SCIENTIFIC AND TECHNICAL AEROSPACE REPORTS

A Biweekly Publication of the National Aeronautics and Space Administration
VOLUME 44, ISSUE 13 - JULY 5, 2006

12 ASTRONAUTICS (GENERAL)
Includes general research topics related to space flight and manned and unmanned space vehicles, platforms or objects launched into, or assembled in, outer space; and related components and equipment.

Also includes manufacturing and maintenance of such vehicles or platforms.

For specific topics in astronautics see categories 13 through 20.

For extraterrestrial exploration see 91 Lunar and Planetary Science and Exploration.

20060017221 Air Force Research Lab., Kirkland AFB, NM USA

Suppression of Doppler Ambiguities for Linear Sparse Arrays

Roman, Jaime R; Nelander, James C; Garnham, John W; Keisling, John D; Black, Lynn M; Apr 2006; 8 pp.; In English; Original contains color illustrations Report No.(s): AD-A444652; No Copyright; ONLINE: http://hdl.handle.net/100.2/ADA444652; Avail.: CASI: A02, Hardcopy

A key trade-off in airborne or spaceborne synthetic aperture radar (SAR) design involves the pulse repetition frequency (PRF) and the number and location or range and Doppler ambiguities. The associated design issues are complicated further when the system involves a sparse array. A methodology is formulated based on selecting the PRF to avoid range ambiguities in the envelope mainbeam. The effects of the Doppler ambiguities falling within the envelope mainbeam are mitigated by using an optimal algorithm to generate weights that place nulls in the pattern of the (sparse or contiguous) array in the directions of the Doppler ambiguities. This approach can be used for the analysis and design of airborne or spaceborne SAR systems with contiguous or sparse arrays. DTIC

Ambiguity; Linear Arrays; Synthetic Aperture Radar

20060017669 Alcatel Space Industries, Cannes la Bocca, France

A New Concept of Synthetic Aperture Instrument for High Resolution Earth Observation from High Orbits

Blanc, Philippe; Falzon, Frederic; Thomas, Eric; Jul 13, 2005; 10 pp.; In English; Original contains color illustrations Report No.(s): AD-A445177; No Copyright; Avail.: CASI: A02, Hardcopy

High Resolution Earth Observation from high orbits (e.g. Geostationnary) requires the use of large diameter telescopes, unfeasible if considering monolithic concepts. It is necessary, to circumvent this problem, to consider a segmented instrument,turning it into a feasible concept that can be put into orbit. Optical Aperture Synthesis (OAS) can be considered as a solution for HR observation from high orbits. In this paper, we describe a new OAS imaging instrument concept (under study in the Alcatel Space Research Department [1]) having variable resolution and field of view by adopting a re-decomposition of thebasic Michelson or Fizeau interferometer schemes. In addition to providing variable resolution power and field of view, this instrument concept is particularly robust to sub-systems failure since it shows a natural redundancy of its imaging capabilities. DTIC

Earth Observations (From Space); High Resolution; Optical Equipment; Synthetic Apertures; Trajectories

20060017711 La Sapienza Univ., Rome, Italy

Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS): Subsurface Performances Evaluation

Picardi, G; Biccari, D; Bazzoni, A; Fois, F; Melacci, P; Federico, C; Frigeri, A; Marinangeli, L; Calabrese, D; Johnson, W T; Apr 14, 2005; 8 pp.; In English; Original contains color illustrations Report No.(s): AD-A445262; No Copyright; Avail.: CASI: A02, Hardcopy

According to the Mars Express mission, the MARSIS primary scientific objectives are to map the distribution of water, both liquid and solid, in the upper portions of the crust of Mars. Three secondary objectives are also defined: subsurface geologic probing, surface characterization, and ionosphere sounding. In order to obtain the primary objectives, the Radar Sounder design was based on the Ice/water interface and Dry/ice interface scenario: defining the material composition of the first layers and porosity and the pore filling materials. Concerning the surface, we have characterized the geometric structure, due to rocks, as superimposed, taking into account also that recently the structure of the planet's surface was described by means of fractals and in particular the new MARS surface models obtained by processing of the MOLA data. According to these models, this provides a description of the operational planning approach and expected performances of MARSIS. DTIC

Mars Atmosphere; Planetary Ionospheres; Radar; Sounding; Space Exploration

20060018894 European Space Research and Technology Centre, Noordwijk, Netherlands

Conclusions of ESA 1st OpticalWireless Onboard CommunicationsWorkshop: Current Status and the Road Forward

Hernandez, Inmaculada; Plancke, Patrick; Jul 13, 2005; 6 pp.; In English Report No.(s): AD-A445911; No Copyright; Avail.: CASI: A02, Hardcopy

The purpose of this workshop was to bring together representatives of European space agencies, aerospace industry, wireless technology industry, academia, research institutions, and end-users to do the following: (1) Review the state-of-the-art of optical free space communications in ground and in space, in short- and medium-link distances, point-to-point, as well as broadcast or other networking schemes; (2) Explore the future needs, potential solutions, and challenges in applying thesetechnologies to communications onboard spacecraft and in ground integration and test facilities; (3) Investigate the challenges imposed by the space environment with regard to opto-electronic component technologies, particularly with respect to space radiation and temperature and vacuum conditions; and (4) Discuss the main techniques and technologies for the optical wireless intra-spacecraft LAN as a distinct spacecraft subsystem. The 'Optical Wireless On-board Communications Workshop,' sponsored by the European Space Research and Technology Centre (ESTEC), was held in September 2004. The workshop presented a complete European vision of the current situation of optical wireless techniques and technologies and their applicability to space. The paper also draws on information that has resulted from the activities of the Computer and Data System Section of the European Space Agency (ESA) over the last 5 years. In addition, the paper integrates the latest results available from on-going complementary development and testing projects. DTIC

Aerospace Systems; Europe; European Space Agency; Optical Communication; Roads; Space Communication; Wireless Communication

Source: NASA