• Aging of Magnetic Recording Tape

      Cuddihy, Edward F.; California Institute of Technology (International Foundation for Telemetering, 1978-11)
      The composition of magnetic recording tape is about 25 wt. % magnetic oxide particles, and 75 wt. % polymeric materials. With the exception of the recording properties of tape which are ascribable to the magnetic oxide particles, almost all of the other properties important to tape, such as aging, storage, tracking, etc., are ascribable to the chemical, physical, and mechanical properties of the polymeric materials.
    • Application of Microprocessors to Spacecraft Synthetic Aperture Radar Processing

      Arens, Wayne E.; California Institute of Technology (International Foundation for Telemetering, 1978-11)
      A ground-based digital synthetic aperture radar (SAR) processor capable of correlating images from raw spacecraft data at real-time rates is currently under development. The processor design requirements are particularly formidable due to (1) range migration effects resulting from planetary curvature and rotation, (2) antenna beam pointing errors, and (3) variation of the doppler reference function with changing orbital parameters. Based upon the current effort, this paper describes a candidate real-time on-board SAR processing implementation approach that might evolve for future spacecraft applications. Key features include the use of custom large scale integration (LSI) charge-coupled device (CCD) technology to accomplish the correlation functions and microprocessor technology to effect control.
    • Correlation Tracking for a Planetary Pointing and Tracking System

      Assefi, Touraj; California Institute of Technology (International Foundation for Telemetering, 1978-11)
      The Planetary Pointing and Tracking System (PPTS) being developed at Jet Propulsion Laboratory is intended to provide precision pointing for science platforms on future autonomous planetary spacecraft. Future missions will impose very stringent platform pointing requirements due to low light levels and very high ground tracking rates. An integral part of PPTS is the correlation tracker, which has the potential to revolutionize autonomous guidance. The tracker provides two-axis pointing information concerning the position of the target body. It consists of a large-area charge-coupled device (CCD) imager and a microprocessor to control the CCD scanning function and data processing. The correlation tracker has three modes of operation: track, acquire and map. The track mode performs precision tracking of a target object. This is initiated after a target has been acquired. The map mode determes the centroidal coordinates, magnitude and size of bodies within the optical field of view. To improve precision pointing, various power spectra, such as shot noise and dark current, are derived. The probability of acquiring a target body is a function of signal-to-noise ratio and the noise equivalent angle. Derivations illustrating the application of these concepts are given. A discussion of mission analysis with the Uranian system as a representative example is provided.
    • A Distributed Microcomputer Telemetry System for Spacecraft Applications

      Lord, Donald D.; California Institute of Technology (International Foundation for Telemetering, 1978-11)
      Three significant difficulties exist in using a set of microcomputers (or any computers) as an integral part of an on-board telemetry system. The difficulties arise in providing for: a) the precise timing required by a telemetry system, including accurate time-tagging of data samples; b) the interconnection of several (many) computers in a controlled, organized, understandable manner; c) the capability to allow computer controlled science instruments to operate relatively autonomously with minimum software interactions with other computers. The three items listed above are desirable features and are achievable with proper telemetry system architecture designs. This paper will address each of the three items and present an architecture that provides the desired features.
    • A Fast Complex Integer Convolution Using a Hybrid Transform

      Reed, I. S.; Truong, T. K.; University of Southern California; California Institute of Technology (International Foundation for Telemetering, 1978-11)
      In this paper it is shown that the cyclic convolution of complex values can be performed by a hybrid transform. This transform is a combination of a Winograd transform, and a fast complex integer transform developed previously by the authors. This new hybrid algorithm requires fewer multiplications than any previously known algorithm.
    • Performances of Regenerative and Nonregenerative Satellite Repeaters with MPSK Signalling

      Woo, K. T.; California Institute of Technology (International Foundation for Telemetering, 1978-11)
      Linear (translation), hard-limited, and demod/remod types of satellite repeaters are considered in this paper. Both uncoded and coded multiple phase shift keyed (MPSK) signals are assumed to be transmitted through these repeaters. Relative performances of these repeaters in the presence of uplink and downlink noises are then compared quantitively. Probabilities of bit errors and the computational cutoff rates are computed for 2, 4, and 8 phases PSK signals, with uplink and downlink SNR's as parameters.
    • Soft Decision Decoding of Block Codes

      Baumert, L. D.; McEliece, R. J.; California Institute of Technology (International Foundation for Telemetering, 1978-11)
      Using a general decoding technique of Solomon we evaluate the performance of certain block codes on a gaussian channel. Quadratic residue codes of lengths 48 and 80 as well as BCH codes of length 128 and rates 1/2 and 1/3 are considered. All four of these codes perform quite favorably with respect to the constraint-length 7 rate 1/2 convolutional code presently used on NASA's Mariner-class spacecraft.