61,887 research outputs found
Structural design of a vertical antenna boresight 18.3 by 18.3-m planar near-field antenna measurement system
A large very precise near-field planar scanner was proposed for NASA Lewis Research Center. This scanner would permit near-field measurements over a horizontal scan plane measuring 18.3 m by 18.3 m. Large aperture antennas mounted with antenna boresight vertical could be tested up to 60 GHz. When such a large near field scanner is used for pattern testing, the antenna or antenna system under test does not have to be moved. Hence, such antennas and antenna systems can be positioned and supported to simulate configuration in zero g. Thus, very large and heavy machinery that would be needed to accurately move the antennas are avoided. A preliminary investigation was undertaken to address the mechanical design of such a challenging near-field antenna scanner. The configuration, structural design and results of a parametric NASTRAN structural optimization analysis are contained. Further, the resulting design was dynamically analyzed in order to provide resonant frequency information to the scanner mechanical drive system designers. If other large near field scanners of comparable dimensions are to be constructed, the information can be used for design optimization of these also
A mission to test the Pioneer anomaly: estimating the main systematic effects
We estimate the main systematic effects relevant in a mission to test and
characterize the Pioneer anomaly through the flight formation concept, by
launching probing spheres from a mother spacecraft and tracking their motion
via laser ranging.Comment: 9 pages, 1 table, 2 figures; based on a talk presented by one of us
(O.B.) at the 2nd. Pioneer Anomaly Group Meeting at the International Space
Science Institute, 19-23 February 200
I.C.E.: a Transportable Atomic Inertial Sensor for Test in Microgravity
We present our the construction of an atom interferometer for inertial
sensing in microgravity, as part of the I.C.E. (\textit{Interf\'{e}rom\'{e}trie
Coh\'{e}rente pour l'Espace}) collaboration. On-board laser systems have been
developed based on fibre-optic components, which are insensitive to mechanical
vibrations and acoustic noise, have sub-MHz linewidth, and remain frequency
stabilised for weeks at a time. A compact, transportable vacuum system has been
built, and used for laser cooling and magneto-optical trapping. We will use a
mixture of quantum degenerate gases, bosonic Rb and fermionic K,
in order to find the optimal conditions for precision and sensitivity of
inertial measurements. Microgravity will be realised in parabolic flights
lasting up to 20s in an Airbus. We show that the factors limiting the
sensitivity of a long-interrogation-time atomic inertial sensor are the phase
noise in reference frequency generation for Raman-pulse atomic beam-splitters
and acceleration fluctuations during free fall
Development of a high brightness ultrafast Transmission Electron Microscope based on a laser-driven cold field emission source
We report on the development of an ultrafast Transmission Electron Microscope
based on a cold field emission source which can operate in either DC or
ultrafast mode. Electron emission from a tungsten nanotip is triggered by
femtosecond laser pulses which are tightly focused by optical components
integrated inside a cold field emission source close to the cathode. The
properties of the electron probe (brightness, angular current density,
stability) are quantitatively determined. The measured brightness is the
largest reported so far for UTEMs. Examples of imaging, diffraction and
spectroscopy using ultrashort electron pulses are given. Finally, the potential
of this instrument is illustrated by performing electron holography in the
off-axis configuration using ultrashort electron pulses.Comment: 23 pages, 9 figure
Technology requirements of exploration beyond Neptune by solar sail propulsion
This paper provides a set of requirements for the technology development of a solar sail propelled Interstellar Heliopause Probe mission. The mission is placed in the context of other outer solar systems missions, ranging from a Kuiper Belt mission through to an Oort cloud mission. Mission requirements are defined and a detailed parametric trajectory analysis and launch date scan performed. Through analysis of the complete mission trade space a set of critical technology development requirements are identified which include an advanced lightweight composite High-Gain Antenna, a high-efficiency Ka-band travelling-wave tube amplifier and a radioisotope thermoelectric generator with power density of approximately 12 W/kg. It is also shown that the Interstellar Heliopause Probe mission necessitates the use of a spinning sail, limiting the direct application of current hardware development activities. A Kuiper Belt mission is then considered as a pre-curser to the Interstellar Heliopause Probe, while it is also shown through study of an Oort cloud mission that the Interstellar Heliopause Probe mission is the likely end-goal of any future solar sail technology development program. As such, the technology requirements identified to enable the Interstellar Heliopause Probe must be enabled through all prior missions, with each mission acting as an enabling facilitator towards the next
3D Energy Harvester Evaluation
This paper discusses the characterization and evaluation of an MEMS based electrostatic generator, a part of the power supply unit of the self-powered microsystem[1,2,3]. The designed generator is based on electrostatic converter and uses the principle of conversion of non-electric energy into electrical energy by periodical modification of gap between electrodes of a capacitor [4]. The structure is designed and modeled as three-dimensional silicon based MEMS. Innovative approach involving the achievement of very low resonant frequency of the structure (about 100Hz) by usage of modified long cantilever spring design, minimum area of the chip, 3D work mode, the ability to be tuned to reach desired parameters, proves promising directions of possible further development
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