• International Telemetering Conference Proceedings, Volume 10 (1974)

      International Foundation for Telemetering, 1974-10
    • Aeroflight Communications and RF Navaids

      Lilly, Douglas S.; Lyndon B. Johnson Space Center (International Foundation for Telemetering, 1974-10)
      The Space Shuttle Program concept of a low cost, reliable and reusable orbital vehicle has proven to be a driving function in systems design and integration. Extensive use of existing designs to satisfy these requirements has been effectively employed in the aeroflight systems. Appropriate planning and a careful appraisal of maturity, cost, performance, vehicle burdens, and operational flexibility were completed prior to a system choice. The aerial navigation and landing systems selected for the orbital vehicle are described and their interfaces with the control and navigation system discussed.
    • A Coding Algorithm for Random Access Satellite Systems

      Wu, W. W. (International Foundation for Telemetering, 1974-10)
      In satellite communications systems, when a code-division scheme is desirable for random multiple access, specific codes must be constructed for the users in the system to share the same satellite channel. This paper develops a coding algorithm for such purposes by means of a binary matrix. Step-by-step procedures are separately described. An example demonstrates the usefulness of the algorithm, and its advantages and disadvantages are discussed. Finally, a problem for future work is suggested.
    • A Central Controller/Display System with Real Time Processing for Remote Data Acquisition Units

      Prichard, Guy D.; Teledyne Controls Company (International Foundation for Telemetering, 1974-10)
      A flexible Data Management and Display Unit (DMDU) has been developed as part of the On-Board Data System developed for the 40' x 80' Wind Tunnel at Ames Research Center. The DMDU can be operated as a slave to a Systems Engineering Laboratories Model SEL-840MP computer or as a standalone system receiving instructions from an operator via data terminal/keyboard inputs. It is capable of controlling the acquisition data from four data acquisition units at software selectable word rates of 250 to 125,000 words per second in increments of 50 words per second. The number of remote acquisition units can be expanded to twenty-nine units providing data point capacity in excess of 10,000 channels. Acquired data can be distributed in real time to the host computer (SEL-840MP), a bar graph CRT display (up to 128 data points), a strip chart recorder (up to 3Z data points), to one or both of two analog magnetic tape recorders (BI0/ -L or DM-M format) or to a PDP-11/05 minicomputer for data processing in real time. The DMDU can be utilized as a "quick-look" playback facility for the playback and display of data previously recorded on magnetic tapes in any of the standard IRIG PCM formats. It receives initialization information consisting of the remote acquisition units and data point address, amplifier gain, each data points required sampling rate and the data output destination entered locally via punched paper tape or from the SEL-840MP computer. Resident software generates a "master sampling format" with sub-commutation and super-commutation as required. Embedded within the master cycle are the minor cycle sampling formats for the individual recorder outputs, complete with software controllable fram ' e synchronization patterns. Conversion from the data acquisition mode to the data playback or data reduction mode can be performed dynamically under interrupt control.
    • Time Response Simulation of the 1975 Viking Orbiter Digital Tape Recorder

      Mukhopadhyay, Asok K.; California Institute of Technology (International Foundation for Telemetering, 1974-10)
      The objective of this study is to verify and understand in depth the performance of the speed control (frequency loop) servo of the 1975 Viking Orbiter (VO75) digital tape recorder (DTR). The linear frequency-domain methods, such as the Bode Plot and the Root Locus, are inadequate in analyzing the VO75 DTR servo due to such dominant non-linear effects as servo signal limiting and static/dynamic Coulomb friction. The Time Response method employed in this study is written in the Continuous System Simulation Language (CSSL) for the Univac 1108 computer system. In order to demonstrate the power and flexibility of the graphic interactive simulation program, four aspects of system dynamics are interactively adjusted to arrive at a number of stable system configurations which has significantly different tape transport and/or summing amplifier gain, larger static/dynamic Coulomb friction, system lag than envisioned in the nominal design by linear methods.
    • The Impact of Robots on Planetary Mission Operations

      Hooke, A. A.; Larman, B. T.; Whitney, W. M.; California Institute of Technology (International Foundation for Telemetering, 1974-10)
      For reasons of efficiency and safety, unmanned roving vehicles sent to explore remote planetary surfaces must carry out some of their tasks without step-by-step human control. To realize the benefits that such semiautonomous machines can provide will require some changes in how planetary missions axe presently planned and conducted. Specifically, mission profiles will have to be based on tasks or functions rather than sequences of timed events, scientists will have to be more directly involved in the control of their instruments, and present ideas concerning spacecraft safety, testing and simulation of vehicle performance, telemetry design, and ground-system implementation must be reexamined.
    • Carrier Tracking, Bit Synchronization, and Coding for S-Band Communications Links

      Odenwalder, J. P.; LINKBIT Corporation (International Foundation for Telemetering, 1974-10)
      This paper presents the results of a study of the performance of Viterbi-decoded convolutional codes in the presence of nonideal carrier tracking and bit synchronization. A constraint length 7, rate 1/3 convolutional code and parameters suitable for the Space Shuttle coded communications links are used. Mathematical models are developed and theoretical and simulation results are obtained to determine the tracking and acquisition performance of the system. It is shown that the combined E(b)/N(o) degradation due to nonideal carrier tracking and bit synchronization over that required for the ideal tracking case can be held to less than 1.5 dB and that combined carrier tracking and bit timing can be acquired in only a few seconds for the parameters and operating ranges of the Space Shuttle coded communications links.
    • Space Shuttle Communications-Wideband Direct Link Signal and System Design

      Batson, Bartus H.; Huth, Gaylord K.; Lyndon B. Johnson Space Center; Axiomatix (International Foundation for Telemetering, 1974-10)
      This paper describes the design of a wideband S-band communications link from the Space Shuttle Orbiter to a ground-based terminal. This link will be used for transmission of television, digital data (various rates), or analog data, and is of interest because of the presence of bandwidth, power, and hardware constraints. The procedure followed to arrive at an overall signal and system design is outlined, and system performance margins are presented for various operational configurations. Finally, the growth potential of this link for digital data transmission is discussed.
    • An Integrated PCM Data System for Full Scale Aeronautics Testing

      Reynolds, Don R.; Ames Research Center (International Foundation for Telemetering, 1974-10)
      An integrated PCM data system is being developed at Ames Research Center to gather test data on advanced STOL propulsive lift, VTOL, rotary wing, and V/STOL control systems concepts as they pass through wind-tunnel, test-stand, flight-simulator and flight-test phases. Identical airborne signal conditioning and PCM encoding is used on test aircraft and wind tunnel models. An 80,000 word/second PCM installation will be the first "all PCM" instrumented rotary wing development project. The system uses both dedicated and time-shared computers for fast data analysis with maximum use of resources. This system development shows one way to bring separate data user groups together over a common data base, while sharing computing resources for minimum cost.
    • Performance of a Tracking Status Detector for a Digital Delay Lock Loop

      Holmes, J. K.; Chen, C. C. (International Foundation for Telemetering, 1974-10)
      A tracking status detector, operating on the principal of detecting the instantaneous phase error is considered in conjunction with a noncoherent τ-dither loop. This detector offers a significant improvement in performance as compared to the conventional loop lock detector. The out-of-lock detection when the loop is not in lock is modeled as a Markov process and the detection probability is the probability that the phase error accumulator (or a digital counter) exceeds a preset threshold in a fixed T seconds. The other performance parameter, the probability of false alarm, is also obtained using a Markov model. The results indicate that at a signal-to-noise ratio of 6 dB, the probability of out-of-lock detection of 0.9999 is attainable. The probability of one or more false alarms in one year was less than 10⁻⁵. A brief discussion on the frequency drift estimator based on the same principal is also included.
    • A Computer-Controlled, On-Board Data Acquisition System for Wind-Tunnel Testing

      Finger, Herbert J.; Cambra, Joseph M.; NASA Ames Research Center (International Foundation for Telemetering, 1974-10)
      A computer-controlled data acquisition system has been developed for the 40x80-Foot Wind Tunnel at Ames Research Center. The system, consisting of several small "on-board" units installed in the model and a data-managing, data-displaying ground station, is capable of sampling up to 256 channels of raw data at a total sample rate of 128,000 samples/sec. Complete signal conditioning is contained within the on-board units. The sampling sequence and channel gain selection is completely random and under total control of the ground station. Outputs include a bar-graph displays digital-to-analog converters, and digital interface to the tunnel's central computer, an SEL 840MP. The system can be run stand-alone or under the control of the SEL 840MP.
    • Flexibility Objectives for Real-Time Telemetry Processing Systems

      Rymer, J. W.; Naval Air Test Center (International Foundation for Telemetering, 1974-10)
      A generalized real-time telemetry processing system model is developed in four blocks: Demod/Synchronization, Data Channel, Processing/Control and Display. Flexibility objectives are stated for each block and illustrated with respect to the Navy's existing Real-time Telemetry Processing System (RTPS). Features and tradeoffs are discussed for each block along with references to the growing and significant body of such systems already existing and currently under development.
    • Use of Pseudo-Random PCM Tape Signatures for Telemetry Ground Station Validation

      Schoeck, K. O.; Pickett, R. B.; Vandenberg Air Force Base (International Foundation for Telemetering, 1974-10)
      This paper describes an improved tape recorder signature using pseudorandom PCM data. The use of the signature for telemetry ground station validation is discussed. Advantages over other techniques in common use are shown.
    • Comparison of Viterbi and Sequential Decoding with a Noisy Carrier Reference

      Hofman, L. B.; Lumb, D. R.; NASA Ames Research Center (International Foundation for Telemetering, 1974-10)
      Performance of convolutionally encoded telemetry systems with Viterbi decoding or sequential decoding is well understood for the additive white Gaussian noise channel with coherent detection of bi-phase-shift-keyed signals. Significant degradation from ideal performance can occur due to correlated noise resulting from low signal-to-noise ratios in the receiver carrier tracking phase-locked loop. Performance at the lower telemetry data rates on the two Pioneer Jupiter deep space probes provides examples of the effect of correlated noise on a sequential decoding system. Performance degradation needs to be quantified as a function of carrier signal-to-noise ratio (P(c)/N(o)2B(lo)) and carrier-tracking- loop-bandwidth-to-symbol-rate ratio (B(l)/R(s)) in order to provide design and analysis information on such effects. Analytical modeling is extremely difficult, particularly where B(l)/R(s) is neither very large nor very small.
    • Some Simulation Results for Convolutional Codes Over a PCM/FM Fading Channel

      Grant, T. L.; Hofman, L.; NASA Ames Research Center (International Foundation for Telemetering, 1974-10)
      NASA is now actively planning entry probe missions for the outer planets. Such an entry probe requires a new telemetry link design. A probable modulation for this link is a continuous phase, narrow-band FSK (or PCM/FM), and this paper reports on simulations which can be used to estimate convolutional code performance with mild fading on such a channel. Simulated decoding has been performed for a range of signal-to-noise ratios on the PCM/FM channel with various fading characteristics.
    • On-Board High Frequency Data Processing

      Maschhoff, Robert H.; Gultron Industries (International Foundation for Telemetering, 1974-10)
      On-board processing of high frequency analog data, such as that derived from vibration and acoustic sensors, offers the telemetry engineer three highly significant advantages over traditional fm/fm transmission of such data. When combined with PCM techniques the result is (1) bandwidth compression, (2) single rf data link, and (3) substantially higher data accuracy. In this processing technique only data representative of the power spectral density of the sensed waveform is transmitted to the ground station. By shifting the data processing function to the on-board telemetry system and transmitting only the processed data, the required transmission channel bandwidth is greatly reduced. As a result of this bandwidth compression the high frequency data can be pulse code modulated. Two significant advantages thereby ensue. The first is that data from multiple sources may now be transmitted over a single rf data link. The second advantage is that the data accuracy is greatly increased.
    • A Flexible Preprocessor for ERTS MSS Data

      Waltz, Edward L.; Bendix Aerospace Systems Division (International Foundation for Telemetering, 1974-10)
      The requirements to preprocess Earth Resources Technology Satellite (ERTS) multispectral scanner (MSS) data from its 24 channel tape format at real time rates can be met most efficiently by a parallel processor with a flexible interface for compatibility with a wide range of digital computers. The ability of the preprocessor and tape unit to playback data at programmable rates (real-time and half and quarter real-time) provides the additional ability to adjust preprocessing rate to optimize system throughput for several image processing computer system configurations, and processing modes. The MSS Data Interface described in this paper has been developed to meet these requirements for ERTS processing facilities of those nations which record ERTS data in the NASA-compatible format on 28 channel tape units. The first MDI which has been delivered to the Brazilian government is compatible with the Digital Equipment Corporation PDP-11 computer and can be operated in either a single or dual processor system configuration.
    • Atmospheric Monitoring Using Infrared Heterodyne Radiometry

      Peyton, Bernard J.; Cutler-Hammer (International Foundation for Telemetering, 1974-10)
      Atmospheric constituents have unique vibrational-rotational signature lines within the infrared spectrum and the signature intensities and line shapes vary with the constituent concentration and the atmospheric density. The recent development of stable, single frequency, single-mode laser local oscillators and nearly quantum-noise-limited heterodyne receivers have permitted the development of infrared heterodyne radiometers (IHR's) which provide good sensitivity and excellent specificity for the remote examination of individual atmospheric constituent signature lines. A 9 to 11 μm IHR employing a CO₂ laser local oscillator has been developed and can be used to resolve the spectral signature of atmospheric constituents such as SO₂, O₃ C₂H₄, and NH₃. The IHR has a bandwidth of 100 MHz (33 x 10⁻³ cm⁻¹) and a minimum detectable power spectral density of 5.4 x 10⁻²⁴ W/Hz for a 1-second integration time. For atmospheric monitoring applications the IHR telescope collects the thermal energy radiating from the earth at: (1) a clear spectral window, and (2) a spectral region in which the signature lines of the constituent gases at various layers of the atmosphere will be energized by the upwelling thermal radiation. When the vertical temperature distribution of the atmosphere is known, the concentration of the atmospheric constituent gas can be determined as a function of altitude from the radiance data collected at the IHR using an iterative mathematical technique.
    • Remote Monitoring of Ozone in the Troposphere Using Earth Reflected Differential Absorption

      Guagliardo, John L.; Bundy, Donald H. (International Foundation for Telemetering, 1974-10)
      A method of remotely monitoring the tropospheric concentration of ozone is proposed. The method uses two lasers, each emitting a different wavelength. It is shown that even though only two laser wavelengths are used, the method is both specific and accurate for oz.one concentrations which are encountered in most urban areas.
    • Design of the Mariner Jupiter/Saturn 1977 Telemetry System

      Wood, Gordon E.; Risa, Thomas; California Institute of Technology (International Foundation for Telemetering, 1974-10)
      In 1977 NASA will launch two spacecraft to perform scientific investigations of the Jupiter and Saturn planetary systems. The science payload includes a total of 10 instruments to support both the interplanetary cruise and planetary encounter phases. These will be the first launches of a new generation of Mariner-class spacecraft designed for outer-planet missions. The telemetry system design for these missions was especially challenging because of extreme communication ranges (1.5 X 10⁹ km), high data rate requirements (up to 115.2 kb/s), and more stringent data quality requirements than previous Mariner missions. This paper discusses the evolution and design of the Mariner Jupiter/Saturn 1977 telemetry system and presents the performance anticipated therefrom.