Peacekeeper ICBM Inertial Measurement Unit

The Advanced Inertial Reference Sphere (AIRS) is a highly accurate

inertial guidance system An inertial navigation system (INS) is a navigation device that uses motion sensors (accelerometers), rotation sensors ( gyroscopes) and a computer to continuously calculate by dead reckoning the position, the orientation, and the velocity (dire ...

designed for use in the

LGM-118A Peacekeeper The LGM-118 Peacekeeper, originally known as the MX for "Missile, Experimental", was a MIRV-capable intercontinental ballistic missile (ICBM) produced and deployed by the United States from 1985 to 2005. The missile could carry up to twelve Mark ...

ICBM An intercontinental ballistic missile (ICBM) is a ballistic missile with a range greater than , primarily designed for nuclear weapons delivery (delivering one or more thermonuclear warheads). Conventional, chemical, and biological weapons c ...

which was intended for precision nuclear strikes against Soviet missile silos.

Details

AIRS is a

Fluid-suspended gyrostabilized platform An inertial navigation system (INS) is a navigation device that uses motion sensors (accelerometers), rotation sensors ( gyroscopes) and a computer to continuously calculate by dead reckoning the position, the orientation, and the velocity (dir ...

system, as opposed to one using a

Gimballed gyrostabilized platform An inertial navigation system (INS) is a navigation device that uses motion sensors (accelerometers), rotation sensors ( gyroscopes) and a computer to continuously calculate by dead reckoning the position, the orientation, and the velocity (dir ...

. It consists of a

beryllium Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to form mi ...

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 is the loss of one degree of freedom in a three-dimensional, three-gimbal mechanism 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 t ...

, 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 Fluid bearings are bearings in which the load is supported by a thin layer of rapidly moving pressurized liquid or gas between the bearing surfaces. Since there is no contact between the moving parts, there is no sliding friction, allowing flui ...

gyroscope A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rota ...

s and SFIR accelerometers which are derivatives of

PIGA accelerometer A PIGA (''Pendulous Integrating Gyroscopic 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 Inertia ...

s. Although this type of

accelerometer An accelerometer is a tool that measures proper acceleration. Proper acceleration is the acceleration (the rate of change of velocity) of a body in its own instantaneous rest frame; this is different from coordinate acceleration, which is accele ...

is most accurate it contains many precise parts which makes them very expensive to build (approximately $6,000,000 per AIRS unit, year 1987 dollar, development cost is not included). 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 AIRS units were manufactured by Northrop.

External links

Detailed descriptionJ. LUKESH. "Characterization testing of the MX AIRS 149 Advanced Inertial Reference Sphere", Guidance and Control Conference, Guidance, Navigation, and Control and Co-located Conferences
doi:10.2514/6.1979-1888 Military technology Missile guidance Navigational equipment