## Let’s do a Halo Orbit

Let’s do a Halo Orbit

Near the end of my previous post I mentioned Halo Orbit at a Lagrange Point, but presented very little detailed information.

I think the subject is interesting and deserves more space on this blog, so here we go . . .

We have been sending satellites into halo orbits at Lagrange Points since the International Sun-Earth Explorer (ISEE-3) was Launched 12 August 1978 and placed into a Halo Orbit at the Sun-Earth L1 Lagrange Point 20 November 1978 and remained in operation there for a few years.

The ISSE-3 satellite’s needed an unobstructed view of the Sun so the Lagrange point located 1.5 million kilometers away from the Earth is an ideal place for it.

The artist drawing below illustrates ISEE-3 in orbit.

Getting a satellite into a Halo Orbit and/or chasing a comet is a rather complicated precess, as illustrated below . . .

The rocket scientists at NASA have their work cut out for them !

The simplified diagram below illustrates how a more recent satellite, Solar and Heliospheric Observatory (SOHO) was placed into a halo orbit at the L1 Sun-Earth Lagrange Point on 14 February 1996. In the diagram, the L1 point is where the X, Y, and Z axis join together. An artists drawing of SOHO in orbit . . . Halo orbits tend to be unstable because of the “three body problem” – the problem that Newton (the genius who invented calculus) couldn’t figure out. Because of the unstable orbit “stationkeeping” is required to keep a satellite in a halo orbit. This gives Ground Controllers something to do between emergencies.

Here is a paraphrased definition of the “three body problem” that I found in Wikipedia:
[[ The three-body problem is a class of problems in classical or quantum mechanics that model the motion of three bodies or particles. ]]

Enough said – let us move on . . .

I’ll end this post with a quote from Wikipedia:

” A halo orbit is a periodic, three-dimensional orbit near the L1, L2 or L3 Lagrange points in the three-body problem of orbital mechanics. Although a spacecraft in a halo orbit moves in a circular path around the Lagrange point, it does not technically orbit the actual Lagrange point, because the Lagrange point is just an equilibrium point with no gravitational pull, but travels in a closed, repeating path near the Lagrange point. Halo orbits are the result of a complicated interaction between the gravitational pull of the two planetary bodies and the Coriolis and centrifugal accelerations on a spacecraft. Halo orbits exist in many three-body systems, such as the Sun–Earth system and the Earth–Moon system. ”

– – – END of Halo Orbits – – – 