Light Beamer | Atmosphere

The atmosphere introduces two effects: absorption (or ‘reduction of transmission from unity’), and loss of beam quality (or ‘blurring of the beam spot’). The transmission of the atmosphere at a wavelength of 1 micron is extremely good, exceeding 90% at high altitude ground-based sites. Going to a high altitude site also significantly reduces atmospheric blurring, which would allow an adaptive optics system to achieve performance near to the diffraction limit.

The effects of atmospheric turbulence on the beam include a broadening of the beam footprint (equivalent to image blurring for telescope observations), random jitter of the beam spot, and intensity fluctuations (or ‘scintillations’). The blurring depends on turbulence and wind profile in the atmosphere. The turbulence amplitude is reduced by a factor of approximately 4 between sea level and an altitude of 5km.

The quality of an image is measured by the Strehl ratio, which reflects the ratio of the peak image intensity from a point source to the diffraction limit of an ideal optical system. The ratio measures phase deviations caused by lens aberrations and atmospheric turbulence. 10m-class telescopes, such as the Large Binocular Telescope (LBT), comprising two 8.4m telescopes, have demonstrated image resolution of 40 milliarcseconds and Strehl ratio of 80% at a wavelength of 1.6 microns.

Breakthrough Starshot aims to achieve the diffraction limit for an optical system of laser beams across 0.2-1km, which is 1-2 orders of magnitude beyond existing demonstrations. There are no fundamental physics limitations to achieving this improvement. A beacon on the nanocraft or near its launch point (for instance on the mothership) could be used to correct for phase variations in real time. The effect of the light beam on the atmosphere could be studied, and corrected for, by adaptive optics, again in real time. Additional beam focusing may also be explored to reduce the beam spot size using pulsed laser filamentation techniques.

Apr 12, 2016 21:22 Jasper Cooremans Posted on: Breakthrough Initiatives

This is probably way to soon to be possible and this also is out of my field of knowledge as a student electromechanical engineering but I've been thinking if it would be a possibility to have an adittional beam site on Mars next to the sites on our planet. The problems regarding diffraction and absorption will probably be less present because of Mars's athmospheric conditions and it may offer a possibility to adjust the heading of the spacecraft(s). If we will start to send manned missions to Mars and possibly start colonizing Mars this could become a real possibilty if the energy capacity needed to power the light beam, the equipment needed to build the site, construction of the site etc. is possible to provide, supply and execute on Mars. Again this is just an idea I had. I have little knowledge about space missions and all the things that are involved with that except for some material and mechanical properties maybe and some physics principals. I also have not really an idea about the chances of this being possible my only aim is to offer some help even if it's useless I still can possibly learn from this and that is as valuable as actually contributing to a solution to me. My apologies for any grammar or spelling errors English is not my native language.

Apr 12, 2016 22:28 Mark Warman Posted on: Breakthrough Initiatives

This may have been considered already, and would (obviously) have an impact on cost (i.e. increasing it), but surely putting the laser array in orbit would have a massive positive impact on eliminating the atmospheric impact on the laser, along with powering the array (a large solar cell array directly could be placed out of the line of fire, and since the array could be fine tuned in pretty much any direction needed wouldn't even get in the way), and cooling of the array as well (both by means of shadow of the solar cell array and by being able to dump excess heat directly into space)? Or would the cost of placing both the solar array and the laser array outweigh the cost of building the array on the surface of the Earth (where we'd also be at the mercy of the earths rotation as to the problem of aiming the beam array)?

Apr 12, 2016 23:26 Luke Dale Posted on: Breakthrough Initiatives

I would be very interested in an answer to Mark Warman's question regarding placing the laser array in orbit, rather than beneath the atmosphere - is it a matter of scale and cost?

Apr 12, 2016 23:26 Derek Motloch Posted on: Breakthrough Initiatives

launch something in orbit around Earth or on the Moon to focus the beam at the crafts.

Apr 12, 2016 23:28 Derek Motloch Posted on: Breakthrough Initiatives

Or, use our Sun's energy in the vacuum of Space and focus it, never touching our Atmosphere.

Apr 13, 2016 00:00 Posted on: Breakthrough Initiatives

I'd support Derek Motlochs remark: Use the sun's energy with giant lenses and mirrors. You can use these for quite a long time until the probe is really far away (and sped up considerably).
Robert Forward has written about this 25 years ago.

Apr 13, 2016 08:23 Rj Hillan Posted on: Breakthrough Initiatives

Placing a Laser array in orbit would be the best solution to avoid atmospheric turbulence. Also it would allow the Laser array to accelerate the Nano craft more easily than with the array being placed on the moon.
However the cost of such an array would be staggering. The array would cost millions of not billions more; accounting for the cost of launch vehicles (possibly cheaper for SpaceX's reusability), but also maintenance and assembly by astronauts (you will most likely need astronauts for assembly, definitely if you must make adjustments or repairs).

If granted enough money, creating a powerful light array in earth orbit would definitely be the best option. However that will bring many other challenges, financial and technological.

Apr 13, 2016 11:42 Mark Warman Posted on: Breakthrough Initiatives

@Rj Hillian

I'm not so sure the cost would be as bad as you suspect. As you've mentioned, the SpaceX project could well be the way to go for the initial leap to orbit, and yes, that's still going to cost on a per trip basis. However, with the current state of miniturisation, the array could simply be formed of multiple modules with a very small payload per (probe sized) module and assembled in orbit into a single large array - Starshot are already discussing sending small lasers with the actual (probes? Starships? What do we call these?), why not build an array out of those lasers in orbit, where we've currently got a fair amount of real-estate to build in (and so issues like available land mass become null). Plus, the technological advance needed to build that array could also be used at the other end - if the probes are capable of forming up into a single mass at the other end, the possibilities become endless. Plus, if it can be constructed out of modules that are reasonably small/cheap to manufacture (at least in the same quantities as the probes themselves) it essentially becomes self maintaining, assuming we can get the modules to the array.

I agree, there's going to be an initial large cost involved for maintenance (and possibly ongoing - see above). But is that really going to be more than the benefits? Again, with the current rate of progress, being able to send a team up for maintenance duty (already possible - we've got long term experiments going on with the ISS) and the required developments in space suit tech, orbital habitat tech etc, are going to have far reaching positive impacts. Not to mention that wherever the array is built, there are going to be maintenance concerns; at least if the engineer has to be a qualified astronaut we know for certain that they have the level of skill needed to actually perform maintenance (cynical I know, but if it's built on Earth then unless you're really on top of personnel, mistakes can and will be made...;) ). Also to be considered: we built a damn great telescope in space, and it's still usable (so far as I know).

My point here is we've still got to be thinking long term at this stage. If we *can* make steps on the path, then we *should* and the financial concerns shouldn't be considered an issue from the perspective of progress, otherwise we'll never get there. Technological concerns are going to need to be surpassed at some point anyway, so why not now? We can already put payloads in orbit, so that's not really a concern any more. Any challenges are simply that, challenges and not problems.

Apr 13, 2016 19:01 Jasper Cooremans Posted on: Breakthrough Initiatives

@ Mr. Warman

Placing the laser in orbit would indeed be the easiest and best solution but I'm concerned about the scale of the device and the energy needed to power it. They were talking about lasers up to 100 gigawatts which is a huge amount of energy to supply. Solarcells would be the best solution but assuming they have solar panels available that can produce 1 MW then they'll need 100 000 panels to be able to power the beam (assuming they want to be able to use the beam at all times and for a certain amount of time).

If you take a look at nuclear energy production the most recent reactors can produce about 1,3 to 1,5 GW we would still need between 67 and 77 reactors to be able to provide 100 GW. Storing the energy and wait until you produced 100 GW is to me at least not really an option either because there is simply no way of doing that for these proportions of energy. Does anybody have an idea or a suggestion to be able to provide this much energy for a device that is in orbit around the earth (apart from fusion technology)?

Apr 13, 2016 20:17 Michael Noble Posted on: Breakthrough Initiatives

Breaking the barrier of Interstellar travel in this way is a great idea, and could create many amazing opportunities, thank you for the vision and the open communication

Would it be simpler to create a two step process, with a main plant on earth that focused on a fixed space based unit that "bounced" the signal directly at the nano units, without earth based interference.

This would reduce the space construction and maintenance costs as it would be a simple focusing unit, we have been using earth built satellites with no maintenance for decades to bounce a signal, why not a focused laser beam

This would also allow for simpler powering up as the space based array would be stable and atmospherically "fixed" to the ground based power supply, but also allow for precision aiming at the nano unit, even at a farther distance for slight course corrections and instructions

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