Army Research Office through a National Defense Science and Engineering Graduate Fellowship
1 September 2001 – 31 August 2004
Unmanned Aerial Vehicles (UAV’s) have many important applications ranging from military to research and everyday civilian uses. The goal of this research is to extend the operational envelope of UAV’s by designing an autonomous in-flight refueling system. One of the most difficult technological hurtles to overcome in autonomous in-flight refueling is the need for a highly accurate sensor to measure the locations of the tanker and the aircraft. Currently GPS is limited by an approximately one-foot accuracy.
This project overcomes the sensor accuracy problem by utilizing a revolutionary Vision-based Navigation system called VisNav. Since 1998, Texas A&M researchers have been developing a revolutionary vision system that accurately determines the line of sight vector between two objects, to an accuracy of millimeters. It is capable of providing the needed six degree-of-freedom information for real-time navigation, and can enable accurate autonomous aerial refueling without extensive alterations in the current refueling systems. It can be applied to both the current probe-and-drogue as well as the boom method for refueling. VisNav comprises a new kind of optical sensor combined with structured active light sources (beacons) to achieve a selective or “intelligent” vision. VisNav structures light in the frequency domain, analogous to radar, so that discrimination and target identification is near-trivial even in a noisy ambient environment. Several Light Emitting Diodes (LED) called beacons, are attached to the refueling target frame ##A##, and an optical sensor, or Position Sensing Diode (PSD), on the aircraft frame ##B##.
The LEDs emit structured light modulated with a known waveform; filtering of the received energy allows all ambient energy to be ignored. Thus VisNAv can be used in 100 percent cloud cover, total darkness, and adverse weather conditions. The position of the light centroid on the PSD is directly related to the centroid of the beacons with respect to the location of the PSD on the aircraft. A Gaussian Least Squares Differential Correction (GLSDC) routine is used to calculate the six-degree of freedom data at an update rate as high as 100 Hz.
Working with me on this program is Graduate Research Assistant:
- Jennifer J. Kimmett