SOFTC is an advanced software implementation of a signal correlator for verylong- baseline interferometry (VLBI) for measuring positions of natural celestial objects and distant spacecraft. Because of increases in processing speeds of general- purpose computers, software VLBI correlators have become viable alternatives to hardware ones. The input to SOFTC consists of digitized samples of raw VLBI-antenna received-signal voltages. Optionally, SOFTC also tracks calibration tones superimposed on the received signals. The outputs of SOFTC are (1) phases and amplitudes as functions of time and frequency for cross-correlated received signals and (2) phases and amplitudes as functions of time, station, and tone number for the calibration tones. SOFTC was created to be as accurate as possible, capable of processing essentially any VLBI data, pass strong debugging tests, have a simple user interface, and have no platform dependencies. SOFTC is written modularly in the C programming language. The great advantage of implementing a correlator in software, in contradistinction to hardware, is that it becomes relatively easy and much less expensive and time-consuming to adapt, modify, improve, and update the correlator.
This program was written by Stephen Lowe of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free online at www.techbriefs.com/tsp under the Software category.
This software is available for commercial licensing. Please contact Karina Edmonds of the California Institute of Technology at (626) 395-2322. Refer to NPO-41072.
This Brief includes a Technical Support Package (TSP).
SOFTC: A Software Correlator for VLBI
(reference NPO-41072) is currently available for download from the TSP library.
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Overview
The document provides a comprehensive overview of SOFTC, a software correlator developed for Very-Long Baseline Interferometry (VLBI), primarily used for high-precision astrometry and spacecraft navigation by NASA. Unlike traditional hardware correlators, which are costly and time-consuming to develop, SOFTC leverages advancements in computer processing to offer a flexible and efficient software-based solution.
SOFTC has been operational for three years under mission-critical conditions, demonstrating its reliability and accuracy in processing VLBI data. It is recognized as one of the most advanced correlators globally, capable of handling various VLBI data types regardless of observation frequencies, sampling rates, or bandpass characteristics. The software's design allows for easy modifications and updates, making it adaptable to evolving technological needs.
The primary function of SOFTC is to extract phase and amplitude measurements from raw antenna voltage samples, which can be substantial in size, often reaching hundreds of gigabytes per experiment. The software compresses this data significantly, producing outputs typically in the tens of megabytes, while ensuring that all necessary information is accurately captured for subsequent processing. This capability is crucial for pinpointing the location of transmitting spacecraft and natural sources with high precision.
SOFTC employs Fourier Transform techniques to process integration sums from observed frequencies, providing detailed spectral information. Additionally, it can track calibration tones injected into the observing station’s electronics, enhancing the accuracy of the measurements.
The document highlights SOFTC's successful application in various NASA missions, including Mars Odyssey, Mars Exploration Rover missions, Deep Space 1, and others. It is slated to become JPL’s primary operational correlator, which will reduce maintenance costs associated with hardware correlators while improving processing accuracy and repeatability.
In summary, SOFTC represents a significant advancement in VLBI technology, combining high precision, flexibility, and efficiency in a software-based platform. Its successful implementation in critical space missions underscores its importance in the field of astrometry and deep space navigation, paving the way for future developments in aerospace technology.
