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The optimum mean-square decoding of general block codes

Information and Control 1976年第4期31卷 341-363页

作者： Redinbo, G. Robert Advanced Systems Concepts Branch Defense Communications Engineering Center Reston VA 22090 1860 Wiehle Avenue United States

We are concerned with the use of linear codes in the channel coding part of a numerical data transmission system in which the performance criterion is the mean-square error. The optimum decoding rule is developed for a fixed code over the finite field GF(q). It is a mapping from the channel alphabet into the real numbers and as such combines both the error-correcting and digital-to-analog converter functions found in most systems. We employ abstract Fourier analysis on groups to determine an optimum 1-1 encoding rule to be used with the corresponding optimum decoder. A procedure for the simultaneous optimization over both rules is presented. We show that there is always a linear encoding rule which is one part of the optimum pairs of permissible encoding-decoding rules. A system which implements the optimum decoding rule is detailed. In this realization the outputs from a bank of generalized bandpass filters are arithmetically combined with the output of a normalizing lowpass filter to produce the optimum estimate in the decoder. These filters are mechanized in the Fourier domain by weighting the spectrum of the indicator function of the received word by selected values of the transforms of the channel transition probabilities. This approach uses complex-valued arithmetic operations as opposed to finite field operations usually found in decoders. We examine a method for reducing the complexity of the decoder and determine an exact expression for the performance of this type of suboptimal decoder. © 1976 Academic Press, Inc.

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Lunar Reconnaissance orbiter (LRO) thermal on-orbit performance

Lunar Reconnaissance orbiter (LRO) thermal on-orbit performa...

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41st International Conference on Environmental systems 2011, ICES 2011

作者： Baker, Charles Cottingham, Christine Peabody, Sharon NASA/Goddard Spaceflight Center Systems Engineering Services and Advanced Concepts Branch Code 592 Greenbelt MD 20771 United States Edge Space Systems Thermal Engineering Branch 545 13860 Kennard Drive Glenelg MD 21737 United States

ISBN: (纸本)9781600869488

The Lunar Reconnaissance Orbiter (LRO) was launched on June 18, 2009. The nominal mission ended on September 15, 2010 and LRO is now on a four-year extended mission. The LRO performances in hot and cold cases are compared to pre-launch analysis predicts, and operational lessons learned are discussed. One instrument has required tighter-thananticipated thermal control, and two others have frequently requested unanticipated calibration maneuvers that had to be evaluated for their thermal performance. A series of off nadir thermal analyses of the entire orbiter were performed prior to launch, and these predictions are compared to actual maneuvers, with a discussion of the process by which maneuvers can be rapidly evaluated for thermal concerns. On December 21st, 2010, LRO experienced its first severe Lunar Eclipse. Operationally, this required the Spacecraft to pre-heat its main avionics panel in order to minimize control heater power during the period when the Earth blocks the sun from the moon. The operational design and in-flight performance are summarized.

关键词： Thermoanalysis

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GSFC information systems technology developments supporting the vision for space exploration

GSFC information systems technology developments supporting ...

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A Collection of Technical Papers - AIAA Space 2004 Conference and Exposition

作者： Hughes, Peter Dennehy, Cornelius Mosier, Gary Smith, Dan Dallas, Lisa NASA Goddard Space Flight Center Greenbelt MD 20771 Mail Code 502 AETD Mission Engineering and Systems Analysis Division Mail Code 590 James Webb Space Telescope Project Systems Engineering Services and Advanced Concepts Branch Mail Code 592 Systems Integration and Engineering Branch Mail Code 581 Advanced Automation and Architectures Branch Mail Code 588

ISBN: (纸本)1563477203

The Vision for Space Exploration will guide NASA's future human and robotic space activities. The broad range of human and robotic missions now being planned will require the development of new system-level capabilities enabled by emerging new technologies. Goddard Space Flight Center is actively supporting the Vision for Space Exploration in a number of program management, engineering and technology areas. This paper provides a brief background on the Vision for Space Exploration and a general overview of potential key Goddard contributions. In particular, this paper focuses on describing relevant GSFC information systems capabilities in architecture development;interoperable command, control and communications;and other applied information systems technology/research activities that are applicable to support the Vision for Space Exploration goals. Current GSFC development efforts and task activities are presented together with future plans.

关键词： Space research

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Geoscience laser altimetry system (GLAS) loop heat pipe anomaly and on orbit testing

Geoscience laser altimetry system (GLAS) loop heat pipe anom...

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41st International Conference on Environmental systems 2011, ICES 2011

作者： Baker, Charles Butler, Dan Grob, Eric Jester, Peggy NASA/Goddard Spaceflight Center Greenbelt MD 20771 United States SGT Wallops Island VA 23337 United States Systems Engineering Services and Advanced Concepts Branch Code 592 United States Thermal Engineering Branch 545 United States Cryospheric Sciences Lab 614.1. United States

ISBN: (纸本)9781600869488

The Geoscience Laser Altimetry System (GLAS) is the sole instrument on the ICESat Satellite. On day 230 of 2003, the GLAS Component Loop Heat Pipe (CLHP) entered a slow circulation mode that resulted in the main electronics box reaching its hot safing temperature, after which the entire instrument was turned off. The CLHP had a propylene working fluid and was actively temperature controlled via a heater on the compensation chamber. The slow circulation mode happened right after a planned propulsive yaw maneuver with the spacecraft. It took several days to recover the CLHP and ensure that it was still operational. The recovery occurred after the entire instrument was cooled to survival temperatures and the CLHP compensation chamber cycled on a survival heater. There are several theories as to why this slow circulation mode exhibited itself, including: accumulation of Non-Condensible Gas (NCG), the secondary wick being under designed or improperly implemented, or an expanded (post-launch) leak across the primary wick. Each of these is discussed in turn, and the secondary wick performance is identified as the most likely source of the anomalous behavior. After the anomaly, the CLHP was controlled to colder temperatures to improve its performance (as the surface tension increases with lower temperature, as does the volume of liquid in the compensation chamber) and only precursor pulses occurred later in the mission. After GLAS's last laser failed, in late 2009, a decision was made to conduct engineering tests of both LHPs to try and duplicate this flight anomaly. The engineering tests consisted of control setpoint changes, sink changes, and one similar propulsive Yaw maneuver. The only test that showed any similar anomaly precursors on the CLHP was the propulsive maneuver followed by a setpoint increase. The ICESat Satellite was placed in a decaying orbit and ended its mission on August 30, 2010 in Barents Sea.

关键词： Geology

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Linking and combining distributed operations facilities using NASA's "GMSEC" system architecture

Linking and combining distributed operations facilities usin...

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SpaceOps 2008 Conference

作者： Smith, Dan Grubb, Thomas Esper, Jaime Software Engineering Division National Aeronautics and Space Administration Goddard Space Flight Center Greenbelt MD 20771 United States Systems Engineering and Advanced Concepts Branch National Aeronautics and Space Administration Goddard Space Flight Center Greenbelt MD 20771 United States

ISBN: (纸本)9781624101670

NASA's Goddard Mission Services Evolution Center (GMSEC) ground system architecture has been in development since late 2001 has successfully supported eight orbiting satellites and is being applied to several of NASA's future missions. GMSEC can be considered an event-driven, service-oriented architecture built around a publish/subscribe message bus middleware. This paper briefly discusses the GMSEC technical approaches which have led to significant cost savings and risk reduction for NASA missions operated at the Goddard Space Flight Center (GSFC). The paper then focuses on the development and operational impacts of extending the architecture across multiple mission operations facilities.

关键词： NASA

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Recent developments in the design, capabilities and autonomous operations of a lightweight surface manipulation system and test-bed

Recent developments in the design, capabilities and autonomo...

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AIAA SPACE Conference and Exposition 2011

作者： Dorsey, John T. Jones, Thomas C. Doggett, William R. Brady, Jeffrey S. Berry, Felecia C. Ganoe, George G. Anderson, Eric J. King, Bruce D. David Mercer, C. Structural Mechanics and Concepts Branch NASA Langley Research Center Hampton VA 23681 United States Mechanical Systems Branch NASA Langley Research Center Hampton VA 23681 United States Advanced Sensing and Optical Measurement Branch NASA Langley Research Center Hampton VA 23681 United States Electromagnetics and Sensors Branch NASA Langley Research Center Hampton VA 23681 United States Mechanical Engineering Department Purdue Universtiy 585 Purdue Mall West Lafayette IN 47907 United States Aeronautics Systems Engineering Branch Lockheed Martin Hampton VA 23681 United States Structural Mechanics and Concepts Branch Stinger Ghaffarian Technologies Hampton VA 23666 United States

ISBN: (纸本)9781600869532

The first generation of a versatile high performance device for performing payload handling and assembly operations on planetary surfaces, the Lightweight Surface Manipulation System (LSMS), has been designed and built. Over the course of its development, conventional crane type payload handling configurations and operations have been successfully demonstrated and the range of motion, types of operations and the versatility greatly expanded. This enhanced set of 1st generation LSMS hardware is now serving as a laboratory test-bed allowing the continuing development of end effectors, operational techniques and remotely controlled and automated operations. This paper describes the most recent LSMS and test-bed development activities, that have focused on two major efforts. The first effort was to complete a preliminary design of the 2nd generation LSMS that has the capability for limited mobility and can reposition itself between lander decks, mobility chassis, and fixed base locations. A major portion of this effort involved conducting a study to establish the feasibility of, and define, the specifications for a lightweight cable-drive waist joint. The second effort was to continue expanding the versatility and autonomy of large planetary surface manipulators using the 1st generation LSMS as a test-bed. This has been accomplished by increasing manipulator capabilities and efficiencies through both design changes and tool and end effector development. A software development effort has expanded the operational capabilities of the LSMS test-bed to include;autonomous operations based on stored paths, use of a vision system for target acquisition and tracking, and remote command and control over a communications bridge. © 2011 by the American Institute of Aeronautics and Astronautics, Inc.

关键词： Manipulators

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Structural sizing of a horizontal take-off launch vehicle with an air collection and enrichment system

Structural sizing of a horizontal take-off launch vehicle wi...

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40th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit

作者： McCurdy, David R. Roche, Joseph M. QSS Group Inc. 21000 Brookpark Rd/MS GES-QSS Brookpark OH 44135 United States Chief Systems Engineering Services and Advanced Concepts Branch NASA Glenn Research Center 21000 Brookpark Rd /MS 86-15 Cleveland OH 44135 United States

In support of NASA's Next Generation Launch Technology (NGLT) program, the Andrews Gryphon booster was studied. The Andrews Gryphon concept is a horizontal liftoff, two-stage-to-orbit, reusable launch vehicle that uses an air collection and enrichment system (ACES). The purpose of the ACES is to collect atmospheric oxygen during a subsonic flight loiter phase and cool it to cryogenic temperature, ultimately resulting in a reduced initial take-off weight. To study the performance and size of an air-collection based booster, an initial airplane like shape was established as a baseline and modeled in a vehicle sizing code. The code, SIZER, contains a general series of volume, surface area, and fuel fraction relationships that tie engine and ACES performance with propellant requirements and volumetric constraints in order to establish vehicle closure for the given mission. A key element of system level weight optimization is the use of the SIZER program that provides rapid convergence and a great deal of flexibility for different tank architectures and material suites in order to study their impact on gross ü'ft-off weight. This paper discusses important elements of the sizing code architecture followed by highlights of the baseline booster study. © 2004 by the American Institute of Aeronautics and Astronautics. Inc.

关键词： Launch vehicles

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MNT-based gossamer space frame

MNT-based gossamer space frame

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Collection of Technical Papers - CANEUS 2004 - Conference on Micro-Nano-Technologies for Aerospace Applications

作者： Cheung, Cynthia Y. Curtis, Steven A. Rilee, Michael L. Oberright, John E. NASA Goddard Space Flight Center Greenbelt MD 20771 United States L3 Communications GSI Greenbelt MD 20771 United States Planetary Magnetospheres Branch NASA GSFC/Code 695 L-3 Communications GSI NASA GSFC/Code 695 Systems Engineering Services and Advanced Concepts Branch NASA GSFC/Code 592

ISBN: (纸本)1563477211

We have developed a new micro-nano-technology-based architecture called Super Miniaturized Addressable Reconfigurable Technology (SMART) to guide the development and control of a "smart" gossamer space frame. Since the SMART architecture is scalable, designs can be realized in the near-term in the macroscopic scale using electro-mechanical systems (EMS) to produce an Addressable Reconfigurable Technology (ART) structure. This will enable us to evolve the design and to examine operational issues such as distributed control, group intelligence and global coordination. As advances in micro- and nanomaterials and fabrication processes become available, the design can be "ported" to MEMS-based and NEMS-based systems. ART is applicable to the new NASA Exploration Initiative by enabling multi-functional systems for Moon and Mars Exploration.

关键词： Structural frames

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RS-34 (Peacekeeper Post Boost Propulsion System) orbital debris application concept study

RS-34 (Peacekeeper Post Boost Propulsion System) orbital deb...

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AIAA SPACE 2013 Conference and Exposition

作者： Esther, Elizabeth A. Burnside, Christopher G. Fincher, Sharon S. Flowers, Tammy D. Russell, Tiffany E. Schnell, Andrew R. Thomas, Dan Wiegmann, Bruce M. Baysinger, Mike Capizzo, Peter D. Garcia, Jay Hornsby, Linda S. National Aeronautics and Space Administration MSFC Advanced Concepts Office ED04 AL 35812 United States National Aeronautics and Space Administration MSFC Propulsion Systems Department ER23 AL 35812 United States National Aeronautics and Space Administration MSFC E3 and Electrical Integration Branch ES42 AL 35812 United States Jacobs Engineering Advanced Concepts Office ED04 Huntsville Al 35806 United States

ISBN: (纸本)9781624102394

The advanced concepts Office (ACO) at the National Aeronautics and Space Administration (NASA) Marshall Space Flight Center (MSFC) conducted a study to evaluate the Rocketdyne produced RS-34 propulsion system as it applies to an active debris removal design reference mission. The existing RS-34 propulsion system is a remaining asset from the de-commissioned United States Air Force Peacekeeper Intercontinental Ballistic Missile program;specifically the pressure-fed storable bi-propellant Stage IV Post Boost Propulsion System. The active debris removal design reference mission closely mimics the heritage RS-34 mission and thus proved as an appropriate design reference mission. The RS- 34 Orbital Debris Application Concept Study identified multiple configurations varying the degree of modification to trade for dry mass optimization and overall capability in evaluation of removal of several target resident space objects. The results of the RS-34 Phoenix Concept Study show that the system is technically sufficient to successfully support capture and de-orbit of the greatest mass, including Hubble and EnviSat class resident space objects, that pose the greatest threats to low earth orbit environment.

关键词： NASA

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A lean, fast Mars round-trip mission architecture: Using current technologies for a human mission in the 2030s

A lean, fast Mars round-trip mission architecture: Using cur...

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AIAA SPACE 2013 Conference and Exposition

作者： Bailey, Lora Foltay, David Barbeez, Brent W. Vaughnx, Frank Kirchman, Frank Englander, Jacob Campbell, Bruce Thronson, Harley Lin, Tzu Yu NASA JSC Code EA32 2101 NASA Parkway Houston TX 77058 United States NASA GSFC Navigation and Mission Design Branch Code 595 Greenbelt MD 20771 United States NASA GSFC Systems Engineering Services and Advanced Concepts Branch Code 592 Greenbelt MD 20771 United States ATK Space Systems Division Beltsville MD 20705 United States NASA GSFC Code 660 Greenbelt MD 20771 United States University of Florida Mechanical and Aerospace Engineering Department Gainesville FL 32611 United States

ISBN: (纸本)9781624102394

We present a lean fast-transfer architecture concept for a first human mission to Mars that utilizes current technologies and two pivotal parameters: an end-to-end Mars mission duration of approximately one year, and a deep space habitat of approximately 50 metric tons. These parameters were formulated by a 2012 deep space habitat study conducted at the NASA Johnson Space Center (JSC) that focused on a subset of recognized high-engineering-risk factors that may otherwise limit space travel to destinations such as Mars or near-Earth asteroid (NEA)s. With these constraints, we model and promote Mars mission opportunities in the 2030s enabled by a combination of on-orbit staging, mission element pre-positioning, and unique round-trip trajectories identified by state-of-the-art astrodynamics algorithms.

关键词： NASA

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