‘Passive Sensors’ Identify Enemy : ‘Eyes in the Night’ May Be Near for U.S. Fighter Pilots

Fighter pilots have only seconds to identify enemy aircraft even when the sky is clear and visibility is virtually unlimited because today’s high-performance jets can pass each other in the blinking of an eye.

But what if the deadly encounter happens at night?

The effort to give night vision to fighter pilots through infrared sensors is one of the hottest new fields in electronics research, a goal that until recently seemed beyond reach.

The infrared scopes carried aboard some large aircraft, such as reconnaissance planes, are too heavy and too big to be fitted on fighter planes where every ounce is precious, and the effort to make those systems compact enough has proved elusive.

But now the Northrop Corp.’s electro-mechanical division in Anaheim has demonstrated a system, using a new generation of microchips, that will allow fighter pilots to see other aircraft more than 100 miles away in the night sky and to identify the type of aircraft when it is still more than 10 miles away, according to Dean Baker, vice president for engineering.

The firm, which will demonstrate the system for the Defense Department next spring, has already tested it on unofficial targets, he said.

“We have done detection and tracking on commercial aircraft well over 100 kilometers (62 miles) away,” Baker said.

The effort to develop night vision is at the cutting edge of the drive to create “passive sensors,” devices that can detect and identify potential targets without giving away their own location. Radar, for instance, bounces a beam of energy off a target, but some missiles can follow a radar beam back to its source and destroy it.

Passive Sensors Draw Energy

Passive sensors, in contrast, capture energy emitted by the target. That can be reflected sunlight, in the case of visual sensors, or infrared light for sensors that detect heat.

Identification of targets, both stationary as well as moving, is of critical importance to the Pentagon, partly because many skirmishes these days require highly selective targeting. But it is also important because of an alarmingly high percentage of “friendly kills” in military exercises.

That was demonstrated during a mock battle in Florida a couple of years ago. When the smoke had cleared, it turned out that more than a third of the U.S. planes that were “shot down” during the exercise were blown away by U.S. forces.

That has increased the Pentagon’s interest in the development of sensors, called “focal plain arrays.” The technology is expected to lead to devices that not only will make pilots more certain of whom they are shooting at, but will also be less vulnerable to detection. The technology could have many applications in the so-called “star wars” program, particularly in the detection of enemy missiles, and there is some evidence that the Defense Department plans to give the technology one of its highest priorities.

The newsletter Inside the Pentagon reported last April that the Pentagon is expected to launch a major program within the next year or so at a cost of about $500 million.

Several firms are already making inroads in the field, including General Electric Co., Hughes Aircraft Co. and Texas Instruments. Northrop’s actual demonstration of its system late last year has given it an edge over its competitors, according to industry sources, and the company, which has financed its own research, is building on a system that already has wide applications in the military.

Among the systems now in use for daytime operations is a television camera and monitor, built by Northrop, for the Navy’s F-14 Tomcat fighter. That system uses a silicon chip as an electronic light detector to create an image on a monitor in the cockpit, giving pilots 10 times the daytime visibility of the unaided eye, Baker said.

The effort to extend that capability to nighttime vision through infrared detectors has had trouble leaping a fundamental hurdle. Silicon, which is extremely sensitive to visible light, but not to infrared light, is much easier to fabricate than the type of material that can be used for infrared sensors.

“Mother Nature really did us a favor with silicon,” Baker said. “Silicon is very well-behaved. It’s very stable. But when you switch away from that, Mother Nature returns to her old tricks and the materials turn out to be very difficult.”

Some materials are very unstable, and others are hard to produce with consistent, high quality, he added.

Infrared Light-Sensitive

But Northrop has succeeded in making chips with another element, indium antimonide, which is sensitive to infrared light, and the company claims to have successfully produced enough chips to prove that the technology will work. That would alleviate fears that infrared chips could not be fabricated with consistently high enough quality and in sufficient numbers to meet the demand.

The chip itself is tiny--a square of about a quarter of an inch on each side--but powerful. It uses 16,384 detectors so small they can only be seen through a microscope, but they collect enough infrared light to reproduce a nighttime image of an object many miles away.

Baker said the nighttime capability can be incorporated into the daytime systems already in use without adding significantly to the weight.

The real test will come next April, he said, when the company puts on a full-scale demonstration for the Defense Department.

One question that the demonstration will have to answer is whether pilots in the heat of battle will be comfortable with infrared images, which are not quite as sharp as visual images.