Characterizing Angle Tracking Radars Using Complex Variables

The receiver signal of a general angle tracking radar where there is asingle target which consists of a set of n reflectors is analyzed. It is shown how the analysis of this radar can be greatly simplified by representing the signals in the receiver as complex variables. This representation also makes it very easy to analyze such problems as scintillation and single-sideband crosstalk.     

The Mercury Dual Imaging System on the MESSENGER Spacecraft

The Mercury Dual Imaging System (MDIS) on the MESSENGER spacecraft will provide critical measurements tracing Mercury’s origin and evolution. MDIS consists of a monochrome narrow-angle camera (NAC) and a multispectral wide-angle camera (WAC). The NAC is a 1.5° field-of-view (FOV) off-axis reflector, coaligned with the WAC, a four-element refractor with a 10.5° FOV and 12-color filter wheel. The focal plane electronics of each camera are identical and use a 1,024×1,024 Atmel (Thomson) TH7888A charge-coupled device detector. Only one camera operates at a time, allowing them to share a common set of control electronics. The NAC and the WAC are mounted on a pivoting platform that provides a 90° field-of-regard, extending 40° sunward and 50° anti-sunward from the spacecraft +Z-axis—the boresight direction of most of MESSENGER’s instruments. Onboard data compression provides capabilities for pixel binning, remapping of 12-bit data into 8 bits, and lossless or lossy compression. MDIS will acquire four main data sets at Mercury during three flybys and the two-Mercury-solar-day nominal mission: a monochrome global image mosaic at near-zero emission angles and moderate incidence angles, a stereo-complement map at off-nadir geometry and near-identical lighting, multicolor images at low incidence angles, and targeted high-resolution images of key surface features. These data will be used to construct a global image base map, a digital terrain model, global maps of color properties, and mosaics of high-resolution image strips. Analysis of these data will provide information on Mercury’s impact history, tectonic processes, the composition and emplacement history of volcanic materials, and the thickness distribution and compositional variations of crustal materials. This paper summarizes MDIS’s science objectives and technical design, including the common payload design of the MDIS data processing units, as well as detailed results from ground and early flight calibrations and plans for Mercury image products to be generated from MDIS data.     

Space security through the transatlantic partnership

On 12–14 June 2011, a conference was convened in Prague entitled ”Space Security through the Transatlantic Partnership“, co-sponsored by the European Space Policy Institute (ESPI) and the Prague Security Studies Institute (PSSI). It was the first non-governmental transatlantic conference of its kind dedicated to this topic, attended by over 100 senior space policy officials and high-level representatives of multilateral institutions, NGOs, academia, and industry from Europe, the USA, and Japan. The overarching goal of the conference was to solicit and assess both converging and diverging views on the multifaceted subject of space security and to seek to establish an on-going “Track II” non-governmental process designed to assist with the crafting of a future architecture for the management of this key dimension of space policy on a trilateral, and eventually global, basis. This report summarizes the proceedings.     

Forging a closer Europe–Japan strategic partnership: The space dimension

This viewpoint explores how a strengthening of Europe–Japan cooperation in four categories of space-related activities (exploration and access to space; Earth observation and related applications; industry-to-industry cooperation; and space security) can contribute to the EU–Japan strategic partnership more broadly. It is argued that integrating key space portfolios into existing venues and agendas for bilateral consultations and decision-making has the potential to bolster the overarching objective of deepening further political, economic, commercial, societal and cultural relations.     

Visions of exploration

The word “exploration” threads its way through every discussion of human space flight and often headlines national policy statements about the US space agency. Yet this concept, so rooted in our culture, remains remarkably ill-defined. In this paper, we examine various presumptions implicit in the term and its ramifications for federally supported space endeavors. We argue that historical examples of exploration, widely used by policy makers, often make poor models for contemporary space travel. In particular, historical precedents of exploration set up a land-biased view of discovery, a restriction which impedes full expression of the Vision for Space Exploration and its possible scientific returns. These same precedents also set up a view of discovery that is biased toward in situ human presence, a view that modern technology is rendering increasingly absurd.     

A review of global satellite-derived snow products

Snow cover over the Northern Hemisphere plays a crucial role in the Earth’s hydrology and surface energy balance, and modulates feedbacks that control variations of global climate. While many of these variations are associated with exchanges of energy and mass between the land surface and the atmosphere, other expected changes are likely to propagate downstream and affect oceanic processes in coastal zones. For example, a large component of the freshwater flux into the Arctic Ocean comes from snow melt. The timing and magnitude of this flux affects biological and thermodynamic processes in the Arctic Ocean, and potentially across the globe through their impact on North Atlantic Deep Water formation.