I'm worried. To think that you can go from the drawing board to an operational craft as complex as this in a few years is a hallucination of the most dangerous sort. And to fit the design, testing, and revising phases into this short period of time, corners will be cut. The result might please technoconservatives, but I think it has a good chance of producing another metal cow—probably one that looks remarkably similar to the current version of the space shuttle.
However, perhaps I'm worried over nothing. NASA has always invested in materials research, and they know it's paid off. Other people know it too; many people realize that high-tech materials have probably been the most important commercial offshoots of space technology thus far.
For example, artificial limbs, crash helmets, and similar devices have been greatly improved by materials originally developed for purposes much different from prosthetics or bicycle safety. Recently obstetricians began training with forceps made with NASA-developed composite materials, along with embedded fiber optics. Doctors use forceps to position an infant during delivery, but a baby's head is soft (the skull bones are still relatively far apart) and too much pressure can have disastrous consequences. The fiber optic sensors help the physician to monitor pressure, giving medical students excellent training before they have to use forceps for real. These materials, by the way, came from the X-33 program's fuel tanks.
Granted, for some jobs it's impossible to replace metal (at least at the present time). But for weight-critical space launches, a long look must be given to composite frames.
* * * *
Shapechangers
Most of the time engineers design static structures that don't respond to the environment. Unlike animals, which collect sensory information in order to move about and adjust to their surroundings, machines are made of “dumb” materials that perform their function in a single way. Even materials such as composites, which can be tailored to suit a wide variety of parameters, are not adjustable once set in place.
Making one size fit all results in serious inefficiencies. Consider airplane wings, for instance. The job of wings varies, depending on whether the plane is landing or taking off, making haste or cruising at high altitude. Aerospace engineers try to account for this by giving wings movable surfaces so that they are more adaptable. The pilot raises or lowers ailerons to turn, and wing flaps can be extended or retracted to change the lift during take-offs and landings.
But there's just so much you can do with simple adjustments like these, and they add to the weight of the craft. “Smart” materials that adapt to changing conditions would prove far superior. And this is the way of the future in materials science.
Adaptive materials are already making their mark. Ground-based astronomical observations suffer from distortions due to rapidly changing atmospheric conditions, even when the observatory is located high on mountaintops (as many are). At the Keck Observatory on Mauna Kea, in Hawaii, as well as at other observatories, astronomers are fighting this problem with techniques called adaptive optics. The reflective telescopes are made with “rubber” mirrors—thin, deformable mirrors, changing shape at hundreds of times a second in response to shifts in the atmosphere. The system senses atmospheric changes by analyzing a reference light, which can be a bright star or, in the latest configurations, a laser beam that travels up into the atmosphere.
Surprisingly, shapechanging isn't new at all in aviation. The first viable airplane, built by the Wright brothers, had wings that were twisted by pulleys and cables. Inspired by the flight of birds, Wilbur and Orville guided and stabilized their plane by adjusting the wing shape.
The Wright brothers’ aviation success caught on, but the flexible wings didn't. Higher speeds rip and destroy fragile surfaces, so ye olde flimsy wings were discarded, and stiff wings became essential. Movable panels took over the job of turning and changing altitude. Engineers started getting fancy a few decades ago, making planes like the F-14, whose wings pivot back and forth. That's fine, but it's still a space age away from what I would call a “morphing” wing—a wing that can alter its shape at will.
But new materials may soon make this possible, opening up a new era in aviation. And it may not be limited to those of us on the planet Earth.
Some of the new materials are called shape memory alloys. These special materials “remember” and can be “trained,” so they can recover an original geometry—and apply a lot of force in the process—with the application of some stimulus, such as heat. One set of shape memory alloys are known by the name Nitinol, and contain roughly equal mixtures of nickel and titanium, along with some other elements to fine tune the properties.
Since I have a bias for plastics, I'd rather talk about shape memory polymers. These materials can go from rigid to floppy and then back to rigid again, all under the command of various stimuli such as heat, electricity, or light (as recently demonstrated by researchers Robert Langer, Andreas Lendlein, and colleagues, as reported in the 14 April 2005 issue of Nature.) The changes don't, or at least shouldn't, weaken the material. Some of these polymers allow a doubling or more of their length, then a return to the smaller size. One proprietary substance is called VeriflexTM, developed by the Cornerstone Research Group.
Engineers are thinking today about wings with drastic shapechanging capability. Structures can suddenly form and shape themselves, do a job—such as turn the plane or provide extra lift—and then disappear, so there is no weight penalty to be paid by having to carry attached structures to perform these functions. Even wings themselves can open and disappear, like gigantic bat wings.
Of course, you have to start small, then think big. Right now people are working on shapeable wings by using simple actuators such as piezoelectric devices (in which electricity causes mechanical alterations and vice versa). Small changes won't cause much of a difficulty, but if you make major structural changes you might end up with gaps. Gaps are a problem because they can act like aerodynamic brakes. A shape memory polymer might be essential to close off the gaps, maintaining the wing's low drag profile.
Wings are usually made with a skeleton of parallel spars wrapped in a skin, either aluminum or composite. In general, the spars keep the wing from bending and the skin keeps it from twisting. Clearly these wings won't morph because the aluminum or composite skin isn't elastic; morphing wings would need to be segmented and/or have shape memory polymers or other flexible materials. Yet these materials must be able to tolerate the serious forces encountered during flight.
In the last few years, people at NASA, Boeing, and the Air Force Research Laboratory have been working on a concept called the active aeroelastic wing. These researchers have been using an F-18 fitted with thin wings, which were part of the plane's original design, but rejected during the testing phase because they twisted too easily. Now engineers are thinking that twisting isn't so bad, if you can control it. The idea is to figure out a way to use the whole wing to steer and maneuver the plane, instead of adding flaps and ailerons and paying a significant weight penalty.
I expect that we might see adaptive wing structures in a few years, but the more ambitious programs may take a long time. One of the biggest problems occurs during the transition from one shape to another. When you're in the air and you want to make a change (such as folding or unfolding a large structure), you're going to have to deal with stability issues. It would be like two guys in a small bass boat who want to switch seats: once they get settled they're fine, but while they're crossing each other in the middle they're likely to tip over the boat.
But people are working on these projects because the rewards would be great. DARPA (Defense Advanced Research Projects Agency) has begun a Morphing Aircraft Structures program with the goal of developing more versatile aircraft. With present technology, you can make a plane that excels at reconnaissance or a plane that's good for attacking, but not both. Yet doing both is theoretically possible. Think of a peregrine falcon, which spreads its wings to soar and sweeps them back to dive at two hundred
miles per hour. That's what the military wants.
Civilian uses of this technology would be, in my opinion, even better. If you want a plane that can maneuver in close quarters, such as a congested urban area, you need something that can dance in the air—sharp spins, dives, and turns. To do that, you really need a shapechanger. The “air car,” that conventional prop of science fiction, would be possible with a morphing structure, as would Batman's amazing flier (which in the movies seems to defy a significant number of aerodynamic principles). Recently engineers at the University of Florida, funded by the Air Force and NASA, have constructed drone prototypes that have morphing wings and are highly agile.
Versatile aircraft would also have plenty of other-world uses. If you need a flying craft that can efficiently explore and maneuver in varied conditions, you'll want a morphing craft. Our Moon has no air and thus no aerodynamics, but the solar system is diverse, ranging from the thin atmosphere of Mars to the thick atmosphere of Venus, and the outer gaseous planets pose even more challenges. Exploration among the diversity of solar system environments, including within the same planet or satellite, may require a craft with a morphing structure, as it would be too expensive to design, build, and launch a different craft for each of these different situations.
Just to prove that my bias against metal isn't complete, I'll mention one last material: metallic glass. The 1991 movie Terminator 2 contained a creature made of flowing metal that could reshape itself at will. Such a material doesn't exist yet, but some of the newest metals have taken the first few steps toward this end. Liquidmetal® Technologies, in Lake Forest, California, makes metal alloys that are amorphous, like glass, rather than crystallizing into a geometric structure, like conventional metal.
The company says that their Liquidmetal alloys are superior to crystalline metals in numerous ways. They have developed zirconium-base and titanium-base Liquidmetal alloys that have two times the strength of conventional titanium alloys. (In the spring of 2005, the company announced that SanDisk Corporation—whose flash drives I use all the time—will make some products with Liquidmetal alloy. This is good news, since my pocketed flash drives often take a beating.) The company also claims that intricate structures are far easier to make with their alloys, due to their superior casting and phase transition properties. And Liquidmetal alloys are elastic and have a shape memory, so they can retain their form even after severe stress.
The company says some of its products have already been tested during four space shuttle missions, and were used on NASA's Genesis mission. (This mission, intended to collect solar wind samples, had an unfortunate end when it crash-landed in 2004 due to a parachute failure.)
One can imagine self-healing spacecraft made from these materials. A hole opening up in a ship due to a small-particle impact would be a disaster for a rigid craft, but if the skin could automatically reseal itself, little air would escape. Not only would it be safer, it would also mean that ships need not be so heavily armored, saving on fuel and the huge weight expense at launch.
Of course the ideal concept of a complete shapechanger will not be feasible anytime soon, no matter what material is contemplated for its design.
Yet we're moving closer to a specific goal that's been on the minds of engineers (and science fiction enthusiasts) for quite a while: machine mobility, as effective as a human's movements. People are agile because of active elasticity—muscular contractions governed by the nervous system. “Smart” materials that can change under various stimuli could make dynamic structures as flexible and agile as the human body.
New materials are coming, and their impact on the world will be as great as the Bronze Age, the Iron Age, and the Industrial Revolution. Whether these materials are made from composites, polymers, ceramics, or metal, they will make a host of things possible that had been just drawing-board dreams before. They may even exceed the amazing capability of the human body—and won't wear out after a mere three score and ten years.
Copyright © 2006 Kyle Kirkland
* * * *
Further Reading:
Advanced Materials & Processes [journal], ASM International
ASM International (The Materials Information Society) web site: www.asminternational.org/
Boeing 787 web site: www.boeing.com/commercial/787family/
Science of Structures and Materials, The, J.E. Gordon, Scientific American Library, 1988
Space Shuttle Reference Manual web site: spaceflight.nasa.gov/shuttle/reference/shutref/
Stuff: The Materials the World is Made of, Ivan Amato, Basic Books, 1997
* * * *
About the Author: Kyle Kirkland earned a Ph.D. in neuroscience from the University of Pennsylvania in 1998. He's interested in many different fields of science and technology, and recently completed a book for young adults on optics (Optics: Illuminating the Power of Light, with Sean M. Grady, to be published by Facts On File). This article is his fourteenth appearance in Analog.
* * *
Kyrie Eleison
by John G. Hemry
"The best-laid plans....” applies to everybody.
Frost rimmed the large, thick windows looking out over a cliff and down to dark water flecked by whitecaps. Sleet rattled against heavy stone walls as an erratic wind swept by. Low on the horizon, a reddish sun glowed through a rare small rent in the clouds that otherwise covered the sky, casting long shadows across the room where Garvis Skein lay abed, snoring heavily under the pile of blankets he favored for warmth.
Francesa walked quietly into the room, her uncovered feet making almost no sound, ignoring with the stoicism of years of experience the searing cold on the soles of her feet whenever she had to leave the comparative comfort of a rug's surface and cross bare stone. Working silently and swiftly, she pulled tinder and coal from the bag she carried and, kneeling in front of the stone fireplace in one corner, got a fire going with efficiency born of long practice.
Garvis stirred under his covers. Francesa froze, her breathing as shallow and quiet as possible. The fire popped, and Garvis’ eyes opened, frowning at the ornate designs carved into the ceiling. The eyes slowly pivoted, coming to rest on Francesa. The man's eyes narrowed in annoyance. “You have broken a rule,” he muttered. “Noisemaking during sleep period. Inform the duty Officer so he may order the appropriate punishment."
Francesa bowed her head silently, then brought her right hand up to touch her forehead. “Aye."
“Go away.” Garvis turned to settle under his blankets.
Francesa snarled at his back, knowing the man wouldn't move again until the fire had warmed the room. Then she left as silently as possible.
Officer Varasan was lingering over breakfast when Francesa found him. One look at her expression and he sighed heavily. “Now what?"
Francesa stood before him, trying not to notice the crumbs on the shirt that stretched over his belly. Her stomach threatened to rumble, something she tried to silence with every fiber of her being. On those few occasions when she and her like were granted good bread, their sunken stomachs offered no purchase for any crumb. “I made a sound, Officer,” she stated tonelessly. “Before call to work."
Varasan sighed again. As Officers went, he wasn't so bad, Francesa thought. But he was an Officer. “Where?"
“The chamber of the First Officer."
This time Officer Varasan flinched. “Stars, girl, couldn't you have picked a less important place?” He let out a long breath of air, a gust the warmth of which actually brushed against Francesa. “Though as you well know every place is less important than that.” He toyed with a remnant of pastry, oblivious to the way Francesa couldn't avoid staring toward it. “Two lashes. After the morning Report."
Francesa's body tensed, then she nodded, once again bringing her right hand to her brow. “Two lashes. After the morning Report."
Varasan flipped his own hand into the general vicinity of his brow in response, then went back to his meal, ignoring her as she left.
* * * *
She veered through the kitchen, coming to a halt near one of the cooks. The cook glanced down at her and smiled. “Francesa. What brings you here?"
“Are there any leftovers?” she asked, trying to keep the neediness from her voice.
The cook's smile turned rueful. “Before most of the Officers and Crew have even eaten? Not likely.” He turned away, hesitated, then shoved something toward her. “This bit was ruined by a new apprentice. Get rid of it, will you?"
Francesa took the roll, her hands shaking. “Aye."
The cook glanced at her for a moment. “The harvest isn't too good, I hear."
Francesa nodded. “My friend Ivry works the fields.” As bad as working around the Officers and Crew could be, at least most of the time Francesa was sheltered inside. Those in the fields took the brunt of the weather for their entire work shifts. “She says the weather went cold too early."
“The weather's always cold,” the cook remarked gloomily, his eyes straying toward a high slit window where a small patch of pale sky could be seen. “Though it seems colder now, in truth. Will there be enough food this year?"
“I...” Francesa looked down at the roll in her hand. “I don't know."
“Not enough, maybe,” the cook murmured. “Third year in a row. Not that there's ever been enough, not since I was younger than you, but it's worse lately. The Officers say the Captain's angry with us. And the Officers and Crew must be fed before workers like us. Captain's orders.” He touched his brow with his right hand.
Francesa kept her face calm despite the anger that surged inside. Nodding politely, she hastened from the kitchen and wolfed down half the roll. She managed to pause after that, staring down at the bread and thinking of a little brother with a belly as thin as her own. Biting her lip, she wrapped the other half carefully in a scrap of rag and stuffed it into a nearby hiding place where it would be safe until her work shift finished.
Analog SFF, September 2006 Page 8