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The Apollo 15 commander bends over to set up a drill at the science station, with instruments standing on the grey ground around him.

First landing: 20 July 1969Status: Not working any more

ALSEP science stations

Image: NASA

Main spot on the Moon:Oceanus Procellarum

Apollo 12, 14, 15, 16 and 17 each set up an ALSEP station, which radioed its measurements to Earth for years. All of them were switched off together on 30 September 1977.

Flat map of The Moon with 9 markers: the main site at Oceanus Procellarum (3.01° S, 23.42° W) and the places of Apollo 11 EASEP, Apollo 11 Laser Ranging Retroreflector, Apollo 14 ALSEP, Apollo 14 Laser Ranging Retroreflector, Apollo 15 ALSEP, Apollo 15 Laser Ranging Retroreflector, Apollo 16 ALSEP, Apollo 17 ALSEP.
Oceanus Procellarum + 8 more places3.01° S, 23.42° WA flat map of the whole Moon, like a world map of Earth. Its middle is the side we always see from Earth. The big dot marks the main spot; the small dots mark other things the mission left behind.

The big map

Where ALSEP science stations can be found on the Moon

This is the whole Moon, unrolled flat like a world map of Earth. The middle of the map is the side of the Moon we always see from Earth. The lines are the coordinates , every 30°. Drag the map to look around, pick a spot, then follow its dashed lines to the numbers on the edges.

Where the mission ended More things it left behind

Flat map of The Moon with 6 numbered spots, listed below the map.

The science stations left behind

The astronauts could only stay on the Moon for a few days. But scientists wanted to know what was happening on the Moon long after the astronauts had gone home.

Echo: Hi! Let's find out how astronauts left a whole science station on the Moon.

The big idea

Leave a science station behind

So, beginning with Apollo 12, astronauts carried a collection of science instruments to the Moon. It was called ALSEP: the Apollo Lunar Surface Experiments Package.

The idea was simple: leave a science station behind.

The astronauts would set up the instruments, switch them on and then walk away. The station would keep collecting information and radio it back to Earth.

But first, they had to get there…

What's in a name?

Apollo Lunar Surface Experiments Package. Say it fast, and you get ALSEP.

By the numbers

Science that stayed behind

ALSEP stations, set up by Apollo 12, 14, 15, 16 and 17
5
years the Apollo 12 station kept working, from 1969 to 1977
Nearly 8
of electricity from the Apollo 12 station's generator
70 W
how far away the first recorded artificial moonquake was felt
60 km

Apollo 11 · July 1969

A small start

Apollo 11 was the first mission to land astronauts on the Moon, in July 1969. Neil Armstrong and Buzz Aldrin spent less than a day there, and only a little over two hours walking outside. But they still left behind a small set of science experiments called the Early Apollo Scientific Experiments Package, or EASEP.

It included a seismometer to feel the Moon shake, and a detector to measure how much dust settled on it. It ran on solar panels, so it could only work during the lunar day, while the Sun was shining.

They also set out a laser reflector: a special panel that bounces laser light sent from Earth straight back towards us.

There was a sheet of foil to catch particles coming from the Sun, too. But that one didn't stay. The astronauts packed it up with their Moon rocks and took it home.

Apollo 11 proved that astronauts could work on the Moon. The next missions could go further.

Buzz Aldrin stands beside the seismometer, with its two solar panels spread out on the dusty ground and bootprints all around.(opens larger view)

Buzz Aldrin sets up Apollo 11's seismometer near Tranquility Base.

Image: NASA

Echo: A seismometer is like a super-sensitive ear that feels the ground shake.

Apollo 12 · November 1969

A station that kept on working

Apollo 12 landed later in 1969, on 19 November. It carried a bigger collection of experiments: the first ALSEP station.

Instead of collecting a few measurements while the astronauts were there, it was built to keep gathering science after they had gone home. It was switched on the day it was set up, and it kept sending data for nearly eight years.

Its six instruments studied things like moonquakes, the Moon's magnetism, dust and the stream of tiny particles flowing out from the Sun, called the solar wind.

Leave a science station behind, and let the Moon keep telling us its secrets.

Power for the long lunar night

Solar panels only work while the Sun shines, and on the Moon, night lasts about two weeks. So ALSEP used a special power source called a radioisotope thermoelectric generator, or RTG.

It made electricity from heat. The heat came from a fuel rod of about 4 kg, filled with radioactive plutonium. That gave about 70 watts, as much as one old-fashioned light bulb, and it didn't need any sunlight at all.

Alan Bean sets up a three-armed instrument far from the camera, with a cable running across the dusty ground towards it and the Lunar Module on the horizon.(opens larger view)

Apollo 12 Alan Bean sets up the station's magnetometer. The Lunar Module stands in the background.

Image: NASA (JSC)

Alan Bean uses a long tool at the generator's fuel cask, mounted on the side of the Lunar Module.(opens larger view)

Alan Bean unloads the generator's fuel cask from the Lunar Module.

Image: NASA

Echo: No sunlight? No problem. The generator ran on heat!

The Apollo 14 science station on the grey lunar surface: a shiny central box with an antenna, flags and cables spread out around it.

The same idea, again and again.

Apollo 14, 15, 16 and 17 each left another science station behind.

Image: NASA (JSC)

1971 to 1972

One station after another

Apollo 14 · February 1971

Apollo 14 landed in the highlands near the crater Fra Mauro. It carried another ALSEP station, with experiments designed to study the Moon's interior and its surroundings, including two different kinds of seismometer.

Apollo 15 · July 1971

Apollo 15, later that year, took things even further. Its astronauts were the first to drive a rover on the Moon, and they covered 27.9 km on their trips outside. Their station had seven instruments, studying everything from moonquakes and magnetism to particles arriving from space, and even the heat escaping from deep inside the Moon.

Apollo 16 · April 1972

Then came Apollo 16. Its astronauts landed in the Descartes highlands, a region NASA wanted them to survey and sample. Once again, they left behind science instruments, so researchers on Earth could keep studying the Moon after the astronauts had left.

Apollo 17 · December 1972

Finally, Apollo 17 landed in December 1972. It was the last Apollo mission to land on the Moon, and it left behind the final ALSEP station. Its instruments even measured the Moon's gravity and sniffed its very thin atmosphere.

By this point, the Moon was no longer just a place astronauts visited. It had become a place where science instruments could be left behind, quietly collecting information for years.

Part of the Apollo 16 science station set out on the lunar surface.(opens larger view)

Apollo 16 The Apollo 16 station: the seismometer in front, the central station behind and the generator on the left.

Image: NASA (JSC)

Watch your step!

On Apollo 16, astronaut John Young tripped on the cable of the heat flow experiment and broke it. Walking in a bulky spacesuit isn't easy!

Echo: Five stations, spread out across the Moon. That's a whole science network!

Imagine this…

You can leave one instrument on the Moon to keep watch for years. What would you want it to measure?

Back on Earth

The Moon kept talking

And that was the real advantage of ALSEP. The astronauts could stay for only a few days. The instruments could stay much longer.

They measured moonquakes, changes in the Moon's surroundings, heat flowing up through the lunar surface and other clues that helped scientists understand how the Moon works.

Scientists could even make their own moonquakes. When the Apollo 12 crew's empty ascent stage was crashed into the Moon on purpose, the seismometer about 60 km away felt it. It was the first artificial moonquake ever recorded.

Scientists in shirts and ties lean over a long paper chart, studying the lines on it with a pen and a magnifier.(opens larger view)

Scientists in Mission Control study the shaking the seismometers recorded when Apollo 15's spent rocket stage hit the Moon.

Image: NASA (JSC)

Echo: They crashed a spacecraft into the Moon on purpose, just to make it shake!

In pictures

A closer look at the stations

Alan Bean sets out the parts of the Apollo 12 science station on the Moon.(opens larger view)

Alan Bean sets up the Apollo 12 science station.

Image: NASA (JSC)

A seismometer chart from 20 November 1969: rows of thin lines, with bursts of spiky marks where the ground shook.(opens larger view)

The Apollo 12 seismometer's record of the empty ascent stage crashing into the Moon.

Image: NASA (JSC)

The Apollo 14 science station on the Moon, with a grey, finned power generator in front.(opens larger view)

The grey, finned generator in front made electricity for the Apollo 14 station.

Image: NASA

Close-up of the Apollo 14 central station standing on the Moon.(opens larger view)

The central station radioed the measurements to Earth.

Image: NASA (JSC)

Timeline

From the first seismometer to the big switch-off

  1. 20 July 1969

    Apollo 11 lands

    Buzz Aldrin sets up the solar-powered seismometer, and the first laser reflector goes out.

  2. 27 August 1969

    Apollo 11's seismometer goes quiet

    It stops answering commands from Earth.

  3. 19 November 1969

    Apollo 12: the first ALSEP

    Switched on the same day it was set up.

  4. 20 November 1969

    The first artificial moonquake

    Apollo 12's empty ascent stage hits the Moon about 60 km from the station.

  5. 5 February 1971

    Apollo 14 lands

    A second station goes up, near the crater Fra Mauro.

  6. 30 July 1971

    Apollo 15 lands

    The first rover on the Moon, and a station that measures heat escaping from inside the Moon.

  7. 21 April 1972

    Apollo 16 lands

    Another station, in the Descartes highlands.

  8. 11 December 1972

    Apollo 17 lands

    The last Apollo landing, and the last ALSEP station.

  9. 30 September 1977

    The big switch-off

    All five stations are shut down on the same day.

Still there

The story didn't end

The astronauts eventually returned to Earth, but the story didn't end when they left.

They had turned the Moon into a place where science could continue long after the astronauts had gone home.

And some of the things they left behind are still there today. The laser reflectors are even still in use: scientists on Earth bounce laser beams off them to measure the distance to the Moon.

The Apollo 14 Lunar Module on the Moon, with the flag and a folded mirror panel near the ladder.(opens larger view)

Antares, the Apollo 14 lander. The laser reflector waits at the foot of the ladder, ready to be set up.

Image: JSC

Echo: The mirror panels are still used, more than 50 years later. Talk about a long job!

Still there today

What the science stations left behind

  • Status: Not working any more

    Apollo 11 EASEP

    The simpler, solar-powered forerunner of ALSEP. It stopped answering commands from Earth on 27 August 1969.

  • Status: Still working

    Apollo 11 Laser Ranging Retroreflector

    A panel of mirrors that needs no power. More than 50 years later, observatories on Earth still bounce laser beams off it to measure the distance to the Moon.

  • Status: Not working any more

    Apollo 12 ALSEP

    Six instruments, including a seismometer and a magnetometer.

  • Status: Not working any more

    Apollo 14 ALSEP

    Included both a passive and an active seismometer.

  • Status: Still working

    Apollo 14 Laser Ranging Retroreflector

    Another mirror panel, set up near the Apollo 14 science station. Still used for laser ranging.

  • Status: Not working any more

    Apollo 15 ALSEP

    Seven instruments, including a heat flow experiment.

  • Status: Still working

    Apollo 15 Laser Ranging Retroreflector

    The largest of the three Apollo mirror panels. Still used for laser ranging.

  • Status: Not working any more

    Apollo 16 ALSEP

    Its heat flow experiment was broken during setup.

  • Status: Not working any more

    Apollo 17 ALSEP

    Included a gravimeter and a mass spectrometer.

Sources and fact-check