ALSE

The ALSE (Apollo Lunar Sounder Experiment) (also known as Scientific Experiment S-209, according to NASA designations) was a ground-penetrating radar (subsurface sounder) experiment that flew on the Apollo 17 mission.wikipedia
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Ground-penetrating radar

ground penetrating radargeoradarGPR
The ALSE (Apollo Lunar Sounder Experiment) (also known as Scientific Experiment S-209, according to NASA designations) was a ground-penetrating radar (subsurface sounder) experiment that flew on the Apollo 17 mission.

Apollo 17

17Apollo 17: SplashdownApollo XVII
The ALSE (Apollo Lunar Sounder Experiment) (also known as Scientific Experiment S-209, according to NASA designations) was a ground-penetrating radar (subsurface sounder) experiment that flew on the Apollo 17 mission.

Moon

lunarthe MoonLuna
This experiment used radar to study the Moon's surface and interior. Being the recorder located in the service module, one of the astronauts (Ron Evans) had to perform an Extra-Vehicular Activity (EVA) during the return flight from the Moon to collect the recorded films.

Radar

radar stationradarsradar system
Radar waves with wavelengths between 2 and 60 meters (frequencies of 5, 15, and 150 MHz) were transmitted through a series of antennas near the back of the Apollo Service Module.

Antenna (radio)

antennaantennasradio antenna
Radar waves with wavelengths between 2 and 60 meters (frequencies of 5, 15, and 150 MHz) were transmitted through a series of antennas near the back of the Apollo Service Module.

Apollo command and service module

command moduleApollo Command/Service ModuleApollo Command Module
Radar waves with wavelengths between 2 and 60 meters (frequencies of 5, 15, and 150 MHz) were transmitted through a series of antennas near the back of the Apollo Service Module.

Space Shuttle

Shuttlespace shuttlesSpace Shuttle Program
(A radar experiment on the space shuttle has been similarly used to map ancient river valleys beneath the Sahara Desert.) This experiment also provided very precise information about the Moon's topography.

Sahara

Sahara DesertSaharanSaharan Desert
(A radar experiment on the space shuttle has been similarly used to map ancient river valleys beneath the Sahara Desert.) This experiment also provided very precise information about the Moon's topography.

Milky Way

Milky Way Galaxygalaxyour galaxy
In addition to studying the Moon, the experiment also measured radio emissions from the Milky Way Galaxy.

Galaxy

galaxiesgalacticgalactic nuclei
In addition to studying the Moon, the experiment also measured radio emissions from the Milky Way Galaxy.

Mare Crisium

CrisiumCrisium basinSea of Crisis
This experiment revealed structures beneath the surface in Mare Crisium, Mare Serenitatis, Oceanus Procellarum, and many other areas.

Mare Serenitatis

SerenitatisSea of SerenitySerenitatis Basin
This experiment revealed structures beneath the surface in Mare Crisium, Mare Serenitatis, Oceanus Procellarum, and many other areas.

Oceanus Procellarum

Ocean of StormsProcellarumProcellarum basin
This experiment revealed structures beneath the surface in Mare Crisium, Mare Serenitatis, Oceanus Procellarum, and many other areas.

High frequency

HFhigh-frequencyHF radio
The ALSE instrument operated in two HF bands (5 MHz - HF1 - and 15 MHz - HF2) center frequencies and one VHF band (150 MHz), each with a bandwidth of 10% (using a chirped signal).

Very high frequency

VHFVHF radioVHF band
The ALSE instrument operated in two HF bands (5 MHz - HF1 - and 15 MHz - HF2) center frequencies and one VHF band (150 MHz), each with a bandwidth of 10% (using a chirped signal).

Chirp

chirp functionChirp modulationchirp signal
The ALSE instrument operated in two HF bands (5 MHz - HF1 - and 15 MHz - HF2) center frequencies and one VHF band (150 MHz), each with a bandwidth of 10% (using a chirped signal).

Dipole antenna

dipoledipoleshalf wave dipole
The two HF bands shared the same center-feed dipole antenna, while a 7 elements Yagi antenna was used for the VHF channel.

Yagi–Uda antenna

Yagi antennaYagi-Uda antennaYagi
The two HF bands shared the same center-feed dipole antenna, while a 7 elements Yagi antenna was used for the VHF channel.

Pulse repetition frequency

PRFpulse repetition frequenciesmedium pulse repetition frequency
Two different transceiver were used for the HF (alternating operation between HF1 and HF2 on a PRF-by-PRF basis) and VHF, sharing a common optical recorder.

Automatic gain control

AGCAutomatic volume controlAVC
An Automatic gain control (AGC) feature was included in all the channels to optimize the signal allocation within the receiver dynamic range.

Dynamic range

DRdynamicdynamic and tonal range
An Automatic gain control (AGC) feature was included in all the channels to optimize the signal allocation within the receiver dynamic range.

Oscillation

oscillatorvibrationoscillators
In both the HF and VHF transceivers, the chirp signal was generated by a swept oscillator synchronized with a STAble Local Oscillator (STALO) in order to preserve the phase coherency for the SAR processing.

Synthetic-aperture radar

synthetic aperture radarSARsynthetic aperture
In both the HF and VHF transceivers, the chirp signal was generated by a swept oscillator synchronized with a STAble Local Oscillator (STALO) in order to preserve the phase coherency for the SAR processing.

Cathode-ray tube

cathode ray tubeCRTcathode ray tubes
The received signal was converted at IF and the signal amplitude was used to amplitude-modulate a CRT (swept at PRF rate), in turn impressing a 70 mm film for optical recording of the data.

Extravehicular activity

spacewalkEVAextra-vehicular activity
Being the recorder located in the service module, one of the astronauts (Ron Evans) had to perform an Extra-Vehicular Activity (EVA) during the return flight from the Moon to collect the recorded films.