Design Considerations and Operational Results of an Attitude Determination Unit

Mark Kuhl, Xinhua Qin, and William Cottrell

Abstract:	The new Ashtech Three-dimensional Direction Finding (3DF) Attitude Determination Unit (ADU) has been developed for users who wish to have a “black box” sensor design for easy integration into their host vehicles. The ADU features four GPS antennas capable of tracking up to six satellites each, and providing differential position and attitude information at twice per second. User interface is through two RS-232 ports which are capable of sending the raw measurement data as well as the computed attitude and position data. With the GPS satellite constellation having reached IOC, navigation users are now able to use GPS receivers virtually 24 hours a day. This is especially important for the 3DF ADU, since it requires a minimum of four satellites tracked by all four antennas in order to initially compute a vehicle’s attitude. (Note that attitude can be maintained with only three satellites.) Even though attitude may be obtained by using only three antennas, the ADU’s four-antenna design provides quick initial ambigu- ity resolution and redundancy for assuring the quality of the computed attitude information. Computed baseline rms errors and phase measurement rms errors are used to gauge attitude solution integrity. Operational results from land, sea and air environments are presented to represent the wide range of applications for the ADU. Notably, each of these environments has its own unique considerations when employing a GPS attitude determination system. Comparisons between the ADU and other instruments which provide precise attitude information are given. Also depicted are the prominent error sources which affect the performance of attitude determination systems.
Published in:	Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994) September 20 - 23, 1994 Salt Palace Convention Center Salt Lake City, UT
Pages:	689 - 696
Cite this article:	Kuhl, Mark, Qin, Xinhua, Cottrell, William, "Design Considerations and Operational Results of an Attitude Determination Unit," Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994), Salt Lake City, UT, September 1994, pp. 689-696.
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