Updated Mapping of Hydrogen in the Lunar Southern Polar Regions according to LEND/LRO data

<p>Determining the amount of water ice in the lunar regolith is an important task not only from a scientific point of view, but it is also important for exploration, since water may be used in many aspects - from the production of rocket fuel to direct use by astronauts during their stay on a habitable lunar base. One of the methods of remote sensing for hydrogen-bearing compounds, such as water ice, in the upper 1–2 m subsurface soil layer of atmosphereless celestial bodies is the spectroscopy of the neutron leakage flux from the surface. To estimate water equivalent hydrogen (WEH) in the lunar soil we have used data of Lunar Exploration Neutron Detector (LEND) aboard the Lunar Reconnaissance Orbiter (LRO), operating almost continuously in orbit around the Moon from 2009 to the present [1].</p><p>LEND is the collimated epithermal neutron telescope which uses the passive neutron collimator to collect most of neutron signal at a narrow field of view (FOV). Dataset gathered by LEND till April 1, 2015 was early used to estimate the water equivalent hydrogen (WEH) and create maps of its distribution [2]. After 5 years of additional data accumulation we update the WEH map in the Southern circumpolar region, including both large permanently shadow regions (PSRs) and neutron suppression regions (NSRs), which might be partially overlapping with PSRs and often extends on sunlit areas.</p><p>The updated map is done not only by the new larger dataset, but by new WEH estimation method also. This method uses precise estimation of the neutron flux at different altitudes of spacecraft orbits modelled with specially developed code based on the Geant4 toolkit with additional treatment of the neutron propagation in the lunar gravity field. Also, the method precisely accounts the fact of the collimator partial transparency, which leads to additional background counting rate in detectors dependent on WEH in the soil at surrounding regions located out of the instrument FOV. </p><p>References:<br>1.    Mitrofanov I. et al. (2010) Space Sci. Rev., 150, 183–207.<br>2.    Sanin A. B. et al. (2017) Icarus, 283, 20-30.</p>

Martian Moons Exploration MMX: Sample Return Mission to Phobos Elucidating Formation Processes of Habitable Planets

Martian moons exploration, MMX, is the new sample return mission planned by the Japan Aerospace Exploration Agency (JAXA) targeting the two Martian moons with a scheduled launch in 2024 and a return to the Earth in 2029. The major scientific objectives of this mission are to determine the origin of Phobos and Deimos, to elucidate the early Solar System evolution in terms of volatile delivery across the snow line to the terrestrial planets having habitable surface environments, and to explore the evolutionary processes of both moons and Mars surface environment. To achieve these objectives, during a stay in circum-Martian space over about 3 years MMX will collect samples from Phobos along with close-up observations of this inner moon and carry out multiple flybys of Deimos to make comparative observations of this outer moon. Simultaneously, successive observations of the Martian atmosphere will also be made by utilizing the advantage of quasi-equatorial spacecraft orbits along the moons’ orbits.

Methods of Orbit Clustering of Serviced Spacecraft

When planning orbital service operations, it is important to rationally divide a set of orbits serviced by a spacecraft into subsets (clusters) of orbits. This article proposes a technique for clustering the orbits of serviced spacecraft in the event of their servicing by a reusable service spacecraft with an electric rocket low thrust engine. The technique is based on the method of K ‑ means. As the distance between any pair of orbits of the serviced spacecraft (metrics) of the method K - means, it was proposed to use the delta-V of the orbital transition between these orbits.In this paper, a technique has been developed for clustering orbits of serviced spacecrafts. The method is based on the method K ‑ means. As a distance between any pair of orbits of the serviced spacecraft orbits (metrics) of the method K ‑ means it is proposed to use the energy metric delta - V of the interorbital transition between these orbits. Using the proposed methodology, a computer program has been developed for clustering the orbits of serviced spacecraft. The results of the test calculations showed the effectiveness of the proposed clustering technique. The technique can be applied when planning orbital service operations.

Quaternion Models and Algorithms of Solving the General Problem of Energetically Optimal Spacecraft Orbit Reorientation

The problem of optimal reorientation of the spacecraft orbit is considered in quaternion formulation. Control (vector of the acceleration of the jet thrust) is limited in magnitude. It is required to determine the optimal orientation of the vector of the acceleration in space to solve the problem. It is necessary to minimize the energy consumption of the process of reorientation of the spacecraft orbit. We used quaternion differential equation of the orientation of the spacecraft orbit to describe the motion of the center of mass of the spacecraft. The problem was solved using the maximum principle of L. S. Pontryagin. We simplified the differential equations of the problem using known partial solution of the equation for the variable conjugated to true anomaly. The problem of optimal reorientation of the spacecraft orbit was reduced to a boundary value problem with a moving right end of the trajectory described by a system of nonlinear differential equations of fifteenth order. For the numerical solution of the obtained boundary value problem the transition to dimensionless variables was carried out. At the same time a characteristic dimensionless parameter of the problem appeared in the phase and conjugate equations. We constructed an original numerical algorithm for finding unknown initial values of conjugate variables. The algorithm is a combination of Runge-Kutta 4th order method and two methods for solving boundary value problems: modified Newton method and gradient descent method. The using of these two methods for solving boundary value problems has improved the accuracy of the solution of the investigated boundary value problem of optimal control. Examples of numerical solution of the problem are given for the cases when the difference (in angular measure) between initial and final orientations of the spacecraft orbit is equals to a few (or tens of) degrees. Graphs of changes component of the quaternion of the spacecraft orbit orientation; variables characterizing the shape and dimensions of the spacecraft orbit; optimal control are plotted. The analysis of the obtained solutions is given. The features and regularities of the process of optimal reorientation of the spacecraft orbit are established. We found that when the difference between initial and final spacecraft orbits is small there is a one point of extremum for the eccentricity of the spacecraft orbit and for modulo of the vector of orbital velocity moment of the spacecraft. And there are a few points of local extremum for these functions when the difference between initial and final spacecraft orbits is large.

Spectro-timing analysis of MAXI J1535–571 using AstroSat

We report the results of the analysis of an AstroSat observation of the black hole candidate MAXI J1535–571 during its hard-intermediate state. We studied the evolution of the spectral and timing parameters of the source during the observation. The observation covered a period of ∼5 d and consisted of 66 continuous segments, corresponding to individual spacecraft orbits. Each segment was analysed independently. The source count rate increased roughly linearly by ∼30 per cent. We modelled the spectra as a combination of radiation from a thermal disc component and a power law. The timing analysis revealed the presence of strong quasi-periodic oscillations with centroid frequency νQPO fluctuating in the range of 1.7–3.0 Hz. We found a tight correlation between the QPO centroid frequency νQPO and the power-law spectral index Γ, while νQPO appeared not to be correlated with the linearly increasing flux itself. We discuss the implications of these results on physical models of accretion.

Synthesizing spacecraft orbits with high inclinations using Venusian gravity assists

An adaptive, semi‑analytical, and geometrically clear method for synthesis of sequences of Venusian gravity‑assist maneuvers setting the desired inclination of a spacecraft orbit is proposed. The geometric constraint on the maximum possible inclination of a spacecraft orbit, which depends on the asymptotic spacecraft velocity relative to Venus, and the dynamic constraint (arising when a gravity‑assist maneuver is performed) on the angle of rotation of the vector of asymptotic velocity relative to Venus are considered simultaneously.

DETECTION OF SPACECRAFT ORBITS IN MULTI-ELEMENT LAUNCHES WITH LOW SCATTERING SPEED. DISTRIBUTION OF MEASUREMENTS OF ORBITS

The paper considers the structure of the algorithm for detecting the orbits of spacecraft in multi‑element launches with low speed of scattering. These launches are used in recent years for the launching of microsatellites into orbits. In the proposed algorithm, the difficult task of distributing measurements to orbits is solved on the basis of taking into account the features of the relative motion of nearby space objects that form a dense cluster at launch. In particular, it is proposed to use the relative distance between the spacecraft in the direction of the velocity vector as a distribution parameter. Then the problem of detecting orbits is reduced to the distribution of measurements in one‑dimensional space of relative distances. The developed structure of the algorithm can significantly reduce the detection time and the number of calculations compared to the standard algorithm. Verification of the proposed method on the example of analyzing data on the actual launch of the spacecraft confirmed its effectiveness.