I Light beam propulsion without lasers?

Tags:
1. May 19, 2017

RobertGC

We now have the capability to do laser launch. The problem is the initial cost outlay for the lasers is still prohibitive to launch a sizable payload.

The estimate of the payload you can launch to Earth orbit dependent on laser power is about 1 kg per megawatt. So to launch thousand kilo payloads would require a gigawatt laser power levels. At current prices this would cost billions of dollars.

But is it possible to do it without using lasers, just using high intensity noncoherent light focused by mirrors or lenses?

I wondered about this because of two reports I saw doing a web search actually on optical communication:

InfiniLED MicroLEDs achieve 300 W/cm2 output density from tiny source. The MicroLEDs semiconductor manufacturing process includes construction of a parabolic reflector to enable optimal light control and high efficiency from micro-meter-sized LEDs. Published on:Jan 29, 2013 By Maury Wright
http://www.ledsmagazine.com/article...up-2-sup-output-density-from-tiny-source.html

and:

Optical communications using coherent and non-coherent light.

The first report discusses micro-scale LED's whose light output scales up to 300 W per square centimeter, 3 megawatts per square meter. From the appearance of these micro-scale LED's, they should permit simple automated production to produce many copies to cover a macro-scale area to generate light even at gigawatt power levels.

The second report discusses experimentation that suggests atmospheric dispersion is actually worse for lasers than for noncoherent light generated by LED's. See for instance the video in Fig. 2 on this page.

The advantage of the lasers however is that generating a parallel beam, you can use a parabolic mirror to focus the light at the focal point (more precisely at the Airy disk). Still, nevertheless a parabolic mirror will still focus a large portion of the light at the focal point even for noncoherent light.

So the question is if the beam is noncoherent, how much of the light can still be focused at the focal point (Airy disk)?

Bob Clark

Last edited: May 19, 2017
2. May 19, 2017

Staff: Mentor

That sounds like a fun project.

1. Would you vary the focus dynamically as the distance to the vehicle gets larger?
2. Your post makes it sound like you have done the calculations $watts/m^2$ and $/watt, and found them to be OK. Now you are just asking about technical obstacles correct? 3. May 19, 2017 BvU I could only find in the link you provided. They don't say you can fill a surface area with the things. In fact, the indicates you can not. 4. May 19, 2017 RobertGC Wow! Thanks for that catch, BvU! I completly missed the part about the beam being collimated. If the beam is collimated, the light rays would be parallel and your mirror or lens would still focus the light to the focal point anyway. The report says this is an intermediate propagation mode than an actual laser, but you only need collimation for this proposal anyway: The MicroLED is built using an LED semiconductor structure and can be driven like standard LEDs. But the manufacturing process, which includes etching of a parabolic reflector at the semiconductor level, delivers a collimated beam like a laser (see the parabolic structure in the nearby photo). The result is both high-intensity light and high efficiency. "This device can be seen as a cross-over between the power and collimation of a laser and the simplicity of an LED. The unique devices enable a range of applications," said chief commercial officer of InfiniLED, Bill Henry. "InfiniLED are proud to have achieved the landmark performance of optical density greater than 300 W/cm2. This was achieved without the need for external optics indicating the potential for further improvement of the performance." If the only thing you needed was a high power beam for a particular application, then you wouldn't need the total beam to be collimated. But that depends on how much light would be lost from a non-collimated beam. However, I found this on the question producing a collimated beam anyway: Collimated light. https://en.wikipedia.org/wiki/Collimated_light It mentions a device called a "collimator" is able to produce collimated light anyway. There would still be the question of how much light would be lost by the collimator. Another key question though about the MicroLED is how much the degree of collimation can be maintained when the pattern is repeated to produce a larger area. If the degree of collimation remains high then you wouldn't need an external collimator and the question about the lack of focusing without using a laser becomes moot. Note also my actual web search was about optical communication. Then the high intensity collimated light produced by the MicroLED would have applications to that as well Bob Clark Last edited: May 19, 2017 5. May 19, 2017 RobertGC To be precise the 1 mW of radiant power from a single 20-µm mentioned in the article scales up to 250 watts per square cm. The authors of the report may simply have rounded off to a single significant digit when reporting it as 300 W/cm2. There is a technical question about the MicroLED about how well the process scales up, but anyway the non-coherent source doesn't have to be the MicroLED. It just provides a means of generating an intense beam in a small space. The technical obstacle I originally asked about was how well a mirror or lens could focus a non-coherent source. It may turn out this is a moot question anyway because there are means of producing a collimated beam anyway, which is what we really need not necessarily coherent. Bob Clark 6. May 19, 2017 BvU Another (much more likely) possibility: the 20 $\mu$m is the diameter of a circular spot 7. May 19, 2017 RobertGC Yes. I think that's right. Bob Clark 8. May 19, 2017 anorlunda Staff: Mentor There are lots types of collimators, and lots of papers about reducing the losses. Just google "collimator losses" Are you sure that the MicroLEDs are cheaper than lasers? I assume that the 1GW number you quoted for the lasers is the light power, not including power losses. I tried looking up some numbers. MicroLED is said to be a bit better than OLED. An OLED TV screen consumes up to 300w (Probably 99% of that is losses and only 1% light, but let me assume 0% heat loss and 100% light). That's 33 million TV screens for 1GW of light power. At$100 each, that is $3.3 billion. Granted that my back-of-the-envelope calculations can be way off, but it sounds like you need $10^3$ to $10^5$ lower costs to make it much cheaper than lasers. Don't forget the cost of cooling to get rid of waste heat and the cost of a 1GW power connection to the utility power distribution. You don't need a 1GW pulse, you need 1GW continuous. (1GW for 100% efficient or 100GW connection for 1% efficient). A typical distribution substation capacity is about 125 MW and a typical nuke power plant makes about 1GW electric. So let me repeat my question from #2. Have you done the$/watt of emitted light calculations for MicroLED?

9. May 19, 2017

Now $10 billion for a reusable launch system is not crazy. Rockets are very expensive and they are not reusable (unless you are SpaceX). A light-based launch system could send many payloads per hour. Rockets can't easily match that. However, the cost difference between lasers and microLED seems minor compared to the scale of the whole project. 11. May 19, 2017 RobertGC Doing some web searching the prices I've seen for lasers are in the range of$15 per watt of laser output power, and above. So regular LED's would still be less than this.
Some references also give the LED conversion efficiency as high as 80%.

Bob Clark

12. May 19, 2017

davenn

do we ??
do you have some reputable references for that please

13. May 21, 2017

RobertGC

The standard reference on laser launch is by Jordin Kare:

Modular Laser Launch Architecture: Analysis and Beam Module Design.
Final Report
USRA Subcontract Agreement No. 07605-003-015
30 April 2004 Revised 18 May 2004
Dr. Jordin T. Kare
Kare Technical Consulting
908 15th Ave. East jtkare@****.***
Seattle, WA 98112 206-323-0795
http://www.niac.usra.edu/files/studies/final_report/897Kare.pdf

The estimate there is 1 kg in payload to orbit per megawatt laser power. Quite key is the fact discussed in the report you can combine separate lasers to get a high power beam for larger payloads.

The Navy has already tested ship-borne lasers at 30 kW power to shoot down
drones:

US Navy Laser Blasts Drone Out Of The Sky.
Published on Dec 11, 2014
"A laser weapon tested for four months by the US Navy can blast drones out
of the sky in seconds."

And a more powerful 150 kW laser is expected to be able to shoot down larger
aircraft:

US Navy will fire 150 kilowatt laser on a test ship in 2018 and then from
carriers and destroyers in 2019.
brian wang | January 26, 2017 |
http://www.nextbigfuture.com/2017/01/us-navy-will-fire-150-kilowatt-laser-on.html

The U.S. Army also expects to field a laser carried by trucks at 60 kW power:

US Army gets world record-setting 60-kW laser | Latest News Updates Today.

About the cost, one of the producers of 10 kW commercial lasers, used for example in laser cutting and welding, gave a price of $472,000. So a thousand would be$472 million for a total power of 10 MW, though for such a large order the price would likely be significantly discounted from this.

According to the standard estimate this could launch 10 kg to orbit. This is small but might be used to launch say propellant to orbit since most of the mass for destinations beyond low Earth orbit is just propellant.

Bob Clark

14. May 21, 2017

davenn

it's only a concept ... not an actual working system

that's irrelevant to the discussion other than the power levels that have been obtained
so you have a 1`MW laser pointing down out of the launch vehicle .... what do you think is going to happen to the Launchpad/ ground etc below the laser ??

15. May 21, 2017

RobertGC

The importance of the Jordin Kare research is that the theory showed that you can combine many of the lasers to get one large beam. This has been confirmed with the U.S. Army's 60 kW laser weapon that is formed by combining separate laser beams.

So you could get over a 1 MW beam by combining 20 of the Army's 60 kW beams. The development cost would be prohibitive however for only delivering about 1 kg to orbit.

Bob Clark

16. May 23, 2017

Dr_Zinj

Still a problem. Neither the Navy ship-borne laser, nor the Army truck-borne one are capable of operating continuously for the period of time necessary to achieve orbit, much less continual acceleration for interplanetary or interstellar missions.

17. May 23, 2017

Staff: Mentor

In your OP, you said 1GW, not 1MW. Also, as @Dr Zinj said, those weapons give pulses, not continuous. So, assuming that the weapon can fire at most 1% of the time, you need 20*1000*100 of those weapon lasers. You're still dropping zeroes all over the place. Please get real.

18. May 23, 2017

RobertGC

Actually not. There are many videos on the net describing the Army system. They are described as continuous systems that can deliver the laser beam continually as long as they are supplied with power. They have their own gas engine electric generators so they can operate continually.

Bob Clark

19. May 23, 2017

BvU

Journalist quotes.

20. May 23, 2017

Staff: Mentor

I would be surprised if the Navy lasers don't overheat from continuous operation. Why should they make an oversized cooling system that they don't need for the purpose of the laser?

It doesn't scale that well. Air drag will make the power/payload highly nonlinear in this region. You also need the propellant, its control system, some steering during launch, attitude control afterwards and so on. All these things are mass going to orbit that is not your payload, and they don't scale proportionally to the payload size.
There is a market for kilogram-sized cubesats, but only if the launch is cheap.
We have a theoretical paper discussing some aspects of it. That is Technology readiness level 2 - maybe 3 if we are optimistic. It is far away from 8 or 9, where we actually have the capability to do so.