Reference

Launch glossary

Every term this site uses, in plain English. Deep-link any entry — for example glossary.html#gto.

NET (No Earlier Than) #: The earliest possible liftoff time. Launch dates routinely slip later — NET is a promise not to launch before that moment, not a guarantee to launch at it.
Launch window #: The span of time a rocket can lift off and still reach its target. Some missions have hours; rendezvous and interplanetary missions can be instantaneous — miss the second, wait for the next day (or the next planetary alignment).
T− / T+ #: The countdown clock. T−10:00 means ten minutes before liftoff; T+02:30 means two and a half minutes after. Built-in holds can freeze the clock while the actual time keeps moving.
Scrub #: A launch attempt called off before liftoff — usually for weather, a technical issue, or a stray boat in the range. The rocket is fine; everyone comes back another day.
Static fire #: A full engine test with the rocket firmly bolted to the pad, days before flight. If you see flame and no movement, it went perfectly.
Max-Q #: The moment of maximum aerodynamic pressure on the vehicle — the sky is pushing back hardest. Engines often throttle down briefly to ease through it.
MECO / SECO #: Main Engine Cutoff and Second-stage Engine Cutoff. Milestones where a stage finishes its burn; SECO usually means the payload has reached its initial orbit.
Stage separation #: The spent booster lets go and the upper stage lights its own engine. Two vehicles now: one coasting to orbit, one falling home.
Fairing #: The nose-cone shell protecting the payload through the atmosphere. Jettisoned once the air thins; SpaceX famously catches and reuses the halves.
RTLS / droneship landing #: How boosters come home: Return To Launch Site (a landing pad near where it left) or a droneship at sea when the mission needs every drop of fuel downrange.
LEO — Low Earth Orbit #: Roughly 200–2,000 km up, circling Earth in about 90 minutes. Home to the ISS, Starlink, and most satellites launched today.
MEO — Medium Earth Orbit #: Between LEO and GEO, around 2,000–35,000 km. Navigation constellations (GPS, Galileo) live here at ~20,000 km.
GEO — Geostationary orbit #: 35,786 km above the equator, where one orbit takes exactly one day — the satellite hangs over the same spot forever. Prime real estate for communications and weather satellites.
GTO — Geostationary Transfer Orbit #: The stretched ellipse a rocket drops a satellite into on the way to GEO: low at one end (perigee), out near GEO altitude at the other (apogee). The satellite finishes the climb with its own engine over weeks.
SSO — Sun-synchronous orbit #: A near-polar orbit tuned so the satellite crosses every point at the same local solar time — perfect lighting for Earth-imaging. These launches head toward the poles, which is why California and New Zealand fly south.
Inclination #: The tilt of an orbit versus the equator, in degrees. 0° hugs the equator, 90° is polar. A launch site can't easily reach inclinations lower than its own latitude — that's why equatorial pads are precious.
Apogee / perigee #: The highest and lowest points of an elliptical orbit. Rockets move slowest at apogee and fastest at perigee — watch a GTO mission's animation and you'll see it.
Escape trajectory / injection #: Burns like TLI (Trans-Lunar Injection) or TMI (Trans-Mars Injection) that push a spacecraft past Earth's grip entirely. No orbit — a departure.
Suborbital #: Up past the 100 km Kármán line and back down without completing an orbit. A few minutes of spaceflight — the New Shepard experience.
Webcast #: The live broadcast, typically starting 15–60 minutes before liftoff. This site's LIVE badge and mission pages link straight to it — and embed it in the final hour.

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