Launches
How orbital launch works, and why schedules move.
Overview
Launch is the most constrained part of spaceflight: a narrow window set by orbital mechanics, a vehicle operating at the limits of its margins, and weather rules that ground flights for conditions that look unremarkable from the ground.
- Launch windows are set by orbital geometry, not by convenience.
- Reaching orbit is mostly about horizontal speed, not altitude.
- Launch site latitude constrains which orbits are efficiently reachable.
- Scrubs are routine, and most are weather or minor technical issues rather than failures.
Orbit is about sideways speed
The common mental model of launch — going up — is misleading. Reaching the altitude of low Earth orbit is comparatively easy; staying there requires roughly 7.8 kilometres per second of horizontal velocity, and the overwhelming majority of a launch vehicle's energy goes into that rather than into altitude.
This is why rockets pitch over shortly after lift-off and spend most of the ascent travelling nearly horizontally. A suborbital flight reaching space and falling back differs from an orbital flight not in height but in speed, by a very large margin.
Why windows are narrow
- Rendezvous missions must launch when the target's orbital plane passes over the launch site, which for the ISS gives windows lasting minutes.
- Interplanetary missions need the correct relative planetary geometry, recurring at intervals of months to years.
- Sun-synchronous orbits require launch at a specific local solar time to achieve the intended orbital plane orientation.
- Geostationary transfers are less constrained but still shaped by the need to minimise plane-change energy.
- Missing a window can mean a delay of a day, a month, or in interplanetary cases years.
Latitude shapes what is reachable
A launch site's latitude sets the minimum orbital inclination directly reachable without an expensive plane change: a vehicle cannot reach an orbit inclined less than the launch latitude without additional manoeuvring. Equatorial sites are therefore advantaged for geostationary missions.
Earth's rotation adds a further benefit, providing roughly 460 metres per second of eastward velocity at the equator and less at higher latitudes. Both effects explain why launch sites cluster at low latitudes where geography and politics permit, and why high-latitude sites specialise in polar and sun-synchronous orbits.
Why launches scrub
Delays are normal and are usually not failures. Weather rules are stricter than they appear: constraints cover upper-level winds, cloud types capable of triggering lightning, and conditions along the ascent corridor and at abort landing sites, so a launch can scrub under a clear blue sky.
Technical scrubs frequently involve sensor readings out of tolerance rather than confirmed faults, and holds are also called for range conflicts such as a boat or aircraft entering the safety zone. A scrubbed launch generally reflects margins being enforced, which is what they exist for. Asteria Star records planned launches as planned and does not present schedules as commitments.
Continue in the data
Catalogues, hubs, and reference pages that hold the underlying records for this topic.
Frequently asked
- Why are launch windows sometimes only a few minutes long?
- Because of orbital geometry. To rendezvous with something already in orbit, a vehicle must launch as the target's orbital plane passes over the site, and that alignment lasts only minutes. Interplanetary launches face the same constraint over much longer cycles, with windows recurring at intervals of months or years.
- Why do rockets tilt over instead of going straight up?
- Because orbit is mainly about horizontal speed, not altitude. Staying in low Earth orbit requires roughly 7.8 kilometres per second sideways, and most of a launch vehicle's energy goes into achieving that. Climbing straight up would reach space and fall straight back down.
- Why does a launch scrub on a clear day?
- Because launch weather rules cover far more than visible conditions at the pad — upper-level winds, cloud types capable of triggering lightning, and conditions along the ascent corridor and at abort landing sites all apply. Technical scrubs are also often triggered by sensor readings out of tolerance rather than by confirmed faults.
- Why are launch sites usually near the equator?
- Two reasons. A site's latitude sets the minimum orbital inclination reachable without an expensive plane change, so equatorial sites suit geostationary missions. And Earth's rotation supplies about 460 metres per second of free eastward velocity at the equator, decreasing toward the poles.