Glossary
Definitions
140 definitions
ADCS (Attitude Determination and Control System)
The satellite subsystem responsible for determining the spacecraft's orientation in space (using star trackers, gyroscopes, and sun sensors) and maintaining it within required pointing accuracy (using reaction wheels, magnetorquers, and thrusters) — critical for antenna pointing, solar array orientation, and instrument alignment.
AIS (Automatic Identification System)
A VHF radio transponder system mandatory on ships over 300 gross tonnes that continuously broadcasts vessel identity, position, course, and speed, used for maritime traffic management and vessel tracking — extended globally via satellite (S-AIS) since the mid-2000s.
Active Debris Removal (ADR)
The emerging space technology field focused on capturing and deorbiting defunct satellites and rocket bodies using robotic spacecraft equipped with nets, harpoons, or robotic arms — considered essential for preventing Kessler Syndrome in densely populated orbital shells.
Amazon Kuiper
Amazon's planned LEO broadband mega-constellation of 3,236 satellites at 590–630 km altitude, authorised by the FCC in 2020, with initial commercial launches underway in 2024–2025, targeting residential broadband, enterprise connectivity, and Amazon Web Services (AWS) infrastructure.
Anti-Jamming (SATCOM)
Technical measures in satellite terminals and system design that maintain communication links in the presence of intentional radio frequency interference — including spread-spectrum waveforms, directional antenna null steering, frequency hopping, and power control — critical for military and government satellite communications.
Asset Tracking via Satellite
The real-time or near-real-time monitoring of mobile assets — vehicles, containers, livestock, equipment — using GPS/GNSS positioning combined with satellite IoT data links to transmit location, status, and sensor data from remote areas beyond cellular coverage.
Bandwidth on Demand (BoD)
A satellite network management capability that dynamically allocates additional bandwidth to a user terminal or site on request — either manually by the network operator or automatically based on traffic demand — enabling efficient sharing of satellite capacity without over-provisioning for peak demand.
Beamforming
A signal processing technique that controls the phase and amplitude of signals across a multi-element antenna array to concentrate transmission or reception in a specific direction, enabling precise spatial targeting, interference suppression, and multiple simultaneous beams.
CNES (Centre National d'Études Spatiales)
The French national space agency, established in 1961 with an annual budget of approximately €2.8 billion — responsible for France's civil space programme, operating launch facilities at Kourou (Guiana Space Centre), and funding satellite R&D through government programmes and ESA contributions.
COSPAS-SARSAT
An international satellite-based search and rescue system established in 1982 by the USA, Russia, Canada, and France, which detects distress signals from EPIRBs (maritime), ELTs (aviation), and PLBs (personal) at 406 MHz and relays them to ground stations to alert rescue authorities worldwide.
Capacity Lease
The traditional satellite business model where operators sell defined frequency bandwidth and power allocations (transponders, MHz, or Mbps) to service providers under multi-year contracts — typically $1–3 million per transponder per year for GEO Ku-band, with the customer providing their own ground equipment and operations.
Chemical Propulsion
Spacecraft propulsion using the combustion of liquid or solid chemical propellants to generate high thrust — used for orbit insertion, large trajectory corrections, and emergency manoeuvres where rapid delta-v is needed, at the cost of lower specific impulse than electric propulsion.
Collision Avoidance Manoeuvre
A propulsive burn executed by an active satellite to change its trajectory when conjunction analysis predicts a collision probability exceeding regulatory thresholds — typically 1-in-10,000 — consuming propellant and requiring coordination between operators to avoid creating new collision risks.
Conjunction Analysis
The process of comparing predicted orbital trajectories for all tracked space objects to identify close approaches (conjunctions) where collision probability exceeds a defined threshold, typically 1 in 10,000, triggering collision avoidance manoeuvre planning for active spacecraft.
Copernicus Programme
The EU and ESA's Earth observation programme — the world's largest — operating the Sentinel satellite family to deliver free, open, near-real-time data on land, ocean, atmosphere, and emergency management, with over 350 TB of data distributed daily to public and commercial users.
CubeSat
A standardised small satellite format based on 10×10×10 cm modules (1U = max 2 kg), developed in 1999 by Cal Poly and Stanford, that has democratised access to space by enabling universities and startups to build satellites for under $1 million.
DVB-S2 / DVB-S2X
Digital Video Broadcasting — Satellite Second Generation (DVB-S2) is the global standard for satellite broadband and broadcasting transmission; DVB-S2X is its 2014 extension delivering up to 51% higher spectral efficiency through finer modulation granularity, lower roll-off factors, and support for very low signal conditions.
Debris Mitigation
A set of design, operational, and disposal practices mandated by ITU guidelines and national regulators to minimise the creation of new orbital debris — including passivation of propulsion systems, controlled deorbit within 5 years of mission end, and avoiding manoeuvres that could cause fragmentation.
Deorbit
The controlled manoeuvre or natural process by which a satellite is removed from its operational orbit and caused to re-enter Earth's atmosphere, either through propulsive retro-burn (controlled deorbit) or gradual atmospheric drag (passive deorbit) — mandated within 5 years of end of life for LEO satellites by FCC rules (2022).
Digital Payload
A satellite communications payload where the signal processing — demodulation, switching, and re-modulation — is performed digitally onboard the spacecraft, enabling flexible beam routing, dynamic bandwidth allocation, and software-upgradable functionality unlike traditional analogue bent-pipe transponders.
Digital Twin (Space)
A virtual replica of a satellite, ground station, or entire constellation — continuously updated with real telemetry — used to simulate performance, predict failures, optimise operations, and test configuration changes before applying them to the physical system.
Direct-to-Device (D2D)
A satellite service architecture where standard, unmodified smartphones communicate directly with LEO satellites using standard cellular protocols (LTE/5G NTN), eliminating the need for specialised satellite handsets or additional hardware.
Dual-Use (Civil & Defense)
The characteristic of satellite systems and technologies that can serve both civilian commercial applications and military or government security requirements — a strategic attribute that enables government investment to subsidise commercial development and vice versa.
EIRP (Effective Isotropic Radiated Power)
The product of a transmitter's output power and its antenna gain relative to an isotropic radiator, expressed in dBW — the fundamental measure of how much radio frequency power is directed toward the target, used in link budget calculations to determine received signal strength.
EPIRB
Emergency Position Indicating Radio Beacon — a maritime safety device that, when activated (manually or by water immersion), transmits a distress signal at 406 MHz via the COSPAS-SARSAT satellite network to alert rescue authorities of a vessel's identity and GPS position within minutes.
ESA (European Space Agency)
An intergovernmental organisation of 22 European member states with an annual budget of approximately €7.8 billion (2023), responsible for Europe's civil space programme — operating the Copernicus Earth observation, Galileo GNSS, Ariane launch, and science missions — and one of the world's primary funders of space technology R&D.
Earth Observation (EO)
The use of satellite-based sensors — optical cameras, SAR radars, multispectral and hyperspectral imagers — to collect imagery and geospatial data about Earth's surface, atmosphere, and oceans for applications ranging from defence and agriculture to climate monitoring and disaster response.
Electric Propulsion
A spacecraft propulsion technology that uses electric power (from solar arrays) to accelerate propellant ions or plasma to exhaust velocities 10–80× higher than chemical rockets, achieving far greater fuel efficiency (Isp) at the cost of very low thrust — ideal for station-keeping and orbit raising over months.
Elevation Angle
The angle between the horizon and the line of sight from a ground station or user terminal to a satellite, measured in degrees from 0° (horizon) to 90° (directly overhead). Higher elevation angles reduce atmospheric path length, rain fade, and multipath interference — most VSAT systems require a minimum elevation of 5–20°.
End-of-Life (EOL) Disposal
The controlled removal of a satellite from its operational orbit at the end of its mission life — deorbit to atmospheric re-entry within 5 years for LEO satellites (per FCC/IADC rules), or boost to a graveyard orbit ~300 km above GEO for geostationary satellites — to prevent accumulation of long-term orbital debris.
Eutelsat OneWeb
A LEO broadband constellation of 648 satellites at 1,200 km altitude, operated by Eutelsat following its 2023 merger with OneWeb, targeting enterprise, government, and B2B customers globally with a focus on connectivity-as-a-service through telecom operator partners.
FCC (Federal Communications Commission)
The US independent regulatory agency responsible for licensing all commercial satellite systems operating in the United States or serving US customers, including spectrum authorisation, orbital debris mitigation rule-making, and Earth station licensing.
Frequency Coordination
The bilateral or multilateral negotiation process between satellite operators — mediated by national administrations and the ITU — to ensure that a new satellite network does not cause harmful radio interference to existing networks operating in the same frequency bands.
Frequency Reuse
The technique of transmitting on the same frequency band simultaneously in multiple geographically separated spot beams, increasing total system capacity by a factor equal to the reuse factor — the foundational principle enabling High Throughput Satellite (HTS) systems to deliver 50–100× the capacity of traditional wide-beam satellites.
G/T (Figure of Merit)
The ratio of receive antenna gain (G) to system noise temperature (T), expressed in dB/K — the fundamental measure of a receiver's sensitivity in a satellite link. A higher G/T means a receiver can detect weaker signals, enabling smaller transmitting antennas or longer link distances.
GEO (Geostationary Orbit)
Fixed orbit at 35,786 km above the equator where satellites appear stationary relative to Earth, enabling permanent coverage of one-third of the globe with a single satellite, but with 550+ ms round-trip latency.
GNSS / GPS
Global Navigation Satellite Systems (GNSS) are constellations of MEO satellites — GPS (USA), Galileo (EU), GLONASS (Russia), BeiDou (China) — that broadcast precise timing signals enabling receivers on Earth to calculate their position with metre or sub-metre accuracy.
GPS Spoofing
A cyberattack that transmits counterfeit GPS signals stronger than genuine satellite signals to deceive a receiver into computing a false position — used to mislead ship navigation, redirect drones, or manipulate timing-dependent systems, with incidents documented in the Black Sea, Persian Gulf, and near conflict zones.
Galileo (GNSS System)
The European Union's global satellite navigation system — 30 satellites at 23,222 km MEO — operated by the EU Agency for the Space Programme (EUSPA), providing civilian open service at 1–5 m accuracy and a High Accuracy Service at better than 20 cm, fully interoperable with GPS and other GNSS.
Gateway
A large ground station that aggregates satellite capacity from one or more spot beams and connects it to the terrestrial internet or private network backbone, acting as the interface between the space and ground segments.
Globalstar
A US mobile satellite operator running 24 LEO satellites at 1,414 km altitude in L-band (user) and S-band (satellite-to-user) for voice, messaging, and IoT services — known for Apple's Emergency SOS satellite feature on iPhone 14+ (2022), which uses dedicated Globalstar frequencies.
Green Propulsion
Spacecraft propulsion technologies that replace highly toxic hydrazine monopropellant with less hazardous alternatives — including ammonium dinitramide (ADN)-based propellants (LMP-103S, AF-M315E), electric propulsion (xenon/krypton ion thrusters), and cold gas thrusters using non-toxic gases — improving safety and reducing handling costs.
Ground Segment
All Earth-based infrastructure that supports a satellite system — including gateway stations, TT&C facilities, network operations centres, and mission control — responsible for controlling the satellite, processing data, and connecting the space segment to terrestrial networks.
Ground Station
Earth-based facility equipped with antennas and signal processing equipment for two-way communication with satellites: transmitting commands and receiving telemetry, data, or user traffic.
HEO (Highly Elliptical Orbit)
Strongly elliptical orbit with a perigee near 600 km and an apogee up to 40,000 km, designed to provide extended dwell time over high-latitude regions unreachable by GEO satellites.
High Throughput Satellite (HTS)
A satellite architecture that uses many narrow spot beams with aggressive frequency reuse to deliver total throughput of 100 Gbps to several Tbps — 20 to 100 times more capacity than traditional wide-beam satellites at a fraction of the cost per bit.
Horizon Europe (Space Funding)
The EU's €95.5 billion research and innovation programme (2021–2027) that includes substantial funding for space research under Cluster 4 and 6 — supporting satellite technology development, Earth observation applications, and space situational awareness through competitive grants to research institutions and companies.
ITU (International Telecommunication Union)
The United Nations specialised agency responsible for global coordination of radio spectrum and satellite orbital positions, whose Radio Regulations are the binding international treaty governing which frequency bands each service type can use and how orbital filings are coordinated.
ITU Filing
The formal submission made by a national administration to the ITU on behalf of a satellite operator, notifying other administrations of the planned satellite network's frequency and orbital parameters — the first step in securing international recognition and coordination priority for spectrum rights.
In-Flight Connectivity (IFC)
Satellite-based internet service delivered to passengers and crew aboard commercial aircraft in flight, with the global market reaching $6.3 billion in 2024 and over 10,000 equipped aircraft, powered by Ku-band and Ka-band VSAT and emerging LEO systems.
In-Orbit Servicing
The emerging capability of sending robotic spacecraft to rendezvous with existing satellites in orbit to refuel them, repair or replace components, extend their operational life, or modify their orbit — transforming satellites from disposable assets into maintainable infrastructure.
Inmarsat
A British GEO satellite operator founded in 1979, originally serving maritime distress communications, now operating L-band (Inmarsat-4), Ka-band Global Xpress (I-6), and EAN (European Aviation Network) services — acquired by Viasat in 2023, creating a global HTS satellite operator.
Intelsat
One of the world's largest GEO satellite operators, founded in 1964 as an intergovernmental organisation and privatised in 2001, operating 50+ GEO satellites across C, Ku, and Ka bands — completed a merger with SES in 2024 to create the world's largest commercial satellite operator.
Inter-Satellite Link (ISL)
A direct communication link between two satellites, using laser (optical) or radio frequency (RF) technology, enabling traffic routing across a constellation without touching the ground and reducing latency by avoiding the uplink-downlink round-trip via ground gateways.
IoT via Satellite
The use of satellite networks to connect sensors, trackers, and devices in remote areas beyond terrestrial cellular coverage — delivering small data packets (position, temperature, status) from ships, trucks, pipelines, weather stations, and agricultural equipment to cloud platforms via LEO or GEO constellations.
Iridium
The only mobile satellite operator with true pole-to-pole global coverage, operating 66 active LEO satellites at 781 km altitude with inter-satellite links — providing satellite phone, IoT (Iridium Short Burst Data), maritime, and aviation services through a second-generation Iridium NEXT constellation completed in 2019.
Ka-band
Satellite frequency band occupying 26.5–40 GHz, with uplinks typically at 27.5–31 GHz and downlinks at 17.3–20.2 GHz, offering approximately 13.5 GHz of available bandwidth — twice as wide as Ku-band — at the cost of greater susceptibility to rain fade.
Kessler Syndrome
A theoretical cascade scenario, described by NASA scientist Donald Kessler in 1978, where the density of objects in LEO becomes high enough that collisions generate debris faster than it naturally decays, creating a self-sustaining chain reaction that could render certain orbital shells unusable.
Ku-band
Satellite frequency band at 12–18 GHz (uplink 14–14.5 GHz, downlink 11.7–12.75 GHz) used extensively for direct-to-home (DTH) broadcasting, maritime VSAT, aeronautical connectivity, and government communications, offering good rain resilience compared to Ka-band.