2,869 research outputs found
Emergency egress requirements for Space Station Freedom
There is a real concern regarding the requirements for safe emergency egress from the Space Station Freedom (SSF). The possible causes of emergency are depressurization due to breach of the station hull by space debris, meteoroids, seal failure, or vent failure; chemical toxicity; and a large fire. The objectives of the current study are to identify the tasks required to be performed in emergencies, establish the time required to perform these tasks, and to review the human equipment interface in emergencies. It was found that a fixed time value specified for egress has shifted focus from the basic requirements of safe egress, that in some situations the crew members may not be able to complete the emergency egress tasks in three minutes without sacrificing more than half of the station, and that increased focus should be given to human factors aspects of space station design
Emergency egress requirements for caution and warning, logistics, maintenance, and assembly stage MB-6 of Space Station Freedom
The safety and survival of the crewmembers has been the prime concern of NASA. Previous studies have been conducted mainly for emergencies occurring during the operating mode of the fully assembled Station. The present study was conducted to evaluate the emergency requirements for the caution and warning, logistics, maintenance, and assembly stage MB-6 of the Station in space. Effective caution and warning is essential to achieve safe egress in emergencies. In order to survive a long period in space, the safety and emergency requirements for maintenance, logistics, and extravehicular assembly operation in space must be met
Emergency egress requirements for Space Station Freedom
An objective was to determine if the pressurized elements and hatchways of the Space Station Freedom support the emergency egress of crewmembers during operation of the station at the stage of Permanently Manned Capacity. Emergency egress was defined as the exit from a pressurized element when an event occurs which makes that element uninhabitable. The possible egress paths for four emergency scenarios considered were: (1) accident occurs in a module and crewmembers translate to the attached node; (2) accident occurs at a node and crewmembers translate through it to the safe node; (3) accident occurs at a module close to a node and crewmembers are not able to translate through the affected area; and (4) accident occurs at a node and crewmembers cannot translate through it. The structural design of the pressurized elements and the hatches studied is adequate for the emergence egress translation requirement. The current location of a few racks may cause some obstruction for egress to the orbiter. The egress time required in the worst situation is estimated to be about 3 mins. There is a chance of getting crewmembers trapped in a module in case of a severe accident. Aids are needed for emergency egress translation
X-Ray Eclipse Timing in the LMXB EXO0748-676
Orbital period changes are an important diagnostic for understanding low mass
X-ray binary (LMXB) accretion-induced angular momentum exchange and overall
system evolution. We present our most recent results for the eclipse timing of
the LMXB EXO0748-676. Since its discovery in 1985 it has apparently undergone
three distinct orbital period "epochs", each characterized by a different
orbital period than the previous epoch. We outline the orbital period behavior
for EXO0748-676 over the past 18 years and discuss the implications of this
behavior in light of current theoretical ideas for LMXB evolution.Comment: 4 Pages, 3 Figures, Submitted to the X-Ray Timing 2003: Rossi and
Beyond conference, November 200
Possible Magnetic Activity in the Low Mass X-ray Binary EXO 0748-676
We report evidence of magnetic activity associated with the secondary star in
the EXO 0748-676 low mass X-ray binary system. An analysis of a sequence of
five consecutive X-ray eclipses observed during December 2003 with the RXTE
satellite brings out a feature occurring during ingress we interpret as the
X-ray photoelectric absorption shadow, as seen by an observer at Earth, of a
plasma structure suspended above the surface of the secondary star. The light
curve feature consists of an initial drop in count rate to near zero (the
absorption shadow) with a very short rebound to a significant fraction of the
pre-ingress count rate and then a final plunge to totality over a total time
scale of ~25 s. The ingress feature persists for at least 5 consecutive orbital
periods (a total of ~19 hr), and possibly up to 5 days in our data. Our data
also show significant post-egress dipping during this eclipse sequence, unusual
for this source, indicating possible secondary star mass ejection during this
episode.Comment: Accepted by Astrophysical Journal Letters; 11 Pages including 3
figures and 1 tabl
Pulsar Timing with the Fermi LAT
We present an overview of precise pulsar timing using data from the Large
Area Telescope (LAT) on Fermi. We describe the analysis techniques including a
maximum likelihood method for determining pulse times of arrival from unbinned
photon data. In addition to determining the spindown behavior of the pulsars
and detecting glitches and timing noise, such timing analyses allow the precise
determination of the pulsar position, thus enabling detailed multiwavelength
follow up.Comment: 6 page, 3 figures, to appear in AIP Conference Proceedings of Pulsar
Conference 2010 "Radio Pulsars: a key to unlock the secrets of the Universe",
Sardinia, October 201
A Strong X-Ray Burst from the Low Mass X-Ray Binary EXO0748-676
We have observed an unusually strong X-ray burst as a part of our regular
eclipse timing observations of the low mass binary system EXO0748-676. The
burst peak flux was 5.2x10^-8 ergs cm^-2 s^-1, approximately five times the
normal peak X-ray burst flux observed from this source by RXTE. Spectral fits
to the data strongly suggest that photospheric radius expansion occurred during
the burst. In this Letter we examine the properties of this X-ray burst, which
is the first example of a radius expansion burst from EXO0748-676 observed by
RXTE. We find no evidence for coherent burst oscillations. Assuming that the
peak burst luminosity is the Eddington luminosity for a 1.4 solar mass neutron
star we derive a distance to EXO0748-676 of 7.7 kpc for a helium-dominated
burst photosphere and 5.9 kpc for a hydrogen-dominated burst photosphere.Comment: 15 pages including 2 figures and 1 table. Accepted for publication in
the Astrophysical Journa
Looking for Stars and Finding the Moon: Effects of Lunar Gamma-ray Emission on Fermi LAT Light Curves
We are conducting a search for new gamma-ray binaries by making high
signal-to-noise light curves of all cataloged Fermi LAT sources and searching
for periodic variability using appropriately weighted power spectra. The light
curves are created using a variant of aperture photometry where photons are
weighted by the probability that they came from the source of interest. From
this analysis we find that the light curves of a number of sources near the
ecliptic plane are contaminated by gamma-ray emission from the Moon. This shows
itself as modulation on the Moon's sidereal period in the power spectra. We
demonstrate that this contamination can be removed by excluding times when the
Moon was too close to a source. We advocate that this data screening should
generally be used when analyzing LAT data from a source located close to the
path of the Moon.Comment: 2012 Fermi Symposium proceedings - eConf C12102
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