A Concept of Guidance for an Air-Launch Vehicle with Compensation of Initial Downrange and Launch Time Errors at Direct Insertion into a Rendezvous Point in the Orbit

A flying launcher (airplane carrier) can generate initial errors in position and time of launch. In order to compensate for these errors, one should have two control parameters in addition to those that provide for a spacecraft's injection into a preset orbit. We suggest the concept of controlling the trajectory of injection by choosing thrust values (within allowable regions of control) of second-stage engines or/and of a space booster of the Polyot carrier launcher. As an example, a rendezvous of the spacecraft at the end of its boost phase with the International Space Station (ISS) is considered. The methodology of the suggested approach can be extended to other mobile systems of launch to rendezvous orbits.     

Measurement of Vibration Microaccelerations onboard the Mir Orbital Station Using the VM-09 System of Accelerometers

The results of processing the data of measurements of microaccelerations, carried out onboard the Mir orbital station using the Russian VM-09 system of accelerometers, are described. The system was developed by the Composite Research-Production Association. The sensitivity of this system was 10^–4 m/s²; its frequency band had limits from a few tenths of a hertz up to 100 Hz. The measurements were carried out in the real-time mode of data transmission to the Earth, when the orbital station flew over the telemetry data receiving point. The instrument's sampling rate was 200 measurements per second, and the length of a continuous run of measurements did not exceed 10 min. The following problems are considered in the paper: (1) isolation of cyclic trends from the measurement data; (2) estimation of spectral density of the data component with a continuous spectrum; and (3) low-frequency filtration of the measurement data     

Results of Space-Flight Tests of the Vibration-Protective Platform VZP-1K

The data of microacceleration measurements performed onboard the Mirstation are analyzed. The data were taken while testing the passive vibration-protective platform VZP-1K developed by the NPO Kompozit. We have processed the results of simultaneous microacceleration measurements on the vibration-protective platform and on the station body close to the platform. Two sets of the French equipment Microaccelerometer were used for these measurements. It was found that the platform reduces the vibrational component of microaccelerations in the band of frequencies above 3 Hz by more than a factor of 10. In this case, all harmonics with large amplitudes are damped by a factor of 50 and more, and some harmonics with small amplitude are damped only by a factor of 10. In the band 0.3–0.6 Hz (close to natural frequencies of the platform), the several-fold increase in amplitude of the vibrational component of microaccelerations is observed, but since the initial values of this amplitude in all performed experiments were small, the above indicated increase practically has not decreased the vibration-protective properties of the platform. The estimations of natural frequencies and damping coefficients of the platform found as a result of data processing of microacceleration measurements made during its free oscillations are obtained. The dependence of frequencies on the amplitude of oscillations is revealed for one mode, which testifies to appreciable nonlinear effects.     

Tetrahedral satellite formation: Geomagnetic measurements exchange and interpolation

This note presents a study of a four-satellite tetrahedral formation to collect, process, and exchange multipoint measurements of geomagnetic field in a near-polar orbit. The study is conducted as a series of numerical experiments based on simulated spacecraft orbits and corresponding geomagnetic field models output. The four satellites are assumed to move in near-circular orbits specifically chosen to maintain the tetrahedron quality. The satellites exchange their simulated magnetometers readings and the collected multipoint measurements are processed on board of any of them thus creating an instantaneous interpolated map of the geomagnetic field in the interior of the tetrahedron. Interpolation is carried out with the use of Kriging algorithms, known in geostatistics for capturing spatial correlation of the data and taking into account statistical properties of the interpolated variables. We propose a concept of a servicing formation, and analyze interpolation accuracy for different formation sizes. It is then discussed how the processed multipoint measurements can be provided as a service to other nearby satellites. Finally, we show that using the existing COTS magnetometers it is possible to obtain real-time interpolation data, which are more precise at a given point and time than a conventional onboard magnetic field model, thus ensuring better attitude determination routines performance in the serviced spacecraft.     

Estimation of foF2 variations using round-the-world sounding data

An estimation of the F2 ionospheric region critical frequency (foF2) variations using analysis of round-the-world radio sounding data has been made. Experimental data obtained by the Russian chirp-sounders network have been used. For the first time, using experimental data and numerical simulation, the quantitative dependency between the minimum foF2 magnitudes over round-the-world propagation paths and round-the-world maximum usable frequencies has been obtained.     

Multi-frequency doppler radio sounding of the ionosphere in the “Equatorial trigger” experiment

Results of processing the data of multi-frequency Doppler sounding of the low-latitude ionosphere are presented. Interesting features in the behavior of time variations of the Doppler frequency shift are found. These features are interpreted as manifestations of wave disturbances in the ionospheric plasma density.     

Numerical simulation of gas dynamics and heat exchange of jet impinging on a surface

The results of verification calculation of single jets impinging on a pedestal are presented; the result of calculations is evaluation of the local Nusselt numbers and flow gas-dynamic characteristics. On the basis of literature analysis we picked out several turbulence models to close the system of equations. The calculation results are compared with the known experimental data. It is shown, that only the v ² ? f turbulence model allows the augmented turbulence characteristics to be predicted adequately that correspond to a change of the flow conditions at short jet-to-surface distances. All models being investigated except the Spalart-Allmaras model show satisfactory agreement both in the stagnation region and in the near-wall jet zone.     

Uncontrolled Attitude Motion of the Foton-12 Satellite and Quasi-Steady Microaccelerations onboard It

The results of determination of the uncontrolled attitude motion of the Foton-12 satellite (placed in orbit on September 9, 1999, terminated its flight on September 24, 1999) are presented. The determination was carried out by the onboard measurement data of the Earth's magnetic field strength vector. Intervals with a duration of several hours were selected from data covering almost the entire flight. On each such interval the data were processed simultaneously using the least squares method by integrating the satellite's equations of motion with respect to the center of mass. The initial conditions of motion and the parameters of the mathematical model employed were estimated in processing. The results obtained provided for a complete representation of the satellite's motion during the flight. This motion, beginning with a small angular velocity, gradually sped up. The growth of the component of the angular velocity with respect to the longitudinal axis of the satellite was particularly strong. During the first several days of the flight this component increased virtually after every passage through the orbit's perigee. As the satellite's angular velocity increased, its motion became more and more similar to the regular Euler precession of an axisymmetric rigid body. In the last several days of flight the satellite's angular velocity with respect to its longitudinal axis was about 1 deg/s and the projection of the angular velocity onto the plane perpendicular to this axis had a magnitude of approximately 0.15 deg/s. The deviation of the longitudinal axis from the normal to the orbit plane did not exceed 60°. The knowledge of the attitude motion of the satellite allowed us to determine the quasi-steady microacceleration component onboard it at the locations of the technological and scientific equipment.     

Micromechanical gyros & accelerometers for digital navigation & control systems

There is no general consensus of opinion about the future of micromechanical gyroscopes and accelerometers. According to the pessimistic estimation, micromechanical gyroscopes and accelerometers have attained the limit of their accuracy. However, optimists believe that micromechamical gyroscopes will soon occupy the niche of fiber-optical gyroscopes and the latter will press laser gyroscopes. The present-day development of micromechanical gyroscopes and accelerometers is aimed at improving the basic and minor parameters: sensitivity, bias, offset, drift, resolution, scale factor, and its non-linearity. High level of performance is provided by application of high technology. This is devoted to the development and manufacturing of "silicon-glass" micromechanical sensors of encapsulated-type with digital output processing. The key technological processes allowing production of micromechanical encapsulated sensors with vacuum insides are considered and the features of their design are described. The methods for maintaining high reliability of encapsulated micromechanical gyroscopes with inner getter structure are discussed. ASIC designs for control and processing of micromechanical sensor outputs allow their accuracy, which is part of modern integrated systems, to be considerably improved. Also considered are various assemblies and packaging of the ASIC and micromechanical sensor as a single product.