Mariner 2
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Mariner 2 (Mariner-Venus 1962), an American space probe to
Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...
, was the first robotic
space probe A space probe is an artificial satellite that travels through space to collect scientific data. A space probe may orbit Earth; approach the Moon; travel through interplanetary space; flyby, orbit, or land or fly on other planetary bodies; or ent ...
to conduct a successful planetary encounter. The first successful
spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...
in the
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...
Mariner program The Mariner program was conducted by the American space agency NASA to explore other planets. Between 1962 and late 1973, NASA's Jet Propulsion Laboratory (JPL) designed and built 10 robotic interplanetary probes named Mariner to explore the in ...
, it was a simplified version of the Block I spacecraft of the
Ranger program The Ranger program was a series of unmanned space missions by the United States in the 1960s whose objective was to obtain the first close-up images of the surface of the Moon. The Ranger spacecraft were designed to take images of the lunar surf ...
and an exact copy of
Mariner 1 Mariner 1, built to conduct the first American planetary flyby of Venus, was the first spacecraft of NASA's interplanetary Mariner program. Developed by Jet Propulsion Laboratory, and originally planned to be a purpose-built probe launched summ ...
. The missions of the Mariner 1 and 2 spacecraft are sometimes known as the Mariner R missions. Original plans called for the probes to be launched on the
Atlas-Centaur The Atlas-Centaur was a United States expendable launch vehicle derived from the SM-65 Atlas D missile. Launches were conducted from Launch Complex 36 at the Cape Canaveral Air Force Station (CCAFS) in Florida. Early development Convair, ...
, but serious developmental problems with that vehicle forced a switch to the much smaller Agena B second stage. As such, the design of the Mariner R vehicles was greatly simplified. Far less instrumentation was carried than on the Soviet
Venera The Venera (, , which means "Venus" in Russian) program was the name given to a series of space probes developed by the Soviet Union between 1961 and 1984 to gather information about the planet Venus. Ten probes successfully landed on the s ...
probes of this period—for example, forgoing a TV camera—as the Atlas-Agena B had only half as much lift capacity as the Soviet 8K78 booster. The Mariner 2 spacecraft was launched from Cape Canaveral on August 27, 1962, and passed as close as to Venus on December 14, 1962. The Mariner probe consisted of a 100 cm (39.4 in) diameter hexagonal bus, to which solar panels, instrument booms, and
antennas In radio engineering, an antenna or aerial is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver. In transmission, a radio transmitter supplies an ...
were attached. The scientific instruments on board the Mariner spacecraft were: two radiometers (one each for the
microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ra ...
and
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
portions of the
spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...
), a
micrometeorite A micrometeorite is a micrometeoroid that has survived entry through the Earth's atmosphere. Usually found on Earth's surface, micrometeorites differ from meteorites in that they are smaller in size, more abundant, and different in composition. T ...
sensor, a solar plasma sensor, a
charged particle In physics, a charged particle is a particle with an electric charge. It may be an ion, such as a molecule or atom with a surplus or deficit of electrons relative to protons. It can also be an electron or a proton, or another elementary pa ...
sensor, and a magnetometer. These instruments were designed to measure the temperature distribution on the surface of Venus and to make basic measurements of Venus'
atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
. The primary mission was to receive communications from the spacecraft in the vicinity of Venus and to perform
radiometric Radiometry is a set of techniques for measuring electromagnetic radiation, including visible light. Radiometric techniques in optics characterize the distribution of the radiation's power in space, as opposed to photometric techniques, which ch ...
temperature measurements of the planet. A second objective was to measure the
interplanetary magnetic field The interplanetary magnetic field (IMF), now more commonly referred to as the heliospheric magnetic field (HMF), is the component of the solar magnetic field that is dragged out from the solar corona by the solar wind flow to fill the Solar Sy ...
and charged particle environment. En route to Venus, Mariner 2 measured the
solar wind The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sol ...
, a constant stream of charged particles flowing outwards from the
Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
, confirming the measurements by
Luna 1 ''Luna 1'', also known as ''Mechta'' (russian: Мечта , '' lit.'': ''Dream''), ''E-1 No.4'' and ''First Lunar Rover'', was the first spacecraft to reach the vicinity of Earth's Moon, and the first spacecraft to be placed in heliocentric or ...
in 1959. It also measured
interplanetary dust The interplanetary dust cloud, or zodiacal cloud (as the source of the zodiacal light), consists of cosmic dust (small particles floating in outer space) that pervades the space between planets within planetary systems, such as the Solar System. ...
, which turned out to be scarcer than predicted. In addition, Mariner 2 detected high-energy charged particles coming from the Sun, including several brief
solar flare A solar flare is an intense localized eruption of electromagnetic radiation in the Sun's atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, solar particle events, and other sol ...
s, as well as
cosmic ray Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...
s from outside the
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
. As it flew by Venus on December 14, 1962, Mariner 2 scanned the planet with its pair of radiometers, revealing that Venus has cool clouds and an extremely hot surface.


Background

With the advent of the
Cold War The Cold War is a term commonly used to refer to a period of geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc. The term '' cold war'' is used because the ...
, the two then- superpowers, the United States and the
Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen national ...
, both initiated ambitious space programs with the intent of demonstrating military, technological, and political dominance. The Soviets launched the
Sputnik 1 Sputnik 1 (; see § Etymology) was the first artificial Earth satellite. It was launched into an elliptical low Earth orbit by the Soviet Union on 4 October 1957 as part of the Soviet space program. It sent a radio signal back to Earth for t ...
, the first Earth orbiting satellite, on October 4, 1957. The Americans followed suit with Explorer 1 on February 1, 1958, by which point the Soviets had already launched the first orbiting animal,
Laika Laika (russian: link=no, Лайка; – 3 November 1957) was a Soviet space dog who was one of the first animals in space and the first to orbit the Earth. A stray mongrel from the streets of Moscow, she flew aboard the Sputnik 2 space ...
in
Sputnik 2 Sputnik 2 (, russian: Спутник-2, ''Satellite 2''), or Prosteyshiy Sputnik 2 (PS-2, russian: Простейший Спутник 2, italic=yes, ''Simplest Satellite 2'') was the second spacecraft launched into Earth orbit, on 3 November 195 ...
. Earth's orbit having been reached, focus turned to being the first to the Moon. The Pioneer program of satellites consisted of three unsuccessful lunar attempts in 1958. In early 1959, the Soviet
Luna 1 ''Luna 1'', also known as ''Mechta'' (russian: Мечта , '' lit.'': ''Dream''), ''E-1 No.4'' and ''First Lunar Rover'', was the first spacecraft to reach the vicinity of Earth's Moon, and the first spacecraft to be placed in heliocentric or ...
was the first probe to fly by the Moon, followed by Luna 2, the first artificial object to impact the Moon. With the Moon achieved, the superpowers turned their eyes to the planets. As the closest planet to Earth,
Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...
presented an appealing interplanetary spaceflight target. Every 19 months, Venus and the Earth reach relative positions in their orbits around the Sun such that a minimum of fuel is required to travel from one planet to the other via a
Hohmann Transfer Orbit In astronautics, the Hohmann transfer orbit () is an orbital maneuver used to transfer a spacecraft between two orbits of different altitudes around a central body. Examples would be used for travel between low Earth orbit and the Moon, or ...
. These opportunities mark the best time to launch exploratory spacecraft, requiring the least fuel to make the trip. The first such opportunity of the Space Race occurred in late 1957, before either superpower had the technology to take advantage of it. The second opportunity, around June 1959, lay just within the edge of technological feasibility, and
U.S. Air Force The United States Air Force (USAF) is the air service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army Sign ...
contractor Space Technology Laboratory (STL) intended to take advantage of it. A plan drafted January 1959 involved two spacecraft evolved from the first Pioneer probes, one to be launched via
Thor-Able The Thor-Able was an American expendable launch system and sounding rocket used for a series of re-entry vehicle tests and satellite launches between 1958 and 1960. It was a two-stage rocket, consisting of a Thor IRBM as a first stage and a Vang ...
rocket, the other via the yet-untested
Atlas-Able The Atlas-Able was an American expendable launch system derived from the SM-65 Atlas missile. It was a member of the Atlas family of rockets, and was used to launch several Pioneer spacecraft towards the Moon. Of the five Atlas-Able rockets built, ...
. STL was unable to complete the probes before June, and the
launch window In the context of spaceflight, launch period is the collection of days and launch window is the time period on a given day during which a particular rocket must be launched in order to reach its intended target. If the rocket is not launched wit ...
was missed. The Thor-Able probe was repurposed as the deep space explorer
Pioneer 5 ''Pioneer 5'' (also known as Pioneer P-2, and Able 4, and nicknamed the "Paddle-Wheel Satellite") was a spin-stabilized space probe in the NASA Pioneer program used to investigate interplanetary space between the orbits of Earth and Venus. It ...
, which was launched March 11, 1960, and designed to maintain communications with Earth up to a distance of as it traveled toward the orbit of Venus. (The Atlas Able probe concept was repurposed as the unsuccessful Pioneer Atlas Moon probes.) No American missions were sent during the early 1961 opportunity. The Soviet Union launched
Venera 1 ''Venera 1'' (russian: Венера-1 meaning ''Venus 1''), also known as Venera-1VA No.2 and occasionally in the West as ''Sputnik 8'' was the first spacecraft to fly past Venus, as part of the Soviet Union's Venera programme. Launched in Febr ...
on February 12, 1961, and on May 19–20 became the first probe to fly by Venus; however, it had stopped
transmitting In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the ...
on February 26. For the summer 1962 launch opportunity, NASA contracted
Jet Propulsion Laboratory The Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center in the City of La Cañada Flintridge, California, United States. Founded in the 1930s by Caltech researchers, JPL is owned by NASA an ...
(JPL) in July 1960 to develop "Mariner A", a spacecraft to be launched using the yet undeveloped
Atlas-Centaur The Atlas-Centaur was a United States expendable launch vehicle derived from the SM-65 Atlas D missile. Launches were conducted from Launch Complex 36 at the Cape Canaveral Air Force Station (CCAFS) in Florida. Early development Convair, ...
. By August 1961, it had become clear that the
Centaur A centaur ( ; grc, κένταυρος, kéntauros; ), or occasionally hippocentaur, is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse. Centaurs are thought of in many Greek myths as being ...
would not be ready in time. JPL proposed to NASA that the mission might be accomplished with a lighter spacecraft using the less powerful but operational
Atlas-Agena The Atlas-Agena was an American expendable launch system derived from the SM-65 Atlas missile. It was a member of the Atlas family of rockets, and was launched 109 times between 1960 and 1978. It was used to launch the first five Mariner uncrew ...
. A hybrid of Mariner A and JPL's Block 1
Ranger A Ranger is typically someone in a military/paramilitary or law enforcement role specializing in patrolling a given territory, called “ranging”. The term most often refers to: * Park ranger or forest ranger, a person charged with protecting and ...
lunar explorer, already under development, was suggested. NASA accepted the proposal, and JPL began an 11-month crash program to develop "Mariner R" (so named because it was a Ranger derivative). Mariner 1 would be the first Mariner R to be launched followed by Mariner 2.


Spacecraft

Three Mariner R spacecraft were built: two for launching and one to run tests, which was also to be used as a spare. Aside from its scientific capabilities, Mariner also had to transmit data back to Earth from a distance of more than , and to survive solar radiation twice as intense as that encountered in Earth orbit.


Structure

All three of the Mariner R spacecraft, including Mariner 2, weighed within of the design weight of , of which was devoted to non-experimental systems: maneuvering systems, fuel, and communications equipment for receiving commands and transmitting data. Once fully deployed in space, with its two solar panel "wings" extended, Mariner R was in height and across. The main body of the craft was hexagonal with six separate cases of electronic and electromechanical equipment: *Two of the cases comprised the power system:
switchgear In an electric power system, a switchgear is composed of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be ...
that regulated and transmitted power from the 9800
solar cells A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physics, physical and Chemical substance, chemical phenomenon.radio receiver In radio communications, a radio receiver, also known as a receiver, a wireless, or simply a radio, is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna. Th ...
, the three-
watt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wa ...
transmitter, and control systems for Mariner's experiments. *The fifth case held electronics for
digitizing DigitizationTech Target. (2011, April). Definition: digitization. ''WhatIs.com''. Retrieved December 15, 2021, from https://whatis.techtarget.com/definition/digitization is the process of converting information into a digital (i.e. computer- ...
the
analog Analog or analogue may refer to: Computing and electronics * Analog signal, in which information is encoded in a continuous variable ** Analog device, an apparatus that operates on analog signals *** Analog electronics, circuits which use analog ...
data received by the experiments for transmission. *The sixth case carried the three
gyroscope A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rota ...
s that determined Mariner's orientation in space. It also held the central computer and sequencer, the "brain" of the spacecraft that coordinated all of its activities pursuant to code in its
memory bank A memory bank is a logical unit of storage in electronics, which is hardware-dependent. In a computer, the memory bank may be determined by the memory controller along with physical organization of the hardware memory slots. In a typical synchro ...
s and on a schedule maintained by an electronic clock tuned into equipment on Earth. At the rear of the spacecraft, a
monopropellant Monopropellants are propellants consisting of chemicals that release energy through exothermic chemical decomposition. The molecular bond energy of the monopropellant is released usually through use of a catalyst. This can be contrasted with biprop ...
(anhydrous
hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...
) 225 N rocket motor was mounted for course corrections. A nitrogen gas fueled stabilizing system of ten jet nozzles controlled by the onboard gyroscopes, Sun sensors, and Earth sensors, kept Mariner properly oriented to receive and transmit data to Earth. The primary high gain parabolic antenna was also mounted on the underside of Mariner and kept pointed toward the Earth. An
omnidirectional antenna In radio communication, an omnidirectional antenna is a class of antenna which radiates equal radio power in all directions perpendicular to an axis (azimuthal directions), with power varying with angle to the axis (elevation angle), declining t ...
atop the spacecraft would broadcast at times that the spacecraft was rolling or tumbling out of its proper orientation, to maintain contact with Earth; as an unfocused antenna, its signal would be much weaker than the primary. Mariner also mounted small antennas on each of the wings to receive commands from ground stations. Temperature control was both passive, involving insulated, and highly reflective components; and active, incorporating
louver A louver (American English) or louvre (British English British English (BrE, en-GB, or BE) is, according to Lexico, Oxford Dictionaries, "English language, English as used in Great Britain, as distinct from that used elsewhere". Mor ...
s to protect the case carrying the onboard computer. At the time the first Mariners were built, no
test chamber An environmental chamber, also called a climatic chamber or climate chamber, is an enclosure used to test the effects of specified environmental conditions on biological items, industrial products, materials, and electronic devices and components ...
existed to simulate the near-Venus solar environment, so the efficacy of these cooling techniques could not be tested until the live mission.


Scientific instruments


Background

At the time of the Mariner project's inception, few of Venus' characteristics were definitely known. Its opaque
atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
precluded telescopic study of the ground. It was unknown whether there was water beneath the clouds, though a small amount of
water vapor (99.9839 °C) , - , Boiling point , , - , specific gas constant , 461.5 J/( kg·K) , - , Heat of vaporization , 2.27 MJ/kg , - , Heat capacity , 1.864 kJ/(kg·K) Water vapor, water vapour or aqueous vapor is the gaseous pha ...
above them had been detected. The planet's rotation rate was uncertain, though JPL scientists had concluded through
radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
observation that Venus rotated very slowly compared to the Earth, advancing the long-standing (but later disproven) hypothesis that the planet was
tidally locked Tidal locking between a pair of co-orbiting astronomical body, astronomical bodies occurs when one of the objects reaches a state where there is no longer any net change in its rotation rate over the course of a complete orbit. In the case where ...
with respect to the Sun (as the Moon is with respect to the Earth). No oxygen had been detected in Venus' atmosphere, suggesting that life as existed on Earth was not present. It had been determined that Venus' atmosphere contained at least 500 times as much
carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
as the Earth's. These comparatively high levels suggested that the planet might be subject to a runaway
greenhouse effect The greenhouse effect is a process that occurs when energy from a planet's host star goes through the planet's atmosphere and heats the planet's surface, but greenhouse gases in the atmosphere prevent some of the heat from returning directly ...
with surface temperatures as high as , but this had not yet been conclusively determined. The Mariner spacecraft would be able to verify this hypothesis by measuring the temperature of Venus close-up; at the same time, the spacecraft could determine if there was a significant disparity between night and daytime temperatures. An on-board magnetometer and suite of charged particle detectors could determine if Venus possessed an appreciable magnetic field and an analog to Earth's Van Allen Belts. As the Mariner spacecraft would spend most of its journey to Venus in interplanetary space, the mission also offered an opportunity for long-term measurement of the
solar wind The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sol ...
of charged particles and to map the variations in the Sun's
magnetosphere In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior dynam ...
. The concentration of
cosmic dust Cosmic dust, also called extraterrestrial dust, star dust or space dust, is dust which exists in outer space, or has fallen on Earth. Most cosmic dust particles measure between a few molecules and 0.1 mm (100 micrometers). Larger particles are c ...
beyond the vicinity of Earth could be explored as well. Due to the limited capacity of the Atlas Agena, only of the spacecraft could be allocated to scientific experiments.


Instruments

* A two-channel
microwave radiometer A microwave radiometer (MWR) is a radiometer that measures energy emitted at one millimeter-to-metre wavelengths (frequencies of 0.3–300 GHz) known as microwaves. Microwave radiometers are very sensitive receivers designed to measure thermally- ...
of the crystal video type operating in the standard Dicke mode of chopping between the main antenna, pointed at the target, and a reference horn pointed at cold space. It was used to determine the absolute temperature of Venus' surface and details concerning its atmosphere through its microwave-radiation characteristics, including the daylight and dark hemispheres, and in the region of the terminator. Measurements were performed simultaneously in two frequency bands of 13.5 mm and 19 mm. The total weight of the radiometer was . Its average power consumption was 4 watts and its peak power consumption 9 watts. * A two-channel
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
radiometer to measure the effective temperatures of small areas of Venus. The radiation that was received could originate from the planetary surface, clouds in the atmosphere, the atmosphere itself or a combination of these. The radiation was received in two spectral ranges: 8 to 9 μm (focused on 8.4 μm) and 10 to 10.8 μm (focused on 10.4 μm). The latter corresponding to the
carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
band. The total weight of the infrared radiometer, which was housed in a magnesium casting, was , and it required 2.4 watts of power. It was designed to measure radiation temperatures between approximately . * A three-axis
fluxgate magnetometer A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, o ...
to measure planetary and interplanetary magnetic fields. Three probes were incorporated in its sensors, so it could obtain three mutually orthogonal components of the field vector. Readings of these components were separated by 1.9 seconds. It had three analog outputs that had each two sensitivity scales: ± 64 γ and ± 320 γ (1 γ = 1 
nanotesla The tesla (symbol: T) is the unit of magnetic flux density (also called magnetic B-field strength) in the International System of Units (SI). One tesla is equal to one weber per square metre. The unit was announced during the General Conferenc ...
). These scales were automatically switched by the instrument. The field that the magnetometer observed was the super-position of a nearly constant spacecraft field and the interplanetary field. Thus, it effectively measured only the changes in the interplanetary field. * An
ionization chamber The ionization chamber is the simplest type of gas-filled radiation detector, and is widely used for the detection and measurement of certain types of ionizing radiation, including X-rays, gamma rays, and beta particles. Conventionally, the term ...
with matched Geiger-Müller tubes (also known as a
cosmic ray Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...
detector) to measure high-energy cosmic radiation. * A particle detector (implemented through use of an Anton type 213 Geiger-Müller tube) to measure lower radiation (especially near Venus), also known as the Iowa detector, as it was provided by the
University of Iowa The University of Iowa (UI, U of I, UIowa, or simply Iowa) is a public university, public research university in Iowa City, Iowa, United States. Founded in 1847, it is the oldest and largest university in the state. The University of Iowa is org ...
. It was a miniature tube having a 1.2 mg/cm2 mica window about in diameter and weighing about . It detected soft
x-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10  picometers to 10  nanometers, corresponding to frequencies in the range 30&nb ...
s efficiently and
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
inefficiently, and was previously used in Injun 1,
Explorer 12 Explorer 12, also called EPE-A or Energetic Particles Explorer-A and as S3), was a NASA satellite built to measure the solar wind, cosmic rays, and the Earth's magnetic field. It was the first of the S-3 series of spacecraft, which also include ...
and Explorer 14. It was able to detect protons above 500 keV in energy and electrons above 35 keV. The length of the basic telemetry frame was 887.04 seconds. During each frame, the counting rate of the detector was sampled twice at intervals separated by 37 seconds. The first sampling was the number of counts during an interval of 9.60 seconds (known as the 'long gate'); the second was the number of counts during an interval of 0.827 seconds (known as the 'short gate'). The long gate accumulator overflowed on the 256th count and the short gate accumulator overflowed on the 65,536th count. The maximum counting rate of the tube was 50,000 per second. * A
cosmic dust Cosmic dust, also called extraterrestrial dust, star dust or space dust, is dust which exists in outer space, or has fallen on Earth. Most cosmic dust particles measure between a few molecules and 0.1 mm (100 micrometers). Larger particles are c ...
detector to measure the flux of cosmic dust particles in space. * A solar plasma
spectrometer A spectrometer () is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where the ...
to measure the spectrum of low-energy positively charged particles from the Sun, i.e. the
solar wind The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sol ...
. The magnetometer was attached to the top of the mast below the
omnidirectional antenna In radio communication, an omnidirectional antenna is a class of antenna which radiates equal radio power in all directions perpendicular to an axis (azimuthal directions), with power varying with angle to the axis (elevation angle), declining t ...
. Particle detectors were mounted halfway up the mast, along with the cosmic ray detector. The cosmic dust detector and solar plasma spectrometer were attached to the top edges of the spacecraft base. The microwave radiometer, the infrared radiometer and the radiometer reference horns were rigidly mounted to a diameter parabolic radiometer antenna mounted near the bottom of the mast. All instruments were operated throughout the cruise and encounter modes except the radiometers, which were only used in the immediate vicinity of Venus. In addition to these scientific instruments, Mariner 2 had a data conditioning system (DCS) and a scientific power switching (SPS) unit. The DCS was a solid-state electronic system designed to gather information from the scientific instruments on board the spacecraft. It had four basic functions: analog-to-digital conversion, digital-to-digital conversion, sampling and instrument-calibration timing, and planetary acquisition. The SPS unit was designed to perform the following three functions: control of the application of alternating current, AC power to appropriate portions of the science subsystem, application of power to the radiometers and removal of power from the cruise experiments during radiometer calibration periods, and control of the speed and direction of the radiometer scans. The DCS sent signals to the SPS unit to perform the latter two functions. Not included on any of the Mariner R spacecraft was a camera for visual photos. With payload space at a premium, project scientists considered a camera an unneeded luxury, unable to return useful scientific results. Carl Sagan, one of the Mariner R scientists, unsuccessfully fought for their inclusion, noting that not only might there be breaks in Venus' cloud layer, but "that cameras could also answer questions that we were way too dumb to even pose".


Mission profile


Prelude to Mariner 2

The launch window for Mariner, constrained both by the orbital relationship of Earth and Venus and the limitations of the Atlas Agena, was determined to fall in the 51 day period between from July 22 through September 10. The Mariner flight plan was such that the two operational spacecraft would be launched toward Venus in a 30-day period within this window, taking slightly differing paths such that they both arrived at the target planet within nine days of each other, between the December 8 and 16. Only Cape Canaveral Launch Complex 12 was available for the launching of Atlas-Agena rockets, and it took 24 days to ready an Atlas-Agena for launch. This meant that there was only a 27 day margin for error for a two-launch schedule. Each Mariner would be launched into a parking orbit, whereupon the restartable Agena would fire a second time, sending Mariner on its way to Venus (errors in trajectory would be corrected by a mid-course burn of Mariner's onboard engines). Real-time radar tracking of the Mariner spacecraft while it was in parking orbit and upon its departure the Atlantic Missile Range would provide real-time radar tracking with stations at Ascension Island, Ascension and Pretoria, while Palomar Observatory provided optical tracking. Deep space support was provided by three tracking and communications stations at Goldstone Deep Space Communications Complex, Goldstone, California, RAAF Woomera Range Complex, Woomera, Australia, and Hartebeesthoek Radio Astronomy Observatory, Johannesburg, South Africa, each separated on the globe by around 120° for continuous coverage. On July 22, 1962, the two-stage
Atlas-Agena The Atlas-Agena was an American expendable launch system derived from the SM-65 Atlas missile. It was a member of the Atlas family of rockets, and was launched 109 times between 1960 and 1978. It was used to launch the first five Mariner uncrew ...
rocket carrying Mariner 1 veered off-course during its launch due to a defective signal from the Atlas and Mariner 1#Program error, a bug in the program equations of the ground-based guidance computer; the spacecraft was destroyed by the Range Safety Officer. Two days after that launch, Mariner 2 and its booster (Atlas vehicle 179D) were rolled out to LC-12. The Atlas proved troublesome to prepare for launch, and multiple serious problems with the autopilot occurred, including a complete replacement of the servoamplifier after it had suffered component damage due to shorted transistors.


Launch

At 1:53 AM EST on August 27, Mariner 2 was launched from Cape Canaveral Air Force Station Launch Complex 12 at 06:53:14 UTC. The bug in the rocket’s software that resulted in the loss of Mariner 1 had not been identified at the time of the launch. In the event the bug caused no issues with the launch since it was in a section of code that was only used when the data-feed from the ground was interrupted and there were no such interruptions during the launch of Mariner 2. The flight proceeded normally up to the point of the Agena booster engine cutoff, at which point the V-2 vernier engine lost pitch and yaw control. The vernier started oscillating and banging against its stops, resulting in a rapid roll of the launch vehicle that came close to threatening the integrity of the stack. At T+189 seconds, the rolling stopped and the launch continued without incident. The rolling motion of the Atlas resulted in ground guidance losing its lock on the booster and preventing any backup commands from being sent to counteract the roll. The incident was traced to a loose electrical connection in the vernier feedback transducer, which was pushed back into place by the centrifugal force of the roll, which also by fortunate coincidence left the Atlas only a few degrees off from where it started and within the range of the Agena's horizontal sensor. As a consequence of this episode, GD/A implemented improved fabrication of wiring harnesses and checkout procedures. Five minutes after liftoff, the Atlas and Agena-Mariner separated, followed by the first Agena burn and second Agena burn. The Agena-Mariner separation injected the Mariner 2 spacecraft into a geocentric escape hyperbola at 26 minutes 3 seconds after liftoff. The NASA NDIF tracking station at Johannesburg, South Africa, acquired the spacecraft about 31 minutes after launch. Solar panel extension was completed approximately 44 minutes after launch. The Sun lock acquired the Sun about 18 minutes later. The high-gain antenna was extended to its acquisition angle of 72°. The output of the solar panels was slightly above the predicted value. As all subsystems were performing normally, with the battery fully charged and the solar panels providing adequate power, the decision was made on August 29 to turn on cruise science experiments. On September 3, the Earth acquisition sequence was initiated, and Earth lock was established 29 minutes later.


Mid-course maneuver

Due to the Atlas-Agena putting Mariner slightly off course, the spacecraft required a mid-course correction, consisting of a roll-turn sequence, followed by a pitch-turn sequence and finally a motor-burn sequence. Preparation commands were sent to the spacecraft at 21:30 UTC on September 4. Initiation of the mid-course maneuver sequence was sent at 22:49:42 UTC and the roll-turn sequence started one hour later. The entire maneuver took approximately 34 minutes. As a result of the mid-course maneuver, the sensors lost their lock with the Sun and Earth. At 00:27:00 UTC the Sun re-acquisition began and at 00:34 UTC the Sun was reacquired. Earth re-acquisition started at 02:07:29 UTC and Earth was reacquired at 02:34 UTC.


Loss of attitude control

On September 8 at 12:50 UTC, the spacecraft experienced a problem with attitude control. It automatically turned on the gyros, and the cruise science experiments were automatically turned off. The exact cause is unknown as attitude sensors went back to normal before telemetry measurements could be sampled, but it may have been an Earth-sensor malfunction or a collision with a small unidentified object which temporarily caused the spacecraft to lose Sun lock. A similar experience happened on September 29 at 14:34 UTC. Again, all sensors went back to normal before it could be determined which axis had lost lock. By this date, the Earth sensor brightness indication had essentially gone to zero. This time, however, telemetry data indicated that the Earth-brightness measurement had increased to the nominal value for that point in the trajectory.


Solar panel output

On October 31, the output from one solar panel (with solar sail attached) deteriorated abruptly. It was diagnosed as a partial short circuit in the panel. As a precaution, the cruise science instruments were turned off. A week later, the panel resumed normal function, and cruise science instruments were turned back on. The panel permanently failed on November 15, but Mariner 2 was close enough to the Sun that one panel could supply adequate power; thus, the cruise science experiments were left active.


Encounter with Venus

Mariner 2 was the first spacecraft to successfully encounter another planet, passing as close as to Venus after 110 days of flight on December 14, 1962.


Post encounter

After encounter, cruise mode resumed. Spacecraft perihelion occurred on December 27 at a distance of . The last transmission from Mariner 2 was received on January 3, 1963, at 07:00 UTC, making the total time from launch to termination of the Mariner 2 mission 129 days. Mariner 2 remains in heliocentric orbit.


Results

The data produced during the flight consisted of two categories--''viz.'', tracking data and telemetry data. One particularly noteworthy piece of data gathered during the pioneering fly-by was the high temperature of the atmosphere, measured to be . Various properties of the
solar wind The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sol ...
were also measured for the first time.


Scientific observations

The microwave radiometer made three scans of Venus in 35 minutes on December 14, 1962, starting at 18:59 UTC. The first scan was made on the dark side, the second was near the terminator, and the third was located on the light side. The scans with the 19 mm band revealed peak temperatures of on the dark side, 595 ± 12 K near the terminator, and 511 ± 14 K on the light side. It was concluded that there is no significant difference in temperature across Venus. However, the results suggest a limb darkening, an effect which presents cooler temperatures near the edge of the planetary disk and higher temperatures near the center. This was evidence for the theory that the Venusian surface was extremely hot and the atmosphere optically thick. The infrared radiometer showed that the 8.4 μm and 10.4 μm radiation temperatures were in agreement with radiation temperatures obtained from Earth-based measurements. There was no systematic difference between the temperatures measured on the light side and dark side of the planet, which was also in agreement with Earth-based measurements. The limb darkening effect that the microwave radiometer detected was also present in the measurements by both channels of the infrared radiometer. The effect was only slightly present in the 10.4 μm channel but was more pronounced in the 8.4 μm channel. The 8.4 μm channel also showed a slight phase effect. The phase effect indicated that if a greenhouse effect existed, heat was transported in an efficient manner from the light side to the dark side of the planet. The 8.4 μm and 10.4 μm showed equal radiation temperatures, indicating that the limb darkening effect would appear to come from a cloud structure rather than the atmosphere. Thus, if the measured temperatures were actually cloud temperatures instead of surface temperatures, then these clouds would have to be quite thick. The magnetometer detected a persistent interplanetary magnetic field varying between 2 γ and 10 γ (
nanotesla The tesla (symbol: T) is the unit of magnetic flux density (also called magnetic B-field strength) in the International System of Units (SI). One tesla is equal to one weber per square metre. The unit was announced during the General Conferenc ...
), which agrees with prior
Pioneer 5 ''Pioneer 5'' (also known as Pioneer P-2, and Able 4, and nicknamed the "Paddle-Wheel Satellite") was a spin-stabilized space probe in the NASA Pioneer program used to investigate interplanetary space between the orbits of Earth and Venus. It ...
observations from 1960. This also means that interplanetary space is rarely empty or field-free. The magnetometer could detect changes of about 4 γ on any of the axes, but no trends above 10 γ were detected near Venus, nor were fluctuations seen like those that appear at Earth's magnetosphere, magnetospheric termination. This means that Mariner 2 found no detectable magnetic field near Venus, although that didn't necessarily mean that Venus had none. However, if Venus had a magnetic field, then it would have to be at least smaller than 1/10 the magnetic field of the Earth. In 1980, the Pioneer Venus project, Pioneer Venus Orbiter indeed showed that Venus has a small weak magnetic field. The Anton type 213 Geiger-Müller tube performed as expected. The average rate was 0.6 counts per second. Increases in its counting rate were larger and more frequent than for the two larger tubes, since it was more sensitive to particles of lower energy. It detected 7 small solar bursts of radiation during September and October and 2 during November and December. The absence of a detectable magnetosphere was also confirmed by the tube; it detected no radiation belt at Venus similar to that of Earth. The count rate would have increased by 104, but no change was measured. It was also shown that in interplanetary space, the
solar wind The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sol ...
streams continuously, confirming a prediction by Eugene Parker, and the cosmic dust density is much lower than the near-Earth region. Improved estimates of Venus' mass and the value of the Astronomical Unit were made. Also, research, which was later confirmed by Earth-based radar and other explorations, suggested that Venus rotates very slowly and in a direction opposite that of the Earth.


See also

* List of missions to Venus * Microwave Radiometer (Juno), another microwave radiometer used in the 2010s on Jupiter


References


External links


Mariner 2 Mission Profile
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NASA's Solar System Exploration

Full-scale engineering prototype of Mariner 2 in the Smithsonian Air and Space Museum, Washington, D.C.

Mariner 2
{{Orbital launches in 1962 Derelict satellites in heliocentric orbit Mariner program Missions to Venus Spacecraft launched in 1962 Derelict space probes Spacecraft launched by Atlas-Agena rockets Articles containing video clips de:Mariner#Mariner 1 und 2