Measurement of the energy resolution and calibration of hybrid pixel detectors with GaAs:Cr sensor and Timepix readout chip

This paper describes an iterative method of per-pixel energy calibration of hybrid pixel detectors with GaAs:Cr sensor and Timepix readout chip. A convolution of precisely measured spectra of characteristic X-rays of different metals with the resolution and the efficiency of the pixel detector is used for the calibration. The energy resolution of the detector is also measured during the calibration. The use of per-pixel calibration allows to achieve a good energy resolution of the Timepix detector with GaAs:Cr sensor: 8% and 13% at 60 keV and 20 keV, respectively

Statistical model of space objects distribution in space of orbital parameters

Abstract: A statistical model of space debris is proposed. The model is based on the catalog of orbits of space objects, constructed using domestic and foreign sources. To build this model, the cataloged objects are clustering using criterion of closeness in a 4d space of orbital parameters characterizing the semimajor axis, eccentricity and position of the plane of the satellite orbits composing a cluster. The distribution of objects in each cluster is determined by the mathematical expectation and the covariance matrix of the spread of the orbital parameters of the cluster.Note: Research direction:Mathematical modelling in actual problems of science and technic

The antenna phase center motion effect in high-accuracy spacecraft tracking experiments

We present an improved model for the antenna phase center motion effect for high-gain mechanically steerable ground-based and spacecraft-mounted antennas that takes into account non-perfect antenna pointing. Using tracking data of the RadioAstron spacecraft we show that our model can result in a correction of the computed value of the effect of up to 2×10-14 in terms of the fractional frequency shift, which is significant for high-accuracy spacecraft tracking experiments. The total fractional frequency shift due to the phase center motion effect can exceed 1×10-11 both for the ground and space antennas depending on the spacecraft orbit and antenna parameters. We also analyze the error in the computed value of the effect and find that it can be as large as 4×10-14 due to uncertainties in the spacecraft antenna axis position, ground antenna axis offset and misalignment, and others. Finally, we present a way to reduce both the ground and space antenna phase center motion effects by several orders of magnitude, e.g. for RadioAstron to below 1×10-16, by tracking the spacecraft simultaneously in the one-way downlink and two-way phase-locked loop modes, i.e. using the Gravity Probe A configuration of the communications links.Astrodynamics & Space Mission