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  • 1
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    A supersensitive accelerometer for spacecraft gradiometry (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: An exact knowledge of the earth's gravity field is needed for advanced studies related to solid earth and ocean physics. A study (GRAVSAT-A) is currently considered by NASA to determine the gravity field with an accuracy of 2-3 mgal change and a resolution of 100 km using satellite to satellite range rate tracking techniques. The present investigation has the objective to prepare the foundation of an advanced GRAVSAT-B mission in the 1990s with an accuracy of about 1 mgal and a resolution of about 50 km. It is possible that satellite to satellite tracking will not be able to satisfy these requirements. However, it appears that a new technology, called "high sensitivity gradient gradiometry", could be employed to achieve the aims of the GRAVSAT-B mission. Attention is given to a new type of gravity gradiometer using superconducting microwave cavity oscillator accelerometers.
    Keywords: SPACECRAFT INSTRUMENTATION
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    The performance of NASA research hydrogen masers (1980)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Field operable hydrogen masers based on prior maser designs are presented. These units incorporate improvements in magnetic shielding, lower noise electronics, better thermal control, and have a microprocessor for operation, monitoring, and diagnostic functions. They are ruggedly built for transportability and ease of service anywhere in the world.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Radio Interferometry; p 223-240
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    NASA TECHNICAL REPORTS
  • 3
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    A modular multiple use system for precise time and frequency measurement and distribution (1978)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A modular CAMAC based system is described which was developed to meet a variety of precise time and frequency measurement and distribution needs. The system was based on a generalization of the dual mixer concept. By using a 16 channel 100 ns event clock, the system can intercompare the phase of 16 frequency standards with subpicosecond resolution. The system has a noise floor of 26 fs and a long term stability on the order of 1 ps or better. The system also used a digitally controlled crystal oscillator in a control loop to provide an offsettable 5 MHz output with subpicosecond phase tracking capability. A detailed description of the system is given including theory of operation and performance. A method to improve the performance of the dual mixer technique is discussed when phase balancing of the two input ports cannot be accomplished.
    Keywords: PHYSICS (GENERAL)
    Type: Proc. of the Tenth Ann. Precise Time and Time Interval (PTTI) Appl. and Planning Meeting; p 293-315
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    NASA TECHNICAL REPORTS
  • 4
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    The NASA/GSFC hydrogen maser program: A review of recent data (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Data is presented on the phase and frequency stability, over time periods extending to one week, of the new NR field operable hydrogen masers developed by the Applied Physics Laboratory (APL) and the older NX and NP field operable hydrogen masers developed by Goddard Space Flight Center and maintained and upgraded by Bendix Field Engineering Corporation (BFEC). Data is presented on the NR masers in the laboratory showing frequency stabilities well into the 10 to the -15th power range and phase stabilities well into the 100 ps range for periods of up to one day. Data is presented on upgraded NP masers in the laboratory showing that the frequency stability has been improved substantially to virtually the NR level. VLBI data is presented on the phase difference between NX-2 at Owens Valley, California and NR-2 at Fort Davis, Texas for a one week period showing, after removal of a constant frequency drift, a 350 ps RMS phase stability.
    Keywords: LASERS AND MASERS
    Type: Proc. of the 14th Ann. Precise Time and Time Interval (PTTI) Appl. Planning Meeting; p 421-450
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    NASA TECHNICAL REPORTS
  • 5
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    Recent progress in the NASA-Goddard Space Flight Center atomic hydrogen standards program (1981)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: At NASA Goddard Space Flight Center and through associated contractors, a broad spectrum of work is being carried out to develop improved hydrogen maser frequency standards for field use, improved experimental hydrogen maser frequency standards, and improved frequency and time distribution and measurement systems for hydrogen maser use. Recent progress in the following areas is reported: results on the Nr masers built by the Applied Physics Laboratory of Johns Hopkins University, the development of a low cost hydrogen maser at Goddard Space Flight Center, and work on a low noise phase comparison system and digitally phase locked crystal oscillator called the distribution and measurement system.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Proc. of the 12th Ann. Precise Time and Time Interval Appl. and Planning Meeting; p 463-493
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    NASA TECHNICAL REPORTS
  • 6
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    Nanosecond time transfer via shuttle laser ranging experiment (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Keywords: LASERS AND MASERS
    Type: Proc. of the 9th Ann. Precise Time and Time Interval (PTTI) Appl. and Planning Meeting; p 319-342
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    NASA TECHNICAL REPORTS
  • 7
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    High stability buffered phase comparator (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A low noise RF signal phase comparator comprised of two high stability driver buffer amplifiers driving a double balanced mixer which operate to generate a beat frequency between the two RF input signals coupled to the amplifiers from the RF sources is described. The beat frequency output from the mixer is applied to a low noise zero crossing detector which is the phase difference between the two RF inputs. Temperature stability is provided by mounting the amplifiers and mixer on a common circuit board with the active circuit elements located on one side of a circuit board and the passive circuit elements located on the opposite side. A common heat sink is located adjacent the circuit board. The active circuit elements are embedded into the bores of the heat sink which slows the effect of ambient temperature changes and reduces the temperature gradients between the active circuit elements, thus improving the cancellation of temperature effects. The two amplifiers include individual voltage regulators, which increases RF isolation.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
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    NASA TECHNICAL REPORTS
  • 8
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    Precise Phase Comparator for Nearly Equal Frequencies (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: New circuit precisely compares phases of two RF signals nearly equal in frequency, such as two hydrogen-maser frequency standards. Measuring circuit minimizes interactions between two sources. Also stabilized against thermal effects and against noise that could produce erroneous readings. Heat sinking, buffer amplifiers, and low-noise zero-crossing detector make picosecond precision possible.
    Keywords: ELECTRONIC COMPONENTS AND CIRCUITS
    Type: GSC-12645 , NASA Tech Briefs (ISSN 0145-319X); 6; 3; P. 252
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    NASA TECHNICAL REPORTS
  • 9
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    NASA atomic hydrogen standards program: An update (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Comparisons are made between the NP series and the NX series of hydrogen masers. A field operable hydrogen maser (NR series) is also described. Atomic hydrogen primary frequency standards are in development stages. Standards are being developed for a hydrogen beam frequency standard and for a concertina hydrogen maser.
    Keywords: LASERS AND MASERS
    Type: NASA-TM-X-71129 , X-814-76-127
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    NASA TECHNICAL REPORTS
  • 10
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    External bulb variable volume maser (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A maser functioning as a frequency standard stable to one part in 10 to the 14th power includes a variable volume, constant surface area storage bulb having a fixed volume portion located in a resonant cavity from which the frequency standard is derived. A variable volume portion of the bulb, exterior to the resonant cavity, has a maximum volume on the same order of magnitude as the fixed volume bulb portion. The cavity has a length to radius ratio of at least 3:1 so that the operation is attained without the need for a feedback loop. A baffle plate, between the fixed and variable volume bulb portions, includes apertures for enabling hydrogen atoms to pass between the two bulb portions and is an electromagnetic shield that prevents coupling of the electromagnetic field of the cavity into the variable volume bulb portion.
    Keywords: LASERS AND MASERS
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    NASA TECHNICAL REPORTS
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