Explorer 19, (Air Density experiment A, or AD-A), was a

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...

satellite launched on 19 December 1963, as part of the

Explorer program The Explorers program is a NASA exploration program that provides flight opportunities for physics, geophysics, heliophysics, and astrophysics investigations from space. Launched in 1958, Explorer 1 was the first spacecraft of the United Stat ...

. It was the third of six identical Explorer satellites launched to study air density and composition, and the second to reach orbit. It was identical to Explorer 9.

Spacecraft

Explorer 19 was launched while Explorer 9, the first satellite in the series, was still active, so that densities in two different portions of the atmosphere were sampled simultaneously. The spacecraft consisted of alternating layers of

aluminium foil Aluminium foil (or aluminum foil in North American English; often informally called tin foil) is aluminium prepared in thin metal leaves with a thickness less than ; thinner gauges down to are also commonly used. Standard household foil is typ ...

and

Mylar BoPET (biaxially-oriented polyethylene terephthalate) is a polyester film made from stretched polyethylene terephthalate (PET) and is used for its high tensile strength, chemical and dimensional stability, transparency, reflectivity, gas and a ...

polyester film. Uniformly distributed over the aluminum surface were diameter dots of white paint for thermal control. The sphere was packed in a tube in diameter and long and mounted in the nose of the fourth stage of the launch vehicle. Upon separation of the fourth stage, the sphere was inflated by a

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

gas bottle, and a separation spring ejected it out into its own orbit. The two hemispheres of aluminum foil were separated with a gap of Mylar at the spacecraft's equator and served as the antenna. A 136.620

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 ...

, 15 mW beacon was carried for tracking purposes. The spacecraft was successfully orbited, but its

apogee An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any ell ...

was lower than planned. The beacon did not have sufficient power to be received by ground tracking stations, making it necessary to rely solely on the SAO Baker-Nunn camera network for tracking.

Experiments

Nonsystematic Changes of Air Density

This experiment was designed to determine nonsystematic changes of upper atmospheric density by conducting studies of the drag on a diameter, low-density sphere caused by short-term variations in solar activity. Density values near perigee were deduced from sequential observations of the spacecraft position using optical (Baker-Nunn camera network) and radio/radar tracking techniques.

Systematic Changes of Air Density

The objective of this experiment was to determine atmospheric density as a function of altitude, latitude, and time by measuring atmospheric drag on a low mass-to-area ratio (0.7680 kg per m²) spherical satellite. The orbit was Sun-synchronized so that near-polar densities would always be obtained along noon and midnight meridians.

Launch

Explorer 19 was launched from Launch Area 3 at the Wallops Flight Facility (WFF), atop a Scout X-4 launch vehicle with the serial number S-122R. It was the second spacecraft launched from Wallops Island to achieve orbit.. The launch occurred at 18:49:25

GMT Greenwich Mean Time (GMT) is the mean solar time at the Royal Observatory in Greenwich, London, counted from midnight. At different times in the past, it has been calculated in different ways, including being calculated from noon; as a cons ...

on 19 December 1963, and resulted in Explorer 19 being deployed into an orbit with an

of , a

perigee An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any ell ...

of , 78.6° of

inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Eart ...

and a

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

of 115.9 minutes. Upon separation of the fourth stage, the sphere was inflated by a

gas bottle, and a separation spring ejected it out into its own orbit. The two hemispheres of aluminium foil were separated with a gap of Mylar at the spacecraft's equator and served as the antenna. A 136.620 MHz, 15 mW

beacon A beacon is an intentionally conspicuous device designed to attract attention to a specific location. A common example is the lighthouse, which draws attention to a fixed point that can be used to navigate around obstacles or into port. More mode ...

was carried for tracking purposes, but the beacon failed on the first orbit and the SAO Baker-Nunn camera network had to be relied upon for tracking. Power was supplied by

solar cell 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 physical and chemical phenomenon.

s and

rechargeable batteries A rechargeable battery, storage battery, or secondary cell (formally a type of energy accumulator), is a type of electrical battery which can be charged, discharged into a load, and recharged many times, as opposed to a disposable or prima ...

. Explorer 19's launch vehicle placed it into a slightly lower than planned orbit.

References

External links

NASA FACTS - EXPLORER XIX
(PDF) {{Explorer program Passive satellites Balloon satellites Explorers Program Spacecraft launched in 1963