Survey-only optical strategies for cataloguing space debris objects in the future European space surveillance system

In the framework of a potential European Space Situational Awareness System (ESSAS), we propose some optical strategies such that try to minimize the requirement of tracking measurements for the orbit determination computation when the catalogue is under construction. We will analyse them in terms of coverage, timeliness and orbit determination accuracy by means of the AS4 simulator (developed by Deimos Space S.L.U.). Moreover, observation campaigns have been performed from La Sagra Observatory in order to check the applicability of those strategies. These strategies are used for defining different choices for the future European Optical Space Surveillance System in the framework of the ESA contract no. 22738/09/D/HK.     

Inter-satellite links for satellite autonomous integrity monitoring

A new integrity monitoring mechanisms to be implemented on-board on a GNSS taking advantage of inter-satellite links has been introduced. This is based on accurate range and Doppler measurements not affected neither by atmospheric delays nor ground local degradation (multipath and interference). By a linear combination of the Inter-Satellite Links Observables, appropriate observables for both satellite orbits and clock monitoring are obtained and by the proposed algorithms it is possible to reduce the time-to-alarm and the probability of undetected satellite anomalies.     

Why does the total pressure on the subsolar magnetopause differ from the solar wind dynamic pressure?

Based on analysis of MHD equations and the results of numerical simulation in the magneto-sheath it is demonstrated that the total pressure on the magnetopause differs from the solar wind dynamic pressure in the majority of cases. From the equation of motion it follows that the total pressure is reduced due to deflection from the Sun-Earth line. At the same time, it increases because of formation of a magnetic barrier. This result is consistent with experimentally observed expansion of the magnetosphere for the radial direction of the interplanetary magnetic field, when no magnetic barrier is formed. In this paper we compare the behavior of pressure along the Sun-Earth line for the northward and radial interplanetary field, using the results of numerical MHD simulation and observational data from THEMIS. In the isotropic MHD approximation, the difference between the total pressure on the subsolar magnetopause at northern and radial IMFs does not exceed 10–12 percent. However, in the anisotropic approximation this difference increases up to 15–20 percent. The results of anisotropic modeling well agree with observed averaged profiles of pressure components in the subsolar magnetosheath.     

Ionospheric disturbances detected by MEXART

The radio telescope MEXART was developed to make observations of interplanetary scintillation (IPS) produced by large scale disturbances associated with solar events. In this work it is shown that on occasion there are disturbances in the ionosphere that are related with these events and which cannot only contaminate the IPS but actually be the main contribution to the observed oscillations. This was the case of the event of 15 December 2006 observed by MEXART, which presented clear scintillation. The total electron content (TEC) of the ionosphere above Mexico was calculated for the same period. It was found that the variations in TEC were associated with the scintillations detected by MEXART.     

Concurrent image-based visual servoing with adaptive zooming for non-cooperative rendezvous maneuvers

An image-based servo controller for the guidance of a spacecraft during non-cooperative rendezvous is presented in this paper. The controller directly utilizes the visual features from image frames of a target spacecraft for computing both attitude and orbital maneuvers concurrently. The utilization of adaptive optics, such as zooming cameras, is also addressed through developing an invariant-image servo controller. The controller allows for performing rendezvous maneuvers independently from the adjustments of the camera focal length, improving the performance and versatility of maneuvers. The stability of the proposed control scheme is proven analytically in the invariant space, and its viability is explored through numerical simulations.     

Temporal variation and asymmetry of sunspot and solar plage types from 1930 to 1936

Using the recently converted to digital format heliophysics catalogues of the Ebro Observatory published in the 1930s, we analyse simultaneously the temporal variation and asymmetry of two different solar structures located at different layers of the solar atmosphere: sunspots and solar plages. In particular, we do the research for all the types of sunspots and plages, including the daily and relative frequencies over the solar cycle. The data were catalogued using the sunspot Cortie classification and a solar plage classification scheme proposed by the Ebro Observatory, which group the phenomena by size and shape. For all types of both sunspots and plages, we observe a decrease in their frequency up to the end of solar cycle 16 and an increase over the beginning of solar cycle 17. Furthermore, we note that small sunspot groups are more likely to happen than bigger groups, although single big spots dominate near the solar minimum. The daily frequency of solar plage occurrences shows that there is not a dominance of compact or scattered solar plages. The North-South occurrence distribution of every type in both sunspots and solar plages shows an asymmetry during the solar cycle: in its declining phase, such asymmetry is directed to the north, while in the beginning of a new cycle is directed to the south.     

ITRS/GCRS transformation: Uncertainty propagation analysis and short-term modelling of IAU 2006/2000A developments

A study of the uncertainty propagation in ITRS/GCRS transformation is presented in this work. General law of propagation of variances is applied to the ITRS/GCRS transformation matrix, deriving the analytical expressions to compute GCRS position uncertainty. This evaluation is based on EOP uncertainties provided by IERS long-term series and formal uncertainties of ITRS-compatible coordinates. Numerical results for the period 1998–2016 are shown and discussed for ITRS positions in different altitudes and latitudes, providing graphical and numerical insights of the mapping of EOP uncertainties to transformed coordinates.Eventually, an analysis of short-term evolution of the Celestial Intermediate Pole coordinates in the GCRS provided by the IAU2006/2000A precession-nutation model is carried out, in order to assess the feasibility to potentially broadcast these parameters in GNSS navigation message. This approach would facilitate the dissemination of terrestrial-celestial transformation parameters for real time users, given that polar motion and UT1-UTC are already foreseen in GPS interface specification. The results presented in this work confirm the feasibility of this idea.     

Morphology: an ambiguous indicator of biogenicity

This paper deals with the difficulty of decoding the origins of natural structures through the study of their morphological features. We focus on the case of primitive life detection, where it is clear that the principles of comparative anatomy cannot be applied. A range of inorganic processes are described that result in morphologies emulating biological shapes, with particular emphasis on geochemically plausible processes. In particular, the formation of inorganic biomorphs in alkaline silica-rich environments are described in detail.     

Linear and circular structures of the Bohemian Massif — Comparison of satellite and geophysical data

Two structural schemes of the Bohemian Massif are presented and compared. The first one is a result of interpretation of various geophysical data and the second one is compiled on the basis of decoding of space imagery from different sources (Kosmos, Landsat etc.). Both schemes have many structural features in common, but there are diversities namely in the hierarchy of directions and regional distribution of linear structures. These problems are discussed in detail. For example, the most impressive system of structures is the NW-SE system in both schemes, whereas the NE-SW is more remarkable in the geophysical scheme; the N-S and the E-W systems are best expressed in the scheme of photolineaments. These facts are due to the genesis, age, development and dynamic characteristics of respective structural systems. The circular structural features namely those of large size are mostly remarkable in space imagery. At present, they are not distinguished genetically but only described regionally.