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Inertial Navigation System (INS) and Ring Laser Gyroscope-For Beginners by a beginner!
Inertial Navigation System is a type of navigation system, used to guide aircrafts, guided missiles etc. There are many other types of guidance systems also, like radar guidance, satellite guidance etc.
For navigation, the current position of the object has to be determined. This involves finding the linear and angular positions of the object.
Linear positioning means, determining the object’s movement forward or backward, up or down, right or left (in straight lines;hence the name linear). Angular positioning means finding the object’s movement in the roll, pitch and yaw axis.
Fig:Linear positioning
Fig:Angular Position
In other types of navigations, usually the current position of the object is determined with the help of external means, for example, in radar navigation, a radar constantly tracks the object, and the position is send to the object.
The problem here is , constant sending and receiving from an external element is required. Any block in this sending and receiving will result in trouble. Intentional blocking of signals is a major problem incase of missiles where the enemy can block external signals, like radar signals or by destroying GPS satelites.
This is where INS comes in handy. Inertial Navigation System is completely self sufficient i.e it can operate without the help of an external element. For this, INS uses a method called “dead reckoning”.
In dead reckoning, the current position of an object is calculated from the previous known position. For example, imagine a boy cycling from a position A to position B which are 5 km apart. Please note that p positions A and B are already known
The starting position, A is known here. Then the boy cycles down at 5 kmph to the point O, makes a turn and reaches point B. There are instruments to measure speed, change in direction etc. So the instruments measure a forward motion from A to O, a left turn, and forward motion from O to B all at a speed of 5 kmph for one hour.
Using the starting point A and the feedback from instruments measuring speed, change in linear and angular directions, the current position is determined as Point B.
INS basically is the combination of the instruments to measure the speed, positions and a computer to combine and process the information from the instruments.
Imagine a missile is to be send from Kerala to New Delhi. The starting point is Kerala and ending point is New Delhi. The entire path is then divided into a series of Waypoints i.e points in between starting and ending points.
The coordinates of the waypoints are already fed into the computers before the launch. So the missiles launches from kerala flies to Tamil Nadu, then to Goa , then to Rajasthan and finally to New Delhi. Simply said, each time the missile reaches a way point, the INS determines missile’s current position and tells it to the main computer which changes the course to the next waypoint.
The common instruments used include a accelerometer (for linear position) gyroscope (angular position) a miniature computer (to integrate all the information).
As INS uses the previous position to find the current position, any error in determining a position will cause error in determining the subsequent positions. For this a cross check using external systems are used. Like, at particular points, the position given by the INS is compared to the position given by a GPS and correction to the INS is made.
INS systems are widely used in commercial aircrafts, where the pilots enters a series of waypoints between the starting point and destination, the autopilot system along with INS then flies the aircraft almost automatically.
Ring Laser Gyroscope
Gyroscopes are used in INS to detect the change in orientation of the body. That means, a gyroscope detects whether the aircraft is rotating to the right or to the left, is climbing up or down etc. Gyroscopes works using what is called “gyroscopic precession”, explaining which will require a new article.
^^^This is how a mechanical gyroscope looks like. Even with modifications, its pretty obvious that, a mechanical gyroscope will have several issues if taken inside a aircraft or a missile. The friction in the axis will cause what is called a gyroscopic drift, resulting in inaccurate results. Also, the mechanical components needs to balanced often.
To overcome these, we have the ring laser gyroscopes. Ring laser gyroscopes offered distinctive advantage over mechanical gyroscopes, primarily due to the absence of moving parts- lesser number of parts, lower the troubles.
For a ring laser gyroscope, the basic components are 3 mirrors forming a equilateral triangle (distances b/w the mirrors are equal), a read out sensor and a laser source
In the figure, A,B,C are the three corners of the triangle, where the mirrors are located. C is a two way mirror, meaning C reflects light and passes light through it too, like a transparent glass. Behind the C is our read out sensor.
The laser source produces laser beam, which travels to in opposite directions, to both A and to B. When the gyroscope is in idle position, the beams reflect from a both the mirrors to reach C at the same time.
That is, Source-A-C and Source-B-C takes the same time. Source-A-C is in clockwise direction (right) and Source-B-C is in anti-clockwise direction(left). This two beams form what is called “counter propagating beams”. Both beams reaching C at the same time creates a uniform pattern with the read out sensor behind C.
Now imagine the aircraft taking a left turn. The left going beam (Source-B-C) will have to cover more distance to reach C, as the point C is moving away from it. On the contrary, the right going beam (Source-A-C) has to travel less distance, as the point C is moving towards it.
In short, the beams reach the sensor at C at unequal time periods, the beam in the direction of rotation reaches slightly after the beam in the opposite direction. This is called “Sagnac Effect”, after the French Scientist who demonstrated it.
The sensor registers this unequal arrival of beams as alternate bands of lightness and darkness. The sensor then processes this band to determine the different parameters of the turn, such as rate of turn.
In actual systems, these triangle setup is put inside inert gases through which the laser travels.
@Slav Defence, @levina
Inertial Navigation System is a type of navigation system, used to guide aircrafts, guided missiles etc. There are many other types of guidance systems also, like radar guidance, satellite guidance etc.
For navigation, the current position of the object has to be determined. This involves finding the linear and angular positions of the object.
Fig:Linear positioning
Fig:Angular Position
In other types of navigations, usually the current position of the object is determined with the help of external means, for example, in radar navigation, a radar constantly tracks the object, and the position is send to the object.
The problem here is , constant sending and receiving from an external element is required. Any block in this sending and receiving will result in trouble. Intentional blocking of signals is a major problem incase of missiles where the enemy can block external signals, like radar signals or by destroying GPS satelites.
This is where INS comes in handy. Inertial Navigation System is completely self sufficient i.e it can operate without the help of an external element. For this, INS uses a method called “dead reckoning”.
In dead reckoning, the current position of an object is calculated from the previous known position. For example, imagine a boy cycling from a position A to position B which are 5 km apart. Please note that p positions A and B are already known
The starting position, A is known here. Then the boy cycles down at 5 kmph to the point O, makes a turn and reaches point B. There are instruments to measure speed, change in direction etc. So the instruments measure a forward motion from A to O, a left turn, and forward motion from O to B all at a speed of 5 kmph for one hour.
Using the starting point A and the feedback from instruments measuring speed, change in linear and angular directions, the current position is determined as Point B.
INS basically is the combination of the instruments to measure the speed, positions and a computer to combine and process the information from the instruments.
Imagine a missile is to be send from Kerala to New Delhi. The starting point is Kerala and ending point is New Delhi. The entire path is then divided into a series of Waypoints i.e points in between starting and ending points.
The coordinates of the waypoints are already fed into the computers before the launch. So the missiles launches from kerala flies to Tamil Nadu, then to Goa , then to Rajasthan and finally to New Delhi. Simply said, each time the missile reaches a way point, the INS determines missile’s current position and tells it to the main computer which changes the course to the next waypoint.
The common instruments used include a accelerometer (for linear position) gyroscope (angular position) a miniature computer (to integrate all the information).
As INS uses the previous position to find the current position, any error in determining a position will cause error in determining the subsequent positions. For this a cross check using external systems are used. Like, at particular points, the position given by the INS is compared to the position given by a GPS and correction to the INS is made.
INS systems are widely used in commercial aircrafts, where the pilots enters a series of waypoints between the starting point and destination, the autopilot system along with INS then flies the aircraft almost automatically.
Ring Laser Gyroscope
Gyroscopes are used in INS to detect the change in orientation of the body. That means, a gyroscope detects whether the aircraft is rotating to the right or to the left, is climbing up or down etc. Gyroscopes works using what is called “gyroscopic precession”, explaining which will require a new article.
^^^This is how a mechanical gyroscope looks like. Even with modifications, its pretty obvious that, a mechanical gyroscope will have several issues if taken inside a aircraft or a missile. The friction in the axis will cause what is called a gyroscopic drift, resulting in inaccurate results. Also, the mechanical components needs to balanced often.
To overcome these, we have the ring laser gyroscopes. Ring laser gyroscopes offered distinctive advantage over mechanical gyroscopes, primarily due to the absence of moving parts- lesser number of parts, lower the troubles.
For a ring laser gyroscope, the basic components are 3 mirrors forming a equilateral triangle (distances b/w the mirrors are equal), a read out sensor and a laser source
In the figure, A,B,C are the three corners of the triangle, where the mirrors are located. C is a two way mirror, meaning C reflects light and passes light through it too, like a transparent glass. Behind the C is our read out sensor.
The laser source produces laser beam, which travels to in opposite directions, to both A and to B. When the gyroscope is in idle position, the beams reflect from a both the mirrors to reach C at the same time.
That is, Source-A-C and Source-B-C takes the same time. Source-A-C is in clockwise direction (right) and Source-B-C is in anti-clockwise direction(left). This two beams form what is called “counter propagating beams”. Both beams reaching C at the same time creates a uniform pattern with the read out sensor behind C.
Now imagine the aircraft taking a left turn. The left going beam (Source-B-C) will have to cover more distance to reach C, as the point C is moving away from it. On the contrary, the right going beam (Source-A-C) has to travel less distance, as the point C is moving towards it.
In short, the beams reach the sensor at C at unequal time periods, the beam in the direction of rotation reaches slightly after the beam in the opposite direction. This is called “Sagnac Effect”, after the French Scientist who demonstrated it.
The sensor registers this unequal arrival of beams as alternate bands of lightness and darkness. The sensor then processes this band to determine the different parameters of the turn, such as rate of turn.
In actual systems, these triangle setup is put inside inert gases through which the laser travels.
@Slav Defence, @levina
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Lol.
