ABSTRACT
Space weather phenomena can threaten space technologies. A hazard among these is the population of relativistic electrons in the Van Allen radiation belts. To reduce the threat, artificial processes can be introduced by transmitting very-low-frequency (VLF) waves into the belts. The resulting wave-particle interactions may deplete these harmful electrons. However, when transmitting VLF waves in space plasma, the antenna, plasma, and waves interact in a manner that is not well-understood. We conducted a series of VLF transmission experiments in the radiation belts and measured the power and radiation impedance under various frequencies and conditions. The results demonstrate the critical role played by the plasma-antenna-wave interaction around high-voltage space antennae and open the possibility to transmit high power in space. The physical insight obtained in this study can provide guidance to future high-power space-borne VLF transmitter developments, laboratory whistler-mode wave injection experiments, and the interpretation of various astrophysical and optical phenomena.
ABSTRACT
Operation of a CCD imager on a curved focal surface offers advantages to flat focal planes, especially for lightweight, relatively simple optical systems. The first advantage is that the modulation transfer function can approach diffraction-limited performance for a spherical focal surface employed in large field-of-view or large-format imagers. The second advantage is that a curved focal surface maintains more uniform illumination as a function of radius from the field center. Examples of applications of curved imagers, described here, include a small compact imager and the large curved array used in the Space Surveillance Telescope. The operational characteristics and mechanical limits of an imager deformed to a 15 mm radius are also described.
