Showing papers on "Inertial reference unit published in 1981"

Control, navigation, and guidance

Abstract: Self-contained systems providing control and navigation for vehicles of all kinds use gyroscopic elements to maintain reference directions with respect to inertial space. Sensors for resultant gravity field and inertial reaction forces along input axes determine the vertical and also linear velocities with respect to inertial space. These components divided by an equivalent Earth radius transfer the motion to Earth coordinates in which integration gives location. Corrections for Earth's rotation projected in and perpendicular to the horizontal plane are made as computed cosine and sine projections of Earth's angular velocity. Current systems result with the order of fractional miles per hour performance.

From kinematical geodesy to inertial positioning

Abstract: WhenH. Moritz (1967, 1971) studied “kinematical geodesy” for the purpose of separation of gravitation and inertia, especially within combined accelerometer-gradiometer systems, it was hard to believe that within five years time inertial survey systems would be available, exactly operating according to his theoretical design. Here, we attempt to give a geodetic introduction into the fundamental equation of inertial positioning materialized by inertial survey systems with emphasis on a careful error model, including 36 parameters of type time interval, initial positions, initial gravity, varying acceleration, varying gravity gradients, accelerometer bias, accelerometer random uncertainty, accelerometer non-orthogonality, initial misalignment angles, accelerometer scale factor uncertainty. The notion of “multipoint” boundary value problem and initial value problem of inertial positioning is reviwed. So-called “post-mission” adjustment techniques for inertial surveys are discussed.

A comparison of models in inertial surveying

Abstract: The output of an inertial measuring unit contains the combined effect of vehicle acceleration, accelerations due to the reference system, gravitational attraction, calibration and alignment errors, and measuring noise. The separation of individual effects from the total output is the task of modelling. Differences in the existing models are mainly due to the treatment of system errors and of the anomalous gravity field.

Inertial Survey Adjustment

Abstract: : The paper discusses primarily a least-squares position adjustment for single or multiple (area coverage) inertial traverses. The adjustment technique is developed and presented in detail for a local-level inertial system and summarily generalized for a space-stable inertial system. Application of the method to other inertially derived geodetic values is discussed. (Author)

Voyager Saturn encounter attitude and articulation control experience

Abstract: The Voyager attitude and articulation control system is designed for a three-axis stabilized spacecraft; it uses a biasable sun sensor and a Canopus Star Tracker (CST) for celestial control, as well as a dry inertial reference unit, comprised of three dual-axis dry gryos, for inertial control. A series of complex maneuvers was required during the first of two Voyager spacecraft encounters with Saturn (November 13, 1980); these maneuvers involved rotating the spacecraft simultaneously about two or three axes while maintaining accurate pointing of the scan platform. Titan and Saturn earth occulation experiments and a ring scattering experiment are described. Target motion compensation and the effects of celestial sensor interference are also considered. Failure of the CST, which required an extensive reevaluation of the star reference and attitude control mode strategy, is discussed. Results analyzed thus far show that the system performed with high accuracy, gathering data deeper into Saturn's atmosphere than on any previous planetary encounter.

OAO-3 end of mission tests report

Abstract: Twelve engineering type tests were performed on several subsystems and experiment(s) of the OAO 3 spacecraft near its end of mission. The systems tested include: Princeton experiment package (PEP), fine error system guidance, inertial reference unit, star trackers, heat pipes, thermal control coatings, command and data handling, solar array; batteries, and onboard processor/power boost regulator. Generally, the systems performed well for the 8 1/2 years life of OAO 3, although some degradation was noted in the sensitivity of PEP and in the absorptivity of the skin coatings. Battery life was prolonged during the life of the mission in large part by carefully monitoring the charge-discharge cycle with careful attention not to overcharge.