AN/ASN-157 Doppler Navigation Set

The AN/ASN-157 Doppler navigation set provides highly accurate 3-D velocity and navigation over the full operational range of helicopters.

The BAE Systems ASN-157 was developed to meet the ongoing need for helicopters with reduced size and weight avionics. The ASN-157 system has an accuracy of 0.15% of total velocity, weighs less than 13 lbs., consists of one LRU, and has a predicted MTBF of over 7,300 hours. An important capability of the ASN-157 is providing accurate navigation from nap-of-the-earth (NOE) operation to 10,000 feet AGL, including hover and backward flight.

Heading, pitch and roll for navigation are provided by the aircraft's heading and attitude sensors in standard 400Hz synchro format, or via a MIL-STD-1553 data bus. All computations in the ASN-157 are performed in a general-purpose, single-chip computer. The use of non-volatile memory enables the computer to retain previously stored destination data during "power-off" periods without the need for a battery. This eliminates the need for periodic maintenance.

The ASN-157 provides data via two interfaces: a dual MIL-STD-1553 data bus and an ARINC 575 serial data output. These two interfaces emulate the earlier ASN-128 and ASN-137 interfaces to simplify replacement of these systems with the newer, lighter and less-expensive ASN-157.

AN/ASN-157 Features

• Single LRU velocity and navigation sensor
• MIL-STD-1553 interface provides all data to external control and display systems
• Standard Doppler 3-D velocity accuracy at all speeds, including hover
• Over 300 systems on order for Longbow Apache
• Can accept GPS data from external GPS systems

Current platforms:

• AH-64D Longbow Apache for the U.S. Army and Royal Netherlands Air Force
• GKN Westland WAH-64D for the United Kingdom

Interfaces:

• Accepts heading, pitch, roll and TAS via a dual MIL-STD-1553 data bus, as well as in analog 3-wire 400 Hz format

• Outputs 3-D velocity, navigation, heading, pitch and roll via MIL-STD-1553 and also via ARINC 575 data buses

Support/Test Equipment:

• No unique support or test equipment required
• Built-in test; both continuous testing and externally initiated end-to-end tests with greater than 95% fault detection capability

Functionality:

• Provides accurate 3-D velocity for fire-control, INS aiding, weapons delivery, hover operations

• Provides navigation including left-right steering to waypoints entered via MIL-STD-1553 data bus, distance and time-to-go, accuracy dependent on heading, pitch and roll input data

• Operates with INS and GPS systems to maintain highly accurate navigation when GPS not available