Lightsail | Structure

Building a skeleton structure that will be able to hold the sail in shape during launch, be resilient to the interaction with the interstellar medium and potentially be able to modify the shape of the sail, is a major challenge given the gram-scale mass constraint. There are a number of composite graphene-based materials that are being considered. These materials change their length depending on the voltage applied across them. There are also various other materials that could be engineered to meet mission requirements. This challenge is the primary argument for ‘replacing structure with spin’: it has already ben demonstrated that centripetal acceleration of tiny tip masses can pull the sail flat.

Apr 17, 2016 21:27 Gary Camp Posted on: Breakthrough Initiatives

I want to provide a heads up here to "structure system". There are several "integrated systems" inefficiencies I am thinking of that may affect the structure. See my comments in the sections in Battery, Camera, Integrity under thrust.

I will add more as I get to them. JPL ACE

Apr 20, 2016 06:46 Dmitry Novoseltsev Posted on: Breakthrough Initiatives

In order of fantasy.
Best material for flat, corrugated, charged sails flying forward edge, would be Borophene (http://science.sciencemag.org/content/350/6267/1513).
For the future I wonder if in the future to perform the electronic components are directly integrated into Borophene sail.

Apr 29, 2016 20:01 David Palmer Posted on: Breakthrough Initiatives

Re: the interstellar medium.

All calculations are order of magnitude.

The ISM is about 1 atom (typically hydrogen: 1 electron, 1 proton) per cm^3. A light year is 1e18 cm. Therefore each square cm of the spacecraft will be hit by 1e19 particles.

At 20% of c, you can't really think of them as 'gas', but as radiation which will take the form of 10 keV betas (electrons) and 20 MeV protons. (Kinetic energy is 2% of rest mass.)

You will have to look at radiation cross sections to figure out how many particles pass through without interaction, what energy and momentum load you get, whether lattice dislocations will shred your sail, and whether the total accumulated dose will turn your semiconductors into goo.

May 02, 2016 10:25 Dmitry Novoseltsev Posted on: Breakthrough Initiatives

In addition to the previous offers. From March 3 to March 5, 1989 by the Progress-40 spaceship experiment "Crab" on research of disclosure, a shaping, and dynamic characteristics of ring frame large-size designs with a diameter of 20 m, of the TN-1 titan nikelid having effect of shape memory using for disclosure of drives from an alloy has been made. Photos are, for example, in April issue of the "Sci Am" (russian) magazine (4/2016). Similarly it is possible to execute an edge of the rotating disk-type sail about which I wrote earlier. Then at you sails fly an edge forward it will carry out additional protective function.

May 26, 2016 12:22 Mike Gorman Posted on: Breakthrough Initiatives

repeated post:
It is beginning to look very clear that the probe will need to be able to dynamically change the shape of the sail in-order to serve multiple purposes:
1. To alter sail shape as a way of altering its acceleration vector slightly in order to remain on the center of the beam. The shape of the sail would require some kind of servo-control feedback loop managed by the chip that would control the shape of the sail and deform it as necessary to remain accelerating on-beam.
2. To alter the shape during flight so as to minimise damage from incident particles and protect the payload.
3. To alter the shape suitably for acting as a communications dish for sending and receiving laser-based communications with earth.
4. To alter the shape on approach to Alpha Centauri inorder to a achieve some degree of deceleration as a solar sail.
5. To alter the shape to aid the onboard telescope/camera as a telescope reflector.

I think that the need for this ability of the sail to change shape is a key engineering challenge for accomplishing this mission, and is one of the key feasibility aspects that the project should focus on in the near term.

May 26, 2016 15:38 michael.million@sky.com Posted on: Breakthrough Initiatives

Having a dielectric grating that deflects some light to one side will give a centrifugal rotation effect to tension the sail could help.

May 28, 2016 21:54 Mark Cossette Posted on: Breakthrough Initiatives

Ok, I have a slightly crazy idea. What if instead of having the sail and chip seperate, they were combined? The chip hardware could instead take the place of the tip masses mentioned in the topic. This could potentially solve the problem of the chip getting in the way of the laser, as well as reduce the overall mass of the craft. If the chips components were distributed around the perimeter of the spinning sail, they could help pull it flat.

I have no idea if this would work, and am far from qualified enough to figure out the details, but I thought I would throw it out there anyway.

May 29, 2016 02:30 Mike Gorman Posted on: Centauri Dreams

Consider that any spin of a flat sail will provide only a centripetal force/acceleration in the plane of the sail. This acceleration does not oppose the transverse acceleration due to the driving laser. The sail material still has to be stiff enough and with enough tensile strength to oppose deformations due to the laser force which is incident perpendicular to the sail, maximizing the shearing force. How can the sail spin fast enough to provide this kind of flattening tension without itself rippling the sail to shreds (if the laser acceleration does not do it first)? Then, again, how does a flat sail ride the beam without minor perturbations making it slide off to one side or another?
I don't think the flat, spinning sail is feasible.
We need a suitably shaped sail (e.g. parabolic) made of a material that is strong, stiff, and light enough to suit the mission profile.
Other challenges will require the capability to deform the shape of the sail. Possibly through magnetic control of a graphene-based material.

Once we have that answer we should know better where the payload chip or centre of mass is located relative to the sail.

re: research material: Other research and collaboration sites (such as 'Big Now') have made it possible to share copyrighted materials as a library through special licensing and software that allows only a limited number of electronic "copies" to be available at any one time. I suggest that the Breakthrough project might employ this type of system to make the relevant materials accessible to contributors.

Jul 26, 2016 14:51 michael.million@sky.com Posted on: Centauri Dreams

If we use total internal reflection using prisms similar to how fibre optics work we could have a plastic cladding on the back with a very thin metal coating to act as a mirror telescope, MEMS could be used to control the surface shape allowing attitude control as well as deforming the sail to form a telescope/comm surface.

Aug 26, 2016 11:28 william@theroses.me.uk Posted on: Breakthrough Initiatives

If we used a network of carbon nanotubes with ultralight ceramic actuators at he joints where it nedds to move we could run the wires from the actuators inside the carbon tubes and it might work so long as the sail is not too hot.

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