Halo Orbit Advantages

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The use of halo orbits instead of lunar orbits for a communication relay constellation provides many powerful advantages:

  • Halo orbits provide good coverage of the lunar far side and poles.
  • Only a few halo orbiters are needed for global coverage.
  • From the Moon's surface, halo orbiters have slow apparent motion for easy antenna tracking.
  • Most halo orbiters will have constant solar illumination for power (no eclipses).
  • Spacecraft can be launched to halo orbits for less ΔV than lunar orbits.
  • Halo orbit dynamics allow for simple autonomous orbit determination.
  • Halo orbit dynamics allow for transfers to other halo orbits or to lunar orbit insertion points for almost no ΔV.
  • A halo orbit constellation could evolve seamlessly from south pole coverage to global coverage.

    Some disadvantages of halo orbits are:

  • Longer communication link distances.
  • Halo orbits are unstable.

    Since more mass can be placed in a halo orbit, the performance of the communications system can be increased to make up for the longer link distances and still save mass. The instability of halo orbits just means that station keeping maneuvers must be performed. For lunar halo orbits, the station keeping budget should only be about 1 m/s/year, which is much less than most lunar orbits. In fact, some lunar orbits are much more unstable than halo orbits due to the extremely asymmetric lunar gravity field.

    The rest of this presentation will provide an in-depth explanation of the low-energy transfers and autonomous orbit determination possible in halo orbits.
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