telescope (GLAST or Fermi) Landsat Data Continuity Mission (LDCM)

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

6 Military Satellites Defense Support Program Hexagon Photo Reconnaissance Satellite

7 Interplanetary Satellites VoyagerMars Exploration Rovers: Spirit and Opportunity

8 Communications Satellites Tracking and Data Relay Satellite Superbird 6 Hughes/Boeing 376

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 moving

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 equipment

11 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

12 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

13 Structure A frame, usually aluminum or composite, is used to mount everything Has to be built to withstand the forces of launch

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 array

15 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)

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 Heaters

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 hydrogen  Solid chemicals  Hydrazine (single propellant) Prop tank

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 rod

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 recorder  Stores data for later playback Electronics Module

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 antenna

21 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.

22 Design Process MISSION POINTING POWER SOURCE PAYLOAD LOCATION SUBSYSTE M LOCATION

23 Design Process MISSION POINTING POWER SOURCE PAYLOAD LOCATION SUBSYSTE M LOCATION First you understand the mission: destination, duration, type and quantity of payloads

24 Design Process MISSION POINTING POWER SOURCE PAYLOAD LOCATION SUBSYSTE M LOCATION The payloads will determine which way the spacecraft points and how accurately you must maintain that pointing.

25 Design Process MISSION POINTING POWER SOURCE PAYLOAD LOCATION SUBSYSTE M LOCATION That will set where the payloads (instruments) are located relative to the other equipment

26 Design Process MISSION POINTING POWER SOURCE PAYLOAD LOCATION SUBSYSTE M LOCATION The next biggest driver is the power source, typically solar arrays. They are large and must not block the view of the instruments.

27 Design Process MISSION POINTING POWER SOURCE PAYLOAD LOCATION SUBSYSTE M LOCATION All of the remaining subsystems are located on the bus structure. This rarely drives the overall layout of the satellite.

28 Satellite Features MISSIONWEATHERCOMMSCIENCEPLANETARYMILITARY PointsDown AnywhereAt the planetDown How long?Always VariousMost of the time Always SpinnerOK Not usually StabilizedOK Better OrbitPolarEquatorialVariousInterplanetaryPolar, usually Life> 7 years 3-5 years years3 -7 years PayloadsCamerasTransmitters, Receivers, Data recorder Sensors, Cameras, Telescopes Sensors, Cameras, Telescopes Sensors, cameras, listening electronics SpecialLong lifeStabilityLong cruiseHardening The end result will vary depending on the type of satellite (mission)

29 Put It All Together Build it, test it, launch it.

30 Put It All Together Collect data and transmit it back to Earth Fermi Gamma Ray Observatory