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  • 1
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    Low data rate coherent optical link demonstration using frequency stabilized solid state lasers (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A low data rate laboratory heterodyne link demonstration operating at 1.06 micron using frequency stabilized Nd:YAG lasers was implemented. The data was modulated onto the optical carrier at 100 kbps using binary pulse position modulation. Phase coherent reception was achieved by closing the receiver phase tracking loop around the piezo-electric and temperature-tuned local oscillator laser. Initial frequency acquisition was accomplished by linearly scanning the LO frequency over the uncertainty range while a combined frequency and phase tracking loop searches for a lock indicator signal. The link performance was experimentally evaluated and compared to the theoretical predictions.
    Keywords: OPTICS
    Type: In: Free-space laser communication technologies III; Proceedings of the Meeting, Los Angeles, CA, Jan. 21, 22, 1991 (A93-18923 05-74); p. 170-181.
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  • 2
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    Word and frame synchronization with verification for PPM optical communications (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A method for obtaining word and frame synchronization in pulse position modulated optical communication systems is described. The method uses a short sync sequence inserted at the beginning of each data frame and a verification procedure to distinguish between inserted and randomly occurring sequences at the receiver. This results in an easy to implement sync system which provides reliable synchronization even at high symbol error rates. Results are given for the application of this approach to a highly energy efficient 256-ary PPM test system.
    Keywords: COMMUNICATIONS AND RADAR
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  • 3
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    Simple method for designing or analyzing an optical communication link (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A simple method is described for determining the performance of a free space optical communication link. The method can be used either in the system design (synthesis) mode, or in the performance evaluation (analysis) mode. Although restricted to photo counting based detection (e.g., photomultiplier tube or equivalent) of pulse position modulated signals, the method is still sufficiently general to accommodate space-based, as well as ground-based, reception.
    Keywords: COMMUNICATIONS AND RADAR
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  • 4
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    Transmitter pointing loss calculation for free-space optical communications link analyses (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: In calculating the performance of free-space optical communications links, the transmitter pointing loss is one of the two most important factors. It is shown in this paper that the traditional formula for the instantaneous pointing loss (i.e., for the transmitter telescope far-field beam pattern) is quite inaccurate. A more accurate and practical approximation is developed in which the pointing loss is calculated using a Taylor series approximation. The four-term series is shown to be accurate to 0.1 dB for the theta angles not greater than 0.9 lambda/D (wavelength/telescope diameter).
    Keywords: COMMUNICATIONS AND RADAR
    Type: Applied Optics (ISSN 0003-6935); 26; 2055-205
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  • 5
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    A new active virtual pivot six-degree-of-freedom hand controller for aerospace applications (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: During 1989 a new six-degree-of-freedom (6-DOF) active hand controller concept was designed and constructed based on the concept of a virtual pivot. This concept, labeled VPHC, was first demonstrated in a 1985 study and a patent was issued in 1990. Operator control input occurs via a force/torque sensor rigidly mounted to the handgrip. Sensed force/torque signals are used by microprocessors to generate motor drive control for each of six independently controlled motors mounted on the three-legged mechanism. The control microprocessor uses input biasing and rate-feedback motor controllers to generate the sensed feel of virtual springs and deadbands found in more conventional designs. An important advantage of this design is that the location of the virtual pivots, reflective forces and torques, breakout force levels, sensed spring rates, and operating modes, can be changed simply by changing the software. This approach yields an autonomous VPHC that can easily adapt itself to an individual operator (by software extension). A proof-of-concept version has been demonstrated, and further improvements are currently being studied and implemented.
    Keywords: MECHANICAL ENGINEERING
    Type: JPL, The 25th Aerospace Mechanisms Symposium; p 323-337
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  • 6
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    Lunar hand tools (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Tools useful for operations and maintenance tasks on the lunar surface were determined and designed. Primary constraints are the lunar environment, the astronaut's space suit and the strength limits of the astronaut on the moon. A multipurpose rotary motion tool and a collapsible tool carrier were designed. For the rotary tool, a brushless motor and controls were specified, a material for the housing was chosen, bearings and lubrication were recommended and a planetary reduction gear attachment was designed. The tool carrier was designed primarily for ease of access to the tools and fasteners. A material was selected and structural analysis was performed on the carrier. Recommendations were made about the limitations of human performance and about possible attachments to the torque driver.
    Keywords: ENGINEERING (GENERAL)
    Type: NASA-CR-184924 , NAS 1.26:184924 , ME-4182
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  • 7
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    Recommended Figures of Merit for Green Monopropellants (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Hydrazine propellant has historically been used as a rocket thruster monopropellant since the mid-1960s. Mission managers are well aware of its characteristics and performance. However, it is a known toxic chemical and a wide effort is underway to reduce and/or eliminate its use worldwide. Several new propellant combinations have been developed in the last few years which tout or promise to provide same or better performance as hydrazine while being "non-toxic" or "green". Yet, there is no consistent definition for what constitutes "non-toxic" or "green", and thus no good figure of merit for which to compare. This paper seeks to review the three major categories of figures of merit, and discusses how they might be used to assess the viability of a propellant.
    Keywords: Astronautics (General); Propellants and Fuels
    Type: NASA/TM-2013-216560 , AIAA Paper 2013-3722 , E-18733 , GRC-E-DAA-TN9862 , AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit; Jul 14, 2013 - Jul 17, 2013; San Jose, CA; United States
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  • 8
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    Recommended Figures of Merit for Green Monopropellants (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Hydrazine propellant has historically been used as a rocket thruster monopropellant since the mid-1960s. Mission managers are well aware of its characteristics and performance. However, it is a known toxic chemical and a wide effort is underway to reduce and/or eliminate its use worldwide. Several new propellant combinations have been developed in the last few years which tout or promise to provide same or better performance as hydrazine while being "non-toxic" or "green". Yet, there is no consistent definition for what constitutes "non-toxic" or "green", and thus no good figure of merit for which to compare. This paper seeks to review the three major categories of figures of merit, and discusses how they might be used to assess the viability of a propellant.
    Keywords: Propellants and Fuels
    Type: NASA/TM-2013-216560 , E-18733 , GRC-E-DAA-TN9862 , International Energy Conversion Engineering Conference; Jul 15, 2013 - Jul 17, 2013; San Jose, CA; United States|AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit; Jul 15, 2013 - Jul 17, 2013; San Jose, CA; United States
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  • 9
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    Additive Manufacturing 2.0 (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Metals and Metallic Materials; Nonmetallic Materials
    Type: GRC-E-DAA-TN31588 , 2016 NASA GRC Technology Day; May 24, 2016; Cleveland, OH; United States
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  • 10
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    Subscale Validation of the Subsurface Active Filtration of Exhaust (SAFE) Approach to the NTP Ground Testing (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Nuclear thermal propulsion (NTP) has been recognized as an enabling technology for missions to Mars and beyond. However, one of the key challenges of developing a nuclear thermal rocket is conducting verification and development tests on the ground. A number of ground test options are presented, with the Sub-surface Active Filtration of Exhaust (SAFE) method identified as a preferred path forward for the NTP program. The SAFE concept utilizes the natural soil characteristics present at the Nevada National Security Site to provide a natural filter for nuclear rocket exhaust during ground testing. A validation method of the SAFE concept is presented, utilizing a non-nuclear sub-scale hydrogen/oxygen rocket seeded with detectible radioisotopes. Additionally, some alternative ground test concepts, based upon the SAFE concept, are presented. Finally, an overview of the ongoing discussions of developing a ground test campaign are presented.
    Keywords: Spacecraft Propulsion and Power; Ground Support Systems and Facilities (Space)
    Type: GRC-E-DAA-TN24477 , Joint Propulsion Conference; Jul 27, 2015 - Jul 29, 2015; Orlando, FL; United States
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