ALSEP

ALSEP, built by the Apollo 16 crew; in the foreground the PSE, behind it the base station with the easily recognizable antenna

Apollo Lunar Surface Experiments Package ( ALSEP ) was the name of a modular set of devices for carrying out long-term scientific experiments on the lunar surface from 1969 to 1977. The data was transmitted to earth via telemetry .

ALSEPs were used by all Apollo missions from Apollo 12 onwards, although the composition of the experiments varied. Apollo 11 carried a simpler device called EASEP ( Early Apollo Scientific Experiments Package ), which consisted of a solar cell powered passive seismometer (PSEP), laser reflector (LRRR) and solar wind foil (SWC) . The ALSEP from Apollo 13 was not used because the moon landing had to be abandoned at short notice because the service module was severely damaged by the explosion of an oxygen tank and the lunar module served as an emergency accommodation.

The individual devices were designed and built by various institutes and research facilities and were mostly designed for a service life of one to two years. The ALSEP was set up by the astronauts about 100 meters away from the lunar module so that the devices would not be damaged by the ascent of the ferry. The common devices were the following:

designation	sketch	image	description
Base station			The picture shows the central station of the ALSEP of Apollo 16 . The base station, the heart of the system, took over all communication with the earth and distributed energy to the actual devices. The radio link with the earth was maintained via a 58 cm long modified helical antenna , which was manually aligned with the earth by the astronauts. With a volume of just under 35 liters, the base station, which weighs around 25 kg and can be folded out by pulling a bolt, contained the relevant transmitters, receivers and data processing. The version of the Apollo 12 to 15 missions also contained a detector to measure deposits of moon dust.
Radionuclide battery (Radioisotope Thermoelectric Generator, RTG)			The RTG of Apollo 14 is shown with the base station in the background. The RTG used the decay heat of plutonium  238 to generate around 70 watts of electrical power to run the experiments.
RTG container			The red-hot capsule with the plutonium pellets had to be reloaded into the generator by the astronauts from a protective container attached to the outside of the Lunar Module . The container was designed to withstand an explosion at the launch site or a re-entry into the earth's atmosphere without releasing radioactivity; in the case of Apollo 13, he fulfilled this function. In the picture, Edgar Mitchell is trying to remove the container on the ground.

The scientific equipment included seismometers of various generations, magnetometers , spectrometers , ion detectors , heat flow meters and dust detectors connected to the base station by cables. The passive laser reflector was also used in three cases, in the following combinations:

designation	sketch	draft	description	11	12	13	14th	15th	16	17th
Laser distance measurement
Laser Retroreflector, Laser Ranging Retroreflector (LRRR)		MIT u. a.	By measuring the transit time of a laser pulse, extremely accurate measurements of the distance between the moon and the earth are possible. The LRRRs of Apollo 11 and 14 are identical (top picture), the Apollo 15 device contains 300 instead of 100 prisms and was brought to its place by the astronauts with the rover, but only performed the same as the smaller devices.	x			x	x
Seismic experiments
Passive Seismic Experiment, Passive Seismic Experiment Package (PSEP)		MIT and Columbia University	The PSEP was similar to the PSE, but independent; H. with its own power supply via solar cells, electronics and radio connection. It also contained a dust detector, which was later integrated on the base station. It worked for 21 days.	x
Passive Seismic Experiment, Passive Seismic Experiment (PSE)		MIT and Columbia University	The PSE was designed to detect moonquakes, both natural and artificially triggered, in order to obtain information about the depth structure of the moon.		x	x	x	x	x
Active Seismic Experiment, Active Seismic Experiment (ASE)		Stanford University and USGS	The ASE added three geophones to the PSE , which were laid out in a line from the base station. In addition, the ASE comprised a "knocker" operated by the astronauts ( Thumper, picture), which contained 22 cartridges for generating small shocks, as well as four larger charges that were remotely ignited after leaving the moon. The aim was the seismic exploration of the landing site at a depth of several hundred meters.				x		x
Seismic depth experiment (Lunar Seismic Profiling Experiment; LSPE)		like ASE	The LSPE was a further development of the ASE with a fourth geophone and stronger loads (up to 2.5 kg) to reach a depth of several kilometers. The charges were deployed at a great distance with the help of the rover and ignited by radio.							x
Investigations of charged particles
Solar Wind Spectrometer, Solar Wind Spectrometer Experiment (SWS)		Jet Propulsion Laboratory	The SWS determined the properties and composition of the solar wind and its influence on the lunar environment.		x			x
Ion detector experiment, Suprathermal Ion Detector Experiment (SIDE)		Rice University	The SIDE was used to measure various properties of positive ions on the moon. The aim was to determine possible interactions with solar plasma and the electrical properties of the lunar surface.		x		x	x
Cold Cathode Ion Gauge (CCIG)			The CCIG was built to determine the extremely low pressure of the lunar atmosphere. It was attached to the side of the SIDE with cables (in the picture on the right), as its strong magnetic field would have caused interference at the originally intended location inside.		(1)		x	x
Cold Cathode Gauge Experiment (CCGE)		like CCIG	The CCGE was a stand-alone version of the CCIG integrated with the SIDE, but was not used.			x
Charged Particle Lunar Environment Experiment (CPLEE)			The CPLEE directly measured the flux density of charged particles, especially electrons and ions from the solar wind.			x	x
Other experiments
Surface magnetometer, Lunar Surface Magnetometer (LSM)		Ames Research Center and Marshall Space Flight Center	The LSM examined the moon's magnetic field in order to derive in particular the electrical properties of the subsurface. The experiment also made it possible to better understand the interaction between solar plasma and the lunar surface.		x			x	x
Heat flow experiment (HFE)		Columbia University	The HFE determined the heat flow from the interior of the moon in order to infer its thermal balance, in particular the warming caused by radioactive decay and possibly a liquid core. It essentially consisted of two temperature sensors that were buried by the astronauts about 2.5 m deep.			x		(2)	(3)	x
Atmospheric Composition, Lunar Atmosphere Composition Experiment (LACE)			The LACE contained a mass spectrometer to allow more precise conclusions to be drawn about the composition of the extremely thin lunar atmosphere. The thermal protection turned out to be insufficient, which led to the device overheating and failure after ten months.							x
Lunar Ejecta and Meteorites Experiment (LEAM)			The purpose of the LEAM was to detect secondary particles released by micrometeorites when they hit the moon, as well as the micrometeorites themselves. The thermal protection turned out to be insufficient, which led to overheating of the device and poor data accuracy.							x
Lunar Surface Gravimeter (LSG)			The LSG was designed to determine the gravity of the moon and a possible change over time with high accuracy. In particular, it was hoped to be able to detect gravitational waves. Due to a design error - the counterweights were not designed precisely enough for the gravitational acceleration of the moon, so that the fine adjustment range was not sufficient to calibrate the device - the LSG only fulfilled its function with considerable restrictions.							x

Note:
(1) failed after only 14 hours of operation
(2) The intended borehole depth was not reached because of the unexpectedly hard subsoil.
(3) The HFE of Apollo 16 became inoperable after it was set up by pulling out a cable. A repair attempt was discarded for reasons of time.

Various failures and malfunctions have occurred over time. In particular, the LSM, the SIDE and the ALSEP of Apollo 14 failed several times. Reception and analysis of the ALSEP data ceased on September 30, 1977; At that time, almost half of the devices were still functional. The transmitters of the ALSEPs of Apollo 15 and 17 continued to be used by the JSC for VLBI experiments until the base station of Apollo 15 and the base station of Apollo 17 ceased operations in the summer of 1978 due to exhaustion of the RTGs. The three purely passive laser reflectors set up by the Apollo 11, 14 and 15 missions are not affected and, like the two similar devices of Russian origin (on the Lunochod rovers), are still used for measuring the distance to the moon, see geodesy .

In 2011 it became known that a new evaluation of the approximately 13,000 recorded moonquakes by the seismometers had led to new results with regard to the interior of the moon, in particular the detection of a liquid core.

Web links

• Description NASA (English) ( Memento of 4 January 2014 Internet Archive )
• Alternative description of NASA (English)
• ALSEP Termination Report (NASA-RP-1036, Lunar and Planetary Institute) (English; PDF; 9.2 MB)

Individual evidence

1. ↑ http://history.nasa.gov/alsj/a12/a12.alsepoff.html
2. ↑ "Apollo" data: Moonquakes reveal the interior of the earth's satellite. In: SPIEGEL ONLINE. January 7, 2011, accessed May 18, 2011 . 
3. ^ Renee C. Weber, Pei-Ying Lin, Edward J. Garnero, Quentin Williams, Philippe Lognonne: Seismic Detection of the Lunar Core . In: Science . January 6, 2011, doi : 10.1126 / science.1199375 ( sciencemag.org [accessed May 18, 2011]).