Home About us Products Services Contact us Bookmark
:: wikimiki.org ::
Interplanetary Travel

Interplanetary travel

By definition, interplanetary travel is travel between bodies in a given star system.

Current achievements in interplanetary travel

NASA's Apollo program landed twelve people on the Moon and returned them to Earth: Apollo 11-17, except 13, i.e. six missions, each with three astronauts of which two landed on the Moon. Robot probes have been sent to fly past most of the major planets of the Solar system. The most distant probe spacecraft Pioneer 10, Pioneer 11, Voyager 1 and Voyager 2 are on course to leave the Solar system, but will cease to function long before reaching the Oort cloud. Robot landers such as Viking and Pathfinder have already landed on the surface of Mars and several Venera and Vega spacecraft have landed on the surface of Venus. The NEAR Shoemaker orbiter successfully landed on the asteroid 433 Eros, even though it was not designed with this maneuver in mind.

Orbital mechanics of interplanetary travel

To date, the only form of spacecraft propulsion used for interplanetary missions is the chemical rocket engine. The limitations of this engine dictate the trajectories and travel times required for interplanetary travel. All objects in a star system are in orbit around the star; if they were not, they would have "left" the system or fallen into the star long ago. This implies that one cannot simply point oneself at another planet and fly in that direction, because upon arrival the planet will be moving at an inappropriate relative velocity or may have moved altogether. For instance, if a spacecraft were to start from the Earth and fly to Mars, its final velocity will be close to Earth's orbital velocity which is much higher than that of Mars. This is because any spacecraft starting on a planet is also in orbit around the Sun, and a brief glance at the planetary speeds and distances demonstrates that the power of a chemical rocket pales in comparison to the relative speeds of the planets. In order to make interplanetary travel possible, a reduction in the total amount of energy needed to do so is required. For many years this meant using the Hohmann transfer orbit. Hohmann demonstrated that the lowest energy transfer between any two orbits is to elongate the orbit so that its apogee lies over the orbit in question. Once the spacecraft arrives, a second application of thrust will re-circularize the orbit at the new location. In the case of planetary transfers this means adjusting the spacecraft, originally in an orbit almost identical to Earth's, such that the apogee is on the far side of the Sun near the orbit of the other planet. A spacecraft traveling from Earth to Mars via this method will arrive near Mars orbit in approximately 18 months, but because the orbital velocity is greater when closer to the center of mass (ie. the Sun) and slower when farther from the center, the spacecraft will be travelling quite slowly and a small application of thrust is all that is needed. If the maneuver is timed properly, Mars will be "arriving" under the spacecraft when this happens. The Hohmann transfer applies to any two orbits, not just those with planets involved. For instance it is the most common way to transfer satellites into geostationary orbit, after first being "parked" in low earth orbit. However the Hohmann transfer takes an amount of time similar to 1/2 of the orbital period of the outer orbit, so in the case of the outer planets this is many years – too long to wait. It is also based on the assumption that the points at both ends are massless, as in the case when transferring between two orbits around Earth for instance. With a planet at the destination end of the transfer, calculations become considerably more difficult. One technique, known as the gravitational slingshot, uses the gravity of the planets to modify the path of the spacecraft without using fuel. In typical example, a spacecraft is sent to a distant planet on a path that is much faster than what the Hohmann transfer would call for. This would typically mean that it would arrive at the planet's orbit and continue past it. However if there is a planet between the departure point and the target, it can be used to bend the path toward the target, and in many cases the overall travel time is greatly reduced. A prime example of this are the two craft of the Voyager program, which used slingshot effects to change trajectories several times in the outer solar system. This method is not easily applicable to Earth-Mars travel however, although it is possible to use other nearby planets such as Venus or even the Moon as slingshots. Another technique uses the atmosphere of the target planet to slow down. In this case the spacecraft is sent on a high-speed transfer, which would normally mean it would go right past its target upon arrival. By passing into the atmosphere this extra speed is lost, and the amount of energy lost to transport the weight of the required heat shield is considerably less than the weight of the rocket fuel that would be needed to provide the same amount of energy. This concept, known as aerobraking, was first used on the Apollo program wherein the returning spacecraft did not bother to re-enter Earth orbit in a transfer, and instead re-entered immediately at the end of the journey. Similar systems are included on most basic plans for a manned mission to Mars. Recent advances in computing have allowed old mathematical solutions to be re-investigated, and have led to a new system for calculating even lower-cost transfers. Paths have been calculated which link the Lagrange points of the various planets into the so-called Interplanetary Superhighway. The transfers on this system are slower than Hohmann transfers, but use even less energy, and are particularly useful for sending spacecraft between the inner planets.

Improved methods

There are a number of designs for more efficient spacecraft propulsion methods (as measured by specific impulse) that could, speed up interplanetary space missions greatly and allow greater design "safety margins" by reducing the imperative to make spacecraft lighter. If developed, such designs would use trajectories far different to Hohmann transfers. The most likely near-term development is that of electric propulsion, which uses an external source such as a nuclear reactor to generate electricity, which is then used to accelerate a chemically inert propellant to speeds far higher than achieved in a chemical rocket. A prototype of this technology has already been used on NASA's Deep Space One, and a more ambitious, nuclear-powered version is intended for an unmanned Jupiter mission, the Jupiter Icy Moons Orbiter, scheduled for "within a decade". See the spacecraft propulsion article for a discussion of a number of other technologies that could, in the medium to longer term, be the basis of interplanetary missions. Unlike the situation with interstellar travel, the barriers to fast interplanetary travel involve engineering and economics rather than any basic physics. While manned interplanetary travel (with the arguable exception of the Apollo program) has not yet been achieved, a trip to Mars is probably feasible, even with chemical rocket propulsion, and could probably be achieved within a decade (at most two) if the funds were made available. NASA's "Design Reference Mission" proposes a Mars exploration program costing $50 billion, but others have made detailed proposals with projected costs much less (see Mars Direct).

See also


- manned space mission
- Space exploration Category:Spacecraft propulsion Category:Spaceflight

Travel

Travel is the transport of people on a trip or journey. Reasons for travel include:
- Tourism—travel for recreation. This may apply to the travel itself, or the travel may just be the necessary investment to arrive at a desired location.
- Visiting friends and family
- Trade
- Commuting–going to various routine activities, such as work or meetings.
- Migration—travel to begin life somewhere else; nomadic people do this
- Pilgrimages—travel for religious reasons The word originates from the Middle English word travailen ("to toil"), which comes from the French word travailler ("travail"). Travel or traveling is also a name applied to a specific violation in the game of basketball. See Traveling (basketball term).

In Fiction


- To Travel or Traveling refers to using a Gateway (in fiction) or 'fold' in the pattern created by either Saidar or Saidin to move from one place to another in The Wheel of Time series by Robert Jordan.
- Travels is also the title of a non-fiction novel by Michael Crichton.

See also


- travel management

External links


- [http://www.instatravel.org/ Instatravel] Travel site offering news and updates on worldwide travel
- [http://europestring.com/ Europe String] Travelling Europe on a Budget
- [http://flyaway-weblog.com/ Flyaway-Weblog] Travel Tips and Reviews
- [http://escapeblog.com/ Escape Blog] Getting there is only part of the equation, making sure you don't piss off the locals is where the excitement begins.
- See Wikitravel at [http://wikitravel.org/en/Main_Page wikitravel.org] for more travelling information.

Moon

:For other moons in the solar system see natural satellite. For the astrological meaning of the Moon, see Solar system in astrology. For other uses see Moon (disambiguation). The Moon is the planet Earth's only natural satellite. It has no formal name other than "The Moon", although it is occasionally called Luna (Latin for moon), or Selene, to distinguish it from the generic "moon" (natural satellites of other planets are also called moons). Its symbol is a crescent (Unicode: ☾). The terms lunar, selene/seleno-, and cynthion (from the Lunar deities Selene and Cynthia) refer to the Moon (aposelene, selenocentric, pericynthion, etc.). The average distance from the Moon to the Earth is 384,403 kilometers (238,857 miles). The Moon's diameter is 3,476 kilometers (2,160 miles). The first manmade object to land on the Moon was Luna 2 in 1959, the first photographs of the otherwise occluded far side of the Moon were made by Luna 3 that same year, and the first people to land on the Moon came aboard Apollo 11 in 1969.

The two sides

The far side is sometimes called the "dark side". In this case "dark" means "unknown and hidden" and not "lacking light" as percieved by the name; in fact the far side receives (on average) as much sunlight as the near side, but at opposite times. Spacecraft are cut off from direct radio communication with the Earth when on the far side of the Moon. One distinguishing feature of the far side is its almost complete lack of maria (singular: mare), which are the dark albedo features.

Orbit

The Moon makes a complete orbit about once every 28 days. Each hour the Moon moves relative to the stars by an amount roughly equal to its angular diameter, or by about 0.5°. The Moon differs from most satellites of other planets in that its orbit is close to the plane of the ecliptic and not in the Earth's equatorial plane. Several ways to consider a complete orbit are detailed in the table below, but the two most familiar are: the sidereal month being the time it takes to make a complete orbit with respect to the stars, about 27.3 days; and the synodic month being the time it takes to reach the same phase, about 29.5 days. These differ because in the meantime the Earth and Moon have both orbited some distance around the Sun. The gravitational attraction that the Moon exerts on Earth is the cause of tides in the sea. The tidal flow period, but not the phase, is synchronized to the Moon's orbit around Earth. The tidal bulges on Earth, caused by the Moon's gravity, are carried ahead of the apparent position of the Moon by the Earth's rotation, in part because of the friction of the water as it slides over the ocean bottom and into or out of bays and estuaries. As a result, some of the Earth's rotational momentum is gradually being transferred to the Moon's orbital momentum, resulting in the Moon slowly receding from Earth at the rate of approximately 38 mm per year. At the same time the Earth's rotation is gradually slowing, the Earth's day thus lengthens by about 15 µs every year. A more detailed discussion follows in the section titled Earth & Moon. The Moon is in synchronous rotation, meaning that it keeps the same face turned to the Earth at all times. This synchronous rotation is only true on average because the Moon's orbit has definite eccentricity. When the Moon is at its perigee, its rotation is slower than its orbital motion, and this allows us to see up to an extra eight degrees of longitude of its East (right) side. Conversely, when the Moon reaches its apogee, its rotation is faster than its orbital motion and reveals another eight degrees of longitude of its West (left) side. This is called longitudinal libration. Because the lunar orbit is also inclined to the Earth's equator, the Moon seems to oscillate up and down (as a person's head does when nodding) as it moves in celestial latitude (declination). This is called latitudinal libration and reveals the Moon's polar zones over about seven degrees of latitude. Finally, because the Moon is only at about 60 Earth radii distance, an observer at the equator who observes the Moon throughout the night moves by an Earth diameter sideways. This is diurnal libration and reveals about one degree's worth of lunar longitude. Earth and Moon orbit about their barycenter, or common center of mass, which lies about 4700 km from Earth's center (about 3/4 of the way to the surface). Since the barycenter is located below the Earth's surface, Earth's motion is more commonly described as a "wobble". When viewed from Earth's North pole, Earth and Moon rotate counter-clockwise about their axes; the Moon orbits Earth counter-clockwise and Earth orbits the Sun counter-clockwise. It may seem curious that the inclination of the lunar orbit and the tilt of the Moon's axis of rotation are listed as varying considerably. One must be reminded here that the orbital inclination is measured with respect to the primary's equatorial plane (in this case the Earth's), and that the axis of rotation's tilt is measured with respect to the normal to the satellite's orbital plane (the Moon's). For most planetary satellites, but not for the Moon, these conventions model physical reality and the values are therefore stable. The plane of the lunar orbit maintains an inclination of 5.145 396° with respect to the ecliptic (the orbital plane of the Earth), and the lunar axis of rotation maintains an inclination of 1.5424° with respect to the normal to that same plane. The lunar orbital plane precesses quickly (i.e. its intersection with the ecliptic rotates clockwise), in 6793.5 days (18.5996 years), mostly because of the gravitational perturbation induced by the Sun. During that period, the lunar orbital plane thus sees its inclination with respect to the Earth's equator (itself inclined 23.45° to the ecliptic) vary between 23.45° + 5.15° = 28.60° and 23.45° - 5.15° = 18.30°. Simultaneously, the axis of lunar rotation sees its tilt with respect to the Moon's orbital plane vary between 5.15° + 1.54° = 6.69° and 5.15° - 1.54° = 3.60°. Note that the Earth's tilt reacts to this process and itself varies by 0.002 56° on either side of its mean value; this is called nutation. The points where the Moon's orbit crosses the ecliptic are called the "lunar nodes": the North (or ascending) node is where the Moon crosses to the North of the ecliptic; the South (or descending) node where it crosses to the South. Solar eclipses occur when a node coincides with the new Moon; lunar eclipses when a node coincides with the full Moon.

Earth & Moon

The tides on Earth are generated by the Moon's gravitation (see tide and tidal force for a more detailed discussion). There are two tidal bulges, one in the direction of the Moon, and one in the opposite direction (figure 1). The buildup of these bulges and their movement around the earth causes an energy loss due to friction. The energy loss decreases the rotational energy of the Earth. Since the Earth spins faster than the Moon moves around it, the tidal bulges are dragged along with the Earth's surface faster than the Moon moves, and move "in front of the Moon" (figure 2). Because of this, the Earth's gravitational pull on the Moon has a component in the Moon's "forward" direction with respect to its orbit. This component of the gravitational forces between the two bodies acts like a torque on the Earth's rotation, and transfers angular momentum and rotational energy from the Earth's spin to the Moon's orbital movement. angular momentum Because the Moon is accelerated in forward direction, it moves to a higher orbit. As a result, the distance between the Earth and Moon increases, and the Earth's spin slows down (figure 3). Measurements reveal that the Moon's distance to the Earth increases by 38 mm per year (lunar laser ranging experiments with laser reflectors are used to determine this). Atomic clocks also show that the Earth's day lengthens by about 15 µs every year. However, the formation of tidal bulges on Earth is irregular and not directly related to the frictional energy loss which accompanies the tides. For example, continents on Earth may cause an increase in frictional energy losses and hamper the buildup of tidal bulges (figure 4). The energy loss of the Earth's spin (loss of rotational energy of the Earth) is related to both the energy transfer to the Moon, which depends on the geometry of the mass distributions on Earth (causing a gravity component which pulls the Moon forward), and also to frictional losses, which depends on the properties of the material moving around within tides. The transfer of angular momentum to the Moon's orbit, in contrast, depends only on the geometry of the mass distribution. In general, the angular momentum transferred to the Moon will not correspond to an equivalent energy transfer. There will be a surplus or a deficit in the transfer of angular momentum to the Moon, compared to the energy transfer (figure 5). Since both angular momentum and energy are conserved, there must be a mechanism on earth to store a surplus or a deficit of angular momentum. Candidates for this mechanism are the Earth's magnetic field and internal material currents of the Earth (figure 6). The lunar surface is also subjected to tides from earth, and rises and falls by around 10 cm over 27 days. The lunar tides comprise a mobile component, due to the Sun, and a selenographically fixed one, due to Earth (the Moon keeps the same face turned to the Earth, but not to the Sun). The vertical motion of the Earth-induced component comes entirely from the Moon's orbital eccentricity; if the Moon's orbit were perfectly circular, there would be solar tides only. The magnitude of the Moon's tides corresponds to a Love number of 0.0266, and supports the idea of a partially melted zone around its core. Moonquake waves lose energy below 1000 km depth, and this may also show that the deep material is at least partially melted. The Earth’s Love number is 0.3, corresponding to a movement of 0.5 metres per day; for Venus the Love number is also 0.3. (Source: Patrick Moore, The Data Book of Astronomy - June 2003 Updates)

Origin and history

magnetic field The inclination of the Moon's orbit makes it implausible that the Moon formed along with the Earth or was captured later; its origin is the subject of some scientific debate. Early speculation proposed that the Moon broke off from the Earth's crust due to centrifugal force, leaving an ocean basin (presumed to be the Pacific) behind as a scar. This concept requires too great an initial spin of the Earth. Others speculated the Moon formed elsewhere and was captured into its orbit. Two of the other theories include the coformation or condensation theory and the impact theory, which speculates that the Moon formed from the debris that resulted from a collision between the early Earth and a planetesimal. The Coformation or Condensation hypothesis posits that the Earth and the Moon formed together at about the same time from the primordial accretion disk, the Moon forming from material surrounding the coalescing proto-Earth, similar to the way the planets formed around the Sun. Some suggest that this hypothesis fails to adequately explain the depletion of iron in the Moon. Recently, the Giant Impact theory has been considered a more viable scientific theory for the moon's origin than the coformation or condensation theory. The Giant Impact theory holds that the Moon formed from the ejecta resulting from a collision between a semi-molten Earth and a planet-like object the size of Mars, which has been referred to as Theia. The geological epochs of the Moon are defined based on the dating of various significant impact events in the Moon's history. Analysis of craters and Moon rocks show that there was a late heavy bombardment by asteroids around the period 4000 to 3800 million years ago. Tidal forces deformed the once molten Moon into an ellipsoid, with the major axis pointed towards Earth.

Physical characteristics

Composition

More than 4.5 billion years ago, the surface of the Moon was a liquid magma ocean. Scientists think that one component of lunar rocks, KREEP (K-potassium, Rare Earth Elements, and P-phosphorus), represents the last chemical remnant of that magma ocean. KREEP is actually a composite of what scientists term "incompatible elements": those which cannot fit into a crystal structure and thus were left behind, floating to the surface of the magma. For researchers, KREEP is a convenient tracer, useful for reporting the story of the volcanic history of the lunar crust and chronicling the frequency of impacts by comets and other celestial bodies. The lunar crust is composed of a variety of primary elements, including uranium, thorium, potassium, oxygen, silicon, magnesium, iron, titanium, calcium, aluminium and hydrogen. When bombarded by cosmic rays, each element bounces back into space its own radiation, in the form of gamma rays. Some elements, such as uranium, thorium and potassium, are radioactive and emit gamma rays on their own. However, regardless of what causes them, gamma rays for each element are all different from one another — each produces a unique spectral "signature", detectable by a spectrometer. A complete global mapping of the Moon for the abundance of these elements has never been performed. However, some spacecraft have done so for portions of the Moon; Galileo did so when it flew by the Moon in 1992. [http://photojournal.jpl.nasa.gov/catalog/PIA00131] The overall composition of the Moon is believed to be similar to that of the Earth other than a depletion of volatile elements and of iron.

Selenography

1992 photo.]] When observed with earth based telescopes, the moon can be seen to have some 30,000 craters having a diameter of at least 1 kilometers, but close up observation from lunar orbit reveals a multitude of ever smaller craters. Most are hundreds of millions or billions of years old; the lack of atmosphere or weather or recent geological processes ensures that most of them remain permanently preserved. In the lunar terrae, it is indeed impossible to add a crater of any size without obliterating another; this is termed saturation. The largest crater on the Moon, and indeed the largest known crater within the solar system, forms the South Pole-Aitken basin. This crater is located on the far side, near the south pole, and is some 2,240 km in diameter, and 13 km in depth. The dark and relatively featureless lunar plains are called maria, Latin for seas, since they were believed by ancient astronomers to be water-filled seas. They are actually vast ancient basaltic lava flows that filled the basins of large impact craters. The lighter-colored highlands are called terrae. Maria are found almost exclusively on the Lunar nearside, with the Lunar farside having only a few scattered patches. Scientists think that this asymmetry of lunar features was caused by the synchronization between the Moon's rotation and orbit about the Earth. This synchronization exposes the far side of the Moon to more asteroid and meteor impacts than the near, thereby allowing the maria on the near side to remain relatively undisturbed for many hundreds of millennia. Blanketed atop the Moon's crust is a dusty outer rock layer called regolith. Both the crust and regolith are unevenly distributed over the entire Moon. The crust ranges from 60 km (38 mi) on the near side to 100 km (63 mi) on the far side. The regolith varies from 3 to 5 m (10 to 16 ft) in the maria to 10 to 20 m (33 to 66 ft) in the highlands. In 2004, a team led by Dr. Ben Bussey of Johns Hopkins University using images taken by the Clementine mission determined that four mountainous regions on the rim of the 73 km wide Peary crater at the Moon's north pole appeared to remain illuminated for the entire Lunar day. These unnamed "mountains of eternal light" are possible due to the Moon's extremely small axial tilt, which also gives rise to permanent shadow at the bottoms of many polar craters. No similar regions of eternal light exist at the less-mountainous south pole, although the rim of Shackleton crater is illuminated for 80% of the lunar day. Clementine's images were taken during the northern Lunar hemisphere's summer season, and it remains unknown whether these four mountains are shaded at any point during their local winter season.

Presence of water

Over time, comets and meteorites continuously bombard the Moon. Many of these objects are water-rich. Energy from sunlight splits much of this water into its constituent elements hydrogen and oxygen, both of which usually fly off into space immediately. However, it has been hypothesized that significant traces of water remain on the Moon, either on the surface, or embedded within the crust. The results of the Clementine mission suggested that small, frozen pockets of water ice (remnants of water-rich comet impacts) may be embedded unmelted in the permanently shadowed regions of the lunar crust. Although the pockets are thought to be small, the overall amount of water was suggested to be quite significant — 1 km³. Some water molecules, however, may have literally hopped along the surface and gotten trapped inside craters at the lunar poles. Due to the very slight "tilt" of the Moon's axis, only 1.5°, some of these deep craters never receive any light from the Sun — they are permanently shadowed. Clementine has mapped ([http://www.lpi.usra.edu/research/clemen/clemen.html]) craters at the lunar south pole ([http://www.lpi.usra.edu/research/clemen/2polar.gif]) which are shadowed in this way. It is in such craters that scientists expect to find frozen water if it is there at all. If found, water ice could be mined and then split into hydrogen and oxygen by solar panel-equipped electric power stations or a nuclear generator. The presence of usable quantities of water on the Moon would be an important factor in rendering lunar habitation cost-effective, since transporting water (or hydrogen and oxygen) from Earth would be prohibitively expensive. Clementine twisting the shadow due to the fact that cosmic rays are charged particles.]] The equatorial Moon rock collected by Apollo astronauts contained no traces of water. Neither the Lunar Prospector nor more recent surveys, such as those of the Smithsonian Institution, have found direct evidence of lunar water, ice, or water vapor. Lunar Prospector results, however, indicate the presence of hydrogen in the permanently shadowed regions, which could be in the form of water ice.

Magnetic field

Compared to that of Earth, the Moon has a very weak magnetic field. While some of the Moon's magnetism is thought to be intrinsic (such as a strip of the lunar crust called the Rima Sirsalis), collision with other celestial bodies might have imparted some of the Moon's magnetic properties. Indeed, a long-standing question in planetary science is whether an airless solar system body, such as the Moon, can obtain magnetism from impact processes such as comets and asteroids. Magnetic measurements can also supply information about the size and electrical conductivity of the lunar core — evidence that will help scientists better understand the Moon's origins. For instance, if the core contains more magnetic elements (such as iron) than Earth, then the impact theory loses some credibility (although there are alternate explanations for why the lunar core might contain less iron).

Atmosphere

The Moon has a relatively insignificant and tenuous atmosphere. One source of this atmosphere is outgassing — the release of gases, for instance radon, which originate deep within the Moon's interior. Another important source of gases is the solar wind, which is briefly captured by the Moon's gravity.

Eclipses

The angular diameters of the Moon and the Sun as seen from Earth overlap in their variation, so that both total and annular solar eclipses are possible. In a total eclipse, the Moon completely covers the disc of the Sun and the solar corona becomes visible to the naked eye. Since the distance between the Moon and the Earth is very slightly increasing over time, the angular diameter of the Moon is decreasing. This means that several million years ago the Moon always completely covered the Sun on solar eclipses so that no annular eclipses occurred. Likewise, in several million years the Moon will no longer cover the Sun completely and no total eclipses will occur. Eclipses happen only if Sun, Earth and Moon are lined up. Solar eclipses can only occur at new moon; lunar eclipses can only occur at full moon. See also Solar eclipse and Lunar Eclipse.

Observation of the Moon

Lunar Eclipse During the brightest full moons, the Moon can have an apparent magnitude of about −12.6. For comparison, the Sun has an apparent magnitude of −26.8. The Moon appears larger when close to the horizon. This is a purely psychological effect (see Moon illusion). The angular diameter of the Moon from Earth is about one half of one degree. Various lighter and darker colored areas (primarily maria) create the patterns seen by different cultures as the Man in the Moon, the rabbit and the buffalo, amongst others. Craters and mountain chains are also prominent lunar features. From any location on Earth, the highest altitude of the Moon on a day varies between the same limits as the Sun, and depends on season and lunar phase. For example, in winter the Moon is highest in the sky when it is full, and the full moon is highest in winter. The orientation of the Moon's crescent side also depends on the latitude of the observing site. Close to the equator an observer can see a boat Moon. [http://curious.astro.cornell.edu/question.php?number=393] Like the Sun, the Moon can also give rise to an optical effect known as a halo. For more information on how the Moon appears in Earth's sky, see Lunar phase.

Exploration of the Moon

Lunar phase prepares to descend towards the surface of the Moon. NASA photo.]] NASA standing next to boulder at Taurus-Littrow during third EVA (extravehicular activity). NASA photo.]] The first leap in Lunar observation was caused by the invention of the telescope. Especially Galileo Galilei made good use of this new instrument and observed mountains and craters on the Moon's surface. The Cold War-inspired space race between the Soviet Union and the United States of America led to an acceleration. What was the next big step is politically laden. In the US (and the West in general) the landing of the first humans on the moon in 1969 is seen as a culmination, indeed of the space race in general. But from a scientific point of view the first photographs of the until then unseen far side of the moon in 1959 constituted the second leap in Lunar observation. 1959 and Luna missions]] The first man-made object to reach the Moon was the unmanned Soviet probe Luna 2, which made a hard landing on September 14, 1959, at 21:02:24 Z. The far side of the Moon was first photographed on October 7, 1959 by the Soviet probe Luna 3. Luna 9 was the first probe to soft land on the Moon and transmit pictures from the Lunar surface on February 3, 1966. It was proven that a lunar lander would not sink into a thick layer of dust, as had been feared. The first artificial satellite of the Moon was the Soviet probe Luna 10 (launched March 31, 1966). The first robot lunar rover to land on the Moon was the Soviet vessel Lunokhod 1 on November 17 1970 as part of the Lunokhod program. On December 24, 1968 the crew of Apollo 8, Frank Borman, James Lovell, and William Anders became the first human beings to see the far side of the Moon with their own eyes (as opposed to seeing it on a photograph). Humans first landed on the Moon on July 20, 1969. The first man to walk on the lunar surface was Neil Armstrong, commander of the American mission Apollo 11. The last man to stand on the Moon was Eugene Cernan, who as part of the mission Apollo 17 walked on the Moon in December 1972. See also: A full list of lunar astronauts. Moon samples have been brought back to Earth by three Luna missions (nrs. 16, 20, and 24) and the Apollo missions 11 through 17 (minus Apollo 13, which almost ended in a disaster). On January 14 2004, US President George W. Bush called for a plan to return manned missions to the Moon by 2020. NASA's [http://www.nasa.gov/missions/solarsystem/cev.html plan] to accomplish that goal was announced on March 19 2005, and was promptly dubbed Apollo 2.0 by critics. The European Space Agency has plans to launch probes to explore the Moon in the near future, too. European spacecraft Smart 1 was launched September 27, 2003 and entered lunar orbit on November 15 2004. It will survey the lunar environment and create an X-ray map of the Moon. [http://news.bbc.co.uk/2/hi/science/nature/2818551.stm] [http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=36091] The People's Republic of China has expressed ambitious plans for exploring the Moon and is investigating the prospect of lunar mining, specifically looking for the isotope Helium-3 for use as an energy source on Earth [http://space.com/missionlaunches/china_moon_030304.html]. Japan has two planned lunar missions, LUNAR-A and Selene; even a manned lunar base is planned by the Japanese Space Agency (JAXA). India will also try an unmanned orbiting satellite, called Chandrayan. From the mid-1960's to the mid-1970's there were 65 moon landings (with 10 in 1971 alone), but after Luna 24 in 1976 it suddenly stopped. The Soviet Union started focusing on Venus and space stations and the US on Mars and beyond. In 1990 Japan visited the moon with the Hiten spacecraft, becoming the third country to orbit the moon. The spacecraft released the Hagormo probe into lunar orbit, but the transmitter failed rendering the mission scientifically useless.

Human understanding of the Moon

Myth and folk culture

The Moon as muse

The Moon has been the subject of many works of art and literature and the inspiration for countless others.

Astrology

Scientific understanding

A 5,000 year old rock carving at Knowth, Ireland may represent the Moon, which would be the earliest depiction discovered. In many prehistoric and ancient cultures, the Moon was thought to be a deity or other supernatural phenomenon. Among the first in the Western world to offer a scientific explanation for the Moon was the Greek philosopher Anaxagoras, who reasoned that the Sun and Moon were both giant spherical rocks, and that the latter reflected the light of the former. His atheistic view of the heavens was one cause for his imprisonment and eventual exile. By the Middle Ages, before the invention of the telescope, more and more people began to recognize the Moon as a sphere, though they believed that it was "perfectly smooth". sphere In 1609, Galileo Galilei drew one of the first telescopic drawings of the Moon in his book Sidereus Nuncius and noted that it was not smooth but had craters. Later in the 17th century, Giovanni Battista Riccioli and Francesco Maria Grimaldi drew a map of the Moon and gave many craters the names they still have today. Francesco Maria Grimaldi. Surprisingly, the Moon is actually brighter than the Sun at gamma ray wavelengths.]] On maps, the dark parts of the Moon's surface were called maria (singular mare) or "seas", and the light parts were called terrae or continents. The possibility that the Moon could contain vegetation and be inhabited by "selenites" was seriously considered by some major astronomers even into the first decades of the 19th century. In 1835, the Great Moon Hoax fooled some people into thinking that there were exotic animals living on the Moon. Almost at the same time however (during 1834–1836), Wilhelm Beer and Johann Heinrich Mädler were publishing their four-volume Mappa Selenographica and the book Der Mond in 1837, which firmly established the conclusion that the Moon has no bodies of water nor any appreciable atmosphere. There remained some controversy over whether features on the Moon could undergo changes. Some observers claimed that some small craters had appeared or disappeared, but in the 20th century it was determined that these claims were illusory, due to observing under different lighting conditions or due to the inadequacy of earlier drawings. It is however known that the phenomenon of outgassing occasionally occurs. During the Nazi era in Germany, the Welteislehre theory, which claimed the Moon was made of solid ice, was promoted by Nazi leaders. The far side of the Moon remained completely unknown until the Luna 3 probe was launched in 1959, and was extensively mapped by the Lunar Orbiter program in the 1960s. From the 1950s through the 1990s, NASA aerodynamicist Dean Chapman and others advanced the "lunar origin" theory of tektites. Chapman used complex orbital computer models and extensive wind tunnel tests to support the theory that the so-called Australasian tektites originated from the Rosse ejecta ray of the large crater Tycho on the Moon's nearside. Until the Rosse ray is sampled, a lunar origin for these tektites cannot be ruled out. In 1997 the asteroid 3753 Cruithne was found to have an unusual Earth-associated orbit, and has been dubbed by some to be a second "moon" of Earth. It is not considered a moon by astronomers, however, and its orbit is not stable in the long term.

Legal status

Though several flags of the United States have been symbolically planted on the moon, the U.S. government makes no claim to any part of the Moon's surface. The U.S. is party to the Outer Space Treaty, which places the Moon under the same jurisdiction as international waters (res communis). This treaty also restricts use of the Moon to peaceful purposes, explicitly banning weapons of mass destruction (including nuclear weapons) and military installations of any kind. A second treaty, the Moon Treaty, was proposed to restrict the exploitation of the Moon's resources by any single nation, but it has not been signed by any of the space-faring nations. Several individuals have made claims to the Moon in whole or in part, though none of these claims are generally considered credible (see Moon for sale).

Satellites


- Clementine mission - Observation and research satellite
- Smart 1 (or SMART-1) - a European Space Agency research satellite

Surface installations

Multiple scientific instruments were installed during the Apollo missions, some of them still function today. Among those were seismic detectors and reflecting mirrors for laser ranging. laser ranging laser ranging

See also


- Apollo moon landing hoax accusations
- Blue moon
- Chang'e (mythology), Chinese moon goddess
- Crescent
- Colonization of the Moon
- Detailed image of an almost full Moon
- Earthshine
- Lunar effect
- Lunar geologic timescale
- Lunar mare
- Lunar meteorite
- Lunar phase
- Moon landing
- Selene, Greek moon goddess
- Transient lunar phenomenon

Lunar location listings


- List of artificial objects on the Moon
- List of craters on the Moon
- List of features on the Moon
- List of maria on the Moon
- List of mountains on the Moon
- List of valleys on the Moon

References


- Ben Bussey and Paul Spudis, The Clementine Atlas of the Moon, Cambridge University Press, 2004, ISBN 0521815282.
- Patrick Moore, On the Moon, Sterling Publishing Co., 2001 edition, ISBN 0304354694.
- Paul D. Spudis, The Once and Future Moon, Smithsonian Institution Press, 1996, ISBN 1-56098-634-4.

External links

Moon phases


- [http://tycho.usno.navy.mil/vphase.html US Naval Observatory: phase of the Moon for any date and time 1800-2199 A.D.]
- [http://www.moonphaseinfo.com/ Current Moon Phase]
- [http://www.bapuli.co.nr/moon.htm Display current moon phase as wallpaper in Windows]

Space missions


- [http://www.lpi.usra.edu/research/lunar_orbiter/ Digital Lunar Orbiter Photographic Atlas of the Moon]
- [http://www.apolloarchive.com/apollo_archive.html The Project Apollo Archive]
- [http://www.cmf.nrl.navy.mil/clementine/clib/ Clementine Lunar Image Browser]

Scientific


- [http://www.solarviews.com/eng/moon.htm The Moon - by Rosanna and Calvin Hamilton]
- [http://seds.lpl.arizona.edu/nineplanets/nineplanets/luna.html The Moon - by Bill Arnett]
- [http://www.inconstantmoon.com Inconstant Moon - by Kevin Clarke]
- [http://www.moonsociety.org The Moon Society (non-profit educational site)]
- [http://cps.earth.northwestern.edu/GHM/ Geologic History of the Moon by Don Wilhelms]
- [http://isthis4real.com/orbit.xml Can you put the moon into orbit? An interactive simulation - (Needs Firefox 1.5)]

Myth and folklore


- [http://www.straightdope.com/classics/a2_337.html Do things get crazy when the moon is full? by Cecil Adams]
- [http://www.infoplease.com/spot/bluemoon1.html Once in a Blue Moon - What is a blue moon? by Ann-Marie Imbornoni]
- [http://www.suite101.com/article.cfm/folklore/10667 The Moon In Folklore - by Virginia Marin]
- [http://www.laputanlogic.com/articles/2004/04/05-0001.html The Rabbit in the Moon - by John Hardy]

Others


- [http://webgis.wr.usgs.gov/the_moon.htm USGS Planetary GIS webserver - the Moon]
- [http://www.perseus.gr/Astro-Lunar-Scenes-Apo-Perigee.htm The Moon at Apogee and Perigee] (striking photographic comparison)
- [http://www.perseus.gr/Astro-Lunar-Scenes-Sounion-01.htm The Full Moon Rising: I] (striking photo - NOT a composite)
- [http://www.perseus.gr/Astro-Lunar-Scenes-Sounion-02.htm The Full Moon Rising: II] (striking photo - NOT a composite)
- [http://www.perseus.gr/Astro-Lunar-Scenes-Sounion-03.htm The Full Moon Rising: III] (striking photo - NOT a composite)
- [http://www.straightdope.com/classics/a2_110.html Why does the Moon appear bigger near the horizon?] (from The Straight Dope)
- [http://www.badastronomy.com Bad Astronomy]: Dr. Philip Plait, an astronomy professor at Sonoma State University, California, runs this site to explain the many cases of incorrect astronomy (and physics) available to the public, including astrology and the Apollo moon landing hoax accusations.
- [http://www.lunarrepublic.com/atlas/index.shtml The Lunar Navigator: Interactive Maps Of The Moon] features free, interactive online access to maps of the Moon's surface
- [http://www.moonpeople.com A comprehensive guide to the Earth's Moon] (Includes a discussion forum)
- [http://www.traipse.com/earth_and_moon/index.html Distance from the Earth to the Moon, illustrated]
- [http://www.ibiblio.org//e-notes/VRML/Globe/Globe.htm 3D VRML Moon globe] zh-min-nan:Go̍eh-niû ko:달 ms:Bulan (satelit) ja:月 simple:Moon th:ดวงจันทร์



Unmanned space mission

Unmanned space missions are those using remote-controlled spacecraft. Many space missions are more suitable for unmanned missions rather than manned space missions, due to lower cost and lower risk factors. The first such mission was Sputnik I, launched October 4, 1957. Since the early 1970s, most unmanned space missions have been based on space probes with built-in mission computers, and as such may be classified as embedded systems. Some people prefer to use gender-neutral terms such as unpiloted or uncrewed space missions, although the terms are less popular than "unmanned" (as of 2005). Unmanned space missions have been flown by many countries. Most American unmanned missions have been coordinated by the Jet Propulsion Laboratory, and European missions by the European Space Operations Centre, part of ESA (the European Space Agency). The ESA has conducted relatively few space exploration missions (one example is the Giotto mission, which encountered comet Halley). ESA has, however, launched various spacecraft to carry out astronomy, and is a collaborator with NASA on the Hubble Space Telescope. There has been a large number of very successful Russian space missions. There have also been a few Japanese,Chinese and Indian missions. Unmanned space missions may be divided into two classes: artificial satellites, which orbit the Earth, and space probes, which leave Earth's orbit to explore other worlds. See the relevant articles for more information.

See also


- geosynchronous satellite
- List of unmanned spacecraft by program
- manned space mission
- satellite
- space exploration
- space observatory
- Timeline of artificial satellites and space probes
- Timeline of planetary exploration
- List of planetary probes
- Landings on other planets
- Unmanned aerial vehicle

External links


- [http://sci.esa.int/home/ourmissions/index.cfm ESA Unmanned Space Missions]
- [http://www.jpl.nasa.gov NASA Jet Propulsion Laboratory]
- [http://www.unmannedspaceflight.com Unmanned spaceflight discussion forum] Category:Space exploration Category:Embedded systems Category:Unmanned vehicles

Pioneer 10

Launched on March 2, 1972 by an Atlas-Centaur rocket, Pioneer 10 (also called Pioneer F) was the first spacecraft to travel through the asteroid belt, and was the first spacecraft to make direct observations of Jupiter. On December 3, 1973, Pioneer 10 sent back the first close-up images of Jupiter. On June 13th 1983 it passed the orbit of Neptune, then the outermost planet because of Pluto's highly eccentric orbit. By some definitions, this made the spacecraft the first artificial object to leave the solar system. However, Pioneer 10 has still not passed the heliopause or Oort cloud. Famed for a time as the most remote object ever made by man, at last contact Pioneer 10 was over 7.60 billion miles away from Earth. (Until February 17, 1998, the heliocentric radial distance of Pioneer 10 had been greater than that of any other man-made object. But later on that date, Voyager 1's heliocentric radial distance, in the approximate apex direction, equaled that of Pioneer 10 at 69.419 AU. Thereafter, Voyager 1's distance will exceed that of Pioneer 10 at the approximate rate of 1.016 AU per year). Voyager 1 Built by TRW[http://quest.nasa.gov/sso/cool/pioneer10/mission/], the spacecraft made valuable scientific investigations in the outer regions of our solar system until the end of its mission on March 31, 1997. The Pioneer 10's weak signal continued to be tracked by the Deep Space Network as part of a new advanced concept study of chaos theory. Before 1997 the probe was used in the training of flight controllers on how to acquire radio signals from space. The last, very weak, signal from Pioneer 10 was received January 23, 2003. A contact attempt February 7, 2003, was not successful and further attempts are not planned. The last successful reception of telemetry was on April 27, 2002; subsequent signals were barely strong enough to detect. Loss of contact was probably due to a combination of increasing distance and the spacecraft's steadily weakening power source, rather than failure of the craft. However, the planetary society mentions in their Pioneer Anomaly pages that there will be one last attempt to get data from the spacecraft on March 4, 2006. After this date the spacecraft antenna will never be aligned correctly anymore. 1997 Pioneer 10 is heading in the direction of the star Aldebaran in the constellation Taurus. It will take Pioneer over 2 million years to reach it.

Fictional references

Pioneer 10 was used for target practice and easily destroyed by a Klingon Bird of Prey in the movie Star Trek V: The Final Frontier.

See also


- Pioneer plaque
- Pioneer anomaly
- Planetary Grand Tour

External links


- [http://spaceprojects.arc.nasa.gov/Space_Projects/pioneer/PNhome.html Pioneer Project Home Page]
- [http://nssdc.gsfc.nasa.gov/database/MasterCatalog?sc=1972-012A NSSDC Pioneer 10 page]
- [http://history.nasa.gov/SP-349/sp349.htm Pioneer Odyssey, NASA SP-396, 1977] - This is an entire book about the Pioneer 10 and 11 project, with all pictures and diagrams, on-line! Scroll down to click on the "Table of Contents" link.
- [http://www.nap.edu/books/0309090504/html/ Mark Wolverton's The Depths of Space online]
- [http://www.cnn.com/2002/TECH/space/12/18/pioneer.contact/index.html A distant Pioneer whispers to Earth] - CNN article, Dec. 19, 2002
- [http://www.pioneer10.net/ PIONEER 10] - Canadian rock band of same name.
- [http://www.planetary.org/programs/projects/pioneer_anomaly/update_200511.html 2005 Pioneer Anomaly Conference ] - Mentions March 4, 2006 Contact Attempt Category:Jupiter spacecraft Category:Pioneer program ko:파이어니어 10호

Voyager 1

The Voyager 1 spacecraft is an 815-kilogram unmanned probe of the outer solar system and beyond, launched September 5, 1977, and currently operational. It is the farthest human-made object from Earth. The Voyager 1 spacecraft has moved into the solar system's final frontier, a vast area where the Sun's influence gives way to interstellar space. At 14 billion kilometers (95 astronomical units or 8.8 billion miles) from the Sun, Voyager 1 has entered the heliosheath, a region beyond termination shock – the heliosheath is the shocked region between the solar system and interstellar space. If Voyager 1 is still functioning when it finally passes the heliopause, scientists will get their first direct measurements of the conditions in the interstellar medium. At this distance, signals from Voyager 1 take more than thirteen hours to reach its control center at the Jet Propulsion Laboratory, a joint project of NASA and Caltech near Pasadena, California. Voyager 1 is on a hyperbolic trajectory and has achieved escape velocity, meaning that its orbit will not return to the inner solar system. Along with Pioneer 10, the now deactivated Pioneer 11, and its sister ship Voyager 2, Voyager 1 is becoming an interstellar probe. Voyager 1 had as its primary targets the planets Jupiter and Saturn and their associated moons and rings; its current mission is the detection of the heliopause and particle measurements of solar wind and the interstellar medium. Both Voyager probes are powered by three radioisotope thermoelectric generators, which have far outlasted their originally intended lifespan, and are now expected to continue to generate enough power to keep communicating with Earth until around the year 2020.

Mission planning and launch

Voyager 1 was originally planned as Mariner 11 of the Mariner program. From the outset, it was designed to take advantage of the then-new technique of gravity assist. By fortunate chance, the development of interplanetary probes coincided with an alignment of the planets called the Grand Tour. The Grand Tour was a linked series of gravity assists that, with only the minimal fuel needed for course corrections, would enable a single probe to visit all four of the solar system's gas giant planets: Jupiter, Saturn, Uranus and Neptune. The identical Voyager 1 and Voyager 2 probes were designed with the Grand Tour in mind, and their launches were timed to enable the Grand Tour if desired. Voyager 1 was launched on September 5, 1977 by NASA from Cape Canaveral aboard a Titan IIIE Centaur rocket, slightly after its sister craft, Voyager 2. Despite being launched after Voyager 2, Voyager 1 was sent on a faster trajectory so it reached Jupiter and Saturn before its sister craft. Initially, an underburn in the second stage of the Titan IIIE rocket left an estimated one second worth of fuel remaining in that stage. Although ground crews were worried that Voyager 1 would not make it to Jupiter, the Centaur upper stage proved to have enough fuel to compensate. For details on the Voyager instrument packages, see the separate article on the Voyager program.

Jupiter

Voyager program Voyager 1 began photographing Jupiter in January 1979. Its closest approach to Jupiter was on March 5, 1979, at a distance of 349,000 kilometers (217,000 miles) from its center. Due to the greater resolution allowed by close approach, most observations of the moons, rings, magnetic fields, and radiation environment of the Jupiter system were made in the 48-hour period bracketing closest approach. It finished photographing the planet in April. The two Voyager spacecraft made a number of important discoveries about Jupiter and its satellites. The most surprising was the existence of volcanic activity on Io, which had not been observed from the ground or by Pioneer 10 or 11.

Saturn

11 The gravity assist at Jupiter was successful, and the spacecraft went on to visit Saturn. Voyager 1s Saturn flyby occurred in November 1980, with the closest approach on November 12 when it came within 124,000 kilometers (77,000 miles) of the planet's cloud-tops. The craft detected complex structures in Saturn's rings, and studied the atmospheres of Saturn and Titan. Because of the earlier discovery of a thick atmosphere on Titan, the Voyager controllers at the Jet Propulsion Laboratory elected for Voyager 1 to make a close approach of Titan and terminate its Grand Tour. (For the continuation of the Grand Tour, see the Uranus and Neptune sections of the Voyager 2 article.) The Titan-approach trajectory caused an additional gravity assist that took Voyager 1 out of the plane of the ecliptic, thus ending its planetary science mission.

Interstellar mission

It is estimated both Voyager craft would have sufficient electrical power to operate at least some instruments until 2020.

Heliopause

2020] As the Voyager 1 space probe heads for interstellar space, its instruments continue to study the solar system; Jet Propulsion Laboratory scientists are using the plasma wave experiments aboard Voyager 1 and 2 to look for the heliopause. Scientists at the Johns Hopkins University Applied Physics Lab believe that Voyager entered the termination shock in February 2003. Some other scientists have expressed doubt, discussed in the journal Nature of November 6 2003. In a scientific session at the American Geophysical Union meeting in New Orleans on the morning of March 25 2005, Dr. Ed Stone presented clear evidence that Voyager 1 crossed the termination shock in December 2004 [http://www.agu.org/cgi-bin/SFgate/SFgate?&directget=1&application=sm05&database=%2Fdata%2Fepubs%2Fwais%2Findexes%2Fsm05%2Fsm05&=%22SH22A-01%22]. The issue will not be resolved for some months as other data become available, since Voyagers solar-wind detector ceased functioning in 1990. However, in May 2005 a NASA press release said that consensus was that Voyager 1 was now in the heliosheath. [http://www.nasa.gov/vision/universe/solarsystem/voyager_agu.html].

Distance travelled

In March 2005, Voyager 1 was at a distance of 14.2 billion kilometers (95.0 AU or 8.83 billion miles) from the Sun, which makes it the most distant man-made object from Earth. It was travelling at a speed of 17.2 kilometers per second (3.6 AU per year or 38,400 miles per hour), 10% faster than Voyager 2. It is not heading straight towards any particular star, but even if Voyager 1 were going straight toward the closest star system, Alpha Centauri, it would take about 80,000 years to get there.

See also


- Voyager program
- Voyager Golden Record

External links


- [http://voyager.jpl.nasa.gov NASA Voyager website]
- [http://voyager.jpl.nasa.gov/spacecraft/spacecraftlife.html Voyager Spacecraft Lifetime] - Interstellar mission coverage.
- [http://www.heavens-above.com/solar-escape.asp Spacecraft Escaping the Solar System] - current positions and diagrams
- [http://www.cnn.com/2005/TECH/space/05/25/voyager.space/index.html CNN: NASA: Voyager I enters solar system's final frontier] - May 25, 2005
- [http://voyager.jpl.nasa.gov/mission/weekly-reports/ Weekly Mission Reports] - includes information on current spacecraft state Category:Jupiter spacecraft Category:Voyager program Category:Saturn spacecraft ko:보이저 1호

Voyager 2

The Voyager 2 spacecraft was launched in 1977. It is identical to its sister Voyager program craft, Voyager 1, but Voyager 2 followed a somewhat different trajectory during its Saturn encounter, bypassing a close encounter with Titan to take advantage of a gravitational slingshot to travel on to Uranus and Neptune. It thus became the first and so far only probe to visit those two planets and the first spacecraft to make the Grand Tour of Jupiter, Saturn, Uranus and Neptune. This was possible only due to a rare geometric arrangement of those four planets that only occurs once every 175 years [http://voyager.jpl.nasa.gov/science/planetary.html]. For details on the Voyager instrument packages, see the separate article on the Voyager program. Voyager program

Mission planning and launch

Voyager 2 was originally planned to be Mariner 12, part of the Mariner program. Voyager 2 was launched on August 20, 1977, from Cape Canaveral, Florida aboard a Titan III-E Centaur rocket. Ground crews became engrossed in a launch problem with Voyager 1 and forgot to send an important activation code to Voyager 2. This caused the probe to shut down its main high-gain antenna. Fortunately, ground crews were able to establish contact through the craft's low-gain antenna and reactivate it.

Jupiter

The closest approach to Jupiter occurred on July 9, 1979.

Saturn

1979The closest approach to Saturn occurred on August 25, 1981. While behind Saturn (as viewed from Earth), Voyager 2 probed Saturn's upper atmosphere with its radar, to measure temperature and density profiles. Voyager 2 found that at the highest levels (70 millibars or 7.0 kilopascals) Saturn's temperature was 70 kelvins, while at the deepest levels measured (1200 millibars or 120 kilopascals) the temperature increased to 143 kelvins. The North pole was found to be 10 kelvins cooler, although this may be seasonal (see also Saturn Oppositions). After the Saturn fly-by, the camera platform on Voyager 2 locked up briefly, putting plans to officially extend the mission to Uranus and Neptune in jeopardy. Fortunately, the mission team were able to fix the problem, and the probe was given the go-ahead to examine Uranus.

Uranus

NeptuneThe closest approach to Uranus occurred on January 24, 1986. Voyager 2 discovered 10 previously unknown moons; studied the planet's unique atmosphere, caused by its axial tilt of 97.77°; and examined its ring system.

Neptune

ring systemThe closest approach to Neptune occurred on August 25, 1989. Since this was the last major planet Voyager 2 could visit, it was decided to make a close flyby of the moon Triton, regardless of the consequences to the trajectory, as with Voyager 1s encounter with Saturn and its moon Titan. This was a wise decision, as Triton turned out to have a fascinating surface. The probe also discovered the Great Dark Spot, which has since disappeared, according to Hubble Space Telescope observations.

Escaping the solar system

Since its planetary mission is over, Voyager 2 is now described as working on an Interspace Mission, which NASA is using to find out what the solar system is like beyond the heliosphere. As of January 11, 2005, Voyager 2 is at a distance of 75.4 AU and is escaping the solar system at a speed of about 3.3 AU per year (ca. 15.6 km/s). Although it has not yet escaped the solar system, it is believed to be on the verge of doing so. Voyager 2 is expected to keep on transmitting into the 2030s.

Current Voyager 2 data processing and operations

There were 41.1 hours of DSN scheduled support for Voyager 2 of which 22.5 hours were large aperture coverage. There were no real-time or scheduled support changes or significant outages during the period. Science instrument performance was nominal for all activities during this period. One frame of GS-4 data was recorded this week. The EDR backlog is 2 days. Voyager 2 command operations consisted of the uplink of seven bracketed command loss timer resets sent on five-minute centers using 1.0 Hz steps on 03/16 [DOY 075/0342z]. The spacecraft received two of the seven commands sent. This information is available from: http://voyager.jpl.nasa.gov/mission/weekly-reports/index.htm

Voyager 2 in fiction and popular culture

:This section contains specific references to Voyager 2. For other references to the Voyagers, see Voyager in fiction and popular culture in the Voyager program article.
- The motion picture Starman portrayed Voyager 2 as having been located by an alien intelligence who subsequently sent one of their own race to investigate intelligent life on Earth.
- In the episode "Parasites Lost" of the animated show Futurama, Leela scrubs the remains of Voyager 2 off the windscreen of her spaceship while refuelling at an interplanetary service station.

See also


- Voyager program for more information about this spacecraft.

External links


- [http://voyager.jpl.nasa.gov NASA Voyager website]
- [http://voyager.jpl.nasa.gov/spacecraft/spacecraftlife.html Voyager Spacecraft Lifetime]
- [http://www.heavens-above.com/solar-escape.asp Spacecraft Escaping the Solar System] - current positions and diagrams
- [http://voyager.jpl.nasa.gov/mission/weekly-reports/ Mission state]

References

Category:Voyager program Category:Jupiter spacecraft Category:Saturn spacecraft Category:Uranus spacecraft Category:Neptune spacecraft ko:보이저 2호

Oort cloud

The Oort cloud (sometimes called the Öpik-Oort Cloud) is a postulated spherical cloud of comets situated about 50,000 to 100,000 AU from the Sun. This is approximately 1000 times the distance from the Sun to Pluto or roughly one light year, almost a quarter of the distance from the Sun to Proxima Centauri, the star nearest the Sun. The Oort cloud would have its inner disk at the ecliptic from the Kuiper belt. Although no direct observations have been made of such a cloud, it is believed to be the source of most or all comets entering the inner solar system (some short-period comets may come from the Kuiper belt), based on observations of the orbits of comets. In 1932 Ernst Öpik, an Estonian astronomer, proposed that comets originate in an orbiting cloud situated at the outermost edge of the solar system. In 1950 the idea was revived and proposed by Dutch astronomer Jan Hendrick Oort to explain an apparent contradiction: comets are destroyed by several passes through the inner solar system, yet if the comets we observe had existed since the origin of the solar system, all would have been destroyed by now. According to the hypothesis, the Oort cloud contains millions of comet nuclei, which are stable because the sun's radiation is very weak at their distance. The cloud provides a continual supply of new comets, replacing those that are destroyed. It is believed that the total mass of comets in the Oort cloud is many times that of Earth, and estimates range between five and 100 Earth masses. The Oort cloud is a remnant of the original nebula that collapsed to form the Sun and planets five billion years ago, and is loosely bound to the solar system. The most widely-accepted hypothesis of its formation is that the Oort cloud's objects initially formed much closer to the Sun as part of the same process that formed the planets and asteroids, but that gravitational interaction with young gas giants such as Jupiter ejected them into extremely long elliptical or parabolic orbits. This process also served to scatter the objects out of the ecliptic plane, explaining the cloud's spherical distribution. While on the distant outer regions of these orbits, gravitational interaction with nearby stars further modified their orbits to make them more circular. It is thought that other stars are likely to possess Oort clouds of their own, and that the outer edges of two nearby stars' Oort clouds may sometimes overlap, causing the occasional intrusion of a comet into the inner solar system. The star with the greatest possibility of perturbing the Oort cloud in the next 10 million years is Gliese 710.

Oort cloud objects

So far, only one potential Oort cloud object has been discovered; (90377) Sedna. With an orbit that ranges from roughly 76 to 928 AU, it is much closer than originally expected and may belong to an "inner" Oort cloud. If Sedna indeed belongs to the Oort cloud, this may mean that the Oort cloud is both denser and closer to the Sun than previously thought. This has been proposed as possible evidence that the Sun initially formed as part of a dense cluster of stars; with closer neighbors during Oort cloud formation, objects ejected by gas giants would have their orbits circularized closer to the Sun than was predicted for situations with more distant neighbors.
Oort cloud objects
Number Name Equatorial diameter
(km)		 Perihelion (in AU) Aphelion (in AU) Date discovered Discoverer Diameter method
90377 Sedna <1800, >1180 76 (±7) 928 2003 Michael E. Brown, Chad Trujillo, David L. Rabinowitz thermal

References

#Oort, J. H., The structure of the cloud of comets surrounding the Solar System and a hypothesis concerning its origin, Bull. Astron. Inst. Neth., vol. 11, p. 91-110 (1950) [http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1950BAN....11...91O&data_type=PDF_HIGH&type=PRINTER&filetype=.pdf Text at Harvard server (PDF)]

External links


- [http://spaceflightnow.com/news/n0308/08comets/oortcloud.jpg Representation, Southwest Research Institute]
- [http://seds.lpl.arizona.edu/nineplanets/nineplanets/kboc.html The Kuiper Belt and The Oort Cloud] Category:Trans-Neptunian objects ko:오르트 구름 ms:Awan Oort ja:オールトの雲 th:เมฆออร์ต

Mars Pathfinder

The Mars Pathfinder was launched on December 4, 1996 by NASA aboard a Delta II rocket, just a month after the Mars Global Surveyor was launched. After a 7-month voyage it landed on Ares Vallis, in a region called Chryse Planitia on Mars, on 4 July 1997. During its voyage the spacecraft had to accomplish four flight adjustments on 10 January, 3 February, 6 May and 25 June. The lander opened, exposing the rover called Sojourner (named after the famous American abolitionist Sojourner Truth) that would go on to execute different experiments on the Martian surface. The mission carried a series of different scientific instruments to analyze the Martian atmosphere, climate, geology and the composition of its rocks and soil. It was the second project from NASA's Discovery Program, which promotes the use of low-cost spacecraft and frequent launches under the motto "cheaper, faster and better" promoted by the then administrator, Daniel Goldin. The mission was directed by the Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology, responsible for NASA's Mars Exploration Program. This mission to Mars, besides being the first of a series of missions to Mars that included rovers (robotic exploration vehicles), was the most important since the Vikings landed on the red planet in 1976, and also was the first mission to send a rover to Mars planet. The Soviet Union suceeded in sending rovers, named Lunokhod 1 & 2 to the Moon in the 1970s. Though completely successful and completing real objectives, the Mars Pathfinder mission can be regarded as a "proof-of-concept" for various technologies, such as airbag-mediated touchdown and automated obstacle avoidance, both later exploited by the Mars Exploration Rovers. The Mars Pathfinder was also remarkable for its extremely low price relative to other unmanned space missions. This was an important achievement, considering that approximately two-thirds of the spacecrafts destined for Mars have either failed to launch or were lost en route.

Landing Site

The landing site was an ancient flood plain in Mars' northern hemisphere called "Ares Vallis" and is among the rockiest parts of Mars. It was chosen because scientists found it to be a relatively safe surface to land on and one which contained a wide variety of rocks deposited during a catastrophic flood. Upon successful landing, the landing site was named The Carl Sagan Memorial Station in honor of the late astronomer and leader in the field of unmanned space exploration.

The Probe

The probe consisted of a lander and a lightweight (10.6 kilograms/23 pounds) wheeled robot (Rover) called Sojourner ("one in a break from journeying"), after the sometime slave, abolitionist, and women's-rights activist Sojourner Truth.

Landing Process

Mars Pathfinder used an innovative method of directly entering the Martian atmosphere, assisted by a parachute to slow its descent through the thin Martian atmosphere and a giant system of airbags to cushion the impact.

Mission

The lander relayed transmissions to and from the robot, allowing it to operate independently of the probe body. The robot was remotely controlled, but had a basic camera-assisted autonomous control system allowing it to navigate and negotiate minor obstacles without operator intervention. The robot's freedom of movement allowed the exploration team to closely analyze many more rocks and soil samples than with a traditional probe. From its landing in July 4, 1997 until the final data transmission on September 27, 1997, Mars Pathfinder returned 16,500 images from the lander and 550 images from the rover, as well as more than 15 chemical analyses of rocks and soil and extensive data on winds and other weather factors. Findings from the investigations carried out by scientific instruments on both the lander and the rover suggest that Mars was at one time in its past warm and wet, with water existing in its liquid state and a thicker atmosphere. The exact reason for the final failure of the lander is not certain, but probably it was a failure of a battery, resulting in night-time cooling of the spacecraft that would render it inoperable. The rover was instructed by automatic backup procedures to return to the lander, but its exact location and state are unknown. However, the lander and rover performed much longer and better than expected. NASA efforts to recontact Pathfinder ended March 10, 1998.

Mars Pathfinder Objectives


- To prove that the development of "faster, better and cheaper" spacecraft is possible (with three years for development and a cost under US$ 150 million).
- To show that it is possible to send a load of scientific instruments to another planet with a simple system and at one fifth the cost of a Viking mission.
- To demostrate NASA's commitment to low-cost planetary exploration finishing the mission with a total expenditure of US$ 280 million, including the launch vehicle and mission operations.

Mission equipment

The Mars Pathfinder executed different investigations on the Martian soil using three scientific instruments. The lander contained a stereoscopic camera with spatial filters on a expandable pole called Imager for Mars Pathfinder (IMP), and the Atmospheric Structure Instrument/Meteorology Package (ASI /MET) which acts as a Mars metereological station, collecting data about pressure, temperature, and winds. The Sojourner rover had a Alpha Proton X-ray Spectrometer (APXS), which was used to analyze the components of the rocks and soil. The rover also had two black and white cameras and a color one. These instruments could make investigations of the geology of the Martian surface from just a few millimeters to many hundreds of meters, the geochemistry and evolutionary history of the rocks and surface, the magnetic and mechanical properties of the land, as well as the magnetic properties of the dust, atmosphere and the rotational and orbital dynamics of the planet.

Mars Pathfinder scientific objectives


- Surface morphology and geology using scaled measurements.
- Petrology and geochemistry of surface materials.
- Magnetic and mechanical properties of the surface.
- Atmospheric structure, besides diurnal and nocturnal metereological variations.
- Rotational and orbital dynamics of Mars.

Mission Stages: entry, descent and landing

Petrology During the entry stages these devices were used: thermic-protection shield and a big braking parachute; the usage of an altimeter radar so that the lander could establish how far it was from the surface; retrorockets to slow-down the lander during its descent; lastly, 24 airbags were opened 8 seconds before impact to muffle the landing once the lander detached from its parachute. Its landing speed was about 10.6 metres per second. The whole process was completed in 4 minutes. Once the lander was placed on the surface, the airbags deflated and retracted with the lander over its base; finally the petals with the solar panels were deployed. The lander arrived at night at 2:56:55 a.m. local time (16:56:55 UTC), so the lander had to wait until sunrise to send its first signals to Earth. The landing site was located at 19.30° north latitude and 33.52° west longitude in Ares Vallis, some 19 kilometres southwest from the planned site. During Sol 1 –or martian days– the lander took pictures and made some metereologic measurements. Once the data was received, the engineers realized that one of the airbags hadn't fully deflated and could be a problem for the forthcoming traverse of Sojourner's descent ramp. To solve the problem, they made the lander to raise and lower one of its petals several times to flatten the airbag. The procedure was a success.

The Sojourner gets out

Sojourner's exit from the lander occurred on Sol 2. As the next sols progressed it approached some rocks which were named (by the scientists) "Barnacle Bill", "Yogi", and "Scooby Doo", after the famous cartoons. The rover made measurements of the elements found in those rocks and in the martian soil, while the lander took pictures of the Sojourner and the surrounding terrain, besides making climate observations. The Sojourner was a six-wheeled vehicle and it was 65 cm long, 48 cm wide, 30 cm tall and weighed 10.6 kg. It could move about 500 metres from the lander and its maximun speed reached one centimeter per second. During its 83 days of operation, it sent 550 photographs to Earth and analyzed the chemical properties of sixteen locations near the lander. Video footage of Sojouner approaching "Yogi" used in the opening credits of Star Trek: Enterprise made that television program the first science fiction television or film production in history to use footage (see image immediately below) taken on another planet.

Sojourner's rock analysis

Star Trek: Enterprise The first analysis on a rock started on Sol 3 with "Barnacle Bill". The Alpha Proton X-ray Spectrometer (APXS) was used to determine its composition, the spectrometer taking 10 hours to make a full scan of the sample. It found all the elements except hydrogen, which constitutes just one tenth of 1% of the rock's or soil's mass. The APXS works by irradiating rocks and soil samples with alpha particles (helium nuclei, which consist of two protons and two neutrons). The results indicated that "Barnacle Bill" is much like Earth's andesites, confirming past volcanic activity. Analysis of "Yogi" rock again using the APXS showed that it was a basaltic rock, more primitive than "Barnacle Bill". Yogi's shape and texture show that it was probably deposited there by a flood. Another rock, named "Moe", was found to have certain marks on its surface, demostrating erosion caused by the wind. Most rocks analyzed showed a high content of silicon. In another region known as Rock Garden the Sojourner encountered crescent Moon-shaped dunes, which are similar to crescentic dunes on Earth. The lander, on the other hand, sent more than 16,500 pictures and made 8.5 million measurements of the atmospheric pressure, temperature and wind speed.

End of the mission

Although the mission was programmed to last a week to a month, it eventually lasted for almost 3 months. The final contact with the Pathfinder was at 10:23 UTC on September 27, 1997. Although the mission planners tried to restore contact during the following five months, the successful mission was terminated March 10, 1998. After the landing, the Mars Pathfinder was renamed as the Sagan Memorial Station in honor of the famous astronomer and planetologist Carl Sagan. The mission had exceeded its goals in the first few days.

Facts

In 2003, the Sojourner Rover was inducted into the Robot Hall of Fame.

See also


- Exploration of Mars
- Mars Exploration Rovers (2003-05 mission)
- Space exploration

References


- [http://mpfwww.jpl.nasa.gov/missions/past/pathfinder.html JPL Mars Pathfinder article]
- This article draws heavily on the corresponding article in the Spanish-language Wikipedia, which was accessed in the version of March 28, 2005.
- Mars Pathfinder Litograph Set, NASA. (1997)
- Poster: Mars Pathfinder –Roving the Red Planet, NASA. (1998)
- Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, Asif A. Siddiqi. Monographs in Aerospace History, #24. June 2002, NASA History Office.
- "Return to Mars", article by William R. Newcott. National Geographic, pp. 2-29. Vol. 194, 2nd edition - August 1998.
- "La misión Pathfinder –rebautizada Carl Sagan Memorial Station, en memoria del célebre astrónomo-, paso a paso todo Marte", de J. Roberto Mallo. Conozca Más, págs. 90-96. Edición número 106 - agosto de 1997.
- "Un espía que anda por Marte", de Julio Guerrieri. Descubrir, págs. 80-83. Edición número 73 - agosto de 1997.
- "Mars Pathfinder: el inicio de la conquista de Marte" EL Universo, Enciclopedia de la Astronomía y el Espacio, Editorial Planeta-De Agostini, págs. 58-60. Tomo 5. (1997)

Bibliography on Mars


- The New Solar System, J. Kelly Beatty, Carolyn Collins Petersen, Andrew Chaikin. Cambridge University Press; 4 edition (1998); ISBN 0521645875
- The Surface of Mars, Michael H. Carr. Yale University Press, New Haven; 1 edition (1981); ISBN 0300027508, ISBN 0300032420
- Exploring the Planets, Eric H. Christiansen, Kenneth W. Hamblin. Prentice-Hall, Englewood Cliffs, New Jersey; 2 edition (1995); ISBN 0023224215
- The Search for Life on Mars: Evolution of an Idea, Henry S.F. Cooper. Holt, Rinehart, and Winston, New York (1980); ISBN 0030461669 (hardcover), ISBN 0030598184
- Mars, Percival Lowell. Houghton, Mifflin, Boston, New York (1895). Kessinger Publishing (2004); ISBN 1419132849
- Journey Into Space: The First Thirty Years of Space Exploration, Bruce Murray. W.W. Norton, New York (1989); ISBN 0393026752 (hardcover), ISBN 0393307034
- Planets & Perception: Telescopic Views and Interpretations, 1609-1909, William Sheehan. University of Arizona Press, Tucson (1988); ISBN 0816510598
- The Planet Mars: A History of Observation and Discovery, William Sheehan. University of Arizona Press, Tucson (1996); ISBN 0816516405 (hardcover), ISBN 0816516413
- The Martian Landscape, Viking Lander Imaging Team. NASA SP-425 (1978)
- Viking Orbiter Views of Mars, Viking Orbiter Imaging Team. NASA SP-441 (1980)
- Mars Beckons, John Noble Wilford. ISBN 0394583590 (hardcove