Robert G. Melton, Ph.D.
Professor of Aerospace Engineering and Director of Undergraduate Studies
229B Hammond Building
Penn State University
University Park, PA 16802
Phone: 814-865-1185 / Fax: 814-865-7092
E-mail: rgmelton@psu.edu
Say you’re the Swift autonomous spacecraft, launched in 2004 to study gamma ray bursts and other fleeting astrophysical phenomena, and you detect something going on out there in the universe and want to turn to get a better look. If you’re not quick, you’ll miss it. Gamma ray bursts last from a few milliseconds to a few minutes. At the same time, you have to be careful. You are carrying delicate sensors that will be damaged if they are pointed even briefly at a bright object like the Sun or the Earth.
With so much to consider, making your move becomes incredibly complicated. The system as a whole is operating in three dimensions, with the orientation of those delicate instruments in relation to the dangerous bright objects constantly shifting. Plus, once you’ve figured out how you need to move, you have another task: You need to instruct your gyroscopes what to do to make it happen.
In fact, the mathematical difficulty of plotting it and performing such a maneuver is so high that currently it would take your onboard computer 20 or 30 minutes to solve for it. The computer is capable of approximating a solution in only a few seconds, but the approximation moves the spacecraft more slowly. Either way, it’s likely that the afterglow of the burst, including X-rays, visible light, and infrared radiation, will have faded before your sensors are aimed at it.
Penn State Aerospace Engineering Professor Robert Melton is trying to figure out a way to make the Swift and other similar autonomous craft respond more quickly so they can do their jobs better. What this amounts to is devising a better way to instruct the computer to do the math, one that results in a faster maneuver without bogging the computer down in its quest for exactitude. “Basically, we are doing what engineers always do --- working on new and better ways to solve a problem,” Melton said.
So far, Melton and a team of students have been working about a year on this particular problem, solving example cases and looking for trends and common properties in the solutions. Armed with the insights they are gaining, they hope to have new instructions for spacecraft computers about a year from now.
Besides orienting a craft that is already in space, Melton is working on the most efficient way to move a craft that has yet to fly. This one would be powered by a solar sail, a means of getting from Point A to Point B in space without relying on propellant. Of course space has no atmosphere, which means no wind in the traditional sense, but it does have radiation from the Sun and other sources. A large membrane mirror made of Kevlar, Mylar, or a similar material could function as a sail, garnering thrust from reflected photons. The force is tiny, only a fraction as great as gravity, which means it would take a sail several kilometers in size to power even a 200-lb., autonomous space craft.
Precisely how to tilt the sails to make the best use of the power source and move the craft where you want it to go takes a boatload of computations, and that’s where Melton comes in. As he explains it, the challenge is even more interesting if you’re moving toward the sun – say from Earth to Venus – than away from it. According to Melton’s calculations, a craft powered by solar sail could travel from the Earth’s orbit to Venus’s orbit in less than five months. Solar sails have been tested and they work, but there are still practical difficulties like being able to unfurl something so big without tangling it up.
“People ask me if I want to go into space,” Melton says, “and I tell them the only way is if I can be harnessed to a sail and feel myself pulled along by the light.”
Melton grew up in Brevard, N.C., the son of a Realtor and a musician. As a boy, he watched NASA space launches on TVs lugged into his classroom, and he loved “all the science stuff,” including magnets, electricity and chemicals. His best friend had a better chemistry set than he did, and the two of them used to experiment in the basements of one another’s houses.
“When the sulfur stink got too bad, the mom would throw us out, and we’d go to the other house for a while,” Melton recalls.
Melton earned his bachelor’s degree in physics at Wake Forest University and his doctorate in engineering physics at the University of Virginia. He joined the Penn State aerospace engineering faculty in 1981. The recipient of multiple awards for teaching and advising, Melton is currently the director of undergraduate studies for the department. His classes include space flight mechanics, system dynamics and controls, and spacecraft design, which he describes as encouraging students to brainstorm and think creatively then “asking them a whole lot of annoying questions.”
“I only try to re-direct them if what they are about to try is physically impossible,” he said.
Today, students visiting his office in Penn State’s Hammond Building see two cardboard models of satellites hanging from the ceiling, one a NASA giveaway representing the Space Shuttle, and the other a detailed model of the Galileo that took Melton several days to assemble. “You use toothpicks and a razor blade and Elmer’s glue,” Melton said. “It takes a while – partly because the glue takes forever to dry. It’s a good diversion from work.”