An interval of time during which conditions are favorable for launching a spacecraft on a specific mission.

An opening in the wall of a building or the body of a vehicle to admit light and usually to permit vision through a transparent or translucent material, usually glass.

A separate viewing area on a display screen that is established by the computer software. Also known as viewport.

A hole in a partition between two cavities or waveguides, used for coupling.

A material having minimum absorption and minimum reflection of radiant energy, sealed into the vacuum envelope of a microwave or other electron tube to permit passage of the desired radiation through the envelope to the output device.

A break caused by erosion of a thrust sheet or a large recumbent anticline that exposes the rocks beneath the thrust sheet. Also known as fenster.

Any range of wavelengths in the electromagnetic spectrum to which the atmosphere is transparent.

The unfrozen part of a river surrounded by river ice during the winter.

A globular defect in a thermoplastic sheet or film caused by incomplete plasticization; similar to a fisheye.

1. An aperture for the passage of particles or radiation in a nuclear reactor.

2. An energy range of relatively high transparency in the total neutron cross section of a material; such windows arise from interference between potential and resonance scattering in elements of intermediate atomic weight, and can be of importance in neutron shielding.

A confusion reflector consisting of strips of chaff, wire, or bars cut to give resonance at expected enemy radar frequencies, and dropped in clusters from aircraft or expelled from shells or rockets as a radar countermeasure.