When GPS (Global Positioning System) is denied or unavailable, Inertial Navigation Systems (INS) become crucial for maintaining accurate navigation. INS relies on inertial sensors (like accelerometers and gyroscopes) to continuously track the position, orientation, and velocity of a moving object. Here’s why INS is needed when GPS is denied:

  1. Continuous Navigation: INS provides continuous navigation information even when GPS signals are blocked or unavailable, such as in tunnels, urban canyons, or during electronic warfare.

  2. Independent Operation: It operates independently of external signals once initialized, making it resilient to signal jamming or spoofing that might affect GPS.

  3. Short-Term Accuracy: Inertial sensors can provide very accurate short-term measurements of position and orientation, although they are subject to drift over time without correction.

  4. Integration with GPS: In practice, INS is often used in conjunction with GPS in systems like Inertial Navigation System/GPS (INS/GPS) to provide accurate and reliable navigation in all conditions.

  5. Military Applications: In military contexts, where GPS denial might occur intentionally or due to operational constraints, INS is essential for navigation of ground vehicles, aircraft, and missiles.

Working Principle of INS:

Inertial Navigation Systems rely on the principles of Newtonian mechanics and the laws of motion. They typically include the following components:

  1. Inertial Measurement Unit (IMU):

    • Accelerometers: Measure acceleration forces (both linear and rotational) acting on the system.
    • Gyroscopes: Measure angular velocity and orientation changes.
  2. Data Processing Unit (DPU):

    • Processes the raw data from IMU.
    • Uses algorithms to integrate acceleration and angular velocity data to compute changes in position, velocity, and orientation over time.

Benefits When GPS is Denied:

  1. Continuous Operation: INS provides continuous navigation capabilities in environments where GPS signals are unavailable or unreliable, such as underground tunnels, dense urban areas, and areas affected by electromagnetic interference.

  2. Resilience to Jamming and Spoofing: GPS signals can be intentionally jammed or spoofed (where false signals are broadcast to deceive receivers). INS, once initialized, operates independently of external signals, making it resilient to such attacks.

  3. Short-Term Accuracy: Inertial sensors provide highly accurate short-term measurements of position, velocity, and orientation. Errors in INS measurements (due to sensor inaccuracies and integration errors) accumulate over time, leading to what is known as inertial drift.

  4. Integration with GPS: INS is often integrated with GPS in hybrid systems (such as Inertial Navigation System/GPS, or INS/GPS). GPS provides absolute position updates periodically to correct the drift that accumulates in the INS over time, thereby maintaining long-term accuracy.

  5. Military Applications: INS is extensively used in military applications where GPS denial might occur due to intentional jamming (electronic warfare) or operational constraints (e.g., in enclosed spaces like tunnels or urban environments). Military platforms such as aircraft, ships, submarines, and ground vehicles rely on INS for navigation in these scenarios.


  1. Inertial Drift: The primary challenge with INS is inertial drift, where errors in position, velocity, and orientation accumulate over time due to the integration of accelerometer and gyroscope measurements. This requires periodic updates from external sources like GPS to maintain accuracy.

  2. Initial Alignment: INS requires an accurate initial alignment to establish the starting position, velocity, and orientation. This can be time-consuming and may require external aids (like GPS or known landmarks) for initialization.

  3. Cost and Complexity: High-accuracy INS systems can be costly and complex, particularly those designed for applications requiring precise navigation over long periods without GPS updates.

Technical Details of INS:

  1. Inertial Measurement Unit (IMU):
      • Accelerometers: Measure specific force along the three orthogonal axes (x, y, z) of the sensor. These sensors detect acceleration caused by movement and gravity.
      • Gyroscopes: Measure angular velocity or rate of rotation around the same three axes. They help determine changes in orientation.
    1. Data Processing Unit (DPU):

      • Kalman Filtering: A common technique used in INS to estimate the state (position, velocity, and orientation) based on sensor measurements and dynamic models of the system. Kalman filters help mitigate errors and improve accuracy over time.
      • Integration Algorithms: Algorithms like Dead Reckoning (DR) integrate accelerometer and gyroscope measurements to compute changes in position, velocity, and orientation over time. These algorithms need to compensate for errors such as bias in sensor readings and noise.

Overall, INS serves as a critical backup and complementary system to GPS, ensuring that navigation capabilities are maintained even under challenging circumstances where GPS signals are not available.