Launch | Keeping beam pointed on meter-scale lightsail

There are a number of effects that make this task difficult. These include beam instabilities, laser mode issues, differential forces on the sail, differential heating of the sail, and instabilities in the atmosphere induced by the energy of the beam.

The above challenges can be mitigated by spinning the sail, and by shaping both the sail and the beam. Feedback from the sail to the array helps, but the short time of flight requires a self-stabilizing system. The firing time of the beamer is on the order of 10 minutes. During this time the Earth rotates, requiring some beam agility on the order of 2 degrees. Coarse sub-element pointing and fine pointing via phase corrections at the array system can provide beam agility on the order of 30 degrees in order to accommodate various targets.

One promising approach is to shape the sail so that its position on the beam is stable— i.e. the spinning sail itself experiences torques and forces that restore its position and orientation as low-frequency pointing errors move the beam away from the sail’s centroid. High-frequency jitter degrades the overall power imparted to the sail, but the sail’s dynamics limit its susceptibility to such disturbances above a certain bandwidth.

Since a phased array would be used to form the spot, the beam profile could be shaped to maximize the sail’s ability to maintain its own position on the beam without active feedback control.

Comments (22)

  1. Nathan Bemis:

    RE: Apr 04, 2017 22:42 Breakthrough Initiatives

    Thanks again for being responsive to not only myself but all of us who post ideas here.

    The dimple idea comes from not only through fluid but through the air, Mythbusters tested the idea on a vehicle (video provided in main post) and it was successful. I'm not one to know the results of how it would work in a space environment. Which is why I pose the question here. I also try to come up with a solution to minimize the drag a sphere design would have from it's trailing side, perhaps a way to have the drag space occupied or some solution for it to negate drag. The ideas could be far off, and I'm far from knowing the science. Just posing some ideas from an average interested persons perspective.
    Personally I think a sphere design is worth the sacrifice in weight and time. I question how easy it can be to send off a flat target in comparison to a sphere. With a sphere, it doesn't matter how it moves/rotates it should stay on track and easily controlled. Plus then you can use the Coanda Effect with the beam onto the target/s. I know there are pros and cons to it. That goes with everything.

    Reply Noted: Jul 24th
    In the least, it's ideas like that which could provide answers to challenges. I wouldn't know how to control/maneuver the light beam around the craft to encompass it completely nor if a scientific law can be apparent to be made use of. I feel a sphere design could help open those opportunities, of course that comes with it's own set of challenges. Thank you again.

    ***Quick question: With the target craft reflecting the laser beam nearly 100% and it being so powerful. Where is this beam going to be reflected to? Will it be controlled to not hit back on earth or Satellites in space?***

    This may be a petty question, but it would be nice to know.

    If only there was a way to manipulate some of the beam to not only push the craft but also pull the craft on the opposing side. I think this can assist in handling the tremendous GForces that it will be under.

  2. Breakthrough Initiatives:

    Apr 22, 2017 17:54Nathan Bemis Posted on: Breakthrough Initiatives

    While there are certainly some analogies that can be made between fluid mechanics and the optics of the beam-sail system, at the end of the day they are quite different. The Coanda effect is fundamentally fluid-mechanical and doesn’t show up in our case.

    - Zac Manchester, Breakthrough Starshot

Please sign in to be able to add new comments.