Changes of properties of the materials of spacecraft solar arrays under the action of atomic oxygen

A procedure is developed for physical and chemical modeling and investigation of the weight, geometrical, and thermo-optical characteristics of polymer paneling materials of solar arrays and of the electric power of solar cells under the prolonged action of supersonic fluxes of atomic oxygen in orbit. The behavior of changes in the material characteristics as a function of the integral fluence of atomic oxygen is found. It is established that the electric power of solar cells is virtually invariable within the errors of measurements under irradiation by atomic oxygen flux with a fluence of no higher than 5 · 10²¹ cm^?2.     

Energy dependence of the fraction of protons of ionospheric origin in the ring current

The energy dependence of a fraction of ring current protons of ionospheric origin is calculated using the AMPTE/CCE data for a typical strong magnetic storm (max|D _st | ≈ 120 nT). It is shown that this fraction monotonically decreases from ～ 83 to 25–30% with an increase in proton energy from 5 to 315 keV at L = 6–7 (L is the McIlwain parameter) and is 30–40% at energy 40–50 keV corresponding to the maximum of proton energy density at L = 6–7. It is demonstrated that the core of the ring current (L = 3.7–4.7) was enriched by solar protons with E ≈ 10–200 keV during the active phase of the storm (the maximum effect is reached at E ≈ 20–50 keV).     

On the limiting mass of a dense stellar matter

In the present work, we have derived an expression $\text{M}{}_{\mathrm{L}}\text{? 4.738 M}{}_{\mathrm{\odot }}$ (M_⊙ = 1.985 × 10³³ g = mass of the Sun) giving the “limiting” value of the mass of a dense stellar matter, by introducing the concept of nuclear size correction in the theory of relativistic Thomas Fermi model for a compressed atom. We find that $\text{M}{}_{\mathrm{L}}\text{? 5.1571 M}{}_{\mathrm{<mtext>Ch</mtext>}}\text{and}\text{=3.2750(M}{}_{\mathrm{<mtext>O</mtext>}}\text{)}{}_{\mathrm{<mtext>Prev</mtext>}}$ [M_Ch and (M_O)_Prev denote respectively the Chandrasekhar and author's “limiting” masses]. By making a comparative study with those of previous results it has been shown that our present treatment would provide satisfactory results for the density ranges from ? ? 10⁸ up to $\text{? ? 10}{}^{11}\text{g}\text{/}\text{cm}{}^3$. Other results of cognate interest in the non-relativistic regime 10³ < ? ? 10⁵ (without the nuclear size effect) are presented. The astrophysical implications of the results are mentioned.     

Effect of reflected ions on the formation of the structure of interplanetary quasi-perpendicular shocks for Mach numbers lower than the first critical mach number

Based on the data of the BMSW instrument installed on the of SPEKTR-R spacecraft, as well as according to the data of instruments of the WIND spacecraft, etc., using two examples, the paper has studied the role of ions reflected from the front and associated structural features of quasi-perpendicular interplanetary shocks (IS) with the Alfvén Mach number М _A lower than the first critical Mach number М _c1 . It has been shown that BSs with the finite parameter 0.1 < β₁ < 1 contain a small fraction of reflected protons, which play a significant role in forming the front structure (β₁ is the ratio of gas-to-magnetic pressure before the shock front). In particular, in the case of a perpendicular shock recorded on August 24, 2013 (the angle between the magnetic field direction and the normal to the front θ_Bn ≈ 85°), an IS with a small Mach number (М_A ≈ 1.4) and small β₁ ≈ 0.2 is shown that the interactions of reflected ions with inflowing solar wind may result in the collisionless heating of ions in front of and behind it. The case of the oblique (θ_Bn = 63°) IS on April 19, 2014 with a small Mach number (М ^A ≈ 1.2) and small β₁ ≈ 0.5 has been investigated. It has been found that, before the front, there is a sequence of trains of magnetosonic waves, the amplitude of which decreases to zero upon increasing their distance from the front. The mechanism of their formation is associated with the development of instability caused by the ions reflected from the front.     

Probabilistic assessment of radiation risk for astronauts in space missions

Accurate estimations of the health risks to astronauts due to space radiation exposure are necessary for future lunar and Mars missions. Space radiation consists of solar particle events (SPEs), comprised largely of medium energy protons (less than several hundred MeV); and galactic cosmic rays (GCR), which include high-energy protons and heavy ions. While the frequency distribution of SPEs depends strongly upon the phase within the solar activity cycle, the individual SPE occurrences themselves are random in nature. A solar modulation model has been developed for the temporal characterization of the GCR environment, which is represented by the deceleration potential, ?. The risk of radiation exposure to astronauts as well as to hardware from SPEs during extra-vehicular activities (EVAs) or in lightly shielded vehicles is a major concern for radiation protection. To support the probabilistic risk assessment for EVAs, which could be up to 15% of crew time² on lunar missions, we estimated the probability of SPE occurrence as a function of solar cycle phase using a non-homogeneous Poisson model [1] to fit the historical database of measurements of protons with energy>30 MeV, Φ₃₀. The resultant organ doses and dose equivalents, as well as effective whole body doses, for acute and cancer risk estimations are analyzed for a conceptual habitat module and for a lunar rover during space missions of defined durations. This probabilistic approach to radiation risk assessment from SPE and GCR is in support of mission design and operational planning for future manned space exploration missions.     

Peculiarities of long-wave radio bursts from solar flares preceding strong geomagnetic storms

Radio bursts in the frequency range of 100–1500 kHz, recorded in 1997–2000 on the INTERBALL-1 satellite during the solar flares preceding the strong geomagnetic storms with D _st < ?100 nT, are analyzed in this paper. The observed long-wave III-type radio bursts of solar origin at frequencies of 1460 and 780 kHz were characterized by large values of the flux S _f = 10^?15 ?10^?17 W/m² Hz and duration longer than 10 min. The rapid frequency drift of a modulated radio burst continued up to a frequency of 250 kHz, which testified that the exciting agent (a beam of energetic electrons) propagated from the Sun to the Earth. All such flares were characterized by the appearance of halo coronal mass ejections, observed by the LASCO/SOHO, and by the presence of a southward B_z-component of the IMF, measured on the ACE and WIND spacecraft. In addition, shortly after radio bursts, the INTERBALL-1 satellite has recorded the fluxes of energetic electrons with E > 40 keV.     

Order of magnitude analysis of convective effects in dendritic solidification

The different types of convective phenomena which may occur during the dendritic solidification of metallic alloys are discussed from an order of magnitude analysis. Bulk thermal convection and/or interdendritic solutal convection have to be considered according to the values of the experimental data. Scaling laws for the solute boundary layer resulting from bulk thermal convection have already been derived. It is shown here that the interdendritic flow depends on a solutal Grashof number Gr based on the horizontal density gradient and a characteristic length L_s which is of the order of the liquid channels width. For Gr < 1, which is generally verified in practical cases, the interdendritic flow velocity U_r is proportional to the Grashof number. This a priori law compares favorably with the results of horizontal solidification experiments where the mean interdendritic flow velocity has been estimated from the resulting measured macrosegregation. In these experiments, as well as for most horizontal dendritic solidifications of metallic alloys at 1 g, the ratio $\text{U}{}_{\mathrm{r}}\text{R}$ (R is the growth rate) is of order one. In order to cancel the interdendritic flow effects, this ratio has to be lowered by one order of magnitude. According to our analysis, this can be obtained by performing the experiments either at a slightly reduced g level (～10^?1 g), or at 1 g in a vertical stable configuration with a sufficiently low residual horizontal thermal gradient.     

An explanation of variable peculiarities in spectra of electrons and positrons of cosmic rays

It is shown that the excesses in the sum of fluxes (e ⁺ + e ^?) in cosmic rays in the energy range (10–1000) GeV and in the flux ratio e ⁺/(e ⁺ + e ^?) in the range > 10 GeV, observed both in recent and old experiments, can be explained by an accelerator of charged particles operating on the heliosphere periphery, in the region beyond the termination shock of the solar wind (～100 AU). Variations in the value and position of peculiarities in the spectra (e ⁺ + e ^?), as well as increasing ratio of fluxes e ⁺/(e ⁺ + e ^?), can be associated with variations of solar activity (and, as a consequence, of acceleration regimes) on different phases of the 11-years solar cycle. The results of numerical simulation of capture and acceleration of charged particles by packets of plasma waves in the heliospheric magnetic field are presented.     

Information protection in space communication systems using changes in radio wave propagation conditions

A technique is developed that allows one to estimate the increase in the probability of erroneous reception of information symbols in space communication systems up to P _err ≥ 10^?2 due to carrier frequency lowering down to 70...60 MHz and changing conditions of radio wave propagation (mainly due to the appearance of fading). The possibility is shown to provide for P _err ≤ 10^?5 by applying, under these conditions, spatially separated reception on five antennas with a small correlation of fading (no more than 0.5) in processing branches.     

Luni-solar perturbations in the extended phase space representation of the Vinti problem

Perturbation theory is applied to the Vinti problem—motion about an oblate spheroid—to include the gravitational effects of the sun and moon. The problem is formulated using the extended phase space method which introduces a new independent variable similar to the true anomaly. The disturbing Hamiltonian H₁ for third bodies is of order J₂² (second order) and the final goal is a theory including second order short and long period terms and third order secular terms. The current paper however carries the development only to the second order in the secular terms and the first order in the periodic terms. Problems of including the higher orders are discussed. Therefore, in the development of H₁ all terms of order 10^?9 or larger are retained. The lunar emphemeris retains terms to e′² in the lunar eccentricity. The perturbation analysis is carried out by means of Lie series and is developed through the first order only which is consistent with the final accuracy desired. The generating function W₁ is obtained and separated into the long period, short period and secular terms. From W₁ the coordinates are defined from the Lie series by means of a transformation equation. These coordinates are non-singular for small eccentricity and inclination. Because of the complexity of the equations all algebraic computations were accomplished by means of a computerized Poisson series manipulator developed at the Naval Research Laboratory.     

Stability of resonance rotation of a satellite with respect to its center of mass in the orbit plane

The stability of resonance oscillations and rotations of a satellite in the plane of its orbit in the case when the difference of the moments of inertia with respect to the principal axes lying in the orbit plane is small is determined at a given rotation number m by the sign of function Φ_m(e), introduced by F.L. Chernous’ko in 1963. In this paper, convenient analytical representations of functions Φ_m(e) are described in the form of integrals and series of Bessel functions regular at e → 1^?. Values of Φ_m(1) are calculated in explicit form. A theorem about the double asymptotic form of functions Φ_m(e) at m → ∞ and e → 1^? is proved by the saddlepoint method.     

Exploration of Mars in the SPICAM-IR experiment onboard the Mars-Express spacecraft: 2. Nadir observations: Simultaneous observations of water vapor and O2 glow in the Martian atmosphere

The SPICAM experiment onboard the Mars-Express spacecraft includes sounding the Martian atmosphere in the ultra-violet (118–320 nm) and near IR (1–1.7 μm) ranges. The infrared spectrometer operates in the range of 1–1.7 μm with a resolution of 3.5 cm^?1 in the mode of nadir observations and solar and stellar occulations. This paper is devoted to analyzing the basic results of nadir observations of the infra-red SPICAM channel during the first Martian year of the instrument operation: from January 2004 to November 2005. One of the primary goals of SPICAM-IR is water vapor monitoring in the atmosphere of Mars in the band of 1.37 μm and ozone abundance determination from the day-time airglow of molecular oxygen O₂(a ¹Δ_g) in the band of 1.27 μm. Simultaneous measurements of these minor constituents of the planet are necessary for understanding photochemical processes in the Martian atmosphere. The degree of their anticorrelation and a comparison with the results of photochemical modeling of the atmosphere will contribute to our knowledge of the Martian atmosphere stability.     

Ignition system for oxygen/hydrogen auxiliary propulsion systems

When the oxygen/hydrogen bipropellant combination was selected for use in the Space Shuttle Main Engine, it became apparent that many advantages may result if the Auxiliary Propulsion System Engines were to use the same propellants. A new ignition system, possessing a dramatically new level of reliability, durability and response, is required because the oxygen/hydrogen combination is not hypergolic and the projected missions will require a very large number of fast-response engine starts.The objective of this program was to obtain basic data for spark torch ignition methods at operating conditions typical of a Space Shuttle Orbiter Auxiliary Propulsion System. The research included ignition analysis and igniter design, fabrication and hot-fire test.Extensive testing of spark torch igniters was performed (chamber pressure, 206.8 N/cm², 300 psia, nominal) in the Igniter-Only and Igniter-Complete Thruster (thrust, 6672 N, 1500 lbF, nominal) operational modes. Reliable, repeatable ignitions were obtained with spark energies of 1–10 mJ. Hot-fire test results showed there is no effect of back pressure (1.013 × 10⁵ to 1.333 × 10^?2 N/m², 7.60 × 10² to 1 × 10^?4 mm Hg) or low temperature (O₂, 170 K, 306 R; H₂, 107 K, 193 R) on the response of the igniter or the ignition delay of the thruster over the ranges tested. Igniter durability and pulse capability were demonstrated with 150 sec of continuous operation and 1000 consecutive pulses, respectively. Durability was further demonstrated with a series of 2500 Igniter-Complete Thruster ignitions at nominal chamber pressure. No limiting variables were encountered. The hot-fire test results showed the spark torch igniter is capable of meeting fully the typical Space Shuttle Orbiter Auxiliary Propulsion System mission requirements.     

Oxygen deficiency structure in iron-based high temperature superconductor GdFeAsO1−δ

Oxygen deficiency in the iron-based HTSC GdFeAsO_1?δ seems to create a parallelogram shaped Fe²⁺-ion/oxygen deficiency pattern in the Fe₂O₂ plane in c-direction. These two-dimensional nanostructures form superconducting current channels which are separated by h=0.828 nm. The doping distance in direction of the super-current shows a strong correlation to the transition temperature.     

原子氧环境对石英晶体微量天平性能影响的分析

随着高可靠、长寿命航天器的发展,对在轨污染检测的要求也越来越高。石英晶体微量天平是分子污染检测的重要工具,为了分析了解原子氧对石英晶体微量天平的影响,文章用理论分析和试验的方法对石英晶片在1×1020 atom/cm2注量的原子氧辐照条件下的性能变化进行了研究。试验证明,石英晶体微量天平在总注量1020 atom/cm2量级的原子氧辐照后,其振荡频率和等效阻容感发生了一定变化,但仍具备污染传感能力和频率输出能力,其功能不受影响。     

NiCrBSi+Ni/MoS_2涂层在空间环境下的摩擦学性能

采用激光熔覆技术在TC4合金基体上制备了Ni Cr BSi+Ni/Mo S2复合涂层,考察了该复合涂层在真空、原子氧辐照环境下的表面形貌及元素变化。利用真空摩擦磨损试验机分别完成了干摩擦条件下2种环境的摩擦磨损性能测试。结果表明:Ni Cr BSi+Ni/Mo S2复合涂层经过原子氧辐照后,有部分元素被氧化及化合物分解的现象,但并没有发生明显的材料性能改变以及润滑涂层的破坏。与TC4合金相比,2种环境下该复合涂层均具有良好的润滑减摩效果,证明Ni Cr BSi+Ni/Mo S2复合涂层具有一定的抗原子氧辐照的能力。     

Large-scale irregularities of the winter polar topside ionosphere according to data from <Emphasis Type="Italic">Swarm</Emphasis> satellites

An analysis of the electron density measurements (Ne) along the flyby trajectories over the high-latitude region of the Northern Hemisphere under winter conditions in 2014 and 2016 has shown that the main large-scale structure observed by Swarm satellites is the tongue of ionization (TOI). At the maximum of the solar cycle (F_10.7 = 160), the average value of Ne in the TOI region at an altitude of 500 km was 8 × 10⁴ cm^–3. Two years later, at F_10.7 = 100, Ne ~ 5 × 10⁴ cm^–3 and Ne ~2.5 × 10⁴ cm^–3 were observed at altitudes of 470 and 530 km, respectively. During the dominance of the azimuthal component of the interplanetary magnetic field, the TOI has been observed mainly on the dawn or dusk side depending on the sign of B _y . Simultaneous observations of the convective plasma drift velocity in the polar cap show the transpolar flow drift to the dawn (B_y < 0) or dusk side (B _y < 0). Observations and numerical simulation of the Ne distribution have confirmed the significant role of the electric field of the magnetospheric convection in the generation of large-scale irregularities in the polar ionosphere.     

红蓝光敏探测器空间环境效应探测数据分析

红蓝光敏太阳电池空间环境效应探测器利用镓铟磷和三结砷化镓太阳电池来探测空间污染、原子氧和辐射环境及效应,搭载在中国空间技术研究院自主研制的“新技术验证一号”卫星上。文章通过分析红蓝光敏探测器在轨1年时间的探测数据,得到如下结论：红蓝光敏探测器污染电池板功率下降2.7%,等效污染累积增加量2.23×10^-5 g/cm^2,日均6×10^-8 g/cm^2;原子氧探测器在轨道高度499.226 km运行11个月,原子氧积分通量探测数据为9.7×10^20 AO/cm^2;辐射效应探测器（三结砷化镓太阳电池）在轨1年后累计接受辐射剂量（等效1 MeV电子注量）5.49×10^11 e/cm^2。     

Fine structure of the interplanetary shock front according to measurements of the ion flux of the solar wind with high time resolution

According to the data of the BMSW/SPEKTR-R instrument, which measured the density and velocity of solar wind plasma with a record time resolution, up to ~3 ×10^–2 s, the structure of the front of interplanetary shocks has been investigated. The results of these first investigations were compared with the results of studying the structure of the bow shocks obtained in previous years. A comparison has shown that the quasi-stationary (averaged over the rapid oscillations) distribution of plasma behind the interplanetary shock front was significantly more inhomogeneous than that behind the bow-shock front, i.e., in the magnetosheath. It has also been shown that, to determine the size of internal structures of the fronts of quasi-perpendicular (θ_BN > 45°) shocks, one could use the magnetic field magnitude, the proton density, and the proton flux of the solar wind on almost equal terms. A comparison of low Mach (М _А < 2), low beta (β₁ < 1) fronts of interplanetary and bow shocks has shown that the dispersion of oblique magnetosonic waves plays an essential role in their formation.     

In situ dating on Mars: A new approach to the K–Ar method utilizing cosmogenic argon

Cosmogenic argon isotopes are produced in feldspars via nuclear reactions between cosmic rays and Ca and K atoms within the lattice. These cosmogenic isotopes can be used as proxies for K and Ca, much like nuclear reactor-derived ³⁹Ar and ³⁷Ar are used as proxies for K and Ca, respectively, in ⁴⁰Ar/³⁹Ar geochronology. If Ca and K are uniformly distributed, then the ratio of radiogenic ⁴⁰Ar (⁴⁰Ar^?) to cosmogenic ³⁸Ar or ³⁶Ar (³⁸Ar_cos or ³⁶Ar_cos) is proportional to the difference between the radioisotopic and exposure ages, as well as the K/Ca ratio of the degassing phase. Thus cosmogenic, radiogenic, and trapped Ar isotopes, all of which can be measured remotely and are stable over geologic time, are sufficient to generate an isochron-like diagram from which the isotopic composition of the trapped component may be inferred. Such data also provide a means to assess the extent to which the system has remained closed with respect to ⁴⁰Ar^?, thereby mitigating otherwise unquantifiable uncertainties that complicate the conventional K–Ar dating method.