Economics of telecommunications space segments

This paper proposes a complete model for assessing the economics of telecommunications satellite systems, accounting for spacecraft development and manufacturing, launch and operations in orbit. This allows to account for such parameters as the mass and lifetime of the satellites, the number and type of payloads, the number of satellites procured and launched, the spare policy, the launch vehicle, the insurances, the satellite average MTTF and the management of the space segment efforts.

The model is divided into four parts: the spacecraft mass model, the spacecraft procurement cost model, the MTTF model and the space segment cost-effectiveness model. It provides for the rapid solution of a number of problems within a wide range of parameters such as assessing the influence on space segment economics of —certain satellite technologies, —satellite and payload mass, —number of payloads per spacecraft, —satellite lifetime, or —spare policy.     

The State of Space Weather Scientific Modeling—An Introduction

The discipline of “Space Weather” is built on the scientific foundation of solar-terrestrial physics but with a strong orientation toward applied research. Models describing the solar-terrestrial environment are therefore at the heart of this discipline, for both physical understanding of the processes involved and establishing the capability to predict the consequences of these processes. This issue of Space Science Reviews contains four topical reviews on primarily European scientific progress in understanding and modeling space weather phenomena. The four reviews deal with (i) monitoring, modeling and predicting solar weather, (ii) the radiation environment of the Earth, (iii) solar wind disturbances and their interaction with geospace, and (iv) the upper atmosphere’s response to space weather events.     

Analysis and implementation of in-plane stationkeeping of continuously perturbed Walker constellations

The stationkeeping of symmetric Walker constellations is analyzed by considering the perturbations arising from a high order and degree Earth gravity field and the solar radiation pressure. These perturbations act differently on each group of spacecraft flying in a given orbital plane, causing a differential drift effect that would disrupt the initial symmetry of the constellation. The analysis is based on the consideration of a fictitious set of rotating reference frames that move with the spacecraft in the mean sense, but drift at a rate equal to the average drift rate experienced by all the vehicles over an extended period. The frames are also allowed to experience the J₂-precession such that each vehicle is allowed to drift in 3D relative to its frame. A two-impulse rendezvous maneuver is then constructed to bring each vehicle to the center of its frame as soon as a given tolerance deadband is about to be violated. This paper illustrates the computations associated with the stationkeeping of a generic Walker constellation by maneuvering each leading spacecraft within an orbit plane and calculating the associated velocity changes required for controlling the in-plane motions in an exacting sense, at least for the first series of maneuvers. The analysis can be easily extended to lower flying constellations, which experience additional perturbations due to drag.     

An Overview of Ionosphere—Thermosphere Models Available for Space Weather Purposes

Our objective is to review recent advances in ionospheric and thermospheric modeling that aim at supporting space weather services. The emphasis is placed on achievements of European research groups involved in the COST Action 724. Ionospheric and thermospheric modeling on time scales ranging from a few minutes to several days is fundamental for predicting space weather effects on the Earth’s ionosphere and thermosphere. Space weather affects telecommunications, navigation and positioning systems, radars, and technology in space. We start with an overview of the physical effects of space weather on the upper atmosphere and on systems operating at this regime. Recent research on drivers and development of proxies applied to support space weather modeling efforts are presented, with emphasis on solar radiation indices, solar wind drivers and ionospheric indices. The models are discussed in groups corresponding to the physical effects they are dealing with, i.e. bottomside ionospheric effects, trans-ionospheric effects, neutral density and scale height variations, and spectacular space weather effects such as auroral emissions. Another group of models dealing with global circulation are presented here to demonstrate 3D modeling of the space environment. Where possible we present results concerning comparison of the models’ performance belonging to the same group. Finally we give an overview of European systems providing products for the specification and forecasting of space weather effects on the upper atmosphere, which have implemented operational versions of several ionospheric and thermospheric models.     

IMPLICIT REPRESENTATION FOR THE MODELLING OF HYBRID DYNAMIC SYSTEMS

Differentmodels are proposed for the study ofhybrid systems that are composed of interactingcontinuous and discrete parts as,for instance,inRef.[1 ].Generally,the discrete part is modelledby an automation,and the continuous part by dif-ferent sets of state equations.Jump functions canbe added to represent the discontinuities.But noindication is given about the relations between thedifferent models and the jump functions.　　This paper isconcerned with the modelling forphysical systems with sw…     

Technology-based design and scaling for RTGs for space exploration in the 100 W range

This paper presents the results of a study on design considerations for a 100 W radioisotope thermo-electric generator (RTG). Special emphasis has been put on designing a modular, multi-purpose system with high overall TRL levels and making full use of the extensive Russian heritage in the design of radioisotope power systems. The modular approach allowed insight into the scaling of such RTGs covering the electric power range from 50 to 200 W_e (EoL). The retained concept is based on a modular thermal block structure, a radiative inner-RTG heat transfer and using a two-stage thermo-electric conversion system.     

Shock wave/turbulent boundary layer interaction and its control

The interaction between a shock wave and a boundary layer often leads to extremely detrimental effects, especially if the shock is strong enough to separate the boundary layer. When this happens, there occurs a rapid growth of the dissipative region along with a dramatic intensifying of turbulent fluctuations with the frequent occurrence of buffeting. In the present review some fundamental properties of the interaction are first considered for a two-dimensional, adiabatic flow developing on a flat surface. The following features are first examined: upstream interaction length, incipient shock-induced separation and evolution of the boundary layer properties during the interaction process. Supersonic and transonic flows are both considered. In a second part, the means envisaged to control shock/boundary layer interactions are presented, with emphasis on the physics of phenomena involved in this process. Control methods can be classified into two categories: those acting on the boundary layer properties before it enters the shock region (e.g. wall cooling, wall mass transfer, upstream blowing) and those having a local action in the shock foot region itself (e.g. suction or injection, boundary layer removal, passive control). The most appropriate technique depends on the specific application under consideration. Finally, some calculation methods are briefly presented, most of them being restricted to laminar interactions.     

Governance of national space activities

Senior political and space agency personnel joined representatives of industry and other space-related institutions for a conference, held in Budapest in January 2009, on how best to structure national and European space governance. Four sessions examined the subject of the conference from a top-down European, a bottom-up national, a theoretical and actor-based and a discursive–participative perspective. The themes and outcomes of the conference are reported below.