EARTH TIDES AND EARTHQUAKE

ABSTRACT An analysis of Earth deformation, earthquakes and tides has been undertaken using Earth tide, GPS data from stations in Southern California and the Parkfield area and interferometric SAR data from ESA satellites. The ability of Earth tides to trigger earthquakes has been investigated by measuring the statistical relation between earthquake occurrence and Earth tides. Earthquakes occurring in the South of California and the Parkfield area, with magnitude M w larger than 3, during the period 1973 to 2009 have been used. The correlation between Earth tides and earthquake occurrences has been measured statistically by applying Schuster's test. Each earthquake is assigned a phase angle between -180 and 180 degrees based on the occurrence time of the earthquake with respect to the local Earth tides. The value of p is used to determine the null hypothesis that the earthquakes occur randomly with respect to the phase angle of the tidal variation. Whilst no significant correlation is observed between earthquake occurrence and Earth tides for the data set of all the earthquakes more detailed analysis does indicate significant correlations. The earthquakes observed are concentrated in two group; the first one near the San Andres Fault (SAF) and the other in Long Valley Caldera to the north east of the San Andreas Fault. A significant correlation has been found for both data sets separately for small magnitude earthquakes (M w less than 4). A further analysis has been done for both sets, by classifying the data set according to the earthquake depth. This produces a more complex result that will be discussed in this paper. To complement this analysis differential ERS SAR interferometry data and GPS data have been used to examine the surface deformation produced by the California earthquakes. The interferometric SAR data showing a number of interference fringes over a wide area due to a particular earthquake has been compared to the GPS data for individual stations

Enhancing spaceflight safety with UOS3 cubesat

Earth orbits are becoming increasingly congested. This will not only impact future space operations but also become a concern for the population on the ground; with more spacecraft being flown, more objects will re-enter the atmosphere in an uncontrolled fashion. Parts of these satellites can reach Earth surface and endanger the ground population (e.g. ROSAT or UARS satellites). A student-run project from the University of Southampton aims to build a 1U cubesat (approx. 10 by 10 by 10 cm satellite), which will gather data that will improve the accuracy of re-entry predictions. The cubesat will record and deliver its position and attitude during the orbital decay, thus providing validation data for re-entry prediction tools. This will reduce the risk to the ground population because more accurate prognoses will allow mitigation measures to be implemented in the areas at risk. The mission could also allow the risk of collision between spacecraft to be estimated more accurately thanks to improvement of the atmospheric models. This would give the decision makers more complete information to use, for instance, in collision avoidance manoeuvre plannin

Future robotic exploration using honeybee search strategy: Example search for caves on Mars

Autonomous control has an increasing role in Earth and Space based applications. High level autonomy can greatly improve planetary exploration and is, in many cases, essential. It has been suggested during the Mars cave exploration programme, that an effective way to explore a larger surface area would be the use of many, small and fully autonomous robots. However, there are many challenges to overcome if such a swarm exploration programme is to be implemented. This paper summarises these challenges and focuses on one of the most crucial one: strategy. Many effective group exploration behaviours can be observed in nature, most of which are optimised to work with agents that have limited capabilities as individuals. For this paper a computer program has been written to simulate the way bees search for new hives and investigate whenever it is an optimal method to search for cave entrances on Mars. It has been found that this method, using simple autonomous robots which can be constructed using available technologies, could greatly improve the speed and range of a planetary exploration mission. The simulation results show that 50 swarm robots can cover an area of over 300 meters square completely in 5 sols while they are searching for cave entrances and returning results to the Lander which is a major performance improvement on any previous mission. Furthermore areas of interests found by the explorers are sorted in order of importance automatically and without the need of computational analysis, hence larger quantities of data were collected from the more important areas. Therefore the system – just like a hive of bees – can make a complex decision easily and quickly to find the place which matches the required criteria best. Using a high performance search strategy such as the one described in this paper is crucial if we plan to search for important resources or even life on Mars and other bodies in the solar system.<br/

Relative trajectory analysis of dissimilar formation flying spacecraft

This paper deals with the differential acceleration effects on spacecraft formation flying. A mathematical model is developed to analyze relative trajectory of spacecraft in the presence of significant perturbative forces.The equations of relative coordinates are derived as a precise solution to the formation geometry problem and are valid for both close and long distance formation patterns and for rendezvous analysis. The coordinates of motion are propagated forward in time for identical and dissimilar spacecraft for different initial conditions. The results of this paper provide a physical insight into the actual behaviour of satellites in a cluster with differential drag-area

Space Environment

The environment in which spacecraft have to function is not only life-threatening for humans but also challenging for the spacecraft itself. To successfully cope with this environment many aspects including acceleration, atmosphere, vacuum, solar radiation and its implications have to be taken into onsideration. Such factors are examined in more detail in the following chapter “Space Environment”

High altitude electrical power generation

This paper investigates the technical feasibility of a system that could be used to collect the solar irradiation at high altitude, convert it into electricity, and then transmit it to the ground via a cable. As a first step to assess the viability of this device, an estimate of the solar irradiation that can be expected at a defined altitude above the ground is presented, based on real atmospheric data. The study demonstrates that locating PV devices at high altitude with the use of an aerostatic platform, could bring a significant advantage in the production of electrical power, if compared with a typical UK ground based PV system. The fundamental equations for a preliminary design of the system are presented together with a first realistic choice of the most relevant engineering parameters that need to be set. An estimate of the cost of the system is provided and the possible risks involved, applications, advantages and disadvantages of the technology are assessed

System design issues of small formation-flying spacecraft

This paper deals with the analysis of the relative trajectory of small formation flying spacecraft and shows how the orbit control requirements of the formation impose particular constraints on the overall spacecraft design. The relative trajectory is simulated in the presence of perturbative forces like drag, solar radiation and J2. The fuel requirements for different formation flying patterns are studied and the feasibility of using either passive or active control methods is discussed. The effects of small differences in drag-area on cluster stability and spacecraft design are addressed. The assessment of the relative trajectory is imperative for selecting the actuators for station keeping, designing control laws and deciding the configuration of the spacecraft

Precise modelling of spacecraft relative motion for formation flying spacecraft

Relative spacecraft motion has long been a problem for mission analysts who plan rendezvous maneuvers. These planners look to the solution devised by Clohessy and Wiltshire as their primary analysis tool. The Clohessy-Wiltshire (CW) equations are usually sufficient for the rendezvous problem that is of short duration and has frequent thruster firings. Consequently, the long-term accuracy of the equations of motion is not as important in the rendezvous problem as in the formation-flying problem. The errors resulting from the assumptions made in the CW equations such as circular reference orbit, very close target orbit are unacceptable for the long-term prediction of relative motion needed for formation flying satellites. A precise analytic solution for the relative motion of and formation flying satellites is needed to minimize fuel consumption and maximize lifetime. In this paper, we derive the relative coordinates of a deputy satellite with respect to a master satellite by a series of transformations and translations from the Earth-centered inertial frame to the spacecraftcentered rotating frame. The equations of relative coordinates derived in this paper are very precise and can be used to analyze orbits of any eccentricity and of any initial separation with or without the inclusion of orbit perturbations