Space probe
A space probe is a robotic spacecraft that does not orbit Earth, but instead, explores further into outer space. A space probe may approach the Moon; travel through interplanetary space; flyby, orbit, or land on other planetary bodies; or enter interstellar space.
The space agencies of the USSR, 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.
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 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.Some notable probes
[Luna 9]
First man-made object to soft land on the Moon, or any other extra terrestrial surface.[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. Launched in 1967.Venera 7
The Venera 7 probe was the first spacecraft to successfully soft land on another planet 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.[Mars 3]
First soft landing on Mars The lander began transmitting to the Mars 3 orbiter 90 seconds after landing. After 20 seconds, transmission stopped for unknown reasons.''Sojourner">Sojourner (rover)">Sojourner''
First successful rover on Mars.''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. JPL continued to attempt to regain contact until May 24, 2011, when NASA announced that efforts to communicate with the unresponsive rover had ended. Opportunity arrived at Endeavour crater on 9 August 2011, at a landmark called Spirit Point named after its rover twin, after traversing from Victoria crater, over a three-year period. 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.[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 Space Agency, European Space Agency, and Japan's ISAS.ICE">International Cometary Explorer">ICE
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.Vega">Vega program">Vega
Two Russian/French spacecraft, Vega 1 and Vega 2, dropped landers and balloons at Venus before their rendezvous with Halley's Comet.''[Sakigake]''
This Japanese probe was the first non-US, non-Soviet interplanetary probe.''Suisei">Suisei (probe)">Suisei''
A second Japanese probe, it made ultraviolet wavelength observations of the comet.''Giotto">Giotto mission">Giotto''
The first space probe to penetrate a comet's coma and take close-up images of its nucleus.''Genesis">Genesis (spacecraft)">Genesis''
First solar wind sample return probe from sun-earth L1.''Stardust">Stardust (spacecraft)">Stardust''
First sample return probe from a comet tail.[NEAR Shoemaker]
First probe to land on an asteroid.''[Hayabusa]''
First sample return probe to launch from an asteroid.''Rosetta''
The Rosetta space probe flew by two asteroids and made a rendezvous and orbited comet 67P/Churyumov-Gerasimenko in November 2014.''[Pioneer 10]''
Launched 1972. 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 from Earth.
''[Pioneer 11]''
First probe to fly by Saturn.''[Voyager 1]''
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. As of September 12, 2013, Voyager 1 is about 12 billion miles from the Sun.
On August 25, 2012, Voyager 1 became the first human made object to enter interstellar space. 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]''
Cassini–Huygens was a 5,712-kg 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. 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.''Dawn">Dawn (spacecraft)">Dawn''
First spacecraft to visit and orbit a protoplanet, entering orbit on July 16, 2011. Entered orbit around dwarf planet Ceres in early 2015. Currently orbiting Ceres as of February 2017.''Juno">Juno (spacecraft)">Juno''
First probe to Jupiter without atomic batteries, 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.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.Probe imagers
Examples of space probe imaging telescope/cameras.| Name | Aperture cm | Type | Where | When |
| Mars Reconnaissance OrbiterHiRISE | 50 cm | R/C | Mars orbit | 2005 |
| Mars Global SurveyorMOC | 35 cm | R/C | Mars orbit | 1996–2006 |
| New HorizonsLORRI | 20.8 cm | R/C | Space | 2006 |
| Lunar Reconnaissance Orbiter LROC-NAC | 19.5 cm | Reflector | Lunar orbit | 2009 |
| CassiniISS-NAC | 19 cm | Reflector | Saturn orbit | 2004–2017 |
| Galileo – Solid State Imager | 17.65 cm | Reflector | Jupiter | 1989–2003 |
| Voyager 1/2, ISS-NAC | 17.6 cm | Catadioptric | Space | 1977 |
| Mariner 10 – TV Photo Experiment | 15 cm | Reflector | Space | 1973–1975 |
| Deep Space 1MICAS | 10 cm | Reflector | Solar orbit | 1998–2001 |
| Voyager 1/2, ISS-WAC | 6 cm | Lens | Space | 1977 |
| CassiniISS-WAC | 5.7 cm | Lens | Saturn orbit | 2004–2017 |
| MESSENGER MDIS-WAC | 3 cm | Lens | Mercury orbit | 2004–2015 |
| MESSENGER MDIS-NAC | 2.5 cm | R/C | Mercury orbit | 2004–2015 |
| Dawn Framing Camera | 2 cm | Lens | Asteroid belt | 2007–2018 |
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.