Lightsail | Stability on the beam

Beam shape and lightsail structure should be optimized for stability during the launch phase. In this period, on the order of 10 minutes, an illumination energy of order 1TJ is delivered to the sail. Because of this requirement, very small differences in the properties of the sail, or beam non-uniformities, will shift the center of pressure from the center of mass of the sail and so offset the sail thrust vector.

Because of this, the sail properties and beam properties must be controlled to high precision. These properties include: composition, density, reflectivity, and absorptivity. By modulating the beam modes, get greater uniformity could be attained, and feedback between the nanocrafts and the beamer array would allow real-time adjustments.

Currently, the optics coating industry achieves the required level of control on mass-produced items, with Angstrom-thick tolerance on common items such as cell phones and telescope optics. These manufacturing procedures and approaches are already mature, but the actual sail material is currently not available and will have to be developed. Mitigating approaches also include beam shaping and spinning of the sail to average out slight sail imperfections in its properties.

Research:

Comments (32)

  1. Breakthrough Initiatives:

    Reply:
    Thank you for your comments.

  2. John Weiss:

    Beam-centering should not require any real-time "adjustments" of the beam or the sail. Adjustments of the laser could affect other crafts. Adjustments of the sail consume battery power. If a craft goes off beam, it might never be recovered.

    Instead, the very shape of the sail should force pressure to the correct location on the sail. There's should be no "active" , moving, or power-consuming aspects to beam-stability system. It should be based purely on physical structure of the sail, the craft, and the shape of the beam.

    If a craft were to veer off-beam, the physical structure of the sail and craft should re-center the craft without any moving parts, on the craft or the ground.

    To save power, and avoid radio-delay, beam-lock should not require any craft-to-beam communication.

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