In December of 1962, Mariner 2 became the first spacecraft to visit another planet—Venus—and return useful data to Earth, initiating a new era of planetary knowledge. In 1967, Mariner 5 provided even more data about Earth’s “sister planet,” including its atmospheric composition of 85-99 percent carbon dioxide.
In 1960, the National Aeronautics and Space Administration
The launch vehicle was to be the Atlas-Centaur
By the summer of 1961, it became apparent that the Centaur upper stage would not be available because of developmental problems. The replacement would be the reliable, but much less powerful, Agena-B
Because the thrust output of the Agena-B was considerably less than that of the proposed Centaur, the weight of the Mariner spacecraft had to be reduced to about 200 kilograms. A spacecraft incorporating features of both the original Mariner A and the Ranger 3 unpiloted lunar landing vehicle was proposed by scientists at the Jet Propulsion Laboratory (JPL). As a result of this recommendation, NASA decided to build two of the smaller Mariner spacecraft and launch both vehicles to the vicinity of Venus in 1962. Key personnel involved in the Mariner project included Jack N. James, Dan Schneiderman, James R. Dempsey, Marshall S. Johnson, Nicholas A. Renzetti, and Robert J. Parks and William H. Pickering of JPL.
The basic structure of the spacecraft was a hexagonal frame made of magnesium and aluminum. A tubular aluminum superstructure, sun sensors, a transmitting antenna, gas jets (which enabled the attitude of the spacecraft to be controlled), and a small rocket engine for in-flight course corrections were attached. Six rectangular cases were attached to the frame of the spacecraft. These structures housed the circuitry for the scientific experiments and for communications and control. Other cases held a computer, the data encoder, and a silver-zinc storage battery. The battery was charged by some ten thousand solar cells, which were located on the Mariner’s solar panels. Because of the battery and the mechanism for recharging, the Mariner spacecraft was self-sufficient in power.
The instruments that would conduct experiments in space were attached, as well as a nondirectional antenna. The instruments consisted of a magnetometer, Geiger-Müller tubes, an ion chamber, a cosmic dust collector, and both microwave and microwave and infrared radiometers. The total weight of the spacecraft was 201.2 kilograms.
There were six major groups of experiments carried on the Mariner spacecraft: the microwave radiometer, infrared radiometer, magnetometer, cosmic dust detectors, charged particle detectors, and the solar plasma spectrometer. In the radiometer experiment, both microwaves and infrared wavelengths were to be gathered simultaneously by the two radiometers as they scanned the planetary surface. The microwaves were to be collected by a small parabolic receiving antenna and focused into a receiving horn. The infrared radiation was passed through a series of filters to separate two distinct wavelength regions. The encoded data were then to be returned to Earth. One of the purposes of this experiment was to observe limb brightening and darkening of Venus during the encounter in an attempt to determine the source of the high surface temperatures that were detected from Earth.
The Mariner 2 spacecraft.
A sensitive fluxgate magnetometer was carried aboard Mariner 2 so that it could detect magnetic fields both in the vicinity of Venus and during the flight to Venus. Measurements of the local magnetic field were to be taken every twenty seconds during the flight.
Several instruments on the Mariner spacecraft were used to detect charged particles. The ionization chamber used in this experiment consisted of a volleyball-sized sphere that contained a pressurized inert gas and a central electrode. The spacecraft power supply would charge the ionization chamber during the experiment, and, as high-energy particles were encountered, the chamber would discharge slowly. This information, along with particle count data taken by three Geiger-Müller tubes, would allow the determination of individual particle energy and types of particles encountered.
The cosmic dust experiment consisted of a piezoelectric crystal composed of lead zirconate attached to a magnesium sounding plate. Any impact on the sounding plate would send out tiny shock waves. The piezoelectric crystal would be compressed slightly as the waves passed through it, and a voltage, which would depend on the momentum of the impacting meteoroid, then would be emitted by the crystal.
The solar plasma spectrometer would detect and study the stream of charged particles, or solar wind, from the Sun. The device consisted of a pair of curved, gold-plated, magnesium plates. An electrical voltage was applied across the plates, which would cause positively charged particles, such as protons and alpha particles, to travel a curved path and impact against a collector. The voltage was adjusted so that only particles of known energy could pass between the plates and be received by the collector.
Early in June of 1962, two Mariner spacecraft and two Atlas-Agena rockets arrived at Cape Canaveral. The intent of NASA was to launch both of these vehicles toward Venus during July and August. Mariner 1 was launched at 4:21
After the failure of Mariner 1, Mariner 2 was moved to the launch pad with a scheduled launch date of August 24. Several technical difficulties postponed the launch until 2:53
A midcourse correction was made at a distance of approximately 2.4 million kilometers from Earth. It had been concluded that the course Mariner 2 was on would carry it too far from Venus. The small rocket motor attached to the Mariner was fired for twenty-nine seconds to act as a brake and allow a closer encounter with Venus. Early in the morning of December 14, 109 days into the flight, Mariner 2 arrived in the vicinity of Venus, and its instruments began to scan the surface of the planet. Data were received from the spacecraft until January 2, 1963, when Mariner 2 was 86.8 million kilometers away from Earth. At that time, radio contact with Mariner 2 was lost.
The flight of Mariner 2 to Venus represented the first time that instruments had been sent to another planet and data had been returned successfully to Earth. This historic mission enabled scientists to revise many long-held views about interplanetary space and Venus.
It was found during the flight that the space between Venus and Earth contained a cosmic dust density about ten thousand times lower than the near-Earth region. The detector plate was positioned approximately perpendicular to the plane of the ecliptic during the experiment and was facing in the direction in which the spacecraft was flying. It was noted that Mariner survived two fairly major impacts on the way to Venus. Near Venus, there was no evidence of a concentration of particles similar to that which surrounds Earth. In fact, the number of particles detected near Venus was not significantly greater than the number recorded during the flight.
The spacecraft’s magnetometer detected slight magnetic fields in interplanetary space, which confirmed a number of widely accepted beliefs. As Mariner 2 passed by Venus, there was no evidence of a magnetic field along the spacecraft’s trajectory or any regions of trapped charged particles as there are near Earth. Since Mariner’s closest approach was 35,000 kilometers, these data did not prove that Venus has no magnetic field at all. Subsequent satellite data did confirm the finding that Venus has no magnetic field, however.
During the flight, there was always a detectable, although widely fluctuating, stream of solar plasma, but scientists concluded that astronauts traveling in this region of space could not be harmed by this intensity of radiation.
Radiometer data revealed that the cloud-top temperature readings are about -35 degrees Celsius at the center of the planet and down to about -50 degrees Celsius at the limbs. This data indicated that there was an apparent limb-darkening effect and that the planet has a surface temperature of approximately 400 degrees Celsius on both its light and dark sides.
The flight of Mariner 2 allowed for a more accurate calculation of the mass of Venus. When first launched, the shape of its path through space was dominated by Earth. Later in the flight, the Sun became the dominant factor, and then finally, Venus. Through careful measurements, it was found that the path of Mariner 2 was deflected some 40 degrees by the gravity of the planet. When a body of known mass and velocity is deflected by a second gravitational body, application of the laws of Isaac Newton and Johannes Kepler allow the calculation of the mass of the second body. It was found that the mass of Venus, in relation to Earth, is 0.81485. Dozens of subsequent visits have been made to Venus since the initial Mariner 2 expedition, including the Pioneer Venus and Magellan spacecraft and visits by the Soviet Venera 7 and Venera 9 spacecrafts, the former being the first to land on the surface of Venus and the latter the first to return pictures of the surface.
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California Institute of Technology, Pasadena. Jet Propulsion Laboratory. Mariner-Venus 1962: Final Project Report. Washington, D.C.: Government Printing Office, 1965. Prepared as a project report on the Mariner 2 spacecraft. Begins with background material on the formation of the program and the pre-Mariner concepts on the nature of Venus and continues into a technical description of the spacecraft and the launch vehicle. Discusses in detail the scientific experiments on board the spacecraft and the data received from the flyby. Best for readers with scientific backgrounds. -
Cattermole, Peter, and Patrick Moore. Atlas of Venus. New York: Cambridge University Press, 1997. Provides a vast number of images of Venus from telescopes and from the Mariner and other spacecrafts that surveyed the planet. Includes a gazetteer of Venusian place names. -
Morrison, David, and Tobias Owen. The Planetary System. 3d ed. San Francisco: Addison Wesley, 2003. Organized by planetary object, this work provides contemporary data on all planetary bodies visited by spacecraft since the early days of the space age. Suitable for high school and college students and for general readers. -
Sobel, Lester A., ed. Space: From Sputnik to Gemini. New York: Facts On File, 1965. A nontechnical volume. Provides a history of the space age from the launching of the Soviet satellite Sputnik 1 in 1957 to the Gemini missions and lunar probes of 1965. A chapter is devoted to each year from 1957 through 1965, in which the significant events in the space race between the United States and the Soviet Union are covered. -
Wheelock, Harold J., comp. Mariner Mission to Venus. New York: McGraw-Hill, 1963. Covers the Mariner 2 spacecraft from the planning stages to its launch and flight to Venus. Describes in detail the spacecraft, the launch vehicle, the tracking network, the flight, the scientific experiments, and the data returned. Well illustrated; suitable for general readers.
Hale Constructs the 200-Inch Telescope
HERMES Builds the First Multistage Rocket
United States Launches Vanguard Satellite Program
Soviet Union Launches the First Artificial Satellite
United States Launches Its First Orbiting Satellite
Van Allen Discovers the Earth’s Radiation Belts
Congress Creates the National Aeronautics and Space Administration
Pioneer Space Program Is Launched
Luna 2 Becomes the First Human-Made Object to Impact on the Moon
Ranger Program
Mariner Missions Conduct Mars Flybys