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 (321GHz 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, user's 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.

This paper describes a variety of interferometric techniques that may be used for measuring the angular location of a spacecraft with respect to natural celestial radio sources or another spacecraft. The differential propagation time-delay techniques largely cancel the common error sources and normally achieve low angular coordinate errors. Currently, the accuracy of the techniques are in the 1-2 nrad range for observations with a duration of one hour and 3-6deg of mean angular separation between the spacecraft and the reference sources at X-band frequencies. There are various possible ways to implement the differential angular measurements depending upon the determination of the phase cycle ambiguities associated with the differential propagation time delays of remote sources. There are methods that utilize a sufficiently large range of observing frequencies and others that rely upon the spatial arrangement of the receiving system and the rotation of the terrestrial platform. We summarize the methodologies and the advantages and disadvantages of the various techniques.

The Very Long Baseline Array (VLBA) consists of ten high performance antennas and a 20-station correlator. The 25-m-diameter reflector antennas are located geographically to optimize spatial frequency coverage for high-duality imaging using VLBI techniques. The antennas are equipped with receivers for nine frequency bands over the range 300 MHz to 45 GHz. A wideband, high-density, recording system allows unattended operation at a sustained data rate of 125 Mb/s for a day, and peak rates of up to 512 Mb/s. The antennas operate unattended most of the time, and are controlled by a single operator in the Array Operations Center (AOC) at Socorro, NM. The correlator, located in the AOC, supports processing of all observations with the array.>