4,191 research outputs found
LSS reference platform control
The long range objective of this task is to develop basic technology in the design, mechanization, and analysis of control systems for large flexible space structures. The focus of the FY'81 platform control effort was on the pointing control problems associated with multiple independently controlled experiment packages operating simultaneously on a single platform. Particular emphasis was placed on obtaining a quantitative comparison of controller performance with and without base motion compensation
A Note on the Biology of the Mosquito, Psorophora Discolor (Coquillett), in Mississippi (Diptera: Culicidae)
Author Institution: Principal Entomologist, Sanitary Engineering Branch, Engineer Research and Development Laboratories, Fort Belvoir, Virgini
LSD and AMAZE: the mass-metallicity relation at z>3
We present the first results on galaxy metallicity evolution at z>3 from two
projects, LSD (Lyman-break galaxies Stellar populations and Dynamics) and AMAZE
(Assessing the Mass Abundance redshift Evolution). These projects use deep
near-infrared spectroscopic observations of a sample of ~40 LBGs to estimate
the gas-phase metallicity from the emission lines. We derive the
mass-metallicity relation at z3 and compare it with the same relation at
lower redshift. Strong evolution from z=0 and z=2 to z=3 is observed, and this
finding puts strong constrains on the models of galaxy evolution. These
preliminary results show that the effective oxygen yields does not increase
with stellar mass, implying that the simple outflow model does not apply at
z>3.Comment: 5 pages, to appear in the IAUS 255 conference proceedings:
"Low-Metallicity Star Formation: from the First Stars to Dwarf Galaxies",
L.K. Hunt, S. Madden and R. Schneider ed
Mariner Mars 1971 attitude control subsystem
The Mariner Mars 1971 attitude control subsystem (ACS) is discussed. It is comprised of a sun sensor set, a Canopus tracker, an inertial reference unit, two cold gas reaction control assemblies, two rocket engine gimbal actuators, and an attitude control electronics unit. The subsystem has the following eight operating modes: (1) launch, (2) sun acquisition, (3) roll search, (4) celestial cruise, (5) all-axes inertial, (6) roll inertial, (7) commanded turn, and (8) thrust vector control. In the celestial cruise mode, the position control is held to plus or minus 0.25 deg. Commanded turn rates are plus or minus 0.18 deg/s. The attitude control logic in conjunction with command inputs from other spacecraft subsystems establishes the ACS operating mode. The logic utilizes Sun and Canopus acquisition signals generated within the ACS to perform automatic mode switching so that dependence of ground control is minimized when operating in the sun acquisition, roll search, and celestial cruise modes. The total ACS weight is 65.7 lb, and includes 5.4 lb of nitrogen gas. Total power requirements vary from 9 W for the celestial cruise mode to 54 W for the commanded turn mode
Control system design for the large space systems technology reference platform
Structural models and classical frequency domain control system designs were developed for the large space systems technology (LSST) reference platform which consists of a central bus structure, solar panels, and platform arms on which a variety of experiments may be mounted. It is shown that operation of multiple independently articulated payloads on a single platform presents major problems when subarc second pointing stability is required. Experiment compatibility will be an important operational consideration for systems of this type
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