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 13, 2016 03:35 abccbc@cox.net Posted on: Breakthrough Initiatives

A lightsail structure that can approach 10^8 times the volume of the launching payload is described at http://www.niac.usra.edu/studies/1314Crowe.html
and also used in this novel: http://www.amazon.com/Degrees-Book-1-Saving-Earth-ebook/dp/B00UR1Y37S/ref=sr_1_1?ie=UTF8&qid=1426596

Apr 13, 2016 05:33 Robin Ordelheide Posted on: Breakthrough Initiatives

A laser can only go in one direction, and if there is any debris that interrupts the process it would be problematic.... also a postage size vehicle would desintegrate upon impact with a larger asteroid etc.... there would have to be some guidance mechanism in place to ensure it arrives at it's location.

Apr 13, 2016 05:35 Karen Pease Posted on: Breakthrough Initiatives

If you ever want to go larger, I've had a rather crazy concept floating around in my head for a while, but never found the Round Tuit to go simulate it: a RF trap (Paul Trap/quadrupole ion trap) reflector.

Basically, you make your spacecraft as a RF trap, weakly trapping a huge cloud of fine, nanoscale reflective dust. So basically you have a shiny cloud gently pinned to your spacecraft. Any forces transferred to the particles get transferred to the trap.

The fluctuating fields could be combined with a fixed field when thrust is being applied to roughly cancel out the force of the thrust so that you don't have to resist the force with the rather weak net force applied by a basic RF trap.

A beauty part of the use of such a trap is, think of what happens if some of your dust heats up to much. It vaporizes and.... so? It's still ionized particles in a fluctuating field. If it cools... it's just going to condense back to a fine dust.

There's a number of ways one could actively induce ionization, and indeed the particles could even be passively ionized if they're radioactive.

The main issue that I'd need to simulate to figure out is, how light could one make such a trap versus how much cross section of dust could it support? What sort of scaling factor can one get?

Apr 13, 2016 08:42 Dmitry Novoseltsev Posted on: Breakthrough Initiatives

The possibility of producing such material experimentally confirmed. So,
introduced a new application to the non-metallic (including polymeric) materials
functional metallic coatings of different composition of nanometer thickness at a temperature well
below the degradation temperature of the substrate material (which excludes the change in its
operational properties of the surface layer). While this coating possess a wide range of operating
temperatures and elasticity comparable to the elastic substrate. Structure may be formed from advanced nanostructured materials, with
high strength metallic coating which is also a carrier and also increases the mechanical strength of the
web. In principle, it is possible to manufacture blades for technology similar to that used directly in the form of pure metallic high nanofilms which are highly reflective (with separation
or dissolution of the substrate after the sputtering of the coating). (http://spacecolonization.info/issues/issue-8-2014/ ).
Ibid. concerning the construction of the sails and anti-dust (last issue http://spacecolonization.info/issues/issue-4-2015/)

Apr 13, 2016 17:10 Andrew Walker Posted on: Breakthrough Initiatives

Please focus on the structural engineering problems. What are the plausible configurations? Dimensions? Spin speed? Material property requirements? Static and dynamic loads? Deflection requirements?

Apr 14, 2016 06:19 Dmitry Novoseltsev Posted on: Breakthrough Initiatives

Please note the pictures of the Mira star in ultraviolet light, made in the GALEX project.
http://www.galex.caltech.edu/media/glx2007-04r_img07.html
Speed of the Mira –about 130 km/s, but before it is clearly visible the detached shock wave in the interstellar gas.
With low weight and higher speed of our device (almost 600 time) the effect will be much stronger, which will lead, firstly, to intensive braking of the sail immediately after disconnection of the accelerating beam, and secondly, to its rapid destruction.
In this connection I consider it expedient after stage laser acceleration to deploy the sail perpendicular to the direction of flight (edge of course). Then the braking and the wear will be minimal.
If the sail is stabilized by rotation around the axis perpendicular to its plane, with a large enough frequency so that the canvas sails kept rigid and is not formed under the action of force from the oncoming flood, you can provide it with minimal even wear around the perimeter.
In this case, the optimal, apparently, the round shape of the sail.
If the sail of electrically charged, as I suggested earlier, this provides partial protection from positive ion colliding at a small angle to the plane of the sails – they will be leaving.
On approaching the target it is expedient again to deploy the sail perpendicular to the direction of flight is then due to the resistance of the interplanetary gas and the oncoming solar wind can some what reduce the speed and increase the time of observation during the flight.

Apr 14, 2016 16:36 Nemo in Nihilum Posted on: Breakthrough Initiatives

Well, at first, I like Karen's idea.


The second thing would be some questions:

1. How would this kind of "sail" behave, regarding its properties of reflecting the communicationlaser from the craft to earth?
2. Would these particles not scatter the laserbeam, unless we use a frequency with a predominant wave characteristic, or unless we find a way to have the particle dust form a proper surface?
3a. Is there an electromagnetic frequency that we can send as a laser, but has enough wave characteristics to be reflected from a conducting, though not perfect surface, like it were mirror?
3b. And if we come up with such a low frequency laser frequency, would the particles in the trap, stay in the trap, if charged by the reflection of an elmag wave?
3c. Is there a way to operate this trap or a kind of dust to use in it, to gain good enough "reflection" properties to reflect a laser, operating within the usual wavelengths?


4. And last but not least, independent of the questions above, can we move the dust in the trap?
(Well its rather a rhetoric question, but a definite answer of someone who knows that concept well enough to program a simulation, would be prudent.)

To be more specific:
Can we move it in a way, to solve the problem mentioned by Dimitry, without having to implement moving parts (i.e.: move the dust close to the centre in front of the waver, like into a sphere or a spindle form or something else with a small surface in the direction of flight, we also could consider a small solid tip, to protect the tip of this spindle from direct impacts)?


The reason for this last Question is the following, which I would like propose as a DesignMemo:
"Moving parts" have been the undoing of many space probes and vehicles in the past, for which we should try to avoid them where ever possible.




P.s.:
Regarding a spin momentum of the craft, there are several reasons why we should try to avoid it:
1. when we try to steer the craft, we receive nutation,
2. when we fly by the target, we not only have to match the camera to a flyby with 0,2c , we also have to match the camera to the rotation of the craft,
3. moreover the rotation costs us camera or sensor time during the fly by.
4. a rotation would put the construction of the sail under constant stress for decades, while a steady craft would experience no forces for most of the time (except for occasional mini impacts).

P.p.s.:
(Well, alas most articles on Paul Traps are pay to read.... having read up what I found, I retract my P.p.s., although I still think this is a concept to be considered.)


P.p.p.p.s.
@Dimitry:
In retrospective, maybe I misunderstood you.
Why do you expect that the detached shockwave in front of Mira is composed of interstellar gas and that this would be a problem for us? Our craft is way smaller, the sail can be formed slightly pointy, so that gas molecules can be reflected to the side. Moreover, please consider, if the Gas molecules are reflected they will travel faster than our craft and will be moved out of the flight path of our craft, before they are slowed down again.
This should be that way, since our craft is in the magnitude of the density of the interstellar gas, which Mira (being a star) clearly isn't.
Moreover Mira accelerates the interstellar gas before it comes in contact with it, and might thereby create such a bow wave, which in turn our craft will not.

Also, to continue with my rhetoric question above, why do you expect the shockwave to be interstellar gas?
The phenomenon of Mira, seems to be rather unique. Therefore it might be possible that the visible phenomenon is based on matter emanating from Mira or having been emanated from it in the past.

Therefore the more solid question:
Do you have some kind of study on that phenomenon so that we can read up on it's physics and consider if it could impact a small craft like ours?


Apr 14, 2016 18:09 Nemo in Nihilum Posted on: Breakthrough Initiatives

Hm, well, again running into pay to read sites...

May I suggest that as Act 1 of this project, the necessary literature (like the one on top of this site and like literature on interesting suggestions, like Karene's) should be made available to the project's participants?

Personally I cannot (and want not) pay hundreds of dollar, for being able to read up and only by chance being able contribute something significant, on an open source project.

I am sure that, if some prominent people politely ask *looking at the board of directors*, those papers and books on the "Research" site which are not yet openly accessible, might be open to public access (or at least our access) quite soon?

With best regards,
Nemo.


P.s.:
Hm, since this made me consider for a second, I noticed something that I have forgotten in my enthusiasm.
To the initiators of this project:

Thanks guys for putting this up and giving it a kickstart!
And also thank you, for giving the community a chance to prove, that a community driven real world science project can work and does quite better so without political tampering.

Apr 15, 2016 06:14 Dmitry Novoseltsev Posted on: Breakthrough Initiatives

@Nemo in Nihilum

"our craft is in the magnitude of the density of the interstellar gas"

Here is what's confusing me. Reminds us of old school experiences – like falling stone and bird feather in a vacuum and in air. Low-mass sails to a large area of the midsection. As far as I know, solid objects, linearly moving with such speed in interstellar gas, has not been observed (the gas jets of black holes is somewhat different). Serious the problem were not engaged, only the first evaluation.
Perhaps before the main probe will need to run a protective probe – the "bulldozer" to clear the path.

Apr 15, 2016 07:27 Dmitry Novoseltsev Posted on: Breakthrough Initiatives

Yes, I made a small inaccuracy above (14.04.16). For improving the protective shielding effect of the rotating circular corrugated sails with a central position of the payload flying on the edge first, his corrugations to perform better not radial, but curved as the blades of the impeller of a radial pump or fan. Better – with a significant curvature, in this case colliding particles towards the centre of the sail will have to overcome several layers of sail material.

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