SN307 GNSS INS INTEGRATION Lecture Notes PDF

1 SN307: GNSS INS INTEGRATION 01: Introduction Dr Mohamed Elfarran Assistant Professor of Aerospace Engineering Dr Mohamed Elfarran 1 Course Description This course is an introduction to systems in which GNSS receivers work with ot...

1 SN307: GNSS INS INTEGRATION 01: Introduction Dr Mohamed Elfarran Assistant Professor of Aerospace Engineering Dr Mohamed Elfarran 1 Course Description This course is an introduction to systems in which GNSS receivers work with other sensors to provide position and navigation when GNSS conditions are difficult. Dr Mohamed Elfarran 2 Course Learning Outcomes (CLOs) Upon successful completion of this course, you should be able to: Develop a good general working knowledge of GNSS/INS integration. Know in depth about Accelerometer, Gyroscopes, Inertial platforms. Get an overview on General sensor fusion concepts. Dr Mohamed Elfarran 3  Chapter 6 & 7 Chapter 28 Dr Mohamed Elfarran 4  5 SN307: GNSS INS INTEGRATION 02: Inertial Navigation (INS) Dr Mohamed Elfarran Assistant Professor of Aerospace Engineering Dr Mohamed Elfarran 5 The Five Basic Forms Of Navigation: Pilotage Inertial Dead navigation reckoning Radio Celestial navigation navigation Dr Mohamed Elfarran 6 The five basic forms of navigation: 1.Pilotage,  which essentially relies on recognizing landmarks to know where you are. It is older than humankind.. Dr Mohamed Elfarran 7 The five basic forms of navigation: 2.Dead reckoning:  which relies on knowing where you started from plus some form of heading information and some estimate of speed. Dr Mohamed Elfarran 8 The five basic forms of navigation: 3. Celestial Navigation:  Using time and the angles between local vertical and known celestial objects (e.g., sun, moon, or stars). Dr Mohamed Elfarran 9 The five basic forms of navigation: 4. RADIO Navigation:  which relies on radio‐frequency sources with known locations (including GNSS satellites, LORAN‐C, Omega, TACAN, US Army Position Location and Reporting System…) Dr Mohamed Elfarran 10 The five basic forms of navigation: 4. Inertial Navigation:  which relies on knowing your initial position, velocity, and attitude and measuring your attitude rates and accelerations.  The operation of inertial navigation systems (INS) depends upon Newton’s laws of classical mechanics.  It is the only form of navigation that does not rely on external references. Dr Mohamed Elfarran 11 INS : Inertial Navigation System Dr Mohamed Elfarran 12 INS : Inertial Navigation System Dr Mohamed Elfarran 13 INS : Few Definitions 1) Inertia  The tendency of bodies to maintain constant translational and rotational velocity, unless disturbed by forces or torques, respectively (Newton’s first law of motion). Dr Mohamed Elfarran 14 INS : Few Definitions 2) An Inertial Reference Frame  is a coordinate frame in which Newton’s laws of motion are valid. Inertial reference frames are neither rotating nor accelerating. Dr Mohamed Elfarran 15 INS : Few Definitions 3) Inertial sensors  Are sensors that measure rotation rate and acceleration, both of which are vector‐ valued variables. Dr Mohamed Elfarran 16 INS : Few Definitions 4) Gyroscopes  Are sensors for measuring rotation: rate gyroscopes measure rotation rate and integrating gyroscopes (also called whole‐angle gyroscopes) measure rotation angle. Dr Mohamed Elfarran 17 INS : Few Definitions 5) Accelerometers  Are sensors for measuring acceleration. However, accelerometers cannot measure gravitational acceleration. That is, an accelerometer in free fall (or in orbit) has no detectable input. Dr Mohamed Elfarran 18 INS : Few Definitions 5) The input axis of an inertial sensor  The input axis of an inertial sensor defines which vector component it measures. Multi‐axis sensors measure more than one component. Dr Mohamed Elfarran 19 INS : Few Definitions 6) Inertial Measurement Unit  An inertial measurement unit (IMU) or inertial reference unit (IRU) contains a cluster of sensors  Accelerometers (three or more, but usually three) and  Gyroscopes (three or more, but usually three). These sensors are rigidly mounted to a common base to maintain the same relative orientation. Dr Mohamed Elfarran 20 INS : Advantages 1. It is autonomous and does not rely on any external aids or visibility conditions. It can operate in tunnels or underwater as well as anywhere else. 2. It is inherently well suited for integrated navigation, guidance, and control of the host vehicle. Its IMU measures the derivatives of the variables to be controlled (e.g., position, velocity, and attitude). 3. It is immune to jamming and inherently stealthy. It neither receivers nor emits detectable radiation and requires no external antenna that might be detectable by radar. Dr Mohamed Elfarran 21 INS : Disadvantages 1. Mean‐squared navigation errors increase with time. 2. Cost, including a) Acquisition cost, which can be an order of magnitude (or more) higher than GPS receivers. b) Operations cost, including the crew actions and time required for initializing position and attitude. Time required for initializing INS attitude by gyrocompass alignment is measured in minutes. TTFF (Time to first fix) for GPS receivers is measured in seconds. c) Maintenance cost. Electromechanical avionics systems (e.g., INS) tend to have higher failure rates and repair cost than purely electronic avionics systems (e.g., GPS). Dr Mohamed Elfarran 22 INS : Disadvantages 3. Size and weight, which have been shrinking. 4. Power requirements, which have been shrinking along with size and weight but are still higher than those for GPS receivers. 5. Heat dissipation, which is proportional to and shrinking with power requirements Dr Mohamed Elfarran 23  INS : Composition  An inertial navigation uses gyroscopes and accelerometers to maintain an estimate of the position, velocity, and attitude rates of the vehicle in or on which the INS is carried, which could be a land vehicle, aircraft, spacecraft, missile, surface ship, or submarine.  An INS consists of the following: 1. An IMU. 2. Instrument support electronics. 3. Navigation computers (one or more) calculate the gravitational acceleration (not measured by accelerometers) and doubly integrate the net acceleration to maintain an estimate of the position of the host vehicle Dr Mohamed Elfarran 24