Advanced Inertial Reference Sphere
Encyclopedia
The Advanced Inertial Reference Sphere, or AIRS, is a highly accurate inertial guidance system designed for use in the LGM-118A Peacekeeper
ICBM
which was intended for precision nuclear strike against Soviet missile silos.
sphere floating in fluid. Jet nozzles are used to stabilize the inertial platform as commanded from the sensors. This design not only eliminates the problem of gimbal lock
, but also makes it extremely accurate (drift less than 1.5×10−5°/h), accurate enough so any further improvement would give a negligible benefit to the missile's CEP
.
The sensors used in AIRS are floated gas bearing gyroscope
s and SFIR accelerometers which are derivatives of PIGA accelerometer
s. Although this type of accelerometer
is most accurate it contains many precise parts which makes them very expensive to build (approximately $300,000 per unit). PIGA/SFIR accelerometers are also very susceptible to failure because of complicated design.
.
LGM-118A Peacekeeper
The LGM-118A Peacekeeper, also known as the MX missile , was a land-based ICBM deployed by the United States starting in 1986. A total of 50 missiles were deployed. They have since been deactivated....
ICBM
Intercontinental ballistic missile
An intercontinental ballistic missile is a ballistic missile with a long range typically designed for nuclear weapons delivery...
which was intended for precision nuclear strike against Soviet missile silos.
Details
AIRS is a fluid stabilized system, as opposed to one using gimbals. It consists of a berylliumBeryllium
Beryllium is the chemical element with the symbol Be and atomic number 4. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl and chrysoberyl...
sphere floating in fluid. Jet nozzles are used to stabilize the inertial platform as commanded from the sensors. This design not only eliminates the problem of gimbal lock
Gimbal lock
Gimbal lock is the loss of one degree of freedom in a three-dimensional space that occurs when the axes of two of the three gimbals are driven into a parallel configuration, "locking" the system into rotation in a degenerate two-dimensional space....
, but also makes it extremely accurate (drift less than 1.5×10−5°/h), accurate enough so any further improvement would give a negligible benefit to the missile's CEP
Circular error probable
In the military science of ballistics, circular error probable is an intuitive measure of a weapon system's precision...
.
The sensors used in AIRS are floated gas bearing gyroscope
Gyroscope
A gyroscope is a device for measuring or maintaining orientation, based on the principles of angular momentum. In essence, a mechanical gyroscope is a spinning wheel or disk whose axle is free to take any orientation...
s and SFIR accelerometers which are derivatives of PIGA accelerometer
PIGA accelerometer
A PIG accelerometer is a type of accelerometer that can measure acceleration and simultaneously integrates this acceleration against time to produce a speed measure as well. The PIGA's main use is in Inertial Navigation Systems for guidance of aircraft and most particularly for ballistic missile...
s. Although this type of accelerometer
Accelerometer
An accelerometer is a device that measures proper acceleration, also called the four-acceleration. This is not necessarily the same as the coordinate acceleration , but is rather the type of acceleration associated with the phenomenon of weight experienced by a test mass that resides in the frame...
is most accurate it contains many precise parts which makes them very expensive to build (approximately $300,000 per unit). PIGA/SFIR accelerometers are also very susceptible to failure because of complicated design.
Usage
The AIRS was originally developed for the LGM-118A Peacekeeper. The first AIRSs were manufactured by NorthropNorthrop Grumman
Northrop Grumman Corporation is an American global aerospace and defense technology company formed by the 1994 purchase of Grumman by Northrop. The company was the fourth-largest defense contractor in the world as of 2010, and the largest builder of naval vessels. Northrop Grumman employs over...
.