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:

Jan 02, 2017 12:00 michael.million@sky.com Posted on: Centauri Dreams

We could incorporate these MEM's gyroscopes into the design to keep the sail orientated correctly and allowing for on-sail active control.

http://web.mit.edu/ashokaj/www/07_Gyro.pdf

Jan 05, 2017 02:28 Breakthrough Initiatives Posted on: Breakthrough Initiatives

RE:
"Dec 06, 2016 08:30 michael.million@sky.com Posted on: Centauri Dreams
The 2D laser can be made very, very small
http://newscenter.lbl.gov/2015/10/20/exciting-breakthrough-in-2d-lasers/
If we use pyramids taking advantage of the total internal reflection principle we could reduce the mass down quite a bit, the material between the pyramids can be a polymer to aid flexibility, lower weight and can be coated with a reflective metal to act as a telescope with a high surface area. With the light sensitive control sensors they can distributed around the sail surface and locally electrical connected to a nest of reflectivity/transparency control pyramids (truncated) which would minimise weight."

Answer:
Thank you for your help in this matter. It is not clear that a pyramid shape is a stable shape or meets the needs of the material requirements.

- Pete Klupar, Breakthrough Starshot

Jan 05, 2017 16:02 michael.million@sky.com Posted on: Centauri Dreams

The beauty of this miniaturisation is that it can be tested in labs without the need for great expense.

Jan 07, 2017 20:30 michael.million@sky.com Posted on: Centauri Dreams

'Thank you for your help in this matter. It is not clear that a pyramid shape is a stable shape or meets the needs of the material requirements.'

Pyramids offer total internal reflection benefits and lower mass than say a 40 layer dielectric mirror for the same thickness, the pyramids can also be stabilised by having 'diamond' CVD bridges upon which nanotube 'perhaps capillary metal filled' can be used for electrical communications. Although the nanotubes themselves could add to the stiffening of the structure.

Jan 07, 2017 23:51 michael.million@sky.com Posted on: Centauri Dreams

What is interesting is using this capillary action to join nanotubes together, we could make much larger nanotubes to string our device together and use it for circuitry. If we had two nanotubes touching the metal/material bead and it is then heated to melting point both nanotubes will pull the material into their tubes and bring the nanotubes very close together. If a catalyst material is used or it may even be hot enough they will join together to form a longer nanotube which would make a great building material.

http://www.nanowerk.com/spotlight/spotid=6371.php

Feb 02, 2017 18:53 Breakthrough Initiatives Posted on: Breakthrough Initiatives

RE:
"Jan 07, 2017 23:51 michael.million@sky.com Posted on: Centauri Dreams
What is interesting is using this capillary action to join nanotubes together, we could make much larger nanotubes to string our device together and use it for circuitry. If we had two nanotubes touching the metal/material bead and it is then heated to melting point both nanotubes will pull the material into their tubes and bring the nanotubes very close together. If a catalyst material is used or it may even be hot enough they will join together to form a longer nanotube which would make a great building material.

http://www.nanowerk.com/spotlight/spotid=6371.php";

Answer:
Thank you for your consideration. This is a great idea, uncertain how it applies to the stability issue.

- Pete Klupar, Breakthrough Starshot

Mar 12, 2017 10:07 michael.million@sky.com Posted on: Centauri Dreams

'Answer:
Thank you for your consideration. This is a great idea, uncertain how it applies to the stability issue.

- Pete Klupar, Breakthrough Starshot'

The nanotubes can be used to pull the surface into different shapes allowing attitude control and comm's dish changes.

Mar 21, 2017 18:48 Breakthrough Initiatives Posted on: Breakthrough Initiatives

RE:
Mar 12, 2017 10:07 michael.million@sky.com Posted on: Centauri Dreams

Answer:
Thanks for your input. Yes, nanotubes maybe the enabling technologies we require.

- Pete Klupar, Breakthrough Starshot

Sep 10, 2017 03:37 jreed440@gmail.com Posted on: Centauri Dreams

If the light sail were increasingly transparent toward the outer edges, would this not force the craft to follow the beam? for instance, if the sail were 1 foot round and the beam 1 inch.........
The theory being less thrust is imparted at the periphery and more at the center making it hard to get off beam?
maybe a precise beam would be more effective originating toward the darker side of the moon or some such?

Sep 21, 2017 20:43 Nathan Bemis Posted on: Breakthrough Initiatives

jreed440,

I was thinking they could use the laser to control a sphere designed craft and control it with the laser like an ice cream cone holds the ice cream. (only the cone (laser) would have contact with the whole craft (scoop)), having the laser energy gradually be stronger towards the outer rim of the craft. I think this cone control idea would be great if they decide to go with a sphere design. A flat faced target would require an insane amount of calculation, programming, and perhaps luck to figure out for a reliable control setup. I imagine it like trying to fly a kite and have it hold position perfectly on a windy day.

I disagree with your example of pushing the sail with it focused on the center and neglecting the rest. One thing for example is that the area you are hitting with the laser will be under 60,000 G-Forces, while the rest of the craft would be under no pressure. The result would be like a bullet hole through the middle. Secondly, Say the craft could stay together and the laser was to be focused on the center. I think the result would be as if you were balancing a ball on your finger.

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