Impact analysis of the transponder time delay on radio-tracking observables

Accurate tracking of probes is one of the key points of space exploration. Range and Doppler techniques are the most commonly used. In this paper we analyze the impact of the transponder delay, $i.e$. the processing time between reception and re-emission of a two-way tracking link at the satellite, on tracking observables and on spacecraft orbits. We show that this term, only partially accounted for in the standard formulation of computed space observables, can actually be relevant for future missions with high nominal tracking accuracies or for the re-processing of old missions. We present several applications of our formulation to Earth flybys, the NASA GRAIL and the ESA BepiColombo missions.     

THE WAVE EXPERIMENT CONSORTIUM (WEC)

In order to get the maximum scientific return from available resources, the wave experimenters on Cluster established the Wave Experiment Consortium (WEC). The WEC's scientific objectives are described, together with its capability to achieve them in the course of the mission. The five experiments and the interfaces between them are shown in a general block diagram (Figure 1). WEC has organised technical coordination for experiment pre-delivery tests and spacecraft integration, and has also established associated working groups for data analysis and operations in orbit. All science operations aspects of WEC have been worked out in meetings with wide participation of investigators from the five WEC teams.     

Characteristics of the decay phase of proton fluxes in solar events as a function of observer’s heliolongitude

Events in energetic solar protons with the energy > 4 MeV at the stage of their decay are considered for the period from 1974 to 2001. It is shown that in the events with the exponential shape of decay for west flares (relative to the observation point), the characteristic decay time τ and the power index γ of the energy spectrum decrease with an increase in the angular distance between the observer and the source of the particles on the Sun, while this effect is absent for east flares.