The Lunar Reconnaissance Orbiter Diviner Lunar Radiometer Experiment

The Diviner Lunar Radiometer Experiment on NASA’s Lunar Reconnaissance Orbiter will be the first instrument to systematically map the global thermal state of the Moon and its diurnal and seasonal variability. Diviner will measure reflected solar and emitted infrared radiation in nine spectral channels with wavelengths ranging from 0.3 to 400 microns. The resulting measurements will enable characterization of the lunar thermal environment, mapping surface properties such as thermal inertia, rock abundance and silicate mineralogy, and determination of the locations and temperatures of volatile cold traps in the lunar polar regions.     

Space: where are we headed?

In a new column, the author reviews NASA space activities since the beginning of 2003 and looks at plans for the future. Topics include the Space Shuttle Columbia, what's in store for the International Space Station (ISS), the development of an orbital space plane, orbiter safety upgrades, and the future of space exploration and research beyond the ISS. He presents arguments for sending astronauts to asteroids, the Moon, and Mars.     

Discrimination of aqueous and aeolian paleoenvironments by atomic force microscopy-- a database for the characterization of martian sediments

In the search for aqueous habitats on Mars direct proof of (ancient) flowing water is still lacking, although remote sensing has provided indications of young fluvial systems. To demonstrate that such proof can be given, we examined surface marks on recent terrestrial sand grains by atomic force microscopy (AFM) and applied a quantitative three-dimensional analysis that can numerically distinguish between aeolian and aquatic transport mechanisms in sedimentary deposits on Earth. The surfaces of natural quartz grains as well as olivine, feldspar pyroxene, and monazite sands of known origin were imaged, each image yielding a three-dimensional map of the mineral surface. A fully automated analysis of distribution patterns of the structural elements that constitute the grain surfaces shows that wind-transported quartz grains have short linear elements irregularly distributed on the surface. Linear elements on water-transported grains, however, are longer with orientations that reflect the mineral symmetry. Because the surface patterns found on aqueous grains are due to preferential etching, they can be used as diagnostic fingerprints for the existence of past or present aqueous transport systems. We used a cluster analysis of the cross-correlation distance of distribution patterns in the structures of aeolian and aquatic sand grains to build a phenogram that provides a map for the relationship of the various sediments found on earth. The analysis shows that the method is highly significant and that water and wind transport can clearly be differentiated. In particular, feldspar and olivine sands contributed even more to the discrimination than quartz grains, which indicated that the method is promising for its application on future missions to Mars. Assuming that martian aqueous sand grains exhibit similar erosional patterns to mineral grains on Earth, simple AFM experiments on a Mars lander would be capable of proving the activity of flowing water in modern runoff systems and of analyzing the paleoenvironments of Mars.     

Stratospheric ozone loss, ulraviolet effects and action spectroscopy

The major effect of stratospheric ozone loss will be an increase in the amount of ultraviolet radiation reaching the ground. This increase will be entirely contained within the UV-B (290–320nm). How this will impact life on Earth will be determined by the UV-B photobiology of exposed organisms, including humans. One of the analytical methods useful in estimating these effects is Action Spectroscopy (biological effect as a function of wavelength). Carefully constructed action spectra will allow us to partially predict the increase in bio-effect due to additional UV exposure. What effect this has on the organism and the system in which the organism resides is of paramount importance. Suitable action spectra already exist for human skin cancer, human cell mutation and killing, and for one immune response. Comprehensive and widely applicable action spectra for terrestrial and aquatic plant responses are being generated but are not yet suitable for extensive analysis. There is little data available for animals, other than those experiments completed in the laboratory as model systems for human studies. Some polychromatic action spectra have proven useful in determining the possible impact of ozone loss on biological systems. The pitfalls and limits of this approach will be addressed.     

Crushing strength of porous ice-mineral bodies-relevance for comets

In laboratory investigations with fluffy, highly porous ice and ice-dust bodies a new mechanism could be identified which strengthens the porous bodies. The process takes place under isothermal conditions and leads to the formation of ice bridges between the ice (dust) particles. It is driven solely by the dependence of the partial pressure of water vapour on the curvature of the particles. This mechanism is generally called “sintering”. A theory for the crushing strength of a porous ice and ice-dust agglomerate is developed which describes the experimental results on isothermal changes is strength due to sintering quantitatively well. The relevance for the evolution of comets is discussed.     

Asteroid surface materials: Mineralogical characterizations from reflectance spectra

The interpretation of diagnostic parameters in the spectral reflectance data for asteroids provides a means of characterizing the mineralogy and petrology of asteroid surface materials. An interpretive technique based on a quantitative understanding of the functional relationship between the optical properties of a mineral assemblage and its mineralogy, petrology and chemistry can provide a considerably more sophisticated characterization of a surface material than any matching or classification technique for those objects bright enough to allow spectral reflectance measurements. Albedos derived from radiometry and polarization data for individual asteroids can be used with spectral data to establish the spectral albedo, to define the optical density of the surface material and, in general, to constrain mineralogical interpretations.Mineral assemblages analogous to most meteorite types, with the exception of ordinary chondritic assemblages, have been found as surface materials of Main Belt asteroids. C1- and C2-like assemblages (unleached, oxidized meteoritic clay minerals plus opaques such as carbon) dominate the population (80%) throughout the Belt, especially in the outer Belt. A smaller population of asteroids exhibit surface materials similar to C3 (CO, CV) meteoritic assemblages (olivine plus opaque, probably carbon) and are also distributed throughout the Belt. The relative size (diameter) distributions for these two populations of objects are consistent with an origin by sequential accretion from a cooling nebula (C2 as surface layers, C3 as interior layers or cores). Based on information from meteoritic analogues and on qualitative models for the behavior of these materials during a heating episode, it seems unlikely that these C2- and C3-like asteroidal bodies have experienced any significant post-accretionary heating event either near surface or in the deep interior.The majority of remaining studied asteroids (20) of 65 asteroids exhibit spectral reflectance curves dominated by the presence of metallic nickel-iron in their surface materials. These objects are most probably the several end products of an intense thermal event leading to the melting and differentiating of their protobodies. These thermalized bodies are concentrated toward the inner part of the Asteroid Belt but exist throughout the Belt.The size of the proto-asteroid has apparently exercised control over the post-accretionary thermal history of these bodies. The available evidence indicates that all asteroids larger than about 450 km in (present) diameter have undergone a significant heating episode since their formation. The post-accretionary thermal history of the asteroidal parent bodies was apparently affected by both distance from the Sun and body size.The C2-like materials which dominate the main asteroid belt population appear to be relatively rare on earth-approaching asteroids. This suggests that most of these Apollo-Amor objects are not randomly derived from the main belt, but (a) may derive from a single event in recent time (10⁷ yr), (b) may derive from a favorably situated source body, (c) may derive from a particular, compositionally anomalous region of the belt, or (d) may derive from an alternate source (e.g. comets).     

International cooperation in remote sensing for global change research: political and economic considerations

Activities concerning international cooperation in space-based remote sensing for global change research have for the most part focused on technical/functional aspects such as data harmonization, research project coordination, and sensor selection and deployment. Until fairly recently, little attention has been directed towards the various political and economic constraints which may act as ‘stumbling blocks’. A review of the contemporary international remote sensing milieu as it relates to the global change research agenda is presented. Several important political and economic conditions affecting this area are identified: (1) data access and pricing policies; (2) national security concerns; (3) developed/developing nation relations; and (4) inconsistent political/financial commitments. A set of recommendations is offered to enhance international cooperation in the use of space-based remote sensing data for global change research.     

Daytime O/N<Subscript>2</Subscript> Retrieval Algorithm for the Ionospheric Connection Explorer (ICON)

The NASA Ionospheric Connection Explorer Far-Ultraviolet spectrometer, ICON FUV, will measure altitude profiles of the daytime far-ultraviolet (FUV) OI 135.6 nm and N₂ Lyman-Birge-Hopfield (LBH) band emissions that are used to determine thermospheric density profiles and state parameters related to thermospheric composition; specifically the thermospheric column O/N₂ ratio (symbolized as \(\Sigma\)O/N₂). This paper describes the algorithm concept that has been adapted and updated from one previously applied with success to limb data from the Global Ultraviolet Imager (GUVI) on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission. We also describe the requirements that are imposed on the ICON FUV to measure \(\Sigma\)O/N₂ over any 500-km sample in daytime with a precision of better than 8.7%. We present results from orbit-simulation testing that demonstrates that the ICON FUV and our thermospheric composition retrieval algorithm can meet these requirements and provide the measurements necessary to address ICON science objectives.     

Apparent rotation properties of space debris extracted from photometric measurements

Knowledge about the rotation properties of space debris objects is essential for the active debris removal missions, accurate re-entry predictions and to investigate the long-term effects of the space environment on the attitude motion change. Different orbital regions and object’s physical properties lead to different attitude states and their change over time.Since 2007 the Astronomical Institute of the University of Bern (AIUB) performs photometric measurements of space debris objects. To June 2016 almost 2000 light curves of more than 400 individual objects have been acquired and processed. These objects are situated in all orbital regions, from low Earth orbit (LEO), via global navigation systems orbits and high eccentricity orbit (HEO), to geosynchronous Earth orbit (GEO). All types of objects were observed including the non-functional spacecraft, rocket bodies, fragmentation debris and uncorrelated objects discovered during dedicated surveys. For data acquisition, we used the 1-meter Zimmerwald Laser and Astrometry Telescope (ZIMLAT) at the Swiss Optical Ground Station and Geodynamics Observatory Zimmerwald, Switzerland. We applied our own method of phase-diagram reconstruction to extract the apparent rotation period from the light curve. Presented is the AIUB’s light curve database and the obtained rotation properties of space debris as a function of object type and orbit.     

Spin motion determination of the Envisat satellite through laser ranging measurements from a single pass measured by a single station

The Satellite Laser Ranging (SLR) technology is used to accurately determine the position of space objects equipped with so-called retro-reflectors or retro-reflector arrays (RRA). This type of measurement allows to measure the range to the spacecraft with high precision, which leads to determination of very accurate orbits for these targets. Non-active spacecraft, which are not attitude controlled any longer, tend to start to spin or tumble under influence of the external and internal torques and forces.If the return signal is measured for a non-spherical non-active rotating object, the signal in the range residuals with respect to the reference orbit is more complex. For rotating objects the return signal shows an oscillating pattern or patterns caused by the RRA moving around the satellite’s centre of mass. This behaviour is projected onto the radial component measured by the SLR.In our work, we demonstrate how the SLR ranging technique from one sensor to a satellite equipped with a RRA can be used to precisely determine its spin motion during one passage. Multiple SLR measurements of one target over time allow to accurately monitor spin motion changes which can be further used for attitude predictions. We show our solutions of the spin motion determined for the non-active ESA satellite Envisat obtained from measurements acquired during years 2013–2015 by the Zimmerwald SLR station, Switzerland. All the necessary parameters are defined for our own so-called point-like model which describes the motion of a point in space around the satellite centre of mass.