Designing For The Mil-aero Market—ground Equipment

When it comes to designing products for the Army and Marine branches of the military, a lot of the focus is on ground equipment—armored personnel carriers, tanks, Humvees, rocket launchers and artillery pieces. For the Marines, there is also amphibious equipment. On the smaller product implementation side there are radios for both Navy and Marine applications along with the appurtenant communication satellites required for keeping everything synced up and connected.

This article will address the challenges in designing the foregoing products and will also describe the similarities they share with other mil-aero products, including navy ships, satellites, and aircraft products.

The Big Gotchas

The factors that have to be taken into account which influence the product design effort include:

• Controlling Shock
• Controlling EMP
• Controlling Temperature
• Preventing Corrosion
• Limiting Power Consumption and Conservation
• Controlling EMI

I will take each of these factors in order and describe their impact on the products included as part this discussion.

Shock and EMP

Similar to satellites, ground equipment is subjected to brutal shock forces. And, as such, the containers which house the PCBs often require ruggedized containers and housings. As Lee Ritchey, Founder and President of Speeding Edge notes, “When I was designing products that were going to be deployed in Vietnam, the standard was you had to satisfy was to put the product as loose cargo in the back of a truck and drive it over a rutted road.”

In addition to dealing with the shock-inducing elements encountered with ground equipment such as personnel carriers and tanks, the missiles launched from land-based rocket launchers have the same requirements as satellites. They have to be able to endure the shock associated with the launch sequence. In addition they have to have a built in defense against EMPs (electromagnetic pulses). When an EMP hits a missile, it can destroy the electronics inside including the all-importance guidance systems.

Temperature and Corrosion

The temperature drivers in ground equipment can best be described as hellish. Ritchey explains, “In contrast to satellites which have to be designed to meet high temperatures, ground equipment has to be designed to address a broad spectrum of temperatures. Because the same type of ground equipment can be used in a variety of environments, from the arctic to the desert, you have to design the PCB such that it works at 60° below zero to 125° above zero. There’s no challenge in designing to a -60° operating environment, it’s the other end of the spectrum—operating out in the desert—that is the challenge. It’s similar to the design requirements you have when you put electronics under the hood of a car.”

In terms of corrosion, in the form of rust, some equipment will be used in jungle climates which have horribly high humidity indexes. Ritchey explains, “Rust is what caused most of the equipment to quit working in Vietnam.”

For amphibious equipment developed for Marine end-applications, a salt environment can be another factor. As noted in the article on equipment developed for the navy, when salt air and moisture are combined with two different metals, a galvanic cell, such as a battery, is formed. The battery generates current flow which leads to the onset of corrosion that can destroy critical electronic components.

Power Consumption

The radios used in field operations are all digital and the only thing that looks like a radio is the antenna and the output transmitter. Essentially, all of these radios are computers. As such, the power consumption issues focus on saving as much power as possible to support the battery lasting as long as Possible.

“All of the troops operating in the desert have a solar system for recharging their electronics,” Ritchey adds. “There are all kinds of fold-up solar systems that soldiers carry in their packs. Without those solar systems, it would be impossible to recharge products out in the field.”

Controlling EMI and Beyond

The EMI standards used in Army and Marine equipment are far more rigorous than those found in the commercial sector. Ritchey states, “There are probably five different EMI standards and each one gets more stringent.”

There are two things that can be done with intercepted EMI. First someone can be located in the dark by detecting their EMI and second, there’s the potential that data can be recovered from the EMI. Ritchey states, “Before people started blocking EMI, it was possible to point a parabolic antenna at a window and pick up the EMI from a computer and perhaps get data out of it. Now, there is sophisticated screening technology that prohibits that.”

Ritchey continues, “One of the things that everybody tries to do is to jam all the radios. You have to design some pretty elegant circuits to keep that from happening.”

Jamming is a concern in the navigation systems of missiles such as the widely deployed Patriot missiles. “The guidance system within a Patriot missile is good enough that it can intercept an incoming missile,” Ritchey notes. “When this missile is launched, it is being aimed based on what the radar picks up following the incoming round. When the missile gets close to its target, it fine tunes its own trajectory with its guidance system. There is both a heat seeking and radar feature within the nose of the missile.”

The Army’s use of global positioning technology was a game changer for military operations. Ritchey explains, “The Gulf war is what made Trimble Navigation a company. Trimble came up with the first “personal” GPS which was the size of an oblong Kleenex box. Initially, the Army was not interested in the technology. But, Trimble sold the devices to officer personnel who bought the GPSs for $1,000 each and used them to figure out where they were in the desert.This is how the military came to own GPS and why it maintains those satellites to this day.”

Design, Manufacturing and Supply Criteria

At Speeding Edge, we have provided design consulting services for several different kinds of mil-aero projects. In one instance, we were providing engineering services for two different divisions within the same company. On one side, we dealt with radios where the requirement was to keep EMI under control and cool the circuits that were in hermetically-sealed boxes so that they could survive in the environment into which they were placed. The circuits were cooled by adding four copper layers in the board and then extending those layers to the edge of the board where they were then bolted to the frame so that the frame became the cooling mechanism.

On the other side of the company, we were dealing with cameras in satellites. There, the challenge was to cool the big imaging ICs that were within the cameras. Again, in this instance, extra layers of copper were added to the PCB to create a heat sink. The additional metal layers conducted the heat away from the performance-critical ICs.

Other mil-aero applications are characterized as having highly specialized PCBs with very limited production quantities. Army and Marine ground equipment differ in this regard as there are far greater volumes of products—thousands of radios, thousands of missiles, etc. However, these products are under the same strictures as other mil-aero products. There is a specific set of fabricators and assemblers that can build the products, and in terms of protecting intellectual property, they are under the same constraints.

Also, Army and Marine equipment is similar to other mill-aero product areas in that there is the desire to manufacture using the same technology for a time span that far exceeds the typical evolutionary cycle of the specified components and PCBs. These mil-aero customers (i.e. branches of the military) want to keep buying the same missiles for ten years. The same dynamic holds true for radios. As a result, the various branches of the military, (aka the government), are forced to have contracts wherein they can buy all the components to satisfy the production lifetime of a specific piece of equipment. On the PCB side of things, the PCB supplier has to commit to building the same PCBs over a long frame of time, often with shrinking profit margins.

One other challenge is the protracted time span between the prototype and production phases of a project. The components that are specified for the prototype phase of a program can be obsolete by the time the production phase of the program kicks in.

In addition, the bulk of products built for mil-aero applications are sourced through mil-aero contractors. The number of these companies keeps getting smaller as companies are acquired by other entities or disappear through attrition.

There is one benefit in terms of the components used in ground equipment. There are very few, if any, instances of Rad-hardened ICs in these Army and Marine products. The component technology is the same as that which is used in commercial applications. The package might be ruggedized (example: ceramic packages) but the silicon itself remains the same.

Summary

Designing ground equipment for military environments carries with it challenges created by various environmental and operating conditions. But careful assessment of those challenges and the manner in which we address them can ensure that the resulting products will work right the first time as specified. 

Find out more about how using a software package like Altium Designer^® helps you design your next military PCBs to the important performance standards on mission-critical systems. Have more questions? Talk to an expert at Altium.