Spaceflightpedia
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Understand how humans reach space.

An encyclopedia of spaceflight built for learning — guided paths, hands-on simulations and verified sources, from the first rocket to the Moon and beyond.

The Saturn V rocket carrying Apollo 11 lifts off from Pad 39A between billowing clouds of smoke and steam
Apollo 11 lifts off, 16 July 1969NASA

5learning paths

96sourced entries

473photographs & illustrations

0lessons you’ve completed

01 — Learning paths

Five lines through the Space Age.

Each line is a short course. Stations are lessons — tap one to preview it, mark it done, and your progress stays on this device.

Intermediate · ≈ 60 min · 6 lessons

The race to the Moon

A decade-long program in eleven crewed flights: the rehearsals, the landings, the near-disaster, and the suit that made it possible.

You’ll be able to
  • Put the Apollo missions in order and say what each proved
  • Explain how Apollo 13’s crew survived
  • Describe what made the A7L suit a spacecraft
Progress0 / 6
Lesson 1 of 6 · Entry

Apollo

The program, 1961–1972

Think about it before you read

Why did it take eight years and 400,000 people to land on the Moon?

Read the entry →

02 — The lab · experiment 1

Why doesn’t the ISS fall down?

It does — constantly. Newton’s cannon, updated: fire a spacecraft sideways from 400 km up and choose how fast.

7.67 km/s
Circular orbit

The ground curves away exactly as fast as it falls. This is the ISS: always falling, never landing.

Lowest point
391 km
Highest point
400 km
One orbit takes
1 h 32 min

Simplified: no air drag, a perfectly round Earth, and a sideways launch. Real rockets climb first, then turn.

Experiment 2 · the rocket equation

Why rockets come in stages.

Tsiolkovsky, 1903: the speed change Δv depends only on engine efficiency and how much of the rocket is fuel.

Δv = Isp · g₀ · ln( mfull / mempty )

89% of the rocket at lift-off is propellant. Easy to build, but not much Δv.

6.7km/s of Δv

2.7 km/s short of orbit. Try splitting the same rocket into two stages.

Targets include typical losses to gravity and drag. Engine figures are rounded vacuum values; illustrative, not mission design.

03 — Check yourself

Three questions on the lab.

Question 1Why doesn’t the ISS fall to Earth?
Question 2At the ISS’s altitude, gravity is about…
Question 3Why do rockets drop stages on the way up?

Pick an answer to see the explanation.

04 — Glossary

The words you’ll meet.

OrbitBasics
Continuous free fall around a body while moving sideways fast enough to keep missing it.
Δv (delta-v)Propulsion
The total change in velocity a spacecraft can make. Mission plans are budgets of Δv.
Specific impulse (Isp)Propulsion
How efficiently an engine uses propellant, in seconds. Higher means more Δv from the same fuel.
StagingPropulsion
Dropping empty tanks and engines during flight so the remaining fuel pushes less dead weight.
Kármán lineBasics
The conventional edge of space, 100 km above sea level.
Low Earth orbit (LEO)Orbits
Orbits roughly 160–2,000 km up. The ISS circles at about 400 km, once every ~93 minutes.
Geostationary orbit (GEO)Orbits
35,786 km above the equator, where one orbit takes a day — so a satellite seems to hang still.
Apogee / perigeeOrbits
The highest and lowest points of an orbit around the Earth.
Escape velocityOrbits
The speed at which a spacecraft never falls back: about 11.2 km/s from Earth’s surface.
Gravity assistNavigation
Swinging past a planet to borrow some of its orbital momentum and change speed or direction.
MicrogravityLiving in space
The weightless feeling of free fall. Gravity at ISS altitude is still about 90% of that on the ground.
EVALiving in space
Extravehicular activity — a spacewalk, outside the spacecraft in a pressure suit.
Launch escape systemSafety
A rocket that pulls the crew capsule clear of a failing launch vehicle within seconds.
HeliopauseDeep space
Where the Sun’s wind gives way to interstellar space. Voyager 1 crossed it in 2012.

05 — For teachers & students

Use it in class. Cite it in one click.

All text is CC BY-SA: copy, adapt and project it, as long as you credit Spaceflightpedia. Every entry lists its sources, and photographs carry their own licences.

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Citation style

Spaceflightpedia. (n.d.). Apollo 11. Retrieved October 9, 2026, from https://spaceflightpedia.com/article/apollo-11

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