Glossary
Definitions
140 definitions
Space Sustainability
The principle that space activities must be conducted in a way that preserves the long-term usability of orbital environments for future generations — encompassing debris mitigation, responsible constellation design, frequency coordination, and emerging frameworks for space traffic management.
Space Traffic Management (STM)
An emerging framework of rules, technical standards, and international coordination mechanisms designed to manage the growing number of objects in Earth orbit and prevent collisions — analogous to air traffic control but for space, currently lacking a binding international authority.
Spectrum Coordination
The process of managing radio frequency allocations between competing users — satellite operators, terrestrial mobile networks, radar systems, and others — to prevent harmful interference, typically involving national regulators, ITU coordination procedures, and bilateral agreements between operators.
Spot Beam
A narrow, concentrated satellite antenna beam that illuminates only a small geographic area (100–500 km diameter) rather than a broad continental region, enabling higher power concentration per unit area, frequency reuse across the coverage region, and the High Throughput Satellite architecture.
Starlink
SpaceX's LEO broadband mega-constellation, the largest satellite fleet in history with over 10,000 satellites at ~550 km altitude, serving 10+ million customers across 150 countries as of early 2026 with 100–300 Mbps download speeds and 25–60 ms latency.
System Integrator
A company that designs, assembles, and delivers complete satellite communication solutions by combining products from multiple vendors — satellite capacity, ground equipment, network management software, and value-added services — into a turnkey system for an end customer.
TT&C (Telemetry, Tracking & Command)
The subsystem and associated ground infrastructure responsible for monitoring satellite health (telemetry), determining its precise orbital position (tracking), and sending operational instructions (command).
Telesat Lightspeed
A Canadian LEO broadband constellation of 198 satellites at approximately 1,000 km altitude, designed and operated by Telesat — one of the world's largest GEO satellite operators — targeting enterprise, government, and mobile network operator customers with committed multi-gigabit throughput and 50 ms latency.
Thermal Control System
The satellite subsystem that maintains all components within their operating temperature range — typically −40°C to +85°C for electronics — using passive techniques (multi-layer insulation, surface coatings, radiators) and active techniques (heaters, heat pipes, louvers) to manage the extreme thermal environment of space.
Throughput
The actual data rate successfully delivered through a satellite communication link, measured in Mbps or Gbps — distinguished from theoretical capacity by the effects of protocol overhead, ARQ retransmissions, adaptive modulation backoff during rain fade, and network contention among multiple users.
Transfer Orbit
An intermediate elliptical orbit used to move a satellite from its initial launch orbit to its final operational orbit — most commonly the Geostationary Transfer Orbit (GTO), with perigee near LEO (~185 km) and apogee near GEO (35,786 km), requiring an apogee kick burn to circularise.
Transponder
The core signal processing unit of a communications satellite that receives an uplink signal, translates it to a downlink frequency, amplifies it, and retransmits it toward Earth — the fundamental element of satellite bandwidth that operators lease to customers.
Uplink / Downlink
The two directions of a satellite communication link: the uplink is the radio transmission from Earth to the satellite; the downlink is the transmission from the satellite back to Earth. Each uses a different frequency band to avoid self-interference between transmit and receive paths.
User Segment
The customer-facing equipment of a satellite system — including VSAT terminals, satellite phones, flat-panel antennas, GPS receivers, and IoT devices — that accesses the satellite service and represents the primary interface between the end user and the space infrastructure.
VLEO (Very Low Earth Orbit)
Experimental orbital region below 400 km altitude offering ultra-low latency and superior imaging resolution, but requiring constant propulsion to counteract atmospheric drag and specialised coatings against atomic oxygen corrosion.
VSAT
A two-way satellite ground station with a small dish (0.75–2.4 m diameter) used to provide broadband internet, voice, and data services to remote locations via geostationary satellites, organised in star (hub-spoke) or mesh network topologies.
Very High Throughput Satellite (VHTS)
The next generation beyond HTS, with total capacity exceeding 1 Tbps from a single satellite, achieved through hundreds of narrow spot beams, aggressive frequency reuse, and Q/V-band feeder links — exemplified by ViaSat-3 (1 Tbps+) and Eutelsat Konnect VHTS (500 Gbps).
Viasat
A US satellite operator and technology company known for pioneering HTS GEO broadband (ViaSat-1, -2, -3) and acquiring Inmarsat in 2023 — combining GEO high-capacity broadband with L-band global mobile services to serve consumer, enterprise, aviation, maritime, and government markets.