Halo orbit

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Halo orbit around the Lagrange point L 2 of the Earth-Moon system

In a three-body system, a halo orbit is an orbit around one of the unstable Lagrangian points  L 1 to L 3 , which - in contrast to a Lissajous orbit  - is approximately periodic . The Lagrange point is mostly circled in an orbit outside the plane of the orbit, so the orbits are not coplanar . The object therefore orbits the Lagrange point in the course of time on many slightly different orbits. This sphere , the halo , gives the orbit its name. Since the path is not stable, regular correction maneuvers are necessary.

Around the stable Lagrange points L 4 and L 5 , objects can also remain in a Halo or Lissajous orbit completely without a drive.

The designation Halo-Orbit goes back to Robert W. Farquhar, who in 1966 suggested placing a relay satellite in an orbit around the L 2 point of the earth- moon system in order to make radio contact with the back of the moon in this way To enable Apollo spaceships . However, these plans were not implemented.

The first mission on a Halo orbit was the ISEE-3, launched in 1978 . In the 1980s, Kathleen Howell, a professor at Purdue University in Indiana , USA, showed that Farquhar's analytical considerations could be improved numerically . As a result, numerous other missions were stationed in Halo orbits, e.g. B. the solar observatory SOHO (1995, around L 1 ), Genesis (2001, also around L 1 ), Herschel (2009, around L 2 Earth-Sun), as well as Queqiao (2018, L 2 Earth-Moon) and Spektr-RG (2019, L 2 Earth-Sun).

literature

  • Gérard Gómez et al: Dynamics and mission design near libration points. World Scientific, Singapore 2001, ISBN 978-981-02-4285-5 .

Individual evidence

  1. ^ Robert W. Farquhar: The control and use of libration-point satellites. Dissertation, Stanford University, 1968 ( online ).
  2. ^ KC Howell: Three-Dimensional, Periodic, 'Halo' Orbits. In: Celestial Mechanics. Vol. 32, No. 53, 1984.
  3. ↑ Luyuan Xu: How China's lunar satellite relay arrived in its final orbit. In: The Planetary Society. June 25, 2018, archived from the original on October 17, 2018 ; accessed on December 8, 2018 .