Engineering topics
Hansen, D.
Publications and source records attributed to Hansen, D..
Measurement of carbon condensates using small-angle x-ray scattering during detonation of the high explosive hexanitrostilbene
The dynamics of carbon condensation in detonating high explosives remains controversial. Detonation model validation requires data for processes occurring at nanometer length scales on time scales ranging from nanoseconds to microseconds. A new detonation endstation has been commissioned to acquire and provide time-resolved small-angle x-ray scattering (SAXS) from detonating explosives. Hexanitrostilbene (HNS) was selected as the first to investigate due to its ease of initiation using exploding foils and flyers, vacuum compatibility, high thermal stability, and stoichiometric carbon abundance that produces high carbon condensate yields. The SAXS data during detonation, collected with 300 ns time resolution, provide unprecedented signal fidelity over a broad q-range. This fidelity permits the first analysis of both the Guinier and Porod/power-law regions of the scattering profile during detonation, which contains information about the size and morphology of the resultant carbon condensate nanoparticles. To bolster confidence in these data, the scattering angle and intensity were additionally cross-referenced with a separate, highly calibrated SAXS beamline. The data show that HNS produces carbon particles with a radius of gyration of 2.7 nm in less than 400 ns after the detonation front has passed, and this size and morphology are constant over the next several microseconds. These data directly contradict previous pioneering work on RDX/TNT mixtures and TATB, where observations indicate significant particle growth (50% or more) continues over several microseconds. The power-law slope is about −3, which is consistent with a complex disordered, irregular, or folded sp{sup 2} sub-arrangement within a relatively monodisperse structure possessing radius of gyration of 2.7 nm after the detonation of HNS.
A method to determine fault vectors in 4H-SiC from stacking sequences observed on high resolution transmission electron microscopy images
A new method has been developed to determine the fault vectors associated with stacking faults in 4H-SiC from their stacking sequences observed on high resolution TEM images. This method, analogous to the Burgers circuit technique for determination of dislocation Burgers vector, involves determination of the vectors required in the projection of the perfect lattice to correct the deviated path constructed in the faulted material. Results for several different stacking faults were compared with fault vectors determined from X-ray topographic contrast analysis and were found to be consistent. This technique is expected to applicable to all structures comprising corner shared tetrahedra.
In-flight testing of onboard UHF equipment
This paper proposes a plan to allow future flight projects to accomplish in-flight testing of on-board UHF equipment which the spacecraft carries for local relay link use at planet Mars only. This plan relies on onboard self-testing to verify receiver functional capabilities at various data rates, and on RF testing with narrow band CW signals transmitted at selected frequencies from an Earth station, non-interfering to existing UHF users, to verify the RF performance of antenna and microwave equipment. The Mars mission planners at JPL have accepted this concept as reasonable. The plan will be practical to implement with a frequency agile local link transceiver, like the next generation UHF transceiver being developed at JPL. The user can test it at one frequency and operate it at a different frequency within the operating range. Possible frequencies for uplink testing are identified. Further effort is needed to select specific test frequencies that will be agreeable to the users to which these bands are allocated.
Frequencies for Mars local high rate link
This paper looks at the options for frequency bands for higher rate links for the next five to ten years.
Frequencies for Mars local communications
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Venus Aerobot Multisonde Mission: Atmospheric Relay for Imaging the Surface of Venus
Robotic exploration of surface of Venus presents many challenges because of thick atmosphere, high surface pressure and temperature.
High Resolution UV Emission Spectroscopy of Molecules Excited by Electron Impact
Photodissociation via discrete line absorption into predissociating Rydberg and valence states is the dominant destruction mechanism of CO and other molecules in the interstellar medium and molecular clouds.