Methodological aspects of accuracy and protection support for space dual-purpose positioning systems.

The high level of dynamism, complexity and aerospace nature of the current combat struggle inevitably stimulates the advanced countries all over the world to actively develop and phase in the wide variety of integrated facilities and systems intended for resolving any information and attack-purpose mission, which provides capability of the operational hitting of any object with high accuracy. Usage efficiency of such advanced precision-guided weapon mostly depends on appropriate quality of the Timing Positioning Support (TPS) employed through all the phases of a combat mission. These days, in short- and long-term perspective the main components of the TPS system used by the Armed Forces of the Russian Federation, U.S. and NATO will consist of Space Medium-Altitude Positioning Systems (SPS) such as GLONASS, GPS and the European GALILEO system currently under deployment.

These SPSs fall into the category of dual-purpose systems equipped with secured and public radio links that are aimed to cope with positioning tasks either for military or for civil customers. Along with accuracy, availability, on-going operation and integrity requirements such SPS used for the benefit of military customers should also be protected, including as an integral part functional security (namely unauthorized access protection for secured radio links) and positive resistance to any disturbing impact.

In parallel with the stepping-up of quality requirements for TPS the outcome of tests conducted and experience gained in the novel weapon employment have revealed a gap between the required and existing level of accuracy characteristics and other SPS features. Using the existing second-generation SPS brings to light its disadvantages from the military customer point of view. Main drawbacks include poor accuracy of timing-positioning measurement under main operational modes, excluding differential one; low survivability of warfare installations used in SPS auxiliary equipment (e.g. Control Correction Station (CCS) integrated in differential sub-systems) and in ground control equipment for the orbital grouping of navigational satellite vehicles (NSV); susceptibility of Customer Positioning Equipment (CPE) used in SPS to a noise impact generated by electronic countermeasure devices of various stationing; and low operational efficiency of ephemeris-timing support for NSV operation. In the case of GLONASS SPS the above shortages are aggravated by the currently incomplete orbital NSV grouping, underdevelopment in quality and quantity aspects of CPE segment, and some problems associated with the development of national element base for appropriate positioning systems.

Several issues related to the improvement of technology and space communication facilities have been brought up many times by experts in a lot of military and technical publications. Well-known ways for improving to some degree the SPS parameters and meeting wide-range requirements of military customers consist in CPE integration with other sources of positioning information, employment of differential positioning mode, implementation of pseudo-range measurement using carrier phase in navigation signal, realization of independent control by CPE of integrity of the navigation field, and an increase in the number of carriers for radio navigation signal. It should be noted that the key issue for progress in timing-positioning support using SPS reckons on qualitative improvements in SPS components (NSV, ground control system, CPE), as well as operational accessories and their operation algorithms.

It is hardly wise, however, to expect that now the prevailing SPS configuration and traditional approaches and principles of development management could allow a speedy disposal of the above-mentioned disadvantages. Thus, the prevailing military and technical problem may be presented as image-building for challenging dual-purpose SPS that meets the requirements of military customers in terms of accuracy and protection aspects for timing-positioning information.

Any justification for such ways of solving the said military and technical problems assumes that appropriate methods be used in any military and technical investigation. As long as we have an extremely wide range of principles, skills and means of fundamental investigation we should delineate some limited sets of methodological approaches intended for providing adequate accuracy and protection for dual-purpose SPS that rely on the proper principles of systems analysis in the military and technical field appropriate for the said issue.

Review of historical data on the development of radio navigation systems enables us to predict possible trends in SPS development in terms of space element enhancement, its amplification in composition, tasks and configuration, as well as the modification of operational SPS parameter values needed for the transition of their efficiency indices to the new level.

We should note that under such separation between operational and communication aspects of SPS, and taking into account the above-mentioned general trends in its development, besides the solution of synchronization problem and parameter determination for the center of inertia movement the customer would be capable of identifying the trajectory parameters with respect to the center of inertia. This intensifies SPS competition with inertial position navigation systems. Moreover, such integration leads to characteristic upgrading of military-purpose SPS, accuracy and protection included. It is likely that SPS parameters will become better as well, under their integration with other available space information systems.

Review of intra-system SPS features reveals ample capabilities due to its inherent properties that have not been yet considered in full. This primarily concerns the second-generation SPS representing space-time systems. These properties are governed by the non-interrogation mechanism for measuring basic Current Positioning Parameters (CPP) in the form of customer pseudo-range and radial speed regarding NSV. These values contain certain coordinate-time information on SPS components that provides, in case of its usage in full, higher accuracy in parameter determination for customer movement and in time correction for CPP measurement, as well as stability in timing-positioning measuring of customers, primarily under an adverse impact of several factors such as an incomplete orbital grouping of GLONASS SPS, blocking of some line-of-sight views for NSV customer boresighting, or disuse of some boresight radio lines toward NSV with high level of interference.

Several researches conducted at the Peter the Great Military Academy of Strategic Missile Forces show that any unfavorable geometry for timing-positioning measurement leads to an increased correlation between random error in the evaluation of customer movement parameters and time correction. Taking into account this function could diminish the influence of unfavorable geometry on accuracy in customer timing-positioning measurement and thereby provide higher SPS stability. Modeling outcome proves that for correlation factor of 0.9-0.95 and higher which is typical of positioning measurement under conditions with unfavorable geometry the random error dispersion for customer coordinate estimation becomes lesser with the factor of 3-5 and more in comparison with a standard method, and random error dispersion for speed components decreases with the factor of 5-[10.sup.6]. Such timing-positioning measurement for SPS information customer taking into account correlation of movement parameter estimation and time correction is preferred in comparison with conventional navigational measurement due to the transition from filtration of movement parameter estimation to filtration of time correction values. In this case any knowledge about customer movement model is unnecessary.

The important factor of SPS protection consists in tolerance for NSV malfunction due to on-board equipment failure and other conditions. Several researches conducted at the Peter the Great Military Academy of Strategic Missile Forces show that accounting of historical data on on-board equipment failure and breakdown at a design stage for timing-positioning support of military customer allows us to raise SPS availability by 5-10%.

Even higher capabilities for improvement of SPS features in terms of accuracy and protection may be gained with fuller consideration of SPS configuration properties but this necessitates some follow-up thorough investigations. These investigations should be primarily focused on the development of intra-system relations among orbital segment components, customer components, and sophisticated radio-positioning signal configuration, its generation and processing conditions.

Thus, any solution of military technical problem related to image-building of advanced dual-purpose SPS meeting the military customer requirements regarding timing-positioning information in terms of accuracy and protection inevitably involves consistent and aggressive implementation of the above-mentioned trends, concepts and approaches to SPS development.

Col. O.A. ALEKSEEV

Department Head, Peter the Great Strategic Missile Forces

Military Academy

Doctor of Technical Sciences

Col. G.V. KALACH

Faculty Deputy Head, Peter the Great Strategic Missile Forces Military Academy

Candidate of Military Sciences

Lt. Col. A.V. MYACHIN

Lecturer, Peter the Great Strategic Missile Forces Military Academy

Candidate of Technical Sciences