A simple control law for reducing the effective characteristic acceleration of a solar sail

The direction and magnitude of a solar sail acceleration are strongly related. For this reason, once the characteristic acceleration has been fixed, it is not possible to modulate the acceleration in a particular direction. In this work, a semi-analytical switching control law is derived, enabling a solar sail to emulate a smaller effective characteristic acceleration (without changes in geometry or optical properties); by periodically changing the pitch (cone) angle of the sail, in average over time, the acceleration produced by the sail matches exactly (in both direction and magnitude) that of a “smaller” sail. The range in which this is possible is determined, and the limitations on this range due to the size difference is computed. The method is validated on optimal Earth-Mars trajectories.     

ARTEMIS Mission Design

The ARTEMIS mission takes two of the five THEMIS spacecraft beyond their prime mission objectives and reuses them to study the Moon and the lunar space environment. Although the spacecraft and fuel resources were tailored to space observations from Earth orbit, sufficient fuel margins, spacecraft capability, and operational flexibility were present that with a circuitous, ballistic, constrained-thrust trajectory, new scientific information could be gleaned from the instruments near the Moon and in lunar orbit. We discuss the challenges of ARTEMIS trajectory design and describe its current implementation to address both heliophysics and planetary science objectives. In particular, we explain the challenges imposed by the constraints of the orbiting hardware and describe the trajectory solutions found in prolonged ballistic flight paths that include multiple lunar approaches, lunar flybys, low-energy trajectory segments, lunar Lissajous orbits, and low-lunar-periapse orbits. We conclude with a discussion of the risks that we took to enable the development and implementation of ARTEMIS.     

Protostellar Disk Formation and Early Evolution

This contribution describes the formation of circumstellar disks and their earliest evolutionary phases when self-gravity in the disk plays a crucial role in eliciting the transport of mass and angular momentum. We first discuss the formation of protostellar disks within the context of analytic infall-collapse solutions. We then discuss our efforts to understand the behavior of the newly formed disks. Our specific approach consists of performing a detailed analysis of a simplified model disk which is susceptible to the growth of a spiral instability. Using a combination of numerical simulation and semi-analytic analysis, we show how the dramatic early phase of mass and angular momentum transport in the disk can be explained by a second-order nonlinear process involving self-interaction of a dominant two-armed spiral mode. This revised version was published online in June 2006 with corrections to the Cover Date.     

Optimum Space-Time Signal Processing and Parameter Estimation

A general-decision theoretic procedure for the design of optimum space-time signal processors is developed. Each antenna element output is processed separately before summing. The parameters for groups of 1, 2, . . . , n targets are estimated, followed by hypothesis testing to decide which group is most likely. Block diagrams for one-and two-target estimators of angular location are derived. The technique can be extended to more than two targets.     

Gene Transfer and the Reconstruction of Life’s Early History from Genomic Data

The metaphor of the unique and strictly bifurcating tree of life, suggested by Charles Darwin, needs to be replaced (or at least amended) to reflect and include processes that lead to the merging of and communication between independent lines of descent. Gene histories include and reflect processes such as gene transfer, symbioses and lineage fusion. No single molecule can serve as a proxy for the tree of life. Individual gene histories can be reconstructed from the growing molecular databases containing sequence and structural information. With some simplifications these gene histories can be represented by furcating trees; however, merging these gene histories into web-like organismal histories, including the transfer of metabolic pathways and cell biological innovations from now-extinct lineages, has yet to be accomplished. Because of these difficulties in interpreting the record retained in molecular sequences, correlations with biochemical fossils and with the geological record need to be interpreted with caution. Advances to detect and pinpoint transfer events promise to untangle at least a few of the intertwined histories of individual genes within organisms and trace them to the organismal ancestors. Furthermore, analysis of the shape of molecular phylogenetic trees may point towards organismal radiations that might reflect early mass extinction events that occurred on a planetary scale.     

Responses of the upper middle atmosphere (60–110 km) to the stratwarms of the four pre-map winters (1978/9–1981/2)

The global developments of the four stratospheric events (～20–50 km) are described, using balloon, satellite and rocket data. Winds data for heights of 60–95 km, derived from L.F. drift (52°N, 15°E; Europe) and M.F. radar (52°N, 107°W; Canada), are then compared with the stratospheric data. There is clear evidence that the preliminary planetary waves often penetrate strongly to ～90 km, and that mean wind reversals also occur. However, there are dramatic differences between European and Canadian mesospheric responses.     

Visual thematic mapping from Landsat and collateral data in support of mineral development

Over the past ten years, the authors and their associates have used Landsat images and collateral data to prepare visual thematic maps. The data are used in a projection-compositor (Procom) system that enlarges Landsat images and other data to scales as great as 1:15 000. Revisions of existing maps for simple themes (e.g. topographic maps) can be completed quickly, accurately and inexpensively. Complex themes, such as geological formations and structures, can be mapped through the optical merging of collateral data sets (e.g. Landsat, geophysics, geology) at a common scale. Such mapping has led to the recognition of a non-parallactic means of obtaining whole image stereo-models with large vertical exaggerations using Landsat images.     

Be/neutron star binaries: Orbital and spin periods

The spin periods of accreting neutron stars in binary systems with Be star primaries are shown to depend more strongly on periastron distance than apastron distance. This is interpreted as showing that neutron stars spin-up on shorter timescales than they spin-down. The pulse and orbital periods of V 0332+53 suggest that the optical counterpart of this source is a Be star.     

The earth observation market: industrial dynamics and their impact on data policy

This paper examines the relationship between public sector objectives in the Earth observation data market and the economic interests of Earth observation data procedures. The Earth observation data market is treated as a particular example of an information market and the economic incentives created by the cultural characteristics of the market, particularly in Europe, are considered to assess the implications for data pricing policies. The analysis focuses upon implications of the vertical and horizontal linkages in the Earth observation industrial participation chain which includes space segment suppliers, space agencies and operators, data intermediaries and end users. A rebalancing of administrative and market decisions is proposed that would result in a shift in the allocation of public resources from space agencies and data intermediaries to data users whose activities are deemed to be in the widest public interest.