From Sandia Lab News, July 26, 1991:
How TTR Helped the Air Force Ready a New Bomb
Desert Shield and Desert Storm spurred the undertaking of many developments at Sandia and elsewhere, but only the quickest moving projects produced results in time for the brief hostilities in the Persian Gulf.
One weapon that was later reported as seeing action there, however, underwent critical testing at Tonopah Test Rang (TTR), a “bunker busting” bomb.
The bomb, formally designated the GBU-28 was a crash project in which the Air Force used sections of 8 inch artillery barrels to create what Aviation Week describes as a 4700 pound , nearly 10 foot long penetrator that could be used against bunkers sheltering Iraq senior commanders. Before use in battle it had to be drop tested.
“An Air Force captain called me on Friday in February and said he had a bomb to drop and hit a concrete target. I told him “We’ve done that hundreds of times – no problem.” That’s how Ron Bump of Range Operations Div. 7513, recounts the deceptively routine beginning of a hectic week between learning about the Air Force’s need and the successful drop of the bomb on an old concrete target at TTR. Ron is one of four TTR test directors and was in charge of this operation.
Unusual Requests Begin
That first call was the last one that sounded like this would be a normal operation. The next day, working on the weekend, Ron got another call, from a different person. “He told me it was a laser-guided bomb, and the laser was on the way to the range.” says Ron. “I told him, ‘You can’t bring a laser here. This is an optics range, and lasers and optical tracking don’t mix!’ He said, ‘Well, it’s on its way, anyway.'”
TTR uses photographic techniques as opposed to radar alone – to track test subjects and obtain data. A test typically includes tracking by cinetheodolites that provide trajectory information, telescopes that record general engineering documentation, and arrays of fixed high-speed cameras that give precise measurements of impact speed and angle. The optical tracking instruments produce data accurate to within about a meter; radar alone can do no better than about 10 meters. Radar is used at TTR to spot targets as they approach the range, and as part of an auto-focusing, auto-pointing system. (See “Cameras and Radar Keep Eyes on the Test“)
The problem with using lasers at TTR is that every tracking station has someone looking through ;a lens. A stray laser beam that happened to hit the lens could injure the operator’s eyes. But because this was an urgent test, TTR people began doing what would be necessary to safely accommodate the laser. That included rounding up filters that could be put over the eyepieces. It also involved some work in the target area – but that comes later.
Airspace by the Minute
Just getting the test scheduled was no routine matter. TTR is part of Nellis Air Force Base, which includes gunnery, bombing, and aerial combat ranges. Time in Nellis airspace, including TTR is scheduled three months in advance, in 15-minute increments. The schedule is reviewed and adjusted as necessary each month, but that still leaves scant opportunity to squeeze in a test on a week’s notice. In the end, the test was conducted the following weekend, when there was less demand for range time.
Another urgent matter was developing a “footprint” – an area, taking into account both the bomb and the laser, from which people would be excluded during the test. For every TTR operation, there is a safety analysis that includes calculating which areas may be hazardous under certain conditions – the failure of a parachute retarding a weapon, or late release by a pilot, and so on. Ron says, “Jim Enlow (7513) and Gary West (7513 Supervisor) did a lot of consulting with people at Albuquerque to find out how to come up with a safe footprint for a laser. We’re used to developing the footprint for a drop but the laser made it extra tricky.”
Avalanche of Test Requirements
Nor was this the last curve thrown at the TTR folks. Say Ron, “Because this was such a hurry-up job, we were getting changes all through that week. I got a call telling me there would be telemetry on the bomb – that was after we had first been told there would be no telemetry. So we had to start finding out what their frequencies were and where they’d want to strip out information, and so on. We managed but new requirements seemed to keep coming at us at avalanche speed.”
The laser being used to guide the bomb was another source of several unusual circumstances. In combat use, the bomb was guided by a laser mounted on the plane. For this test, however, the laser was to be mounted on a pole near the target, the beam reflecting off the target upward toward the plane. The laser operator would be several miles away, controlling the laser remotely by microwave.
“The laser operator told me he had to have certain microwave frequencies for communication,” says Ron. “But the frequencies used here are allocated, you can’t just pick a frequency and start transmitting. So we got a list of the frequencies he needed , and Ken Mulkey (Telemetry and Communications Div. 7511) spent that first Saturday afternoon talking to people at Nellis who control the frequencies. Ken came up with enough usable frequencies to control the laser.”
The pole for mounting the laser wasn’t a trivial matter, either. It had to be 65 feet tall and at a surveyed location. For the pole, Ron relied on the Reynolds Electrical and Engineering Co. (REECo) people who support TTR operations. Says Ron, “I went to the REECo supervisor and told him what we needed. He said, ‘Where are we going to get that in the time we have?’ I told him I didn’t know, but we had to have one. They found the pole and put it in the ground. Then Lloyd Young (7513) surveyed the pole’s location.”
As the test day approached, the laser pole and the target for the bomb were both ready. The target was a 40-foot square, with a smaller concrete area inside it. The idea was to hit the concrete, if possible, but anywhere inside the square would be considered a success. A black plastic tarp surrounded the concrete to form three-quarters of the target and serve as a laser reflector , the remaining quarter was left earth. Ron says, “It was a whale of an effort that the REECo guys made out here on the target, getting it ready.”
Finally, the next weekend after Ron got his Friday call, everything was ready for the test. As Ron recounts it, this climax was in danger of being anticlimactic.
“It was a morning test,” he says, “and the temperature was pretty low. The cold got to the laser. The aircraft was getting close to the range and it looked like the laser wasn’t going to work. So we used a typical field-test maneuver. We put the laser under the heater of a truck, warmed it up, put a coat over it, and got it back on the pole. It was back up and working just in time.”
All the intricate things that happen during a TTR operation then meshed smoothly and normally – radar acquisition, camera tracking, telemetry, computer, fixed cameras. The bomb, dropped from about 20,000 feet, hit the target, missing the concrete by no more than a foot or so. Assured that the weapon could hit and penetrate a target, the Air Force sent the only two “live” bombs to Saudi Arabia. Both were used during Desert Storm, one of them destroyed a deep, hardened bunker occupied by senior Iraqi officers. The Air Force is said to be continuing work on the bomb as a permanent addition to US armaments.
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