Satrack

Abstract

          The origin of the missile can be traced back to the roman war machine the catapult. The guided missile was born when Werner Von Siemens suggested a guide torpedo for submarines in the late 19th century. From these beginnings the present day trident and tomahawk are guided from the skies using the GPS signals. This seminar deals with the measurement concept that tests the missile accuracy. SATRACK receives, rebroadcast, records and tracks the satellite signals sent by the GPS signals. The reception and rebroadcast of the signals is done by a missile hardware called the GPS translator.

Portable Ground Equipment

          This hardware is used for the post flight processing and tracking of the satellite signals. The SATRACK facility processes the raw data into a time series of range and Doppler measurements for each satellite, and the Kalman filter, which incorporates various corrections and generates a navigation solution for the missile. The system has undergone a lot of redesign and development as the requirements evolved with new type of translators and receivers. The latest system processes the wideband L1/L2 signals dual frequency P-code as required by wide band translators. The system hardware is based on Analog Device SHARC processor. Most of the custom GPS processing hardware is based on field programmable gate arrays [FPGA]. Each board has the ability to track up to eight channels. The user interface is done using windows based PC workstations.

Batch Mode Processing

          This type of processing allows hardware to operate with software like flexibility. As the pure software system was too slow, hardware that is fully configurable under software control implemented the most computing intensive portions of the process such as signal correlation, generation of local code and carrier signal mixing. It is possible to acquire the signal with virtually no acquisition delay by conducting extensive searches with initial batch of data until all the signals are found.

Field Support Equipment

          SATRACK is the most useful tool because of its post flight processing facility .The ground equipment consists of receiving antenna, data recorder and auxiliary reference timing systems. The equipment receives the translated GPS signal along with other telemetry signals and distributes it to the data recorder. Most ground stations are capable of generating a precise atomic timing standard. The earlier equipments were narrowband recorders that relied on high-speed tape recorders. These gave up to 14 tracks of recording channels with four mega samples per second. The translator processing system was developed for the national missile defence exoatmospheric re-entry intercept subsystem where it served as a real-time GPS processor for range safety as well as data recorder.

Introduction

          According to the dictionary guidance is the ‘process of guiding the path of an object towards a given point, which in general may be moving’. The process of guidance is based on the position and velocity if the target relative to the guided object. The present day ballistic missiles are all guided using the global positioning system or GPS.GPS uses satellites as instruments for sending signals to the missile during flight and to guide it to the target. SATRACK is a system that was developed to provide an evaluation methodology for the guidance system of the ballistic missiles. This was developed as a comprehensive test and evaluation program to validate the integrated weapons system design for nuclear powered submarines launched ballistic missiles.this is based on the tracking signals received at the missile from the GPS satellites.

Full Digital Implementation

          The full digital implementation is of the Portable ground equipment and processing facility. So, the results are expected to be repeatable. This is a very big improvement over the Analog circuitry such as the Analog PLLs used for carrier- phase tracking loop. In addition, the digital implementation removes the need for periodic hardware calibration that accompanies the analog circuits.

Conclusion

          SATRACK is a significant contributor to the successful development of and operational success of the trident weapons system. It provides a unique monitoring function that is critical to the maintenance of strategic weapons systems. The development and research leading up to this technology has been instrumental in bringing out the latest in GPS receiver, translators, data recorders etc.several special test have been conducted with various combinations of inertial systems, GPS receivers, translators as well as RF/antenna designs.