Misplaced Pages

#585414

132-546: Sakigake ( さきがけ , lit.   ' pioneer', 'pathfinder ' ) , known before launch as MS-T5 , was Japan's first interplanetary spacecraft , and the first deep space probe to be launched by any country other than the USA or the Soviet Union. It aimed to demonstrate the performance of the new launch vehicle , test its ability to escape from Earth gravity , and observe the interplanetary medium and magnetic field . Sakigake

264-447: A delta-v ), in this case an increase, of about 3.8 km/s. Then, after intercepting Mars, it must change its speed by another 2.3 km/s in order to match Mars' orbital speed around the Sun and enter an orbit around it. For comparison, launching a spacecraft into low Earth orbit requires a change in speed of about 9.5 km/s. For many years economical interplanetary travel meant using

396-590: A dust ring-cloud , with a suspected origin either from Venus–trailing asteroids, interplanetary dust migrating in waves, or the remains of the Solar System's original circumstellar disc that formed the planetary system . Earth and Venus have a near orbital resonance of 13:8 (Earth orbits eight times for every 13 orbits of Venus). Therefore, they approach each other and reach inferior conjunction in synodic periods of 584 days, on average. The path that Venus makes in relation to Earth viewed geocentrically draws

528-538: A nuclear reactor or solar cells to generate electricity , which is then used to accelerate a chemically inert propellant to speeds far higher than achieved in a chemical rocket. Such drives produce feeble thrust, and are therefore unsuitable for quick maneuvers or for launching from the surface of a planet. But they are so economical in their use of working mass that they can keep firing continuously for days or weeks, while chemical rockets use up reaction mass so quickly that they can only fire for seconds or minutes. Even

660-408: A pentagram over five synodic periods, shifting every period by 144°. This pentagram of Venus is sometimes referred to as the petals of Venus due to the path's visual similarity to a flower. When Venus lies between Earth and the Sun in inferior conjunction, it makes the closest approach to Earth of any planet at an average distance of 41 million km (25 million mi). Because of

792-476: A space-based economy . Aerobraking uses the atmosphere of the target planet to slow down. It was first used on the Apollo program where the returning spacecraft did not enter Earth orbit but instead used a S-shaped vertical descent profile (starting with an initially steep descent, followed by a leveling out, followed by a slight climb, followed by a return to a positive rate of descent continuing to splash-down in

924-458: A supercritical state at Venus's surface. Internally, Venus has a core ,  mantle , and  crust . Venus lacks an internal dynamo, and its weakly induced magnetosphere is caused by atmospheric interactions with the solar wind . Internal heat escapes through active volcanism , resulting in resurfacing instead of plate tectonics . Venus is one of two planets in the Solar System ,

1056-456: A 2023 survey found that Americans rate basic research as their third-highest priority for NASA, after monitoring Earth-endangering asteroids and understanding climate change. Support for scientific research is about four times higher than for human flight to the Moon or Mars. Besides spinoffs, other practical motivations for interplanetary travel are more speculative. But science fiction writers have

1188-451: A 4" telescope. Although naked eye visibility of Venus's phases is disputed, records exist of observations of its crescent. When Venus is sufficiently bright with enough angular distance from the sun, it is easily observed in a clear daytime sky with the naked eye, though most people do not know to look for it. Astronomer Edmund Halley calculated its maximum naked eye brightness in 1716, when many Londoners were alarmed by its appearance in

1320-414: A Venusian year (243 versus 224.7 Earth days). Slowed by its strong atmospheric current the length of the day also fluctuates by up to 20 minutes. Venus's equator rotates at 6.52 km/h (4.05 mph), whereas Earth's rotates at 1,674.4 km/h (1,040.4 mph). Venus's rotation period measured with Magellan spacecraft data over a 500-day period is smaller than the rotation period measured during

1452-459: A change that would have occurred over the course of billions of years. The rotation period of Venus may represent an equilibrium state between tidal locking to the Sun's gravitation, which tends to slow rotation, and an atmospheric tide created by solar heating of the thick Venusian atmosphere. The 584-day average interval between successive close approaches to Earth is almost exactly equal to 5   Venusian solar days (5.001444 to be precise), but

SECTION 10

#1733084899586

1584-561: A depression. These features are volcanic in origin. Most Venusian surface features are named after historical and mythological women. Exceptions are Maxwell Montes, named after James Clerk Maxwell , and highland regions Alpha Regio , Beta Regio , and Ovda Regio . The last three features were named before the current system was adopted by the International Astronomical Union , the body which oversees planetary nomenclature . The longitude of physical features on Venus

1716-463: A dynamo at its core. A dynamo requires three things: a conducting liquid, rotation, and convection . The core is thought to be electrically conductive and, although its rotation is often thought to be too slow, simulations show it is adequate to produce a dynamo. This implies that the dynamo is missing because of a lack of convection in Venus's core. On Earth, convection occurs in the liquid outer layer of

1848-478: A fairly good track record in predicting future technologies—for example geosynchronous communications satellites ( Arthur C. Clarke ) and many aspects of computer technology ( Mack Reynolds ). Many science fiction stories feature detailed descriptions of how people could extract minerals from asteroids and energy from sources including orbital solar panels (unhampered by clouds) and the very strong magnetic field of Jupiter. Some claim that such techniques may be

1980-706: A flyby of Halley's Comet on March 11, 1986 at a distance of 6.99 million km. There were plans for the spacecraft to go on to an encounter with 21P/Giacobini-Zinner in 1998 but the flyby had to be abandoned due to lack of propellant . Telemetry contact was lost on November 15, 1995, though a beacon signal continued to be received until January 7, 1999. Interplanetary spaceflight A number of techniques have been developed to make interplanetary flights more economical. Advances in computing and theoretical science have already improved some techniques, while new proposals may lead to improvements in speed, fuel economy, and safety. Travel techniques must take into consideration

2112-932: A human crew, such as Mars 96 , Deep Space 2 , and Beagle 2 (the article List of Solar System probes gives a full list). Many astronomers, geologists and biologists believe that exploration of the Solar System provides knowledge that could not be gained by observations from Earth's surface or from orbit around Earth. However, they disagree about whether human-crewed missions justify their cost and risk. Critics of human spaceflight argue that robotic probes are more cost-effective, producing more scientific knowledge per dollar spent; robots do not need costly life-support systems, can be sent on one-way missions, and are becoming more capable as artificial intelligence advances. Others argue that either astronauts or spacefaring scientists, advised by Earth-based scientists, can respond more flexibly and intelligently to new or unexpected features of whatever region they are exploring. Some members of

2244-399: A malfunction could be disastrous. Fission-based thermal rocket concepts produce lower exhaust velocities than the electric and plasma concepts described below, and are therefore less attractive solutions. For applications requiring high thrust-to-weight ratio, such as planetary escape, nuclear thermal is potentially more attractive. Electric propulsion systems use an external source such as

2376-449: A more massive primary atmosphere from solar nebula have been proposed to explain the enrichment. However, the atmosphere is depleted of radiogenic argon, a proxy for mantle degassing, suggesting an early shutdown of major magmatism. Studies have suggested that billions of years ago, Venus's atmosphere could have been much more like the one surrounding the early Earth, and that there may have been substantial quantities of liquid water on

2508-455: A mothership (providing life support for the crews of smaller spacecraft which hitch a ride on it). Cyclers could also possibly make excellent cargo ships for resupply of a colony. A space elevator is a theoretical structure that would transport material from a planet's surface into orbit. The idea is that, once the expensive job of building the elevator is complete, an indefinite number of loads can be transported into orbit at minimal cost. Even

2640-745: A part of the Halley Armada together with Suisei, the Soviet Vega probes, the ESA Giotto and the NASA International Cometary Explorer , to explore Halley's Comet during its 1986 sojourn through the inner Solar System. Unlike its twin Suisei , it carried no imaging instruments in its instrument payload. Sakigake was launched January 7, 1985, from Kagoshima Space Center by M-3SII launch vehicle on M-3SII-1 mission. It carried out

2772-408: A reduced-g centrifuge providing artificial gravity for crew health to ameliorate the effects of long-term 0g exposure, and the capability to mitigate the space radiation environment. The electric propulsion missions already flown, or currently scheduled, have used solar electric power, limiting their capability to operate far from the Sun, and also limiting their peak acceleration due to the mass of

SECTION 20

#1733084899586

2904-403: A result, aerobraking is only helpful in cases where the fuel needed to transport the heatshield to the planet is less than the fuel that would be required to brake an unshielded craft by firing its engines. This can be addressed by creating heatshields from material available near the target. Several technologies have been proposed which both save fuel and provide significantly faster travel than

3036-432: A small application of thrust is all that is needed to put it into a circular orbit around Mars. If the manoeuver 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,

3168-531: A trip to the Moon is long enough for an electric propulsion system to outrun a chemical rocket – the Apollo missions took 3 days in each direction. NASA's Deep Space One was a very successful test of a prototype ion drive , which fired for a total of 678 days and enabled the probe to run down Comet Borrelly, a feat which would have been impossible for a chemical rocket. Dawn , the first NASA operational (i.e., non-technology demonstration) mission to use an ion drive for its primary propulsion, successfully orbited

3300-508: Is 81.5% of Earth's, making it the third-smallest planet in the Solar System . Conditions on the Venusian surface differ radically from those on Earth because its dense atmosphere is 96.5% carbon dioxide, with most of the remaining 3.5% being nitrogen . The surface pressure is 9.3 megapascals (93 bars ), and the average surface temperature is 737 K (464 °C; 867 °F), above the critical points of both major constituents and making

3432-594: Is adaptable to a variety of mission-specific propulsion units of various low-thrust, high specific impulse (I sp ) designs, nuclear ion-electric drive is shown for illustrative purposes. It is intended for integration and checkout at the International Space Station (ISS), and would be suitable for deep-space missions from the ISS to and beyond the Moon, including Earth/Moon L1 , Sun/Earth L2 , near-Earth asteroidal , and Mars orbital destinations. It incorporates

3564-519: Is called Ishtar Terra after Ishtar , the Babylonian goddess of love, and is about the size of Australia. Maxwell Montes , the highest mountain on Venus, lies on Ishtar Terra. Its peak is 11 km (7 mi) above the Venusian average surface elevation. The southern continent is called Aphrodite Terra , after the Greek mythological goddess of love, and is the larger of the two highland regions at roughly

3696-405: Is currently volcanically active, specifically the detection of olivine , a volcanic product that would weather quickly on the planet's surface. This massive volcanic activity is fuelled by a superheated interior, which models say could be explained by energetic collisions from when the planet was young. Impacts would have had significantly higher velocity than on Earth, both because Venus's orbit

3828-492: Is energetically more favorable than fission, which releases only about 0.1% of the fuel's mass-energy. However, either fission or fusion technologies can in principle achieve velocities far higher than needed for Solar System exploration, and fusion energy still awaits practical demonstration on Earth. One proposal using a fusion rocket was Project Daedalus . Another fairly detailed vehicle system, designed and optimized for crewed Solar System exploration, "Discovery II", based on

3960-483: Is expressed relative to its prime meridian . The original prime meridian passed through the radar-bright spot at the centre of the oval feature Eve, located south of Alpha Regio. After the Venera missions were completed, the prime meridian was redefined to pass through the central peak in the crater Ariadne on Sedna Planitia . The stratigraphically oldest tessera terrains have consistently lower thermal emissivity than

4092-636: Is far from certain. Studies reported on 26 October 2023 suggest for the first time that Venus may have had plate tectonics during ancient times and, as a result, may have had a more habitable environment , possibly one capable of sustaining life . Venus has gained interest as a case for research into the development of Earth-like planets and their habitability . Much of the Venusian surface appears to have been shaped by volcanic activity. Venus has several times as many volcanoes as Earth, and it has 167 large volcanoes that are over 100 km (60 mi) across. The only volcanic complex of this size on Earth

Sakigake - Misplaced Pages Continue

4224-576: Is faster due to its closer proximity to the Sun and because objects would require higher orbital eccentricities to collide with the planet. In 2008 and 2009, the first direct evidence for ongoing volcanism was observed by Venus Express , in the form of four transient localized infrared hot spots within the rift zone Ganis Chasma , near the shield volcano Maat Mons . Three of the spots were observed in more than one successive orbit. These spots are thought to represent lava freshly released by volcanic eruptions. The actual temperatures are not known, because

4356-462: Is formed by sulphur dioxide and water through a chemical reaction resulting in sulfuric acid hydrate. Additionally, the clouds consist of approximately 1% ferric chloride . Other possible constituents of the cloud particles are ferric sulfate , aluminium chloride and phosphoric anhydride . Clouds at different levels have different compositions and particle size distributions. These clouds reflect, similar to thick cloud cover on Earth, about 70% of

4488-452: Is induced by an interaction between the ionosphere and the solar wind , rather than by an internal dynamo as in the Earth's core . Venus's small induced magnetosphere provides negligible protection to the atmosphere against solar and cosmic radiation . The lack of an intrinsic magnetic field on Venus was surprising, given that it is similar to Earth in size and was expected to contain

4620-404: Is most likely at least partially liquid because the two planets have been cooling at about the same rate, although a completely solid core cannot be ruled out. The slightly smaller size of Venus means pressures are 24% lower in its deep interior than Earth's. The predicted values for the moment of inertia based on planetary models suggest a core radius of 2,900–3,450 km. This is in line with

4752-450: Is moving around the Sun at a different speed than the planet to which the spacecraft is travelling (in accordance with Kepler's Third Law ). Because of these facts, a spacecraft desiring to transfer to a planet closer to the Sun must decrease its speed with respect to the Sun by a large amount in order to intercept it, while a spacecraft traveling to a planet farther out from the Sun must increase its speed substantially. Then, if additionally

4884-432: Is not known with certainty, but speculation has ranged from elemental tellurium to lead sulfide ( galena ). Although Venus has no seasons, in 2019 astronomers identified a cyclical variation in sunlight absorption by the atmosphere, possibly caused by opaque, absorbing particles suspended in the upper clouds. The variation causes observed changes in the speed of Venus's zonal winds and appears to rise and fall in time with

5016-508: Is possible to put stations or spacecraft on orbits that cycle between different planets, for example a Mars cycler would synchronously cycle between Mars and Earth, with very little propellant usage to maintain the trajectory. Cyclers are conceptually a good idea, because massive radiation shields, life support and other equipment only need to be put onto the cycler trajectory once. A cycler could combine several roles: habitat (for example it could spin to produce an "artificial gravity" effect), or

5148-406: Is speculation on the possibility that life exists in the upper cloud layers of Venus, 50 km (30 mi) up from the surface, where the atmospheric conditions are the most Earth-like in the Solar System, with temperatures ranging between 303 and 353 K (30 and 80 °C; 86 and 176 °F), and the pressure and radiation being about the same as at Earth's surface, but with acidic clouds and

5280-420: Is that the absence of a late, large impact on Venus ( contra the Earth's "Moon-forming" impact) left the core of Venus stratified from the core's incremental formation, and without the forces to initiate/sustain convection, and thus a "geodynamo". The weak magnetosphere around Venus means that the solar wind is interacting directly with its outer atmosphere. Here, ions of hydrogen and oxygen are being created by

5412-459: Is the Big Island of Hawaii. More than 85,000 volcanoes on Venus were identified and mapped. This is not because Venus is more volcanically active than Earth, but because its crust is older and is not subject to the same erosion process. Earth's oceanic crust is continually recycled by subduction at the boundaries of tectonic plates, and has an average age of about 100 million years, whereas

Sakigake - Misplaced Pages Continue

5544-481: Is the third brightest object in Earth's sky after the Moon and the Sun. In 1961, Venus became the target of the first interplanetary flight, Venera 1 , followed by many essential interplanetary firsts , such as the first soft landing on another planet by Venera 7 in 1970. These probes demonstrated the extreme surface conditions, an insight that has informed predictions about global warming on Earth. This finding ended

5676-415: Is the closest in mass and size to its orbital neighbour Earth . Venus has by far the densest atmosphere of the terrestrial planets, composed mostly of carbon dioxide with a thick, global sulfuric acid cloud cover. At the surface it has a mean temperature of 737 K (464 °C; 867 °F) and a pressure 92 times that of Earth's at sea level. These extreme conditions compress carbon dioxide into

5808-450: Is visible in dark skies long after sunset. As the brightest point-like object in the sky, Venus is a commonly misreported " unidentified flying object ". As it orbits the Sun, Venus displays phases like those of the Moon in a telescopic view. The planet appears as a small and "full" disc when it is on the opposite side of the Sun (at superior conjunction ). Venus shows a larger disc and "quarter phase" at its maximum elongations from

5940-417: Is −4.14 with a standard deviation of 0.31. The brightest magnitude occurs during the crescent phase about one month before or after an inferior conjunction. Venus fades to about magnitude −3 when it is backlit by the Sun. The planet is bright enough to be seen in broad daylight, but is more easily visible when the Sun is low on the horizon or setting. As an inferior planet , it always lies within about 47° of

6072-482: The Magellan spacecraft imaged a highly reflective substance at the tops of the highest mountain peaks, a " Venus snow " that bore a strong resemblance to terrestrial snow. This substance likely formed from a similar process to snow, albeit at a far higher temperature. Too volatile to condense on the surface, it rose in gaseous form to higher elevations, where it is cooler and could precipitate. The identity of this substance

6204-485: The Hohmann transfer orbit . Hohmann demonstrated that the lowest energy route between any two orbits is an elliptical "orbit" which forms a tangent to the starting and destination orbits. 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 directing the spacecraft, originally in an orbit almost identical to Earth's, so that

6336-429: The Moon as slingshots in journeys to the outer planets. This maneuver can only change an object's velocity relative to a third, uninvolved object, – possibly the “centre of mass” or the Sun. There is no change in the velocities of the two objects involved in the maneuver relative to each other. The Sun cannot be used in a gravitational slingshot because it is stationary compared to rest of the Solar System, which orbits

6468-447: The Saturn V launch vehicle, but the tests revealed reliability problems, mainly caused by the vibration and heating involved in running the engines at such high thrust levels. Political and environmental considerations make it unlikely such an engine will be used in the foreseeable future, since nuclear thermal rockets would be most useful at or near the Earth's surface and the consequences of

6600-464: The Sun . Venus "overtakes" Earth every 584 days as it orbits the Sun. As it does so, it changes from the "Evening Star", visible after sunset, to the "Morning Star", visible before sunrise. Although Mercury, the other inferior planet, reaches a maximum elongation of only 28° and is often difficult to discern in twilight, Venus is hard to miss when it is at its brightest. Its greater maximum elongation means it

6732-447: The aphelion of the transfer orbit 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 8.5 months, but because the orbital velocity is greater when closer to the center of mass (i.e. the Sun) and slower when farther from the center, the spacecraft will be traveling quite slowly and

SECTION 50

#1733084899586

6864-401: The decreasing eccentricity of Earth's orbit , the minimum distances will become greater over tens of thousands of years. From the year   1 to 5383, there are 526 approaches less than 40 million km (25 million mi); then, there are none for about 60,158 years. While Venus approaches Earth the closest, Mercury is more often the closest to Earth of all planets. Venus has

6996-422: The dissociation of water molecules from ultraviolet radiation. The solar wind then supplies energy that gives some of these ions sufficient velocity to escape Venus's gravity field. This erosion process results in a steady loss of low-mass hydrogen, helium, and oxygen ions, whereas higher-mass molecules, such as carbon dioxide, are more likely to be retained. Atmospheric erosion by the solar wind could have led to

7128-480: The gravity of planets and moons to change the speed and direction of a 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

7260-412: 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. Solar sails rely on the fact that light reflected from a surface exerts pressure on

7392-415: The sulphur in the atmosphere may indicate that there have been recent eruptions. About 80% of the Venusian surface is covered by smooth, volcanic plains, consisting of 70% plains with wrinkle ridges and 10% smooth or lobate plains. Two highland "continents" make up the rest of its surface area, one lying in the planet's northern hemisphere and the other just south of the equator. The northern continent

7524-492: The 16-year period between the Magellan spacecraft and Venus Express visits, with a difference of about 6.5   minutes. Because of the retrograde rotation, the length of a solar day on Venus is significantly shorter than the sidereal day, at 116.75 Earth days (making the Venusian solar day shorter than Mercury 's 176 Earth days — the 116-day figure is close to the average number of days it takes Mercury to slip underneath

7656-418: The D He reaction but using hydrogen as reaction mass, has been described by a team from NASA's Glenn Research Center . It achieves characteristic velocities of >300 km/s with an acceleration of ~1.7•10 g , with a ship initial mass of ~1700 metric tons, and payload fraction above 10%. Fusion rockets are considered to be a likely source of interplanetary transport for a planetary civilization . See

7788-558: The Earth in its orbit [the number of days of Mercury's synodic orbital period]). One Venusian year is about 1.92   Venusian solar days. To an observer on the surface of Venus, the Sun would rise in the west and set in the east, although Venus's opaque clouds prevent observing the Sun from the planet's surface. Venus may have formed from the solar nebula with a different rotation period and obliquity, reaching its current state because of chaotic spin changes caused by planetary perturbations and tidal effects on its dense atmosphere,

7920-479: The Hohmann transfer takes an amount of time similar to ½ 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. The gravitational slingshot technique uses

8052-620: The Solar System. Currently, the only spacecraft to use a solar sail as the main method of propulsion is IKAROS which was launched by JAXA on May 21, 2010. It has since been successfully deployed, and shown to be producing acceleration as expected. Many ordinary spacecraft and satellites also use solar collectors, temperature-control panels and Sun shades as light sails, to make minor corrections to their attitude and orbit without using fuel. A few have even had small purpose-built solar sails for this use (for example Eurostar E3000 geostationary communications satellites built by EADS Astrium ). It

SECTION 60

#1733084899586

8184-477: The Solar System. NASA 's Apollo program , however, landed twelve people on the Moon and returned them to Earth . The American Vision for Space Exploration , originally introduced by U.S. President George W. Bush and put into practice through the Constellation program , had as a long-term goal to eventually send human astronauts to Mars. However, on February 1, 2010, President Barack Obama proposed cancelling

8316-487: The Sun and thus receives only 25% of Mercury's solar irradiance , of 2,600 W/m (double that of Earth). Because of its runaway greenhouse effect , Venus has been identified by scientists such as Carl Sagan as a warning and research object linked to climate change on Earth. Venus's atmosphere is rich in primordial noble gases compared to that of Earth. This enrichment indicates an early divergence from Earth in evolution. An unusually large comet impact or accretion of

8448-470: The Sun's 11-year sunspot cycle . The existence of lightning in the atmosphere of Venus has been controversial since the first suspected bursts were detected by the Soviet Venera probes . In 2006–07, Venus Express clearly detected whistler mode waves , the signatures of lightning. Their intermittent appearance indicates a pattern associated with weather activity. According to these measurements,

8580-422: The Sun, and appears at its brightest in the night sky. The planet presents a much larger thin "crescent" in telescopic views as it passes along the near side between Earth and the Sun. Venus displays its largest size and "new phase" when it is between Earth and the Sun (at inferior conjunction). Its atmosphere is visible through telescopes by the halo of sunlight refracted around it. The phases are clearly visible in

8712-664: The Sun. It may be used to send a spaceship or probe into the galaxy because the Sun revolves around the center of the Milky Way. A powered slingshot is the use of a rocket engine at or around closest approach to a body ( periapsis ). The use at this point multiplies up the effect of the delta-v, and gives a bigger effect than at other times. Computers did not exist when Hohmann transfer orbits were first proposed (1925) and were slow, expensive and unreliable when gravitational slingshots were developed (1959). Recent advances in computing have made it possible to exploit many more features of

8844-548: The US component of a joint NASA/ESA program for the exploration of Europa and Ganymede . A NASA multi-center Technology Applications Assessment Team led from the Johnson Spaceflight Center , has as of January 2011 described "Nautilus-X", a concept study for a multi-mission space exploration vehicle useful for missions beyond low Earth orbit (LEO), of up to 24 months duration for a crew of up to six. Although Nautilus-X

8976-590: The Venusian surface is estimated to be 300–600   million years old. Several lines of evidence point to ongoing volcanic activity on Venus. Sulfur dioxide concentrations in the upper atmosphere dropped by a factor of 10 between 1978 and 1986, jumped in 2006, and again declined 10-fold. This may mean that levels had been boosted several times by large volcanic eruptions. It has been suggested that Venusian lightning (discussed below) could originate from volcanic activity (i.e. volcanic lightning ). In January 2020, astronomers reported evidence that suggests that Venus

9108-411: The atmosphere before reaching the ground. Without data from reflection seismology or knowledge of its moment of inertia , little direct information is available about the internal structure and geochemistry of Venus. The similarity in size and density between Venus and Earth suggests that they share a similar internal structure: a core , mantle , and crust . Like that of Earth, the Venusian core

9240-474: The atmosphere of Venus. On 29 January 2013, ESA scientists reported that the ionosphere of Venus streams outwards in a manner similar to "the ion tail seen streaming from a comet under similar conditions." In December 2015, and to a lesser extent in April and May 2016, researchers working on Japan's Akatsuki mission observed bow-shaped objects in the atmosphere of Venus. This was considered direct evidence of

9372-443: The atmosphere. Later research attributed the spectroscopic signal that was interpreted as phosphine to sulphur dioxide, or found that in fact there was no absorption line. Thermal inertia and the transfer of heat by winds in the lower atmosphere mean that the temperature of Venus's surface does not vary significantly between the planet's two hemispheres, those facing and not facing the Sun, despite Venus's slow rotation. Winds at

9504-512: The carbon dioxide air. Venus's atmosphere could also have a potential thermal habitable zone at elevations of 54 to 48 km, with lower elevations inhibiting cell growth and higher elevations exceeding evaporation temperature. The putative detection of an absorption line of phosphine in Venus's atmosphere, with no known pathway for abiotic production, led to speculation in September 2020 that there could be extant life currently present in

9636-420: The core because the bottom of the liquid layer is much higher in temperature than the top. On Venus, a global resurfacing event may have shut down plate tectonics and led to a reduced heat flux through the crust. This insulating effect would cause the mantle temperature to increase, thereby reducing the heat flux out of the core. As a result, no internal geodynamo is available to drive a magnetic field. Instead,

9768-552: The crust. Then, over a period of about 100   million years, subduction occurs on an enormous scale, completely recycling the crust. Venusian craters range from 3 to 280 km (2 to 174 mi) in diameter. No craters are smaller than 3   km, because of the effects of the dense atmosphere on incoming objects. Objects with less than a certain kinetic energy are slowed so much by the atmosphere that they do not create an impact crater. Incoming projectiles less than 50 m (160 ft) in diameter will fragment and burn up in

9900-455: The currents and drag of its atmosphere. It takes 224.7 Earth days for Venus to complete an orbit around the Sun, and a Venusian solar year is just under two Venusian days long. The orbits of Venus and Earth are the closest between any two Solar System planets, approaching each other in synodic periods of 1.6 years. Venus and Earth have the lowest difference in gravitational potential of any pair of Solar System planets. This allows Venus to be

10032-412: The daytime with overcast clouds". Strong 300 km/h (185 mph) winds at the cloud tops go around Venus about every four to five Earth days. Winds on Venus move at up to 60 times the speed of its rotation, whereas Earth's fastest winds are only 10–20% rotation speed. The surface of Venus is effectively isothermal ; it retains a constant temperature not only between the two hemispheres but between

10164-579: The daytime. French emperor Napoleon Bonaparte once witnessed a daytime apparition of the planet while at a reception in Luxembourg . Another historical daytime observation of the planet took place during the inauguration of the American president Abraham Lincoln in Washington, D.C., on 4   March 1865. A transit of Venus is the appearance of Venus in front of the Sun, during inferior conjunction . Since

10296-496: The dwarf planet Ceres , arriving in March 2015. Remotely controlled landers such as Viking , Pathfinder and the two Mars Exploration Rovers have landed on the surface of Mars and several Venera and Vega spacecraft have landed on the surface of Venus, with the latter deploying balloons to the planet's atmosphere. The Huygens probe successfully landed on Saturn's moon, Titan . No crewed missions have been sent to any planet of

10428-578: The early solar system orbital dynamics have shown that the eccentricity of the Venus orbit may have been substantially larger in the past, reaching values as high as 0.31 and possibly impacting early climate evolution. All planets in the Solar System orbit the Sun in an anticlockwise direction as viewed from above Earth's north pole. Most planets rotate on their axes in an anticlockwise direction, but Venus rotates clockwise in retrograde rotation once every 243 Earth days—the slowest rotation of any planet. This Venusian sidereal day lasts therefore longer than

10560-417: The electric power source. Nuclear-electric or plasma engines, operating for long periods at low thrust and powered by fission reactors, can reach speeds much greater than chemically powered vehicles. Fusion rockets , powered by nuclear fusion reactions, would "burn" such light element fuels as deuterium, tritium, or He. Because fusion yields about 1% of the mass of the nuclear fuel as released energy, it

10692-670: The energy cost close to zero. Space elevators have also sometimes been referred to as " beanstalks ", "space bridges", "space lifts", "space ladders" and "orbital towers". A terrestrial space elevator is beyond our current technology, although a lunar space elevator could theoretically be built using existing materials. A skyhook is a theoretical class of orbiting tether propulsion intended to lift payloads to high altitudes and speeds. Proposals for skyhooks include designs that employ tethers spinning at hypersonic speed for catching high speed payloads or high altitude aircraft and placing them in orbit. In addition, it has been suggested that

10824-442: The equator and the poles. Venus's minute axial tilt —less than 3°, compared to 23° on Earth—also minimizes seasonal temperature variation. Altitude is one of the few factors that affect Venusian temperatures. The highest point on Venus, Maxwell Montes , is therefore the coolest point on Venus, with a temperature of about 655 K (380 °C; 715 °F) and an atmospheric pressure of about 4.5 MPa (45 bar). In 1995,

10956-415: The existence of perhaps the largest stationary gravity waves in the solar system. Venus orbits the Sun at an average distance of about 0.72  AU (108 million  km ; 67 million  mi ), and completes an orbit every 224.7 days. Although all planetary orbits are elliptical , Venus's orbit is currently the closest to circular, with an eccentricity of less than 0.01. Simulations of

11088-621: The first observation-based estimate of 3,500 km. The principal difference between the two planets is the lack of evidence for plate tectonics on Venus, possibly because its crust is too strong to subduct without water to make it less viscous . This results in reduced heat loss from the planet, preventing it from cooling and providing a likely explanation for its lack of an internally generated magnetic field . Instead, Venus may lose its internal heat in periodic major resurfacing events. In 1967, Venera 4 found Venus's magnetic field to be much weaker than that of Earth. This magnetic field

11220-405: The five planets known to the ancients: The first being Venus ( Venera 7 , 1970), Mars ( Mariner 9 , 1971), Jupiter ( Galileo , 1995), Saturn ( Cassini/Huygens , 2004), and most recently Mercury ( MESSENGER , March 2011), and have returned data about these bodies and their natural satellites . The NEAR Shoemaker mission in 2000 orbited the large near-Earth asteroid 433 Eros , and

11352-465: The following 200 years , but most were determined to be stars in the vicinity. Alex Alemi's and David Stevenson 's 2006 study of models of the early Solar System at the California Institute of Technology shows Venus likely had at least one moon created by a huge impact event billions of years ago. About 10   million   years later, according to the study, another impact reversed

11484-440: The general public mainly value space activities for whatever tangible benefits they may deliver to themselves or to the human race as a whole. So far the only benefits of this type have been "spin-off" technologies which were developed for space missions and then were found to be at least as useful in other activities. However, public support, at least in the US, remains higher for basic scientific research than for human space flight;

11616-568: The gravity fields of astronomical bodies and thus calculate even lower-cost trajectories . Paths have been calculated which link the Lagrange points of the various planets into the so-called Interplanetary Transport Network . Such "fuzzy orbits" use significantly less energy than Hohmann transfers but are much, much slower. They aren't practical for human crewed missions because they generally take years or decades, but may be useful for high-volume transport of low-value commodities if humanity develops

11748-429: The heat from the core is reheating the crust. One possibility is that Venus has no solid inner core, or that its core is not cooling, so that the entire liquid part of the core is at approximately the same temperature. Another possibility is that its core has already been completely solidified. The state of the core is highly dependent on the concentration of sulphur , which is unknown at present. Another possibility

11880-488: The human species from being exterminated by several possible events (see Human extinction ). One of these possible events is an asteroid impact like the one which may have resulted in the Cretaceous–Paleogene extinction event . Although various Spaceguard projects monitor the Solar System for objects that might come dangerously close to Earth, current asteroid deflection strategies are crude and untested. To make

12012-399: The hypothesis of a spin-orbit resonance with Earth has been discounted. Venus has no natural satellites. It has several trojan asteroids : the quasi-satellite 524522 Zoozve and two other temporary trojans, 2001 CK 32 and 2012 XE 133 . In the 17th century, Giovanni Cassini reported a moon orbiting Venus, which was named Neith and numerous sightings were reported over

12144-516: The impact craters, mountains, and valleys commonly found on rocky planets. Among these are flat-topped volcanic features called " farra ", which look somewhat like pancakes and range in size from 20 to 50 km (12 to 31 mi) across, and from 100 to 1,000 m (330 to 3,280 ft) high; radial, star-like fracture systems called "novae"; features with both radial and concentric fractures resembling spider webs, known as " arachnoids "; and "coronae", circular rings of fractures sometimes surrounded by

12276-476: The imperative to make spacecraft lighter. All rocket concepts are limited by the Tsiolkovsky rocket equation , which sets the characteristic velocity available as a function of exhaust velocity and mass ratio, of initial ( M 0 , including fuel) to final ( M 1 , fuel depleted) mass. The main consequence is that mission velocities of more than a few times the velocity of the rocket motor exhaust (with respect to

12408-485: The large main-belt asteroids 1 Ceres and 4 Vesta . A more ambitious, nuclear-powered version was intended for a Jupiter mission without human crew, the Jupiter Icy Moons Orbiter (JIMO), originally planned for launch sometime in the next decade. Due to a shift in priorities at NASA that favored human crewed space missions, the project lost funding in 2005. A similar mission is currently under discussion as

12540-402: The lightning rate is at least half that on Earth, however other instruments have not detected lightning at all. The origin of any lightning remains unclear, but could originate from clouds or Venusian volcanoes . In 2007, Venus Express discovered that a huge double atmospheric polar vortex exists at the south pole. Venus Express discovered, in 2011, that an ozone layer exists high in

12672-492: The loss of most of Venus's water during the first billion years after it formed. However, the planet may have retained a dynamo for its first 2–3 billion years, so the water loss may have occurred more recently. The erosion has increased the ratio of higher-mass deuterium to lower-mass hydrogen in the atmosphere 100 times compared to the rest of the solar system. Venus has a dense atmosphere composed of 96.5% carbon dioxide , 3.5% nitrogen—both exist as supercritical fluids at

12804-421: The lowest gravitational potential difference to Earth than any other planet, needing the lowest delta-v to transfer between them. Tidally Venus exerts the third strongest tidal force on Earth, after the Moon and the Sun, though significantly less. To the naked eye , Venus appears as a white point of light brighter than any other planet or star (apart from the Sun). The planet's mean apparent magnitude

12936-412: The main challenges in interplanetary travel is producing the very large velocity changes necessary to travel from one body to another in the Solar System. Due to the Sun's gravitational pull, a spacecraft moving farther from the Sun will slow down, while a spacecraft moving closer will speed up. Also, since any two planets are at different distances from the Sun, the planet from which the spacecraft starts

13068-420: The most accessible destination and a useful gravity assist waypoint for interplanetary flights from Earth. Venus figures prominently in human culture and in the history of astronomy. Orbiting inferiorly (inside of Earth's orbit), it always appears close to the Sun in Earth's sky, as either a "morning star" or an "evening star". While this is also true for Mercury , Venus appears more prominent, since it

13200-686: The observed planets of the Solar System from Mercury to Neptune , with the New Horizons probe having flown by the dwarf planet Pluto and the Dawn spacecraft currently orbiting the dwarf planet Ceres . The most distant spacecraft, Voyager 1 and Voyager 2 have left the Solar System as of 8 December 2018 while Pioneer 10 , Pioneer 11 , and New Horizons are on course to leave it. In general, planetary orbiters and landers return much more detailed and comprehensive information than fly-by missions. Space probes have been placed into orbit around all

13332-426: The ocean) through Earth's atmosphere to reduce its speed until the parachute system could be deployed enabling a safe landing. Aerobraking does not require a thick atmosphere – for example most Mars landers use the technique, and Mars' atmosphere is only about 1% as thick as Earth's. Aerobraking converts the spacecraft's kinetic energy into heat, so it requires a heatshield to prevent the craft from burning up. As

13464-423: The only way to provide rising standards of living without being stopped by pollution or by depletion of Earth's resources (for example peak oil ). There are also non-scientific motives for human spaceflight, such as adventure or the belief that humans have a spiritually fated destiny in space. Finally, establishing completely self-sufficient colonies in other parts of the Solar System could, if feasible, prevent

13596-404: The orbit of Venus is slightly inclined relative to Earth's orbit, most inferior conjunctions with Earth, which occur every synodic period of 1.6 years, do not produce a transit of Venus above Earth. Consequently, Venus transits above Earth only occur when an inferior conjunction takes place during some days of June or December, the time where the orbits of Venus and Earth cross a straight line with

13728-437: The other being Mercury , that have no moons . Conditions perhaps favourable for life on Venus have been identified at its cloud layers. Venus may have had liquid surface water early in its history with a habitable environment , before a runaway greenhouse effect evaporated any water and turned Venus into its present state. The rotation of Venus has been slowed and turned against its orbital direction ( retrograde ) by

13860-461: The path toward the target, and in many cases the overall travel time is greatly reduced. A prime example of this are the two crafts of the Voyager program , which used slingshot effects to change trajectories several times in the outer Solar System. It is difficult to use this method for journeys in the inner part of the Solar System, although it is possible to use other nearby planets such as Venus or even

13992-425: The payload, and therefore even more fuel is needed to put both the spacecraft and the fuel required for its interplanetary journey into orbit. Thus, several techniques have been devised to reduce the fuel requirements of interplanetary travel. As an example of the velocity changes involved, a spacecraft travelling from low Earth orbit to Mars using a simple trajectory must first undergo a change in speed (also known as

14124-405: The planet underwent a global resurfacing event 300–600   million years ago, followed by a decay in volcanism. Whereas Earth's crust is in continuous motion, Venus is thought to be unable to sustain such a process. Without plate tectonics to dissipate heat from its mantle, Venus instead undergoes a cyclical process in which mantle temperatures rise until they reach a critical level that weakens

14256-421: The planet's spin direction and the resulting tidal deceleration caused the Venusian moon gradually to spiral inward until it collided with Venus. If later impacts created moons, these were removed in the same way. An alternative explanation for the lack of satellites is the effect of strong solar tides, which can destabilize large satellites orbiting the inner terrestrial planets. The orbital space of Venus has

14388-581: The planet's surface with a density 6.5% that of water —and traces of other gases including sulphur dioxide . The mass of its atmosphere is 92 times that of Earth's, whereas the pressure at its surface is about 93 times that at Earth's—a pressure equivalent to that at a depth of nearly 1 km ( 5 ⁄ 8  mi) under Earth's ocean surfaces. The density at the surface is 65 kg/m (4.1 lb/cu ft), 6.5% that of water or 50 times as dense as Earth's atmosphere at 293 K (20 °C; 68 °F) at sea level. The CO 2 -rich atmosphere generates

14520-628: The program in Fiscal Year 2011. An earlier project which received some significant planning by NASA included a crewed fly-by of Venus in the Manned Venus Flyby mission, but was cancelled when the Apollo Applications Program was terminated due to NASA budget cuts in the late 1960s. The costs and risk of interplanetary travel receive a lot of publicity—spectacular examples include the malfunctions or complete failures of probes without

14652-408: The reactive chemicals in a traditional rocket engine . Due to the low molecular mass and hence high thermal velocity of hydrogen these engines are at least twice as fuel efficient as chemical engines, even after including the weight of the reactor. The US Atomic Energy Commission and NASA tested a few designs from 1959 to 1968. The NASA designs were conceived as replacements for the upper stages of

14784-448: The rotating skyhook is "not engineeringly feasible using presently available materials". The SpaceX Starship is designed to be fully and rapidly reusable, making use of the SpaceX reusable technology that was developed during 2011–2018 for Falcon 9 and Falcon Heavy launch vehicles. Venus Venus is the second planet from the Sun . It is a terrestrial planet and

14916-425: The simplest designs avoid the vicious circle of rocket launches from the surface, wherein the fuel needed to travel the last 10% of the distance into orbit must be lifted all the way from the surface, requiring even more fuel, and so on. More sophisticated space elevator designs reduce the energy cost per trip by using counterweights , and the most ambitious schemes aim to balance loads going up and down and thus make

15048-442: The size of South America. A network of fractures and faults covers much of this area. There is recent evidence of lava flow on Venus (2024), such as flows on Sif Mons, a shield volcano, and on Niobe Planitia, a flat plain. There are visible calderas . The planet has few impact craters , demonstrating that the surface is relatively young, at 300–600   million years old. Venus has some unique surface features in addition to

15180-523: The size of the hot spots could not be measured, but are likely to have been in the 800–1,100 K (527–827 °C; 980–1,520 °F) range, relative to a normal temperature of 740 K (467 °C; 872 °F). In 2023, scientists reexamined topographical images of the Maat Mons region taken by the Magellan orbiter. Using computer simulations, they determined that the topography had changed during an 8-month interval, and concluded that active volcanism

15312-477: The spacecraft wishes to enter into orbit around the destination planet (instead of just flying by it), it must match the planet's orbital speed around the Sun, usually requiring another large velocity change. Simply doing this by brute force – accelerating in the shortest route to the destination and then matching the planet's speed – would require an extremely large amount of fuel. And the fuel required for producing these velocity changes has to be launched along with

15444-410: The strongest greenhouse effect in the Solar System, creating surface temperatures of at least 735 K (462 °C; 864 °F). This makes the Venusian surface hotter than Mercury 's, which has a minimum surface temperature of 53 K (−220 °C; −364 °F) and maximum surface temperature of 700 K (427 °C; 801 °F), even though Venus is nearly twice Mercury's distance from

15576-443: The sunlight that falls on them back into space, and since they cover the whole planet they prevent visual observation of Venus's surface. The permanent cloud cover means that although Venus is closer than Earth to the Sun, it receives less sunlight on the ground, with only 10% of the received sunlight reaching the surface, resulting in average daytime levels of illumination at the surface of 14,000 lux , comparable to that on Earth "in

15708-459: The surface are slow, moving at a few kilometres per hour, but because of the high density of the atmosphere at the surface, they exert a significant amount of force against obstructions, and transport dust and small stones across the surface. This alone would make it difficult for a human to walk through, even without the heat, pressure, and lack of oxygen. Above the dense CO 2 layer are thick clouds, consisting mainly of sulfuric acid , which

15840-489: The surface atmosphere a supercritical fluid out of mainly supercritical carbon dioxide and some supercritical nitrogen. The Venusian surface was a subject of speculation until some of its secrets were revealed by planetary science in the 20th century. Venera landers in 1975 and 1982 returned images of a surface covered in sediment and relatively angular rocks. The surface was mapped in detail by Magellan in 1990–91. The ground shows evidence of extensive volcanism, and

15972-503: The surface. After a period of 600 million to several billion years, solar forcing from rising luminosity of the Sun and possibly large volcanic resurfacing caused the evaporation of the original water and the current atmosphere. A runaway greenhouse effect was created once a critical level of greenhouse gases (including water) was added to its atmosphere. Although the surface conditions on Venus are no longer hospitable to any Earth-like life that may have formed before this event, there

16104-470: The surface. The radiation pressure is small and decreases by the square of the distance from the Sun, but unlike rockets, solar sails require no fuel. Although the thrust is small, it continues as long as the Sun shines and the sail is deployed. The original concept relied only on radiation from the Sun – for example in Arthur C. Clarke 's 1965 story " Sunjammer ". More recent light sail designs propose to boost

16236-420: The surrounding basaltic plains measured by Venus Express and Magellan , indicating a different, possibly a more felsic , mineral assemblage. The mechanism to generate a large amount of felsic crust usually requires the presence of water ocean and plate tectonics , implying that habitable condition had existed on early Venus with large bodies of water at some point. However, the nature of tessera terrains

16368-505: The task more difficult, carbonaceous chondrites are rather sooty and therefore very hard to detect. Although carbonaceous chondrites are thought to be rare, some are very large and the suspected " dinosaur-killer " may have been a carbonaceous chondrite. Some scientists, including members of the Space Studies Institute , argue that the vast majority of mankind eventually will live in space and will benefit from doing so. One of

16500-487: The theories and then popular science fiction about Venus being a habitable or inhabited planet. Venus is one of the four terrestrial planets in the Solar System, meaning that it is a rocky body like Earth. It is similar to Earth in size and mass and is often described as Earth's "sister" or "twin". Venus is close to spherical due to its slow rotation. Venus has a diameter of 12,103.6 km (7,520.8 mi)—only 638.4 km (396.7 mi) less than Earth's—and its mass

16632-524: The thrust by aiming ground-based lasers or masers at the sail. Ground-based lasers or masers can also help a light-sail spacecraft to decelerate : the sail splits into an outer and inner section, the outer section is pushed forward and its shape is changed mechanically to focus reflected radiation on the inner portion, and the radiation focused on the inner section acts as a brake. Although most articles about light sails focus on interstellar travel , there have been several proposals for their use within

16764-507: The traditional methodology of using Hohmann transfers . Some are still just theoretical, but over time, several of the theoretical approaches have been tested on spaceflight missions. For example, the Deep Space 1 mission was a successful test of an ion drive . These improved technologies typically focus on one or more of: Besides making travel faster or cost less, such improvements could also allow greater design "safety margins" by reducing

16896-415: The vehicle) rapidly become impractical, as the dry mass (mass of payload and rocket without fuel) falls to below 10% of the entire rocket's wet mass (mass of rocket with fuel). In a nuclear thermal rocket or solar thermal rocket a working fluid, usually hydrogen , is heated to a high temperature, and then expands through a rocket nozzle to create thrust . The energy replaces the chemical energy of

17028-768: The velocity changes necessary to travel from one body to another in the Solar System. For orbital flights, an additional adjustment must be made to match the orbital speed of the destination body. Other developments are designed to improve rocket launching and propulsion, as well as the use of non-traditional sources of energy. Using extraterrestrial resources for energy, oxygen, and water would reduce costs and improve life support systems. Any crewed interplanetary flight must include certain design requirements. Life support systems must be capable of supporting human lives for extended periods of time. Preventative measures are needed to reduce exposure to radiation and ensure optimum reliability. Remotely guided space probes have flown by all of

17160-701: Was also supposed to act as a frame of reference for data received from probes that flew closer to Halley's Comet . Early measurements would be used to improve the mission of the Suisei probe launched several months later. Sakigake was developed by the Institute of Space and Astronautical Science for the National Space Development Agency (both of which are now part of the Japanese Aerospace Exploration Agency , or JAXA). It became

17292-420: Was even successfully landed there, though it had not been designed with this maneuver in mind. The Japanese ion-drive spacecraft Hayabusa in 2005 also orbited the small near-Earth asteroid 25143 Itokawa , landing on it briefly and returning grains of its surface material to Earth. Another ion-drive mission, Dawn , has orbited the large asteroid Vesta (July 2011 – September 2012) and later moved on to

17424-458: Was the cause. Almost a thousand impact craters on Venus are evenly distributed across its surface. On other cratered bodies, such as Earth and the Moon, craters show a range of states of degradation. On the Moon, degradation is caused by subsequent impacts, whereas on Earth it is caused by wind and rain erosion. On Venus, about 85% of the craters are in pristine condition. The number of craters, together with their well-preserved condition, indicates

#585414