45,348 research outputs found
Hubble Space telescope thermal cycle test report for large solar array samples with BSFR cells (Sample numbers 703 and 704)
The Hubble space telescope (HST) solar array was designed to meet specific output power requirements after 2 years in low-Earth orbit, and to remain operational for 5 years. The array, therefore, had to withstand 30,000 thermal cycles between approximately +100 and -100 C. The ability of the array to meet this requirement was evaluated by thermal cycle testing, in vacuum, two 128-cell solar cell modules that exactly duplicated the flight HST solar array design. Also, the ability of the flight array to survive an emergency deployment during the dark (cold) portion of an orbit was evaluated by performing a cold-roll test using one module
Significant events in low-level flow conditions hazardous to aircraft
Atmospheric parameters recorded during high surface winds are analyzed to determine magnitude, frequency, duration, and simultaneity of occurrence of low level flow conditions known to be hazardous to the ascent and descent of conventional aircraft and the space shuttle. Graphic and tabular presentations of mean and extreme values and simultaneous occurrences of turbulence (gustiness and a gust factor), wind shear (speed and direction), and vertical motion (updrafts and downdrafts), along with associated temperature inversions are included as function of tower height, layer and/or distance for six 5 sec intervals (one interval every 100 sec) of parameters sampled simultaneously at the rate of 10 speeds, directions and temperatures per second during an approximately 10 min period
Wind speed and direction shears with associated vertical motion during strong surface winds
Strong surface winds recorded at the NASA 150-Meter Ground Winds Tower facility at Kennedy Space Center, Florida, are analyzed to present occurrences representative of wind shear and vertical motion known to be hazardous to the ascent and descent of conventional aircraft and the Space Shuttle. Graphical (percentage frequency distributions) and mathematical (maximum, mean, standard deviation) descriptions of wind speed and direction shears and associated updrafts and downdrafts are included as functions of six vertical layers and one horizontal distance for twenty 5-second intervals of parameters sampled simultaneously at the rate of ten per second during a period of high surface winds
Understanding the assembly of Kepler's compact planetary systems
The Kepler mission has recently discovered a number of exoplanetary systems,
such as Kepler-11 and Kepler-32, in which ensembles of several planets are
found in very closely packed orbits (often within a few percent of an AU of one
another). These compact configurations present a challenge for traditional
planet formation and migration scenarios. We present a dynamical study of the
assembly of these systems, using an N-body method which incorporates a
parametrized model of planet migration in a turbulent protoplanetary disc. We
explore a wide parameter space, and find that under suitable conditions it is
possible to form compact, close-packed planetary systems via traditional
disc-driven migration. We find that simultaneous migration of multiple planets
is a viable mechanism for the assembly of tightly-packed planetary systems, as
long as the disc provides significant eccentricity damping and the level of
turbulence in the disc is modest. We discuss the implications of our preferred
parameters for the protoplanetary discs in which these systems formed, and
comment on the occurrence and significance of mean-motion resonances in our
simulations.Comment: 12 pages, 4 figures, 2 tables. Accepted for publication in Monthly
Notices of the Royal Astronomical Societ
Observation of atom wave phase shifts induced by van der Waals atom-surface interactions
The development of nanotechnology and atom optics relies on understanding how
atoms behave and interact with their environment. Isolated atoms can exhibit
wave-like (coherent) behaviour with a corresponding de Broglie wavelength and
phase which can be affected by nearby surfaces. Here an atom interferometer is
used to measure the phase shift of Na atom waves induced by the walls of a 50
nm wide cavity. To our knowledge this is the first direct measurement of the de
Broglie wave phase shift caused by atom-surface interactions. The magnitude of
the phase shift is in agreement with that predicted by quantum electrodynamics
for a non-retarded van der Waals interaction. This experiment also demonstrates
that atom-waves can retain their coherence even when atom-surface distances are
as small as 10 nm.Comment: 4 pages, 4 figures, submitted to PR
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