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.

Aug 26, 2016 11:34 william@theroses.me.uk Posted on: Breakthrough Initiatives

I have just realised that I don't think it necessary to launch from Earth where they will have to pass through the atmosphere. Why not take them in parts up to the ISS and have astronauts construct them there where they then drop them out of the airlock away from the ISS and when they are far enough away you fire up the laser and get them out of orbit. this would mean they wouldn't have to be as strong.

Aug 26, 2016 15:08 michael.million@sky.com Posted on: Centauri Dreams

We could have a torus balloon go up with steerable lens in the middle which could be used to focus some laser light onto a craft with on-board propellant which carries the light sails into orbit. The laser system could also be used to propel other craft into orbit on non sail launch days, it is this integration with other systems that will aid the whole project immensely. We should not just look at the laser system as a dedicated sail project but how it could be used to aid a lot of space projects at once.

Perhaps you have a separate heading on this site to see how many other projects can be integrated into the design concept, more the merrier, which will ultimately bring down the cost of the system.

Oct 01, 2016 18:18 Stan Evans Posted on: Breakthrough Initiatives

If they were to be launched from earth then why not do so from a position which has a thinner atmosphere, such as higher up or at one of the poles, the latter of which could have to be weighed up against the benefits of launching from near to the equator.

Nov 05, 2016 03:11 Breakthrough Initiatives Posted on: Breakthrough Initiatives

RE:
"Oct 01, 2016 18:18Stan EvansPosted on: Breakthrough Initiatives
If they were to be launched from earth then why not do so from a position which has a thinner atmosphere, such as higher up or at one of the poles, the latter of which could have to be weighed up against the benefits of launching from near to the equator."

Answer:
Our current target systems are only visible from the south pole and significantly out of the plane of the ecliptic. We considered going to the south pole which has many advantages of thin stable atmosphere, good view etc. But it was estimated that the cost would be 2 to 5 times more expensive than placing the array in other locations.

- Avi Loeb, Breakthrough Starshot

Apr 19, 2017 14:08 michael.million@sky.com Posted on: Centauri Dreams

It may be an idea to accelerate out graphene sails using the very reflective heavier sail which is then ejected so that the graphene sail goes on its way to the target star. The graphene layer sail which is doped say with lithium can then behave as a super conducting magsail which allows a large magnetic field to be generated to slow the sail down against the target stars stellar wind. These two processes of mag and photonic braking could potentially allows us more time to view the system, so instead of a fly it could be more like a drive by.

https://www.extremetech.com/extreme/213816-lithium-doping-turns-graphene-into-a-superconductor

Apr 21, 2017 12:50 michael.million@sky.com Posted on: Breakthrough Initiatives

Interestingly Calcium doped graphene (Ca-GIC) shows high reflectance for its weight as well as been superconductive, so it could potentially be used for acceleration by our laser system and allow a slowing down in the target star system.

https://www.nature.com/articles/srep23254/figures/3

https://www.nature.com/articles/srep23254

Apr 28, 2017 09:21 michael.million@sky.com Posted on: Centauri Dreams

Modifying the silicon surface and subsurface looks like it can increase the reflectivity a fair amount over a laser wavelength range that we could use, 1.5 micron, this structure may also be stronger than a solid surface improving the mechanical response to the huge forces that will be applied.

http://www.nanowerk.com/news/newsid=23296.php

This material should also be very light weight as it will be mostly empty space reducing the weight considerably.

Apr 28, 2017 09:43 michael.million@sky.com Posted on: Centauri Dreams

Interestingly it may be possible to use this technique (in link) not only to produce a highly reflective mirror but also to allow the response to be steerable allowing active control of the probes attitude and possibly a communication surface.

http://nanophotonics.eecs.berkeley.edu/research/sweepr/sweepr.htm

https://pdfs.semanticscholar.org/2e8e/6b8e6d22e75a335adee9f171e17f236840b1.pdf

Apr 29, 2017 10:36 michael.million@sky.com Posted on: Centauri Dreams

It looks like silicon wires would be the best means of circuitry, not only can they be made very thin and conductive they will also be very transparent to the laser radiation and so could be used all over the sail. They need only be used once the beamed phase is over to reduce an over heat situation occurring.

Jun 11, 2017 17:24 Robert Clark Posted on: Centauri Dreams

For the solar sail material I want to suggest some adaptations of the transparent carbon nanotube sheets discussed here:

Saturday, April 19, 2014
Economical Space Solar Power Now Possible.
http://exoscientist.blogspot.com/2014/04/economical-space-solar-power-now_19.html

It refers to this research:

Researchers produce strong, transparent carbon nanotube sheets.
Aug 18, 2005
"Strength normalized to weight is important for many applications,
especially in space and aerospace, and this property of the nanotube
sheets already exceeds that of the strongest steel sheets and the Mylar
and Kapton sheets used for ultralight air vehicles and proposed for
solar sails for space applications, according to the researchers. The
nanotube sheets can be made so thin that a square kilometer of solar
sail would weigh only 30 kilograms. While sheets normally have much
lower strength than fibers or yarns, the strength of the nanotube
sheets in the nanotube alignment direction already approaches the
highest reported values for polymer-free nanotube yarns."
http://www.physorg.com/news5890.html

A 1 km square sail weighing only 30 kg, corresponds to 0.03 gm/sq.m. So for the 4m x 4m sail discussed by the Starshot project, it would be a weight of 0.48 gm, which is likely sufficient for a 1 gm scale micro spacecraft.

However, these nanosheets are transparent. We could coat them with aluminum but the 100 nm thick aluminum coating normally put on mirrors would make our sail 4.4 gm. This would slow down our acceleration.

It would be cool if we could use or adapt the transparent nanotube sheets themselves. One possibility is using the fact that nanotube's electronic properties are highly tunable according to the arrangement of the carbon atoms. See for instance:

https://en.wikipedia.org/wiki/Carbon_nanotube#Electrical

https://www.researchgate.net/publication/221922911_Carbon_Nanotube-_and_Graphene_Based_Devices_Circuits_and_Sensors_for_VLSI_Design/figures?lo=1

and:

Atomic structure and electronic properties of single-walled carbon nanotubes.
Teri Wang Odom1, Jin-Lin Huang1, Philip Kim2 & Charles M. Lieber1,2
Nature 391, 62-64 (1 January 1998) | doi:10.1038/34145; Received 10 October 1997; Accepted 26 November 1997
http://www.nature.com/nature/journal/v391/n6662/full/391062a0.html

Then we might be able create lightweight sheets that are instead reflective as a mirror.

Another possibility is that their electronic properties can also be changed by doping. So we may thereby be able to make the sheets reflective.

A different possibility would use them in their transparent form. We would shape the sheets so they act as a lens. Then the collecting area of the sheet would focus the collected light down to a smaller mirror area, thus having a smaller weight which would still have the effect of inducing an acceleration on the spacecraft.

Bob Clark

Comments: 36

Pages:

Please sign in to be able to add new comments.