Gravitation effect on a flux of sporadic micrometeoroids in the vicinity of near-Earth orbits

The new approach to gravitation effect determination in calculating the flux of sporadic micrometeoroids in the near-Earth space is proposed. The technique is based on integration of the equations of motion of sporadic micrometeoroids with accounting for bending their trajectories when particles are approaching the Earth. The technique and results of calculation of the gravitational focusing factor k_g for various conditions are presented. The feature of the proposed technique for calculating coefficient k_g consists in the fact that this coefficient does not explicitly depend on the values of particles velocity at the last point. The results of investigation of coefficient k_g have shown that, for the given initial velocity of micrometeoroids, the values of this coefficient depend on deflection of its direction from the direction to the Earth center. It is shown that for low-altitude orbits the flux density can increase up to 60%. The distribution of probabilities of various directions of particles flying to spacecraft structural elements is found to be non-uniform.     

Cross-cultural issues in space operations: A survey study among ground personnel of the European Space Agency

Today's space operations involve co-working of people with different ethnical, professional and organisational backgrounds. The aim of this study was to examine the implications of cultural diversity for efficient collaboration within the European Space Agency (ESA), and between ESA employees and representatives from other agencies. ESA employees from European countries (N=576) answered to the CULT Ground Survey. The results showed that differences in relation to leadership and decision making were the most important issues thought to interfere with efficient co-working within ESA, and between ESA employees and colleagues from other agencies. Employees who collaborated with more than three nationalities within ESA indicated most challenges in co-working due to differences in compliance, behavioural norms and competitiveness. Challenges in co-working differed between agencies, and these differences were consistent with value differences in the national populations. The results may have applied value for training of European employees working in international space program teams.     

Robust attitude stabilization of spacecraft subject to actuator failures

A robust nonlinear control scheme is developed to stabilize the 3-axis attitude of the spacecraft for cases where there is no control available on either roll or yaw axis. The stability conditions for robustness against unmatched uncertainties and disturbances are derived to establish the regions of asymptotic 3-axis attitude stabilization. The properties of the proposed sliding surface are investigated to obtain the domains of sliding mode for the closed-loop system. Several numerical simulations are presented to demonstrate the efficacy of the proposed controller and validate the theoretical results. The control algorithm is shown to compensate for time-varying external disturbances including solar radiation pressure, aerodynamic forces, and magnetic disturbances; and uncertainties in the spacecraft inertia parameters. The numerical results also establish the robustness of the proposed control scheme to negate disturbances caused by orbit eccentricity.     

Influences of the turbulence model and the slot width on the transverse slot injection flow field in supersonic flows

Transverse slot injection scheme is very important for the mixing process between the air and the fuel in supersonic flows. The effect of the turbulence model and slot width on the transverse slot injection flow field has been investigated numerically based on the grid independency analysis, and the predicted results have been compared with the experimental data available in the open literature. The obtained results show that the grid scale makes only a slight difference to the wall pressure profiles for all jet-to-crossflow pressure ratios employed in this study, and the wall pressure profile with low jet-to-crossflow pressure ratio is predicted accurately by the RNG k–ε turbulence model, the SST k–ω turbulence model for the flow field with high jet-to-crossflow pressure ratio. High jet-to-crossflow pressure ratio can increase the jet penetration depth in supersonic flows, and the gradient of the length of the upstream separation region is larger than that of the height of the Mach surface. At the same time, when the jet-to-crossflow pressure ratio is maintained constant, the jet penetration depth increases with the increase of the slot width.     

Absorbed doses in October–November 2003 onboard the Russian segment of the International Space Station according to the data of radiation control system

The results of radiation control onboard the Service Module of the International Space Station are considered for the period of increased radiation background from 28 to 30 October, 2003. The values of additional irradiation dose caused by strong solar proton events on October 28 and 29, 2003 are obtained. A comparison is made with similar data obtained in the periods of disturbed radiation conditions of fall 2001. The results of estimating the dependence of the absorbed dose on the shield thickness, based on the onboard measurements, are presented. It is established that the daily-averaged dose power onboard the International Space Station increased after the solar proton events of October 2003.     

Numerical investigation on cavity structure of solid-fuel scramjet combustor

The influences of miscellaneous combustor structures for solid fuel scramjet combustion on the performance are investigated, including a detailed interaction analysis between shocks/waves and combustion. Hydroxyl-terminated polybutadiene is chosen as the solid fuel with the non-premixed equilibrium probability density function combustion model. The results show combustion enhancement when structure of combustor is modified. The radical emphasis is to examine the sensitivity of the properties due to variations on the length-to-depth ratio of cavity, aft wall angle, and offset ratio. It is noted that there is an appropriate structure of cavity (L/D=4, θ=45°, and D_d/D_u=1.25–1.5) regarding the combustion efficiency, total pressure loss and specific impulse. The observation of function for combustor components provides instructional insight into the design considerations for a combustor of a solid-fuel scramjet.     

First results of the intercosmos satellite IK 21

First results are presented of technical tests of a Data Collection System and a multispectral remote sensing complex. The aim of this experiment is to test the hard ware for in situ and remote sensing data collection of oceanographic parameters.     

Prediction of turbulent diffusion flames with a four-equation turbulence model

For turbulent flame prediction a four-equation turbulence model consisting of the turbulent kinetic energy, the dissipation rate and the density-velocity correlations using unweighted statistics is suggested. The fluctuating concentrations are taken into account by using Spalding's (1971) equation for the variance of the mixture fraction f and by defining the probability density function of f as beta-function. The thermodynamic model for the combustion of H₂ with air assumes infinitely fast reaction in a global single step. Preliminary results are shown for the calculation of Kent and Bilger (1972) turbulent H₂-air diffusion flame. For this flame with fluctuating density the inclusion of the velocity-density correlations appears to be essential, because they have a strong effect especially on the development of the turbulent viscosity and the mean velocity and mass fraction profiles. Consequently the mean concentrations are in good agreement with the experimental results.     

Similarity solutions for oscillating pointed-nose slender axisymmetric bodies — part I: circular cones

Similarity solutions for pointed-nose slender circular cones performing small-amplitude pitching oscillatons in hypersonic flow at zero angles of attack, are obtained in this paper. A three-dimensional unsteady hypersonic flow perturbation theory found recently by the present author for the pitching oscillations of such bodies is further studied here. It is shown that the equations can be reduced to four sets of boundary-value problems on ordinary differential equations by seeking a perturbation solution in the reduced frequency parameter k. Closed-form simple formulas for the stability derivatives are obtained showing the effect of all the parameters included in the problem except k. The obtained results show good agreement with the few available results.     

Definition and analysis of properties of optimal three-impulse point-to-orbit transfers under time constraint

This paper deals with energetically optimal multi-impulse transfers of a spacecraft in the central Newtonian gravitational field near a planet. The transfer from a point on initial orbit to the final orbit with the given angular momentum and energy constants is considered. The transfer time is bounded above.With the distance from spacecraft to planet limited and the time free, such parameters of given orbits are chosen that the 3-impulse apsidal transfer T_r is optimal with an intermediate impulse at the maximum distance. On the basis of necessary optimality conditions an algorithm is developed to numerically determine the desired optimal transfer trajectory T_t under time constraint, the apsidal trajectory T_r being taken as initial approach. From the geometry and energy viewpoints, both trajectories T_t and T_r are close to each other. The trajectory T_t is also 3-impulsive, all impulses on it are nonapsidal. The distance from the planet is larger and the sum of impulses is less for this trajectory than for the initial trajectory T_r with the same transfer time.The simplified solution of the problem is constructed producing good approximation to the exact numerical optimization results. The solution asymptotics is found when the transfer time tends to infinity.     

Mass-, time-, and energy-characteristics of the interstellar flights during the long proper time of astronauts

The existence of extraterrestrial intelligence (ETI) and extraterrestrial scientific-technical civilization (STC) is of principal importance for CETI (communication with extraterrestrial intelligence) and SETI (search for extraterrestrial intelligence). According to Kardashev and Bracewell, the Earth-like STC in their farther development can expand to the nearby planetary systems of the Galaxy, creating galactic community (Bracewell's galactic club).In a previous paper the possibilities of the one-step relativistic rocket interstellar flight during the proper time of life of one-two generations of astronauts were analysed. The realization of such interstellar flights is very improbable, even to the nearest stars. These results could be true for the case of the comparatively short proper time of astronauts, i.e. large acceleration. But flights to the nearest stars could be realized with small and very small accelerations. In the present paper are calculated the proper times t in the reference systems connected with the astronauts (S₂), as well as the times T in the reference systems (S₁)-inertial, velocities v in S₁, mass ratios, powers and energies for various flights, exhaust velocities u and accelerations a. Results are critically discussed.     

A method of calculation of vertical cutoff rigidity in the geomagnetic field

On the basis of generalization of the results of extensive trajectory calculations for trial charged particles moving in the geomagnetic field the method of calculation of effective vertical cutoff rigidity, taking into account the values of K _p -index and local time, is developed. The IGRF and Tsyganenko-89 models are used for the geomagnetic field. A comparison of the results of model simulations with the experimental data on penetration of charged particles into near-Earth space is made, and penetration functions for typical spacecraft orbits are calculated.     

Rapid generation of entry trajectories with waypoint and no-fly zone constraints

Waypoints are positions for multiple payload deployments or reconnaissance missions, and no-fly zones are exclusion zones that cannot be passed for threat avoidance or due to geopolitical restrictions. This paper proposes a rapid entry trajectory generation approach satisfying waypoint and no-fly zone constraints for entry vehicles with relatively high lift-to-drag ratio. A lateral planning algorithm based on a Newton iteration scheme is developed to simultaneously design both the magnitude and sign of the control variable according to waypoints and no-fly zones. The algorithm converts the highly constrained trajectory planning problem into a series of one-parameter search problems based on a reduced-order system. Then, the quasi-equilibrium glide phenomenon is employed to extract the remaining state variables corresponding to longitudinal motion. The algorithm is tested using the Common Aero Vehicle model, and the results demonstrate that the algorithm can generate flyable entry trajectories rapidly within allowable tolerances while satisfying all the flight constraints.     

Thermal structure of dayside plasmasphere according to the data of Tail and Auroral Probes, and Magion-5 satellite

We consider the results of measurements of density and temperature of cold plasma in the dayside sector of the plasmasphere. The measurements were made by Interball-1 (Tail Probe) in November 1995, by Interball-2 (Auroral Probe) in August 1996 (the periods close to the solar cycle minimum), and by the Magion-5 satellite in June 2000 (this period is close to the solar cycle maximum). It was shown by the measurements in the dayside sector of the plasmasphere that, contrary to expectations of model distributions of temperature in the plasmasphere [1, 2], under quiet geomagnetic conditions the temperature of hydrogen ions of the cold plasma filling the plasmasphere was observed to increase at altitudes 5000 km < H < 10000 km. Its altitude gradient was equal to ～0.5 deg/km, the geomagnetic latitude being variable within the limits 10° < λ < 40°. The maximum values of temperature of protons, as measured by Tail Probe and Auroral Probe deep in the plasma-sphere, were equal to ～4000–6000 K. According to the data obtained by the Magion-5 satellite in the depth of the plasmasphere, these temperatures varied within the limits 7500–8500 K. These results can be considered as some indication of a dependence of the plasmasphere thermal structure on the phase of the solar cycle. In the region 2.5 < L < 5 and at geomagnetic latitudes λ < 40°, drops of the ion temperature were regularly observed with values reaching ～2000 K.     

Study of radiation conditions onboard the International space station by means of the Liulin-5 dosimeter

For estimating radiation risk in space flights it is necessary to determine radiation dose obtained by critical organs of a human body. For this purpose the experiments with human body models are carried out onboard spacecraft. These models represent phantoms equipped with passive and active radiation detectors which measure dose distributions at places of location of critical organs. The dosimetric Liulin-5 telescope is manufactured with using three silicon detectors for studying radiation conditions in the spherical tissue-equivalent phantom on the Russian segment of the International space station (ISS). The purpose of the experiment with Liulin-5 instrument is to study dynamics of the dose rate and particle flux in the phantom, as well as variations of radiation conditions on the ISS over long time intervals depending on a phase of the solar activity cycle, orbital parameters, and presence of solar energetic particles. The Liulin-5 dosimeter measures simultaneously the dose rate and fluxes of charged particles at three depths in the radial channel of the phantom, as well as the linear energy transfer. The paper presents the results of measurements of dose rate and particle fluxes caused by various radiation field components on the ISS during the period from June 2007 till December 2009.     

Survival of dormant organisms after long-term exposure to the space environment

The RF SRC—Institute of Biomedical Problems, Russian Academy of Sciences, developed Biorisk hardware to study the effects of long-term exposure of dormant forms of various organisms to outer space and used it to complete a series of experiments on the Russian Module (RM) of the International Space Station (ISS).The experiments were performed using prokaryotes (Bacillus bacteria) and eukaryotes (Penicillium, Aspergillus, and Cladosporium fungi), as well as spores, dormant forms of higher plants, insects, lower crustaceans, and vertebrates. The biological samples were housed in two containers that were exposed to outer space for 13 or 18 months. The results of the 18-month experiment showed that, in spite of harsher temperature than in the first study, most specimens remained viable.These experiments provided evidence that not only bacterial and fungal spores but also dormant forms of organisms that reached higher levels of evolutionary development had the capability to survive a long-term exposure to outer space. This observation suggests that they can be transferred on outer walls of space platforms during interplanetary missions.     

Thermodynamics and dynamics of surface phases

The paper presents and discusses the set of field-equations for an interface between two immiscible, uncharged, unpolarized, non-elastic and non micro-polar fluids modelled as a geometrical surface S in arbitrary motion and with thermodynamic and dynamic properties. The crucial assumptions are those implied by a local formulation of the equilibrium thermodynamics of S. The set of equations derived comprises: integral and local forms of the surface balance-equation for a scalar or vectorial extensive property; continuity, normal and tangential momentum and energy equations; surface entropy production; linear phenomenological relations for irreversible surface diffusions and non-equilibrium exchanges of extensive properties between surface and volume phases. Momentum and energy conservation equations are formulated also in terms of a suitably defined surface total enthalpy. Available previous formulations are either not as complete or hold only in more particular cases. Whenever applicable, their results are compared with the present ones and commented upon.     

On some spacecraft fatigue-crack propagation problems

For thin-gauge sheet structures the effective critical range of stress-intensity factor ΔK_c can be calculated by curve fitting to the results of the crack propagation tests. A new, more exact, coordinate transformation method based on the Forman formula has been developed for this purpose.The method can be extended to cover the determination of the threshold stress-intensity range ΔK_th as well. There are two candidate transportation formulae for this purpose. The correct one of them will be singled out on the base of practical experience.Recent test data may indicate that even pure atmospheric air can exert a corrosion-like influence on the crack-growth rate of certain light-metal alloys. Should this prove to be true, then respective tests will have to be run in the proper environment and/or corrections will have to be applied for the corrosion influence.