Sandia LabNews

Telemetry systems for flight test units

Telemetry systems for flight test units become distributed in stockpile life extension project

The newest design that lead telemetry designer Rex Eastin (8232) is working on serves a dual purpose.

The instrumentation to monitor the W76-1 warhead in flight will not only be used as a joint test assembly in the stockpile life extension program, it will also provide information to weapons systems engineers for weapons development purposes.

The design is notable, he says, because it is one of the first to move toward a new concept of distributed sensor systems rather than placing all the telemetry instrumentation in a single package. The new approach obtains more information while consuming less space, which is at a premium.

Customers — both DOE and military — would like more high-fidelity information from the flight test units. In addition, the two physics laboratories, Los Alamos and Lawrence Livermore, drive requirements for increased fidelity of their nuclear explosive systems, making less volume available for test instrumentation within the flight test units.

For instance, electronic circuits to monitor performance of the arming, fuzing, and firing (AF&F) system are being embedded within the system itself. Dept. 2331 is responsible for designing the instrumentation assembly that will provide the AF&F diagnostic information to the telemetry for retransmission. Using one interface for digital information instead of the previous approach of individual channels and circuits has helped shrink the data acquisition components.

Less than two square inches

The new W76-1 JTA1 will also include a distributed telemetry module. This module allows the gathering of accelerometer data using a digital interface. The module contains the signal-conditioning circuitry, analog-to-digital conversion, control logic, digital interface, and power-conditioning circuits. All of the electronics cover less than two square inches of board space.

The overall volume of the new telemetry assembly takes up less than two-thirds the volume of the most current telemetry package in the W76 Type 2F. In two instances, three printed wiring boards have been shrunk to just one; that occurred with both the terminal data analyzer and the integrated telemetry processor. The processor is not only smaller, it will record more than double the previous number of channels (250 instead of about 100).

The changes are spurred in part because of the natural progression of technology, Rex says. That is also a factor that drives the stockpile life extension program. Replacing aging components with better technology enhances weapon surety and in some cases is required because manufacturers have quit making parts that were formerly used.

The ground station communication recording system will move to a digital interface because analog recording heads are no longer being made. The recording tapes will also be more compact to store, an added advantage.

Compactness is attractive since the push to obtain more data from fewer flights constrains available space. In the W76-1, for instance, the initial requirement for a reduction in volume was to free some space that will be taken up by an inertial measurement unit (first, one built by Sandia, and later one designed by Honeywell for the Navy).

Passing major in-house tests

The laboratory test unit in December passed major in-house testing of circuits and environmental conditions, such as vibration and heating/cooling. Still to come is assembly of a complete telemetry unit in the reentry body for ground test qualification this year. The ground test qualification unit will be subjected to a mechanical and shock environment that will simulate a complete flight from launch to reentry. After the mechanical environment testing is completed, the AF&F will be armed and fire detonators. Along with the warhead functions that will be monitored, the detonator fire-down test will subject the terminal data analyzer to electrical noise and explosive shock environments that it must operate through.

The first development flight, FCET-32, of the new AF&F and telemetry will occur in late 2004. There will be two more additional development flights, FCET-34 and FCET-36, before production begins in 2007. Design work on the telemetry began in 2002. The design team consists of Rex; Brett Chavez (8233), development tester design and terminal data analyzer software; Pete Royval (8233), lead mechanical engineer; Matt Johnson (8235), terminal data analyzer design and telemetry system software, and Michael Newman (2132), W76-1 JTA1 lead system engineer.