A Lightweight Doppler Navigation System

The need for a low-cost, accurate, reliable light-weight airborne navigation system has been recognized within the military for several years. More recently, the added desirability of a self-contained system capable of providing accurate navigation under dynamic flight conditions, such as might be encountered in low level nap-of-the-earth (NOE) flights, and under low visibility flight conditions has become apparent. In addition, a number of helicopter applications require accurate velocity information for aid in hovering. With recent advances in solid-state technology (e. g., single integrated circuit computers) and in procurement policies (e.g., design-to-cost, life cycle cost driven designs with competitive contracts), navigation systems based upon Doppler radar principles constitute a viable low-cost solution to the emerging needs. To develop such a capability for low to medium velocity rotary and fixed-wing aircraft, the U. S. Army has let a contract to Teledyne Ryan for the development of a Lightweight Doppler Navigation System (LDNS). The LDNS, denoted as AN/ASN-128(XE-1) is a two-box system consisting of a Doppler Radar Velocity Sensor (DRVS) and a Computer/Display Unit (CDU) with a combined predicted MTBF of more than 2000 hours and a 0.38% CEP (assuming a perfect heading reference). Because a Doppler Navigation System is one that operates by dead-reckoning, a heading and attitude reference system (not contractor supplied equipment in this instance) must be used. The DRVS, which accurately measures aircraft ground speed in orthogonal axes, is the primary system velocity sensor. A reversionary mode in the form of true airspeed is described as is the capability to integrate with radio-aided navigation systems such as LORAN, OMEGA, AND TACAN.