Performance of a 2-layer radial hole effective media lens
The outer polyethylene layer of a 8λ0 radius 2-layer polyethylene/cross-linked polystyrene lens was implemented as a radial hole effective media that allows the entire lens to be milled from a single billet of cross-linked polystyrene, simplifying construction by avoiding layer fitting problems. Full wave simulations in a commercially available simulator showed that increasing the number of radial holes to 3000 gave peak directivity within 0.3dB of the original cross-linked polystyrene/polyethylene lens. Both Particle Swarm Optimization and icosahedron based methods were trialed for distributing the holes evenly over the sphere. The latter method produced symmetrical meshes allowing symmetry planes to be used to minimize computational burden, but was bound to the numbers of holes produced by successive triangular face subdivision iterations.
ADVANCED LIGHTWEIGHT ELECTRONICALLY STEERED ANTENNAS FOR RESPONSIVE SPACE PAYLOADS
Due to the mix of missions that Responsive Space payloads will be called upon to execute, and the available launcher technology, it appears likely that initial implementations will consist of constellations of small LEO satellites. It is likely that most Responsive Space payloads will need to maintain multiple simultaneous data links to the battlefield, even if the spacecraft's primary mission is something other than providing tactical communications. In order to maintain broadband communications with multiple fixed or mobile terminals distributed across a theater of interest, these LEO satellites will require agile high gain communications antennas. Providing such an antenna within the size, mass, and cost constraints of a Responsive Space payload presents a number of technical challenges. This paper presents some of the design trades involved in selecting an antenna technology for this application. It also gives examples of some recently developed antenna and beam forming technologies that show promise for addressing Responsive Space payload requirements. The devices shown have adequate performance for a wide variety of missions, were developed for space or military airborne applications, and can be qualified for the Responsive Space mission with low risk * .
Application of Aerosondes to Melt-Pond Observations over Arctic Sea Ice
Abstract Continuous observation of sea ice using a small robotic aircraft called the Aerosonde was made over the Arctic Ocean from Barrow, Alaska, on 20–21 July 2003. Over a region located 350 km off the coast of Barrow, images obtained from the aircraft were used to characterize the sea ice and to determine the fraction of melt ponds on both multiyear and first-year ice. Analysis of the data indicates that melt-pond fraction increased northward from 20% to 30% as the ice fraction increased. However, the fraction of ponded ice was over 30% in the multiyear ice zone while it was about 25% in the first-year ice zone. A comparison with a satellite microwave product showed that the ice concentration derived from the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) has a negative bias of 7% due to melt ponds. These analyses demonstrate the utility of recent advances in unmanned aerial vehicle (UAV) technology for monitoring and interpreting the spatial variations in the sea ice wi...