Space After Dark

Exhibition 5 · To the Moon

How do you send three people to the Moon, and bring them back?

Apollo 11 left Florida at 13:32 UTC on 16 July 1969 and came home 195 hours later, a little over eight days, across nine calendar dates. The clock on this page is its mission clock, counted from liftoff. It moves as you scroll, whether or not you finish each experiment.

Who was winning the race to the Moon?

Twelve years earlier, nobody had put anything into orbit at all. Then two countries started racing.

Display · The race
  1. 4 Oct 1957 Sputnik 1 The first artificial satellite.
  2. 3 Nov 1957 Sputnik 2 Carries the dog Laika.
  3. Dec 1957 Vanguard Explodes on the pad.
  4. 31 Jan 1958 Explorer 1 The first US satellite.
  5. 2 Jan 1959 Luna 1 Flies past the Moon.
  6. 14 Sep 1959 Luna 2 Hits the Moon: the first human-made object to reach another world.
  7. 7 Oct 1959 Luna 3 Photographs the Moon’s far side.
  8. 12 Apr 1961 Vostok 1 Yuri Gagarin, the first person in orbit.
  9. 5 May 1961 Freedom 7 Alan Shepard, the first American in space: 15 minutes, up and down.
  10. 20 Feb 1962 Friendship 7 John Glenn, the first American in orbit.
  11. 16 Jun 1963 Vostok 6 Valentina Tereshkova, the first woman in space.
  12. 18 Mar 1965 Voskhod 2 Alexei Leonov makes the first spacewalk.
  13. Jun 1965 Gemini 4 Ed White, the first American spacewalk.
  14. 1965–66: the lead changes hands
  15. 15 Dec 1965 Gemini 6A and 7 The first crewed rendezvous.
  16. 3 Feb 1966 Luna 9 The first soft landing on the Moon, and the first pictures from its surface.
  17. 16 Mar 1966 Gemini 8 Neil Armstrong and David Scott: the first docking of two spacecraft.
  18. 31 Mar 1966 Luna 10 The first spacecraft to orbit the Moon.
  19. 30 May 1966 Surveyor 1 Launched: the first US soft landing on the Moon.
  20. 27 Jan 1967 Apollo 1 A fire during a test on the pad kills Grissom, White and Chaffee.
  21. Sep 1968 Zond 5 Flies around the Moon and brings tortoises back to Earth.
  22. 21 Dec 1968 Apollo 8 The first crew to orbit the Moon. “Earthrise” is taken on 24 December.
  23. 13 Jul 1969 Luna 15 Launched. It is orbiting the Moon while Apollo 11 lands.
  24. 20 Jul 1969 Apollo 11 The first people land on the Moon.
  25. 1969–1972 N1 The Soviet Moon rocket fails on all four launches.
In twelve years the lead changed hands. The Soviets were first to orbit, first to the Moon and first to send a person up. Apollo answered with rendezvous, docking and, in July 1969, a landing.

How big a rocket does it take to send three people to the Moon?

Three rockets, stacked. Each one drops away when it is empty, so the ones above don’t carry its dead weight. Scroll down past it: this is the Saturn V at full height.

Display · Saturn V

110.6 m tall 2,938 t at liftoff 34 MN of thrust Drawn at 1 px = 0.1 m

10 m
  1. Spacecraft 50 t: the command and service modules, the lunar module and the escape tower
  2. Instrument Unit IBM · 0.9 m × 6.6 m The guidance computer for the whole rocket, including the burn to the Moon
  3. S-IVB McDonnell Douglas · 17.8 m × 6.6 m 119 t at ignition, 90% of it propellant 1 × J-2 · burned twice: 147 s and 347 s Liquid hydrogen and liquid oxygen
  4. S-II North American · 24.8 m × 10.1 m 480 t at ignition, 93% of it propellant 5 × J-2 · burned 384 s Liquid hydrogen and liquid oxygen
  5. S-IC Boeing · 42.1 m × 10.1 m 2,279 t at ignition, 94% of it propellant 5 × F-1 · burned 168 s Kerosene (RP-1) and liquid oxygen

Stage lengths overlap at the joints, so they don’t add up exactly to the full height. Masses are as loaded on the day of launch.

Of the 2,900 tonnes that left the pad, about 44 tonnes went to the Moon, and 5 tonnes came home.

12 minutes after launch the ship is circling Earth 185 km up, at 7.79 km/s. The Moon is 384 thousand kilometres away, and it won’t wait: it moves about 13° around Earth every day. To get there the third stage has to relight and add about 3 km/s.

When do you relight the engine so you meet the Moon three days later?

Saturn V (default)3.17 km/s left once in orbit
Experiment

Leaving Earth orbit

When do you relight the engine so you meet the Moon three days later?

Goal Pass within 1,000 km of the Moon

Predict first. Where should the ship be when it relights?

Not tried yet Earth and Moon in one plane · burn treated as instant

The engines are off. For three days the ship coasts, slowing as Earth pulls back on it, then speeding up as the Moon pulls it in. It needs only one small correction on the way out. Behind the Moon, out of radio contact, the service module’s engine fires for 6.0 minutes to slow down into lunar orbit.

Michael Collins stays in Columbia, circling about 111 km up. Neil Armstrong and Buzz Aldrin take Eagle down.

10 minutes into the powered descent, the computer is sounding alarms, and the spot it is flying to is a field of boulders. Armstrong takes over the steering about 400 feet (122 m) up and flies on, looking for flat ground. The engine has to cancel every bit of speed, down and sideways: there is no air and there are no wings.

Can you land with the fuel you have?

Apollo 11’s fuel (default)184 s of hovering left at 400 ft
Experiment

Lunar descent

Can you land with the fuel you have?

Goal Touch down under 1 m/s on clear ground
Not tried yet g = 1.62 m/s² · throttle 10–60% · 2D, flat ground

About 6.6 hours after landing, Armstrong steps onto the Moon. You are wearing an 83 kg suit and backpack, and the ground pulls on you about a sixth as hard as Earth does. The crew have 2 h 32 min outside, and one of their jobs is to set up a seismometer about 17 m from Eagle.

What changes when you walk where gravity is a sixth of Earth’s?

A standing jump (default)0.50 m on Earth becomes 0.63 m here, in the suit
Experiment

On the surface

What changes when you walk where gravity is a sixth of Earth’s?

Goal Level the seismometer and record your footsteps

Predict first. In the suit, with the same push, how high does your jump go?

Not tried yet g = 1.62 m/s² · 70 kg body + 83 kg suit

After 22 hours on the Moon, Eagle’s top half lifts off, using the bottom half as its launch pad. It has one engine. It can’t be throttled and it can’t be relit: if it doesn’t light, nobody can come and get them. Fuel left over from the landing can’t help, because the ascent stage has its own tanks.

How do you leave the Moon with one engine and no spare?

Experiment

Getting back

How do you leave the Moon with one engine and no spare?

Goal Reach a safe orbit and catch up with Columbia

Predict first. Columbia is ahead of you in orbit. To catch up, should your orbit be…

Not tried yet One engine, always full thrust · smooth Moon · catch-up without the four burns

Behind the Moon again, Columbia’s engine fires for 2.5 minutes and sends the crew home. 2.5 days later the command module hits the top of the air at about 11 km/s, and splashes down in the Pacific at 16:50 UTC on 24 July 1969, 195 hours after launch.

Of the 2,938 tonnes of Saturn V on the pad, about 5 tonnes came home.

End of To the Moon · Ends with people coming home

Further out, we send machines. How?

Next: Robots on Mars Exhibition 6 · Rovers