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Aviation History
1985
1985 - 0687.PDF
UK follows laser path Almost ten years of British ring laser gyro development preceded January's award of laser inertial navigation system development contracts to British Aerospace and Ferranti, Graham Warwick discovers. Aring laser gyro is not a ring; neither is it a gyro. It does not possess those t. essential characteristics of a gyro, rigidity in space and precession. A ring laser gyro (RLG) is, in fact, a rate sensor— one with extremely wide dynamic range and extraordinary reliability. The reliability benefits of using ring laser gyros in an inertial navigation system (INS) have been known for 20 years. Systems began flying in the USA as long ago as 1974, and Honeywell delivered the first production laser inertial refer ence systems to Boeing in 1981 for its 757 and 767 airliners. The first British experi mental laser INS flew later that same year. Now British Aerospace and Ferranti are developing production-standard laser inertial nav/attack systems for flight-test in 1986. Despite the US lead in laser-gyro application, a reluctance by the US military to accept laser-based inertial navigation, means that British equipment suitable for high-performance combat aircraft will be available at about the same time as equivalent US systems. When the UK development effort began in the mid-1970s, the mirror technology available dictated a 43cm path-length RLG for airborne applications, larger than the 30cm gyros then being developed in the USA. In 1978 British Aerospace (then Sperry Gyroscope) and Ferranti, received UK Ministry of Defence contracts to supply for flight test experimental laser inertial navigation systems using 43cm gyros. Each company supplied two systems. In October 1981 BAe's two-box experimental laser INS became the first to fly, in a Comet of the Royal Aircraft Establish ment (RAE), Farnborough. Ferranti's single-box FIN3000 laser INS first flew late in 1982. In two years of flight tests both systems exceeded the 3 n.m./hr design accuracy, demonstrating around 2 n.m./hr. In addition to the Comet flights, both systems were subsequently installed in an RAE Buccaneer and subjected to attack and air-combat manoeuvres. In 1983 BAe's laser INS was installed in an RAE Britannia for polar navigation flight tests. Also on board were two conventional inertial navigation systems, Ferranti's Three of the four types of laser gyro currently under development at British Aerospace Dynamics' Bracknell Division: Left 12cm missile-grade gyro; right 30cm aircraft-grade gyro; centre Triad three-axis gyro FIN1012 and Litton's LTN-76, and two commercial laser inertial reference systems from Honeywell and Litton. In January of this year the UK MoD awarded British Aerospace Dynamics' Bracknell Division and Ferranti Defence Systems, Edinburgh, £1 million contracts towards development of production- standard laser inertial navigation systems meeting the US Air Force's ENAC 77-1 specification and suitable for use in future Royal Air Force programmes. Each company is to deliver two systems by January 1986 for flight test by the RAE in a Buccaneer, a Tornado, and a Sea King helicopter. Although both systems will meet the medium-accuracy, 0-8 n.m./hr specification, BAe's laser INS will use 30cm RLGs, while Ferranti's FIN3020 will stay with 43cm gyros. British Aerospace began development of ring laser gyros in 1975 when, as Sperry Gyroscope, it was denied access to US RLG technology through its parent company Sperry. Between 1975 and 1978 BAe conducted basic research, partly MoD funded, into laser gyros. After the October 1978 MoD award BAe built four experimental laser inertial navigation systems, supplying two to the RAE. BAe has since diversified into other laser gyro applications, receiving an MoD contract in 1981 to develop a 12cm path- length RLG for use in missiles. The following year BAe began development of a high-accuracy, 1 n.m./hr, 70cm gyro for use in ship navigation systems. In 1983 BAe began private-venture development of a laser INS for military aircraft, using the USAF ENAC 77-1 specification. The company decided to develop a 30cm path-length gyro for this application. This required an order of magnitude improvement in mirror quality, and BAe elected to produce its own mirrors. The first step in mirror production is the optical polishing of the substrate to a surface finish of better than one Angstrom—less than atomic size. Mirrors for the 43cm gyros were then given a reflective coating using a method known as evaporation deposition. For its 30cm gyro BAe has moved to a method known as ion beam deposition, in which a beam of ions is directed at a target from which material is knocked off atom by atom to coat the mirror. This requires new FLIGHT International, 9 March 1985 25
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