Halo orbit

Halo orbit

From the Moon to Mars

Published in Jonathan Allday, Apollo in Perspective, 2019

The Solar and Heliospheric Observatory (SOHO, 1996) and Advanced Composition Explorer (ACE, 1997) solar observational satellites are in halo orbits about the Sun–Earth L1 point. Although they are required to adjust their orbits from time to time, both have enough propellant left to operate into the 2020s. Also, NASA's plans for replacing the Hubble Space Telescope with the James Webb Space Telescope will place the new observatory in a halo orbit about the Sun–Earth L2 point facing away from Earth, so that it does not have to contend with solar glare.

Robust control of the circular restricted three-body problem with drag

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Journal Information

Published in International Journal of Control, 2022

David J. N. Limebeer, Deon Sabatta

Halo orbits are used by man-made spacecraft to maintain line-of-sight contact with the Earth. These orbits are usually modelled in the context of a CRTBP (Szebehely, 1967). As is well known, the CRTBP describes the motion of a body of small mass, subject to the gravitational attraction of two massive (primary) bodies that are in a circular motion around their mass centre. The circular rate is governed by Kepler's third law. In its classical form, the CRTBP analysis identifies five points in space, called Lagrange points, where small objects maintain their position relative to the two larger bodies – at the Lagrange points, the gravitational and centripetal forces cancel. These five points are usually labelled to . The points , and are on the line joining the centres of the two primary bodies and thus referred to as the collinear Lagrange points. Points and form equilateral triangles with the primary bodies. All five points are in the orbital plane.

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From the Moon to Mars

Robust control of the circular restricted three-body problem with drag