The connection between radiation belt and auroral processes

Space Science Reviews - The aurora with its associated electric fields and energetic particles affects the structure of the ionosphere, plasmaphere, and ring current. It injects protons and heavier...     

Measuring Techniques Applied in an MHD-Augmented Shock Tunnel

The determination of the detailed performance of an MHD-augmented high-enthalphy shock tunnel requires the simultaneous measurment of a large number of aerodynamic, electrical, and electromagnetic parameters in a test time interval of the order of several hundred microseconds. In the feasibility study currently being conducted in our laboratory of such a device, an extensive measuring system was set up and evaluated, and is being used to acquire facility performance data. This paper describes this measuring system, discusses the modifications and adaptations applied to make the various components of the system operable and compatible, and gives illustrative examples of the performance of the system.     

The X-Ray Spectrometer on the MESSENGER Spacecraft

NASA’s MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) mission will further the understanding of the formation of the planets by examining the least studied of the terrestrial planets, Mercury. During the one-year orbital phase (beginning in 2011) and three earlier flybys (2008 and 2009), the X-Ray Spectrometer (XRS) onboard the MESSENGER spacecraft will measure the surface elemental composition. XRS will measure the characteristic X-ray emissions induced on the surface of Mercury by the incident solar flux. The Kα lines for the elements Mg, Al, Si, S, Ca, Ti, and Fe will be detected. The 12° field-of-view of the instrument will allow a spatial resolution that ranges from 42 km at periapsis to 3200 km at apoapsis due to the spacecraft’s highly elliptical orbit. XRS will provide elemental composition measurements covering the majority of Mercury’s surface, as well as potential high-spatial-resolution measurements of features of interest. This paper summarizes XRS’s science objectives, technical design, calibration, and mission observation strategy.     

Radiation climate map for analyzing risks to astronauts on the mars surface from galactic cosmic rays

The potential risks for late effects including cancer, cataracts, and neurological disorders due to exposures to the galactic cosmic rays (GCR) is a large concern for the human exploration of Mars. Physical models are needed to project the radiation exposures to be received by astronauts in transit to Mars and on the Mars surface, including the understanding of the modification of the GCR by the Martian atmosphere and identifying shielding optimization approaches. The Mars Global Surveyor (MGS) mission has been collecting Martian surface topographical data with the Mars Orbiter Laser Altimeter (MOLA). Here we present calculations of radiation climate maps of the surface of Mars using the MOLA data, the radiation transport model HZETRN (high charge and high energy transport), and the quantum multiple scattering fragmentation model, QMSFRG. Organ doses and the average number of particle hits per cell nucleus from GCR components (protons, heavy ions, and neutrons) are evaluated as a function of the altitude on the Martian surface. Approaches to improve the accuracy of the radiation climate map, presented here using data from the 2001 Mars Odyssey mission, are discussed.     

A Superlimiting Phased-Array Receiving System in a Two-Source Environment

The performance of a uniformly spaced phased-steered line array with element channel superlimiting is studied for far-field sources consisting of 1) two sinusoidal signals with different frequencies and angular locations, and 2) a sinusoid and a noise signal at different angular locations. Attention is focused on the nonlinear case where internal noise is negligible compared to both input signals. The analysis for the two-sinusoid case gives the precise frequencies, positions, and amplitudes of all apparent sources. In addition to the two active sources, the array output has an array of images arranged symmetrically in sine space about the larger input, at intervals equal to the spacing between the two active sources. For the case of a separated sinusoid and a noise source, the analysis shows that the angular positions and average powers of the array outputs duplicate the double-sinusoid results, but the images have noise-like spectra. The analyses are confirmed by experimental results obtained with a 60-element superlimiting X-band array.     

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.     

Oxygen Isotopes and Sampling of the Solar System

The atmospheres of the four giant planets of our Solar System share a common and well-observed characteristic: they each display patterns of planetary banding, with regions of different temperatures, composition, aerosol properties and dynamics separated by strong meridional and vertical gradients in the zonal (i.e., east-west) winds. Remote sensing observations, from both visiting spacecraft and Earth-based astronomical facilities, have revealed the significant variation in environmental conditions from one band to the next. On Jupiter, the reflective white bands of low temperatures, elevated aerosol opacities, and enhancements of quasi-conserved chemical tracers are referred to as ‘zones.’ Conversely, the darker bands of warmer temperatures, depleted aerosols, and reductions of chemical tracers are known as ‘belts.’ On Saturn, we define cyclonic belts and anticyclonic zones via their temperature and wind characteristics, although their relation to Saturn’s albedo is not as clear as on Jupiter. On distant Uranus and Neptune, the exact relationships between the banded albedo contrasts and the environmental properties is a topic of active study. This review is an attempt to reconcile the observed properties of belts and zones with (i) the meridional overturning inferred from the convergence of eddy angular momentum into the eastward zonal jets at the cloud level on Jupiter and Saturn and the prevalence of moist convective activity in belts; and (ii) the opposing meridional motions inferred from the upper tropospheric temperature structure, which implies decay and dissipation of the zonal jets with altitude above the clouds. These two scenarios suggest meridional circulations in opposing directions, the former suggesting upwelling in belts, the latter suggesting upwelling in zones. Numerical simulations successfully reproduce the former, whereas there is a wealth of observational evidence in support of the latter. This presents an unresolved paradox for our current understanding of the banded structure of giant planet atmospheres, that could be addressed via a multi-tiered vertical structure of “stacked circulation cells,” with a natural transition from zonal jet pumping to dissipation as we move from the convectively-unstable mid-troposphere into the stably-stratified upper troposphere.

     

An International Environmental Agreement for space debris mitigation among asymmetric nations

We investigate how ideas from the International Environmental Agreement (IEA) literature can be applied to the problem of space debris mitigation. Space debris pollution is similar to other international environmental problems in that there is a potential for a “tragedy of the commons” effect: individual nations bear all the cost of their mitigation measures but share only a fraction of the benefit. As a consequence, nations have a tendency to underinvest in mitigation. Coalitions of nations, brought together by IEAs, have the potential to lessen the tragedy of the commons effect by pooling the costs and benefits of mitigation. This work brings together two recent modeling advances: (i) a game theoretic model for studying the potential gains from IEA cooperation between nations with asymmetric costs and benefits, (ii) an orbital debris model that gives the societal cost that specific actions, such as failing to deorbit an inactive spacecraft, have on the environment. We combine these two models with empirical launch-share data for a “proof of concept” of an IEA for a single mitigation measure—deorbiting spacecraft at the end of operational lifetime. Simulations of empirically derived and theoretical launch distributions among nations suggest the possibility that voluntary coalitions can provide significant deorbiting gains relative to nations acting in the absence of an IEA agreement.