149 research outputs found
EPA/ECLSS consumables analyses for the Spacelab 1 flight
The results of electrical power system (EPS) and environmental control/life support system (ECLSS) consumables analyses of the Spacelab 1 mission are presented. The analyses were performed to assess the capability of the orbiter systems to support the proposed mission and to establish the various non propulsive consumables requirements. The EPS analysis was performed using the shuttle electrical power system (SEPS) analysis computer program. The ECLSS analysis was performed using the shuttle environmental consumables requirements evaluation tool (SECRET) program
Electrical-power-system data base for consumables analysis. Volume 1: Electrical equipment list, activity blocks, and time lines
A standardized data base is described which consists of a space shuttle electrical equipment list, activity blocks defining electrical equipment utilization, and activity-block time lines for specific mission analyses. Information is presented to facilitate utilization of the data base, to provide the basis for the electrical equipment utilization to enable interpretation of analyses based on the data contained herein
Electrical-power-system data base for consumables analysis. Volume 2: Electrical equipment utilization
A catalogue is presented of space shuttle electrical equipment as used within a standardized data base for EPS consumables analyses. The general function and expected usage of each type of electrical equipment are described, and the usage of specific equipment of each type in the performance of EPS consumables analyses is defined
EPS analysis of nominal STS-1 flight
The results of electrical power system (EPS) analysis of the planned Shuttle Transportation System Flight 1 mission are presented. The capability of the orbiter EPS to support the planned flight and to provide program tape information and supplementary data specifically requested by the flight operations directorate was assessed. The analysis was accomplished using the orbiter version of the spacecraft electrical power simulator program, operating from a modified version of orbiter electrical equipment utilization baseline revision four. The results indicate that the nominal flight, as analyzed, is within the capabilities of the orbiter power generation system, but that a brief, and minimal, current overload may exist between main distributor 1 and mid power controlled 1, and that inverter 9 may the overloaded for extended periods of time. A comparison of results with launch commit criteria also indicated that some of the presently existing launch redlines may be violated during the terminal countdown
Electrical power requirements analysis. Single failure tolerant entry
The results of an analysis of the orbiter electrical power system for the case of a single failure tolerant (SFT) entry are presented. The analysis was performed using the shuttle electrical power system analysis computer program. It was performed to permit assessment of the capability of the orbiter systems to support the proposed entry configuration and to provide the data necessary to identify potential constraints and limitations. Three contingency modes have been identified which would require an SFT entry. This analysis addresses an SFT entry resulting from the loss of two fuel cell powerplants, while on orbit. The results of the analysis indicate that, even under near optimum conditions, the fuel cell power demand will exceed the tested operating capacity of 16 kw, and that various electrical components may experience voltages below 24 VDC
Gas-phase CO2 emission toward Cepheus A East: the result of shock activity?
We report the first detection of gas-phase CO2 emission in the star-forming
region Cepheus A East, obtained by spectral line mapping of the v2 bending mode
at 14.98 micron with the Infrared Spectrograph (IRS) instrument onboard the
Spitzer Space Telescope. The gaseous CO2 emission covers a region about 35'' x
25'' in extent, and results from radiative pumping by 15 micron continuum
photons emanating predominantly from the HW2 protostellar region. The gaseous
CO2 exhibits a temperature distribution ranging from 50 K to 200 K. A
correlation between the gas-phase CO2 distribution and that of H2 S(2), a
tracer of shock activity, indicates that the CO2 molecules originate in a cool
post-shock gas component associated with the outflow powered by HW2. The
presence of CO2 ice absorption features at 15.20 micron toward this region and
the lack of correlation between the IR continuum emission and the CO2 gas
emission distribution further suggest that the gaseous CO2 molecules are mainly
sputtered off grain mantles -- by the passage of slow non-dissociative shocks
with velocities of 15-30 km/s -- rather than sublimated through grain heating.Comment: 11 pages, 6 figures, accepted for publication in ApJ
Spitzer observations of HH54 and HH7-11: mapping the H2 ortho-to-para ratio in shocked molecular gas
We report the results of spectroscopic mapping observations carried out
toward the Herbig-Haro objects HH7-11 and HH54 over the 5.2 - 37 micron region
using the Infrared Spectrograph of the Spitzer Space Telescope. These
observations have led to the detection and mapping of the S(0) - S(7) pure
rotational lines of molecular hydrogen, together with emissions in fine
structure transitions of Ne+, Si+, S, and Fe+. The H2 rotational emissions
indicate the presence of warm gas with a mixture of temperatures in the range
400 - 1200 K, consistent with the expected temperature behind nondissociative
shocks of velocity ~ 10 - 20 km/s, while the fine structure emissions originate
in faster shocks of velocity 35 - 90 km/s that are dissociative and ionizing.
Maps of the H2 line ratios reveal little spatial variation in the typical
admixture of gas temperatures in the mapped regions, but show that the H2
ortho-to-para ratio is quite variable, typically falling substantially below
the equilibrium value of 3 attained at the measured gas temperatures. The
non-equilibrium ortho-to-para ratios are characteristic of temperatures as low
as ~ 50 K, and are a remnant of an earlier epoch, before the gas temperature
was elevated by the passage of a shock. Correlations between the gas
temperature and H2 ortho-to-para ratio show that ortho-to-para ratios < 0.8 are
attained only at gas temperatures below ~ 900 K; this behavior is consistent
with theoretical models in which the conversion of para- to ortho-H2 behind the
shock is driven by reactive collisions with atomic hydrogen, a process which
possesses a substantial activation energy barrier (E_A/k ~ 4000 K) and is
therefore very inefficient at low temperature.Comment: 45 pages, including 16 figures. Accepted for publication in Ap
Fully Sampled Maps of Ices and Silicates in Front of Cepheus A East with Spitzer
We report the first fully sampled maps of the distribution of interstellar
CO2 ices, H2O ices and total hydrogen nuclei, as inferred from the 9.7 micron
silicate feature, toward the star-forming region Cepheus A East with the IRS
instrument onboard the Spitzer Space Telescope. We find that the column density
distributions for these solid state features all peak at, and are distributed
around, the location of HW2, the protostar believed to power one of the
outflows observed in this star-forming region. A correlation between the column
density distributions of CO2 and water ice with that of total hydrogen
indicates that the solid state features we mapped mostly arise from the same
molecular clumps along the probed sight lines. We therefore derive average CO2
ice and water ice abundances with respect to the total hydrogen column density
of X(CO2)_ice~1.9x10^-5 and X(H2O)_ice~7.5x10^-5. Within errors, the abundances
for both ices are relatively constant over the mapped region exhibiting both
ice absorptions. The fraction of CO2 ice with respect to H2O ice is also
relatively constant at a value of 22% over that mapped region. A clear
triple-peaked structure is seen in the CO2 ice profiles. Fits to those profiles
using current laboratory ice analogs suggest the presence of both a
low-temperature polar ice mixture and a high-temperature methanol-rich ice
mixture along the probed sightlines. Our results further indicate that thermal
processing of these ices occurred throughout the sampled region.Comment: 26 pages, 8 figures, accepted for publication in Ap
New Young Brown Dwarfs in the Orion Molecular Cloud 2/3 Region
Forty new low mass members with spectral types ranging from M4-M9 have been
confirmed in the Orion Molecular Cloud 2/3 region. Through deep, I, z', J, H, K
photometry of a 20' x 20' field in OMC 2/3, we selected brown dwarf candidates
for follow-up spectroscopy. Low resolution far-red and near-infrared spectra
were obtained for the candidates, and 19 young brown dwarfs in the OMC 2/3
region are confirmed. They exhibit spectral types of M6.5-M9, corresponding to
approximate masses of 0.075-0.015 M_solar using the evolutionary models of
Baraffe et al. (1998). At least one of these bona fide young brown dwarfs has
strong Halpha emission, indicating that it is actively accreting. In addition,
we confirm 21 new low mass members with spectral types of M4-M6, corresponding
to approximate masses of 0.35-0.10 M_solar in OMC 2/3. By comparing pre-main
sequence tracks to the positions of the members in the H-R diagram, we find
that most of the brown dwarfs are less than 1 Myr, but find a number of low
mass stars with inferred ages greater than 3 Myr. The discrepancy in the
stellar and substellar ages is due to our selection of only low luminosity
sources; however, the presence of such objects implies the presence of an age
spread in the OMC 2/3 region. We discuss possible reasons for this apparent age
spread.Comment: Accepted for publication in ApJ. 52 pages, 17 figures, 4 tables; main
body: 23 page
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