The Russian Academy of Sciences and Federal Space Agency, together with the participation of many international organizations, worked toward the launch of the RadioAstron orbiting space observatory with its onboard 10-m reflector radio telescope from the Baikonur cosmodrome on July 18, 2011. Together with some of the largest ground-based radio telescopes and a set of stations for tracking, collecting, and reducing the data obtained, this space radio telescope forms a multi-antenna groundspace radio interferometer with extremely long baselines, making it possible for the first time to study various objects in the Universe with angular resolutions a million times better than is possible with the human eye. The project is targeted at systematic studies of compact radio-emitting sources and their dynamics. Objects to be studied include supermassive black holes, accretion disks, and relativistic jets in active galactic nuclei, stellar-mass black holes, neutron stars and hypothetical quark stars, regions of formation of stars and planetary systems in our and other galaxies, interplanetary and interstellar plasma, and the gravitational field of the Earth. The results of ground-based and inflight tests of the space radio telescope carried out in both autonomous and ground-space interferometric regimes are reported. The derived characteristics are in agreement with the main requirements of the project. The astrophysical science program has begun.
A new algorithm is presented for the formation of an analytical time scale that takes into account the fl uctuations of atomic clock signal frequencies over several time scales. Numerical simulation shows that the algorithm can obtain a group time scale for an ensemble of atomic clocks with rather high frequency stability characteristics. The proposed algorithm is compared with the algorithm for calculating a time scale based on the Kalman fi lter. Analytical time scales are widely used in time and frequency standards based on an ensemble of atomic clocks to increase precision and stability characteristics. At this time, there are a large number of algorithms for computing analytic time scales. Among them there are algorithms which process results a posteriori and algorithms in which the corrections for atomic clock signals constituting a reference group are calculated in real time. The most frequently used computational methods are various modifi cations of the basic equations of the time scale (ALGOS, FAT, AT1, METS) [1-6], Kalman fi ltering (Kred, IEM) [7-9], as well as their combination (KAS-2, KPW) [10 -11]. Algorithms based on the Kalman fi lter enable a suffi ciently precise estimate of signal frequency and phase; as a rule, they give better results compared with algorithms based only on the basic equations of the time scale, such as AT1 and ALGOS. However, their operation requires a priori information about the parameters of the phase noise of atomic clock signals; moreover, the Kalman fi lter signifi cantly complicates accounting for fl icker frequency noise [12]. We also note that the computational complexity of algorithms based on the Kalman fi lter increases nonlinearly with increasing number of atomic clocks in the ensemble, and the procedure for adding or excluding an atomic clock from the group turns out to be more complicated than in other methods.Previously there was proposed an algorithm using a frequency-locked loop with an auxiliary generator relative to an ensemble of quantum clocks to form the group signal [13]. This algorithm uses the moving average method to estimate the fl uctuation frequency of the input signals over different time intervals. Unlike the Kalman fi lter, it does not require information about the model of the random process and its parameters for describing the atomic clock signals. According to the simulation results presented in [13], the Allan deviation of the group signal generated by this algorithm is close to the minimum possible values for the entire range of measurement time intervals considered. Thus, the control algorithm has to be comparable in stability characteristics of the formed weighted average frequency to the presently known algorithms for the
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