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Earth–Moon–Earth communication (EME), also known as Moon bounce, is a
radio communications Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connected t ...
technique that relies on the
propagation Propagation can refer to: *Chain propagation in a chemical reaction mechanism *Crack propagation, the growth of a crack during the fracture of materials *Propaganda, non-objective information used to further an agenda *Reproduction, and other forms ...
of
radio waves Radio waves (formerly called Hertzian waves) are a type of electromagnetic radiation with the lowest frequencies and the longest wavelengths in the electromagnetic spectrum, typically with frequencies below 300 gigahertz (GHz) and wavelengths ...
from an
Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...
-based
transmitter In electronics and telecommunications, a radio transmitter or just transmitter (often abbreviated as XMTR or TX in technical documents) is an electronic device which produces radio waves with an antenna (radio), antenna with the purpose of sig ...
directed via reflection from the surface of the
Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...
back to an Earth-based receiver.


History

The use of the Moon as a
passive Passive may refer to: * Passive voice, a grammatical voice common in many languages, see also Pseudopassive * Passive language, a language from which an interpreter works * Passivity (behavior), the condition of submitting to the influence of ...
communications
satellite A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scient ...
was proposed by W.J. Bray of the British
General Post Office The General Post Office (GPO) was the state postal system and telecommunications carrier of the United Kingdom until 1969. Established in England in the 17th century, the GPO was a state monopoly covering the dispatch of items from a specific ...
in 1940. It was calculated that with the available
microwave transmission Microwave transmission is the transmission of information by electromagnetic waves with wavelengths in the microwave frequency range of 300 MHz to 300 GHz (1 m - 1 mm wavelength) of the electromagnetic spectrum. Microwave signal ...
powers and low-noise receivers, it would be possible to beam
microwave Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequency, frequencies between 300&n ...
signal A signal is both the process and the result of transmission of data over some media accomplished by embedding some variation. Signals are important in multiple subject fields including signal processing, information theory and biology. In ...
s up from Earth and reflect them off the Moon. It was thought that at least one voice channel would be possible. Radar reflections off the moon were received and recognized as such in 1943 during German experiments with radio measurement equipment, as reported by Dr. Ing. W. Stepp in ''Der Seewart'' magazine. Stepp noted a "perturbation", which "appeared, had a duration of several impulses, and larger impulse strength than the strongest nearby targets. It didn't appear until about two seconds after switching on the transmitter and disappeared (pulsatingly) correspondingly later after switching it off. But the rest of the echo image appeared and disappeared at the instance of switching the transmitter on/off. The 'perturbation' only occurred when the antenna was aimed to the east, and it disappeared immediately upon a major change of direction, but reappeared only about two seconds after rotating back to the original direction. Apparently we had detected the rising moon behind the clouds with the equipment. It explained the gradual disappearance of the impulses by the reflecting body slowly moving out of the strongly focussed, horizontally aimed beam, as it rises above the horizon." It was not until the close of
World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
, however, that techniques specifically intended for the purpose of bouncing radar waves off the moon to demonstrate their potential use in defense, communication, and
radar astronomy Radar astronomy is a technique of observing nearby astronomical objects by reflecting radio waves or microwaves off target objects and analyzing their reflections. Radar astronomy differs from ''radio astronomy'' in that the latter is a passive ob ...
were developed. The first successful attempt was carried out at
Fort Monmouth Fort Monmouth is a former installation of the Department of the Army in Monmouth County, New Jersey and the site of a major upcoming Netflix film production campus, alongside a variety of other redevelopment. The site is surrounded by the commun ...
, New Jersey, on January 10, 1946, by a group code-named
Project Diana Project Diana, named for the Roman moon goddess Diana, was an experimental project of the US Army Signal Corps in 1946 to bounce radar signals off the Moon and receive the reflected signals. This was the first experiment in radar astronomy ...
, headed by John H. DeWitt. It was followed less than a month later, on February 6, 1946, by a second successful attempt, by a Hungarian group led by Zoltán Bay. The Communication Moon Relay project that followed led to more practical uses, including a
teletype A teleprinter (teletypewriter, teletype or TTY) is an electromechanical device that can be used to send and receive typed messages through various communications channels, in both point-to-point and point-to-multipoint configurations. Init ...
link between the naval base at
Pearl Harbor Pearl Harbor is an American lagoon harbor on the island of Oahu, Hawaii, west of Honolulu. It was often visited by the naval fleet of the United States, before it was acquired from the Hawaiian Kingdom by the U.S. with the signing of the Reci ...
,
Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...
and
United States Navy The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...
headquarters in
Washington, D.C. Washington, D.C., formally the District of Columbia and commonly known as Washington or D.C., is the capital city and federal district of the United States. The city is on the Potomac River, across from Virginia, and shares land borders with ...
In the days before
communications satellite A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a Transponder (satellite communications), transponder; it creates a communication channel between a source transmitter and a Rad ...
s, a link free of the vagaries of
ionospheric propagation In radio communication, skywave or skip refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere. Since it is not limited by the curvature of ...
was revolutionary. The development of
communication satellite A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. ...
s in the 1960s made this technique obsolete. However,
radio amateur An amateur radio operator is someone who uses equipment at an amateur radio station to engage in two-way personal communications with other amateur operators on radio frequencies assigned to the amateur radio service. Amateur radio operators ...
s took up EME communication as a hobby; the first
amateur radio Amateur radio, also known as ham radio, is the use of the radio frequency radio spectrum, spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emer ...
moon bounce communication took place in 1953, and amateurs worldwide still use the technique. Radio ham Ray Noughton (VK3ATN) of Birchip, Victoria, Australia accomplished Australia's first moon bounce with a home-built 250 m wide, 30 m antenna with a 100 watt signal in 1970. (NASA scientists, having had ridiculed his DIY project, claiming that at least a kilowatt would be required, invited him to the U.S., all expenses paid, to learn from his grassroots engineering. Naughton later became involved in Australia's first satellite,
Australis-OSCAR 5 Australis-OSCAR 5 (a.k.a. AO-5) is an amateur radio satellite that was launched into Low Earth Orbit on 23 January 1970 by a Thor Delta launcher from Vandenberg Air Force Base, Lompoc, California. AO-5 was launched piggyback with TIROS-M (I ...
). The effect has even been put to artistic use. Composer
Pauline Oliveros Pauline Oliveros (May 30, 1932 – November 24, 2016) was an American composer, accordionist and a central figure in the development of post-war experimental and electronic music. She was a founding member of the San Francisco Tape Music Center ...
used moonbounce in her 1987 work ''Echoes from the Moon,'' and in 2024 German musician Hainbach experimented with moonbounce and created an
audio plug-in An audio plug-in, in computer software, is a Plug-in (computing), plug-in that can add or enhance audio-related functions in a computer program, typically a digital audio workstation. Such functions may include digital signal processing or soun ...
to reproduce the effect.


Current EME communications

Amateur radio (ham) operators utilize EME for
two-way communication Two-way communication is a form of transmission in which both parties involved transmit information. Two-way communication has also been referred to as interpersonal communication. Common forms of two-way communication are: * Amateur radio, CB or ...
s. EME presents significant challenges to amateur operators interested in weak signal communication. EME provides the longest communications path any two
stations Station may refer to: Agriculture * Station (Australian agriculture), a large Australian landholding used for livestock production * Station (New Zealand agriculture), a large New Zealand farm used for grazing by sheep and cattle ** Cattle stat ...
on Earth can use. Amateur frequency bands from 50 MHz (6
meter The metre (or meter in US spelling; symbol: m) is the base unit of length in the International System of Units (SI). Since 2019, the metre has been defined as the length of the path travelled by light in vacuum during a time interval of of ...
wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...
) to 47 GHz (6.38 mm) have been used successfully, but most EME communications are on the 2 meter, 70-centimeter, or 23-centimeter bands. Common modulation modes are
continuous wave A continuous wave or continuous waveform (CW) is an electromagnetic wave of constant amplitude and frequency, typically a sine wave, that for mathematical analysis is considered to be of infinite duration. It may refer to e.g. a laser or particl ...
with Morse code, digital ( JT65) and when the link budgets allow, voice. Recent advances in
digital signal processing Digital signal processing (DSP) is the use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations. The digital signals processed in this manner are a ...
have allowed EME contacts, admittedly with low data rate, to take place with powers in the order of 100 watts and a single
Yagi–Uda antenna A Yagi–Uda antenna, or simply Yagi antenna, is a directional antenna consisting of two or more parallel Antenna (radio)#Resonant antennas, resonant antenna elements in an Antenna array#Types, end-fire array; these elements are most often metal ...
. World Moon Bounce Day, June 29, 2009, was created by Echoes of Apollo and celebrated worldwide as an event preceding the 40th
anniversary An anniversary is the date on which an event took place or an institution was founded. Most countries celebrate national anniversaries, typically called national days. These could be the List of national independence days, date of independen ...
of the
Apollo 11 Apollo 11 was a spaceflight conducted from July 16 to 24, 1969, by the United States and launched by NASA. It marked the first time that humans Moon landing, landed on the Moon. Commander Neil Armstrong and Lunar Module pilot Buzz Aldrin l ...
Moon landing. A highlight of the celebrations was an interview via the Moon with
Apollo 8 Apollo 8 (December 21–27, 1968) was the first crewed spacecraft to leave Sphere of influence (astrodynamics), Earth's gravitational sphere of influence, and the first human spaceflight to reach the Moon. The crew orbited the Moon ten times ...
astronaut
Bill Anders William Alison Anders (17 October 1933 – 7 June 2024) was an American United States Air Force (USAF) major general, electrical engineer, nuclear engineer, NASA astronaut, and businessman. In December 1968, he was a member of the crew of ...
, who was also part of the backup crew for Apollo 11. The
University of Tasmania The University of Tasmania (UTAS) is a public research university, primarily located in Tasmania, Australia. Founded in 1890, it is Australia's fourth oldest university. Christ College (University of Tasmania), Christ College, one of the unive ...
in Australia with their 26-meter (85') dish were able to bounce a data signal off the surface of the Moon which was received by a large dish in the Netherlands,
Dwingeloo Radio Observatory The Dwingeloo Radio Observatory is a single-dish radio telescope near the village of Dwingeloo () in the northeastern Netherlands. Construction started in 1954, and the telescope was completed in 1956. The radio telescope has a diameter of 25  ...
. The data signal was successfully resolved back to data setting a world record for the lowest power data signal returned from the Moon with a transmit power of 3 milliwatts, about 1,000th of the power of a
flashlight A flashlight (US English) or electric torch (Commonwealth English), usually shortened to torch, is a portable hand-held electric lamp. Formerly, the light source typically was a miniature incandescent light bulb, but these have been displaced ...
lamp. The second World Moon Bounce Day was April 17, 2010, coinciding with the 40th anniversary of the conclusion of the Apollo 13 mission. In October 2009 media artist Daniela de Paulis proposed to the CAMRAS radio amateur association based at the Dwingeloo Radio Observatory to use Moon bounce for a live image transmission performance. As a result of her proposal, in December 2009 CAMRAS radio operator Jan van Muijlwijk and radio operator Daniel Gautchi made the first image transmission via the Moon using the open source software MMSSTV. De Paulis called the innovative technology "Visual Moonbounce" and since 2010 she has been using it in several of her art projects, including the live performance called OPTICKS, during which digital images are sent to the Moon and back in real time and projected live.


Echo delay and time spread

Radio waves Radio waves (formerly called Hertzian waves) are a type of electromagnetic radiation with the lowest frequencies and the longest wavelengths in the electromagnetic spectrum, typically with frequencies below 300 gigahertz (GHz) and wavelengths ...
propagate Propagation can refer to: *Chain propagation in a chemical reaction mechanism *Crack propagation, the growth of a crack during the fracture of materials *Propaganda, non-objective information used to further an agenda *Reproduction, and other forms ...
in vacuum at the
speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant exactly equal to ). It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time i ...
''c'', exactly 299,792,458 m/s. Propagation time to the Moon and back ranges from 2.4 to 2.7 seconds, with an average of 2.56 seconds (the average distance from Earth to the Moon is 384,400 km). The Moon is nearly spherical, and its radius corresponds to about 5.8 milliseconds of wave travel time. The trailing parts of an echo, reflected from irregular surface features near the edge of the lunar disk, are delayed from the leading edge by as much as twice this value. Most of the Moon's surface appears relatively smooth at the typical microwave wavelengths used for amateur EME. Most amateurs do EME contacts below 6 GHz, and differences in the moon's reflectivity are somewhat hard to discern above 1 GHz. Lunar reflections are by nature quasi-
specular Specular reflection, or regular reflection, is the mirror-like reflection of waves, such as light, from a surface. The law of reflection states that a reflected ray of light emerges from the reflecting surface at the same angle to the surf ...
(like those from a shiny ball bearing). The power useful for communication is mostly reflected from a small region near the center of the disk. The effective time spread of an echo amounts to no more than 0.1 ms. Antenna polarization for EME stations must consider that reflection from a smooth surface preserves
linear polarization In electrodynamics, linear polarization or plane polarization of electromagnetic radiation is a confinement of the electric field vector or magnetic field vector to a given plane along the direction of propagation. The term ''linear polarizati ...
but reverses the sense of
circular polarization In electrodynamics, circular polarization of an electromagnetic wave is a polarization state in which, at each point, the electromagnetic field of the wave has a constant magnitude and is rotating at a constant rate in a plane perpendicular to ...
s. At shorter wavelengths the lunar surface appears increasingly rough, so reflections at 10 GHz and above contain a significant
diffuse Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...
component as well as a quasi-specular component. The diffuse component is depolarized, and can be viewed as a source of low level system noise. Significant portions of the diffused component arise from regions farther out toward the lunar rim. The
median The median of a set of numbers is the value separating the higher half from the lower half of a Sample (statistics), data sample, a statistical population, population, or a probability distribution. For a data set, it may be thought of as the “ ...
time spread can then be as much as several milliseconds. In all practical cases, however, time spreading is small enough that it does not cause significant smearing of CW keying or
intersymbol interference In telecommunications, intersymbol interference (ISI) is a form of distortion of a signal in which one symbol interferes with subsequent symbols. This is an unwanted phenomenon as the previous symbols have a similar effect as noise, thus making ...
in the slowly keyed
modulation Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information. The process encodes information in form of the modulation or message ...
s commonly used for digital EME. The diffused component may appear as significant noise at higher message data rates. EME time spreading does have one very significant effect. Signal components reflected from different parts of the lunar surface travel different distances and arrive at Earth with random phase relationships. As the relative geometry of the transmitting station, receiving station and reflecting lunar surface changes, signal components sometimes add and sometimes cancel, depending on their
phase Phase or phases may refer to: Science *State of matter, or phase, one of the distinct forms in which matter can exist *Phase (matter), a region of space throughout which all physical properties are essentially uniform *Phase space, a mathematica ...
relationship, creating large amplitude fluctuations in the received signal. These "libration fading" amplitude variations are well correlated over the
coherence bandwidth Coherence bandwidth is a statistical measurement of the range of frequencies over which the channel can be considered "flat", or in other words the approximate maximum bandwidth or frequency interval over which two frequencies of a signal are like ...
(typically a few kHz). The libration
fading In wireless communications, fading is the variation of signal attenuation over variables like time, geographical position, and radio frequency. Fading is often modeled as a random process. In wireless systems, fading may either be due to mul ...
components are related to the time spread of reflected signals.


Modulation types and frequencies for EME

VHF * CW * JT65A, JT65B, Q65
UHF Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range between 300 megahertz (MHz) and 3 gigahertz (GHz), also known as the decimetre band as the wavelengths range from one meter to one tenth of a meter ...
* CW * JT65, Q65 * SSB
Microwave Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequency, frequencies between 300&n ...
* CW * SSB * Q65


Other factors influencing EME communications

Doppler effect The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. The ''Doppler effect'' is named after the physicist Christian Doppler, who described ...
at 144 MHz band is 300 Hz at moonrise or moonset. The doppler offset reduces to around zero when the Moon is overhead. At other frequencies other doppler offsets will exist. At moonrise, returned signals will be shifted approximately 300 Hz higher in frequency. As the Moon traverses the sky to a point due south or due north, the Doppler effect approaches zero. By Moonset, they are shifted 300 Hz lower. Doppler effects cause many problems when tuning into, and locking onto, signals from the Moon. Polarization effects can reduce the strength of received signals. One component is the geometrical alignment of the transmitting and receiving antennas. Many antennas produce a preferred plane of polarization. Transmitting and receiving station antennas may not be aligned from the perspective of an observer on the moon. This component is fixed by the alignment of the antennas and stations may include a facility to rotate antennas to adjust polarization. Another component is
Faraday rotation The Faraday effect or Faraday rotation, sometimes referred to as the magneto-optic Faraday effect (MOFE), is a physical magneto-optical phenomenon. The Faraday effect causes a polarization rotation which is proportional to the projection of the ...
on the Earth-Moon-Earth path. The plane of polarization of radio waves rotates as they pass through ionized layers of the Earth's atmosphere. This effect is more pronounced at lower VHF frequencies and becomes less significant at 1296 MHz and above. Some of the polarization mismatch loss can be reduced by using a larger antenna array (more Yagi elements or a larger dish).Larry Wolfgang, Charles Hutchinson, (ed), ''The ARRL , Handbook for Radio Amateurs, Sixty Eighth Edition '', American Radio Relay League, 1990 , pages 23-34, 23-25,


Gallery

Image:EA6VQ_EME.jpg, An array of eight Yagi antennas for 144 MHz EME at EA6VQ, Balearic Islands, Spain Image:144MHz_EME.jpg, A part of 144 MHz EME antenna array at WA6PY in California, U.S. Image:EME_dish.jpg, A dish antenna for microwave EME work at WA6PY, California, U.S. Image:I2FZX_UHF_EME_Antenna.png, A dish antenna for UHF EME at I2FZX, Milan, Italy File:SM3PWM EME Antenna.jpg, Amateur radio antenna array used for Earth–Moon–Earth communication on 144 MHz. Location Kilafors in central Sweden. File:SM5BSZ EME Antenna.jpg, Amateur radio antenna array used for Earth–Moon–Earth communication on 144 MHz. Location Jäder, central Sweden. File:SM7BAE EME Antenna.jpg, Amateur radio antenna array used for Earth–Moon–Earth communication on 144 MHz. Location Staffanstorp, southern Sweden.


See also

* Communication Moon Relay *
Information theory Information theory is the mathematical study of the quantification (science), quantification, Data storage, storage, and telecommunications, communication of information. The field was established and formalized by Claude Shannon in the 1940s, ...
*
Lunar Laser Ranging experiment Lunar Laser Ranging (LLR) is the practice of measuring Lunar distance (astronomy), the distance between the surfaces of the Earth and the Moon using Lidar, laser ranging. The distance can be calculated from the Round-trip delay, round-trip time ...
*
Meteor burst communications Meteor burst communications (MBC), also referred to as meteor scatter communications, is a radio propagation mode that exploits the ionized trails of meteors during atmospheric entry to establish brief communications paths between radio statio ...
*
Passive repeater A passive repeater or passive radio link deflection, is a reflective or sometimes refractive panel or other object that assists in closing a radio or microwave link, in places where an obstacle in the signal path blocks any direct, line of si ...
* Radar equation * Unified S-band


References


External links


NASA, ''Beyond the Ionosphere: the development of satellite communications''


(gives formulas for EME path loss calculation)
Dwingeloo Radiotelescoop , CAMRAS – Dwingeloo Radiotelescoop , PI9RD
site of CAMRAS radio amateurs association at Dwingeloo radio telescope
Opticks , live art performance earth-moon-earth

World Moon Bounce Day 2010 April 17th , Echoes of Apollo Space News
World Moon Bounce Day - Echoes of Apollo
The Wireless Institute of Australia
Amateur Radio - August 2009 - Wireless Institute of Australia

K3PGP - UHF TV reception via Earth–Moon–Earth communication *
OPTICKS and Visual Moonbounce in Live Performance
{{DEFAULTSORT:Earth-Moon-Earth communication Radio frequency propagation Lunar science