Check this out, Light powered propulsion is real!!

[rrl2]

Has any one heard about light crafts. They are smal crafts made of reflected metal. A laser powers it by shining a laser a it the craft will heat up the air under it and propel it upwards.<br /><br />If we could could create a full size model it could propel its way to the upper reaches of the atmosphere. THen an on board laser could heat a water rocket and sending it zooming off in to space a super fast speeds. Then it could release small satelites. It should be a cost effective way to launch satelites. <br /><br />If anyone finds a website on this or has suggestions they are welcome to submit them.

 

[mlorrey]

Yeah, I've got some stuff on that project from the mid-late 90's. They had some pretty good videos of their tests, but they were small things, only a few inches in diameter, with performance like a water rocket, though they only had a relatively low powered laser. That being said, the amount of money it would take to build a large enough bank of lasers to provide meaningful propulsion for a ship capable of useful payload would make the SDI budget look penny ante.<br /><br />People get unrealistically excited about concepts like these because they are somehow "clean" propulsion concepts, because there are no smokey contrails of exhaust, no messy cryogenic storage and handling issues or toxic fuels to deal with, but realistically the power just isn't there unless battle station sized laser systems become a lot more common and cheap.<br /><br />That, of course, isn't impossible, but it hasn't happened yet, and if certain political factions have their way, such devices will never get built.<br /><br />Fans of laser propulsion also ignore the glaring but easily put out of the picture fact that the power has to come from somewhere: gas fired power plants, coal fired power plants, or nuclear power plants. Solar doesn't provide anywhere near enough power for such propulsion.

 

[rrl2]

Look at this!

 

[tomnackid]

"People get unrealistically excited about concepts like these because they are somehow "clean" propulsion concepts, because there are no smokey contrails of exhaust, no messy cryogenic storage and handling issues or toxic fuels to deal with, but realistically the power just isn't there unless battle station sized laser systems become a lot more common and cheap. "<br />----------------------------------------------------------------------------------------<br />I don't think people were excited about this concept because it is "clean". The real advantage is that the spacecraft doesn't have to lift its own engines and propellants (except for a small amount for orbital insertion). The theoretical efficiencies of beamed powered spacecraft are much higher than any conventional rocket--even nuclear. The other advantage is that one laser launch system can sit at home (where it can be serviced and upgraded easily) and launch capsule after capsule--its the ultimate in reusable launch systems. Lasers big enough to launch crewed capsules are not beyond the realm of possibility--they were being looked into back in the 70s! i think the real stumbling block so far is that really big lasers are the province of the military and are highly classified. The Air Force and Navy already have big, powerful anti-missile lasers.<br /><br />Here's one for the "secret aircraft" crowd. The pulsed laser used for the "light craft" experiments produces a distinct "donuts on a rope" contrail. This is the same kind of contrail observed in the past few years near Air Force bases that test classified aircraft in the South west. I have wondered if the Air force is using their big airborne laser (ABL) system (which mounted in the nose of a 747-400 cargo plane) to propel unmanned spy drones, or maybe hypervelocity projectiles?<br />

 

[chriscdc]

I saw a picture of one of those contrails on a satellite image once crossing the entire USA, it might of been faked but I don't know of any other process that would produce them.<br /><br />Wouldn't it be ironic for all these anti-ICBM lasers, to be copied by say Iran and used to launch any nukes they build. Thus nicely cutting out the boost phase where these lasers are planned to shoot down the ICBMs.<br /><br />The marines are supposedly looking into sub-orbital craft for rapid deployment purposes, perhaps they coud use such a system.

 

[rrl2]

I just know there has got to be a way though. Maybe in the future.

 

[annodomini2]

I read about this a few years ago and saw some documentries on the subject.<br /><br />While a very clever idea, i believe there were too many problems, first being reproducibility. Yes they were using a relatively low power laser and with this they were having significant problems with the 'mirror ring' melting under the heat (it reflects the light into a concentrated point which superheats the air passing through and over the body)<br /><br />I believe they had to be quite heavy for stability and needed to be spun at 3-4000 rpm to stabalise the trajectory, if the laser aiming was wrong it also did a lot of damage to the projectile.<br /><br />Also the higher the altitude the less air (i.e. fuel is available) and therefore impractical for space launch as fuel would need to be carried to achieve orbit, increasing the weight of the vehicle, etc..etc.<br /><br />Nice idea and pratical from certain aspects, but very impractical from others. <div class="Discussion_UserSignature"> </div>

 

[tomnackid]

A more powerful laser would help immensely. Instead of the ring mirror and the kludgy spin stabilization system a larger, heavier projectile could use a simple parabolic reflector/reaction chamber and have an active reaction control system. Another promising approach is to have a solid slug of propellant on the back of the projectile--ice, wax, and polyethylene have been proposed as possibilities--the pulsed laser would vaporize the propellant a bit at a time to produce thrust. The advantages over a standard rocket are that a laser can heat the propellant to far higher temps (and thus produce higher ISPs) than a chemical reaction can--higher even than the temps in a gas core fission reactor. In fact even modest lasers can reach temps typically found in fusion reactions. Also all the heaviest and most complicated pieces stay on the ground.

 

[why06]

what if, hypothetically, a huge mirror array was formed and floated around the sun<br /><br />All the light was focused into a single point then focused int a beam.<br />Would that be enough energy? <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[tomnackid]

Since a laser light is monochromatic (all one wavelength) and coherent (all of the waves line up and reinforce each other rather than some reinforcing and some canceling each other out) you will always be able to pack a lot more energy into a beam of laser light than you could in a beam of ordinary white light. Even the relatively modest, off-the-shelf laser used in the Lightcraft experiments was able to produce temperatures 5 times higher than the surface of the sun! Since ISP is directly related to exhaust temperatures this is pretty impressive.<br /><br />

 

[mlorrey]

I can do the same with a plasma cutting torch and 120 VAC. With a silver electrode I can get over 50,000 degrees. Big whoopie doo. Ion drives get their high Isp by accelerating their reaction mass to extremely high energies that correlate to hundreds of thousands, even millions of degrees.

 

[tap_sa]

<font color="yellow">"Since ISP is directly related to exhaust temperatures this is pretty impressive. "</font><br /><br />To be more specific, Isp is related to <i>chamber</i> temperature and nozzle exit/chamber pressure ratio. Heating the propellant to tens of thousands of kelvins is no good if it doesn't go through controlled expansion where pressure and temperature drops turning thermal energy into kinetic energy of unidirectional massflow.

 

[tomnackid]

"I can do the same with a plasma cutting torch and 120 VAC. With a silver electrode I can get over 50,000 degrees. Big whoopie doo. Ion drives get their high Isp by accelerating their reaction mass to extremely high energies that correlate to hundreds of thousands, even millions of degrees."<br />------------------------------------------<br /><br />OK wise guy, how much would a plasma cutting torch that could heat enough working fluid to lift a spacecraft into orbit weigh??? How much would the power source for it weigh???? The whole point of a laser launch system is not just that lasers can generate a lot of heat--they can efficiently TRANSMIT that energy over long distances. Thats the whole point--the heaviest part of the rocket stays on the ground where weight and size don't matter. <br /><br />Its definitely a launch system that deserves serious consideration. Its a lot closer to reality than a space elevator and would probably have similar operational costs. There is no inherent reason why large (on the order of 50 megawatt) lasers can't be built right now. Its an engineering challenge, but there are probably plenty of companies that would do it for the right price (Boeing and Grumman both build big lasers for the military--this could be a lucrative new business if rocket sales slip.) The Air Forces ABL system's actual output is classified but it is in the "megawatt range" and that is for a laser that has to be carried in a 747. When size and weight are no object building big lasers gets a lot easier.

 

[mlorrey]

Well, I could use josh's microwave beams to beam the energy to the launchers rectennae, which would convert the energy to electricity, which would provide the arc to an airstream. I didn't say it would be feasibly, I was simply blowing out of the water your attitude that making air hotter than the sun was at all important or special. The Sun's surface is only about 4-5k degrees, which is a little hotter than LH2/LOX combustion in the SSME combustion chamber pressure. If you had an engine that could withstand higher chamber pressures, you'd match or exceed the sun's surface temp. So what? A plasma core nuclear engine can heat H2 to several times hotter than the sun. How is that any different from your laser system, and how is your laser system more efficient or useful once your vehicle is in orbit.<br /><br />There are other problems with laser launching: the vehicle must keep its annulus pointed at the laser source at all times, which does not correlate to a useful launch trajectory.

 

[mcbethcg]

"the vehicle must keep its annulus pointed at the laser source at all times, which does not correlate to a useful launch trajectory."<br /><br />There could be many lasers in different locations.<br /><br />You launch straight up. The projectile tips to the east. You have another laser west of the lauch point that takes over.<br /><br />The projectile moves east. The original laser re-aquires the job when the annulous is pointed appropriately.<br /><br />Down range you could have other lasers.

 

[tomnackid]

"A plasma core nuclear engine can heat H2 to several times hotter than the sun. How is that any different from your laser system,"<br />----------------------------------------------------------------------------<br />Well for one thing lasers that can achieve those temperatures already exist and can be bought off the shelf and have been tested for launching vehicles! For another, a gas-core reactor (if one is ever built) is likely too be a fairly heavy item that the spacecraft will have to drag along. A laser can not only generate those temps in a working fluid, but can transmit that energy from a distance.<br /><br />"...and how is your laser system more efficient or useful once your vehicle is in orbit."<br />-----------------------------------------------------------------------------<br />Its not! Its not intended to be. Its a LAUNCH system. A shuttle main engine is nothing but dead weight once it achieves orbit--that doesn't mean its totally useless. Ar car is useless once you arrive at your destination--more than useless, its a liability if you have to find a parking space! At least the laser launcher stays on the ground ready for the next capsule.<br /><br />"There are other problems with laser launching: the vehicle must keep its annulus pointed at the laser source at all times, which does not correlate to a useful launch trajectory."<br />--------------------------------------------------------------------------------------<br />Untrue. Tests sow that even with a single laser (more likely a bank of phased lasers) you can achieve useful orbits. Secondary lasers spaced at intervals or orbiting reflectors could give you more flexibility, but they are not required by any means. Also there are many different ways of extracting kinetic energy from a laser beam that don't require mirrors on the craft focusing the beam as is the case in the Lightcraft experiments. They involve ablative materials and heat exchangers of various designs. Most likely a full size, operational s

 

[mlorrey]

<blockquote><font class="small">In reply to:</font><hr /><p>"There are other problems with laser launching: the vehicle must keep its annulus pointed at the laser source at all times, which does not correlate to a useful launch trajectory." <br />-------------------------------------------------------------------------------------- <br />Untrue. Tests sow that even with a single laser (more likely a bank of phased lasers) you can achieve useful orbits. <p><hr /></p></p></blockquote><br /><br />What tests? No laser launched vehicle has ever travelled more than a few hundred yards. I've seen the videos of all of the tests, and NONE have even resembed an orbital ballistic trajectory.<br /><br />Your arguments are also wrong: a laser strong enough to propel a light craft will quickly shove a mirror out of the way.

 

[tomnackid]

OK, now you are just being a dick. Why? You got me? <br /><br />If you refuse to believe me look up the literature for yourself. Jordin Kare first proposed the idea back in the early 70s and since then its has been the subject of much study--especiall at Lawrence Livermore labs. Goddard didn't need to put his first liquid fuel rocket into orbit to know it was physically and mathematically possible. Duh! People calculated orbits even before flying machines were invented. Double duh!<br /><br />As for an orbital mirror moving--as long as it reflects most o f the light and doesn't ablate it WON'T move appreciably--we are not talking about a photon drive or a light sail here--we are talking about a relatively small diameter laser beam used to heat a propellant material. Get your facts straight.<br /><br />Here is a link I found to Kevin Parkin's website. He is an engineer working on laser and microwave propulsion. He and Kare just published a paper (available on the site) comparing laser and microwave launch systems. They calculate ISPs from 600 second to 1000 seconds using various launch systems and architectures.<br /><br />http://monolith.caltech.edu/Blog/Archives/000218.html<br />

 

[mlorrey]

I've read the literature, I've seen the LLNL and USAF test videos and reports. They did two types of tests:<br /><br />a) straight up<br />b) horizontal along a suspension wire with the laser at the point of origin.<br /><br />They never did any tests of propelling the lightcraft through an entire ballistic trajectory when the flight path of the object would require the object be oriented at an incident angle to the laser beam, which would result in defocusing and uneven thrust which would cause further flight instabilities.<br /><br />90% of a launchers trajectory acceleration happens in parallel to the ground, ergo any beam originating from the ground will always hit the annulus of a light craft at an angle askew from the lightcrafts needed thrust vector, AND because of this skewed angle of incidence, the lightcraft will always generate more thrust on the WRONG side of the lightcraft from that needed to keep the proper trajectory to reach a circular orbit.<br /><br />I agree that a lightcraft could reach a highly eccentric orbit, one which will likely have a perigee below ground level, but its source laser will not be able to contribute anything to the circularization of that orbit in any way.

 

[tomnackid]

Again you are focusing solely on the Lightcraft experiment which tested only one mode of operation intended for use in the lower atmosphere to set up your starwman argument. Do you really think dozens of engineers working on these projects are so stupid that they can't add up acceleration vectors or or calculate the impingement angle of a laser beam from a fixed location?

 

[tap_sa]

I'll spray this thread and participants with flame-retardant.<br /><br />*Swoosh swoosh* <img src="/images/icons/wink.gif" /><br /><br />mlorrey seems to have temporarily forgotten that laser beam and thrust vector aren't necessarily paraller, but then again they have to be in the prototype that started this thread. And he will read Jordin Kare's latest papers about beam powered vehicles employing relatively simple heat exchanger on their bellies. This tech will not reach five times the sun but is limited to the melting points of exchanger materials, but will still reach solid NTR 800-1000s Isps using hydrogen, which is nice.<br /><br />And it's a nice Friday and people should watch something relaxing from telly. I'll watch the newest episode of Invasion about now.

 

[tomnackid]

"And it's a nice Friday and people should watch something relaxing from telly. I'll watch the newest episode of Invasion about now."<br />-----------------------------------------------------------------------------<br />Hey that's right! Battlestar Galactica tonight! Whoohoo! Except my wife and I have a date so we'll have to tape it. Good old fashioned video tape. None of this sissy Tivo stuff! <img src="/images/icons/smile.gif" />

 

[yevaud]

<i>Good old fashioned video tape. None of this sissy Tivo stuff!</i><br /><br />Get the Scribes and tell them to start writing, fast!<br /><br /><img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[mlorrey]

I have, in fact, seen the heat exchanger propulsion concepts as well, and they do solve the problems of angles of incidence to trajectories. By the prototype that started this thread, which is what we were discussing (the only device that has actually been tested at all), it cannot follow any trajectory without the laser always being tangential to the exact point in the trajectory the vehicle is at at any given time....<br /><br />The heat exchanger concepts seem to deal with that problem other than how to get off the ground so as to start being hit by a laser. Perhaps a tow launch can fix it.<br /><br />I'd propose something in between: a winged craft with a ventral ramjet that can be powered by 'tail burning' laser/air to get off the ground. Once its in the air, the heat exchanger in the belly of the craft would absorb either laser or maser energy to pre-heat a fuel, which would enter the ramjet and react with rammed air. This would get 1500-4000+ sec Isp (whatever the impulse would be would be a bit more than regular ramjet propulsion, whatever the fuel). Above the atmosphere, it would work on purely preheated fuel.

 

[mcbethcg]

"I agree that a lightcraft could reach a highly eccentric orbit, one which will likely have a perigee below ground level, but its source laser will not be able to contribute anything to the circularization of that orbit in any way."<br /><br />A highly eccentric orbit IS a useful orbit- it gets you to a position where onboard circulization rockets could correct it.