Optimal control of the Shuttle-Tethered-Subsatellite system

Alternate control laws based on an application of the linear regulator problem are developed for possible use in the operation of the Shuttle-Tethered-Subsatellite system. Control is assumed to be provided only by modulating the tension level in the tether as a function of the difference between actual and commanded tether line length, length rate, in (orbital) plane swing angle and swing angle rate. Necessary and sufficient conditions for stability of the (linear) system motion in the vicinity of its nominal local vertical orientation are developed. By proper selection of the state and control penalty matrices it is possible to obtain faster responses with no increase in maximum power levels for use in station keeping when compared with alternate control strategies. The weighting matrices are adjusted in a piecewise adaptive manner to provide control law gains in order to achieve a smooth deployment history. Successful retrievel is dependent mainly on the initial conditions and the rate at which the commanded length is reduced.     

IUE observations of hot stars

Stellar winds are found in hot and luminous stars of all types. We see evidence of these winds in P Cygni profiles of resonance lines in the UV spectral regions, and obtain density information from them, and from optical emission lines and from free-free radiation in the infrared and radio continua from the ionized plasma. Data recently acquired from the IUE satellite are now sufficient to enable us to outline the broad parameters of these winds. It is found that for the hottest stars, those of 0-type, the mass loss rate ? is proportional to L^α. A proportionality between ? and L is predicted by the theory of radiatively driven winds; the value for α is also anticipated by the details of the theory. The dispersion of individual stellar values may be due to observational uncertainty alone, but it may also suggest that other physical parameters affect the stellar winds. The kinetic energy input of the stellar winds to the interstellar medium is considerable and may, in aggregate, be of the same order as the contribution of supernovae.     

A reappraisal of the habitability of planets around M dwarf stars

Stable, hydrogen-burning, M dwarf stars make up about 75% of all stars in the Galaxy. They are extremely long-lived, and because they are much smaller in mass than the Sun (between 0.5 and 0.08 M(Sun)), their temperature and stellar luminosity are low and peaked in the red. We have re-examined what is known at present about the potential for a terrestrial planet forming within, or migrating into, the classic liquid-surface-water habitable zone close to an M dwarf star. Observations of protoplanetary disks suggest that planet-building materials are common around M dwarfs, but N-body simulations differ in their estimations of the likelihood of potentially habitable, wet planets that reside within their habitable zones, which are only about one-fifth to 1/50th of the width of that for a G star. Particularly in light of the claimed detection of the planets with masses as small as 5.5 and 7.5 M(Earth) orbiting M stars, there seems no reason to exclude the possibility of terrestrial planets. Tidally locked synchronous rotation within the narrow habitable zone does not necessarily lead to atmospheric collapse, and active stellar flaring may not be as much of an evolutionarily disadvantageous factor as has previously been supposed. We conclude that M dwarf stars may indeed be viable hosts for planets on which the origin and evolution of life can occur. A number of planetary processes such as cessation of geothermal activity or thermal and nonthermal atmospheric loss processes may limit the duration of planetary habitability to periods far shorter than the extreme lifetime of the M dwarf star. Nevertheless, it makes sense to include M dwarf stars in programs that seek to find habitable worlds and evidence of life. This paper presents the summary conclusions of an interdisciplinary workshop (http://mstars.seti.org) sponsored by the NASA Astrobiology Institute and convened at the SETI Institute.     

Hemispheric asymmetry of chemical species and its effect on stratospheric ozone: Emphasis on halogen loading

Differences between the dynamical characteristics of the northern hemisphere (NH) and southern hemisphere (SH) stratosphere (e.g., the temperature, the strength of polar vortex, and the mean meridional circulation) produce hemispherically asymmetrical distributions of chemical species. In this paper, we use global models to briefly discuss various effects on chemical species caused by this asymmetrical distribution, especially on stratospheric ozone. The role of hemispheric asymmetries in chlorine and bromine loadings on mid- and high latitude ozone depletion is particularly discussed.     

Extreme solar cycle variability in strong lines between 200 and 400 NM

Our study of solar cycle irradiance variability in the UV between 200 and 400 nm requires a detailed knowledge of the composition of the solar spectrum in this wavelength range. We compute the synthetic spectrum from 250 to 300 nm and compare it with ATLAS3 and SOLSTICE observations. Synthetic solar spectra for solar minimum and maximum conditions show large variations in broad, strong UV lines. Strong lines of FeI between 260 nm and 264 nm show increases between 0.4× and 3×in their max/min ratio. Our ``broad lines' database shows 167 lines with similar properties between 200 nm and 400 nm. Our results raise issues of the importance of such large variability in narrow bands and the difficulty of detection in measurements with spectral resolutions of 1 nm.     

A 60 GHz Phased Array System Analysis and Its Phase Shifter in a 40 nm CMOS Technology

A 60 GHz phased array system for mm-wave frequency in 5 G is introduced and a 5 bit digitally controlled phase shifter in 40 nm CMOS technology is presented. In a phased array system,the signal to noise ratio(SNR)of the receiver is improved with the beaming forming function. Therefore,the communication data rate and distance are improved accordingly. The phase shifter is the key component for achieving the beam forming function,and its resolution and power consumption are also very critical. In the second half of this paper,an analysis of phase shifter is introduced,and a 60 GHz 5 bit digitally controlled phase shifter in 40 nm complementary metal oxide semiconductor(CMOS)technology is presented. In this presented phase shifter,a hybrid structure is implemented for its advantage on lower phase deviation while keeping comparable loss. Meanwhile,this digitally controlled phase shifter is much more compact than other works. For all 32 states,the minimum phase error is 1.5°,and the maximum phase error is 6.8°. The measured insertion loss is-20.9±1 d B including pad loss at 60 GHz and the return loss is more than 10 d B over 57—64 GHz. The total chip size is 0.24 mm2 with 0 m W DC power consumption.     

Solar Ultraviolet Bursts

The term “ultraviolet (UV) burst” is introduced to describe small, intense, transient brightenings in ultraviolet images of solar active regions. We inventorize their properties and provide a definition based on image sequences in transition-region lines. Coronal signatures are rare, and most bursts are associated with small-scale, canceling opposite-polarity fields in the photosphere that occur in emerging flux regions, moving magnetic features in sunspot moats, and sunspot light bridges. We also compare UV bursts with similar transition-region phenomena found previously in solar ultraviolet spectrometry and with similar phenomena at optical wavelengths, in particular Ellerman bombs. Akin to the latter, UV bursts are probably small-scale magnetic reconnection events occurring in the low atmosphere, at photospheric and/or chromospheric heights. Their intense emission in lines with optically thin formation gives unique diagnostic opportunities for studying the physics of magnetic reconnection in the low solar atmosphere. This paper is a review report from an International Space Science Institute team that met in 2016–2017.     

The Mars Environment Analogue Platform long duration balloon flight

The MEAP (Mars Environment Analogue Platform) mission was to fly a stratospheric balloon on a semicircular trajectory around the North Pole in summer 2008. The balloon platform carried the high-resolution neutral gas mass spectrometer P-BACE (Polar Balloon Atmospheric Composition Experiment) as scientific payload. MEAP/P-BACE is a joint project between the Esrange Space Center, Sweden, the University of Bern, Switzerland and the Swedish Institute of Space Physics (IRF), Kiruna, Sweden. Mission objectives were to validate the platform for future long duration flights around the North pole, to validate the P-BACE instrument design for planetary mission applications (conditions in the Earth stratosphere are similar to the conditions at the Mars surface), to study variation of the stratospheric composition during the flight and to gain experience in balloon based mass spectrometry. All objectives were fulfilled.     

The Lunar Orbiter Laser Altimeter Investigation on the Lunar Reconnaissance Orbiter Mission

The Lunar Orbiter Laser Altimeter (LOLA) is an instrument on the payload of NASA’s Lunar Reconnaissance Orbiter spacecraft (LRO) (Chin et al., in Space Sci. Rev. 129:391–419, 2007). The instrument is designed to measure the shape of the Moon by measuring precisely the range from the spacecraft to the lunar surface, and incorporating precision orbit determination of LRO, referencing surface ranges to the Moon’s center of mass. LOLA has 5 beams and operates at 28 Hz, with a nominal accuracy of 10 cm. Its primary objective is to produce a global geodetic grid for the Moon to which all other observations can be precisely referenced.