On the Final Frontier, Even Robots Need Circuit Protection
In the 1979 film Alien, we were warned that “in space no one can hear you scream,” to which engineers at Littelfuse, Inc. might add, “especially when you get zapped by static.” The Speed2Design™ program is one way that Littelfuse is striving to minimize the consequences of unexpected jolts. And it’s not just astronauts who need protection from electrical hazards on the International Space Station (ISS) and other outposts on the final frontier. The equipment that keeps humans alive and healthy on ISS and the robotic systems that will be used to explore Mars and even more distant bodies also demand comprehensive circuit protection.
Although static shocks might typically be little more than a wintertime annoyance to humans on earth, these discharges can spell real trouble for critical electronics in orbit or on extraterrestrial missions. For example, the soil on Mars is so dry that a robot or an astronaut could easily pick up an electrostatic charge that, when discharged, could disrupt mission-critical circuitry.
This phenomenon, known as triboelectric charging, occurs when certain dissimilar materials rub together (like Martian soil and the various materials used in spacesuits and spacecraft such as aluminized mylar, neoprene-coated nylon, Dacron, urethane-coated nylon, tricot, and stainless steel). One material gives up some of its electrons to the other, and the separation of charge can create a strong electric field. When astronauts walk or rovers roll across the ground, their boots or wheels gather electrons as they rub through the soil. The soil is highly insulating, providing no path to ground, which can allow a space suit or rover to build up tremendous triboelectric charge. A simple touch could produce a discharge that would interfere with the operation of sensitive electrical or electronic elements and logic circuits.
Since Littelfuse was founded in 1927, the company’s engineers have been designing innovative circuit protection solutions for use on earth; in the 1960s, Littelfuse first developed sub-miniature fuses that went on to be used as mission-critical components of the NASA space program.
That commitment to space-worthy innovation continues today, with the Exploration & Discovery Experience for the engineering community included as part of the Littelfuse 2013 Speed2Design promotion. Winning design engineers will get an opportunity to go behind the scenes to spend time with NASA engineers at Ames Research Center in Moffett Field, Calif., on August 15 and Johnson Space Center in Houston, Texas, on October 24. Winners will get a chance to talk with mission and equipment designers about the challenges of circuit protection in space, the “final frontier” of electronic circuit design.
It’s not just astronauts who need protection from electrical hazards on the International Space Station (ISS) and other outposts on the final frontier. (Image source: NASA)
“Astronomical” time-to-market pressures
In 2013, the overall goal of the Speed2Design program continues to be to provide support and solutions for time-pressured electronic engineers seeking answers and information about proper circuit protection technology, selection, and best practices in design. A recent electronics industry survey revealed that today’s engineers are experiencing greater time-to-market pressure than ever before as new product design cycles continue to shrink. In fact, they’re down 13 percent over just the past three years. Thane Parker, director of North American OEM sales for Littelfuse, explains, “Design engineers are being challenged today to get their product correct the first time and release it to market at a speed that’s never been seen before. And that’s what Littelfuse can bring to the table. We have the expertise that we can give the customer the answers at the speed that they need. And that’s what Speed2Design is all about.”
Littelfuse created the 2013 Speed2Design Exploration & Discovery experience to bring engineers face-to-face with some of the most impressive technology on the planet. The design engineers we work with appreciate the technology challenges, demands and reliability required of the electronics that go into modern spacecraft and support systems. This year’s Speed2Design events offer design engineers an opportunity to get an ‘up close and personal’ look at the world’s most advanced technologies and to talk to space exploration experts who create these innovations.
Already this year, Littelfuse has touched base with space technology experts from NASA Ames, who offered insights into some of the challenges NASA is preparing to face with new programs under development for use on the International Space Station and in the exploration of Mars. These engineers are currently working on technological breakthroughs in small spacecraft, intelligent robotics, 3D printing, bioengineering and the NASA Space Portal.
PICA-X heat shield protects spacecraft re-entering Earth’s atmosphere at 15,660 MPH. (Artist’s rendition. Image source: NASA)
Safe circuitry for hazardous environments
Whether on earth or “out of this world,” certain environments pose special safety requirements for circuit designs. Bharat Shenoy, director of technical marketing, Electronics Business Unit at Littelfuse, notes, “From my perspective, I see the biggest safety challenges in hazardous work zones, like those you’ll find in petrochemical plants, oil/gas refineries, mines, fertilizer plants, even large-scale bakeries and cosmetics manufacturing. Equipment designers must be vigilant about circuit protection wherever there are volatile gases, liquids, or combustible dust present in the atmosphere. By their very nature, these substances tend to be explosive if sources of sparks or excess heat are present. That’s why we developed the PICO® 259-UL913 Intrinsically Safe Fuse, which is designed to operate safely within environments where there is danger of explosion from faulty circuits. It’s encapsulated, which means it can be used in areas where flammable gases or vapors are present. The encapsulation eliminates the need for an added conformal coating of the circuit board where the fuse is placed and prevents particles from entering the fuse body. The encapsulation also limits the surface temperature of the fuse during operation, so it can be used where flammable dust particles are a concern.”
Being aware of safety in environments where high levels of moisture or humidity are present is important, especially those that also have a corrosive agent, such as in marine applications. These circuits usually require Ingress Protection (IP) to protect them from corrosion and shorts. Another safety concern is limiting access to circuits in order to prevent someone from being shocked or to prevent arcing to other materials. Special insulation or placement is necessary to prevent these hazards.
Recent discussions conducted with NASA engineers as part of the Speed2Design program offered important reminders that space holds even greater hazardous potential than earth for electronics. Dan Rasky, director and co-founder of NASA’s Space Portal, is recognized as an expert on advanced entry systems and thermal protection materials, including SIRCA (Silicone Impregnated Reusable Ceramic Ablator). This close technological “cousin” of the original PICA (Phenolic Impregnated Carbon Ablator) material, has been used as part of the thermal protection system for the Mars Exploration Rover to protect components like the parachute, payload, rover, and various electronics, from the extreme heating caused by deceleration into Mars’ atmosphere during the entry phase of the mission. Rasky notes, “SIRCA is essentially a silica-based tile impregnated with silicone. It’s ideal for use in thermal protection in electronics applications like antennas because it’s both RF transparent and non-conductive.”
PhoneSat 1.0 during high-altitude balloon test. (Image source: NASA Ames Research Center)
Now that’s a long-distance call
Many people tend to think of technological transfer between the space program and industry as going all one way, with industry adapting technologies developed for spaceflight to earth-bound applications. But, sometimes, the opposite is true, as in the nano-satellite program funded by NASA’s Small Spacecraft Technology Program. The program, which won Popular Science magazine’s 2012 “Best of What’s New” Award for innovation in aerospace, demonstrated the ability to launch one of the least expensive, easiest-to-build satellites ever flown in space by using off-the-shelf consumer smartphones.
NASA engineers kept the total cost of the components to build each prototype satellite to just a few thousand dollars by using only commercial hardware and establishing minimum design and mission objectives for the first flights. Out-of-the-box smartphones offer many of the capabilities satellites need, including a highly capable operating system, gyroscopes, fast processors, multiple miniature sensors, high-resolution cameras, GPS receivers, and several radios. They also offer the advantage of built-in circuit protection. The first prototype nano-satellites were 4-inch cubes that weighed just three pounds.
Chad Frost, chief of the Mission Design Division at NASA Ames, explains, “We’re really excited about being able to leverage the global community of application developers to do exciting things on this next generation of tiny spacecraft. They’re an ideal platform for demonstrating and developing technology that will be applicable to bigger spacecraft. We’ve already shown it’s possible to use tiny spacecraft to do perfectly legitimate, peer-reviewed, high-end science. For example, we’ve been able to miniaturize a biological lab down to the size of a French baguette for a variety of biological research payloads, including spores, bacteria, etc. They can fly completely independently on their own as satellites, and deliver their data back down to the ground.”
Littelfuse circuit protection devices, from fuses to TVS diode arrays, are as diverse as the applications they are designed to protect both on Earth and in space.
Circuit protection safety begins at home
Back on earth, Littelfuse continues to develop technologies designed to protect both human life and sensitive electronics. “Silicon overvoltage protection devices like the SP3304NUTG Lightning Surge TVS Diode Array and the AK Series TVS Diode protect life by maintaining the reliability and operability of equipment in the field, such as telecommunications and medical devices,” says Chad Marak, director of technical marketing Semiconductor Business Unit at Littelfuse. “Equipment that’s installed outdoors or that people handle regularly is especially prone to failure because of the threats posed by nearby lightning strikes and electrostatic discharge.”
All too often, earth-bound circuit design engineers tend to overlook circuit protection during the early stages of product design. Failing to take the actual protection level a component can provide into account is extremely common. For example, selecting the proper fuse is crucial to achieving optimal protection. The protected circuit’s damage threshold requires thorough analysis, as does the maximum overload/short circuit that can be sourced from the power supply. The fuse selected must be able to open fast enough to prevent damage to sensitive components during both high current short circuits and low-level overall faults, which can be just as damaging from a slow heating damage standpoint. In fact, when customers choose to use fusible resistors rather than fuses, they put themselves into a dangerous scenario because fusible resistors have dangerous opening modes during low overload conditions.
In some instances, inexperienced designers are so focused on solving the circuit’s main task that they forget to consider safety or regulatory standards during the layout of the board. That means the circuit has to be modified after the fact in order to meet these standards, becoming less efficient and more expensive. As designers become more experienced, they learn how to employ best practices and to consider safety regulations from the beginning.
Chad Marak explains, “The most common mistake is simply not thinking about circuit protection early enough in the design process! This can lead to under-designed protection elements because there’s not enough space left on the circuit board or not enough capacitance budget left on a data line to allow the right device to be used. Ultimately, this leads to products prone to premature failure in the field.”
Fortunately, there are resources that circuit designers can turn to in order to learn which industry safety standards are relevant for a particular application, Will Li, global standards manager at Littelfuse notes that UL should probably always be part of the process. “Circuit designers are unique in that they need to understand the standards at the component level, as well as at the system level,” says Li. “This means these designers must conform to more than one industry and/or safety standards. For example, Littelfuse engineers must design circuit protection components that satisfy the component standards, as well as being compliant with the standards related to the end-product they’re designing. It is not always easy to understand or figure out which ‘end product’ standard a component should comply with – for example, there’s no standard out there that’s specific to designing a circuit protection component for a toaster or a juicer. In these cases, our technical marketing staff will help to determine the appropriate market. From there, we can figure out the applicable standards. LED lighting, solar panel, and battery protection applications are just a few examples of the scenarios we’ve worked on most recently.”