New cameras make image capture easier at AEDC ballistics range

  • Published
  • By Patrick Ary
  • AEDC/PA
ARNOLD AIR FORCE BASE, Tenn. --  Until recently, getting new parts for the laser camera system at AEDC's Hypervelocity Ballistic Range G was a lot like antique shopping.

In a time when it's hard to buy a new camera that isn't digital, workers at Range G have been stretching their resources to keep their film-based camera equipment viable.

But now, after six years of planning, they have a new digital system in place that brings them into the 21st century and makes the process of capturing high-velocity images a more amicable process for both them and the base's test customers.

The new system is more of a necessity than a luxury, according to instrumentation engineer Ed Erickson.

"The cameras had been around about 40 years, and the system as it existed up until now was around about 20 years," Erickson said. "Needless to say, spare parts aren't available for it anymore."

Range G is used to conduct kinetic energy lethality and impact phenomenology tests. Its two-stage gas-gun launcher is the largest in the United States, firing projectiles down a 930-foot-long instrumented tank.

Impact testing and examining aerodynamic features of projectiles are primary functions of the tunnel and having a camera capable of capturing an image as the projectile flies by is important.

Erickson started looking for funding to put a new system in place in 2005 - which was the last chance he had to get spare parts for the old system. The man who made illumination lamps for the laser system was retiring, so he stocked up with as many lamps as he could get. The ruby laser used in the system isn't available anymore, and there's only one place left selling the image intensifiers used to get a sharper image in the old cameras.

The old camera system was a box-shaped film camera. Because projectiles fired through the tank travel as fast as 18,000 feet per second - six times faster than a bullet - a flashbulb isn't capable of illuminating the tunnel for a photo. A laser is used instead.

The old cameras' laser systems used a ruby laser that sat inside a custom high-intensity lamp, which had a water cooling system and a 20,000-volt power supply. The old rig was the size of a steamer trunk and because of the way it was built, a series of mirrors had to reflect the laser beam from one side of the box into the tank. If a customer wanted a photograph from a different section of the tank, it could take a full day to reposition the camera.

The new systems are "everything we need in a compact package," according to Erickson. Each of the three systems consists of a Dicam Pro camera made by the Cooke Corporation and a Quantel Laser CFR200 - both off-the-shelf commercial items that have easy-to-replace parts. The only part of the systems that was built in-house is the triggering system.

"We chose a YAG (yttrium aluminium garnet) laser because they're common and relatively inexpensive," Erickson said. "The camera is sensitive to the same wavelength of light that the laser puts out, so the selection of one drove the specification of the other."

One camera and laser system is about the size of a briefcase, with the laser capable of firing directly into the tank. If it needs to be moved, the new system can be repositioned and ready to go in about two hours.

"Before, I'd tell Ed or some of the other folks I wanted to move the laser camera," said project engineer David Woods. "They'd look down and they'd just start shaking their heads. Now it's not so bad."

The new digital imaging system is also much faster than the film system, according to Erickson. They have a photo of the projectile upstairs from the range as soon as the camera snaps the picture and stores it. It's instant viewing as opposed waiting hours for the chance to go into the facility and physically retrieve the film.

"When they fire the launcher, carbon monoxide is generated," Erickson said. "Hydrogen could leak out of the tank. They have to take steps to purge the tank and make the downstairs safe for a person to re-enter. So it takes about an hour and a half to two hours before the service tunnel is ready for entry. And then it would take another half hour to develop the film."

Once the film was developed, negatives were placed between plates of glass and projected onto a large table. Data points were digitized into a software program that output a list of coordinates. Those points were fed into yet another data reduction program. The new system speeds up that process.

"Because this is digital now, we can use software with our data reduction to help us," said Rick Rushing, the Air Force's ballistics range lead at AEDC. "It's more efficient."

Woods likes another aspect of the digital system: it gets rid of the possibility that the film could be accidentally dropped or exposed to light, destroying the data.

"The thing I like about this system is as soon as it's done, it immediately gets transferred into memory and saved, and we don't have to worry about what happens if there are extenuating circumstances," he said. "We have our data."

Laser photography expands the capabilities of the ballistics range at AEDC. It can be used to determine erosion data and the recession rate of a projectile. Images captured at each photography station could be colored and overlaid to determine changes at each station when a projectile is fired through dust, rain or ice.

It also can be used in lethality testing to photograph the first touch of a projectile on a target.

"Back when we had the old TV-based quick-look camera, it gave the customer a good indication that things hadn't gone too terribly awry," Woods said. "After they saw that their model was still intact, the first thing they always asked was 'Where is it and what angles is it at?' The next thing you know, people are holding protractors up against the TV and trying to find good reference lines.

"Now with this system, as soon as we get two images of the same field of view saved, we've already done the calibration, so we can throw it into the software and draw a line between two points to get the pitch, the yaw and how far it is from the center line."

The range cameras are ready to go; a final checkout confirmed readiness recently. A customer test is lined up for October. By then, Range G workers may be able to use the equipment they have to measure the attitude and positions of a projectile within a 3-D field of view. That will allow them to look at aerodynamic stability information and determining hit point for lethality customers.

"I expect that as we continue to move forward with using these things on our test shots, we will continue to improve," Woods said. "These images are pretty good but there are some things I'd like to see more clearly, and that's just the sort of thing that's going to come with time as we continue to use the systems."