SpinSat Mission Overview
Abstract : The SpinSat flight is a small satellite mission proposed by the Naval Research Laboratory and Digital Solid State Propulsion (DSSP) LLC to demonstrate and characterize the on-orbit performance of electrically controlled solid propellant technology in space. This is an enabling technology for the small satellite community that will allow small satellites to perform maneuvers. The mission consists of a spherical spacecraft fitted with Electrically Controlled Solid Propellant thrusters and retro-reflectors for satellite laser ranging (SLR). The spacecraft will be deployed from the International Space Station. This paper presents a mission overview and emphasis will be placed on the design, thruster design, optical layout, and unique SSA observation opportunities of the mission.
A Spherical Micro Satellite Design and Detection Method for Upper Atmospheric Density Estimation
A spherical microsatellite, aimed at technology verification of upper atmospheric density detection and precision orbit determination in low Earth orbit (LEO), has been developed by Tsinghua University and is scheduled to launch in the second half of 2019. In order to reduce the influence of other nonconservative forces, the area-to-mass ratio of the satellite was designed to ensure that the aerodynamic drag of the satellite is more than one to two orders of magnitude greater than the solar pressure perturbation. The influence of the components of the antenna, separation support, and solar cell arrays (SCAs) on the spherical structure for the area-to-mass ratio is reduced by reasonable design of the satellite flight attitude. In addition, a novel method has been developed to estimate and correct the parameters for atmospheric density (correlated to the drag) calculation, using precise orbit data (POD) obtained from an onboard dual-frequency global position system (GPS) receiver. The method is used to obtain the partial derivative of the total acceleration of the satellite to the initial state (position, velocity) and Harris-Priester (HP) density model parameters (antapex and apex density). Further, the least squares estimation method is used to solve the overdetermined linear equations and obtain the change of initial state of the satellite and the HP density model parameters relative to change of the satellite state. The validity of this method has been verified through numerical simulations with the parametric setup of the satellite. The estimated density precision was found to be higher than two to three orders of the initial HP density model with continuous iteration.
BIOSYNTHESIS OF DAUNORUBICIN GLYCOSIDES: ANALYSIS WITH BLOCKED MUTANTS
ABSTRACT Daunorubicin (daunomycin; NSC 82151) is an anthracycline antibiotic that is useful in the treatment of human leukemias. Several Streptomyces species accumulate higher glycosides of daunorubicin, which can be converted to daunorubicin by simple hydrolysis. We isolated a number of mutants of a daunorubicin glycoside-producing streptomycete, and found that some were deficient in accumulation of daunorubicin glycosides. One such mutant accumulated no detectable anthracyclines, while other mutants accumulated anthracyclines or aglycones that have not been reported before or have been described as co-metabolites of daunorubicin glycosides. Some of these anthracyclines and aglycones were purified and used as substrates in bioconversion experiments with various mutants. The results allowed us to construct a proposed pathway for the biosynthesis of daunorubicin glycosides by this streptomycete. KEYWORDS Anthracycline; daunorubicin; biosynthesis; blocked mutants; biotransformation.