A report discusses aspects of a ranging system in which the distance between the Earth and a spacecraft is determined from the difference between the phases of (1) modulation on a radio signal trans- mitted to the spacecraft and (2) a replica of the modulation transmitted back to Earth by a transponder on the spacecraft, received at Earth a roundtrip- light-time after the original transmission. The system correlates the transmitted and return modulation for different phase shifts. The phase shift for which the correlation is maximum is deemed to be related to the round-trip signal-propagation time and, hence, to the distance. The modulations used in prior such systems were sequential square-wave tones or repeating pseudo- noise tones, but not both in the same system. A proposed improvement would equip a ranging system to use either square-wave or pseudonoise tones. The report presents mathematical analyses and comparisons of the performances of square-wave and pseudonoise ranging. It is shown that in comparison with the existing system using sequential square-wave tones, a system using a set of pseudonoise codes would perform better (in terms of integration time and variance in distance) and could be configured and operated more easily.
This work was done by Jeff Berner and Scott Bryant of Caltech for NASA’s Jet Propulsion Laboratory. To obtain a copy of the report, “Operations Comparison of Deep Space Ranging Types: Sequential Tone vs. Pseudo-Noise,” access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Electronic Components and Systems category.
This Brief includes a Technical Support Package (TSP).
Depp-Space Ranging Using Pseudonoise Codes
(reference NPO-30387) is currently available for download from the TSP library.
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Overview
The document is a technical support package prepared under NASA's sponsorship, detailing advancements in deep-space ranging using pseudonoise codes. Authored by Jeff B. Berner and Scott H. Bryant from the Jet Propulsion Laboratory (JPL), it discusses a novel approach to measuring the distance between Earth and spacecraft by analyzing the phases of radio signals.
Traditionally, ranging systems relied on sequential square-wave tones or repeating pseudonoise tones, but not both simultaneously. The proposed system enhances this methodology by allowing the use of either modulation type, which significantly improves performance metrics. The core principle involves determining the distance based on the phase difference between a transmitted signal and its replica sent back by a spacecraft's transponder. The system correlates these signals for various phase shifts, identifying the maximum correlation to ascertain the round-trip signal propagation time and, consequently, the distance.
The report presents mathematical analyses comparing the performance of square-wave and pseudonoise ranging systems. It demonstrates that utilizing pseudonoise codes results in lower variances and shorter integration times compared to existing systems that use sequential square-wave tones. This improvement is attributed to the ability of new hardware to optimize the use of pseudonoise codes for parallel integration and correlation, which was not feasible with older technologies.
The document emphasizes the operational advantages of pseudonoise codes, which require less mission operations involvement than sequential tones. This simplification is crucial for future space missions, as it can lead to more efficient operations and reduced complexity in managing the ranging process.
In summary, the work outlined in this document represents a significant advancement in deep-space ranging technology. By integrating pseudonoise codes into the ranging system, the authors propose a method that not only enhances accuracy and performance but also streamlines operational procedures for space missions. This innovation could play a vital role in the future of space exploration, enabling more precise navigation and communication with distant spacecraft.
