Space and Solar Definitions - O

One-way - Communications mode consisting only of downlink received from a spacecraft.

Oort cloud - A large number of comets theorized to orbit the sun in the neighborhood of 50,000 AU.

OPCT - Operations Planning and Control Team at JPL, "OPSCON." Obsolete, replaced by DSOT, Data Systems Operations Team.

OPNAV - Optical Navigation (images).

OSI - ISO's Open Systems Interconnection protocol suite.

OSR - Optical Solar Reflector, thermal control component onboard a spacecraft.

OSSA - Office Of Space Science and Applications, NASA.

OTM - Orbit Trim Maneuver, spacecraft propulsive maneuver.

OWLT - One-Way Light Time, elapsed time between Earth and spacecraft or solar system body.