• An Expert System for Satellite Control

      Pazzani, Michael; Brindle, Anne; The Aerospace Corporation (International Foundation for Telemetering, 1985-10)
      As on-board satellite systems develop increased sophistication and autonomous capabilities, failures become fewer, but the diagnosis of the remaining failures becomes more complex. In addition, autonomy requirements for space vehicles are being issued along with requirements for reduced staffing of ground stations. Thus successful groundbased fault handling in the future will require greatly increased automation of fault detection and diagnosis. This paper investigates the use of an expert system as a ground system component for diagnosis. The diagnostic cycle of the system is presented, along with requirements for its knowledge base. The results of implementing the design to diagnose part of a satellite attitude control system are given. Knowledge acquisition for this problem centered on the generation and analysis of terminal displays of telemetry which look much like strip charts. Correct diagnosis by the expert system derived from the use of extensive telemetry analysis, operations and satellite status databases, and satellite modeling.

      Aure, Jean Marie; Telemetering and System Department (International Foundation for Telemetering, 1985-10)
      It is difficult to transmit directly the data circulating on a 1553-B bus by microwave link during a missile test, given that it is not a synchronous message. For the ANS missile the AEROSPATIALE tactical missile division has decided to include the 1553 message in a PCM message to IRIG standards. In view of the asynchronism between the traditional telemetering data and the bus message it has been necessary to develop a specific controller providing the interface between the bus and the IRIG PCM. This controller performs the functions of synchronization, encoding, structural analysis of message, adaptatin of the input speed to the PCM rate and also dating of the data. Moreover, during tests on the missile, it is necessary to process the bus data on the ground. A conventional decommutator, although suitable for the usual analog channels, cannot be used in real time. It is therefore been necessary to develop equipment providing on the ground the reconstitution of a 1553 bus that can be processed by ordinary standard equipment. After synchronizing and sorting the data in the IRIG format the equipment creates three types of messages corresponding: to the missile message, to the dating and to the message found erroneous during acquisition on board.

      Sullivan, Arthur; Electro Magnetic Processes, Inc. (International Foundation for Telemetering, 1985-10)
      Over a decade ago the author developed a unique conically scanning tracking antenna feed (RADSCAN) with only one moving part and extremely high reliability. While the system had many advantages over single-channel monopulse (SCM), there were two disadvantages: one was weight due to the drive motor; the other was the fact that the scan speed was constant. EMP is just completing the development of a conscan tracking feed which is pneumatically driven (Pneu-Scan) - thus eliminating the heavy electric drive motor. Since most telemetry tracking antennas require a dehydrator/pressurizer for environmental reasons, no additional drive power is required to scan the feed since the pressurized air from the dehydrator system is used to drive the feed. In addition, the scan speed is proportional to the continuously varying pressure. If increased reliability is required, then redundant dehydrators can be used. The feed system has only one moving part constructed from graphite fiber that weighs less than an ounce. The feed is driven by a small lightweight impeller. An S-band tracking feed of this design is less than five inches in diameter - as compared to 12 inches for an SCM feed. It is also considerably lighter than an SCM feed. Decreased aperture blocking - by more than a factor of two enhances sidelobe levels and maximizes gain. The new feed illuminates a lightweight 5-foot diameter graphite-epoxy constructed paraboloidal reflector positioned by an elevation-over-azimuth pedestal. Both the elevation and azimuth assemblies of the pedestal are constructed of graphite fiber composite material - which greatly reduces both weight and cost as compared with the conventional steel or aluminum construction. An inflatable rotodome surrounds the elevation assembly and rotates with azimuth. The rotating sphere has minimum wind induced torque thereby minimizing the required drive power. The weight of the entire system is less than 135 pounds - yielding an extremely light weight, low cost, versatile two-axis telemetry tracking system.

      Ng, Wai-Hung; The Aerospace Corporation (International Foundation for Telemetering, 1985-10)
      For space monitoring systems, it is necessary to compress the transmitted data to minimize the power and bandwidth requirements. Although there are many data compression techniques, here we will only discuss the sample reduction technique because it is the best candidate for cases when the signal contains many redundant samples and the resolution requirement for the reconstructed signal is very high. In this paper, we introduce a new code to further reduce the compressed signal data derived from the sample reduction technique. The main advantage of this approach is that we can minimize the transmission data rate without requiring a priori knowledge of the signal distribution property. In addition, it can also reduce the buffer size requirement. Examples are given for clarification and discussion.

      Vorce, Richard G.; Fairchild Weston Systems Inc. (International Foundation for Telemetering, 1985-10)
      The unit to be described differs from present tunable discriminator products chiefly because it is designed to simultaneously demodulate all the subcarrier channels in a frequency division multiplex. In addition the demodulated output data is presented in digital format that is compatible for direct computer entry. The discriminator implementation techniques will be discussed at the block diagram level. Particular emphasis will be given to the use of “Finite Impulse Response” filters and also to the internal tape speed compensation process.

      Nardou, Alain; Telemetering and Systems Department (International Foundation for Telemetering, 1985-10)
      INTERTECHNIQUE which manufactures the TM 77.600, I.R.I.G. format decommutator, has had to extend the PCM message acquisition performance range to the DANIEL format, and has thus developed the TM 78.420. The TM 78420, capable therefore of acquiring both DANIEL and IRIG PCM messages, meets the requirements of the users of the Avions Marcel Dassault methods service telemetering station at Istres. This equipment provides for the acquisition and display, in different forms and in real time, of values of parameters contained in a PCM message. The following values can be displayed simultaneously on five cathode screens: - 128 parameters in analog form, bar-graph type - 32 parameters in digital form, in physical magnitudes. The values of 16 parameters can be restored in the form of analog voltages and those of four parameters in binary form. An operator terminal, consisting of a display console/alphanumeric keyboard unit, prepares the deswitching program and monitors the equipment in general. The system consists of the following subassemblies; - 4 analog display terminals designated as A, B, C, D - 1 alphanumeric terminal unit E - 1 logging rack - 1 operator terminal

      Thom, Gary A.; General Data Products, Inc. (International Foundation for Telemetering, 1985-10)
      The advent of Bit Slice Processors and related architectures has produced numerous high performance PCM Data Simulators. Many of these fall into the category of stored program simulators, which give the user unlimited flexibility and power. These simulators allow the user to program almost any imaginable format, with combinations of subframes, subsubframes, and asynchronously embedded subframes. The drawback is that the user is forced to program the simulator using a very detailed machine level language which usually has no obvious relation to PCM frame formats. A new simulator architecture allows the user to describe the frame format to be simulated in familiar terms. This eliminates the need to learn yet another programming language or develop a Compiler. The user identifies common parameters such as frame length, subframe length, and where special words should be located. These special words can be unique sensor data words, a table of sensor data, ID counters, subframe slots and so on.

      Hoefener, Carl E.; Stone, James; Interstate Electronics Corporation (International Foundation for Telemetering, 1985-10)
      When applying the Global Positioning System (GPS) to Time, Space, and Position Information (TSPI), the use of GPS frequency translators should be considered. The primary space positioning problem in the test and evaluation applications is trajectory reconstruction. Although this can be accomplished by flying a GPS receiver on the test vehicle and telemetering its position to the ground, there are significant advantages to translating the “L” band GPS signals to “S” band, and transmitting the broad band signal to the ground for processing. A translator-based system offers several advantages. Physical advantages include smaller size, lower weight, and lower cost. Technical advantages include: 1) ground station data aiding that provides a 6 dB advantage, 2) elimination of system bias errors, 3) computation complexity at the ground station vs. the vehicle under test, and 4) the ability to reconstruct a test scenario enabling flexibility in data analysis techniques.

      TROVER, WILLIAM F.; Teledyne Controls (International Foundation for Telemetering, 1985-10)
      Research and Test Activities have a continuing need to cope with more and more channels of data and at continually wider data bandwidths. There is a consensus in the test community that compressed EU and derived parameter data presented in realtime can significantly reduce total test costs because test engineers can make realtime judgements on the validity of a given test point (mode). Classical telemetry preprocessors usually cannot handle these more demanding realtime processing requirements because, when they were designed, it was assumed that raw data was in a single PCM word and only a simple mx+b EU conversion, or simple data compression was required. Present preprocessors typically use special bit slice technology to speed up the realtime process and they’re only one or two bus systems whose processing capacity is typically less than 300k to 400k parameters per second. Furthermore, many cannot handle word concatenation (except for adjacent PCM words) and none can handle complex derived parameters such as thrust, lift, gross weight, center of gravity, stall speed, harmonic analysis, etc. To address these limitations, a massively parallel computer system has been developed based on up to sixty, general purpose, 1MFLOP floating point computers operating in parallel to support realtime processing of any type, at aggregate throughputs up to 1.5 Mwps. This system can merge realtime data from up to eight different asynchronous sources having word rates up to 2.0 Mwps from any source. Up to 32,768 different parameters can be accepted as inputs with an additional 32,768 ID tags available for concatenated and derived parameter identification. A powerful realtime software package permits the user of the computer system to apply any, or many algorithms) to any or an parameters being processed.

      Lindsay, Robert A.; Cox, B.V.; Communications Corporate Technology Center (International Foundation for Telemetering, 1985-10)
      Universal and adaptive data compression techniques have the capability to globally compress all types of data without loss of information but have the disadvantage of complexity and computation speed. Advances in hardware speed and the reduction of computational costs have made universal data compression feasible. Implementations of the Adaptive Huffman and Lempel-Ziv compression algorithms are evaluated for performance. Compression ratios versus run times for different size data files are graphically presented and discussed in the paper. Required adjustments needed for optimum performance of the algorithms relative to theoretical achievable limits will be outlined.

      Skiffington, Barbara; Carrig, Jim; Kornell, Jim; General Research Corporation (International Foundation for Telemetering, 1985-10)
      This paper describes an expert system prototype which approaches some issues of satellite command and control. The task of the prototype system is to assist a spacecraft controller in maneuvering a geosynchronous satellite for the purpose of maintaining an accurate spacecraft pointing angle, i.e. station keeping. From an expert system’s point of view, two features of the system are notable. First, a tool for automated knowledge acquisition was employed. Because the domain experts were in Maryland while the AI experts were in California, a means to automate knowledge acquisition was required. Second, the system involves a blend of simulation and expert systems technology distributed between a DEC VAX computer and a LISP machine (a special purpose AI computer). This kind of distribution is a plausible model for potential real-world installations.

      Breedlove, Phillip M.; Stephens, Charles R.; Loral Instrumentation (International Foundation for Telemetering, 1985-10)
      As MIL-STD-1553 Multiplex Data Bus usage proliferates, the ability to remotely monitor bus traffic has become important. Common applications include flight testing of missiles and aircraft, and the field maintenance of vehicles. Due to the high data rate and asynchronous characteristics of the 1553 Data Bus, special problems exist in the acquisition and analysis of 1553 bus traffic. The acquisition of the complete bus traffic is especially important during system testing and diagnostic operations. Several approaches are being utilized today to transmit 1553 bus traffic. The first approach is an extension of the PCM technique in which all of the bus traffic, during a specific time window, is buffered and then output in a PCM style format. This has the advantage of being synchronous, but a significant amount of bus information is lost, primarily the protocol and bus timing. An alternative approach is to transmit raw unbuffered bus traffic. Bus timing and protocol are retained, but the telemetry signal is asynchronous. A third approach, developed by Loral Data Systems in conjunction with Loral Instrumentation, is a 1553 Data Acquisition System that retains bus timing and protocol and synchronizes the signal to a common clock.

      Wickham, M. E.; COMSAT Laboratories (International Foundation for Telemetering, 1985-10)
      An advanced microwave power leveling loop (MPLL) was conceived, designed, fabricated, tested, and used during spacecraft in-orbit testing. The primary function of the MPLL is to maintain constant RF power transmitted from an earth station antenna during spacecraft in-orbit transponder testing. The MPLL utilizes nonlinear analog electronics with flexible signal path routing under microprocessor control. It achieves a power control dynamic range of greater than 50 dB with better than 0.1 dB of control resolution. Power level step changes of 20 dB can be accomplished in under 10 ms. The MPLL is IEEE-488 bus controllable and is designed for use in automated in-orbit test systems to facilitate the measurement process and produce more repeatable results than have previously been possible. Measurements performed with the aid of the MPLL include transponder frequency response, group delay, gain, and saturation level. The system can also be operated in a manual mode, and utilizes state-ofthe-art human interfacing techniques such as a display/entry panel and a rotary encoder control knob. This paper describes the MPLL design process, including computer simulation work and breadboard testing. Performance and temperature chamber test results are presented for breadboard and manufactured units.

      Ren, Li Ke; Beijing Research Institute of Telemetry (International Foundation for Telemetering, 1985-10)
      Generally, the data acquisition equipment used in space vehicles mainly consists of logic program control, multiplexer-encoder, output driver, power supply for dc conversion and so on. Today telemetry technology has been deeply concerned with computer science. So how to make the telemetry system more flexible and versatile and how to design a multiplexer-encoder (data collector or remote unit as is called in a programmable telemetry system) with good compatibility and powerful function has become one of the most important things of developing a new generation of telemetry system. In 1960s, most of the telemetry systems were of typical coded time-division multiplexing. The sampling program of this system is fixed and its bit rate and frame format are unvaried, so it is difficult for a system to accommodate the requirements of various kinds of measurements, especially when there are comparatively more parameters to be measured, and most of which are of slow-changing. As the sampling rate is designed in accordance with the upper-limited signal frequency that we need to measure, so the validity of the slow-changing data is very low. And onced the telemetry equipment has been developed, it is very difficult to change the sampling rate, the bit rate and the frame format. With the development of electronic devices, more devices can be integrated in a small chip, so the programmable telemetry had been pulled off in early 1970s. This article deals with mainly a few programmable multiplexer-encoders and microprocessor-controlled multiplexer-encoders used in our actual research work and applications.
    • International Telemetering Conference Proceedings, Volume 21 (1985)

      Unknown author (International Foundation for Telemetering, 1985-10)

      Martini, Willy; Telemetering and Systems Department (International Foundation for Telemetering, 1985-10)
      After a brief glimpse of the composition of a modern airborne transmitter, a reminder is given of how the choice of a servoed carrier scheme after frequency division on a quartz crystal reference, favoring transmissions at high data speed, has opened up the way to a whole generation of frequency synthesis transmitters covering the 2.1 - 2.7 GHz band in sub-bands of 150 MHz with a pitch of 0.5 MHz. The advantages of frequency synthesis from the quadruple aspect of maintenance, availability “on the shelf”, flexible use in a congested frequency plan and discretion, are then commented on. Finally, in a last section - more theoretical than the previous ones - the technical difficulties which arise from the “spirit” of frequency synthesis are referred to.

      Uzunoglu, Vasil; Maiorano, Ann B.; Fairchild Industries (International Foundation for Telemetering, 1985-10)
      At bit rates lower than 100Mbit/s, the Synchronous Oscillator (SO) [1-4] has substantial tracking band combined with steep skirt selectivity to satisfy all the requirements of a carrier recovery network without the need for a phase correction network. At higher bit rates however, there is a need for a phase correction or phase cancelling network, if the BER variations with respect to hard wired case must be confined to less than 0.2dB with IF offsets of ±30kHz. At bit rates higher than 100Mbit/s, the multiply by four process in a QPSK modem deteriorates the signal-to-noise ratio by more than 15 dB (18dB at Eb/No = 6.4 dB) and the synchronization signal-to-noise ratio at the input to the SO drops below 0dB (!5dB at Eb/No = 6.4dB). This reduction in the signal-to-noise ratio reduces the tracking band of the SO which in turn increases the phase shift per unit frequency offset.

      Natali, Francis D.; Socci, Gerard G.; Stanford Telecommunications, Inc. (International Foundation for Telemetering, 1985-10)
      Digital processing techniques and related algorithms for receiving and processing space vehicle downlink signals are discussed. The combination of low minimum signal to noise density (C/No), large signal dynamic range, unknown time of arrival, and high space vehicle dynamics that is characteristic of some of these downlink signals results in a difficult acquisition problem. A method for rapid acquisition is described which employs a Fast Fourier Transform (FFT). Also discussed are digital techniques for precise measurement of space vehicle range and range rate using a digitally synthesized number controlled oscillator (NCO).

      LAUTZENHISER, LLOYD L.; EMHISER RESEARCH INC. (International Foundation for Telemetering, 1985-10)
      DoD has established a goal of having range telemtry and video RF links on all national test ranges secure and/or encrypted in the near future. Emhiser Research has developed a new family of digitally synthesized, frequency agile, video transmitter and receiver sets. These video sets, which operate at L-band, S-band, or C-band frequencies, are frequency agile, changing frequency on each video line. The frequency changes take place during retrace in about 6 microseconds. Through the use of novel, frequency synthesization techniques, each new frequency is immediately stable at the new frequency value and frequency synchronization and lock problems have been solved. This paper describes the operation of both the transmitter and receiver, presents block diagrams and outlines test results on the prototype units, novel features and advantages will be outlined and possible applications will be discussed.
    • Autonomous Control and Data Acquisition for Advanced Satellite Systems

      Turner, Tim; Gulton Industries, Inc. (International Foundation for Telemetering, 1985-10)
      Autonomous operation is rapidly becoming a requirement for most new spacecraft systems. An autonomous spacecraft greatly simplifies the ground station processing and monitoring requirements, freeing ground station capabilities for other important tasks. The T2C2 (Telemetry, Timing, Command and Control) System has been conceived and architected to facilitate spacecraft autonomy. The T2C2 architecture is ideally suited for onboard closed-loop control, redundancy management, housekeeping and other autonomous functions. This paper provides an overview of the T2C2 architecture and its applications in the design and implementation of an autonomous spacecraft.