Sandia LabNews

Testing acceleration data recorders

Testing acceleration data recorders leaves Sandia department feeling like it’s the Fourth of July

Every time instrumentation developed by Telemetry and Instrumentation Dept. 2665 is fired in a projectile or bomb into concrete, rock, water, or earth targets to support a customer’s test, it’s like the Fourth of July.

So says Dept. 2665 Manager Mike Partridge.

"It’s both exciting and nerve- wracking," Mike says. "The team works hard to get the instrumentation right, but the worry is that something might go wrong. And when the experiment is a success, everyone feels a sense of elation."

That feeling of exuberance was evident April 30 when the Penetrator Instrumentation Team participated in an experiment at Sandia’s rocket sled track. They put instruments designed to monitor acceleration inside a casing of a test unit, which was rocket propelled along the track into a water target — Styrofoam blocks containing a two-foot-deep water trough. When the test unit hit the target, it was traveling at more than Mach 2.

The instrumentation survived the test.

Acceleration data gathered from the instrumentation will be compared with computer simulations to determine how accurate the models are.

For nearly three decades Dept. 2665 has been designing, building, and fielding flight instrumentation data recorders that are put into various size projectiles and used to measure acceleration and velocity as a projectile is fired and penetrates targets.

What’s new is the development of recorders that are smaller, more sensitive, and more rugged than any of their predecessors.

"Our new acceleration recorders use a microcontroller-based architecture for test flexibility, while maintaining electronics and packaging techniques developed over many years of penetrator testing at Sandia," Mike says. "Because of their small size, they can go where no recorders have gone before."

There are several versions of the new small recorders: the 2.5-inch-diameter-by-6-inch AdPen2, the 2-inch-by-3.5-inch MinPen2, and the 1-inch diameter-by-1.8-inch MilliPen. The design team for these versions was led by Tedd Rohwer, former member of the Earth Penetrator Instrumentation Team who is now in Dept. 2131. A next-generation MilliPen is being developed by Tony Mittas (2665).

The small size and weight of these modern acceleration recorders allow their use in smaller and more compact projectiles, which greatly reduces testing costs.

Tom Togami of Applied Engineering and Technical Development Dept. 15414 says his department uses the instrumentation "on the majority of our penetration tests," which "usually means a few full-scaled tests and multiple mid-scale tests per year."

"When we obtain data they are always compared with pretest simulations and are also used to further the development of our predictive models," Tom says. "We have performed suites of experiments with the MilliPen that provide comprehensive data sets for the DOE/DoD community to benchmark their modeling and simulation efforts."

Tom’s colleague in Dept. 15414, Danny Frew, says, "Much of the test data collected over the past few years has been outstanding, and we are using this data to benchmark existing computer codes."

And, he adds, Dept. 2665 is the only organization at Sandia that can do this work.

Another customer that frequently uses Dept. 2665’s instrumentation is B61 System Engineering Dept. 2111.

"We have used instrumentation packages from Mike’s department in B61 testing over the past eight to ten years," says Steve Pink (2111). "We have been extremely happy with the performance of their recording systems and the responsiveness of Dept. 2665’s personnel in meeting aggressive schedules and supplying quality data. During the B61 Alt 354 program, for example, we flew 13 flight tests and did not lose so much as one channel of data during the test series."

Ed Henry (2665), who leads the Earth Penetrator Instrumentation Team, says among the biggest challenges in building the small and highly sensitive measuring instruments is to make them rugged enough to survive impacts of as much as 40,000 Gs. Over many years of field experience, his team has learned numerous "tricks."

One advantage to the new recording technologies is that they are designed to operate with minimal support equipment in remote test areas.

"Only a small interface box and a laptop computer are needed to initialize the recorder for the test or download and plot the data after the unit is recovered," Ed says.

After the projectile is dropped, it is retrieved and the recorder is removed so that data can be downloaded. Researchers in Dept. 2665 have designed a version using radio frequencies — still in the experimental stage — that will allow for real-time data recovery without having to wait for penetrator recovery.

The small recorders have been used in supporting a wide range of deployment methods. They have been fired from a cannon, flown on rocket sleds, and dropped from aircraft like F-16s, B-2s, B-52s, helicopters, and even a hot air balloon.

Most of the time Ed and his crew are given a full definition of mission requirements and objectives, but sometimes they are not.

"Occasionally a customer will come in with a request for instrumentation for a project they can’t talk about" Ed says. "We’re given specs — like the instrumentation must be built to withstand certain levels of Gs — and that’s all we know."

Over the years Dept. 2665 has had many successes. One they like to talk about was an experiment conducted several years ago when a projectile containing an acceleration data recorder was fired into 18 feet of concrete.

"It was interesting to see the ‘before scene’ when the target was six concrete blocks solidly stacked together and afterwards when it was all in pieces," Mike says. "The amazing part is that we can design electronics that routinely survive such extreme environments."

Working on the penetrator instrument team are Ed, Tony, John Heise, Phil Reyes, Dave Faucett, and Randy Lockhart (all 2665).