During the first moonwalk, Neil Armstrong and Buzz Aldrin set up several experiments designed to find out what the moon was made of and how old it was. The solar-powered and nuclear-heated Early Apollo Surface Experiments Package (EASEP), was the precursor of a more comprehensive set of experiments that would be carried on subsequent Apollo missions. The package consisted two main experiments: a set of seismic monitors and a sophisticated mirror that would reflect laser beams back to Earth.

The seismic recorder was comprised of a square base with an antenna and flanked by two solar panels facing east and west. The seismometers were designed to measure events such as meteorite impacts and moonquakes. Studying the seismic signature of such shakes would help scientists answer daunting questions about the moon's interior: questions such as whether the moon had a solid or molten center, and how thick was the moon's crust. Later, scientists would determine that the moon has a partially melted interior, with a mantle similar to, but thicker than, Earth's.

The seismic recorder carried the first major use of nuclear energy in a manned space-flight mission. To protect the recorder from the cold of lunar night, which can drop to minus 279 degrees Fahrenheit during 340 hours of darkness, the device used two radioactive isotopic heaters. Each harnessed the heat given off by the decay of 1.2 ounces of plutonium 238. A similar process uses plutonium to heat and power components in the Cassini probe now bound for Saturn.

The second chief experiment in the Apollo 11 science package was the Laser Ranging Retro-Reflector, or LRRR. Roughly one foot square, the LRRR was a configuration of specialized mirrors that possessed the property of always reflecting light in the same direction as its source. The reflector was set up about 16 feet (5 meters) from the solar-powered seismic recorder. Resting on the lunar surface it resembled an oversize hotplate with a shiny top. It would be used to reflect laser beams sent from Earth in order to make very precise measurements of Earth-Moon distances. Although the moon is on average about 238,000 miles (385,000 kilometers) away from Earth, using this method, scientists can measure the Earth-moon distance to an accuracy of about 1 1/4 inches (3 centimeters).

The Apollo 11 retro-reflector and similar units left by the Apollo 14 and Apollo 15 missions have produced many important measurements. Scientists now have a precise knowledge of the moon's orbit and spin rate, and the speed at which the moon is receding from Earth (about 1.5 inches or 3.8 centimeters per year). They also know more about Earth's spin and as a result of LRRR data.

Because it was solar powered, the seismic recorder only functioned during the lunar day. Aldrin set up the experiment package on the ground a short distance from the Lunar Module and controllers turned it on while the astronauts were still at the landing site. It returned data for two weeks before lunar twilight turned down the power.

The EASEP was deployed approximately 17 meters south of the Lunar Module and was turned on by ground command July 21, 1969 while the astronauts were still on the surface. It functioned for two weeks before twilight turned off the power. During the next lunar day, the recorder returned a week's worth of data before it stopped obeying commands from Earth and was shut down.