ORBIT
A FIELD GUIDE TO ISS & MIR
Ten chapters on why spacecraft don't fall, how two stations were built four hundred kilometres overhead, and what it costs to bring one home. Scroll to begin the mission.
BEGIN — CHAPTER 01 →Falling and missing the ground
Every satellite, station, and spacecraft in orbit is falling. Gravity never releases its grip. What keeps them from hitting the ground is not an absence of gravity — it is sideways speed.
Isaac Newton described it with a thought experiment: fire a cannonball fast enough, horizontally, from a tall enough mountain, and the curve of its fall will match the curve of the Earth falling away beneath it. It never lands. It orbits.
Adjust the launch speed below and watch the same cannonball find three different fates.
Three thresholds, three destinies
Soviet and Russian spaceflight literature names three critical speeds. Each one is the minimum required to escape one gravitational well and fall into the next.
The minimum horizontal speed for a stable circular orbit just above the atmosphere. Below it, an object falls back to Earth.
Escape velocity — the speed needed to break free of Earth's gravity entirely and never return, coasting outward with no more fuel spent.
Measured from Earth's orbit around the Sun, this is what's needed to leave the Solar System entirely — the speed of Voyager and Pioneer.
Humanity's largest orbital laboratory
Assembly began in 1998 when the Russian module Zarya and the American node Unity docked in orbit. Fifteen more major elements followed over more than a decade, built by five space agencies representing 15 nations — the largest cooperative engineering project ever flown.
FIG. 3.1 — SCHEMATIC MODULE MAP (NOT TO SCALE). SELECT A MODULE.
A day with no up or down
The station runs on Greenwich Mean Time, regardless of the sixteen sunrises its crew sees each day. Select a phase of the schedule.
Sixteen sunrises a day
Because the ISS orbits roughly once every 93 minutes while Earth turns underneath it, its ground track shifts west with every pass. A location isn't overflown at the same time twice in a row, and how often it's crossed at all depends on latitude — the station never flies over the poles.
Why a laboratory in freefall
Microgravity removes one variable — weight — that every experiment on Earth has to work around. That makes the ISS a testbed for medicine, materials, and the technology that will carry humans further.
The legendary predecessor
Mir — Russian for both 'peace' and 'world' — orbited for fifteen years, twice its planned lifetime, and hosted 28 long-duration crews from twelve countries. Scrub through the timeline.
A station built one module at a time
Mir pioneered the principle every later station would copy: a small core, expanded module by module until it became six pressurised compartments docked around a single node. Select one.
A controlled ending
By 1999, Mir's systems were failing faster than crews could repair them, and its Russian operators could no longer fund the station alongside their new commitment to ISS. Rather than let an uncontrolled reentry scatter debris unpredictably, engineers planned a precise, deliberate descent. Step through the sequence.
From Salyut to whatever comes next
Every station is an argument for the next one. Fifty-five years of continuous, overlapping design lineage sit between the first crewed station and the ones now being planned for the Moon and beyond.