Sandia LabNews

Compact 'enhanced fidelity instrumentation' will boost confidence level of weapons flight tests

Maintenance of the nation’s nuclear stockpile demands a rigorous testing program. The test regime, or stockpile surveillance, includes periodic flight testing of instrumented test models of a given weapon — as close to the real thing possible — called Joint Test Assemblies, or JTAs. Stockpile surveillance tests (non-nuclear), while always vital, have assumed paramount importance in the present climate, with no new weapons in the pipeline and the average age of weapons in the stockpile the oldest in history.

EFI is smaller, potentially better

In a relatively new program supporting the W87 nuclear weapon, a Sandia team is designing so-called Enhanced Fidelity Instrumentation, or EFI, to provide more reliable data during W87 test flights. Compared to existing instrumentation, EFI is much smaller and holds the potential to provide more detailed information.

In May, the first flight of an EFI-configured W87 was conducted from Vandenberg Air Force Base. The payload, carried atop a Peacekeeper missile, performed nominally. Data returned by the EFI are still being analyzed.

The EFI program began about two years ago, says Dan Hardin (8416). Although a W87 JTA goes through routine, periodic testing, he says, "The weapon lab across the street [Lawrence Livermore National Laboratory ] was interested in having flight test instrumentation that was not as intrusive into their parts as the existing JTAs."

Intrusive? In existing JTAs, Dan says, "We fill up their [LLNL’s] volume with all of our [telemetry] parts for monitoring the signals during flight." With EFI, Sandia has reduced the volume of the telemetry package by a factor of four, Dan estimates. That reduction in scale, just the first step in a program that is aiming for far greater size reductions, translates into an increase in test unit fidelity.

The Sandians directly associated with the EFI project are, in Telemetry Systems Design, Dan Hardin (lead), Scott Anderson, Jim Berg, and John Becker (all 8416), and in the Weapons Project Group, Ed Talbot (lead), Cheryl Lari, and John Liebenberg (all 2266).

Dan says weaponeers want to fly their parts "as pristinely as possible." In other words, the driver behind the EFI program is the desire to have a telemetry package that occupies much less volume and thus causes much less perturbation on the system during testing than is currently the case.

The first EFI test flight, FTU-12 (flight test unit 12), conducted in coordination with the Stockpile Life Extension Program, carried out a wide range of flight characteristic measurements during the unit’s arcing flight down the Pacific range.

FTU-12, Dan says, incorporated gyros, magnetometers, accelerometers, vibration sensors, pressure transducers, and other instruments, all far smaller than similar instruments carried in W87’s traditional JTAs. The instruments gave weapon designers a highly detailed picture of how the weapon actually flies along its trajectory and what happens to it as it separates from the launch vehicle, spins up, and reenters the atmosphere.

"It was a very successful flight test," Dan says. "We’re still reducing the data now, but we had good data reception from launch to impact and everyone seems quite interested in the data that were collected."

For FTU-12, Dan says, the reduced size of the instrumentation filled a relatively small portion of the physics package space. With the EFI instrumentation in place, most of the physics package was intact, and that suited LLNL’s purposes precisely: it wants to test units as close to the real thing as possible.

High fidelity meets enhanced fidelity

Dan explains: The concern with the conventional JTA-type flight tests "is that you don’t have this critical part in there. You’ve got some instrumentation in there that is supposed to have the same mass properties as the real part. It’s supposed to act like the real weapon, but it’s not the real thing, so there’s always the question, ‘Is this reality?’ The closer you can get to the real thing with elements like mass distribution, the more confidence you can have in the test data." The less intrusive the measurement system is, then, the more confidence you can have that the data reflect the characteristics of the actual weapon in flight.

With nuclear weapons having to serve in the stockpile for far longer than originally intended, rigorous testing is a necessity.

"They actually pull a unit at random from the stockpile," Dan says, "take the special nuclear parts out, put instrumentation in and test it. They want to know, ‘Has there been any degradation from sitting in the stockpile. Something that we haven’t predicted?’ "

To get the highest possible fidelity in these tests, Dan says, most weapon systems — including the W87 — now fly "high fidelity" test articles. These units carry no instrumentation. During flight, they are monitored using off-board sensors like radar and visual tracking. Tests incorporating these so-called hi-fi articles have yielded useful results, but there’s only so much you can learn via remote sensing, Dan says.

"The EFI program," he says, "is an effort to move toward a test unit that is like a hi-fi article but is still instrumented and gives you the data you need to diagnose performance problems and the data that you need to score the weapon so that you can say with confidence, ‘This system would have functioned as designed.’ "

As the EFI program moves forward, Dan says, increasingly sophisticated EFI-configured flight tests are scheduled for March 1999 and sometime in FY2000.

"Ultimately, we’re trying to develop a system that measures everything that anybody can dream of that takes no space and no power."