TDRSS Scheduling Algorithm for Non-Uniform Time-Space Distributed Missions

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

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 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.

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.

An expert system for scheduling requests for communications links between TDRSS and ERBS

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>

In Fall 2021, SpaceLink Corporation was selected by the Center for the Advancement of Science in Space (CASIS), manager of the International Space Station (ISS) U.S. National Laboratory, for a demonstration of its end-to-end space data relay service. SpaceLink will provide secure, continuous communications between terrestrial operators and an optical terminal on the ISS, enabling real-time, high-throughput connectivity for the onboard crew, systems, and various science experiments. In a highly competitive process, made available for companies and research teams to propose technology development concepts operating in Low Earth Orbit (LEO), CASIS selected the SpaceLink concept. With this selection, SpaceLink will advance its flight project in collaboration with the ISS National Laboratory. The SpaceLink relay network will succeed and exceed NASA's Tracking and Data Relay Satellite System (TDRSS) with unprecedented capacity that leverages the latest optical communications technology advances. Demand for high-throughput, continuous orbital connectivity continues to grow with the ongoing proliferation of LEO satellites. SpaceLink's network is designed to help close the business case for Earth observation companies, commercial space stations, satellite services, launch vehicles, and space tugs. It also meets the requirements of the U.S. Government and close allies that are leveraging real-time, secure communications solutions. The SpaceLink ISS demonstration will validate a 10 Gigabit per second (Gbps) optical terminal communication link for real-time voice, video, and data relay for the ISS. Axiom Space, SpaceLink's implementation partner, will leverage its expertise in working with NASA and the ISS National Laboratory to support the SpaceLink payload mission integration, launch, and operations. Axiom will support SpaceLink as a liaison with NASA and will lead safety reviews to ensure SpaceLink hardware meets all ISS requirements. The SpaceLink-ISS Connectivity End to End Demonstration (SLICED) will demonstrate the highest data rates that can be achieved between SpaceLink relay spacecraft in Medium Earth Orbit (MEO) and the ISS, an example user satellite in LEO. The demonstration will include MEO-LEO edge case geometries where the relative range rates between the satellites are the highest and required contact acquisition times are shortest. SpaceLink's real-time gigabit user data rates are possible via optical inter-satellite communications between spacecraft, as well as high-bandwidth QN-band communications between SpaceLink's relay spacecraft and terrestrial gateways. SpaceLink has designed an innovative system architecture, implementing high-security services and continuous availability so that satellite data is available in real time when it matters the most. This study will discuss the technical foundation behind SpaceLink's ISS demonstration infrastructure.

TDRS (Tracking and Data Relay Satellite) can be seen as a bridge between user spacecrafts and ground station. The TDRSS (Tracking and Data Relay Satellite System) single access link scheduling problem is an important application field of TDRSS. The important character of the scheduling problem lies in that there is time windows constraint between TDRS and user spacecrafts. Tasks can be completed only within given time windows. The paper builds the CP (constraint programming) model of the scheduling problem based on reasonable assumption. The CP model is solved with improved GA (genetic algorithm) based on path representation of valid genes. Computational experiments indicate that it is quite good to solve the scheduling problem by building the CP model and solving it with improved GA

As future communications in space require increasing data rates, Ka-band technology is needed to enable wider bandwidths and higher data rates. Linear frequency translation is essential in enabling higher order modulation schemes for high data rates, which in turn enhances flexibility and software defined capability. This paper summarizes the key design features and data results of Ka-band forward and reverse link frequency translators compatible with the Tracking and Data Relay Satellite System (TDRSS) bands (26 GHz); future work could expand operation to the Deep Space Network Ka-band. The technology developed was a set of Ka-band transmit and receive multi-chip module (MCM) frequency translators with associated low phase noise local oscillator (LO) synthesizer boards. This set of hardware converts between S-band and Ka-band. The translators are designed for a 1 GHz bandwidth and for a center frequency that is re-tunable in this 1 GHz range. The MCMs offer a versatile design that can be used for both exciter and receiver translators and provide areas for future expansion. Furthermore, the MCM and LO synthesizer form a low power system with 1.6W of power consumption for the exciter hardware and 1.8W for the receiver portion. Finally, the LO synthesizer has low phase noise under 2.5 degrees rms from 100 Hz to 40 MHz which enables high data rates and high order modulation schemes. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1 2</sup>

&#x0D; &#x0D; &#x0D; A reliability trend/growth analysis methodology for satellite systems is suggested. A satellite system usually consists of many satellites successively launched over many years, and its satellites typically belong to different satellite generations. This paper suggests an approach to reliability trend/growth data analysis for the satellite systems based on grouped data and the Power Law (Crow-AMSAA) Non- Homogeneous Poisson process model, for both one (time) and two (time and generation) variables. Based on the data specifics, the maximum likelihood estimates for the Power Law model parameters are obtained. In addition, the Cumulative Intensity Function (CIF) of a family of satellite systems was analyzed to assess its similarity to that of a repairable system. The suggested approaches are illustrated by a case study based on Tracking and Data Relay Satellite System (TDRSS) and Geostationary Operational Environmental Satellite (GOES) data.&#x0D; &#x0D; &#x0D;

• Examines scheduling on m identical parallel machines with a common server. • Considers sequence-dependent setup times in parallel machine scheduling. • Introduces an arc-based MILP formulation for makespan minimization. • Presents a GRASP-enhanced Iterated Greedy algorithm with strong performance. • Reports 21 new best-known solutions across benchmark test instances. The identical parallel machine scheduling problem with a single server and sequence-dependent setup times is a challenging optimization problem with important applications in manufacturing and service industries. In such environments, several machines depend on a common server to perform setup operations before production can begin, which creates strong interdependencies and demands more effective scheduling strategies. This characteristic highlights the practical relevance of the problem. The interaction between machine availability and server operations often becomes a critical bottleneck. This study introduces two complementary approaches. The first is an exact method based on a novel arc-based mixed-integer linear programming (ABF) model, which extends the modeling capability of existing formulations by capturing server-related constraints more effectively. The second is an approximation method built on an Iterated Greedy (IG) algorithm. The IG procedure is improved by two evaluation mechanisms: one model-based evaluation derived from the proposed ABF model, and another employing a greedy randomized adaptive search procedure (GRASP)-based strategy that integrates greedy selection, randomization, and reconstruction to enhance solution quality. Computational experiments are conducted on existing benchmark instances. The results show that the proposed ABF model performs well on small and medium-sized instances compared to existing exact methods, while the IG variants, particularly the proposed GRASP-based version, deliver strong performance against state-of-the-art metaheuristics developed for this problem. In addition, 21 new best-known solutions are reported, further demonstrating the effectiveness of the proposed approaches.

ABSTRACTNurse rostering is a complex scheduling problem which requires the assignment of various shifts to different types of registered nurses and is subject to a set of constraints encompassing patient demand coverage and working and rest regulations. In addition to these constraints, the flexibility and fairness of shift assignments have become a pressing issue that directly affects nurse satisfaction. In this article, a two-stage heuristic algorithm is proposed to fulfill the fairness and flexibility objectives on nurse shift assignment. The first stage identifies the shift type combination that meets the demanded staffing level for each time interval of the day, and makes the shift assignments also comply with the set of working constraints. The second stage generates nurse rosters that allocate the weekend shifts as evenly as possible over a given planning horizon based on a hospital's requests. A case study using data from a US hospital is presented to illustrate the applicability of the method, and comparisons of the three most commonly used shift length designs are discussed. The results show that cost savings and fairness can be achieved through appropriate shift designs.