Glossary - R

Radian
unit of angular measurement (equal to 57.296°) equal to the angle at the centre of a circle subtended by an arc equal in length to the radius of the circle
(mathematics)

Radio broadcasting
transmission of radio programmes intended for reception by the general public
(broadcasting)

Radio distribution
transmission of radio programmes (or parts of programmes such as news or advertising) from a central location for reception by local radio stations which then rebroadcast the transmissions, usually terrestrially
(broadcasting)

Radiation hardening
designing equipment (usually electronics) and materials to make them less susceptible to damage and spurious behaviour due to exposure to radiation (such as during spaceflight)
(technology)

Radio waves
a form of electromagnetic radiation with a frequency lower than 1 GHz
(physics)

Rain outage
loss of signal due to absorption and increased sky noise temperature caused by heavy rainfall
(communications)

Rake receiver
a receiver having a number of individual digital channels (called tines or fingers) which can combine these channels to form a stronger received signal
(technology)

Rapid Unscheduled Disassembly (RUD)
the unintended disintegration or explosion of a launch vehicle or spacecraft
(technology)

Red dwarf
a small, cool type of main sequence star
(astronomy, astrophysics)

Re-entry
the return of a spacecraft, through the Earth’s atmosphere, of a spacecraft originally launched from Earth
(spacecraft technology)

Reflection
the effect by which electromagnetic waves bounce off a surface they are incident on
(physics)

Reflection coefficient
numerical ratio of the reflected voltage to the incident voltage
(technology)

Refraction
the effect by which the direction in which electromagnetic waves are travelling changes when they pass between different transparent media
(physics)

Registration
in a mobile satellite system the locating of a user terminal to determine which gateway should serve it
(satellite communications)

Regolith
a layer of unconsolidated, loose, heterogeneous material covering solid rock and created by weathering on planets with an atmosphere and by meteorite impact on planets, moons, asteroids and comets
(planetary science)

Repeater
signal path through a communications satellite payload which receives, amplifies and retransmits a channel; another name for repeater is transponder
(satellite communications)

Retrograde
1: an orbit around the Sun in which the orbiting body orbits in the opposite direction to the planets in the Solar System
(orbits)

Retrograde
2: an orbit around a celestial body in which the orbiting body orbits in the opposite direction to which the celestial body rotates
(orbits)

Retrograde burn
a thruster burn which decreases the velocity of a spacecraft in the direction of its orbital motion around a celestial body
(orbital dynamics)

Rideshare
a rocket launch shared between several spacecraft; the launch may be primarily for a large spacecraft along with several smaller rideshare secondary spacecraft, or may just be for several rideshare spacecraft; on a particular launch the rideshare spacecraft often have different owners
(launcher technology)

Right Ascension (RA)
the angular distance (measured in hours, minutes and seconds) measured eastwards along the celestial equator from the plane which includes the Earth’s axis of rotation and the vernal equinox to the plane which includes the Earth’s rotational axis and the celestial object being observed
(astronomy)

Rotational period
the time taken for a celestial object (such as an asteroid, planet or star) to rotate 360° about its rotational axis
(planetary science)