Space probe

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Abandoned 1974 probe, Pioneer H, on display in the National Air and Space Museum Pioneer H.JPG
Abandoned 1974 probe, Pioneer H, on display in the National Air and Space Museum
Diagram of extant Solar System missions 20180504 solar-system-missions2018-05 f840.png
Diagram of extant Solar System missions

A space probe is a robotic spacecraft that does not orbit Earth, but instead, explores further into outer space. [1] A space probe may approach the Moon; travel through interplanetary space; flyby, orbit, or land on other planetary bodies; or enter interstellar space.

Robotic spacecraft uncrewed spacecraft, usually under telerobotic control

A robotic spacecraft is an uncrewed spacecraft, usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to lower cost and lower risk factors. In addition, some planetary destinations such as Venus or the vicinity of Jupiter are too hostile for human survival, given current technology. Outer planets such as Saturn, Uranus, and Neptune are too distant to reach with current crewed spacecraft technology, so telerobotic probes are the only way to explore them.

Earth Third planet from the Sun in the Solar System

Earth is the third planet from the Sun, and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space, especially the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in 365.26 days, a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times.

Outer space Void between celestial bodies

Outer space, or just space, is the expanse that exists beyond the Earth and between celestial bodies. Outer space is not completely empty—it is a hard vacuum containing a low density of particles, predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, neutrinos, dust, and cosmic rays. The baseline temperature of outer space, as set by the background radiation from the Big Bang, is 2.7 kelvins. The plasma between galaxies accounts for about half of the baryonic (ordinary) matter in the universe; it has a number density of less than one hydrogen atom per cubic metre and a temperature of millions of kelvins; local concentrations of this plasma have condensed into stars and galaxies. Studies indicate that 90% of the mass in most galaxies is in an unknown form, called dark matter, which interacts with other matter through gravitational but not electromagnetic forces. Observations suggest that the majority of the mass-energy in the observable universe is dark energy, a type of vacuum energy that is poorly understood. Intergalactic space takes up most of the volume of the universe, but even galaxies and star systems consist almost entirely of empty space.


The space agencies of the USSR (now Russia and Ukraine), the United States, the European Union, Japan, China, India, and Israel have collectively launched probes to several planets and moons of the Solar System, as well as to a number of asteroids and comets. Approximately 15 missions are currently operational. [2]

Soviet space program organization

The Soviet space program comprised several of the rocket and space exploration programs conducted by the Soviet Union (USSR) from the 1930s until its collapse in 1991. Over its 60-year history, this primarily classified military program was responsible for a number of pioneering accomplishments in space flight, including the first intercontinental ballistic missile (R-7), first satellite, first animal in Earth orbit, first human in space and Earth orbit, first woman in space and Earth orbit, first spacewalk, first Moon impact, first image of the far side of the Moon and unmanned lunar soft landing, first space rover, first sample of lunar soil automatically extracted and brought to Earth, and first space station. Further notable records included the first interplanetary probes: Venera 1 and Mars 1 to fly by Venus and Mars, respectively, Venera 3 and Mars 2 to impact the respective planet surface, and Venera 7 and [[Mars 3 German rocket program, was performed mainly by Soviet engineers and scientists after 1955, and was based on some unique Soviet and Imperial Russian theoretical developments, many derived by Konstantin Tsiolkovsky, sometimes known as the father of theoretical astronautics. Sergey Korolev was the head of the principal design group; his official title was "chief designer". Unlike its American competitor in the "Space Race", which had NASA as a single coordinating agency, the USSR's program was split among several competing design bureaus led by Korolev, Mikhail Yangel, Valentin Glushko, and Vladimir Chelomei.

NASA space-related agency of the United States government

The National Aeronautics and Space Administration is an independent agency of the United States Federal Government responsible for the civilian space program, as well as aeronautics and aerospace research.

European Space Agency intergovernmental organisation dedicated to the exploration of space

The European Space Agency is an intergovernmental organisation of 22 member states dedicated to the exploration of space. Established in 1975 and headquartered in Paris, France, ESA has a worldwide staff of about 2,200 in 2018 and an annual budget of about €5.72 billion in 2019.

Interplanetary trajectories

Once a probe has left the vicinity of Earth, its trajectory will likely take it along an orbit around the Sun similar to the Earth's orbit. To reach another planet, the simplest practical method is a Hohmann transfer orbit. More complex techniques, such as gravitational slingshots, can be more fuel-efficient, though they may require the probe to spend more time in transit. Some high Delta-V missions (such as those with high inclination changes) can only be performed, within the limits of modern propulsion, using gravitational slingshots. A technique using very little propulsion, but requiring a considerable amount of time, is to follow a trajectory on the Interplanetary Transport Network. [3]

Heliocentric orbit Solar orbit around the sun

A heliocentric orbit is an orbit around the barycenter of the Solar System, which is usually located within or very near the surface of the Sun. All planets, comets, and asteroids in the Solar System, and the Sun itself are in such orbits, as are many artificial probes and pieces of debris. The moons of planets in the Solar System, by contrast, are not in heliocentric orbits, as they orbit their respective planet.

Sun Star at the centre of the Solar System

The Sun is the star at the center of the Solar System. It is a nearly perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process. It is by far the most important source of energy for life on Earth. Its diameter is about 1.39 million kilometers, or 109 times that of Earth, and its mass is about 330,000 times that of Earth. It accounts for about 99.86% of the total mass of the Solar System. Roughly three quarters of the Sun's mass consists of hydrogen (~73%); the rest is mostly helium (~25%), with much smaller quantities of heavier elements, including oxygen, carbon, neon, and iron.

Hohmann transfer orbit elliptical orbit used to transfer between two circular orbits of different altitudes, in the same plane

In orbital mechanics, the Hohmann transfer orbit is an elliptical orbit used to transfer between two circular orbits of different radii in the same plane. In general a Hohmann transfer orbit uses the lowest possible amount of energy in traveling between two objects orbiting at these radii, and so is used to send the maximum amount of mission payload with the fixed amount of energy that can be imparted by a particular rocket. Non-Hohmann transfer paths may have other advantages for a particular mission such as shorter transfer times, but will necessarily require a reduction in payload mass and/or use of a more powerful rocket.

Some notable probes

<i>Lunokhod 1</i>

Lunokhod 1 was the first of two robotic lunar rovers landed on the Moon by the Soviet Union as part of its Lunokhod program. The Luna 17 spacecraft carried Lunokhod 1 to the Moon in 1970. Lunokhod 1 was the first remote-controlled robot "rover" to freely move across the surface of an astronomical object beyond the Earth. Lunokhod 0 (No.201), the previous and first attempt to do so, launched in February 1969 but failed to reach orbit.

Moon Earths natural satellite

The Moon, also known as Luna, is an astronomical body that orbits planet Earth and is Earth's only permanent natural satellite. It is the fifth-largest natural satellite in the Solar System, and the largest among planetary satellites relative to the size of the planet that it orbits. The Moon is after Jupiter's satellite Io the second-densest satellite in the Solar System among those whose densities are known.

<i>Curiosity</i> (rover) American robotic rover exploring the crater Gale on Mars

Curiosity is a car-sized rover designed to explore the crater Gale on Mars as part of NASA's Mars Science Laboratory mission (MSL). Curiosity was launched from Cape Canaveral on November 26, 2011, at 15:02 UTC and landed on Aeolis Palus inside Gale on Mars on August 6, 2012, 05:17 UTC. The Bradbury Landing site was less than 2.4 km (1.5 mi) from the center of the rover's touchdown target after a 560 million km (350 million mi) journey. The rover's goals include an investigation of the Martian climate and geology; assessment of whether the selected field site inside Gale has ever offered environmental conditions favorable for microbial life, including investigation of the role of water; and planetary habitability studies in preparation for human exploration.

Luna 9

First man-made object to soft land on the Moon, or any other extra terrestrial surface. [4]

Luna 3

First mission to photograph the far side of the Moon, launched in 1959.

Luna 16

First robotic sample return probe from the Moon.

Lunokhod 1

First rover on Moon. It was sent to the Moon on November 10, 1970.

Mariner 10

First probe to Mercury.

Venera 4

First successful in-place analysis of another planet. It may have also been the first space probe to impact the surface of another planet, although it is unclear whether it reached Venus' surface. [5]

Venera 7

The Venera 7 probe was the first spacecraft to successfully soft land on another planet (Venus) and to transmit data from there back to Earth.

Mariner 9

Upon its arrival at Mars on November 13, 1971, Mariner 9 became the first space probe to maintain orbit around another planet. [6]

The Huygens landing site on Titan Huygens surface color.jpg
The Huygens landing site on Titan

Mars 3

First soft landing on Mars (December 2, 1971 [7] ) The lander began transmitting to the Mars 3 orbiter 90 seconds after landing. After 20 seconds, transmission stopped for unknown reasons. [7]


First successful rover on Mars. [8]

Spirit and Opportunity

The Mars Exploration Rovers, Spirit and Opportunity landed on Mars to explore the Martian surface and geology, and searched for clues to past water activity on Mars. They were each launched in 2003 and landed in 2004. Communication with Spirit stopped on sol 2210 (March 22, 2010). [9] [10] JPL continued to attempt to regain contact until May 24, 2011, when NASA announced that efforts to communicate with the unresponsive rover had ended. [11] [12] [13] Opportunity arrived at Endeavour crater on 9 August 2011, at a landmark called Spirit Point named after its rover twin, after traversing 13 miles (21 km) from Victoria crater, over a three-year period. [14] After a planet wide dust storm in June 2018, the final communication was received on June 10, 2018, and Opportunity was declared dead on February 13, 2019. The rover lasted for almost fifteen years on Mars although the rover was intended to last only three months. [15]

Halley Armada

The first dedicated missions to a comet; in this case, to Halley's Comet during its 1985–86 journey through the inner Solar System. It was also the first massive international coordination of space probes on an interplanetary mission, with probes specifically launched by the Soviet (now Russian) Space Agency, European Space Agency, and Japan's ISAS (now integrated with NASDA to JAXA).


Originally a solar observatory in the International Sun-Earth Explorer series, it was sent into solar orbit to make the first close observations of a comet, Comet Giacobini–Zinner, in 1985 as a prelude to studies of Halley's Comet.


Two Russian/French spacecraft. They dropped landers and balloons (first weather balloons deployed on another planet) at Venus before their rendezvous with Halley's Comet.


This Japanese probe was the first non-US, non-Soviet interplanetary probe.[ citation needed ]


A second Japanese probe, it made ultraviolet wavelength observations of the comet.[ clarification needed ]


The first space probe to penetrate a comet's coma and take close-up images of its nucleus.


First solar wind sample return probe from sun-earth L1. [16]


First sample return probe from a comet tail.

NEAR Shoemaker

First probe to land on an asteroid.


First sample return probe to launch from an asteroid.


The Rosetta space probe flew by two asteroids and made a rendezvous and orbited comet 67P/Churyumov-Gerasimenko in November 2014. [17]

Pioneer 10

First probe to Jupiter. Radio communications were lost with Pioneer 10 on January 23, 2003, because of the loss of electric power for its radio transmitter, with the probe at a distance of 12 billion kilometers (80 AU) from Earth.

Pioneer 11

First probe to fly by Saturn. (Communications were later lost due to power constraints and vast distance.)

Voyager 1

Voyager 1's view of Solar System (artist's impression). Voyager 1's view of Solar System (artist's impression).jpg
Voyager 1's view of Solar System (artist's impression).

Voyager 1 is a 733-kilogram probe launched September 5, 1977. It visited Jupiter and Saturn and was the first probe to provide detailed images of the moons of these planets.

Voyager 1 is the farthest human-made object from Earth, traveling away from both the Earth and the Sun at a relatively faster speed than any other probe. [19] As of September 12, 2013, Voyager 1 is about 12 billion miles (19 billion kilometers) from the Sun. [20]

On August 25, 2012, Voyager 1 became the first human made object to enter interstellar space. [21] Voyager 1 has not had a functioning plasma sensor since 1980, but a solar flare in 2012 allowed scientists from NASA to measure vibrations of the plasma surrounding the craft. The vibrations allowed scientists to measure the plasma to be much denser than measurements taken in the far layers of our heliosphere, thus concluding the craft had broken beyond the heliopause.

Voyager 2

Voyager 2 was launched by NASA on August 20, 1977. The probe's primary mission was to visit the ice giants, Uranus and Neptune, which it completed on October 2, 1989. It is currently the only probe to have visited the ice giants. It is the fourth of five spacecraft to have left the solar system. It has been operational for 41 years and 2 months as of October 20, 2018.


Cassini–Huygens was a 5,712kg (12,593lb) space probe designed to study gas giant Saturn, along with its ringed system and moons. The NASA probe was launched with ESA lander Huygens on October 1, 1997 from Cape Canaveral. The Cassini probe entered Saturn orbit on July 1, 2004, and Huygens landed on Titan, Saturn's largest moon, on January 14, 2005. [22] On September 15, 2017, the probe was de-orbited and burned up in Saturn's atmosphere, after almost 20 years in space.

New Horizons

First probe to be launched to Pluto. Launched on January 19, 2006, it flew by the Pluto–Charon system on July 14, 2015. [23]


First spacecraft to visit and orbit a protoplanet (4 Vesta), entering orbit on July 16, 2011. [24] [25] Entered orbit around dwarf planet Ceres in early 2015. Currently orbiting Ceres as of February 2017.


First probe to Jupiter without atomic batteries, [26] launched August 8, 2011.

Chang'e 2

Chang'e 2 was deployed to orbit the Moon, visit Sun–Earth L2 Lagrangian point, and make a flyby of asteroid 4179 Toutatis.[ citation needed ]

Beyond the Solar System

Along with Pioneer 10 , Pioneer 11 , and its sister space probe Voyager 2 , Voyager 1 is now an interstellar probe. Voyager 1 and 2 have both achieved solar escape velocity, meaning that their trajectories will not return them to the Solar System. [27] [28]

Probe imagers

Examples of space probe imaging telescope/cameras (focused on visible spectrum).

Name Aperture
cm (in.)
Type WhereWhen
Mars Reconnaissance Orbiter HiRISE 50 cm (19.7″) R/C Mars orbit2005
Mars Global Surveyor MOC [29] 35 cm (13.8″) R/C Mars orbit1996–2006
New Horizons LORRI[ citation needed ]20.8 cm (8.2″) R/C Space (33+ AU from Earth)2006
Lunar Reconnaissance Orbiter LROC-NAC [30] 19.5 cm (7.68″)ReflectorLunar orbit2009
Cassini ISS-NAC [31] 19 cm (7.5″)ReflectorSaturn orbit2004–2017
Galileo – Solid State Imager [32] 17.65 cm (6.95″) Reflector Jupiter1989–2003
Voyager 1/2, ISS-NAC [33] 17.6 cm (6.92″) Catadioptric Space1977
Mariner 10 – TV Photo Experiment (x2) [34] 15 cm (5.9″) Reflector Space1973–1975
Deep Space 1 MICAS [35] 10 cm ( 3.94″)ReflectorSolar orbit1998–2001
Voyager 1/2, ISS-WAC [33] 6 cm (2.36″)LensSpace1977
Cassini ISS-WAC [31] 5.7 cm (2.2″)LensSaturn orbit2004–2017
MESSENGER MDIS-WAC [36] 3 cm (1.18″) Lens Mercury orbit2004–2015
MESSENGER MDIS-NAC [37] 2.5 cm (0.98″)R/CMercury orbit2004–2015
Dawn Framing Camera (FC1/FC2) [38] 2 cm (0.8″)LensAsteroid belt2007–2018

Image forming systems on space probes typically have a multitude of specifications, but aperture can be useful because it constrains the best diffraction limit and light gathering area.[ citation needed ]

See also

Related Research Articles

Interplanetary spaceflight spaceflight between planets

Interplanetary spaceflight or interplanetary travel is travel between planets, usually within a single planetary system. In practice, spaceflights of this type are confined to travel between the planets of the Solar System.

Space exploration discovery and exploration of outer space

Space exploration is the discovery and exploration of celestial structures in outer space by means of evolving and growing space technology. While the study of space is carried out mainly by astronomers with telescopes, the physical exploration of space is conducted both by unmanned robotic space probes and human spaceflight.

<i>Voyager 2</i> Space probe and the second-farthest man-made object from Earth

Voyager 2 is a space probe launched by NASA on August 20, 1977, to study the outer planets. Part of the Voyager program, it was launched 16 days before its twin, Voyager 1, on a trajectory that took longer to reach Jupiter and Saturn but enabled further encounters with Uranus and Neptune. It is the only spacecraft to have visited either of these two ice giant planets.

Spacecraft manned vehicle or unmanned machine designed to fly in outer space

A spacecraft is a vehicle or machine designed to fly in outer space. Spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, planetary exploration, and transportation of humans and cargo. All spacecraft except single-stage-to-orbit vehicles cannot get into space on their own, and require a launch vehicle.

Gravity assist space maneuver

In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement and gravity of a planet or other astronomical object to alter the path and speed of a spacecraft, typically to save propellant and reduce expense.

Uncrewed spacecraft spacecraft without people on board

Uncrewed or unmanned spacecraft are spacecraft without people on board, used for robotic spaceflight. Uncrewed spacecraft may have varying levels of autonomy from human input; they may be remote controlled, remote guided or even autonomous, meaning they have a pre-programmed list of operations, which they will execute unless otherwise instructed. Many habitable spacecraft also have varying levels of robotic features. For example, the space stations Salyut 7 and Mir, and the ISS module Zarya were capable of remote guided station-keeping, and docking maneuvers with both resupply craft and new modules. The most common uncrewed spacecraft categories are robotic spacecraft, uncrewed resupply spacecraft, space probes and space observatories. Not every uncrewed spacecraft is a robotic spacecraft; for example, a reflector ball is a non-robotic uncrewed spacecraft.

Discovery Program NASAs space exploration missions

NASA's Discovery Program is a series of lower-cost, highly focused American scientific space missions that are exploring the Solar System. It was founded in 1992 to implement then-NASA Administrator Daniel S. Goldin's vision of "faster, better, cheaper" planetary missions. Discovery missions differ from traditional NASA missions where targets and objectives are pre-specified. Instead, these cost-capped missions are proposed and led by a scientist called the Principal Investigator (PI). Proposing teams may include people from industry, small businesses, government laboratories, and universities. Proposals are selected through a competitive peer review process. All of the completed Discovery missions are accomplishing ground-breaking science and adding significantly to the body of knowledge about the Solar System.

Mariner Mark II

Mariner Mark II was NASA's planned family of unmanned spacecraft for the exploration of the outer Solar System that were to be developed and operated by JPL between 1990 through the year 2010.

Outer planets Planet in the Solar System beyond the orbits of the its Main-belt asteroids

The outer planets are those planets in the Solar System beyond the asteroid belt, and hence refers to the gas giants and ice giants, which are in order of their distance from the Sun:

Sample-return mission space mission to retrieve tangible samples from an extraterrestrial location and return with them to Earth for analysis

A sample-return mission is a spacecraft mission with the goal of collecting and returning samples from an extraterrestrial location to Earth for analysis. Sample-return missions may bring back merely atoms and molecules or a deposit of complex compounds such as loose material ("soil") and rocks. These samples may be obtained in a number of ways, such as soil and rock excavation or a collector array used for capturing particles of solar wind or cometary debris.

Outline of space exploration Overview of and topical guide to space exploration

The following outline is provided as an overview of and topical guide to space exploration:

Exploration of Saturn

The exploration of Saturn has been solely performed by crewless probes. Three missions were flybys, which formed an extended foundation of knowledge about the system. The Cassini–Huygens spacecraft, launched in 1997, was in orbit from 2004 to 2017.

Discovery and exploration of the Solar System

Discovery and exploration of the Solar System is observation, visitation, and increase in knowledge and understanding of Earth's "cosmic neighborhood". This includes the Sun, Earth and the Moon, the major planets Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune, their satellites, as well as smaller bodies including comets, asteroids, and dust.

The Solar System — our Sun’s system of planets, moons, and smaller debris — is humankind’s cosmic backyard. Small by factors of millions compared to interstellar distances, the spaces between the planets are daunting, but technologically surmountable

Planetary Science Decadal Survey

The Planetary Science Decadal Survey is a publication of the United States National Research Council produced for NASA and other United States Government Agencies such as the National Science Foundation. The document identifies key questions facing planetary science and outlines recommendations for space and ground-based exploration ten years into the future. Missions to gather data to answer these big questions are described and prioritized, where appropriate.

Flyby (spaceflight)

A flyby is a spaceflight operation in which a spacecraft passes in close proximity to another body, usually a target of its space exploration mission and/or a source of a gravity assist to impel it towards another target. Spacecraft which are specifically designed for this purpose are known as flyby spacecraft, although the term has also been used in regard to asteroid flybys of Earth for example. Important parameters are the time and distance of closest approach.


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Further reading