Small tech meets ‘impossible’ defense goals
Aerospace systems engineers are famous for their tendency to levy impossible specifications on materials and components. Now micro- and nanotechnologies are proving that goals once thought impossible are actually realistic.
By Richard Gaughan
Perhaps no other picture conveys cutting-edge technology better than that of a pristine satellite, unfurling its solar cells as it begins its on-orbit mission. Paradoxically, however, the aerospace industry is naggingly slow to adopt new technologies.
The defense and aerospace industries exist in an environment where system failure means much more than inconvenience. Breakdown of a critical component means the loss of a million-dollar system, at best, and at worst, the loss of lives. It makes sense, then, that reliability is top priority (see the sidebar, “What’s your readiness level?” p. 25).
But since the best proof of reliability is performance in the field, implementation of new technology becomes a classic Catch-22: Systems can’t be adopted until they’re proven reliable, and they can’t be proven reliable until they’re adopted. What is the path, then, for nanotechnologies to be accepted in the military marketplace?
Here it is: Find an application where the innovative technology offers a clear performance advantage, get a government agency to invest in the technology development, subject the device to rigorous lifetime and reliability tests, and get one of the large defense corporations to incorporate the device into one of their systems.
Charles Volk, chief technologist at the Navigation Systems Division of Northrop Grumman, says, “Technology is cool, it’s sexy, it’s fun to work on, but the world wants solutions to problems. It’s not always easy to find what the actual problems are, but once you identify a problem and make the connection with how your device addresses that problem, life becomes a little bit easier.” The key is to identify those applications where the nanotechnology offers compelling advantages, logistically, operationally, or in cost or performance. The problem is that, as Volk puts it, “working better tends to be not that compelling.”
“Better is the enemy of good enough” is an aerospace-industry mantra. If the current technology works, why not stick with it? Existing solutions have already demonstrated their reliability, and if the performance meets requirements then there’s no reason to take a chance on new technology. Applications ripe for new technology are those whose current solutions are not “good enough.”
For example, the US Navy operates minesweepers that scour shipping lanes for underwater mines. Because the sensors must be kept away from steel, they are towed along under the water, suspended by a brass umbilical cord to the ship above. But the corrosive effects of salt water on brass drives an expensive annual maintenance schedule. By coating the brass cables with a nanostructured material, the corrosion resistance has been improved to the point where the sensor assemblies have not required dry-dock maintenance in three years, and counting.
Another example is evident in satellites flown by the US Air Force. Gimballed joints connect satellite subsystems that rotate with respect to one another, such as solar arrays, which remain pointed at the sun, or telescope and antenna assemblies that point at specific targets. The gimballed joints must stay lubricated, both on the ground for system testing and in space for on-orbit operations. But lubricants that work in one environment don’t work in the other, so complicated solutions had to be implemented. A nanostructured multiphase tribological coating now provides effective lubrication in both the warm, humid environment of Earth and the vacuum of space.
Richard Vaia, chair of the nano-science and technology strategic technology team at the Air Force Research Laboratory, cites applications like these as demonstrating the role of nanotechnology as an enabler, where nanotech-nology “improves performance as part of a larger system-not necessarily providing the central capability, but producing a better overall system.”
Lower cost, better performance, new platforms
There are, of course, existing systems that could benefit from nano- and microtechnologies. For many devices, their micro or nano equivalents offer cost and performance advantages. Again, though, just being better is not usually compelling enough for this market. But if cost and performance of the current system are limiting its application, and there’s an unfilled need, then motivation to adopt the technology becomes stronger. That’s the current situation for phased array radar systems.
A phased array radar tunes its direction by modifying the antenna receiver system. Adding tightly controlled time delays to the signal sent to and from different antennas or antenna sections within an array has the effect of steering the beam in a specific direction. Electronically varying the delay time in a regular pattern sweeps the beam through a desired angular range, without any moving parts. The gallium arsenide (GaAs) transistors typically used to electronically shift the phase are effective, but not ideal. Limitations of the devices means the overall system must include additional circuitry to compensate, adding about a million dollars of cost to each system. Because phased array radar is so effective, field commanders would like to see them not just on ships and aircraft, but also included in missile guidance systems, and even on Humvees. But the current solution is too expensive.
XCom Wireless produces a MEMS microbeam relay that can replace the GaAs switching elements in the phase shifter and do the job less expensively. The MEMS relay technology also offers a simple but significant performance advantage: The closed relay has extremely small contact resistance, and the open relay has no leakage current. Dave DeRoo, vice president of product development at XCom, points out, “Our technology offers a real advantage; it allows a sort of passive construction, right on the antenna, rather than trying to do it further downstream.” The compensating circuitry required with semiconductor switching is not required with the MEMS microbeam switch. The technology improves performance and reduces cost, making it reasonable to consider putting phased array radar systems into some of those additional platforms where military planners would like to see them.
Will it work 10 years from now?
Dan Hyman, XCom Wireless’s president and CTO, outlined the strategy his company is following to demonstrate the reliability of its devices. First, XCom has placed one of its standard commercial products, a single-pole, double-throw relay, into test equipment dedicated to defense applications. This has the dual effect of demonstrating the cost and performance advantages of the technology, and also demonstrating device reliability and lifetime.
The device XCom designed for the phased-array switch is not identical to its standard commercial product, so the company has performed extensive device testing to identify failure mechanisms and quantify device lifetime. XCom has also produced a phase shifter design that has demonstrated the system performance. “Everyone is convinced that the component is what he or she wants,” says Hyman, “but people are not necessarily convinced of the reliability of the subsystem-the component reliability is accepted, the phase shifter design has convincing performance; the next step is to put the system together and verify the reliability.” Although the company may eventually develop modules and sub-systems, “we are being sensible about our testing and development,” says Hyman, “and we’re looking to work with partners at the subsystem and module level.”
AFRL’s Vaia agrees with XCom’s approach. “People aren’t averse to new technology, but they want proof of the new technology as it moves from non-critical to critical applications,” he says. “Put the new technology in a non-critical component, let it fly around for a while; show the supply chain it’s there, material is available, and it’s durable.”
What lies ahead
Vaia sees particular promise in nanomaterials integrated into shape memory polymers, materials in which small changes in chemical structure-induced by some external stimulus-create changes in macroscopic properties, allowing the material to take on different shapes. One problem with the existing materials is that they have limitations at larger sizes. Adding carbon nanotubes improves the strength of shape memory polymers. This allows larger shape-changing structures and, fortuitously, also makes the material sensitive to additional external stimuli, which enables shape recovery to be triggered by light or electrical current. “This is an area where nanotechnology will open the possibility space for shape memory polymers,” says Vaia.
Northrop Grumman’s Volk sees opportunity in the area of materials mismatch. With the drive to make modules and systems smaller, dissimilar materials, with different coefficients of thermal expansion, are placed in close proximity. “If you have materials that buffer that,” he says, “that would be an excellent opportunity as we’re trying to crunch things down to smaller size.” These opportunities are representative of a class of problems where there is no effective incumbent solution. On the face of it, these seem to be open doors for new technologies that can offer unique capabilities, but such opportunities have their own challenges.
One of the opportunities that XCom Wireless has identified is with the Joint Tactical Radio System, JTRS. Communications terminals in the new system, whether on board a ship or in a soldier’s backpack, must be software-reconfigurable to take advantage of different communication modes. “Field radios require ruggedness,” says Hyman, “but they also need the highest-possible performance, something that is impossible to meet with semiconductor components.”
But even though the door is open for new technologies, amorphous requirements make it impossible to design the exact part for the need. Combine that with a general unfamiliarity within the industry for how to create specifications for MEMS devices, and the situation becomes frustrating for both the device designers and the system integrators. It’s a situation that calls for more cooperation among suppliers at different levels. Although that’s not always easy, the payoff is the ability to integrate what could potentially be 300 different components into a single package.
Matching capabilities to needs
For companies looking to introduce new technologies, cooperation with system level corporations is key. “Sometimes smaller companies forget that the military is not their customer, they’re the investor,” says Hyman. “The system integrators are the customers, and it’s their job to find new technologies.”
Volk echoes that sentiment: “Northrop Grumman is always looking for new technologies.” They look to SBIR contracts to see what’s available and also attend conferences where they can hear about new developments.
Vaia also emphasized the importance of establishing connections among military organizations, system integrators, and technology developers. The SBIR programs establish visibility for a technology, but face-to-face interaction at conferences such as the upcoming Nanomaterials for Defense Applications Symposium is also valuable. “There are a very surprising number of programs with some aspect of nanotechnology that are being explored-everything from the mundane to the ‘science fiction,’ ” he says. “The tools of nanoscience are providing new ways of solving problems.”
What’s your readiness level?
Aerospace and defense programs are traditionally risk-averse because of the consequences of failure. A metric commonly used to quantify the anticipated risk of a technology is the “technology readiness level,” or TRL. TRL levels vary from 1 to 9 and are intended to provide a quick measure of the maturity of a technical approach. The TRL scale can be compared to evaluating a cake recipe. It varies from 1 (“I have an idea for a cake that might taste good”), through 3 (“the batter is tasty”) and 6 (“I served it at a party and the people liked it”), to 9 (“I’ve been selling the cake in my bakery for years, and no one has ever complained”).
It’s much easier for a DoD or NASA program manager to include “nines” than it is to specify “sixes” or “sevens” in a system design. Where does your technology come in? Download a TRL calculator at https://acc.dau.mil/CommunityBrowser.aspx?id=25811&view=c