This is a list of known objects which occupy, have occupied, or are planned to occupy any of the five Lagrange points of two-body systems in space.
L1 is the Lagrange point located approximately 1.5 million kilometers from Earth towards the Sun.
L2 is the Lagrange point located approximately 1.5 million kilometers from Earth in the direction opposite the Sun. Spacecraft at the Sun–Earth L2 point are in a Lissajous orbit until decommissioned, when they are sent into a heliocentric graveyard orbit.[ citation needed ]
L3 is the Sun–Earth Lagrange point located on the side of the Sun opposite Earth, slightly outside the Earth's orbit. Direct communication with spacecraft in this position is blocked by the sun.
L4 is the Sun–Earth Lagrange point located close to the Earth's orbit 60° ahead of Earth.
L5 is the Sun–Earth Lagrange point located close to the Earth's orbit 60° behind Earth.
Asteroids in the L4 and L5 Sun–Mars Lagrangian points are sometimes called Mars trojans, with a lower-case t, as "Trojan asteroid" was originally defined as a term for Lagrangian asteroids of Jupiter. They may also be called Mars Lagrangian asteroids.
Asteroids in the L4 and L5 Sun–Jupiter Lagrangian points are known as Jupiter Trojan asteroids or simply Trojan asteroids .
Minor planets in the L4 and L5 Sun–Neptune Lagrangian points are called Neptune trojans, with a lower-case t, as "Trojan asteroid" was originally defined as a term for Lagrangian asteroids of Jupiter.
Data from: Minor Planet Center
Color key:
Unflown or planned mission Mission en route or in progress (including mission extensions) Mission at Lagrangian point completed successfully (or partially successfully)
Mission | Lagrangian point | Agency | Description |
---|---|---|---|
International Sun–Earth Explorer 3 (ISEE-3) | Sun–Earth L1 | NASA | Launched in 1978, it was the first spacecraft to be put into orbit around a libration point, where it operated for four years in a halo orbit about the L1 Sun–Earth point. After the original mission ended, it was commanded to leave L1 in September 1982 in order to investigate comets and the Sun. [21] Now in a heliocentric orbit, an unsuccessful attempt to return to halo orbit was made in 2014 when it made a flyby of the Earth–Moon system. [22] [23] |
Advanced Composition Explorer (ACE) | Sun–Earth L1 | NASA | Launched 1997. Has fuel to orbit near L1 until 2024. Operational as of 2019 [update] . [24] |
Deep Space Climate Observatory (DSCOVR) | Sun–Earth L1 | NASA | Launched on 11 February 2015. Planned successor of the Advanced Composition Explorer (ACE) satellite. |
LISA Pathfinder (LPF) | Sun–Earth L1 | ESA, NASA | Launched one day behind revised schedule (planned for the 100th anniversary of the publication of Einstein's General Theory of Relativity), on 3 December 2015. Arrived at L1 on 22 January 2016. [25] LISA Pathfinder was deactivated on 30 June 2017. [26] |
Solar and Heliospheric Observatory (SOHO) | Sun–Earth L1 | ESA, NASA | Orbiting near L1 since 1996. Operational as of 2020 [update] . [27] |
WIND | Sun–Earth L1 | NASA | Arrived at L1 in 2004 with fuel for 60 years. Operational as of 2019 [update] . [28] |
Wilkinson Microwave Anisotropy Probe (WMAP) | Sun–Earth L2 | NASA | Arrived at L2 in 2001. Mission ended 2010, [29] then sent to solar orbit outside L2. [30] |
Herschel Space Telescope | Sun–Earth L2 | ESA | Arrived at L2 July 2009. Ceased operation on 29 April 2013; will be moved to a heliocentric orbit. [31] [32] |
Planck Space Observatory | Sun–Earth L2 | ESA | Arrived at L2 July 2009. Mission ended on 23 October 2013; Planck has been moved to a heliocentric parking orbit. [33] |
Chang'e 2 | Sun–Earth L2 | CNSA | Arrived in August 2011 after completing a lunar mission before departing en route to asteroid 4179 Toutatis in April 2012. [12] |
ARTEMIS mission extension of THEMIS | Earth–Moon L1 and L2 | NASA | Mission consists of two spacecraft, which were the first spacecraft to reach Earth–Moon Lagrangian points. Both moved through Earth–Moon Lagrangian points, and are now in lunar orbit. [34] [35] |
WIND | Sun–Earth L2 | NASA | Arrived at L2 in November 2003 and departed April 2004. |
Gaia Space Observatory | Sun–Earth L2 | ESA | Launched 19 December 2013. [36] Operational as of 2020 [update] . [37] |
Chang'e 5-T1 Service Module | Earth–Moon L2 | CNSA | Launched on 23 October 2014, arrived at L2 halo orbit on 13 January 2015. [2] |
Queqiao | Earth–Moon L2 | CNSA | Launched on 21 May 2018, arrived at L2 halo orbit on June 14 for Chang'e 4 mission. [38] Queqiao is the first ever communication relay and radio astronomy satellite at operating its location. [39] |
Spektr-RG | Sun–Earth L2 | IKI RAN DLR | Launched 13 July 2019. Roentgen and Gamma space observatory. Operational as of June 2020. [40] |
James Webb Space Telescope (JWST) | Sun–Earth L2 | NASA, ESA, CSA | Launched on 25 December 2021, arrived at L2 point on 24 January 2022. Operational as of 2022. [41] |
Euclid | Sun–Earth L2 | ESA, NASA | Launched on 1 July 2023, arrived at L2 point on 28 July 2023. Currently in testing phase as of September 2023. [42] |
Aditya-L1 | Sun–Earth L1 | ISRO | Launched on 2 September 2023 [43] and was successfully inserted into an orbit about Sun-Earth L1 point on 6 January 2024. [44] |
Mission | Lagrangian point | Agency | Description |
---|---|---|---|
"Lunar Far-Side Communication Satellites" | Earth–Moon L2 | NASA | Proposed in 1968 for communications on the far side of the Moon during the Apollo program, mainly to enable an Apollo landing on the far side—neither the satellites nor the landing were ever realized. [45] |
Space colonization and manufacturing | Earth–Moon L4 or L5 | — | First proposed in 1974 by Gerard K. O'Neill [46] and subsequently advocated by the L5 Society. |
EQUULEUS | Earth–Moon L2 | University of Tokyo, JAXA | 6U CubeSat, launch planned in 2021 as a secondary payload onboard SLS Artemis 1. [47] |
DESTINY+ | Earth–Moon L2 | JAXA | JAXA "Medium-Sized Focused Mission"; launch planned for 2025. [48] |
Exploration Gateway Platform | Earth–Moon L2 [49] | NASA | Proposed in 2011. [50] |
Nancy Grace Roman Space Telescope (WFIRST) | Sun–Earth L2 | NASA, USDOE | Launch planned for 2026. [51] |
LiteBIRD | Sun–Earth L2 [52] | JAXA, NASA | JAXA's next "Strategic Large Mission"; launch planned for 2032. [53] [54] |
Interstellar Mapping and Acceleration Probe (IMAP) | Sun–Earth L1 | NASA | Planned for launch in early 2025. |
Space Weather Follow On - Lagrange 1 (SWFO-L1) | Sun–Earth L1 | NOAA | Planned for launch in early 2025 as a rideshare to IMAP. |
Planetary Transits and Oscillations of stars (PLATO) | Sun–Earth L2 | ESA | Planned for launch in 2026 for an initial six-year mission. [55] |
Space Infrared Telescope for Cosmology and Astrophysics (SPICA) | Sun–Earth L2 | JAXA, ESA, SRON | As of 2015 [update] , awaiting approval from both Japanese and European side, launch proposed for 2032. [56] |
Advanced Telescope for High Energy Astrophysics (ATHENA) | Sun–Earth L2 | ESA | Launch planned for 2035. [57] |
ESA Vigil | Sun–Earth L5 | ESA | Observatory for early warning of increased solar activity. Launch planned for 2029. |
Sun Chaser [58] | Sun–Earth L4 | — | Observatory for early warning of solar particle events. Early proposal phase. |
Spektr-M | Sun–Earth L2 | Roscosmos | Possible launch after 2030. [59] |
In celestial mechanics, the Lagrange points are points of equilibrium for small-mass objects under the gravitational influence of two massive orbiting bodies. Mathematically, this involves the solution of the restricted three-body problem.
The Jupiter trojans, commonly called trojan asteroids or simply trojans, are a large group of asteroids that share the planet Jupiter's orbit around the Sun. Relative to Jupiter, each trojan librates around one of Jupiter's stable Lagrange points: either L4, existing 60° ahead of the planet in its orbit, or L5, 60° behind. Jupiter trojans are distributed in two elongated, curved regions around these Lagrangian points with an average semi-major axis of about 5.2 AU.
The Interplanetary Transport Network (ITN) is a collection of gravitationally determined pathways through the Solar System that require very little energy for an object to follow. The ITN makes particular use of Lagrange points as locations where trajectories through space can be redirected using little or no energy. These points have the peculiar property of allowing objects to orbit around them, despite lacking an object to orbit. While it would use little energy, transport along the network would take a long time.
In astrodynamics, orbital station-keeping is keeping a spacecraft at a fixed distance from another spacecraft or celestial body. It requires a series of orbital maneuvers made with thruster burns to keep the active craft in the same orbit as its target. For many low Earth orbit satellites, the effects of non-Keplerian forces, i.e. the deviations of the gravitational force of the Earth from that of a homogeneous sphere, gravitational forces from Sun/Moon, solar radiation pressure and air drag, must be counteracted.
The International Cometary Explorer (ICE) spacecraft, was launched 12 August 1978, into a heliocentric orbit. It was one of three spacecraft, along with the mother/daughter pair of ISEE-1 and ISEE-2, built for the International Sun-Earth Explorer (ISEE) program, a joint effort by NASA and ESRO/ESA to study the interaction between the Earth's magnetic field and the solar wind.
The following outline is provided as an overview of and topical guide to space exploration.
In orbital mechanics, a Lissajous orbit, named after Jules Antoine Lissajous, is a quasi-periodic orbital trajectory that an object can follow around a Lagrangian point of a three-body system with minimal propulsion. Lyapunov orbits around a Lagrangian point are curved paths that lie entirely in the plane of the two primary bodies. In contrast, Lissajous orbits include components in this plane and perpendicular to it, and follow a Lissajous curve. Halo orbits also include components perpendicular to the plane, but they are periodic, while Lissajous orbits are usually not.
A halo orbit is a periodic, three-dimensional orbit associated with one of the L1, L2 or L3 Lagrange points in the three-body problem of orbital mechanics. Although a Lagrange point is just a point in empty space, its peculiar characteristic is that it can be orbited by a Lissajous orbit or by a halo orbit. These can be thought of as resulting from an interaction between the gravitational pull of the two planetary bodies and the Coriolis and centrifugal force on a spacecraft. Halo orbits exist in any three-body system, e.g., a Sun–Earth–orbiting satellite system or an Earth–Moon–orbiting satellite system. Continuous "families" of both northern and southern halo orbits exist at each Lagrange point. Because halo orbits tend to be unstable, station-keeping using thrusters may be required to keep a satellite on the orbit.
An Earth trojan is an asteroid that orbits the Sun in the vicinity of the Earth–Sun Lagrangian points L4 (leading 60°) or L5 (trailing 60°), thus having an orbit similar to Earth's. Only two Earth trojans have so far been discovered. The name "trojan" was first used in 1906 for the Jupiter trojans, the asteroids that were observed near the Lagrangian points of Jupiter's orbit.
Aditya-L1 is a coronagraphy spacecraft for studying the solar atmosphere, designed and developed by the Indian Space Research Organisation (ISRO) and various other Indian Space Research Institutes. It is orbiting at about 1.5 million km from Earth in a halo orbit around the Lagrange point 1 (L1) between the Earth and the Sun, where it will study the solar atmosphere, solar magnetic storms, and their impact on the environment around the Earth.
Chang'e 2 is a Chinese uncrewed lunar probe that was launched on 1 October 2010. It was a follow-up to the Chang'e 1 lunar probe, which was launched in 2007. Chang'e 2 was part of the first phase of the Chinese Lunar Exploration Program, and conducted research from a 100-km-high lunar orbit in preparation for the December 2013 soft landing by the Chang'e 3 lander and rover. Chang'e 2 was similar in design to Chang'e 1, although it featured some technical improvements, including a more advanced onboard camera. Like its predecessor, the probe was named after Chang'e, an ancient Chinese moon goddess.
2010 TK7 is a sub-kilometer Near-Earth asteroid and the first Earth trojan discovered; it precedes Earth in its orbit around the Sun. Trojan objects are most easily conceived as orbiting at a Lagrangian point, a dynamically stable location (where the combined gravitational force acts through the Sun's and Earth's barycenter) 60 degrees ahead of or behind a massive orbiting body, in a type of 1:1 orbital resonance. In reality, they oscillate around such a point. Such objects had previously been observed in the orbits of Mars, Jupiter, Neptune, and the Saturnian moons Tethys and Dione.
The ISEE-2 was an Explorer-class daughter spacecraft, International Sun-Earth Explorer-2, was part of the mother/daughter/heliocentric mission. ISEE-2 was a 165.78 kg (365.5 lb) space probe used to study magnetic fields near the Earth. ISEE-2 was a spin-stabilized spacecraft and based on the design of the prior IMP series of spacecraft. ISEE-1 and ISEE-2 were launched on 22 October 1977, and they re-entered on 26 September 1987.
A distant retrograde orbit (DRO), as most commonly conceived, is a spacecraft orbit around a moon that is highly stable because of its interactions with two Lagrange points (L1 and L2) of the planet–moon system.
EQUULEUS is a nanosatellite of the 6U CubeSat format that will measure the distribution of plasma that surrounds the Earth (plasmasphere) to help scientists understand the radiation environment in that region. It will also demonstrate low-thrust trajectory control techniques, such as multiple lunar flybys, within the Earth-Moon region using water steam as propellant. The spacecraft was designed and developed jointly by the Japan Aerospace Exploration Agency (JAXA) and the University of Tokyo.
The Vigil mission, formerly known as Lagrange, is a Space weather weather mission developed by European Space Agency. The mission will provide the ESA Space Weather Office with instruments able to monitor the Sun, its solar corona and interplanetary medium between the Sun and Earth, to provide early warnings of increased solar activity, to identify and mitigate potential threats to society and ground, airborne and space based infrastructure as well as to allow 4 to 5 days space weather forecasts. To this purpose the Vigil mission will place for the first time a spacecraft at Sun-Earth Lagrange point 5 (L5) from where it would get a 'side' view of the Sun, observing regions of solar activity on the solar surface before they turn and face Earth.