Apr 13, 2016 21:11 James Hostetter Posted on: Breakthrough Initiatives

Maybe I'm misunderstanding what this is, but the intensity of a Gaussian beam decreases by a factor of two every Rayleigh length, i.e. pi*waist^2/wavelength. For a 1 micron wavelength beam with a waist of 1 meter, the Rayleigh length is 3*10^6 m, or .01 light-seconds. Unless all of the acceleration is done very quickly, I don't see how the laser array will be effective over two minutes ending at 1/5 the speed of light.

Apr 13, 2016 23:13 Daniel Dugmore Posted on: Breakthrough Initiatives

If I understand correctly, the lasers in the array are coherent and form one very large Gaussian beam (~1km diameter). This beam's waist will be kept at the sail throughout the acceleration process by adjusting the relative phase of each laser to reshape the combined wavefront.

Apr 14, 2016 23:28 Tom Bonofiglio Posted on: Breakthrough Initiatives

Uh, any consequences back on earth of shining a high intensity laser directly at a perfect mirror??

Apr 15, 2016 13:36 Mike Gorman Posted on: Breakthrough Initiatives

I have read that in order to ride the beam effectively, the sail-mirror will likely have to have some convex curvature, so the reflected light would also have a nearby focal point and after that would no longer be collimated; i.e., not a ground hazard.

Apr 18, 2016 12:25 awnd329@gmail.com Posted on: Breakthrough Initiatives

The EHT is a radio telescope in the mm range. There is nothing here to say how a km sized optical phased array would be achieved. Also no mention of the Thinned array curse (https://en.wikipedia.org/wiki/Thinned-array_curse). This needs to be remedied.

Apr 24, 2016 14:05 Mihai Ionescu Posted on: Breakthrough Initiatives

HIGH-POWER LASERS
There are several N x PW (1,000,000 GW) lasers operational in 2016 in the world, like the 2x 10PW ELI-NP laser in Magurele, Romania, the most powerful one built so far (becoming operational this year), the LFEX laser in Osaka, Japan, operational from 2015, which has a power of 2PW, or the Petawatt Laser in Austin, Texas, which is operational since 2008, with a power of 1.1PW. Please note that these PW lasers produce high-energy trains of laser pulses with a duration (of each individual pulse) from 10-20 femtoseconds to 10-20 picoseconds, with pulses fired at a repetition rate of 1-10 KHz. The cost of building a 2x 10PW laser is around $300 million. Another Nx 10PW laser is under construction in Czech Republic, anticipated to become operational in 2018. So, no beam array needs to be purposely built, as ground-based PW laser facilities are available today.

LASER BEAM FACILITIES
Although beam-time could be requested, in principle, at any of these facilities for powering nanocrafts (as for any other scientific program), none of them have any off-atmosphere high-accuracy laser beam targeting equipment available today. Furthermore, the beam-shots timing has to be scheduled depending on clear-sky weather conditions at the respective facilities, as well as on other constraints, like the safety of airplanes or satellites that could intersect the laser beam path (it can destroy such vehicles in flight, something that has already been demonstrated on small drones, with less powerful lasers).

LASER BEAM TARGETING
All these PW laser facilities are located in the northern hemisphere, between 30-50 degrees Latitude, which makes Alpha Centauri not visible from any of them. The best technical solution for powering the nanocrafts could be the use of optical deflector high-accuracy laser beam targeting equipment placed on-board geostationary satellites with fixed position above these locations. This solution reduces to the minimum the atmosphere thickness the laser beam has to go through, allowing the powering of nanocrafts heading towards the Alpha Centauri or any other star system. The cost of launching a geo-stationary satellite is $40-50m, with the cost of the satellite itself around $50-80m.

HEAVIER NANOCRAFTS
The use of laser beams 10,000 times more powerful than initially considered, may allow the use of heavier nanocrafts (in the pounds/kg range), with better reflective solutions for the sail (based on technologies available today), larger sails and improved protection for the main body, allowing similar flight dynamics and performance for nanocrafts heavier than the grams range, initially considered.

THE SOLAR SYSTEM
This solution may even allow the same concept to be used for extending the solar system exploration in an cost-effective way and placing all the planets within days or weeks of travel time reach, for nanocrafts in the pounds/kg weight range, for quick planetary flyby missions.

PW laser facilities websites:
ELI-NP: http://www.eli-np.ro/
LFEX: http://www.osaka-u.ac.jp/en/apru2015/tour/institute-of-laser-engineering
Texas Petawatt Laser: http://texaspetawatt.ph.utexas.edu/

Apr 29, 2016 00:34 themis.chapoul@hotmail.fr Posted on: Breakthrough Initiatives

Sorry miss topic.

May 01, 2016 19:02 orenah@yahoo.com Posted on: Breakthrough Initiatives

Light Beamer Based on technologies of reciprocating laser beam:

Recent analysis of reciprocating laser beam between two carriages with relative velocity reveals some puzzling results regarding the energy transferred from mechanical energy to light energy by wavelength's changes.

Based on this analysis we can postulate building a spaceship with a sail shaped like a retro-reflector and a laser beam station located on the moon surface.

http://www.slideshare.net/OrenAharon2/reciprocating

The above article mentions the following:

"4.1. Propulsion of a Space Shuttle from a Remote Location.

In this case, we need two carriages where one propels the other. Propulsion is achieved by a high energy beam, reciprocating between a ground station and a high speed departing shuttle.
For this application a laser station could be activated from the moon. The laser will be directing its energy to a departing space shuttle equipped with a retro-reflector. Due to the lasers' frequency decaying process, (reciprocation will elongate the lasers' wavelength and thus reduce total beams energy) energy from the laser will be delivered to the space shuttle at a very high rate. The obvious advantage of this arrangement is that the space shuttle does not need to carry fuel.
The same procedure could be used for slowing down incoming objects from space such as a returning shuttle. "

The article shows that laser light energy is transformed into mechanical movement with very high efficiency compared to very low efficiency when using the radiation pressure alone, which is given by:

P = (2Ef \ C )* cos(α)^2 ( N·m−2 or Pa )

where P is pressure, Ef is the energy flux (intensity) in W/m2, C is speed of light in vacuum, α is the angle between the surface normal and the incident radiation. Where Ef (the energy flux) delivers only a small part of the total beam energy to the spacecraft since it is divided by C.

May 01, 2016 19:03 orenah@yahoo.com Posted on: Breakthrough Initiatives

Light Beamer Based on technologies of reciprocating laser beam:

Recent analysis of reciprocating laser beam between two carriages with relative velocity reveals some puzzling results regarding the energy transferred from mechanical energy to light energy by wavelength's changes.

Based on this analysis we can postulate building a spaceship with a sail shaped like a retro-reflector and a laser beam station located on the moon surface.

http://www.slideshare.net/OrenAharon2/reciprocating

The above article mentions the following:

"4.1. Propulsion of a Space Shuttle from a Remote Location.

In this case, we need two carriages where one propels the other. Propulsion is achieved by a high energy beam, reciprocating between a ground station and a high speed departing shuttle.
For this application a laser station could be activated from the moon. The laser will be directing its energy to a departing space shuttle equipped with a retro-reflector. Due to the lasers' frequency decaying process, (reciprocation will elongate the lasers' wavelength and thus reduce total beams energy) energy from the laser will be delivered to the space shuttle at a very high rate. The obvious advantage of this arrangement is that the space shuttle does not need to carry fuel.
The same procedure could be used for slowing down incoming objects from space such as a returning shuttle. "

The article shows that laser light energy is transformed into mechanical movement with very high efficiency compared to very low efficiency when using the radiation pressure alone, which is given by:

P = (2Ef \ C )* cos(α)^2 ( N·m−2 or Pa )

where P is pressure, Ef is the energy flux (intensity) in W/m2, C is speed of light in vacuum, α is the angle between the surface normal and the incident radiation. Where Ef (the energy flux) delivers only a small part of the total beam energy to the spacecraft since it is divided by C.

May 01, 2016 19:03 orenah@yahoo.com Posted on: Breakthrough Initiatives

Light Beamer Based on technologies of reciprocating laser beam:

Recent analysis of reciprocating laser beam between two carriages with relative velocity reveals some puzzling results regarding the energy transferred from mechanical energy to light energy by wavelength's changes.

Based on this analysis we can postulate building a spaceship with a sail shaped like a retro-reflector and a laser beam station located on the moon surface.

http://www.slideshare.net/OrenAharon2/reciprocating

The above article mentions the following:

"4.1. Propulsion of a Space Shuttle from a Remote Location.

In this case, we need two carriages where one propels the other. Propulsion is achieved by a high energy beam, reciprocating between a ground station and a high speed departing shuttle.
For this application a laser station could be activated from the moon. The laser will be directing its energy to a departing space shuttle equipped with a retro-reflector. Due to the lasers' frequency decaying process, (reciprocation will elongate the lasers' wavelength and thus reduce total beams energy) energy from the laser will be delivered to the space shuttle at a very high rate. The obvious advantage of this arrangement is that the space shuttle does not need to carry fuel.
The same procedure could be used for slowing down incoming objects from space such as a returning shuttle. "

The article shows that laser light energy is transformed into mechanical movement with very high efficiency compared to very low efficiency when using the radiation pressure alone, which is given by:

P = (2Ef \ C )* cos(α)^2 ( N·m−2 or Pa )

where P is pressure, Ef is the energy flux (intensity) in W/m2, C is speed of light in vacuum, α is the angle between the surface normal and the incident radiation. Where Ef (the energy flux) delivers only a small part of the total beam energy to the spacecraft since it is divided by C.