A halo orbit of the Sun refers to a special type of three-dimensional, periodic orbit around one of the Sun-Earth system's Lagrange points, specifically L1, L2, or L3. These orbits are non-planar and form a "halo" shape around the Lagrange point, which itself is a point of gravitational equilibrium in the three-body system of the Sun, Earth, and a spacecraft

. Key characteristics of a Sun halo orbit:

• It is associated with the L1, L2, or L3 Lagrange points in the Sun-Earth system, located roughly 1.5 million kilometers from Earth along the line connecting the Earth and the Sun

• The orbit is periodic and three-dimensional, typically with an orbital period of about 177 to 180 days

• The orbit is not stable on its own, so spacecraft require periodic station-keeping maneuvers to maintain position

• Halo orbits allow continuous, unobstructed observation of the Sun, as the spacecraft remain in a fixed relative position with respect to Earth and the Sun, outside Earth's magnetosphere

• The dimensions of such orbits can be extensive, with semi-diameters on the order of hundreds of thousands of kilometers in different directions around the Lagrange point

Applications:

• Scientific satellites like the SOHO solar observatory, Aditya-L1, and the James Webb Space Telescope use halo orbits around Sun-Earth Lagrange points to maintain a stable vantage point for observations

• These orbits minimize fuel consumption for station-keeping and provide a stable environment for continuous solar observation

In summary, a halo orbit of the Sun is a periodic, three-dimensional orbit around a Sun-Earth Lagrange point, enabling spacecraft to maintain a stable position for solar observation with minimal fuel usage, despite the orbit's inherent instability requiring occasional corrections