High Explosive Radio Telemetry System

Federal Manufacturing & Technologies

R. Johnson, FM&T;

B. Mclaughlin, FM&T;

T. Crawford, Los Alamos National Laboratory; and

R. Bracht, Los Alamos National Laboratory

KCP-613-6058

Published November 1998

Approved for public release; distribution is unlimited.

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HIGH EXPLOSIVE RADIO TELEMETRY SYSTEM

R. Johnson, FM&T;

B. Mclaughlin, FM&T;

T. Crawford, Los Alamos National Laboratory; and

R. Bracht, Los Alamos National Laboratory

Published November 1998

Paper submitted to 1998 International Telemetering Conference

October 26-29, 1998

San Diego, CA

High Explosive Radio Telemetry System

Ted Crawford

Roger Bracht

Los Alamos National Laboratories

Richard Johnson

Barry Mclaughlin

Alli edSignal Federal Manufacturing & Technologies*

ABSTRACT

This paper overviews the High Explosive Radio Telemetry (HERT) system, underco-development by Los Alamos National Laboratories and Alli edSignal Federal Manufacturing& Technologies. This telemetry system is designed to measure the initial performance of anexplosive package under flight environment conditions, transmitting data from up to 64 sensors.It features high speed, accurate time resolution (10 ns) and has the abilit y to completetransmission of data before the system is destroyed by the explosion. In order to affect theresources and performance of a flight delivery vehicle as littl e as possible, the system is designedsuch that physical size, power requirements, and antenna demands are as small as possible.

KEY WORDS

High Explosive Telemetry, Explosive Time of Arrival Sensors, High Data Rate Transmission,Quadulature Amplitude Modulation Transmission, QAM

INTRODUCTION

The High Explosive Radio Telemetry (HERT) is a telemetry system that measures the initialperformance of an explosive package in flight. The key period of interest during the explosiveevent occurs during the first 100 microseconds. This requires a telemetry system with accurate,fast time resolution (10 nanoseconds), and the abilit y to get the data transmitted before thesystem is destroyed. The telemetry system is being designed to affect the resources of thedelivery vehicle as littl e as possible by minimizing the size and power requirements. In order tosimpli fy the design and fabrication, no attempt is made to measure anything beyond event time ofarrival at a specific sensor, relative to another sensor. Because the measurements are taking placein an environment of induced electromagnetic interference, fiber-optic isolation is utili zedbetween the sensors and the telemetry package.

BACKGROUND

The High Explosive Radio Telemetry (HERT) project was initiated to determine the practicalityof a system to measure performance of a weapon’s high explosive material in a flightenvironment. Traditionally, under flight test conditions, test results of an explosion event weredetermined from review of remote instrumentation data and high speed photography. Flight testdata could not be collected to verify "burn" performance during the criti cal first microseconds ofthe detonation. Instead, such measurements were ground based, with the device under testextensively modified to introduce sensors and to protect the test system from damage by theexplosion being monitored. At best, the ground based tests were performed under simulatedflight test conditions.

To instrument an explosion during flight, development of some form of a wireless datatransmission link was required, and modification of the explosive needed to be minimized topreserve flight characteristics and to maintain a realistic or "high-fidelity" model of the actualweapon. The problem of making sub-microsecond measurements and transmitting them beforethe explosion destroyed the system was obvious.

The plans for the development of HERT from an experimental concept to a flight-capablesystem consisted of feasibilit y, acceptabilit y, and developmental stages. The feasibilit y stage wasto determine if the problems associated with this task could be overcome by existing techniquesand technology. The acceptabilit y stage was to determine if the accuracy and limited number ofchannels in such a system are adequate to make a practical decision on the explosive system

performance. The developmental stage is where the system is tested and hardened to meet therigors of the flight environment, and is eventually operated in actual flight. To date, the HERTproject team has successfully completed the feasibilit y stage, and is progressing through theacceptabilit y and development stages.

TECHNICAL APPROACH

The basic concept of HERT simply is to collect and transmit data about metal housingdeformation during the initial stages of detonation of high explosive (HE). During this phase of afew microseconds, the explosion can be considered a "burn" which generates and appliespressure to deform a metal housing. Sensors are positioned a few millimeters away from themetal. As the metal deforms and moves, each sensor is used to detect physical arrival of a pointon the metal. The sensors detect arrival as event data, which is then collected, encoded withtiming information, and transmitted through free space. The transmitted data is received by aground station for post explosion analysis.

FIGURE 1

Figure 1 shows the simpli fied block design of the HERT flight system. The system conceptemploys sensors designed to create light pulses upon contact with the explosively deformedmetal plate or housing. The light from each sensor is channeled through fiber optic cable to theHERT module, which is to be located within the flight vehicle at such a distance as to ensuresurvivabilit y during the first 100 microseconds of the detonation. In the HERT module an opticaldetector circuit converts the light pulse to an electrical signal, which is conditioned and theninput to a XILINX™ field programmable gate array. The gate array encodes the detectedevent along with a time stamp. This data is then formatted and transmitted by an RF Systemoperated at S-Band, utili zing digital encoding and Quadrature Amplitude Modulation (QAM).

TESTS AND RESULTS

A series of test sequences, termed HERT 1, 2, 3, and 4, have been utili zed in the "feasibilit y"and "acceptabilit y" phases of the HERT project. The HERT 1 and HERT 2 test sequences wereperformed in 1995 and 1996 with analog pulse encoding and X band transmission of data,experimenting with various types of shock sensors. HERT 3, also in 1996, was the first testperformed on the initial QAM system design, capable of collecting and transmitting data fromeight sensor channels. These tests were "planar" tests, where flat disks of high explosive weredetonated at stationary ground sites. HERT 1, 2, and 3 test results have convinced us that theconcept is feasible. Air to ground transmission tests of the system have been successfullyconducted with Sandia Labs in New Mexico, using their ground station, which duplicates theactual receiving stations in the field, and RF path characterization studies have been performed atDugway Proving Grounds.

The second stage, acceptabilit y, consists of testing configurations with the best technologyavailable. The purpose is to determine if the actual data obtained is useful for weapons designersin certification of high explosive system performance. The acceptabilit y stage is broken into twoparts, additional "planar" tests and then "representative geometry" tests. To date, all explosivetests have been planar. Representative geometry tests are being scheduled to be performed in1999. Four planar test shots under the HERT 3 sequence plus two additional planar test shotsunder a HERT 4 sequence in July 1997 have been successfully conducted. The HERT 4 sequenceutili zed a 32 channel, digital QAM design. Additional test shots in this sequence are beingperformed in July 1998 to test self-check features for inclusion in the system. All test results todate have been highly positive, have advanced the project forward in the acceptabilit y stage, andhave served to guide development of the system. Once the representative geometry tests aresuccessfully completed, flight environment tests and actual flight tests are to be scheduled.

DEVELOPMENT

The development stage of the HERT project has progressed in conjunction with the feasibilit yand acceptabilit y stages. The HERT MK1 design (Figure 2) was completed and fielded for HERT