Vanguard 2 (or Vanguard 2E before launch) is an Earth-orbiting

satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotope ...

launched 17 February 1959 at 15:55:02 GMT, aboard a Vanguard SLV-4 rocket as part of the

United States Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...

Project Vanguard Project Vanguard was a program managed by the United States Navy Naval Research Laboratory (NRL), which intended to launch the first artificial satellite into low Earth orbit using a Vanguard rocket. as the launch vehicle from Cape Canaveral ...

. The satellite was designed to measure cloud cover distribution over the daylight portion of its orbit, for a period of 19 days, and to provide information on the density of the atmosphere for the lifetime of its orbit (about 300 years). As the first

weather satellite A weather satellite or meteorological satellite is a type of Earth observation satellite that is primarily used to monitor the weather and climate of the Earth. Satellites can be polar orbiting (covering the entire Earth asynchronously), or ge ...

and one of the first orbital space missions, the launch of Vanguard 2 was an important milestone in the

Space Race The Space Race was a 20th-century competition between two Cold War rivals, the United States and the Soviet Union, to achieve superior spaceflight capability. It had its origins in the ballistic missile-based nuclear arms race between the tw ...

between the

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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 ...

. Vanguard 2 remains in orbit. upright=1.3, The Vanguard 2 satellite sketch

Previous satellites

Before the successful 1959 launch of the satellite that became known as Vanguard 2, multiple attempted launches of satellites named "Vanguard 2" were made in 1958. All of these launches failed to reach orbit. The satellites that failed to reach orbit were: * Vanguard 2A: launched 29 April 1958, by the

Vanguard TV-5 Vanguard TV-5, also called Vanguard Test Vehicle-Five, was a failed flight of the American Vanguard rocket following the successful launch of Vanguard 1 on Vanguard TV-4. Vanguard TV-5 launched on 29 April 1958 at 02:53:00 GMT, from Launch Co ...

rocket * Vanguard 2B: launched 28 May 1958, by the

Vanguard SLV-1 Vanguard SLV-1, also called Vanguard Satellite Launch Vehicle-1 was hoped to be the second successful flight of the American Vanguard rocket following the successful launch of the Vanguard 1 satellite on rocket Vanguard TV-4 in March 1958. B ...

rocket * Vanguard 2C: launched 26 June 1958, by the

Vanguard SLV-2 Vanguard SLV-2, also called Vanguard Satellite Launch Vehicle-2 hoped to be the second successful flight of the American Vanguard (rocket), Vanguard rocket following successful Vanguard 1 satellite on rocket Vanguard 1, Vanguard TV-4. Backgro ...

rocket * Vanguard 2D: launched 26 September 1958, by the Vanguard SLV-3 rocket The satellite whose launch was successful and that became known as the Vanguard 2 was the Vanguard 2E.

Spacecraft

The spacecraft is a magnesium sphere in diameter. It contains two optical telescopes with two

photocells A photoresistor (also known as a photocell, or light-dependent resistor, LDR, or photo-conductive cell) is a passive component that decreases resistance with respect to receiving luminosity (light) on the component's sensitive surface. The resi ...

. The sphere was internally

gold-plated Gold plating is a method of depositing a thin layer of gold onto the surface of another metal, most often copper or silver (to make silver-gilt), by chemical or electrochemical plating. This article covers plating methods used in the modern ele ...

, and externally covered with an

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...

deposit coated with

silicon oxide Silicon oxide may refer to either of the following: *Silicon dioxide or quartz, SiO2, very well characterized *Silicon monoxide Silicon monoxide is the chemical compound with the formula SiO where silicon is present in the oxidation state +2. In ...

of sufficient thickness to provide

thermal control A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...

for the

instrumentation Instrumentation a collective term for measuring instruments that are used for indicating, measuring and recording physical quantities. The term has its origins in the art and science of scientific instrument-making. Instrumentation can refer to ...

. Radio communication was provided by a 1

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, 108.03

MHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...

telemetry transmitter and a 10 mW, 108 MHz beacon transmitter that sent a continuous signal for tracking purposes. A command receiver was used to activate a tape recorder that relayed telescope experiment data to the

telemetry Telemetry is the in situ data collection, collection of measurements or other data at remote points and their automatic data transmission, transmission to receiving equipment (telecommunication) for monitoring. The word is derived from the Gr ...

transmitter. The power supply for the instrumentation was provided by mercury batteries.

Instruments

Optical scanner

The optical scanner experiment was designed to obtain

cloud cover Cloud cover (also known as cloudiness, cloudage, or cloud amount) refers to the fraction of the sky obscured by clouds on average when observed from a particular location. Okta is the usual unit for measurement of the cloud cover. The cloud co ...

data between the

equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...

and 35° to 45° N latitude. As the satellite circled Earth, two

, located at the focus of two optical telescopes aimed in diametrically opposite directions, measured the intensity of sunlight reflected from

cloud In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may co ...

s (about 80%), from land masses (15 to 20%), and from sea areas (5%). The satellite motion and rotation caused the photocells to scan the Earth in successive "lines" (akin to a

whisk broom scanner A whisk broom or spotlight sensor, also known as an across-track scanner, is a technology for obtaining satellite images with optical cameras. It is used for passive remote sensing from space. In a whisk broom sensor, a mirror scans across the satel ...

). Separate solar batteries turned on a recorder only when the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

beneath the satellite was in sunlight and about 50 minutes of data per orbit were obtained. The measured reflection intensities were stored on tape. Ground stations interrogated the satellite by signaling its command receiver, which caused the entire tape to be played back in 60 seconds. The tape was then erased and rewound. For the planned 19 days of the weather experiment, the equipment functioned normally. The satellite was spin-stabilized at 50

rpm Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines. Standards ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...

, but the optical instrument's data was poor because of an unsatisfactory orientation of the spin axis.

Satellite drag atmospheric density

Because of its symmetrical shape, Vanguard 2 was selected by the experimenters for use in determining upper atmospheric densities as a function of

altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...

latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...

season A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's tilted orbit around the Sun. In temperate and pol ...

, and

solar activity Solar phenomena are natural phenomena which occur within the atmosphere of the Sun. These phenomena take many forms, including solar wind, radio wave flux, solar flares, coronal mass ejections, coronal heating and sunspots. These phenomena are ...

. As the spacecraft continuously orbited, it would lead its predicted positions slightly, accumulating greater and greater advance as it spiraled lower and faster due to the drag of the residual atmosphere. By measuring the rate and timing of orbital shifts, the relevant atmosphere's parameters could be back-calculated knowing the body's drag properties. It was determined that atmospheric pressures, and thus drag and orbital decay, were higher than anticipated, as Earth's upper atmosphere gradually tapered into space. This experiment was planned in great detail prior to launch. Initial

Naval Research Laboratory The United States Naval Research Laboratory (NRL) is the corporate research laboratory for the United States Navy and the United States Marine Corps. It was founded in 1923 and conducts basic scientific research, applied research, technological ...

(NRL) proposals for

included conical satellite bodies; this eliminated the need for a separate fairing and ejection mechanisms, and their associated weight and failure modes. Radio tracking would gather data and establish a position. Early in the program, optical tracking (with a

Baker-Nunn camera A Schmidt camera, also referred to as the Schmidt telescope, is a catadioptric astrophotographic telescope designed to provide wide fields of view with limited aberrations. The design was invented by Bernhard Schmidt in 1930. Some notable ex ...

network and human spotters) was added. A panel of scientists proposed changing the design to spheres, at least in diameter and hopefully . A sphere would have a constant optical reflection, and constant

coefficient of drag In fluid dynamics, the drag coefficient (commonly denoted as: c_\mathrm, c_x or c_) is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment, such as air or water. It is used in the drag equ ...

, based on size alone, while a cone would vary with orientation. James Van Allen proposed a cylinder, which eventually flew. The Naval Research Lab finally accepted spheres as a "test vehicle", with for follow-on satellites. The payload weight savings, from reduced size as well as decreased instrumentation in the early satellites, was considered acceptable for the initial launches. Afterwards, the later Vanguard rockets had some test instrumentation removed, lightening them enough for the 50.8 cm bodies.C. McLaughlin Green, M. Lomask,
Vanguard, A History
", Chapter 5, Battle over Vehicle Specifications NASA SP-4202

Post mission

After the scientific mission ended, both ''Vanguard 2'' and the upper stage of the rocket used to launch the satellite became derelict

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that would continue to orbit Earth for many years. Both objects remain in orbit. As

Vanguard 1 Vanguard 1 (Harvard designation: 1958-Beta 2, COSPAR ID: 1958-005B ) is an American satellite that was the fourth artificial Earth-orbiting satellite to be successfully launched, following Sputnik 1, Sputnik 2, and Explorer 1. It was launched ...

, Vanguard 2, and

Vanguard 3 Vanguard 3 (Harvard designation: 1959 Eta 1) is a scientific satellite that was launched into Earth orbit by the Vanguard SLV-7 on 18 September 1959, the third successful Vanguard launch out of eleven attempts. Vanguard rocket: Vanguard Satell ...

are still orbiting with their drag properties essentially unchanged, they form a baseline data set on the

atmosphere of Earth The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing for ...

that is over 60 years old and continuing. Vanguard 2 has an expected orbital lifetime of 300 years.

References

External links

Historic newsreel footage of the Vanguard II Satellite
{{Orbital launches in 1959 Spacecraft launched in 1959 1959 in the United States Derelict satellites orbiting Earth Project Vanguard Weather satellites of the United States