A system of autonomous navigation and orientation for satellites based on virtual measurements of zenith distances of stars

An onboard astronomical system is suggested, based on the developed method using virtual measurements of zenith distances of stars. Two algorithms of the method are described, their theory is given, and statistical results of the system’s simulation are presented.     

Protons with energy of E P ≥ MeV under the earth’s radiation belts

Variations in fluxes of quasi-trapped energetic protons were studied on the basis of the data of the CORONAS-I satellite. These variations are characterized by an increase in the proton fluxes with E _P ≥ 1 MeV both in the vicinity of the geomagnetic equator and in the high-latitude region of the magnetosphere. The analysis of structural features of the proton distributions in the regions at L ～ 1–1.1; 3 < L < 4; and L > 4, was performed and made it possible to detect reliably the type of the proton flux increase in this region. The mechanisms of particle scattering leading to the precipitation of energetic protons under conditions of various types of geomagnetic disturbances are considered.     

A Study of a Possible Method of Observing Solar Eclipses from Satellite Orbits

We study a possibility of observing the eclipses of the Sun by the Moon from satellite orbits. The scientific tasks planned to be solved onboard satellites are considered. The requirements for the observation of eclipses and for the appropriate satellite trajectories are formulated. A technique of the analysis and synthesis of such trajectories is developed, and some results of preliminary ballistic studies are presented. These results confirm the efficiency of observing the eclipses onboard satellites.     

Determination of K,Ar, Cl,S, Si and Al flare abundances from RESIK soft X-ray spectra

The RESIK is a high sensitivity, uncollimated bent crystal spectrometer which successfully operated aboard Russian CORONAS-F solar mission between 2001 and 2003. It measured for the first time in a systematic way solar soft X-ray spectra in the four wavelength channels from 3.3 Å to 6.1 Å. This range includes characteristic strong lines of H- and He-like ions of K, Ar, Cl, Si, S and Al in the respective spectral channels. A distinguishing feature of RESIK is its possibility of making reliable measurements of the continuum radiation in flares. Interpretation of line and the continuum intensities observed in vicinity of respective strong lines provides diagnostics of plasma temperature and absolute abundances of K, Ar, Cl, S, Si and Al in several flares. We analyzed the observed intensities of spectral lines and the nearby continuum using the CHIANTI v5.2 atomic data package. A specific, so-called “locally isothermal” approach has been used in this respect allowing us to make not only flare-averaged abundance estimates, but also to look into a possible variability of plasma composition during the course of flares.     

On the Ballistic Efficiency of Bicalibre Aerial Vehicles with Prevailing Coast Phase

The advantages of the bicalibre configuration of the volumetric packaging in comparison with the single-calibre one are shown within the framework of the concept of ballistic efficiency (BE) enhancement of the aerial vehicles (AV) with prevailing coast phase. The rational range of booster and coaster calibre ratios of bicalibre aerial vehicles for both solid propellant jet engines and combined propulsion units are defined.     

Influence of nonuniform magnetic fields on orientation of plant seedlings in microgravity conditions.

Experiments on the spatial behavior of the flax (Linum usitatissimum, L.) seedlings in a nonuniform magnetic field were conducted on the orbital space stations "Salut" and "Mir". This field can displace sensory organelles (statoliths) inside receptor cells and such displacement should cause a physiological reaction of the plant-tropistic curvature. Experiments were conducted in the custom-built "Magnetogravistat" facility, where seeds were germinated and grown for 3-4 days in a magnetic field with the dynamic factor grad (H2/2) approximately equal to 10(7) Oe2/cm, then fixed on orbit and returned to Earth for analysis. It was found, that 93% of the seedlings were oriented in the field consistently with curvature in response to displacement of statoliths along the field gradient by ponderomotive magnetic forces, while control seedlings grew in the direction of the initial orientation of the seed. This suggests, that gravity receptors of plants recognized magnetic forces on statoliths as gravity, and that gravity stimulus can be substituted for plants by a force of a different physical nature.     

The Rate of Single Event Upsets in Electronic Circuits onboard Spacecraft

Models and methods in use for quantitative estimates of the occurrence of single event upsets in microchips of orbiting spacecraft are considered. A calculation and experimental technique for determining the rate of these effects is described, taking into account spatial and temporal distributions of the fluxes of high-energy particles in the space and their penetration through protective shields. Examples of its application for the orbit of the International Space Station are presented.     

Nonlinear Evolution of a Balloon Satellite Orbit

The motion of a spherically symmetric balloon satellite near the equatorial plane is considered. Taking the Earth's oblateness and solar light pressure into account, the integral of motion can be obtained under certain simplifications. The eccentricity is related to the solar angle which represents an angle between pericenter and the Sun. This analytical approximation describes a large and complicated evolution of the eccentricity in corresponding areas of the phase space and the space of parameters. Phase portraits contain fixed saddle points and separatrices that divide different types of oscillations of the eccentricity. In the unsimplified problem, separatrices break down, and specific stochastic motions arise. The aims of the present study are (1) evaluation of the accuracy of analytical approximation with the help of numerical integration using a sufficiently complete model of motion and (2) numerical investigation of stochastic motions and dimensions of stochastic zones in the region of broken separatrices for an adequate model of motion. For a balloon satellite with a semimajor axis of 2.15 Earth's radii and a windage of 30 cm²/g the dimensions of a stochastic zone in eccentricity and solar angle are 10^–5and 0.1°, respectively. The analytical approximation describes the orbit evolution in the right way, except for the cases of large eccentricities, e> 0.4, which corresponds to a pericenter height of less than 1400 km, where the atmospheric drag is already significant.     

Creation of model of quasi-trapped proton fluxes below Earth’s radiation belt

The object of investigation is the phenomenon of proton (from tens keV to several MeV) flux enhancement in near-equatorial region (L < 1.15) at altitude up to ∼1300 km (the storm-time equatorial belt). These fluxes are quite small but the problem of their origin is more interesting than the possible damage they can produce. The well known sources of these protons are radiation belt and ring current. The mechanism of transport is the charge-exchange on neutral hydrogen of exosphere and the charge-exchange on oxygen of upper atmosphere. Therefore this belt is something like the ring current projection to low altitudes. Using the large set of satellites data we obtain the average energy spectrum, the approximation of spectrum using kappa-function, the flux dependence on L, B geomagnetic parameters. On the basis of more than 30 years of experimental observations we made the empiric model that extends model of proton fluxes below 100 keV in the region of small L-values (L < 1.15). The model was realized as the package of programs integrated into COSRAD system available via Internet. The model can be used for revision of estimation of dose that low-orbital space devices obtain.