An Optimally Integrated Track Recovery System for Aerial Bathymetry

An airborne system has been developed for charting shallow coastal and inland waters. The primary components of this system are an aerial survey camera, a profiling laser radar, an analytical stereo plotter, and a multisensor track recovery system (TRS). The TRS comprises a gimbaled inertial navigation system and a number of auxiliary sensors which acquire redundant position and attitude information. The sensor data are combined postmission using a U-D factorized Kalman filter and modified Bryson-Frazier smoother to compute accurate estimates of the orientation parameters of the survey camera at the times of film exposure. These parameters are used to position each overlapping pair of photographs on the analytical plotter to form a stereo image and corresonding analytical stereomodel from which water depth measurements are made. Flight trial results demonstrate that the TRS can achieve radial position and attitude accuracies which exceed 1 m and 2 arcmin root mean square (rms), respectively, and that this level of performance is sufficient to enable water depth measurements to be made to an accuracy of better than 0.65 m (rms).     

Fuel Savings in the WHECON Attitude Control System Using an Asymmetric Controller

This paper investigates the possibility of generating an on-off limit cycle mode in the WHECON attitude control system. lt is shown that, by eliminating the off set angle ? in the roll-actuated control torquer, the WHECON system can be reduced to the structure considered earlier by Mendel and, therefore, an on-off limit cycle can be generated simply by introducing an appropriate amount of asymmetry into the deadzone characteristic of the WHECON controller. Because with this mode of on-off limit cycle the thruster jets will fire only once in each cycle of the oscillation, it is claimed that a considerable amount of fuel can be saved by the proposed modifications to the original WHECON design. Dynamic simulation study was conducted with the actual nonlinear model of the WHECON system considered and the results indicate that, for both zero and nonzero values of the off set angle ?, substantial fuel savings can be achieved by using the asymmetric controller.     

Cardiovascular effects of simulated zero-gravity in humans

Head-down and head-up [correction of heat-up] tilted bedrest (5 degrees) and head out water immersion (HOWI) for 6 hr were compared. Parameters: Cardiac output (rebreathing method), blood pressure (arm cuff), forearm blood flow (venous occlusion plethysmography), total peripheral (TPR), and forearm vascular (FVR) resistances, Hct, Hb, relative plasma volume (PV) changes, and plasma catecholamines (single-isotope assay). During HOWI there was as expected a decrement in TPR, FVR, Mean arterial pressure (MAP, from 100 to 80 mmHg), Hct, and PV, and--as a new finding--catecholamines, which were 30-50% lower compared with both +5 and -5 degrees bedrest. During head down tilt, MAP was elevated (to 100-110 mmHg) and catecholamines did not fall, while TPR and EVR slowly decreased over 6 hr. HOWI is a stronger stimulus than -5 degrees bedrest, probably because HOWI elevates central venous pressure more markedly emptying the peripheral veins, while bedrest permits a distension of veins, which induces an increase in sympathetic nervous activity.     

Application of Recursive Estimation and Kalman Filtering to Doppler Tracking

The techniques of recursive estimation and Kalman filtering are applied to the problem of estimation of space vehicle orbits and trajectories using only measurements of the Doppler shifts in radio signals transmitted by or reflected from the target. Two approaches are described. One is a global fit technique in which the parameters of an assumed trajectory model are estimated. The second is a pointwise mapping technique in which the trajectory estimate is extrapolated as the target tracking data is received. The paper provides a tutorial illustration of the direct application of recursive optimization techniques to a class of engineering problems.     

Experiments with injection of powerful plasma jet into the ionosphere

This paper describes two rocket experiments “Aelita” with high power lithium plasma injection. The results of onboard magnetometer, massspectrometer, photometer, plasma, corpuscular and ground radar measurements are given. Dynamics and structure of plasma formation are discussed.     

Determination of Bounds on Performance Measure and Min-Max Controllers in Time-Lag Systems

The effect of bounded deterministic disturbances (external and/or internal) on a chosen performance index (PI) is investigated. Upper and lower bounds of the PI about a nominal value are determined by the application of the optimum control theory. A computational procedure is also proposed to determine an approximately optimal feedback controller for time-lag systems. Such a controller is designed here on the basis of min-max criteria. Numerical examples illustrate the proposed approach.     

Performance Degradation Due to Specular Multipath Intersymbol Interference

Plots of performance degradation are used to compare the effects of fading and intersymbol interference in a two- component specular multipath digital communications channel. Similar plots are then used to compare two practical receivers designed to combat the interference. Degradation plots are shown to allow easy identification of each receiver's range of usefulness, as well as identification of variance bounds demanded of channel parameter estimates which the receivers require.     

Airglow atmospheric imager on board the ‘IK-Bulgaria-1300’ satellite

This paper shows the possibilities of the optical scanning imager for investigation of the structure of the auroral, SAR and tropical arcs and in this way to study the particle precipitation, neutral winds across the magnetic equator, drifts, electric fields and the current systems in the ionosphere.     

Stability of Gyro in a Vehicle Spinning with Uncertain Angular Velocity

The analysis of a single-axis rate gyroscope mounted in a vehicle which is spinning with uncertain angular velocity about the spin axis of the gyro is presented. The nonlinearity in the equation of motion of the gimbal is retained. Using circle criterion, it is shown that the gimbal motion is globally asymptotically stable if Nyquist plot of the linear transfer function of the gyro lies in the interior of a certain disk. A simple analytical relation for the selection of gyro parameters for stability is derived.