Joseph I. Statman

Spread-spectrum code acquisition in the presence of Doppler shift and data modulation

A spread-spectrum code acquisition technique for a direct-sequence (DS) system in the presence of Doppler effect and data modulation is investigated. Both the carrier-frequency offset and code-frequency offset due to severe Doppler effect are considered. The code-chip slipping during the correlation process caused by code-frequency offset can degrade the acquisition performance significantly. However, this issue can be alleviated by compensating code-frequency offset in an appropriate manner. Results are presented for the cases with and without data modulation. Coherent detection is considered when there is no data modulation. If data modulation is present, the authors partition the correlation time into subintervals and the integration results in these subintervals are square-law noncoherently combined for detection. The implementation of this code acquisition technique using the fast Fourier transform (FFT) algorithm is described. The use of theoretical results to estimate the hardware complexity of an actual system is illustrated step by step, showing that implementation is feasible with existing technology. The tradeoff between hardware complexity and acquisition performance is discussed. >

Proposed Array-Based Deep Space Network for NASA

The current assets of the deep space network (DSN) of the National Aeronautics and Space Administration (NASA), especially the 70-m antennas, are aging and becoming less reliable. Furthermore, they are expensive to operate and difficult to upgrade for operation at Ka-band (321 GHz is shorthand for the allocated 31.8-32.3 GHz. GHz). Replacing them with comparable monolithic large antennas would be expensive. On the other hand, implementation of similar high-sensitivity assets can be achieved economically using an array-based architecture, where sensitivity is measured by G/T, the ratio of antenna gain to system temperature. An array-based architecture would also provide flexibility in operations and allow for easy addition of more G/T whenever required. Therefore, an array-based plan of the next-generation DSN for NASA has been proposed. The DSN array would provide more flexible downlink capability compared to the current DSN for robust telemetry, tracking and command services to the space missions of NASA and its international partners in a cost-effective way. Instead of using the array as an element of the DSN and relying on the existing concept of operation, we explore a broader departure in establishing a more modern concept of operations to reduce the operations costs. This paper presents the array-based architecture for the next-generation DSN. It includes system block diagram, operations philosophy, users view of operations, operations management, and logistics like maintenance philosophy and anomaly analysis and reporting. To develop the various required technologies and understand the logistics of building the array-based low-cost system, a breadboard array of three antennas has been built. This paper briefly describes the breadboard array system and its performance.

An estimator-predictor approach to PLL loop filter design

The design of digital phase locked loops (DPLL) using estimation theory concepts in the selection of a loop filter is presented. The key concept, that the DPLL closed-loop transfer function is decomposed into an estimator and a predictor, is discussed. The estimator provides recursive estimates of phase, frequency, and higher-order derivatives, and the predictor compensates for the transport lag inherent in the loop. >

Deep Space Network Array - Update

JPL, in conjunction with the NASA HQ Science Mission Directorate, is evaluating a cost-effective method of obtaining large apertures for deep space communications, by arraying many small-diameter antennas. Drivers are the need to increase greatly the amount of information received from and transmitted to deep-space mission, both human and robotic, increase the precision of deep space navigation as NASA moves to the Kaband, and replace aging DSN assets. Plans and analysis were previously presented. This paper presents recent updates in the following areas: 1. Results on the cost-effectiveness and performance of small (6m-12m) antennas, at Xand Ka-band. We show performance data for two classes of low-cost antenna that nevertheless meet difficult performance requirements, including blind-pointing at Kaband and use of compact cryogenic front-ends. 2. Results on signal arraying. We show the flexible architecture and initial results of field tests in real-time combining broadband (500 MHz) signals from small antennas, to generate an effective large antenna 3. Methods to achieve a cost-effective uplink, in particular through arraying of uplink signals. We show that using an architecture that separates the uplink antennas from the downlink antennas, and through arraying of uplink antennas, we can achieve highly-efficient allocation of uplink capability to meet a wide range of mission needs in or nominal, emergency, and high-demand scenarios. 4. Selection process for antenna sites, through application of methodology for scoring and weighting of multiple criteria for all candidate sites. The methodology balances factors that tend to favors remote, desert sites that are superior for Ka-band operations, with factors that favor populated areas, e.g. the need to locate operations and maintenance staff near-by. The methodology can be adapted to other applications.

Operation's concept for array-based deep space network

The array-based deep space network (DSN-Array) will be a part of more than 103 times increase in the downlink/telemetry capability of the deep space network (DSN). The key function of the DSN-array is to provide cost-effective, robust telemetry, tracking and command (TT&C) services to the space missions of NASA and its international partners. It provides an expanded approach to the use of an array-based system. Instead of using the array as an element in the existing DSN, relying to a large extent on the DSN infrastructure, we explore a broader departure from the current DSN, using fewer elements of the existing DSN, and establishing a more modern concept of operations. This paper gives architecture and operations philosophy of DSN-array. It also describes customers view of operations, operations management and logistics, and maintenance philosophy, anomaly analysis and reporting

Analysis of near-field of circular aperture antennas with application to study of high intensity radio frequency (HIRF) hazards to aviation from JPL/NASA Deep Space Network antennas

This work includes a simplified analysis of the radiated near to mid-field from JPL/NASA Deep Space Network (DSN) reflector antennas and uses an averaging technique over the main beam region and beyond for complying with FAA regulations in specific aviation environments. The work identifies areas that require special attention, including the implications of the very narrow beam of the DSN transmitters. The paper derives the maximum averaged power densities allowed and identifies zones where mitigation measures are required.

Challenging Implementation and Operations Traditions

The Deep Space Network (DSN) that provides for the communications link between the deep space missions and the science users currently consists of a small set of very large monolithic tracking antennas. This ground-based network includes a total of 12 antennas located in three roughly equidistant longitudes around the earth and utilizes a decentralized approach to it operations. Recently, however, studies have suggested that the number, complexity, and data throughput of the future set of space probes will be increasing dramatically. This demands more performance from the DSN than is currently available. In identifying the architecture for the future DSN required to support this mission set, one concept that proves promising is one that consists of a great many number of much smaller antennas configured in an array. This concept has been supported by the developments in antenna manufacturing technology and the consistent decrease in the cost of electronics required to receive, amplify, and combine signals from deep space probes. Furthermore, it is clear that past developments in the DSN have not benefited from the applications of economies of scale.

Deep Space Network Revitalization: Operations for the 21st Century

The National Aeronautics and Space Administration (NASA) supports unmanned space missions through a Deep Space Network (DSN) that is developed and operated by the Jet Propulsion Laboratory (JPL) and its subcontractors. The DSN capabilities have been incrementally upgraded since its establishment in the late ’50s and are delivered from three Deep Space Communications Complexes (DSCC’s) near Goldstone, California, Madrid, Spain, and Canberra, Australia. At present each DSCC includes large antennas with diameters from 11 meters to 70 meters, that operate largely in S-band and X-band frequencies. In addition each DSCC includes all the associated electronics to receive and process the low-level telemetry signals, and radiate the necessary command with high-power transmitters. To accommodate support of the rapidly increasing number of missions by NASA and other space agencies, and to facilitate maintaining and increasing the level of service in a shrinking budget environment, JPL has initiated a bold road map with three key components: 1. A Network Simplification Project (NSP) to upgrade aging electronics, replacing them with modern commercially based components. NSP and related replacement tasks are projected to reduce the cost of operating the DSN by 50% relative to the 1997 levels. 2. Upgrade of all 34-m and 70-m antennas to provision of Ka-Band telemetry downlink capability, complemented by an existing X-band uplink capability. This will increase the effective telemetry downlink capacity by a factor of 4, without building any new antennas. 3. Establishment of an optical communications network to support for high-data-rate unmanned missions that cannot be accommodated with radio-frequency (RF) communications, as well as establish a path toward support of manned missions at Mars.

Communications for low cost planetary missions

Abstract Does a science-rich planetary mission require a high downlink data rate? Answering in the affirmative tends to increase mission cost, requiring highly directional spacecraft antennas and sophisticated attitude control. However, as the current Galileo experience shows, it is possible to design science-rich mission around a low gain, wide-beam antenna, with a maximum downlink rate of 160 bits-per-second. Applying the techniques presented below to future planetary missions could significantly reduce their complexity and cost. JPL is currently implementing this new downlink design to support the Galileo mission, in response to the failure of the High Gain Antenna. The capabilities to be provided enable other low data rate missions, or mission phases. The new design features on-board data buffering to eliminate short-term peak demand on the downlink, onboard data compression, recording and automatic recovery of pre-detection data at the ground stations, antenna arraying, improved synchronization, demodulation, and errorcorrecting coding, and reduced sensitivity to errors in tracking predicts. The ground equipment, currently under development, will become operational in early 1996.