2,214 research outputs found
Propulsion system advances that enable a reusable Liquid Fly Back Booster (LFBB)
This paper provides an overview of the booster propulsion system for the Liquid Fly Back Booster (LFBB). This includes, system requirements, design approach, concept of operations, reliability, safety and cost assumptions. The paper summarizes the findings of the Boeing propulsion team that has been studying the LFBB feasibility as a booster replacement for the Space Shuttle. This paper will discuss recent advances including a new generation of kerosene and oxygen rich pre-burner staged combustion cycle main rocket engines. The engine reliability and safety is expected to be much higher than current standards by adding extra operating margins into the design and normally operating the engines at 75% of engine rated power. This allows for engine out capability. The new generation of main engines operates at significantly higher chamber pressure than the prior generation of gas generator cycle engines. The oxygen rich pre-burner engine cycle, unlike the fuel rich gas generator cycle, results in internally self-cleaning firings which facilitates reusability. Maintenance is further enhanced with integrated health monitoring to improve safety and turn-around efficiency. The maintainability of the LFBB LOX/kerosene engines is being improved by designing the vehicle/engine interfaces for easy access to key engine components
Multiple Cyclotron Lines in the Spectrum of 4U 0115+63
We report phase resolved spectroscopy of the transient accreting pulsar,
4U0115+63. For the first time, more than two cylotron resonance scattering
features are detected in the spectrum of an X-ray pulsar. The shape of the
fundamental line appears to be complex, and this is in agreement with
predictions of Monte-Carlo models. As in other pulsars, the line energies and
optical depths are strong functions of pulse phase. One possible model for this
is an offset of the dipole of the neutron star magnetic field.Comment: 5 pages. To appear in "Proceedings of the 5th Compton Symposium
Disappearing Pulses in Vela X-1
We present results from a 20 h RXTE observation of Vela X-1, ncluding a
peculiar low state of a few hours duration, during which the pulsation of the
X-ray emission ceased, while significant non-pulsed emission remained. This
``quiescent state'' was preceded by a ``normal state'' without any unusual
signs and followed by a ``high state'' of several hours of increased activity
with strong, flaring pulsations. while there is clear spectral evolution from
the normal state to the low state, the spectra of the following high state are
surprisingly similar to those of the low state.Comment: 5 pages, 5 figures, Proceedings of the 5th Compton Symposium, AIP, in
pres
Discovery of a Cyclotron Resonance Scattering Feature in the X-ray Spectrum of XTE J1946+274
Observations of the transient accreting pulsar XTE J1946+274 made with the
Rossi X-ray Timing Explorer during the course of the 1998 September-November
outburst, reveal a cyclotron resonance scattering feature (or "cyclotron line")
in the hard X-ray spectrum near 35 keV. We determine a centroid energy of 36.2
+0.5/-0.7 keV, which implies a magnetic field strength of 3.1(1+z)x10^12 G,
where z is the gravitational redshift of the scattering region. The optical
depth, Tau = 0.33 +0.07/-0.06, and width, sigma = 3.37 +0.92/-0.75 keV, are
typical of known cyclotron lines in other pulsars. This discovery makes XTE
J1946+274 one of thirteen pulsars with securely detected cyclotron lines
resulting in direct magnetic field measurements.Comment: Five pages including four postscript figures and two tables. Uses
emulateapj5. Published in ApJ Letters:
http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001ApJ...563L..35
Discovery of a New 89 Second X-ray Pulsar XTE J1906+09
We report on the discovery of a new pulsating X-ray source during Rossi X-ray
Timing Explorer observations of a low galactic latitude field centered at RA
(J2000) = 19 hr 05 m 43 s and Dec (J2000) = +08 deg 58 arcmin 48 arcsec.
Significant pulsations were detected by both the PCA and HEXTE instruments
aboard RXTE at a fundamental period of 89.17 +/- 0.02 seconds, with higher
harmonics also visible in the 2-10 keV power spectrum. The folded lightcurve
from the source is multiply peaked at lower energies, and changes to single
peaked morphology above ~20 keV. The phase averaged spectrum from the source is
well fit by strongly absorbed power law or thermal bremsstrahlung spectral
models of photon index 1.9 +/- 0.1 or temperature 19.5 +/- 4.6 keV,
respectively. The mean neutral hydrogen column density is approximately 10^23
cm^-2, suggesting a distance of >10 kpc to the source and a minimum 2-10 keV
X-ray luminosity of 2*10^{35} ergs s^{-1}. By comparison with other pulsars
with similar periods and luminosities, we suggest that XTE J1906+09 has a
supergiant companion with an underfilled Roche lobe. We speculate further that
one of the M stars in a peculiar M star binary system may be the companion.Comment: 14 pages, 2 figures. Accepted by ApJ Letter
Rapid Communication: MspI Restriction Fragment Length Polymorphism at the Swine MYF6 Locus
Source and Description of Probe. A 1,296-bp rat cDNA clone for MRF4 (also called MYF6) was excised from the EcoRI site of the plasmid pBluescript KS+ (Rhodes and Konieczny, 1989
Stability of the Cyclotron Resonance Scattering Feature in Her X-1 with RXTE
Five observations of the hard X-ray spectrum of Her X-1 from \xte show that
the keV energy of the cyclotron scattering line is constant within
statistics of a few percent per observtion. Comparison with other observations
over many years indicates strongly that the centroid energy of this absorption
line has increased some time between 1991 and 1993 by 23%, from 34 keV to 41
keV. Moreover, the cutoff energy of the spectral continuum increased at the
same time from 16 keV to 20 keV, which is, within the statistical error of 5%,
in direct proportion to the centroid. This may be a sign thatboth these
characteristics of the spectrum are controlled in the same way by the magnetic
field strength in the region of scattering.Comment: 30 page, 5 figure
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