During the Apollo missions, astronauts didn't just travel to the Moon—they conducted experiments, both on the surface of the Moon and while in orbit. Experimenting in orbit helped determine things such as the composition of the lunar surface, but required special tools. Let's take a closer look at twelve tools used to carry out experiments in orbit, and what we learned from them. 

Apollo 15, 16, and 17 all carried a scientific instrument module (SIM) bay in the Service Module. A variety of experiments were carried out, including command module pilots partaking in a deep space extra-vehicular activity (EVA), or a spacewalk, to retrieve film from a 24-inch panoramic camera, used to capture high resolution images of the lunar surface.

During the Apollo 15 mission, eight tools were used to carry out 8 different experiments in the SIM bay: 

X-Ray Florescence Spectrometer: This experiment was the second of the geochemical experiment trio, which were done to measure the composition of the lunar surface from orbit. The X-Ray Florescence Spectrometer detected X-ray florescence caused by solar X-ray interaction with the Moon. It also analyzed the sunlit portion of the Moon under the spacecraft.  

Gamma-Ray Spectrometer: No Bruce Banner here! While some may be familiar with the gamma-rays that created the fictional superhero known as the Incredible Hulk, the gamma ray spectrometer used during the Apollo missions served a different purpose.  Attached to a 25-foot extendable boom, it measured the chemical composition of the lunar surface in conjunction with X-ray and alpha particle experiments in order to create a “map” of the composition of the lunar surface ground track. 

Alpha-Particle Spectrometer: This experiment measured mono-energetic alpha-particles emitted from the lunar crust and fissures. 

24-inch Panoramic Camera: This camera was used to gather stereo and high-resolution photographs of the lunar surface from orbit. Since the camera was mounted outside the spacecraft, it featured a rotating lens system so that it could be stowed to face inward, and therefore avoid contamination from the spacecraft’s exhaust. The 72-pound film cassette of 1,650 frames was retrieved by the command module pilot during a trans-earth EVA. The camera worked in conjunction with the 3-inch mapping camera and the laser altimeter to gain data for construction of a comprehensive map of the lunar surface. About 8 percent of the lunar surface was covered by the Apollo 15 mission. 

3-inch Mapping Camera: This camera provided 20-meter resolution terrain mapping photography on 5-inch film with a 3-inch focal length lens. It also simultaneously took images of the star field on 35mm film. The stellar photos allowed accurate correlation of mapping photography by comparing simultaneous star field photos with lunar surface photos. The stellar camera film was retrieved during the same EVA as the panoramic camera. 

Laser Altimeter: The laser altimeter measured spacecraft altitude above the lunar surface to within one meter. The instrument was aligned, or bore sighted, using the 3-inch mapping camera. 

Mass Spectrometer: The mass spectrometer was used in an attempt to measure composition and distribution of the ambient lunar atmosphere. It was attached to a 24-foot extendable boom.  

Subsatellite: The subsatellite was ejected into lunar orbit from the SIM bay and carried three additional experiments: S-Band Transponder, Particle Shadows/Layer Experiment, and Subsatellite Manometer. 

During Apollo 16, eight more experiments similar to those carried out on Apollo 15 were conducted from the SIM bay. For the Apollo 17 mission, three new tools were used to carry out experiments in the SIM bay: 

Lunar Sounder: The lunar sounder beamed electromagnetic impulses toward the lunar surface in high frequency (HF) and very high frequency (VHF) bands. These impulses provided data for developing a geological model of the lunar interior to a depth of 1.3 km or 4280 feet. In addition to stratigraphic (relating to the layers of rock on the Moon), structural, tectonic (relating to the structure of the Moon’s crust) and topographic (relating to the Moon’s geographical features) data on regions of the Moon Apollo 17 flew over, the lunar sounder measured the ambient electromagnetic noise levels in the lunar environment at 5, 15, and 20 mHz and the occultation (when one object passes in front of another) by the Moon of electromagnetic waves generated at the lunar surface by the electrical properties experiment transmitter. 

Infrared Scanning Radiometer (ISR): The purpose of the ISR experiment was to measure lunar nighttime temperatures and cooling rates.  

Far-Ultraviolet Spectrometer: The far-UV spectrometer was used in an attempt to measure ultraviolet emissions from the thin lunar atmosphere. The far-UV spectrometer was mounted on the bottom shelf of the SIM bay. Controls for activating and deactivating the experiment and for opening and closing a protective cover were located in the command module. 

Also mounted in the SIM bay during the Apollo 17 mission were the panoramic camera, mapping camera and laser altimeter, all of which were also used during Apollo 15 and 16.