ALASKA MICROGRAVITY TEAM
The Alaska Microgravity Team has recently submitted a proposal, titled "Investigation of Small Satellite Attitude Control Systems," to the NASA Microgravity University. We are currently under consideration for a flight session with the Reduced Gravity Student Flight Opportunities Program, where we will test small satellite attitude control systems in the zero-g environment of a NASA C-9 aircraft!
Our proposal focuses on the concern of small satellite accuracy and stability. Because they are confined to volumes defined by mere centimeters, small satellites face unique design challenges -- especially in the area of attitude control. There is no room for a complex combustion system, and safety considerations make such a control system impractical besides. Therefore small satellites use more unconventional systems such as magnetic torque coils and reaction wheels.
An area of concern for satellites is how efficiently they can achieve a target attitude (pointing direction). Attitude control systems rely on feedback from sensors to tell the satellite if it is pointing in the right direction -- the result is that satellites may wobble back and forth over a target location as they figure out and "settle into" a desired attitude. This is because the satellite turns past the desired attitude before realizing it, turns around, passes it again (only not so far this time), and so on until it is pointing in the desired direction. The opposite extreme is that the satellite moves extremely slowly into its desired attitude, with a control system constantly checking to see if the target direction has been reached.
The objective of the Alaska Microgravity Team's proposal is to investigate the behavior of two common small satellite attitude control systems (magnetic torque coils and reaction wheels) with the intent of characterizing the "wobble" of a small satellite as it settles into a desired orientation. The zero-gravity environment of the C-9 will allow the attitude control platforms to function in 3-D space, providing test data that can not be obtained in an earth-based lab's gravity-restrained environment.
Please check back in December to see if we've made it into the Reduced Gravity Flight Program!
TEAM MEMBERS
Dr. Denise Thorsen, Faculty Advisor - Dr. Thorsen is an Assistant Professor of Electrical and Computer Engineering at UAF. She has worked with the Alaska Space Grant for several years and is very interested in small satellite technology. She is currently pursuing the creation of a small satellite design class to be offered at UAF and intends to use the Alaska Microgravity Team's research as a stepping stone in the eventual launch of a small satellite built by UAF students!
Mathew Anctil - Mathew is a junior in Electrical Engineering. He interned at NASA Johnson Space Center during the summer of 2007, where our inspiration to develop an experiment for RGSFP began.
Lindsay Briggs - Lindsay is a junior in Electrical Engineering. She has extensive EE background through student projects and is also skilled at speaking with young people.
Tess Caswell - Tess is a senior in Mechanical Engineering. She was a member of the 2007 NASA Academy at Goddard Space Flight Center and has also worked with the space shuttle program at Boeing.
Jesse Frey - Jesse is a junior in electrical engineering. He has worked with the Alaska Space Grant for two years and is well-versed in space flight electronics.
Devin Hahne - Devin is a senior in mechanical engineering. He is currently the project manager for the Alaska Student Rocket Project and has previously interned at Goddard Space Flight Center.
PROJECT ABSTRACT
Current aerospace trends encourage satellites to be smaller, faster, and cheaper. However, the physical limitations of such small satellites create unique design challenges. To define one of these challenges for future small satellite missions built by students at the University of Alaska Fairbanks, a team of mechanical and electrical engineering students will study the accuracy and stability of small satellite attitude control systems (ACS).
This experiment will focus on the challenge of reaching an attitude position quickly and efficiently. Many small satellites experiences oscillations as their attitude control system stabilizes in the desired orientation. This oscillation reduces the efficiency of an attitude control system and imposes a greater draw on the satellite's already limited power supply. This project's mission is to investigate such instability and characterize it with the objective of overcoming the problem on future missions.
After designing and constructing two control systems, one mechanical and one electromagnetic, the students will evaluate the pointing accuracy and short-term stability of platforms employing these systems in zero gravity. Because the platforms cannot realistically "hover" while maintaining a reasonable 3-axis test environment, this evaluation is not possible in a one-g environment. Zero-g flights through the Reduced Gravity Student Flight Program will allow investigation of the ACS platforms in a three-dimensional environment similar to space, where the systems will eventually be required to function, without relying on a costly in-situ evaluation of attitude control systems in orbit.
Further evaluation of the platforms based on small satellite requirements such as mass, volume, and power will provide a research and design foundation for future missions.