A halo orbit is a periodic, three-dimensional
orbit
In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as ...
near one of the L
1, L
2 or L
3 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
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 without requiring any propulsion. Lyapunov orbi ...
or 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
In Newtonian mechanics, the centrifugal force is an inertial force (also called a "fictitious" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It is directed away from an axis which is paralle ...
on a spacecraft. Halo orbits exist in any three-body system, e.g., a
Sun–
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...
–orbiting satellite system or an Earth–
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
–orbiting satellite system. Continuous "families" of both northern and southern halo orbits exist at each Lagrange point. Because halo orbits tend to be unstable,
stationkeeping may be required to keep a satellite on the orbit.
Most satellites in halo orbit serve scientific purposes, for example as
space telescopes.
Definition and history
Robert W. Farquhar first used the name "halo" in 1966 for orbits around L which were made periodic using thrusters. Farquhar advocated using spacecraft in such an orbit beyond the Moon (Earth–Moon ) as a communications relay station for an
Apollo
Apollo, grc, Ἀπόλλωνος, Apóllōnos, label=genitive , ; , grc-dor, Ἀπέλλων, Apéllōn, ; grc, Ἀπείλων, Apeílōn, label=Arcadocypriot Greek, ; grc-aeo, Ἄπλουν, Áploun, la, Apollō, la, Apollinis, label= ...
mission to the
far side of the Moon. A spacecraft in such an orbit would be in continuous view of both the Earth and the far side of the Moon, whereas a Lissajous orbit would sometimes make the spacecraft go behind the Moon. In the end, no relay satellite was launched for Apollo, since all landings were on the near side of the Moon.
In 1973 Farquhar and Ahmed Kamel found that when the in-plane amplitude of a Lissajous orbit was large enough there would be a corresponding out-of-plane amplitude that would have the same period, so the orbit ceased to be a Lissajous orbit and became approximately an ellipse. They used analytical expressions to represent these halo orbits; in 1984,
Kathleen Howell showed that more precise trajectories could be computed numerically. Additionally, she found that for most values of the ratio between the masses of the two bodies (such as the Earth and the Moon) there was a range of stable orbits.
The first mission to use a halo orbit was
ISEE-3
The International Cometary Explorer (ICE) spacecraft (designed and launched as the International Sun-Earth Explorer-3 (ISEE-3) satellite), was launched 12 August 1978, into a heliocentric orbit. It was one of three spacecraft, along with the ...
, a joint
ESA and
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeedin ...
spacecraft launched in 1978. It traveled to the Sun–Earth point and remained there for several years. The next mission to use a halo orbit was
Solar and Heliospheric Observatory (SOHO), also a joint ESA/NASA mission to study the Sun, which arrived at Sun–Earth in 1996. It used an orbit similar to ISEE-3. Although several other missions since then have traveled to Lagrange points, they (eg.
Gaia
In Greek mythology, Gaia (; from Ancient Greek , a poetical form of , 'land' or 'earth'),, , . also spelled Gaea , is the personification of the Earth and one of the Greek primordial deities. Gaia is the ancestral mother—sometimes parthen ...
astrometric space observatory) typically have used the related non-periodic variations called
Lissajous orbit
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 without requiring any propulsion. Lyapunov orbi ...
s rather than an actual halo orbit.
In May 2018, Farquhar's original idea was finally realized when China placed the first communications relay satellite,
Queqiao, into a halo orbit around the Earth-Moon point. On 3 January 2019, the
Chang'e 4 spacecraft landed in the
Von Kármán crater on the far side of the Moon, using the Queqiao relay satellite to communicate with the Earth.
The
James Webb Space Telescope entered a halo orbit around the Sun-Earth point on 24 January 2022.
See also
*
Interplanetary Transport Network
*
Interplanetary spaceflight
*
Lissajous orbit
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 without requiring any propulsion. Lyapunov orbi ...
, another Lagrangian-point orbit which generalizes halo orbits.
*
Near-rectilinear halo orbit
*
:Spacecraft using halo orbits
*
Libration point orbit In orbital mechanics, a libration point orbit (LPO) is a quasiperiodic orbit around a Lagrange point. Libration is a form of orbital motion exhibited, for example, in the Earth–Moon
The Moon is Earth's only natural satellite. It is t ...
References
External links
SOHO - The Trip to the L1 Halo OrbitLow Energy Interplanetary Transfers Using Halo Orbit Hopping Method with STK/Astrogatornbsp;— a Lissajous-type orbit, ''i.e.'', a near-circular ellipse or "halo"
{{DEFAULTSORT:Halo Orbit
Three-body orbits
Trojans (astronomy)
Lagrangian mechanics