Discovering Signal and Data Processing/Analysis Through Satellite Communications

Transcription

1 Discovering Signal and Data Processing/Analysis Through Satellite Communications Dr. Christopher Kitts Robotic Systems Laboratory Santa Clara University, Santa Clara, CA, USA IEEE Senior Member Courtesy Santa Clara University 1 Courtesy NASA

2 Overview Uses, Benefits and Challenges of Spacecraft Space System Functions and Technologies Communications and Data Handling Exploring Spacecraft Signals and Data Analysis 2

3 How We Use Spacecraft Spacecraft perform functions that benefit people in the form of commercial products, governmental services and socially beneficial knowledge Typical spacecraft applications include: Communications: satellites are used to broadcast and relay TV, radio, internet and phone conversations 3 The EchoStar XIV is a Direct Broadcast Satellite that broadcasts television signals, which are received by simple ground antenna systems. (Courtesy Space Systems Loral)

4 How We Use Spacecraft Photography: satellites are used to take photos of the Earth to monitor weather, the health of crops, damage from disasters, and the location of enemies Navigation: satellites are used to provide signals to GPS receivers in order to calculate location on the Earth The GOES satellite takes imagery of large scale weather systems. (Courtesy NOAA) GPS spacecraft transmit signals to receivers on the ground. The receivers use signals from multiple GPS satellites to compute their position. 4

5 How We Use Spacecraft Science: satellites are used to observe remote galaxies and to explore The Hubble Telescope takes photographs the planets in our solar of distant galaxies and astronomical phenomenon. (Courtesy NASA) system Tourism: spaceships are beginning to be used to take humans into space for tourism; this is a relatively new application for space Spaceships such as Spaceship One are being developed to take ordinary people into space as tourists. (Courtesy NASA) 5

6 Benefits of Using Spacecraft Many products and services are created without the use of a spacecraft. So, why are satellite-based systems sometimes the best approach? Global view: From space, large regions of Earth can be seen. This makes it possible broadcast signals across large areas (for navigation and communications) and to monitor large-scale events (like photographing storm systems). 6 From space, entire continents, oceans, and hemispheres can be simultaneously seen. (Courtesy NASA)

7 Benefits of Using Spacecraft Above Earth s atmosphere: Satellites can observe astronomical objects without having to look through the Earth s atmosphere. Because the atmosphere distorts and attenuates light and radio signals, this means that satellites are able to produce higher quality images of planets and galaxies. The atmosphere distorts and removes energy from electromagnetic signals (light, radio, etc.) that are used to observe objects in space. (Courtesy NASA) 7

8 Benefits of Using Spacecraft Space environmental characteristics: The space environment offers microgravity conditions, higher levels of radiation that on Earth, and other characteristics that may be advantageous for the product or service we want to offer. Microgravity is an example of a condition in space that leads to different behaviors in materials and biological systems than those we experience on Earth. This can be useful for studying fundamental phenomena. It can also be useful for applications such as creating new materials. (Courtesy NASA) 8

9 Benefits of Using Spacecraft In situspace characterization and exploration: In order to perform certain types of science, equipment must be placed at the location of interest. This allows a space system to directly measure conditions and interact with objects in the environment of interest. Space-rated rovers are used to explore the surface of Mars. By being located on the planets surface, they can do more than take photos from a distance. For example, the rovers use a tool to chip away at rocks and to study the geology and chemistry of the planet. (Courtesy NASA) 9

10 Challenges of Using Spacecraft There are many challenges that spacecraft must address and which may make it too difficult or costly to use spacecraft for some applications. Challenges include: The space environment: Microgravity, radiation, vacuum conditions, the lack of convection, the outgassingof materials and many other conditions can make designing spacecraft a challenge. In microgravity, objects don t settle into a stable resting position like they do on Earth. (Courtesy NASA) 10

11 Challenges of Using Spacecraft The need for infrastructure: Spacecraft are remotely operating vehicles that must provide their own infrastructure services that we often take for granted. For example, they must generate and store their own power. They must control their own positioning and pointing. They must communicate with us over long distances. And so on. The International Space Station s purpose is to host astronauts in order to perform experiments in space. But to do this, the Station must generate its own power using giant solar arrays, move itself using thrusters, communicate with Earth using large antenna, etc. (Courtesy NASA) 11

12 Challenges of Using Spacecraft Orbital Motion: Most spacecraft orbit the Earth, which means that they are constantly moving in ellipse that has the Earth at one of its foci. As they move, the Earth rotates underneath the spacecraft s path. This complicates their operation, such as often requiring antennae to be continuously realigned in order to provide communications between the spacecraft and ground. This map shows the instantaneous location of several spacecraft above their Earth, and the regions on the Earth for which they have line of sight visibility. Over time, the satellites move with respect to the Earth s surface. This means that the regions of Earth that they can see and the locations of communication stations with which they can communicate will change over time. (Courtesy Santa Clara Univ.) 12

13 Overview Uses, Benefits and Challenges of Spacecraft Space System Functions and Technologies Communications and Data Handling Exploring Spacecraft Signals and Data Analysis 13

14 Space Systems Space systems include everything required to use a satellite for producing a service The satellite itself The launch vehicle that puts it in orbit The communication stations on the ground that are used to relay information to/from the satellite The mission control center where operators command and monitor the satellite Any devices directly used by customers to process satellite broadcasts 14

15 Space System Example Satellite Launch system Orbit Satellite A direct broadcast television satellite in orbit, broadcasting shows to subscribers on Earth User Receiver Television Service Communication Station Control Center 15

16 Satellite System The satellite is often divided into two sections: the payload and the bus Payload: The payload is the component or instrument that is used to create the satellite service. For example: For a photographic satellite, the payload is the camera and lens For a communication satellite, the payload is the multi-channel broadcast system 16 This large mirror is part of the telescope payload in the Hubble Telescope spacecraft. (Courtesy NASA.)

17 Satellite System Bus: The bus includes all of the other subsystems that provide infrastructure services for the payload. These include: Power generation and storage Pointing sensing and control Wireless communications Computation and processing Thermal sensing and control Structural housing and protection This satellite has large solar panels to generate power. Antennae on the bottom side of the satellite are used for wireless communication with the Earth. (Courtesy USAF Research Laboratory) 17

18 Overview Uses, Benefits and Challenges of Spacecraft Space System Functions and Technologies Communications and Data Handling Exploring Spacecraft Signals and Data Analysis 18

19 Communications & Data Handling To operate a spacecraft, information must be routinely transferred to/from the satellite and the ground The information we want to transfer (commands, telemetry, data products, voice) is usually in the form of (relatively) low frequency digital or analog signals Microwave frequency radio waves are generally used to wirelessly transmit this data. During transmission, these waves suffer from noise injection, attenuation and distortion Therefore, the information must be processed and converted in order to prepare it for robust wireless transfer. Once received, it must be converted back to its original form 19

20 Information To Be Transferred 1. Commands Sent from operators on ground to the satellite Digital words (pre-arranged strings of bits: 1 s and 0 s) with specific rules for creating and interpreting the strings in order to specify specific actions Examples of commands include Turn on the payload Switch from Battery A to Battery B Set the Frequency to the Following Value 20

21 Information To Be Transferred 2. Telemetry Sent from the satellite to operators on ground Analog and digital values that convey information about the satellite and which are analyzed to ensure that the satellite is operating properly. Examples of telemetry data includes Battery Voltage Payload Current Computer Temperature 21

22 Information To Be Transferred 3. Data Products Sent from the satellite to users on the ground (sometime via the control center) These are the files or streams of information that constitute the products or services provided by the space system. Examples of data products include: Photographic files (for photographic satellites), Television broadcasts or phone conversations (for communication satellites), Files of experimental data (for scientific satellites) 22

23 Information To Be Transferred 4. Voice Conversations Sent between astronauts on space ships/stations and humans on the ground These are audio conversation streams Examples of voice conversations include: Conversations between astronauts and operators in the mission control center using NASA communications channels Conversations between astronauts and amateur radio operators using HAM radio equipment 23

24 Radio Frequency Communications Electromagnetic (E&M) waves travel ~3x10 8 m/sec Radio uses E&M waves in microwave range (MHz-GHz) Although several propagation modes exist, we are interested in direct line-of-sight wave travel Advantage far more efficient to use radio frequencies to transmit data over long distance Our information is generally at a much lower frequency Drawbacks - the signal will be corrupted as it travels: Atmospheric energy attenuation, wave rotation, etc. Noise from the sun, aurora, lightning, magnetic storms, etc. Interference by objects: reflections, diffraction, multipath, etc. 24

25 The Conversion Process We must convert our information to radio waves in order to allow for wireless transmission. This is done through a combination of: Communications functions/equipment: these focus on aspects of converting the information signals to/from radio waves and wirelessly directing/receiving those waves Data handling functions/equipment: these focus on efficiently pre-processing and packaging the information into a data stream that can be fed into the communications equipment for transmission (and postprocessing and un-packaging data that has been received by communications equipment) 25

26 The Conversion Process Communications equipment/functions: Transmitter: Modulates the (relatively) low frequency information with a higher frequency radio signal Amplifier: Amplifies the signal so that they are powerful enough to be properly received Antenna: Transforms the signal from electrical form to a wave that wirelessly travels through space. In addition, the shape of the antenna can focus the wave in order to concentrate its power in a specific direction. Antenna pointing system: Points the antenna so that the wave is directed to the location of the receiver 26

27 The Conversion Process Data Handling equipment/functions: Digitization: analog signals are converted to digital signals so that they can be processed by computers Signal Encoding: a policy is adopted to represent digital information with specific voltage levels Error Encoding: digital signals are processed so that any corruptions (bit-flips) can be identified and possibly fixed Multiplexing : Information from several sources is placed into a specific sequence for serial transmission Packetization: Information is grouped together into packets for modular transmission Encryption: information is rearranged and processed based on a password so that it is hard to determine the content 27

28 Communication and Data Handling Functions A communications and data handling system relays information from one point to another. In Standard Form Noise Attenuation Distortion Info Convert To Converted Converted Convert Form Info At Info At Back to Location A Suitable Wirelessly Location B its For Wireless Relay Standard Transfer Information Form Info In Standard Form Conversion Functions: Digitize Encode Multiplex Packetize Encrypt Transmission & Reception Functions: Modulation Amplification Electrical-Wave Conversion Focusing of radio energy Pointing of radio energy 28 Deconversion Functions: Decrypt De-packetize De-multiples Decode Calibrate

29 Overview Uses, Benefits and Challenges of Spacecraft Space System Functions and Technologies Communications and Data Handling Exploring Spacecraft Signals and Data Analysis 29

30 Lab Exercises In this hands-on series of laboratory exercises, you will develop a simple but fully functional communication system that can receive signals from spacecraft. This series of exercises will focus on the Communications elements of the system The Data Handling elements of the system will be explored in a future set of laboratory exercises 30

31 Amateur Radio You will use amateur radio (HAM radio) communication standards and will only receive broadcasts (you will not be transmitting). These standards are simple and will make it easier to understand the functions being performed The necessary equipment is inexpensive and some parts can be made by hand You will not need a license to do these exercises 31

32 Amateur Radio Spacecraft There are many spacecraft that broadcast amateur radio signals that you can receive Astronauts on the International Space Station use HAM radio to talk to students around the world Universities often use HAM radios for their science or test spacecraft HAM radio organizations build and launch their own satellites for disaster relief communications and to support their hobby 32

33 Amateur Radio Communications and Data Handling Equipment Typical HAM equipment for receiving satellite broadcasts includes: Antenna: concentrates radio wave energy and converts wave into an electrical signal Pointing system: points the antenna to the satellite Receiver: demodulates radio signals into audio frequency signals Modem: demodulates audio frequency signals into digital information Computer: performs most data handling functions Satellite signal Antenna Receiver Modem Audio Computer Processed Data Pointing System 33

34 Amateur Radio Communications and Data Handling Equipment Regarding the different types of information (commands, telemetry, data products, voice): This is a receive-only system from the satellite, so there are no commands Voice communications (which is audio) can be heard directly from the receiver, which has a speaker Voice Antenna Receiver Modem Computer Audio Voice Pointing System Processed Data 34

35 Amateur Radio Communications and Data Handling Equipment Regarding the different types of information (commands, telemetry, data products, voice): Telemetry and data products are digital information. This data is demodulated in 2 steps. The first step converts radio frequency signals to audio frequency signals. These signals can be heard using the receiver s speaker. A modem and computer are used to further process these signals so that they can be understood by a human operator. Telemetry Data Products Antenna Receiver Modem Audio Computer Telemetry Data Products Pointing System Audio Tones at Discrete Frequencies 35

36 Amateur Radio Communications and Data Handling Equipment For the current set of laboratory exercises, you will focus on the first portion of a receive station: You will be able to hear voice broadcasts. You will also be able to hear the discrete audio tones produced by digital telemetry and data broadcasts, but you will not yet be able to decode this information A future set of laboratory exercises will focus on the data handling back end of the station. Voice, Telemetry, Data Products Satellite signal Antenna Receiver Audio Voice, and Audio Tones at Discrete Frequencies Pointing System 36

37 Amateur Radio Communications and Data Handling Equipment Antenna: You will build or use a pre-made Yagi antenna which is appropriate for the UHF radio signals that you will receive Voice, Telemetry, Data Products Satellite signal Antenna Pointing System Receiver Audio Voice, and Audio Tones at Discrete Frequencies 37

38 Amateur Radio Communications and Data Handling Equipment Pointing System: You can handpoint your antenna, or you can build your own manual pointing platform for better results Voice, Telemetry, Data Products Satellite signal Antenna Pointing System Receiver Audio Voice, and Audio Tones at Discrete Frequencies 38

39 Amateur Radio Communications and Data Handling Equipment Pointing System: To find out where to point the antenna, you can use free/shareware software that will compute pointing angles for you Voice, Telemetry, Data Products Satellite signal Antenna Pointing System Receiver Audio Voice, and Audio Tones at Discrete Frequencies 39

40 Amateur Radio Communications and Data Handling Equipment Receiver: You can use an inexpensive handheld HAM radio receiver to tune into broadcasts Voice, Telemetry, Data Products Satellite signal Antenna Pointing System Receiver Audio Voice, and Audio Tones at Discrete Frequencies 40

41 Summary Spacecraft provide a wide range of services that benefit society A spacecraft s location in space provides several benefits for providing certain services, but it also leads to several challenges Space systems include the spacecraft, the launch systems used to place the spacecraft into orbit, and the ground equipment used to communicate with and control the spacecraft 41

42 Summary Communications and Data Handling systems are used to relay information between the spacecraft and people on the ground Communications functions include modulation, amplification, converting electrical signals to radio waves, and focusing/pointing the radio waves Data Handling functions include digitizing analog data, encoding the data, multiplexing/packetizing the data, and possibly encrypting the data 42

43 Summary In the upcoming laboratory exercises, you will receive amateur radio broadcasts from spacecraft in orbit You will focus on the communication system aspects of your receive station Future laboratory exercises will allow you to explore data handling functions 43