• Digital Data Recording at Five Million Bits Per Square Inch

      Thompson, C. R.; Waring, John; RCA (International Foundation for Telemetering, 1975-10)
      A 24 megabit per second, serial bit stream recording system using rotating shed recording techniques has been developed. This system provides maximum data density on an area basis (5 x 106 bits per square inch) with reliable in-track packing density (24,000 bits per linear inch). The two-inch tape width accommodates the 24 Mb/s data rate at a longitudinal tape speed of 2.4 inches per second. A fourteen inch diameter reel of tape stores a trillion bits of data. A bit error rate of one error per million bits has been demonstrated. An error correction system has been designed to improve the bit error rate to one error per billion bits. Commercially available television tape is utilized on a modified industry standard data format. A track width of 2.5 x 10⁻³ inches and a track spacing of 3.75 x 10⁻³ inches provide approximately 260 tracks per inch along the length of the tape.
    • Performance of Coded MFSK in a Rician Fading Channel

      Modestino, J. W.; Mui, S. Y.; R.P.I. (International Foundation for Telemetering, 1975-10)
      The performance of convolutional codes in conjunction with noncoherent multiple frequency shift-keyed (MFSK) modulation and Viterbi maximum likelihood decoding on a Rician fading channel is examined in detail. While the primary motivation underlying this work has been concerned with system performance on the planetary entry channel, it is expected that the results are of considerably wider interest. Particular attention is given to modeling the channel in terms of a few meaningful parameters which can be correlated closely with the results of theoretical propagation studies. Fairly general upper bounds on bit error probability performance in the presence of fading are derived and compared with simulation results using both unquantized and quantized receiver outputs. The effects of receiver quantization and channel memory are investigated and it is concluded that the coded noncoherent MFSK system offers an attractive alternative to coherent BPSK in providing reliable low data rate communications in fading channels typical of planetary entry missions.
    • The Influence of an Ambient Magnetic Field on Magnetic Tape Recorders

      Jorgensen, Finn; TRW Systems (International Foundation for Telemetering, 1975-10)
      Magnetic recorders are susceptible to external magnetic fields and hence prone to data degradation. This is primarily observed in instrumentation (space and ground) and computer recorders, where little or no shielding of the heads is provided. The magnetic core material in the heads attracts flux lines and will with certain orientations concentrate these in the record, play back or erase gaps. During recordings a foreign field may therefore be superimposed on the intended recording field and may cause errors in the form of phase shift and dc offset; these affects are agravated when AC bias is used in the recording process. If an external field is present during playback only, partial or complete erasure may take place. One external field is always present: The earth s magnetic field which has a magnitude of roughly one Gauss (or Oersted). The writer is not aware of any errors per se caused by this field, but it has numerous times caused difficulties in achieving a perfect demagnetization of heads (An oscillating and simultaneously decreasing field from a degausser does then in essence record a permanent magnetization into the heads, which in turn will result in noisy and distorted recordings). Other fields are man made, such as originating from heavy currents in cable harnesses. The analysis presented in this paper was undertaken to establish susceptibility limits for a field generated by a magnetic attitude control system for spacecrafts. This is illustrated in Figure 1, where three orthogonal electromagnets on board a spacecraft generate a magnetic moment (M), variable in magnitude and orientation. The attitude correcting torque (T) on the spacecraft is expressed as the cross product between this moment and the earth's field. Recording equipment may be located within a few feet of the center of the attitude control field, which must be limited in magnitude or the recorder shielded to avoid data errors and/or erasure.
    • Some Characteristics of the International Space Channel

      Noack, T. L.; Poland, W. B., Jr.; University of Missouri-Rolla; NASA (International Foundation for Telemetering, 1975-10)
      Some physical characteristics of radio transmission links and the technology of PCM modulation combine with the Radio Regulations of the International Telecommunications Union to define a communications channel having a determinable channel capacity, error rate, and sensitivity to interference. These characteristics and the corresponding limitations on EIRP, power flux density, and power spectral density for space service applications are described. The ITU regulations create a critical height of 1027 km where some parameters of the limitation rules change. The nature of restraints on power spectral density are discussed and an approach to a standardized representation of Necessary Bandwidth for the Space Services is described. It is shown that, given the PFD (power flux density) and PSD (power spectral density) limitations of radio regulations, the channel performance is determined by the ratio of effective receiving antenna aperture to system noise temperature. Based on this approach, the method for a quantitative trade-off between spectrum spreading and system performance is presented. Finally, the effects of radio frequency interference between standard systems is analyzed.
    • Intersatellite (Nd:YAG) Laser Communications; A System For The 1980's

      Barry, J. D.; Wright-Patterson AFB (International Foundation for Telemetering, 1975-10)
      It is now a certainty that laser communication systems will be operating in space within this decade. The development of a laser communications satellite package began this fall and is to be launched in 1979. The system is to operate at 1000 megabits per second. Laser communications technology has proceeded from purely exploratory research just over five years ago to the successful completion and operation this year of an engineering feasibility model of the satellite system. Laboratory tests have verified the system capability at a serial data rate of 1000 megabits per second. Thermal and vibrational tests have been successfully completed to the test levels of the Defense Meteorological Satellite program.
    • The Application of Fiber Optics to Army Communications

      Dworkin, Larry U.; Coryell, Louis A.; Dragoo, Robert E.; USAECOM (International Foundation for Telemetering, 1975-10)
      We will examine a broad class of army communications applications for optical waveguides. Of principal interest is the multimode low-loss fiber. The applications receiving primary attention are (a) a long haul time division cable (TDM) system, (b) local distribution cable used to connect telephone users to central switches within a command post. A cost trade-off analysis reveals a cost saving up to $3K/km of a fiber optic TDM cable system over a conventional metallic cable system now in the army inventory. A review of a feasibility model design that employs a low-loss ruggedized Corning fiber cable, with special sources and detectors designed for ECOM application, is conducted. The resulting cable facilities appear fully capable of meeting all aspects of army cabling requirements and possesses all of the traditional advantages of fiber optic transmission system.
    • Low Frequency Telemetry from Terradynamic Vehicles

      Galbraith, L. K.; Sandia Labs. (International Foundation for Telemetering, 1975-10)
      A telemetry system has been designed and built which transmits digital data from a buried earth-penetrating vehicle to the surface by magnetic induction. The transmitting package is a cylinder 10 cm in diameter by 30 cm long and draws 5 watts of dc power while transmitting. Error rates of 1.16 x 10⁻⁴ have been obtained at a range of 52 meters through soil at a data rate of 50 bits/second, utilizing only the 0-50 Hz region of the electromagnetic spectrum. Projected performance of the system in high-conductivity media indicates useful ranges exceeding 50 meters in media as conductive as sea water (4 mho/meter). System improvements are discussed which should allow severalfold increases in data rate or range over the experimentally obtained values.
    • A Telemetry Link for an Earth Penetrator

      Caffey, Thurlow W. H.; Sandia Laboratories (International Foundation for Telemetering, 1975-10)
      The design and field-testing of a telemetry link to send signals to the surface of the earth from an earth penetrator are described. The link uses a PCM/FM format at a frequency of 10.5 kHz, dissipates 8 watts, and fits within a cylinder with an inside diameter of 100 mm. A bit error rate of less than 10⁻⁵ was achieved from a depth of 52 meters at a bit rate of 10³ bits per second.
    • Use of TSE Computers Aboard Spacecraft

      Schaefer, David A.; NASA-Goddard Space Flight Center (International Foundation for Telemetering, 1975-10)
      The Goddard Space Flight Center has undertaken a program to develop improved methods of handling two-dimensional data. From this, the concept of a new family of computers known as "tse computers," has evolved. These computers utilize entire binary images as their basic computational entity. This is in contrast to conventional computers that utilize a bit as their basic computational entity. Because of their ability to perform thousands of operations simultaneously, they have the potential of operating orders of magnitude faster than conventional computers. They are ideally suited for spacecraft onboard image processing tasks.
    • A Decision Directed Detector for the Phase Incoherent Gaussian Channel

      Kazakos, D.; NASA Johnson Space Center (International Foundation for Telemetering, 1975-10)
      A general vector digital signalling scheme for data communication through an additive Gaussian channel is made adaptive for the purpose of simultaneous communication of information and phase estimation. The phase estimate is shown to converge to the true value, therefore the adaptive nature of the detector effectively achieves phase acquisition and improvement in performance. Qualitative comparison to other phase acquisition techniques is made. The basic virtues of the proposed method are that no separate synchronization interval is required, and phase fluctuations can be tracked simultaneously with the transmission of information.
    • The Geostationary Operational Environmental Satellite/GOES/Imaging Communication System

      Baker, W. L.; Savides, J.; Aeronutronic Ford Corporation (International Foundation for Telemetering, 1975-10)
      The SMS/GOES Satellite obtains day and night weather information from synchronous geostationary orbit by means of (a) earth imaging, (b) collection of environmental data from ground based sensors, platforms, and (c) monitoring of the space environment. SMS-1 and SMS-2 have been in orbit for 17 months and 8 months respectively and are presently taking full earth disc images in the visible and infrared every 30 minutes. SMS-1 is positioned to cover the eastern portion of the United States while SMS-2 is positioned to cover the western portion. This paper provides a general overview of the imaging communication portions of the SMS/GOES, related to the image data encoding and transmission as well as the method of the data time multiplexing and the manner in which the scan line to line synchronization is achieved.
    • A Review of RPV Programs in the USAF

      Palmer, John A.; US. Air Force (International Foundation for Telemetering, 1975-10)
      A brief explanation of the background behind development and employment of operational RPV systems will be followed by a resume of their accomplishments and shortcomings. Reconnaissance, electronic warfare and strike systems will be covered. The main portion of the paper will discuss systems under development to support specific missions or improve RPV capabilities in general. The Compass Cope high altitude RPV, multi-mission RPVs, expendable drones, and mini-PPVs will be considered as a family of vehicles desianed to support a variety of mission requirements. In addition, programs to improve capabilities for launch, recovery, controls and sensor integration will be included. The overall emphasis is on an appreciation for the purpose and direction of the Air Force RPV development program.
    • Removing Resonances in Automotive Crash Test Instrumentation

      Gardenhire, Lawrence W. (International Foundation for Telemetering, 1975-10)
      Unwanted resonances can make analysis of crash instrumentation extremely difficult. These resonances are a natural part of the acceleration measurements and in many cases are allowed to be present to maintain the needed high-frequency responses. Crystal accelerometers are, for instance, essentially undamped, and have resonance humps 40 dB above unity in order to maintain a flat response to approximately one-half the resonance or natural frequency of the accelerometer. This resonance also allows the phase angle response to be close to zero well out towards the natural frequency. Additional resonance problems exist in the mounting brackets, or as frame resonances which carry little or no information. The process of removing them, however, can produce extreme errors in both amplitude and phase. The SAE J211a Recommended Practice recommends four channel classes for impact tests: c1asses 60, 180, 600, and 1000. The frequency response is flat to +1/2, -1 dB to these frequencies, and to +1, -4 dB to the break frequencies of 100, 300, 1000, and 1650 Hertz. The filter rolloff is nominally 12 dB/octave (second order) from these break points. Second order filters are normally used for impact tests since accelerometers have second order response. This filtering will provide satisfactory results, if no resonance is present at less than several times the class frequency. Often the next lower class is used to remove a resonance, a step that may cause large errors. A better solution is to follow the typical class filter with a sharper cutoff filter that will remove the resonance without affecting the amplitude and phase of the initial impulse. A method that determines when data is lost by excessive filtering is presented and demonstrated on two crashes. One crash has a resonance about 15 times higher than the class; one is less than 3 times higher.
    • The Automatic Analysis of Aerial Photographic Data

      Chen, C. H.; Southeastern Mass. Univ. (International Foundation for Telemetering, 1975-10)
      As the volume of aerial photographic data increases in various applications, there is increasing demand for automated data analysis. Faster and larger computer alone is not the solution. In this paper effective and computationally efficient techniques for computer processing of the aerial photographic data are presented. They include: (1) picture data compression, (2) feature exttraction using the histograms of the original and sharpened pictures, (3) sequential target and classification, (4) threshold selection, and (5) Walsh power spectrum analysis. All of these techniques may be incorporated in a fully automated data analysis system to meet certain real-time on-line system requirement.
    • Surface Acoustic Wave Devices for Communications

      Webb, D. C.; Naval Research Laboratory (International Foundation for Telemetering, 1975-10)
      Many surface acoustic wave (SAW) devices are now sufficiently well-developed that they can have a significant impact on systems design. This paper reviews the properties and limitations of SAW devices which seem particularly well suited to communications. The simple bandpass filter is considered in detail as it will undoubtedly see the widest usage of all SAW devices. The application of SAW analog matched filters in phase-shift-keyed synchronization and data demodulation is also discussed. Finally, SAW resonators and oscillators are briefly considered. A number of examples are included which show how system performance can be improved through use of SAW technology.
    • Charge Coupled Device (CCD) Analog Signal Processing

      White, Marvin H.; Westinghouse Defense & Electronic Systems Center (International Foundation for Telemetering, 1975-10)
      A discussion of the CCD basic building blocks for analog signal processing with particular emphasis on application for telemetry. Serial in/Serial out (SI/SO) blocks provide time base translation electrically alterable delay, and sequential TDM filters, Parallel In/Serial Out blocks are useful in time divisions multiplexing (TDM) and Serial In/Parallel Out blocks for variable tapped delay lines, filters and correlators. Combinations of the above linear or one-dimensional blocks provides two-dimensional arrays for filter banks, multiple correlators, etc. Particular telemetry applications are FM filters, Parallel Correlators, Matched Filters, Single Sideband Modulators and Adaptive line equalizers.
    • Multimission Spacecraft Dataplexer

      Cosme, Rafael; Lokerson, Donald; NASA, Goddard Space Flight Center (International Foundation for Telemetering, 1975-10)
      A low power, small size, building block type of central data system has been designed for use in a number of explorer type missions. The Data Multiplexing Unit was designed to satisfy a wide range of requirements among the several spacecraft. The resulting design includes preprogrammed Read Only Memories (ROM's) to generate the telemetry format tailored to the particular mission requirements. The relatively small size and low weight and power dissipation attained was largely due to the use of PMOS technology. The addition of sub-commutators in groups adequate to meet the particular spacecraft requirements allows low data rate experiments to be time multiplexed into a single main input channel for a more efficient data collection and processing operation.
    • A Fixed Sampling Rate Vocoplexer

      Lerner, Theodore; Textron Bell Aerospace (International Foundation for Telemetering, 1975-10)
      The vocoplexer is a system which permits a reduction in the data rate required to transmit voice signals when many such signals are multiplexed onto a common digital line. This is accomplished through the use of a coding technique which is based on the statistical properties of voice signals. The reduction in data rate that can be realized by the vocoplexer is a function of the speech quality required. Typically, for a speech quality equivalent to PCM at 8,000 samples per second and five bits per sample, a reduction in data rate to about 1/3 can be accomplished. The descriptions in this paper are based on this quality requirement. However, for a somewhat reduced quality requirement, even greater savings can be accomplished. For example, if quality equivalent to PCM at 8,000 samples per second at four bits per sample is adequate, the vocoplexer will require approximately 9,600 bits per second. For quality equivalent to delta modulation at 18,000 bits per second the vocoplexer requires approximately 6,400 bits per second per voice channel.
    • Runs of Significant Samples for Processes with Sharp Non-Stationarities: Application to Seismogram Compression

      Babkin, V. F.; Rybeva, N. E.; Shtarkov, Yu. M.; Institute for Space Research (International Foundation for Telemetering, 1975-10)
      An algorithm for threshold compression of the processes with the sharp variations of a level is considered. In broadening the concept on an significant sample we are successful in transmitting completely almost all the samples appropriate to the phenomenon studied; at the same time the compression ratio at the quiet parts is kept at the acceptable level. The experimental results of seismogram compression are given.
    • Real Time Data Compression for Rae-B Spacecraft Camera

      Miller, W. H.; NASA-Goddard Space Flight Center (International Foundation for Telemetering, 1975-10)
      A real time data compression unit was designed and fabricated for the Radio Astronomv Explorer Lunar Mission Antenna Aspect Camera. The camera takes a panoramic view of spacecraft, moon, etc. of ±35 degrees by 360 degrees. This data compressor combined information reduction and redundancy reduction. The information reduction was accomplished by subsampling (used every fourth line): and the redundancy reduction was accomplished by an adaptive run-length encoder. The adaptive run-length encoder used a zero-order predictor. Two different maximum run-lengths were used with two different data formats. Selection of the operating format depended on the sampled gray level compared to a fixed threshold. Statistical data and images indicate that the redundancy reduction technique yields a compression ratio of 8:1. Thus a combined compression ratio of 32:1 was obtained on an entire panoramic view.