Application of time-variable process noise in terrestrial reference frames determined from VLBI data

In recent years, Kalman filtering has emerged as a suitable technique to determine terrestrial reference frames (TRFs), a prime example being JTRF2014. The time series approach allows variations of station coordinates that are neither reduced by observational corrections nor considered in the functional model to be taken into account. These variations are primarily due to non-tidal geophysical loading effects that are not reduced according to the current IERS Conventions (2010). It is standard practice that the process noise models applied in Kalman filter TRF solutions are derived from time series of loading displacements and account for station dependent differences. So far, it has been assumed that the parameters of these process noise models are constant over time. However, due to the presence of seasonal and irregular variations, this assumption does not truly reflect reality. In this study, we derive a station coordinate process noise model allowing for such temporal variations. This process noise model and one that is a parameterized version of the former are applied in the computation of TRF solutions based on very long baseline interferometry data. In comparison with a solution based on a constant process noise model, we find that the station coordinates are affected at the millimeter level.     

Feedstocks of the Terrestrial Planets

The processes of planet formation in our Solar System resulted in a final product of a small number of discreet planets and planetesimals characterized by clear compositional distinctions. A key advance on this subject was provided when nucleosynthetic isotopic variability was discovered between different meteorite groups and the terrestrial planets. This information has now been coupled with theoretical models of planetesimal growth and giant planet migration to better understand the nature of the materials accumulated into the terrestrial planets. First order conclusions include that carbonaceous chondrites appear to contribute a much smaller mass fraction to the terrestrial planets than previously suspected, that gas-driven giant planet migration could have pushed volatile-rich material into the inner Solar System, and that planetesimal formation was occurring on a sufficiently rapid time scale that global melting of asteroid-sized objects was instigated by radioactive decay of ²⁶Al. The isotopic evidence highlights the important role of enstatite chondrites, or something with their mix of nucleosynthetic components, as feedstock for the terrestrial planets. A common degree of depletion of moderately volatile elements in the terrestrial planets points to a mechanism that can effectively separate volatile and refractory elements over a spatial scale the size of the whole inner Solar System. The large variability in iron to silicon ratios between both different meteorite groups and between the terrestrial planets suggests that mechanisms that can segregate iron metal from silicate should be given greater importance in future investigations. Such processes likely include both density separation of small grains in the nebula, but also preferential impact erosion of either the mantle or core from differentiated planets/planetesimals. The latter highlights the important role for giant impacts and collisional erosion during the late stages of planet formation.     

Space Debris Mitigation in France,Germany, Italy and United Kingdom

The Space systems today provide growing benefits to enhance the quality of humankind. However, as a by-product, the orbiting objects inevitably leaves some debris which after 50 years of space activities represent a concern for all space agencies and manufacturers and operators. Since last year no international agreement was in place to mitigate the growing population of space debris objects. The successful result obtained at UN-COPUOS in 2007 and available in the OOSA web site, now gives to the public, a set of voluntary international guidelines that could, if adopted by each space fairing Country, help in maintaining the present space environment. More further steps are necessary in the future to define a legal and normative framework. The paper will present the seven established UN Space Debris guidelines as well as examples of the minimum steps to be carried out at national level to enable the UN-COPUOS to start the discussion of the legal aspect associated with the space debris issue.     

An Overview of the Lunar Crater Observation and Sensing Satellite (LCROSS)

The Lunar Crater Observation Sensing Satellite (LCROSS), an accompanying payload to the Lunar Reconnaissance Orbiter (LRO) mission (Vondrak et al. 2010), was launched with LRO on 18 June 2009. The principle goal of the LCROSS mission was to shed light on the nature of the materials contained within permanently shadowed lunar craters. These Permanently Shadowed Regions (PSRs) are of considerable interest due to the very low temperatures, <120?K, found within the shadowed regions (Paige et al. 2010a, 2010b) and the possibility of accumulated, cold-trapped volatiles contained therein. Two previous lunar missions, Clementine and Lunar Prospector, have made measurements that indicate the possibility of water ice associated with these PSRs. LCROSS used the spent LRO Earth-lunar transfer rocket stage, an Atlas V Centaur upper stage, as a kinetic impactor, impacting a PSR on 9 October 2009 and throwing ejecta up into sunlight where it was observed. This impactor was guided to its target by a Shepherding Spacecraft (SSC) which also contained a number of instruments that observed the lunar impact. A?campaign of terrestrial ground, Earth orbital and lunar orbital assets were also coordinated to observe the impact and subsequent crater and ejecta blanket. After observing the Centaur impact, the SSC became an impactor itself. The principal measurement goals of the LCROSS mission were to establish the form and concentration of the hydrogen-bearing material observed by Lunar Prospector, characterization of regolith within a PSR (including composition and physical properties), and the characterization of the perturbation to the lunar exosphere caused by the impact itself.     

Balloon-borne air traffic management (ATM) as a precursor to space-based ATM

The International Space University—Balloon Air traffic control Technology Experiment (I-BATE¹) has flown on board two stratospheric balloons and has tracked nearby aircraft by receiving their Automatic Dependent Surveillance-Broadcast (ADS-B) transmissions. Air traffic worldwide is facing increasing congestion. It is predicted that daily European flight volumes will more than double by 2030 compared to 2009 volumes. ADS-B is an air traffic management system being used to mitigate air traffic congestion. Each aircraft is equipped with both a GPS receiver and an ADS-B transponder. The transponder transmits an equipped aircraft's unique identifier, position, heading, and velocity once per second. The ADS-B transmissions can then be received by ground stations for use in traditional air traffic management. Airspace not monitored by these ground stations or other traditional means remains uncontrolled and poorly monitored. A constellation of space-based ADS-B receivers could close these gaps and provide global air traffic monitoring. By flying an ADS-B receiver on a stratospheric balloon, I-BATE has served as a precursor to a constellation of ADS-B-equipped Earth-orbiting satellites. From the ～30 km balloon altitude, I-BATE tracked aircraft ranging up to 850 km. The experiment has served as a proof of concept for space-based air traffic management and supports a technology readiness level 6 of space-based ADS-B reception.     

Criteria for developing and testing Transparency and Confidence-Building Measures (TCBMs) for outer space activities

Space systems play an important role in sustaining the development, prosperity and security of many nations. As more nations become critically reliant on space systems, questions of maintaining safety and strategic stability in outer space have come to the fore. Transparency and Confidence-Building Measures (TCBMs) for outer space activities have an important role to play in providing clarity about the intentions of States and in articulating norms of behaviour in outer space. TCBMs take several forms. They may be the elaboration of basic principles related to the exploration and use of outer space, political measures related to establishing norms of conduct, information-sharing activities to improve the transparency of outer space activities, operational practices which demonstrate a commitment to mutual cooperation in outer space, or consultative mechanisms. We present an analytical framework for evaluating potential TCBMs and illustrate the application of this framework to examples of potential operational, regulatory, treaty-based and declaratory TCBMs.     

A technique for mapping environmental change using digital Landsat data

This paper describes a procedure for detecting and mapping changes in vegetation cover using LANDSAT digital analysis techniques, and demonstrates how the procedure can be used as an aid to environmental monitoring. Digital image analysis is used to perform a historical comparison, and a computerized colour plotter is used to map the changes in vegetation.     

Basic space sciences in Africa

Through space applications, a number of social and economic programmes in education, communications, agro-climatology, weather forecasting and remote sensing are being realized within the African continent. Regional and international organizations and agencies such as the African Remote Sensing Council, the Pan-African Telecommunication Union and the United Nations system have been instrumental in making Africa conscious of the impact and implications of space science and technology on its peoples.The above notwithstanding, discernible interests in space research, to date, in Africa, have been limited to the work on the solar system and on interplanetary matters including satellite tracking, and to the joint African-Indian proposal for the establishment of an International Institute for Space Sciences and Electronics (INISSE) and the construction, in Kenya, of a Giant Equatorial Radio Telescope (GERT).During this “Transport and Communications Decade in Africa,” Africa's basic space research efforts would need to initially focus on the appropriateness, modification and adaptation of existing technologies for African conditions with a view to providing economic, reliable and functional services for the continent. These should include elements of electronics, communications, structural and tooling industries, and upper-atmosphere research. The experience of and collaborative work with India, Brazil and Argentina, as well as the roles of African scientists, are examined.