Journal of Space Science and Technology
Year:2015 | Volume:8 | Issue:2|Papers Count:7

Comparison of direct and indirect methods for georeferencing of satellite linear array stereo images is proposed in this paper. In direct method, collinear condition and orbital elements are used for geolocation of pixels and ground control points (GCPs) are used in indirect method. After geolocation of initial points, a polynomial transformation is used to change pixels coordinates into corresponding geographical values. We validate these methods through experiment with SPOT-4 and IRS-P6 images. Experimental results indicate that indirect method can be used for georeferencing of satellite linear array images and the accuracy is as much as or even better than that of the direct method but it is time- and cost-consuming and also needs operator.

In this paper, a continuous globally stable tracking control algorithm is proposed for spacecraft in the presence of unknown actuator failure. The design method is based on nonlinear dynamic inversion and in contrast to traditional fault-tolerant control methods, the proposed controller does not require knowledge of the actuator faults and is implemented without explicit fault detection and isolation processes. The stability proof is based on a Lyapunov analysis and the properties of the singularity free quaternion representation of spacecraft dynamics. Results of numerical simulations state that the proposed controller is successful in achieving high attitude performance in the presence of external disturbances and actuator failures.

Preliminary orbit determination of unknown space object such as satellites that are launched by other countries, military satellites and uncatalogued Space debris is important in space activities. So by means of information of ground based electro-optics systems, orbital elements of satellite can be estimated accurately. In this paper we studied most famous three methods of classical orbit determination analytically which are based on angles-only observations of orbit. Then, by using observable data and simulations, results of computational codes of three methods are compared and the effect of time separation between observed points of satellite path is demonstrated and results are analyzed.

Collaborative optimization is one of bi-level multidisciplinary optimization methods which consists of system level and discipline level and is applied for complex engineering problems. since this method is rigidly convergent at discipline level because of noisy constraints at system level on one hand and minimizing objective function necessity at system level on the other hand, this optimization method is forced to use evolutionary algorithms in order to minimize objective function at system level, also, It has been proved that, applying this algorithms according to their nature is expensive and time consuming. This paper with performed inspections is a new method for applying innovated optimization algorithms through which considerable results are obtained in solving sample problems. It is shown that using this method will decrease function calls number or problem solving time and therefore calculating costs will decrease considerably. Also it is shown that this method sometimes increase accuracy.

For precise locating, Differentials Global Positioning System requires prediction of differential corrections for the future times. The system is comprised of both fixed and mobile stations. If the satellites of the two stations are exactly the same, the sources of errors will be close to each other at the two stations; in this case, reference position components factors can be used as corrective factors for offsetting user station positioning error. In this paper, Genetic and Artificial Neural Network hybrid algorithms (Evolutionary Neural Network), Support Vector Machines, Autoregressive Moving Average and Recurrent Neural Network have been used for corrections. In order to test the algorithms, static sampling of the position data of an inexpensive receiver was used and the predicted reference position components error corrections were applied elsewhere. The tests performed as post-process showed that the positioning RMS error decreases up to 0.5 m. The evolutionary neural network prediction model is more accurate than other models and its RMS error is 0.12 m.

In this paper a new method for satellite authomatic tracking presented by earth station via doppler frequency. This method done by calculating time diviation through difference between real dopper frequency by communication equipment and software Doppler frequency by theoretical TLE via STK Software. Then Kepler parameters are chaned so this deviation limit to zero. By this action correct antenna direction to satellite and receiving signal without error. Method test was done by amature satellite in UHF frequency band & CW Modulaition.

In this Paper, The online optimal integrated guidance and control algorithm design has been provided for two-stages Launch Vehicle. The flight equations are nonlinear and has been derived in flight plane. In order to solve it based on numerical solution and shooting method logic by the combination between ODE - start to end solver algorithm by considering initial conditions for integrated states and co-states- and optimization fmincon SQP algorithm has been acted. In order to verify designing method the results of this algorithm solutions has been compared with the results of a valid separated guidance and control algorithm for launch vehicle. The result function involves minimum control effort, terminal terms and minimizing burning time. The results indicate the satisfaction of three mentioned identities achieving high accurate orbital insertion and more coordination between the operation of guidance and control algorithms in integrated logic comparing with separated ones.