A new flight-control method created by UMR researchers to launch missiles and aircraft may one day send unmanned space vehicles on voyages to the moon, Mars or beyond.
The technique developed by researchers in UMR’s mechanical and aerospace engineering department outperformed four other control methods during tests conducted last fall by NASA at the agency’s Marshall Space Flight Center in Huntsville, Ala. Termed the Theta-D Approximation, the UMR control technique was tested in a simulated "fly-off" against alternative methods that had been developed over longer periods of time.
"Our method is very robust, and this recent simulated fly-off has produced excellent results," says Dr. S.N. Balakrishnan, professor of mechanical and aerospace engineering at UMR, who led the research effort. Working with Balakrishnan were Ming Xin, a post-doctoral fellow at UMR who created the Theta-D Approximation for his Ph.D. dissertation, and David Drake, a graduate student in aerospace engineering.
Balakrishnan’s team originally developed the control through funding from the U.S. Navy’s Naval Surface Warfare Center. The Theta-D system was designed to control the launch of Navy missiles, Balakrishnan says. The Navy featured the UMR method’s performance in the NASA fly-off in a recent Naval Surface Warfare Center newsletter.
"The underlying principle for this method is robust control," says Balakrishnan, who is known internationally for his work in developing fundamental algorithms for intelligent control systems. "We wanted to develop a method that would respond to changes in parameters and still be able to deliver the performance."
Robustness is crucial for controlling aircraft and missiles because parameters could change depending on weather, wind speed, geography, flight path and other factors, Balakrishnan says. But future space vehicles will require similarly robust controls if they are to launch successfully and be directed from Earth as they explore other planets, he adds.
After successfully developing the Theta-D Approximation for the military (Ming’s dissertation was completed in December 2002), Balakrishnan’s team began applying the same nonlinear control principles to NASA’s proposed Reusable Launch Vehicle (RLV). The RLV is considered a replacement for the space shuttle. Nonlinear control captures the physics or the fundamentals of the space vehicle motion better than the current methods.
Drake then began developing the controller for the RLV in September 2002. The work was completed in one year, a time frame substantially shorter than the three to five years required for the other methods tested by NASA.
Last September, the UMR group put its method to the test against four other methods, including one developed by NASA, in a simulated fly-off. The computer simulation evaluated the performance of each control method in taking an RLV through the ascent phase, from liftoff to the cutoff of the main engine. The fly-off involved 49 different tests involving 150 different parameters. The UMR method topped all others with a weighted score of 74.8 percent, with Georgia Tech coming in second.
Balakrishnan hopes to next assess the Theta-D Approximation’s abilities in a simulated RLV entry and landing for different kinds of space vehicles.