An Analysis of the Low-Frequency Component in Measurements of Angular Velocity and Microacceleration onboard the Foton-12 Satellite

We compare the results of two methods used to determine the angular velocity of the Foton-12 satellite and the low-frequency component of microaccelerations onboard it. The first method is based on reconstruction of the satellite's rotational motion using the data of onboard measurements of the strength of the Earth's magnetic field. The motion (time dependence of the orientation parameters and angular velocity) was found from the condition of best approximation of the measurement data by the functions calculated along the solutions to equations of attitude motion of the satellite. The solutions found were used to calculate the quasistatic component of microaccelerations at certain points of the satellite, in particular, at the point of location of an accelerometer of the QSAM system. Filtration of the low-frequency component of the angular velocity and microacceleration from the data of measurements by a sensor of angular velocity and by the accelerometer of this system served as a second method. The filtration was made using the discrete Fourier series. A spectral analysis of the functions representing the results of determining the angular velocity and microacceleration by both methods is performed. Comparing the frequencies and amplitudes of the harmonic component of these functions allowed us to estimate the accuracy of measurements made by the QSAM system in the low-frequency range.     

Experiments with the DAKON-M convection sensor

We have described an express technique for processing the results of experiments with a DAKON-M convection sensor on board the Service Module of the International Space Station (ISS) in 2011. The technique uses a certain rule to compare the sensor measurements with the calculated data on the quasistatic component of microacceleration at the point of installation. The sensor experiments have been conducted during shuttle docking and undocking, when low-frequency microaccelerations on the ISS were significant. The microaccelerations have been calculated using measurement data of the MAMS low-frequency accelerometer installed in the Lab module and the telemetry data on the ISS rotational motion. This has made it possible to convert the MAMS measurement data to the DAKON-M convection sensor installation point. A comparison of sensor readings with calculated microaccelerations has revealed fairly good agreement between them.     

Investigation of Thermal Convection and Low-Frequency Microgravity by the DACON Sensor aboard the MirOrbital Complex

The DACON instrument for studying the convection caused by low frequency microaccelerations aboard spacecraft is described. The convection sensor serves as a measuring element of this instrument. This is a cylindrical cavity filled with air, where two crossed differential thermocouples are located. The thermocouple junctions lay on two mutually perpendicular lines parallel to the bases of the cylinder and crossing at its axis. The distances from the junctions to this axis are equal. The lateral surface of the cylinder is thermally insulated, the difference of temperatures on its bases being kept constant. One of the tasks for the sensor is to prepare the data for checking the adequacy of mathematical models of fluid convection under weightlessness conditions and for obtaining quantitative characteristics of the microgravitational medium. The results of ground-based tests of the DACON instrument and the results of experiments with it aboard the Mirstation are presented.     

Effect of Microaccelerations on the Distribution of a Dopant in a Semiconductor Melt during Space Flight

The effect of residual microaccelerations on the distribution of a dopant in a semiconductor melt located in a heated closed cavity onboard an Earth-orbiting satellite is considered in the context of a model problem of thermal convection. The amplitude–frequency characteristics of the response of this distribution to the perturbing microaccelerations are obtained. It is demonstrated that the effect of low-frequency microaccelerations decreases when the frequency increases. A comparison is made of the macroscopic inhomogeneities of the dopant concentration due to the actual low-frequency (quasi-static) component of microaccelerations onboard different spacecraft: the orbital station Mir, the satellite Foton-11, a Space Shuttle orbiter, and the International Space Station. A substantial effect of the rotational motion of the spacecraft on the character of the time behavior of a macroscopic inhomogeneity is demonstrated.     

Analysis of Low-Frequency Microaccelerations onboard the Foton-11Satellite

The method and the results of investigating the low-frequency component of microaccelerations onboard the Foton-11satellite are presented. The investigation was based on the processing of data of the angular velocity measurements made by the German system QSAM, as well as the data of measurements of microaccelerations performed by the QSAM system and by the French accelerometer BETA. The processing was carried out in the following manner. A low-frequency (frequencies less than 0.01 Hz) component was selected from the data of measurements of each component of the angular velocity vector or of the microacceleration, and an approximation was constructed of the obtained vector function by a similar function that was calculated along the solutions to the differential equations of motion of the satellite with respect to its center of mass. The construction was carried out by the least squares method. The initial conditions of the satellite motion, its aerodynamic parameters, and constant biases in the measurement data were used as fitting parameters. The time intervals on which the approximation was constructed were from one to five hours long. The processing of the measurements performed with three different instruments produced sufficiently close results. It turned out to be that the rotational motion of the satellite during nearly the entire flight was close to the regular Eulerian precession of the axially symmetric rigid body. The angular velocity of the satellite with respect to its longitudinal axis was about 1 deg/s, while the projection of the angular velocity onto the plane perpendicular to this axis had an absolute value of about 0.2 deg/s. The magnitude of the quasistatic component of microaccelerations in the locations of the accelerometers QSAM and BETA did not exceed 5 × 10^–5–10^–4m/s²for the considered motion of the satellite.     

Study of microaccelerations onboard the <Emphasis Type="Italic">International Space Station</Emphasis> with the DAKON-M convection sensor

The results of experiments with the DAKON-M convection sensor onboard the Russian orbital segment of the International Space Station are described. A comparison of the sensor measurements with the results of calculation of the quasistatic microacceleration component at the point of installation is made. For this comparison we have used three measurement intervals of the experiments in 2009, during which spacecraft were docked with the station, undocked from it, and actuation of jet engines of the attitude control system took place. When calculating microacceleration, we use the measurement data of the low-frequency MAMS accelerometer, installed on the American segment, and the telemetry data on the ISS rotational motion. This information allowed one to convert the MAMS measurements to the point of installation of the DAKON-M convection sensor. A comparison of sensor measurements with calculated microaccelerations showed sufficiently accurate coincidence between the calculated and measured data.     

Low-Frequency Microaccelerations onboard the Foton-11 Satellite

We analyze the microacceleration measurements carried out onboard the Foton-11 satellite with the three-component accelerometer BETA. The microaccelerations were recorded virtually throughout the entire orbital flight of the Foton-11 satellite. The data obtained were analyzed in the following way. First they were used to determine the actual rotational motion of the satellite for several arbitrarily selected time intervals 4 h long. This problem was solved by constructing the approximation of the microacceleretation low-frequency component (previously determined from the data) by its calculated analog computed along the solutions to differential equations of rotational motion of the satellite. The approximation was made by the least squares method. As a result, those mathematical model parameters and the solutions to equations of motion were found that gave the best consistency of the microacceleretation low-frequency component and its calculated analog. Then the spectral analysis of the low-frequency component and its calculated analog was made. It was shown that, although basic harmonics of these functions coincided sufficiently well, some harmonics of the low-frequency component failed to be interpreted in terms of the satellite's rotational motion.     

The Mode of Gravitational Orientation for the International Space Station

The results of the determination of the uncontrolled attitude motion of the International Space Station during its unmanned flight in 1999 are presented. The data of onboard measurements of three components of the angular velocity are used for this determination. These data covering an interval of slightly less than one orbit were jointly processed by the least squares method, by integrating the equations of motion of the station relative to its center of mass. As a result of this processing, the initial conditions of the motion and the parameters of the mathematical model used were estimated. The actual motion of the station has been determined for 20 such intervals during April–November. Throughout these intervals, the station rotated about the axis of the minimum moment of inertia, the latter executing small oscillations relative to the local vertical. Such a mode, known as the mode of gravitational orientation of a rotating satellite or the mode of generalized gravitational orientation, was planned before the flight. The measurements were made to verify it. The quasistatic component of the microaccelerations aboard the station is estimated for this mode.     

Estimation of residual microaccelerations on board an artificial earth satellite in the monoaxial solar orientation mode

The mode of monoaxial solar orientation of a designed artificial Earth satellite (AES), intended for microgravitational investigations, is studied. In this mode the normal line to the plane of satellite’s solar batteries is permanently directed at the Sun, the absolute angular velocity of a satellite is virtually equal to zero. The mode is implemented by means of an electromechanical system of powered flywheels or gyrodynes. The calculation of the level of microaccelerations arising on board in such a mode, was carried out by mathematical modeling of satellite motion with respect to the center of masses under an effect of gravitational and restoring aerodynamic moments, as well as of the moment produced by the gyrosystem. Two versions of a law for controlling the characteristic angular momentum of a gyrosystem are considered. The first version provides only attenuation of satellite’s perturbed motion in the vicinity of the position of rest with the required velocity. The second version restricts, in addition, the increase in the accumulated angular momentum of a gyrosystem by controlling the angle of rotation of the satellite around the normal to the light-sensitive side of the solar batteries. Both control law versions are shown to maintain the monoaxial orientation mode to a required accuracy and provide a very low level of quasistatic microaccelerations on board the satellite.     

Quasistatic Microaccelerations onboard the Foton Satellite during Its Flight at High-Altitude Orbits

The level of quasistatic microaccelerations onboard the Foton-M satellite is predicted for its flights in two orbits: the planned orbit with the altitudes in perigee h = 262 km and in apogee h = 304 km and the orbit with h = 262 km and h = 350 km. The prediction is based on mathematical simulation of the satellite motion with respect to its center of mass under the action of gravitational and aerodynamic moments. The model is represented by the system of equations of the satellite rotational motion. Parameters of this system are chosen from the condition of coincidence of the motion of preceding Foton satellites (h 220 km and h 400 km) calculated using this model with the results of determination of actual rotational motion of the Foton-11 and Foton-12 satellites. With the help of the model thus calibrated, a calculation is made of the rotational motion of the Foton-M satellite and of the quasistatic microaccelerations onboard it. As is shown by the results of simulation, the use of the first and the second orbits will result in reductions of microaccelerations by 30% and 60%, respectively.     

Mathematical Modeling of Convection in the DACON Sensor under Conditions of Real Space Flight

A mathematical model of the operation of the sensor of convection under ground and space conditions is described, and the results of modeling are compared to experimental data. A good agreement of the model and experiment is obtained for ground conditions. The sensor operation under conditions of a space flight is simulated using actual microaccelerations that took place onboard the Mirstation. Good sensitivity of the sensor to the measured components of acceleration is demonstrated. The results of simulation are compared to the results of space experiments carried out with the DACON instrument onboard the Mirstation.     

Realization of modes of satellite attitude motion with a small level of microaccelerations using electromechanical executive devices

Quasi-static microaccelerations are estimated for a satellite specially designed to perform space experiments in the field of microgravity. Three modes of attitude motion of the spacecraft are considered: passive gravitational orientation, orbital orientation, and semi-passive gravitational orientation. In these modes the lengthwise axis of the satellite is directed along the local vertical, while solar arrays lie in the orbit plane. The second and third modes are maintained using electromechanical executive devices: flywheel engines or gyrodynes. Estimations of residual microaccelerations are performed with the help of mathematical modeling of satellite’s attitude motion under the action of gravitational and aerodynamic moments, as well as the moment produced by the gyro system. It is demonstrated that all modes ensure rather low level of quasi-static microaccelerations on the satellite and provide for a fairly narrow region of variation for the vector of residual microacceleration. The semi-passive gravitational orientation ensures also a limited proper angular momentum of the gyro system.     

The Influence of Arrangement of Growth Setups onboard a Spacecraft on Microgravity Conditions of Experiments: An Example of Floating Zone Melting of InSb:Te onboard the Foton-3 Satellite

The results of experiments on the growth of InSb:Te by the floating zone melting in the Zona-4 setup during a flight of the Foton-3 satellite are discussed in comparison with the data on the microgravity situation typical for satellites of this type. When analyzing inhomogeneities in the crystals obtained, we reveal the frequencies corresponding to periodical variations of the impurity channel position (the facet effect), to interleaving of packs in which the growth layers are grouped, and to location of subgroups of the growth layers inside the packs. These frequencies are close to those discovered during measurements of low-frequency (quasistationary) microaccelerations (g) onboard the spacecraft Foton-8, Foton-10, Foton-11, and Foton-12. Calculated values of g at the place where the Zona-4 setup is installed confirm the possibility of impact of such g on the heat and mass transfer in the melt.     

Convective Motions in Near-Critical Fluids under Real Zero-Gravity Conditions

The results of processing and interpreting the data of joint Russian–French experiments for studying the heat and mass transfer in near-critical fluids are presented. The experiments were carried out with the ALICE-1 instrument during an orbital flight of the Mirstation from September 30 to October 2, 1995 [1]. For such fluids with a point-like source of heat, when they are placed in the field of uncontrolled inertial accelerations of the spacecraft, the influence of thermovibrational and thermogravitational mechanisms of convection on the propagation of the region of optical irregularity is investigated. It is shown that, near the thermodynamic critical point, local heating of the medium leads to generation of either intense thermogravitational convection or averaged vibroconvective flow, depending on the frequency of variations of the microaccelerations. The structure and characteristics of discovered motions are studied. The results of numerical simulations are presented that confirm the conclusion about a possibility of generation of an averaged convective flow of a vibrational type by the high-frequency component of microaccelerations.     

Study of vibration microaccelerations onboard the International Space Station

The results of studying vibration microaccelerations aboard the International Space Station are presented. The study was performed using the measurement data of the MAMS low-frequency and the SAMS high-frequency accelerometers. For the study, six intervals of measurements were selected, performed in 2005. During these intervals the station was flying in the standard orbital orientation, attitude control engines were not switched on, and the crew rested. Discrete and continuous spectra were analyzed on selected intervals. The most significant disturbances with the discrete spectrum (cyclic trends) have been found. Using the second order autoregression model, parameters of the most significant disturbances with the continuous spectrum were determined. This study was carried out as a part of the technical experiment “The ISS environment”.     

Processing the data of measurements of angular velocity and microaccelerations onboard the <Emphasis Type="Italic">Foton-12</Emphasis> satellite

The results of reconstruction of uncontrolled rotational motion of the Foton-12 satellite using the measurement data of onboard sensors are presented. This problem has already been solved successfully several years ago. The satellite motion was reconstructed using the data of measuring the Earth’s magnetic field. The data of measuring the angular velocity and microaccelerations by the QSAM system were actually not used for this purpose, since these data include a clearly seen additional component whose origin was at that time unclear. This component prevented one from using these data directly for reconstruction of the angular motion. Later it became clear that the additional component was caused by the Earth’s magnetic field. Discovery of this fact allowed us to make necessary corrections when processing the QSAM system data and to use them for reconstruction of rotational motion of Foton-12. Below, a modified method of processing the QSAM system data is described together with the results of its application. The main result is obtained by comparing the motion reconstructed from measurements of angular velocity or acceleration with that found by way of processing the measurements of the Earth’s magnetic field. Their coincidence turned out to be rather accurate.     

Determination of quasi-static microaccelerations onboard a satellite using video images of moving objects

A space experiment aimed at determination of quasi-static microaccelerations onboard an artificial satellite of the Earth using video images of the objects executing free motion is considered. The experiment was carried out onboard the Foton M-3 satellite. Several pellets moved in a cubic box fixed on the satellite’s mainframe and having two transparent adjacent walls. Their motion was photographed by a digital video camera. The camera was installed facing one of the transparent walls; a mirror was placed at an angle to another transparent wall. Such an optical system allowed us to have in a single frame two images of the pellets from differing viewpoints. The motion of the pellets was photographed on time intervals lasting 96 s. Pauses between these intervals were also equal to 96 s. A special processing of a separate image allowed us to determine coordinates of the pellet centers in the camera’s coordinate system. The sequence of frames belonging to a continuous interval of photography was processed in the following way. The time dependence of each coordinate of every pellet was approximated by a second degree polynomial using the least squares method. The coefficient of squared time is equal to a half of the corresponding microacceleration component. As has been shown by processing made, the described method of determination of quasi-static microaccelerations turned out to be sufficiently sensitive and accurate.     

Determination of the Quasistatic Component of Microaccelerations at the MirStation

We describe the determination of the quasistatic component of microaccelerations, as it was done during the space experiments with the instruments DACON and ALICE-2. This component was calculated using the telemetric information related to the motion of the station with respect to its center of mass. The information consists of the values of the station angular velocity vector and the quaternion which specifies its orientation, determined at discrete instants of time. The quaternion is determined with a step of about 1 min, the angular velocity with a step of about 10 s. The information is used in the following manner. At first, the quaternion components corresponding to some time interval are smoothed by splines. Then, employing the obtained splines and kinematic equations, the angular velocity and acceleration of the station are calculated on this interval. Finally, the microacceleration is calculated as a function of time at the point of the location of the instrument. The data of measurements of the angular velocity are used for the purpose of control. As a rule, the available telemetric information allows one to find the quasi-static component for the entire time interval of carrying out the experiment. Examples of determination of this component for some experiments are presented. A comparison with the results of calculating the microacceleration quasistatic component by other methods is made.     

Influence of Microaccelerations on the Impurity Distribution in the InSb:Te Crystals Grown in Orbital Flights by the Method of Floating Zone Melting

The periodicity of the structure of impurity heterogeneities in the longitudinal section of an indium antimonide monocrystal doped by tellurium (InSb:Te) is investigated. The monocrystal was grown by the method of floating zone melting onboard the Foton-3 satellite. It is shown that the frequencies of harmonic components of heterogeneities converted into the time region coincide with frequencies of microaccelerations in the range 0–0.005 Hz arising onboard the Foton satellites. This fact confirms the hypothesis stated previously that residual microaccelerations onboard the satellite were the cause of occurrence of indicated periodicities.     

Reconstruction of spacecraft rotational motion using a Kalman filter

Quasi-static microaccelerations of four satellites of the Foton series (nos. 11, 12, M-2, M-3) were monitored as follows. First, according to measurements of onboard sensors obtained in a certain time interval, spacecraft rotational motion was reconstructed in this interval. Then, along the found motion, microacceleration at a given onboard point was calculated according to the known formula as a function of time. The motion was reconstructed by the least squares method using the solutions to the equations of satellite rotational motion. The time intervals in which these equations make reconstruction possible were from one to five orbital revolutions. This length is increased with the modulus of the satellite angular velocity. To get an idea on microaccelerations and satellite motion during an entire flight, the motion was reconstructed in several tens of such intervals. This paper proposes a method for motion reconstruction suitable for an interval of arbitrary length. The method is based on the Kalman filter. We preliminary describe a new version of the method for reconstructing uncontrolled satellite rotational motion from magnetic measurements using the least squares method, which is essentially used to construct the Kalman filter. The results of comparison of both methods are presented using the data obtained on a flight of the Foton M-3.