Constraint Programming Model of Tdrss Single Access Link Scheduling Problem

Adaptive subsequence adjustment with evolutionary asymmetric path-relinking for TDRSS scheduling

Simultaneous orbit determination is demonstrated using live range and Doppler data for the NASA/Goddard tracking configuration defined by the White Sands Ground Terminal (WSGT), the Tracking and Data Relay Satellite (TDRS), and the Earth Radiation Budget Satellite (ERBS). A physically connected sequential filter-smoother was developed for this demonstration. Rigorous necessary conditions are used to show that the state error covariance functions are realistic; and this enables the assessment of orbit estimation accuracies for both TDRS and ERBS.

Both kinematics and measurement model help process the trajectory data and estimate aerodynamic parameters of vehicle. In this paper, three dynamics are proposed, which are aerodynamics parameter's model, acceleration's model and α - β - γ model. The measurement model is TDRS (Tracking and Data Relay Satellite), which produces a complicated trajectory in reentering purpose. A fuzzy IMM algorithm is proposed in this paper, which through a fuzzy inference to get the matching degree of every UKF filtering model, instead of calculating model transition probabilities in IMM. With the matched degrees, the estimation from each filtering is weighted to get maneuvering target overall estimation and its covariance. Simulation results show that the FIMM algorithm performs well in tracking re-entering vehicle and estimating the aerodynamics parameters as well.

Landsats 4 and 5, the latest in the series of unmanned earth observation satellites, are used as the space platform for two remote sensing, mechanical scanning instruments: the multispectral scanner (MSS) and the recently developed thematic mapper (TM). The primary objective of the experimental portion of the Landsat 4 and 5 missions is to assess the capability of the TM to provide improved information relative to the MSS. The higher spatial resolution of the TM over the MSS requires a higher degree of flight segment attitude stability than the earlier Landsats; therefore, a more stable, low-orbit space platform must be provided. This paper describes the orbital, electrical, mechanical, and thermal chihracteristics of Landsat 4 and 5 flight segment with special emphasis on the TM and MSS interfaces. Also described are flight segment disturbances caused by the TM and MSS scanning mirrors, motion from the Tracking and Data Relay Satellite (TDRS) antenna, solar array, and the attitude control system (ACS).

In this study, the U-type assembly line balancing problem (UALBP) with assignment restrictions (AR-UALBP) is considered. Linked and incompatible distance and station restrictions are taken into account. New mathematical programming (MP) and constraint programming (CP) models are proposed. The objective function of the models is minimizing the cycle time for a given number of workstations. In addition to this objective, line efficiency and CPU time are also considered as other performance measurements. Numerical experiments on some problems from the literature are performed to evaluate the effectiveness of the proposed models. The results are compared with the results of the CP model of the straight ALBP with assignment restrictions and also the results from MP and CP models are compared with each other. The numerical results indicate that the proposed CP and MP models are more effective in obtaining better and optimal results when solving the AR-UALBP.

The Air Force Satellite Control Network (AFSCN) is a global configuration of common user and dedicated control nodes and space/ground link resources whose mission is to support space vehicle telemetry, tracking, and control (TT&C) requirements and to receive, process and disseminate mission data for a variety of operational DoD space systems. The primary space/ground link resources include 9 remote tracking stations (RTS) supporting 16 antennas that operate at S-band using the Space-Ground Link System (SGLS). A study was performed last year [1] to evaluate the capability of the current NASA Tracking and Data Relay Satellite System (TDRSS) to provide space-ground connectivity for AFSCN-supported space vehicles. The results of this study were extended this year in support of a DoD/NASA TT&C Integrated Product Team (IPT) whose purpose was to explore options available to significantly reduce cost and improve mission effectiveness through increased DoD use of TDRSS. The purpose of this paper is to report the results of these studies, which address the various technical, regulatory, and economical considerations associated with TDRSS providing support to the AFSCN.

A constraint programming approach for resource-constrained flexible assembly flow shop scheduling problem with batch direct delivery

In a Ku-band single access return (KSAR) communication link via the tracking and data relay satellite system (TDRSS), the interference between spacecraft can be discriminated by opposite antenna polarizations, pseudo-noise code, and by TDRSS antenna beam pointing. For the Space Station Freedom (SSF) KSAR and the Space Shuttle Orbiter (SSO) KSAR links, the pseudo-noise coding technique is not exploited. In addition, the two KSAR links use the same carrier frequency. Therefore, if the SSF and SSO are in close proximity, it is expected that mutual interference will be significant. Mutual interference effects on the SSO-KSAR I-channel and the SSF-KSAR links are analytically derived and compared to the simulation results. For the analysis, the channel is assumed ideally bandlimited and linear. It is demonstrated that a simplified (linear bandlimited channel) analytical approach yields results of adequate accuracy in an estimation of the signal degradation by interference.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The simulation performance of simultaneous tracking and data-relay satellite system (TDRSS) support of Space Station and Space Shuttle communication is discussed. Eight Ku- and S-band forward and return links are considered. The models and parameters of the systems are described in detail in an accompanying paper (see ibid., p.1-9).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

It may be very difficult to achieve the optimal shift schedule in call centers which have highly uncertain and peaked demand during short time periods. Overlapping shift systems are usually designed for such cases. This paper studies shift scheduling and rostering problems for inbound call centers where overlapping shift systems are used. An integer programming model that determines which shifts to be opened and how many operators to be assigned to these shifts is proposed for the shift scheduling problem. For the rostering problem both integer programming and constraint programming models are developed to determine assignments of operators to all shifts, weekly days-off, and meal and relief break times of the operators. The proposed models are tested on real data supplied by an outsource call center and optimal results are found in an acceptable computation time. An improvement of 15% in the objective function compared to the current situation is observed with the proposed model for the shift scheduling problem. The computational performances of the proposed integer and constraint programming models for the rostering problem are compared using real data observed at a call center and simulated test instances. In addition, benchmark instances are used to compare our Constraint Programming (CP) approach with the existing models. The results of the comprehensive computational study indicate that the constraint programming model runs more efficiently than the integer programming model for the rostering problem. The originality of this research can be attributed to two contributions: (a) a model for shift scheduling problem and two models for rostering problem are presented in detail and compared using real data and (b) the rostering problem is considered as a task-resource allocation and considerably shorter computation times are obtained by modeling this new problem via CP.

Requirements related to increases in data volume for missions projected for the 1990's could be met by increasing the number of satellites in the Tracking and Data Relay Satellite System (TDRSS) constellation or by providing a new tracking and data acquisition satellite system having greater capacity (gigabits), increased reliability, and more direct user-to-relay connectivity. The program to develop the heir to TDRSS for the 1990's, has been defined as Tracking and Data Acquisition System (TDAS). A description is presented of the system architectural considerations which have to be studied in order to develop a cost effective TDAS. Attention is given to basic TDAS design parameters, TDAS spacecraft architectures, system considerations, technology considerations, and TDAS constellation options involving 2, 3, and 4 satellites.

A number of applications of autonomous satellite navigation are discussed. They include the onboard annotation of all experimental data and the onboard correction of imaging data. The accuracy levels required for each function are presented. Two alternative techniques for achieving autonomous satellite navigation are considered. One technique utilizes data from the Global Positioning System (GPS). The other approach utilizes data from a geosynchronous relay satellite system such as the Tracking and Data Relay Satellite System (TDRSS). The TDRSS approach makes use of one-way range and Doppler data along with a time transfer mechanism. Comparative accuracy levels for the onboard determination of position, velocity, and time based upon the GPS and TDRSS approaches are presented.

NASA has operated two separate worldwide ground-based tracking and data acquisition networks for support of its various missions. The Spaceflight Tracking and Data Network (STDN) has provided support to all NASA earth orbiting spacecraft. The Deep Space Network (DSN) supports almost exclusively those unmanned exploratory spacecraft which have been sent far from earth. The Tracking and Data Relay Satellite System (TDRSS), which is conceptually a part of the STDN, will soon be added to the first two networks. The TDRSS will consist of two geosynchronous satellites together with a single ground terminal in White Sands, New Mexico. The TDRSS was conceived as a means of providing improved tracking and data relay service for a large class of the earth orbiting satellites. An investigation was conducted with the objective to reduce the costs of providing support to those spacecraft which were not TDRS-compatible. It was recommended that the core sites of the Ground segment of the STDN (GSTDN) be consolidated into the DSN

Introducing new communication equipment or system to the Tracking and Data Relay Satellite System (TDRSS) ground segment is a complicated process that involves a lengthy development and test cycle. Complexity arises due to the presence of the variety of signaling formats, operation and user constraints, monitor and control parameters, and the requirement to ensure the new piece of ground equipment or system meets the functional and performance requirements for all different combinations of system configuration parameters and operational scenarios. The development cycle starts with extensive software simulations to establish the performance parameters of the new equipment or system followed by a prototyping stage. The prototype system undergoes a battery of tests in a laboratory environment to verify that it is capable of meeting the performance levels derived from the software simulations. Testing must be performed using simulated signals generated either using software or hardware. The current practice is to use a chain of test equipment, each piece in the chain dedicated to a single function. This requires manual setup between different test configurations and test reporting is also handled manually. This is costly both in terms of test hardware investment and the manpower involved. The options available to reduce the cost are to use either a software or hardware simulator that can combine multiple functions in a single unit. Software simulation involves generating signal files that can be played back repeatedly. Depending on the data rate being simulated, each test file can occupy several Terabytes (TBs); in addition, it requires a playback system which tends to be relatively expensive to acquire and maintain. On the other hand, with more advanced signal processing technology the hardware simulation can be achieved with low cost Field Programmable Gate Array (FPGA). A low cost hardware simulator that can support data rates up to 25 Mbps is selected for the simulation system. The simulator supports baseband digital data formats and different modulation and coding schemes used in the TDRSS. Channel impairments applicable for communicating with orbiting platforms and signal impairments generated by the TDRSS itself are also simulated by the system; these include stressing profiles of delay, Doppler, and multipath. Hardware distortions of customer platforms are simulated by a set of software defined distortion filters designed according to the user constraints specified in the Space Network user's guide. In order to reduce the time spent during the prototype testing phase, an automated test system is being developed. Simulator architecture and the test automation approach will be presented.

Collaborative robots are progressively employed to support human workers in assembly tasks or independently assigned to one station to complete assembly tasks in U-shaped assembly lines. This study develops two exact methods, based on constraint programming (CP) model and Combinatorial Benders’ decomposition algorithm (CBDA), to tackle the U-shaped assembly line balancing problem with collaborative robots. The CBDA is based on distinct decomposition strategies that address the master problem and the subproblem, formulated by a mixed integer linear programming (MILP) model and a CP model, which is designed to obtain a real objective value and generate cuts that refine the master problem. Additionally, MILP-based and CP-based local search techniques are proposed to improve the algorithm's performance. The computational study demonstrates that both the proposed methods, namely CP and CBDA, outperform the current state-of-the-art methods (the MILP model and simulated annealing algorithm). Furthermore, the CP outperforms the CBDA in terms of the number of optimal solutions, achieving the optimal solutions for 574 out of 1500 test instances, and might be regarded as the new state-of-the-art methodology.