Glossary of LEO Satellite Industry Terms Every Professional Should Know

Satellite industry conversations fail on vocabulary more often than on substance: a buyer who cannot distinguish committed information rate from advertised throughput signs a worse contract, and an investor who conflates constellation size with capacity misprices an operator. This LEO satellite industry glossary collects the 50-plus terms that carry real weight in filings, procurement documents and earnings calls — defined the way professionals actually use them.

On this page

• How This LEO Satellite Industry Glossary Is Organized
• Orbits and Orbital Mechanics
• Constellation Architecture
• Spectrum and Link Engineering
• Regulation and Policy
• LEO Satellite Industry Glossary: Business and Investment Terms
• Industry Implications
• What to Watch

How This LEO Satellite Industry Glossary Is Organized

Terms are grouped into five domains in the order most readers encounter them: orbital mechanics first, then constellation architecture, the spectrum and link engineering that governs performance, the regulatory vocabulary that governs market access, and the business metrics that govern valuations. Cross-domain fluency is the point — the industry’s defining decisions happen where these vocabularies meet. [INTERNAL LINK: what is low earth orbit → our foundational LEO explainer]

Orbits and Orbital Mechanics

LEO (Low Earth Orbit) — the band from roughly 160 to 2,000 km altitude. Home to broadband mega-constellations, Earth observation and the ISS; satellites orbit in 90–110 minutes at ~7.8 km/s.

MEO (Medium Earth Orbit) — 2,000 km to 35,786 km. Hosts navigation constellations (~20,000 km) and O3b-class communications fleets (~8,000 km).

GEO (Geostationary Orbit) — exactly 35,786 km over the equator, where orbital period matches Earth’s rotation and a satellite appears fixed in the sky. Approximately 480 ms of round-trip physics.

VLEO (Very Low Earth Orbit) — informal band below ~450 km where drag is severe but latency, link budgets and imaging resolution improve. An active area of platform development.

Sun-synchronous orbit (SSO) — a near-polar LEO whose plane precesses to cross any point at the same local solar time each pass; the standard choice for Earth-observation constellations needing consistent lighting.

Inclination — the angle between an orbital plane and the equator. Determines the latitudes a satellite covers; a 53° shell serves most population, polar inclinations serve everything.

Orbital plane / shell — a plane is one orbital path shared by several satellites; a shell is the set of planes at a common altitude and inclination. Constellation filings are specified plane by plane, shell by shell.

Orbital decay — altitude loss from atmospheric drag. Below ~500 km it deorbits dead spacecraft within years — LEO’s built-in debris mitigation.

Station-keeping — propulsive corrections that hold a satellite in its assigned slot or shell. Electric (ion) propulsion is now standard on broadband LEO satellites.

TLE (Two-Line Element set) — the standard data format describing a satellite’s orbit, used for tracking and conjunction screening.

Conjunction — a predicted close approach between two orbiting objects. Conjunction warnings drive collision-avoidance maneuvers — thousands per year across large constellations, per operator disclosures.

Constellation Architecture

Constellation — a coordinated network of satellites in similar orbits operated as one system. Mega-constellation informally means hundreds to thousands of satellites.

Inter-satellite link (ISL) — laser or RF links between satellites enabling in-space routing. Optical ISLs — up to 25 Gbps per link on today’s largest mesh — let traffic cross oceans without touching ground stations.

Ground segment — all Earth-based infrastructure: gateways, network operations centers (NOCs), points of presence and user terminals.

Gateway (teleport) — a high-capacity ground station connecting the constellation to the internet backbone, typically sited near cheap fiber and licensed spectrum clearance.

User terminal — the customer-side antenna and modem. Terminal economics — cost, subsidy, installation — are the gating unit economics of consumer LEO.

Phased array antenna — an electronically steered flat-panel antenna that forms and moves beams in milliseconds with no moving parts. Do not call it a dish; the distinction is load-bearing in LEO, where satellites cross the sky in minutes.

Handoff — the transfer of a user’s connection between satellites (or beams) as they pass overhead. Handoff quality shows up in jitter, not in advertised speed.

Bent-pipe vs regenerative payload — a bent-pipe satellite relays signals without processing them; a regenerative payload demodulates and routes onboard. Modern broadband LEO is increasingly regenerative, enabling mesh routing.

Mesh routing — carrying traffic across the constellation via ISLs, touching ground only near the destination. The basis of coverage over oceans, poles and jurisdictions without local gateways.

Spectrum and Link Engineering

The frequency bands, at a glance:

Band	Approx. range	Typical LEO role
L	1–2 GHz	Mobile satellite services, IoT, GNSS
S	2–4 GHz	TT&C, mobile services, some D2D
X	8–12 GHz	Government and military
Ku	~12–18 GHz	User links, established broadband
Ka	~26.5–40 GHz	High-throughput user and gateway links
Q/V	~40–75 GHz	Feeder/gateway links, next-generation capacity
E	71–86 GHz	Experimental high-capacity feeders

Link budget — the end-to-end accounting of signal power, gains and losses that determines whether a link closes at a given data rate. The math behind every “can it reach a phone?” question.

EPFD (Equivalent Power Flux Density) — the ITU regulatory metric capping the interference NGSO constellations may impose on GEO systems. The single most commercially consequential acronym in current LEO regulation.

Spot beam — a narrow, high-gain beam serving a small cell of coverage; frequency reuse across many spot beams is where modern capacity comes from. Beamforming is the electronic shaping and steering of those beams.

Rain fade — signal attenuation from precipitation, worsening with frequency (Ka and above). Managed with adaptive coding and modulation, site diversity and link margin — a link-budget issue at any orbit.

Throughput vs capacity — capacity is what the system could deliver; throughput is what a user gets. Conflating them is the oldest trick in satellite marketing.

CIR (Committed Information Rate) — contractually guaranteed minimum throughput, as opposed to “up to” rates. The number that matters in enterprise agreements.

Contention (oversubscription) ratio — how many users share the same capacity. Determines real-world performance in busy cells; rarely published, always worth asking.

Jitter — variation in latency over time. LEO handoffs make worst-case jitter, not median latency, the figure of merit for real-time applications.

Regulation and Policy

ITU (International Telecommunication Union) — the UN agency coordinating global spectrum and orbital filings. Priority in its filing queues is a strategic asset operators litigate over.

WRC (World Radiocommunication Conference) — the ITU treaty conference, held roughly every four years, where allocation and EPFD rules are revised. WRC-27 agenda items are already shaping operator strategy.

NGSO (Non-Geostationary Orbit) — regulatory umbrella term for LEO and MEO systems; most FCC and ITU rulemaking language says “NGSO,” not “LEO.”

Market access / landing rights — national authorization to sell service and operate gateways in a country. Constellations are global; revenue is licensed country by country.

Spectrum coordination — the negotiated deconfliction of frequency use between systems, bilateral and via ITU procedures. Where constellation deployments quietly slow down.

Post-mission disposal (PMD) — the requirement to remove satellites after service; FCC rules require deorbit within five years of mission end for satellites licensed under them.

Space traffic management (STM) — the emerging framework of tracking, coordination and rules-of-the-road for orbital operations; institutionally unsettled between agencies and nations.

Kessler syndrome — the runaway scenario where collisions generate debris that causes further collisions, degrading an orbital band for decades. The reference risk case in every debris policy debate. [INTERNAL LINK: kessler syndrome space debris LEO → our debris threat analysis]

Active debris removal (ADR) — missions that capture and deorbit defunct objects. Technically demonstrated, commercially embryonic.

LEO Satellite Industry Glossary: Business and Investment Terms

Replacement cycle — the permanent capex rhythm set by 5–7 year LEO satellite lifetimes. Constellations are production lines, not projects; model capex accordingly.

Cost per bit — the all-in cost of delivering a unit of data. The metric that ultimately ranks operators in abundance economics.

ARPU (Average Revenue Per User) — monthly revenue per subscriber, segmented consumer vs enterprise vs mobility; blended ARPU hides where the margin lives.

Subscriber acquisition cost (SAC) — marketing plus hardware subsidy per net new customer. Terminal subsidies make LEO SAC look more like wireless carriers than ISPs.

Wholesale capacity — selling constellation throughput to distributors, telcos or governments rather than end users — OneWeb’s model, and a growing share of the market.

Backhaul — carrying traffic from a network aggregation point (like a rural cell site) to the core network. A major LEO enterprise segment: satellite as supplier to telcos, not competitor.

Direct-to-device (D2D) / direct-to-cell — service from satellite to unmodified phones and IoT hardware, typically via partnerships using carrier spectrum. Messaging first, broadband progressively. [INTERNAL LINK: direct to device satellite technology → how D2D works and who leads]

MVNO (Mobile Virtual Network Operator) — a service brand running on another operator’s network; the template for how satellite capacity increasingly reaches retail customers.

Vertical integration — owning launch, manufacturing, network and distribution. The structural cost advantage that defines the current market leader; the strategic question for everyone else.

Launch cadence — the rate of orbital launches an operator can buy or perform. The binding constraint on constellation deployment and replenishment — and a leading indicator worth tracking quarterly.

Proliferated LEO (pLEO) — defense terminology for resilient many-satellite architectures, popularized by the US Space Development Agency; the Pentagon’s answer to high-value single-target satellites.

Frequently Asked Questions

What is the difference between a constellation and a mega-constellation?

No formal threshold exists. “Constellation” means any coordinated multi-satellite system (Iridium’s 66 qualifies); “mega-constellation” is industry shorthand for systems in the hundreds to thousands, used for the broadband networks filed since the mid-2010s.

What is EPFD and why does it matter commercially?

Equivalent Power Flux Density is the ITU limit on interference NGSO constellations may impose on GEO networks. It caps how aggressively LEO systems can use shared spectrum, so revising it — a live WRC-27 battleground — effectively reallocates commercial value between orbits.

What is the difference between CIR and advertised throughput?

CIR is a contractual floor the operator must deliver; advertised “up to” throughput is a ceiling under ideal conditions. Enterprise agreements are priced on CIR; consumer plans are marketed on ceilings. Knowing which one is on the page changes negotiations.

Is direct-to-device the same as direct-to-cell?

Effectively yes — both describe satellite service to unmodified phones, usually via carrier partnerships and terrestrial spectrum. “Direct-to-device” is the broader term, also covering IoT hardware; “direct-to-cell” is the phone-specific branding some operators use.

What is Kessler syndrome in practical terms?

A debris-cascade scenario: collisions create fragments that cause further collisions until an orbital band becomes hazardous for decades. It is a risk model, not a prediction — and the reason post-mission disposal rules and conjunction screening are now core operating costs.