Friday, August 7, 2009
The Science & Engineering Apprenticeship Program at the university’s Applied Research Laboratories (ARL:UT) is a competitive program for graduating seniors from primarily Austin area high schools. The apprentices receive hands-on experience in laboratory research and development projects during the summer before they begin college.
Twenty one students are participating in the program this summer–16 at ARL:UT and five at the university’s Institute for Advanced Technology.
Two of the apprentices have shared their summer experiences with Further Findings. First up is Jay Kapoor. We’ll hear from Kanish Mehta next week.
He graduated from Anderson High School in May 2009 and will attend The University of Texas at Austin in fall 2009. His supervisor is Christina Chomel, Engineering Scientist, Advanced Technology Laboratory. His project: Determining the Performance Boundary of the Navigation Filter for an IMU.
He explains:How do you keep track of where you are or even what direction you are facing when you are in the deep reaches of space? The space shuttle needs to know its heading to within hundredths of a degree and this cannot be done by simply “eye-balling” the moon or earth. This is why NASA uses a system called an Inertial Navigation System (INS).
An INS consists of a main component called an Inertial Measurement Unit (IMU), some other sensors which vary depending on the accuracy and intended purpose of the unit, and the software that integrates all of the information from these various sensors to compute a navigation solution. An IMU contains three-axis gyroscopes and accelerometers. The gyroscopes measure angular velocities and the accelerometers measure linear acceleration. The software integrates the angular velocities to find the vehicle’s current orientation based on its original orientation in the inertial reference frame. The software also integrates the linear accelerations to find the vehicle’s position relative to its starting point in the inertial reference frame. The fact that the orientation and angular velocity and the linear acceleration, velocity and position are not independent is accounted for in the equations of motion in the software.
IMUs vary in accuracy depending on the cost of the unit and the intended purpose. As expected, when the performance of the IMU goes up, so does the cost. The IMU located in a car to detect rollovers and collisions simply needs to be accurate enough to detect a very large linear acceleration or angular velocity, whereas the one in the space shuttle needs to be able to detect changes in heading down to a hundredth of a degree.
The problem with an INS is that its current position is calculated from its previous position, so any errors in measuring angular velocity and linear acceleration from each measurement are continuously propagated into the next calculation of position. Thus the navigation solution begins to ‘drift’ even though it thinks that it is still ‘on course.’
The units used in the space shuttle are accurate enough for NASA but cost millions to produce. Recently, MEMS (Microelectromechanical systems) IMUs have been developed. These IMUs are a 10th of the size of a normal IMU but are much less accurate.
The goal of the project that I am working on is to create a unit that combines many of these low cost inaccurate IMUs to create a system that is equivalent in accuracy to a much larger and more expensive IMU. In addition to size and cost, an advantage is that even if one of the IMUs in the unit were to fail, the unit would still be functioning albeit a little less accurately. This kind of redundancy is not available on the Space Shuttle and IMUs can not simply be replaced in space.
My experience at ARL:UT is one that I will never forget. The project that I worked on was my first hands-on experience into the cutting edge of engineering research. It exposed me to many new concepts and programs that I had never seen before.
At times I was overwhelmed by the math behind some of the programs that my group utilized, but it gave me a glance into what I will be learning in years to come. I enjoyed working on this project because I was working on something that actually mattered for the first time in my life.
Overall, it was a fun experience and I look forward to a future career in engineering