Parametric study of the diversion of a near Earth object on an Earth intersecting trajectory

To date, NASA's “Near Earth Object Program” has discovered over 5500 comets and asteroids on trajectories that bring them within “the neighborhood” of Earth's orbit. Nearly 1000 of these objects are classified as “potentially hazardous,” passing within 0.05 astronomical units of Earth's orbit. Discovery rates of such threatening bodies increase each year. Given this multitude of threats, in addition to evidence that the planet has absorbed many impacts over its history, it is reasonable to assume that another object will strike the Earth at some point in the future. Consequently, researchers have studied and proposed several mitigation techniques for such an occurrence. This study seeks to determine how effectively the attachment of a tether and ballast mass would divert the trajectory of such threatening objects. Specifically, the study analyzes the effects over time of such a system on objects of varying orbital semimajor axis and eccentricity, using various tether lengths and ballast masses. It was determined that the technique is most effective for NEOs with high eccentricity and small semimajor axis, and that system performance increases as tether length and ballast mass increase.     

The Lunar Reconnaissance Orbiter Laser Ranging Investigation

The objective of the Lunar Reconnaissance Orbiter (LRO) Laser Ranging (LR) system is to collect precise measurements of range that allow the spacecraft to achieve its requirement for precision orbit determination. The LR will make one-way range measurements via laser pulse time-of-flight from Earth to LRO, and will determine the position of the spacecraft at a sub-meter level with respect to ground stations on Earth and the center of mass of the Moon. Ranging will occur whenever LRO is visible in the line of sight from participating Earth ground tracking stations. The LR consists of two primary components, a flight system and ground system. The flight system consists of a small receiver telescope mounted on the LRO high-gain antenna that captures the uplinked laser signal, and a fiber optic cable that routes the signal to the Lunar Orbiter Laser Altimeter (LOLA) instrument on LRO. The LOLA instrument receiver records the time of the laser signal based on an ultrastable crystal oscillator, and provides the information to the onboard LRO data system for storage and/or transmittal to the ground through the spacecraft radio frequency link. The LR ground system consists of a network of satellite laser ranging stations, a data reception and distribution facility, and the LOLA Science Operations Center. LR measurements will enable the determination of a three-dimensional geodetic grid for the Moon based on the precise seleno-location of ground spots from LOLA.     

Fast solar radiation pressure modelling with ray tracing and multiple reflections

Physics based SRP (Solar Radiation Pressure) models using ray tracing methods are powerful tools when modelling the forces on complex real world space vehicles. Currently high resolution (1?mm) ray tracing with secondary intersections is done on high performance computers at UCL (University College London). This study introduces the BVH (Bounding Volume Hierarchy) into the ray tracing approach for physics based SRP modelling and makes it possible to run high resolution analysis on personal computers. The ray tracer is both general and efficient enough to cope with the complex shape of satellites and multiple reflections (three or more, with no upper limit). In this study, the traditional ray tracing technique is introduced in the first place and then the BVH is integrated into the ray tracing. Four aspects of the ray tracer were tested for investigating the performance including runtime, accuracy, the effects of multiple reflections and the effects of pixel array resolution.Test results in runtime on GPS IIR and Galileo IOV (In Orbit Validation) satellites show that the BVH can make the force model computation 30–50 times faster. The ray tracer has an absolute accuracy of several nanonewtons by comparing the test results for spheres and planes with the analytical computations. The multiple reflection effects are investigated both in the intersection number and acceleration on GPS IIR, Galileo IOV and Sentinel-1 spacecraft. Considering the number of intersections, the 3rd reflection can capture $99.12\%\text{,}99.14\%$, and $91.34\%$ of the total reflections for GPS IIR, Galileo IOV satellite bus and the Sentinel-1 spacecraft respectively. In terms of the multiple reflection effects on the acceleration, the secondary reflection effect for Galileo IOV satellite and Sentinel-1 can reach 0.2?$\text{nm}/{\text{s}}^2$ and 0.4?$\text{nm}/{\text{s}}^2$ respectively. The error percentage in the accelerations magnitude results show that the 3rd reflection should be considered in order to make it less than $0.035\%$. The pixel array resolution tests show that the dimensions of the components have to be considered when choosing the spacing of the pixel in order not to miss some components of the satellite in ray tracing. This paper presents the first systematic and quantitative study of the secondary and higher order intersection effects. It shows conclusively the effect is non-negligible for certain classes of misson.     

Astrobiological considerations for the selection of the geological filters on the ExoMars PanCam instrument

The Panoramic Camera (PanCam) instrument will provide visible-near IR multispectral imaging of the ExoMars rover's surroundings to identify regions of interest within the nearby terrain. This multispectral capability is dependant upon the 12 preselected "geological" filters that are integrated into two wide-angle cameras. First devised by the Imager for Mars Pathfinder team to detect iron oxides, this baseline filter set has remained largely unchanged for subsequent missions (Mars Exploration Rovers, Beagle 2, Phoenix) despite the advancing knowledge of the mineralogical diversity on Mars. Therefore, the geological filters for the ExoMars PanCam will be redesigned to accommodate the astrobiology focus of ExoMars, where hydrated mineral terrains (evidence of past liquid water) will be priority targets. Here, we conduct an initial investigation into new filter wavelengths for the ExoMars PanCam and present results from tests performed on Mars analog rocks. Two new filter sets were devised: one with filters spaced every 50?nm ("F1-12") and another that utilizes a novel filter selection method based upon hydrated mineral reflectance spectra ("F2-12"). These new filter sets, along with the Beagle 2 filter set (currently the baseline for the ExoMars PanCam), were tested on their ability to identify hydrated minerals and biosignatures present in Mars analog rocks. The filter sets, with varying degrees of ability, detected the spectral features of minerals jarosite, opaline silica, alunite, nontronite, and siderite present in these rock samples. None of the filter sets, however, were able to detect fossilized biomat structures and small (<2?mm) mineralogical heterogeneities present in silica sinters. Both new filter sets outperformed the Beagle 2 filters, with F2-12 detecting the most spectral features produced by hydrated minerals and providing the best discrimination between samples. Future work involving more extensive testing on Mars analog samples that exhibit a wider range of mineralogies would be the next step in carefully evaluating the new filter sets.     

The simulated silicification of bacteria--new clues to the modes and timing of bacterial preservation and implications for the search for extraterrestrial microfossils

Evidence of microbial life on Earth has been found in siliceous rock formations throughout the geological and fossil record. To understand the mechanisms of silicification and thus improve our search patterns for evidence of fossil microbial life in rocks, a series of controlled laboratory experiments were designed to simulate the silicification of microorganisms. The bacterial strains Pseudomonas fluorescens and Desulphovibrio indonensis were exposed to silicifying media. The experiments were designed to determine how exposure time to silicifying solutions and to silicifying solutions of different Si concentration affect the fossilization of microbial biofilms. The silicified biofilms were analyzed using transmission electron microscopy (TEM) in combination with energy-dispersive spectroscopy. Both bacterial species showed evidence of silicification after 24 h in 1,000 ppm silica solution, although D. indonensis was less prone to silicification. The degree of silicification of individual cells of the same sample varied, though such variations decreased with increasing exposure time. High Si concentration resulted in better preservation of cellular detail; the Si concentration was more important than the duration in Si solution. Even though no evidence of amorphous silica precipitation was observed, bacterial cells became permineralized. High-resolution TEM analysis revealed nanometer-sized crystallites characterized by lattice fringe-spacings that match the (10-11) d-spacing of quartz formed within bacterial cell walls after 1 week in 5,000 ppm silica solution. The mechanisms of silicification under controlled laboratory conditions and the implication for silicification in natural environments are discussed, along with the relevance of our findings in the search for early life on Earth and extraterrestrial life.     

Molecular identification of cyanobacteria associated with stromatolites from distinct geographical locations

Modern stromatolites represent a significant resource for studying microbial ecology and evolution. A preliminary investigation was undertaken employing specific genetic probes to characterize the cyanobacteria responsible for stromatolite construction in a range of environments, including microbial mats found in Australia not previously examined with molecular methods. Isolates of cyanobacteria were collected from stromatolites in thermal springs, hypersaline lakes, and oceanic fringes on two continents. A polymerase chain reaction specific for DNA of cyanobacterial 16S rRNA was developed, the resulting products of the DNA amplification reaction were sequenced, and the data were used to infer relatedness between the isolates studied and other members of the cyanobacterial radiation. Complete sequence was generated for the region from position 27 to 408 for 13 strains of cyanobacteria associated with stromatolites. All stromatolite-derived sequences were most closely related to cyanobacteria, as indicated by local sequence alignment. It was possible to correlate genetic identity with morphological nomenclatures and to expand the phylogeny of benthic cyanobacteria. These inferences were also expanded to temporal variation in the dominant resident cyanobacterial species based on sampling of surface and core sinter laminations. Under the methods employed, only one cyanobacterial strain was detected in each sample, suggesting the possible dominance of a specific clonal population of cyanobacteria at any one time in the biota of the samples tested. The data indicate that internal core samples of a stromatolite at least 10 years old can be successfully analyzed by DNA-based methods to identify preserved cyanobacteria.     

The magnetosheath and magnetotail of Venus

We describe the observational history and assess the current understanding of the magnetosheath and magnetotail of Venus, stressing recent developments. We make recommendations for research that can be done using existing observations, as well as desirable trajectory and instrumentation characteristics for future spacecraft missions.     

Key science questions from the second conference on early Mars: geologic, hydrologic, and climatic evolution and the implications for life

In October 2004, more than 130 terrestrial and planetary scientists met in Jackson Hole, WY, to discuss early Mars. The first billion years of martian geologic history is of particular interest because it is a period during which the planet was most active, after which a less dynamic period ensued that extends to the present day. The early activity left a fascinating geological record, which we are only beginning to unravel through direct observation and modeling. In considering this time period, questions outnumber answers, and one of the purposes of the meeting was to gather some of the best experts in the field to consider the current state of knowledge, ascertain which questions remain to be addressed, and identify the most promising approaches to addressing those questions. The purpose of this report is to document that discussion. Throughout the planet's first billion years, planetary-scale processes-including differentiation, hydrodynamic escape, volcanism, large impacts, erosion, and sedimentation-rapidly modified the atmosphere and crust. How did these processes operate, and what were their rates and interdependencies? The early environment was also characterized by both abundant liquid water and plentiful sources of energy, two of the most important conditions considered necessary for the origin of life. Where and when did the most habitable environments occur? Did life actually occupy them, and if so, has life persisted on Mars to the present? Our understanding of early Mars is critical to understanding how the planet we see today came to be.     

A management approach for allocating instrument development resources

The Cassini Science Management Plan was developed for NASA's Cassini mission to Saturn to assist the Science Instrument Manager in guiding the development of the spacecraft's science payload. This plan, unlike previous development approaches, allocated the entire mass, power, data rate and budget resources for the science instruments to the Principal Investigators. The result removed the Cassini Project from adjudicating and reallocating resources for instrument development problems. Instrument development problems that did occur were resolved by the Principal Investigators themselves through the use of a ‘resource exchange’. The exchange allowed Principal Investigators to submit ‘bids’ (i.e. a request for resources) to a database. Principal Investigators were allowed to barter their own resources with other investigators. The resulting exchange or multilateral trade allowed the investigators to reallocate their resource to ‘better’ their current position.