Reliable, consistent power to sensitive electronics is a critical factor in the design of intelligent munitions, says Christian Jonglas, Customer Support Manager at GAIA Converter, requiring close attention to the need for flexibility in input power, thermal, size and certification requirements
Weapons technology has changed dramatically in recent years with the development of intelligent munitions. Taking advantage of advancements in high-reliability computing, advanced sensors and guidance systems, these intelligent munitions can locate, identify and attack targets over long distances. In doing so, they have been shown to have a higher success rate with less collateral damage compared to traditional weapons designs.
A key foundation of the reliability of intelligent munitions lies in the power-delivery subsystems that support the advanced computing, sensor and actuation devices that are needed to complete a mission. These power systems need to be compact and able to handle environmental extremes, such as shock, vibration and high transient temperatures. In doing so, they ensure that the supply rails provided to each electronic control unit remain stable.
The development of intelligent munitions began with the Paveway series of laser-guided bombs, tested in combat by the US Air Force in the late 1960s. Though the firing of bombs and missiles remains a human decision, intelligent munitions have gained more autonomous capabilities, such as with infrared or radar guidance, where the weapon follows the heat signature or the trajectory of a designated target. With artillery shells, inertial guidance is a common component. The shell steers itself in order to follow a pre-programmed trajectory using data from internal gyroscopes and accelerometers.
For longer-range situations, precision-guided artillery shells use the signals from the Global Positioning System (GPS) to guide them towards targets – increasing the likelihood of a successful strike and reducing the risk of hitting bystanders or friendly forces. Concern over collateral damage is helping to drive interest in the use of intelligent munitions. Defensive applications are also gaining ground. Smart surface-to-air missiles have in recent conflicts become crucial to the protection of civilians, with a variety of techniques from laser guidance to full automation being used to strike incoming targets. In many of these smart munitions, compact electronics are crucial. The full system may need to fit 55mm or 155mm in diameter or missiles that are compatible with man-portable air-defence (MANPAD) launchers.
There are several additional electronic elements required by intelligent munitions used for artillery compared to conventional shells. Though both dumb and smart shells will contain a fuse, the intelligent form will include a more complex fuse system that relies on sensor readings and decisions made by a microcontroller before detonating the payload. Sensor components will include an inertial measurement unit, comprising accelerometers and a gyroscope to determine the shell’s orientation and speed at every point from launch to impact. A GPS receiver will often augment this, helping to determine precise location. A radio-frequency (RF) transceiver may allow remote control from a command unit or to relay data to other battlefield assets.
The RF and position-assessment sensors will, together with other sensors measure temperature, humidity and pressure that are used to help compensate for environmental changes during transport and after firing, feeding data to a central computing unit. This processor will execute guidance algorithms and send commands to actuators used to control trajectory. For example, stepper motors can change the attitude of external fins to turn the shell and control its air velocity. An onboard energy source will supply power through one or more DC/DC converters. As the sensors and other components require stable supply rails, the power delivered needs to be consistent and within tight tolerance levels.
Energy can come from diverse sources. Lithium batteries are commonly used in smaller guided munitions because of their high energy density. Similarly, onboard generators based on small internal combustion engines or microturbines can offer sustained power generation though they may have long startup times, demanding a secondary power source for transient functions. Supercapacitors, in contrast, deliver quick bursts of power for functions like steering or detonation and are particularly valuable for short-duration engagements. For a growing number of situations where munitions are programmed to loiter for long periods before launch or detonation, ambient energy harvesting from light, vibration or air movement can deliver long-term but low levels of energy. Because of the complementary nature of these energy sources, a smart munitions design may contain more than one energy-generation subsystem.
The voltage output from battery cells, for example, may decline rapidly as they reach the end of their discharge cycle, which will tend to occur close to the point of final detonation. Backup energy systems used to supplement the primary source if it becomes depleted, but which may take time to reach full power output may lead to the input voltage changing rapidly. A DC/DC converter designed for intelligent munitions can guarantee the electronic subsystems receive consistent power even when switching between sources even under periods of high stress and with large variations in the voltage generated by the energy source. A wide input voltage range ensures the voltage rail outputs remain consistent after the munition is fired up to the point of detonation. In DC/DC converters designed for this application, such as the MGDD range supplied by GAIA Converter, it is possible to find products that offer a range as wide as 12V to 16V.
The DC/DC converters play a key role in optimising energy efficiency and avoiding damage to components that can result from voltage variations if unregulated supplies are used. As the components that ensure electronic subsystems are powered correctly, high reliability is essential. And because the casings of intelligent munitions have limited space inside given the need to pack in explosives, energy sources, actuators and electronics, the converters must be lightweight and small. An issue that can face power-supply designs is that of height. Though many off-the-shelf products are designed to consume a relatively small area of PCB space, the height of passive components, such as capacitors and inductors, can make a power supply more difficult to fit into shell casings. The MGDD series manufactured by GAIA Converter avoids this issue, implementing a complete DC/DC converter with a height of just 8mm for designs that need 40W or 12.5mm for up to 500W of delivered power.
DC/DC converters should be able to withstand large swings in temperature both during storage and when they are deployed. A storage temperature range of –40 to +125°C, supported by the GAIA Convertor MGDD series, satisfies this objective. By potting the converter module using a two-component compound with high thermal conductivity, the modules ensure optimum heat dissipation under harsh environmental conditions. The potting compound has the additional advantage of providing protection against damage to the components by shock and vibration.
Just as important is the ability to pass stringent military standards on product quality and behaviour. Several standards are important to the electronics in smart munitions. MIL-STD-810 provides a range of tests that determine the system’s ruggedness through its ability to withstand changes in temperature, humidity, shock, vibration and altitude. MIL-STD-461 determines the electromagnetic compatibility (EMC) of the military system, ensuring in the case of intelligent munitions that that they are not adversely affected by interference from external sources. And MIL-STD-331 provides a framework for testing electronic components to ensure the overall reliability of the final system.
As smart munitions become more common, and the functions integrated into smaller casings to support a wider range of battlefield scenarios, integration and development speed will become key elements in the design. For the power subsystems, this will be supported by the provision of integrated power modules, such as the PSDG-48. This DC/DC converter delivers 48W across three output power rails from a single 16-60V DC input. An integrated filter delivers high EMC and a holdup function based on an external capacitor lets the supply ride out temporary interruptions from the onboard energy sources during deployment.
The supply of reliable, consistent power to sensitive electronics continues to be a key requirement in the design of intelligent munitions. By paying attention to the need for flexibility in input power, thermal, size and certification requirements, GAIA is ideally positioned to be a dependable long-term partner for the development of these systems.
