First Results from ARTEMIS, a New Two-Spacecraft Lunar Mission: Counter-Streaming Plasma Populations in the Lunar Wake

We present observations from the first passage through the lunar plasma wake by one of two spacecraft comprising ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon??s Interaction with the Sun), a new lunar mission that re-tasks two of five probes from the THEMIS magnetospheric mission. On Feb 13, 2010, ARTEMIS probe P1 passed through the wake at ??3.5 lunar radii downstream from the Moon, in a region between those explored by Wind and the Lunar Prospector, Kaguya, Chandrayaan, and Chang??E missions. ARTEMIS observed interpenetrating proton, alpha particle, and electron populations refilling the wake along magnetic field lines from both flanks. The characteristics of these distributions match expectations from self-similar models of plasma expansion into vacuum, with an asymmetric character likely driven by a combination of a tilted interplanetary magnetic field and an anisotropic incident solar wind electron population. On this flyby, ARTEMIS provided unprecedented measurements of the interpenetrating beams of both electrons and ions naturally produced by the filtration and acceleration effects of electric fields set up during the refilling process. ARTEMIS also measured electrostatic oscillations closely correlated with counter-streaming electron beams in the wake, as previously hypothesized but never before directly measured. These observations demonstrate the capability of the comprehensively instrumented ARTEMIS spacecraft and the potential for new lunar science from this unique two spacecraft constellation.     

Retention Probability in a Track-While-Scan Radar

The probability of maintaining the track file, after acquisition in a track-while-scan (TWS) radar, has been formulated and computed under various conditions of initial range, velocity, and track drop time. All calculations are based on a predetermined update probability versus range characteristic. Results, obtainable with a digital computer in just seconds of computing time, readily demonstrate the relative superiority of retention characteristics achievable for TWS radar with an electronically steerable array antenna.     

Synthetic Aperture Imaging with Maneuvers

A digital processing approach has been devised for performing motion compensation in a high-resolution airborne synthetic aperture radar in the presence of simultaneous longitudinal (speed change), lateral (turn), and vertical (climb or dive) maneuvers. Both side-look and squint are accommodated in a unified scheme, which is validated by various simulation runs reported herein. Present attention is focused on theoretical verification, irrespective of mechanization or specific parameter values.     

Comment on "Gyro Misalignment and Encoder Quantization Effects During Multi-Axis Evaluation of Strapdown Gyros"

A recent paper1 discusses certain aspects of strapdown attitude error sources. It is pointed out here that the long term effects of these and several additional sources have previously been determined, within the framework of a complete attitude reference [4] and navigation [5] system.