Glossary - O

Occasional use transponder
a satellite transponder leased out to multiple clients on a short term (usually hourly) basis
(satellite communications)

On-station
in its operational position in orbit
(orbits)

Oort cloud
a vast cloud of icy planetesimals thought to orbit around the Sun in the outer solar system at a distance of between 2,000 and 200,000 AU
(planetary science)

Open network
a network implemented to an industry accepted standard
(communications)

Opposition
the configuration in which one celestial body is directly opposite another celestial body in the celestial sphere
(astronomy)

Optical ground station
a ground station that uses laser beams to communicate with spacecraft
(earth station technology)

Orbit
circular or elliptical path an object follows around the Sun, a planet such as the Earth, or a smaller body such as an asteroid
(orbits)

Orbital slot
a location on the geostationary orbit allocated to a satellite; slots are typically 2°, 3° or 6° apart, depending on frequency and application, to minimise interference
(orbits, satellite communications, regulations)

Orbit lowering
reduction in the altitude of a spacecraft’s orbit, often done to deorbit a spacecraft
(orbits)

Orbit raising
increase in the altitude of a spacecraft’s orbit, often done either to counter a reduction in orbital altitude due to atmospheric drag or to move a satellite out of an operational orbit (such as geostationary orbit) at the end of the satellite’s life to avoid collisions with satellites remaining in the orbit
(orbits)

Outage
temporary loss of service
(communications)

Outbound
in a VSAT system, a carrier transmitted from the hub to remote terminals
(satellite communications)

Output backoff
the amount of power below saturation that an amplifier (usually a power amplifier) is set to
(technology)

Oxididant
a rocket propellant which provides oxygen to burn the fuel; typical oxidants are liquid oxygen and hydrogen peroxide
(rocketry)