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Space Probe

Space probe

Aspace probe is any unmanned instrumented spacecraft designed to carry out physical studies of space environment. As distinguished from satellites orbiting Earth under the influence of gravitational attraction, a space probe is rocketed into space with sufficient speed to achieve escape velocity (the velocity needed to obtain parabolic or hyperbolic orbit) and to reach a trajectory aimed at a pre-selected target.

The first recorded mention of a possibility of an unmanned probe dates back to 1919, when American physicist R. H. Goddard (18821945) suggested a series of space based experiments. However, in large part to Goddard's advancements in rocketry, it took only 33 years for the concept of space experiment to reappear. In 1952, the term "space probe" was introduced by E. Burgess and C. A. Cross in a short paper presented to the British Interplanetary Society.

The space probe is used mostly for the acquisition of scientific data enriching general knowledge on properties of outer space and heavenly bodies. Each probe (sometimes a series of several identical craft) is constructed to meet specific goals of a particular mission, and thus, represents a unique and sophisticated creation of contemporary engineering. Nevertheless, whether it is an Earth satellite , a crewed flight, or an automated probe, there are some common problems underlying any space mission: how to get to the destination point, how to collect the information required, and, finally,

how to transfer the information back to Earth. Successful resolution of these principal issues is impossible without a developed net of high-tech Earth-based facilities used for assembling and testing the spacecraft-rocket system, for launching the probe into the desired trajectory, and for providing necessary control of probe-equipment operation, as well as for receiving data transmitted back to Earth.

As compared to crewed flights, automated space missions are far more economical and, of course, less risky to human life.

A probe's journey into far space can be divided into several stages. First, the probe has to overcome Earth's gravity . Escape velocities vary for different types of trajectories. During the second stage, the probe continues to move under the influence of its initial momentum and the combined gravitational influences of the Sun and bodies with substantial mass near its flight path. The third (approach) stage starts when the probe falls under the gravitational attraction of its destination target. The calculation of the entire trajectory from Earth to the point of destination is a complicated task. It must take into consideration numerous mutually conflicting demands: to maximize the payload but to minimize the cost, to shorten mission duration but to avoid such hazards as solar flares or meteoroid swarms, to remain within the range of the communication system but to avoid the unfavorable influence of large spatial bodies, etc.

Sometimes, strong gravitational fields of planets can be utilized to increase the probe's velocity and to change its direction considerably without firing the engines and using fuel. For instance, if used properly, Jupiter's massive gravitational pull can accelerate a probe enough to leave the solar system in any direction. The gravitational assistance or "swing-by" effect was successfully used, for example, in the American missions to Mercury via Venus, and in the voyage of the Galileo craft to Jupiter.

Projecting of payloads into designated trajectories is achieved by means of expendable launch vehicles (ELVs). A wide variety of ELVs possessed by the United States uses the same basic technologytwo or more rocket-powered stages that are discarded when their engine burns are completed. Similar to the operation of a jet aircraft, the motion of a rocket is caused by a continuous ejection of a stream of hot gases in the opposite direction. The rocket's role as a prime mover makes it very important for the system's overall performance and cost. Out of 52 space-probe missions launched in the United States during the period from 1958 to 1988, 13 failed because of launch vehicle failures and only five because of probe equipment's malfunctions.

All supporting Earth-based facilities can be divided into three major categories: test grounds, where the spacecraft and its components are exposed to different extreme conditions to make sure that they are able to withstand tough stresses of outer space; check-out and launch ranges, where the lift-off procedure is preceded by a thorough examination of all spacecraft-rocket interfaces; and post-launch facilities, which are used to track, communicate with, and process the data received from the probe.

Hundreds of people and billions of dollars worth of facilities are involved in following the flight of each probe and in intercepting the data it transmits toward Earth. Already-developed facilities always have to be adopted in accordance with the specific spacecraft design. Today, the United States, Russia, and France (for unmanned flights only) possess major launch ranges, worldwide tracking networks, and dozens of publicly and privately owned test facilities. China is also actively developing space launch facilities and, in 1999, launched its first unmanned test of a program designed to enable China to launch a manned mission by 2003.

Any space probe is a self-contained piece of machinery designed to perform a variety of prescribed complex operations for a long time, sometimes for decades. There are ten major constituents of the spacecraft entity that are responsible for its vital functions: (1) power supply, (2) propulsion, (3) attitude control, (4) environmental control, (5) computer subsystem, (6) communications, (7) engineering, (8) scientific instrumentation, (9) guidance control, and (10) structural platform.

(1) The power supply provides well-regulated electrical power to keep the spacecraft active. Usually the solar-cell arrays transforming the Sun's illumination into electricity are used. Far from the Sun, where solar energy becomes too feeble, electricity may be generated by nuclear power devices. (2) The propulsion subsystem enables the spacecraft to maneuver when necessary, either in space or in a planet's atmosphere, and has a specific configuration depending upon the mission's goals. (3) The attitude-control subsystem allows orientation of the spacecraft for a specific purpose, such as to aim solar panels at the Sun, antennas at Earth, and sensors at scientific targets. It also aligns engines in the proper direction during the maneuver. (4) The environmental-control subsystem maintains the temperature , pressure, radiation and magnetic field inside the craft within the acceptable levels to secure proper functioning of equipment. (5) The computer subsystem performs data processing, coding, and storage along with routines for internal checking and maintenance. It times and initiates the pre-programmed actions independently of Earth. (6) The communication subsystem transmits data and receives commands from Earth. It also transmits identifying signals that allow ground crews to track the probe. (7) The engineering-instrumentation subsystem continuously monitors the "health" of the spacecraft's "organism" and submits status reports to Earth. (8) The scientific-instrumentation subsystem is designed to carry out the experiments selected for a particular mission, for example, to explore planetary geography, geology , atmospheric physics or electromagnetic environment. (9) The guidance-and-control subsystem is supposed to detect deviations from proper performance, determine corrections and to dispatch appropriate commands. In many respects, this subsystem resembles a human brain, since it makes active decisions, having analyzed all available information on the spacecraft's status. (10) The structural subsystem is a skeleton of the spacecraft; it supports, unites and protects all other subsystems.

Depending upon a mission's target, the probes may be classed as lunar, solar, planetary (Mercurian, Venusian, Martian, Jovian) or interplanetary probes. Another classification is based upon the mission type: flyby, orbiter, or soft-lander.

See also Astronomy; History of manned space exploration; Space and planetary geology; Spacecraft, manned

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Space Probe

Space probe

A space probe is any unmanned spacecraft designed to carry out physical studies of the Moon, other planets, or outer space. Space probes take pictures, measure atmospheric conditions, and collect soil samples then bring or report the data back to Earth.

More than 30 space probes have been launched since the former Soviet Union first fired Luna 1 toward the Moon in 1959. Probes have now visited every planet in the solar system except for Pluto. Two have even left the solar system and headed into the interstellar medium.

Moon probes

The earliest probes traveled to the Moon. The Soviets launched a series of Luna probes that took the first pictures of the far side of the Moon. In 1966, Luna 9 made the first successful landing on the Moon and sent back television footage from the Moon's surface.

The National Aeronautics and Space Administration (NASA) landed Surveyor on the Moon four months after Luna 9. The Surveyor had more sophisticated landing capability and sent back more than 11,000 pictures.

Planetary probes

In the meantime, NASA launched the first series of planetary probes, called Mariner. Mariner 2 first reached Venus in 1962. Later Mariner spacecraft flew by Mars in 1964 and 1969, providing detailed images of that planet. In 1971, Mariner 9 became the first spacecraft to orbit Mars. During its year in orbit, Mariner 9 transmitted footage of an intense Martian dust storm as well as images of 90 percent of the planet's surface and the two Martian moons.

The Soviets also put probes in orbit around Mars in 1971. Mars 2 and Mars 3 carried landing vehicles that successfully dropped to the planet's surface, but in each case radio contact was lost after about 20 seconds.

In 1976, the U.S. probes Viking 1 and Viking 2 had more direct encounters with Mars. Viking 1 made the first successful soft landing on Mars on July 20, 1976. Soon after, Viking 2 landed on the opposite side of the planet. The Viking probes reported on the Martian weather and photographed almost the entire surface of the planet. Twenty years after the Voyager probes were released, NASA launched the Mars Global Surveyor and the Mars Pathfinder to revisit Mars. The Mars Global Surveyor completed its mapping mission of Mars in early 2001 after having sent back tens of thousands of images of the planet. Its main mission accomplished, NASA engineers hope to use Surveyor to relay commands to twin rovers slated to land on the planet in early 2004. The Mars Pathfinder landed on the planet's surface on July 4, 1997, and released the Sojourner rover, which sent back to Earth images and analyses of the Martian terrain, including chemical analyses of rocks and the soil.

Not all probe sent to Mars were as productive as the Mars Global Surveyor and the Mars Pathfinder. In 1999, NASA lost two probes, the Mars Climate Orbiter and the Mars Polar Lander. As its name implies the Mars Climate Orbiter was to have explored the Martian atmosphere, while the Mars Polar Lander was to have explored the planet's landscape in search of water. Neither was able to land successfully due to an error in converting English and metric measurements (for the Mars Climate Orbiter ) and a software glitch (for the Mars Polar Lander ).

From 1970 to 1983, the Soviets concentrated mostly on exploring Venus. They sent out a series of Venera and Vega probes that landed on Venus, analyzed its oil, took detailed photographs, studied the atmosphere, and mapped the planet using radar.

Mercury was visited by a probe in 1974 when Mariner 10 came within 470 miles (756 kilometers) of the planet and photographed about 40 percent of its surface. The probe then went into orbit around the Sun and flew past Mercury twice more in the next year before running out of fuel.

Space probes to the outer planets

NASA sent Pioneer probes to explore the outer planets. Pioneer 10 reached Jupiter in 1973 and took the first close-up photos of the giant planet. It then kept traveling, crossing the orbit of Pluto and leaving the solar system in 1983. Pioneer 11 traveled to Saturn, where it collected valuable information about the planet's rings.

NASA next introduced the Voyager 1 and 2 probes, more sophisticated versions of the Pioneers. Launched in 1977, they flew by Jupiter two years later and took pictures of the planet's swirling colors, volcanic moons, and its previously undiscovered ring.

The Voyager space probes then headed for Saturn. In 1980 and 1981, they sent back detailed photos of Saturn's spectacular rings and its vast collection of moons. Voyager 2 then traveled to Neptune, which it reached in 1989, while Voyager 1 continued on a path to the edge of the solar system and beyond.

After many delays, the U.S probe Galileo was launched from the space shuttle Atlantis in 1989. It reached Jupiter in December 1995, and dropped a barbecue-grill-sized mini-probe down to the planet's surface. That mini-probe spent 58 minutes taking extremely detailed pictures of the gaseous planet before being incinerated near the surface. As of the

beginning of 2001, Galileo was still sending valuable scientific information about Jupiter and its moons back to Earth.

In February 1996, NASA launched NEAR (Near Earth Asteroid Rendezvous) Shoemaker, an unmanned spacecraft that was to become the first to orbit an asteroid. In April 2000, it began a circular orbit around the asteroid Eros. During its one-year mission around Eros, the spacecraft took measurements to determine the mass, density, chemical composition, and other geological characteristics of the asteroid. It also beamed some 160,000 images of Eros back to Earth. In February 2001, NEAR Shoemaker used the last of its fuel in a successful attempt to land on the surface of the asteroid. Once on the surface, it continued to collect invaluable data about the oddly shaped Eros before it was finally shut down by NASA.

Future space probe missions

NASA has plans underway for many more space probes. The Cassini orbiter, which was launched in October 1997, will study Saturn and its moon. It is scheduled to reach the planet in 2004. Cassini will drop a mini-probe, called Huygens, onto the surface of Titan, Saturn's largest moon, for a detailed look. Cassini will then go into orbit around Saturn.

With a desire to return to Mars, NASA launched the Mars Odyssey in April 2001. Once in orbit around the planet by the fall of that year, the spacecraft will examine the composition of the planet's surface and try to detect water and shallow buried ice. In a mission planned by the European Space Agency and the Italian space agency, NASA will launch the Mars Express in mid-2003. It will search for subsurface water from orbit and deliver a lander, Beagle 2, to the Martian surface. NASA will also launch two powerful rovers to Mars in 2003, each to a different region of the planet to look for water. And in 2005, NASA plans to launch the Mars Reconnaissance Orbiter, a powerful scientific orbiter that will map the Martian surface with an high-definition camera.

NASA had hoped to explore Pluto sometime in the twenty-first century by sending the Pluto-Kuiper Express. This probe was to have consisted of two spacecraft, each taking about eight years to reach the farthest planet in our solar system. Originally scheduled to launch in 2004 and arrive at Pluto in 2012, the Pluto-Kuiper Express was put on hold by NASA in the fall of 2000 because of high costs. It was then scraped in the spring of 2001 after President George W. Bush unveiled his 2002 budget, which provided no money for the project.

[See also Jupiter; Mars; Mercury; Moon; Neptune; Pluto; Satellite; Saturn; Spacecraft, manned; Venus ]

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space probe

space probe, space vehicle carrying sophisticated instrumentation but no crew, designed to explore various aspects of the solar system (see space exploration). Unlike an artificial satellite, which is placed in more or less permanent orbit around the earth, a space probe is launched with enough energy to escape the gravitational field of the earth and navigate among the planets. Radio-transmitted commands and on-board computers provide the means for midcourse corrections in the space probe's trajectory; some advanced craft have executed complex maneuvers on command from earth when many millions of miles away in space. Radio contact between the control station on earth and the space probe also provides a channel for transmitting data recorded by on-board instruments back to earth. Instruments carried by space probes include radiometers, magnetometers, and television cameras sensitive to infrared, visible, and ultraviolet light; there also may be special detectors for micrometeors, cosmic rays, gamma rays, and solar wind. A probe may be directed to orbit a planet, to soft-land instrument packages on a planetary surface, or to fly by as close as a few thousand miles from one or more planets. The particulars of trajectory and instrumentation of each space probe are tailored around the mission's scientific and technological objectives; the data provided by a single space probe may require months or even years of analysis. Much has been learned from probes about the origins, composition, and structure of various bodies in the solar system. Scientists trying to understand the earth's weather by constructing theoretical models of global weather systems make use of the knowledge that is gained concerning the atmospheres and meteorology of the planets. Because conditions on other planets are simpler than on earth, scientists can check each of their hypotheses separately in isolation from complicating factors.

The earliest space probes in the U.S. space program were the Mariner series, which investigated Mars, Venus, and Mercury, and the Pioneer series, which explored the outer planets. Pioneer 10 was the first human-made object to entirely escape the solar system. Several Viking space probes voyaged to Mars in the late 1970s, mapping the planet and searching for life. The Voyager probes, launched in 1977, returned spectacular photos and data from brushes by Jupiter, Saturn, Uranus, Neptune, and their moons, and have continued toward the outer limits of the heliosphere, where the effects of the sun's solar wind interact with the interstellar magnetic field. The Magellan spacecraft succeeded in orbiting Venus in 1990, returning a radar map of the planet's hidden surface. The Japanese probes Sakigake and Suisei and the European Space Agency's (ESA) probe Giotto both rendezvoused with Halley's comet in 1986, and Giotto also came within 125 mi (200 km) of the nucleus of the comet Grigg-Skjellerup in 1992. The U.S. probe Ulysses returned data about the poles of the sun in 1994, and the ESA Solar and Heliospheric Observatory (SOHO) was orbited in 1995. Launched in 1989, the Galileo spacecraft followed a circuitous route that returned data about Venus (1990), the moon (1992), and the asteroids 951 Gaspra (1991) and 243 Ida (1993) before it reached Jupiter in 1995 and sent a small probe into the Jovian atmosphere to study its composition. Over the next eight years it orbited Jupiter 35 times, returning data about the planet's atmosphere and also about Jupiter's largest moons, Io, Ganymede, Europa, and Callisto. The joint U.S.-ESA mission Cassini, launched in 1997, began exploring Saturn and some of its moons in 2004 and deployed the lander Huygens on the surface of Saturn's moom Titan. The Mars Pathfinder and Mars Global Surveyor, both of which arrived at the red planet in 1997, were highly successful, the former in analyzing the Martian surface and the latter in mapping it. Both the Mars Climate Orbiter and Mars Polar Lander, however, were lost upon their arrival at Mars in 1999, setting NASA's Mars exploration program back by at least two years. In 2003 the ESA's Mars Express achieved orbit around Mars, and although its Beagle 2 lander proved unsuccessful, the orbiter returned data on the planet. NASA's Spirit and Opportunity rovers landed on the planet shortly afterward in early 2004. In 2008 NASA's Phoenix lander touched down in the planet's north polar region, and in 2012 the NASA rover Curiosity landed near the equator.

The NEAR (for Near Earth Asteroid Rendezvous)-Shoemaker probe returned data about the asteroid Mathilde as it flew by in 1997 and the asteroid Eros as it orbited it in 1999 and 2000 and then landed on its surface in 2001, returning unparalleled data about a minor planet. Other probes have since studied asteroids, including ESA's Rosetta, Japan's Hayabusa, which returned with samples of the asteroid Itokawa in 2010, and NASA's Dawn, which orbited and studied Vesta (2011–12) and Ceres (2015–). In 2014, Rosetta, which had also conducted a flyby of Mars (2007), went into orbit around Comet 67P. The first space probe to orbit a comet, Rosetta also deployed a lander on the comet. Messenger, launched by NASA in 2004, became in 2011 the first space probe to orbit Mercury, and continued to study Mercury until its mission ended in 2015; it also made flybys of Venus (2006–7) and Mercury (2008–9).

See W. E. Burrows, Exploring Space (1990); R. D. Launius et al., NASA and the Exploration of Space (1998); D. Fischer, Mission Jupiter: The Spectacular Journey of the Galileo Space Probe (1999); J. Kluger, Journey beyond Selene: Remarkable Expeditions past Our Moon and to the Ends of the Solar System (1999); S. J. Pyne, Voyager: Seeking Newer Worlds in the Third Great Age of Discovery (2010).

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space probe

space probe • n. see probe.

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