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Dr. Young Bae stands next to his invention, which he built from off the shelf components.  (Source: The Bae Institute)

The PLT in action, producing a weapons grade beam in a small package.  (Source: The Bae Institute)
Dr. Young Bae has created a working prototype that promises to provide effective laser propulsion in space at unprecedented speeds.

Dr. Young Bae of the Bae Institute definitely thinks outside the box when it comes to aerospace propulsion techniques.  Where others are thinking fuel, he's thinking photons.

Last December, Dr. Young Bae unveiled a unique invention: the Photonic Laser Thruster (PLT) with an amplification factor of 3,000 in December, 2006.  The engine promised to provide a novel new means of transportation in space.

Word spread fast and before long Dr. Bae had visitors from some of aerospace's strongest organizations--NASA JPL, DARPA (Defense Advanced Research Projects Agency), and AFRL (Air Force Research Laboratory) --among others.

Dr. Franklin Mead, Senior Aerospace Engineer, and leading rocket scientist in laser and advanced propulsion at the Air Force Research Laboratory (AFRL) was quoted in Bae Institute press release as stating, "I attended Dr. Bae's presentation about his PLT demonstration and measurement of photon thrust here at AFRL. It was pretty incredible stuff and to my knowledge, I don’t think anyone has done this before. It has generated a lot of interest around here."

In the past, photons thrusters have been relegated to science fiction as they were considered too unpractical for modern space flight.  While such a device would have the advantage of nearly constant thrust, unlike a fuel rocket, photons have no mass so it could take years to equal the speed of traditional propulsion techniques.

Part of the Photonic Laser Thrust's secret lies in amplifying and bouncing the photon beam.  The photon beam is bounced back and forth between a set of mirrors, creating a powerful net propulsion force.

Dr. Bae Young built the PLT using off the shelf components at the Southern California laboratory of the Bae Institute.  The patent pending device uses an egg-size laser head to produce a laser so powerful, only massive weapons and commercial grade lasers are able to match it.

The laser generates 35 uN of thrust and is scalable to much larger amounts of propulsion.  Dr. Young Bae has stated that the device could propel a spacecraft to speeds well beyond 100 km/sec.  He recently announced that a spacecraft utilizing the PLT could transit the 100 million km to Mars in less than a week.

Aside from being used as propulsion, the device could be used to control a group of objects in space to carefully fly together in formation--think something like an Air Force jet squadron.  Dr. Bae is patenting a process to use the PLT in a Photon Tether Formation Flight (PTFF), which could offer control of spacecraft flying in formation with nanometer precision. The laser’s current power requirements are within current acceptable space limits and its abilities could accommodate a wide range of NASA spacecraft formation flight configurations, such as SPECS and MAXIM.

The project was built on a very small budget and its accomplishments have helped it secure funding from a prestigious Phase II NIAC grant (NASA Institute for Advanced Concepts), which funds only the most revolutionary ideas for the next generation NASA space missions.

Dr. Bae's PLT demonstration paper, "Photonic Laser Propulsion: Proof-of-Concept Demonstration" has been accepted for publication later this year in the peer-reviewed AIAA (American Institute of Aeronautics and Astronautics) Journal.  In the paper Dr. Bae contrasts his technique with past attempts at laser propulsion.  In the paper Dr. Bae reveals the secret to the PLT's coherency and stability--placing the laser medium in a resonant optical cavity.

Dr. Bae presented his PLT concepts this week with demonstrations at the AIAA Space 2007 Conference in four sessions: Space Transportation Systems, Promising Space Concepts from the NASA Institute of Advanced Concepts (NIAC), Space Systems for the Next 50 Years, and Advanced Vehicle Systems.

The device is pretty incredible and the idea that it could cut the journey to Mars to only a week shows its potential.  Much more work is to be done, but Dr. Young Bae's PLT may revolutionize the aerospace propulsion industry.

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This article is over a month old, voting and posting comments is disabled
small correction
By masher2 (blog) on 9/21/2007 11:28:49 AM , Rating: 1
quote:
The patent pending device uses an egg-size laser head to produce a laser so powerful, only massive weapons and commercial grade lasers are able to match it.
The beam isn't as powerful as those weapon-grade lasers, the propulsive force from the beam is, due to the repeatedly bouncing the beam between two points.

Details on the site are a bit sketchy, but its important to realize this isn't a standalone propulsion system. As I read it, its feasible only for surface launching of micro-payloads. The beam is generated here on Earth, then bounces back and forth between the launch site and the payload, generating additional thrust each time.

Quite obviously, once the payload is more than a few thousand miles from Earth, problems with beam collimation and alignment are going to make it unfeasible...and of course, the payload will need to aerobrake (or find some other way to decelerate) once it reaches its destination.

Sounds like an excellent system for launching tiny deep-space probes...but if people are seeing this as a rocket engine we can use to flit between planets, they're wrong.




RE: small correction
By masher2 (blog) on 9/21/2007 11:33:33 AM , Rating: 2
Another benefit, of course, is the potential to drastically cut lifting costs to NEO. A laser-based launch system could drastically cost the costs of getting small packages into orbit, which would go a long way towards making the commercialization of space feasible.


RE: small correction
By 16nm on 9/21/2007 12:23:21 PM , Rating: 3
But could continual use eventually push the planet closer toward the sun thereby exacerbating global warming? An important question that we must spend a few billion dollars of education funding to answer. (tongue-in-cheek)


RE: small correction
By jak3676 on 9/21/2007 12:28:52 PM , Rating: 4
I'll take that cheque and begin researching immediatly. If you give me enough money I'll even produce a sensationalized movie about it.


RE: small correction
By Polynikes on 9/21/2007 12:32:13 PM , Rating: 5
Hmm, good point. I think we should ban basketball; all that jumping up and down is surely causing us to get closer to the sun, thereby increasing global warming. The NBA was founded in 1946, and a lot of climate data shows our average temperatures going up a lot in the last 40 or 50 years! I SEE A CORRELATION!


RE: small correction
By jak3676 on 9/21/2007 12:40:09 PM , Rating: 5
But wait - if we only play basketball on the lighted side of the earth - wouldn't that push us further away from the sun. We need to get the NBA to balance their schedule between day and night games or we could either fall into the sun or bounce ourselves out of orbit. Quick someone go secure government funding to fight this pending catastrophy.

We also need an agency set up to study the possible negative impact of all this wasting of gravity. If we are not careful we may exhaust our supply of gravity.


RE: small correction
By Polynikes on 9/21/2007 2:03:55 PM , Rating: 3
Well the NBA season is during the winter months, so most of the games are played at night. Hence, we are being pushed towards the sun! Maybe not quite straight at it, but we're certainly getting closer.


RE: small correction
By Polynikes on 9/21/2007 2:05:52 PM , Rating: 4
I forgot to reply to your comment about gravity. Egads, I had no idea we were running out of it! I'm building a shelter underground so I don't fall off the earth!


RE: small correction
By jak3676 on 9/21/2007 7:54:55 PM , Rating: 5
Here's a quick list we can all follow to start conserving gravity.

1. Just make sure you move all the heavy objects in your house to the floor or to the lowest possible shelf.

2. Don't do any needless jumping (or any exercise for that matter - just do your part by packing on that extra mass so gravity doesn't have to work so hard to keep you to the ground - or at least when we start running out of gravity you'll be one of the last few people flung into outer space.

3. Call/write your congressman and your presidential candidate of choice.

4. The gravity conservation movement really needs a good celebrity spokesperson. Write to all your favorite celebrities to get them involved.

5. We should all start wearing some color of ribbon on our lapels to proclaim to the world that we are serious about our cause. (Anyone know a cheap slave-labor type sweat shop in a 3rd world country that can make us the ribbons for cheap? I'd like to start selling them for personal profit).

p.s. Can someone explain how I get rated up for my first jokes on this topic, then rated down for the 2nd? I know we don't generally have a sense of humor here - but I at least thought we'd be consistent.


RE: small correction
By Spoelie on 9/22/2007 9:26:27 AM , Rating: 3
Because trying too hard to sound funny isn't funny.

And making jokes just to get rated up isn't either :p Not saying you did all that, it's just a general trend: funny post -> lame follow-ups


RE: small correction
By jak3676 on 9/22/2007 12:31:53 PM , Rating: 1
Well I fully except all the blame for my warped sense of humor. It's just weird that one post will go to -1, then the next day it's back up to 5. Good for me we seem to have a pretty fickle readership here - who knows if I could live with myself if I got a negative rating. Unless I'm going to get banned here, you all are stuck with me.


RE: small correction
By Visual on 9/24/2007 3:36:32 AM , Rating: 1
well in fact due to preservation of momentum, it is obvious that no amount of jumping or dribbling or anything in basketball at all can cause a change in earth's motion. if players or balls were floating off into space, yes that would mean a net momentum change for the earth. but if they are returning to a previous position, then they are canceling out their own effect.

but lets not let reality interfere with our jokes, huh? your post still was fun to read :)


RE: small correction
By McTwist on 9/21/2007 1:09:58 PM , Rating: 2
Do you really think this system can be used to launch anything into space? This thing only has a thrust of 35 µN. It says it is scalable but even if you made it one million times bigger to get just 35 N, the laser would be huge and the reflector would have to be much heavier to reflect such a powerful beam. It seems like this thing will be confined to the formation flying missions that the linked articles mention. But even then spacecraft could only push off from each other. Once they push off, how do they stop from drifting further apart? It'll be interesting to read the paper in AIAA Journal.


RE: small correction
By masher2 (blog) on 9/21/2007 1:51:11 PM , Rating: 1
> "Do you really think this system can be used to launch anything into space?"

Not until we can build bigger lasers. That's most likely why Bae is looking at this for attitude control of satellites now.

> "Once they push off, how do they stop from drifting further apart?"

In a satellite formation, they wouldn't impart enough momentum to escape orbit entirely. Just entire to correct your orbital parameters slightly.

Imagine three geosynch satellites spaced around the globe. Each of the 3 could bounce a beam off the other two, lifting all three into a slightly higher orbit, for instance.


RE: small correction
By McTwist on 9/21/2007 2:14:14 PM , Rating: 2
quote:
Not until we can build bigger lasers.

Bigger lasers mean stronger reflectors which means more weight. I'm curious what the trade-off between laser power vs. reflector weight is.
quote:
In a satellite formation, they wouldn't impart enough momentum to escape orbit entirely. Just entire to correct your orbital parameters slightly.

I wasn't talking about trying to escape Earth. This and above is why I don't think you feasibly use this thing to launch spacecraft. That's why I think this is confined to on-orbit operations during formation flying missions.

I like the idea of using this to push a constellation of GEO satellites to a higher orbit though.


RE: small correction
By wordsworm on 9/21/2007 9:38:53 PM , Rating: 2
quote:
Bigger lasers mean stronger reflectors which means more weight. I'm curious what the trade-off between laser power vs. reflector weight is.
hmmm... no engine means lighter weight. I don't know where you got the idea that having a reflector in place of an engine would signify a heavier vehicle.


RE: small correction
By AnnihilatorX on 9/21/2007 2:03:44 PM , Rating: 5
35µN may seem small. But note that this is a constant force

If you can scale it to say 35N, in a week 7 days, assuming mass of a small spacecraft is 1000kg;

Applying a = F / m = 0.035m/s^2
7 days = 7 * 24 * 60 * 60 = 604800 seconds
Initial velocity u = Escape velocity = 11.2km/s
distance travelled = ut + 0.5*at^2 = 11200 * 604800 + 0.5*0.035*604800^2
= 13174963200 metres
= 13174963.2 km

Minimum distance between Earth and Mars is about 100 million km. So not quite there yet. Also, at half way you want to reverse the propulsion to slow down the spacecraft, otherwise you will be a blazing shooting star flying pass Mars at insane speed.


RE: small correction
By McTwist on 9/21/2007 2:32:58 PM , Rating: 2
Thanks for the elementary physics lesson. I do understand that it is a constant force but it would only be constant as long as the laser was able to bounce back and forth between the spacecraft and another body. As the distance grows, this becomes exceedingly hard to do.

Speaking of distances, while the minimum distance between Earth and Mars is more like 80 million km, spacecraft don't move in straight lines to their destinations. Kepler showed they move along paths defined by conic sections. A common interplanetary trajectory would escape from Earth on a hyperbolic trajectory and then appear to be elliptical with respect to the Sun and then approach Mars on another hyperbolic path. This adds a significant amount of time and distance to the flight. Therefore you need to fly farther than the minimum distance.

All this still doesn't change the fact that you aren't going to be able to launch a 1000 kg satellite with a 35 N thruster, which was the point of my original post.


RE: small correction
By masher2 (blog) on 9/21/2007 2:54:44 PM , Rating: 3
> "As the distance grows, this becomes exceedingly hard to do."

Right, which is why Bae suggests this for micro satellites, rather than massive probes. Until we can build far more powerful lasers, we won't be launching anything but very small payloads or things already in orbit (and destined to remain so).

> " Kepler showed they move along paths defined by conic sections."

That's true only for ballistic flight...powered flight can follow any arbitrary path it desires.

The typical path from Earth to another planet is the Hohmann transfer. But that's done to minimize fuel requirements, not flight time. A payload with a much higher dV budget has much more options.


RE: small correction
By McTwist on 9/21/2007 4:05:57 PM , Rating: 3
quote:
Until we can build far more powerful lasers, we won't be launching anything but very small payloads

I would argue that we won't be able to launch anything even very small payloads. Even with a 1 N laser (much larger than this one), you could only levitate a 1/9.8 kg object. You'd need more than that just to lift such a small object off the table. I bet the mirror used in this experiment weighed more than that and it was only producing 35 µN.

quote:
That's true only for ballistic flight...

Yeah, you are right about that one. Silly me. Well technically one is always on a conic section. It's just that during powered flight the conic is changing instantaneously throughout the burn. And it is highly energy inefficient to try and travel in straight lines.

In as much, this will only be able to provide a force in the radial direction from the central gravitational body. Generally, interplanetary transfer occurs from increasing the tangential velocity. I suppose you could use the Moon to give you a pulse in the tangential component but it wouldn't be for very long. This is actually turning into an interesting problem. I'm sure somebody has looked at this problem before but maybe not.


RE: small correction
By masher2 (blog) on 9/21/2007 4:22:35 PM , Rating: 1
> "I would argue that we won't be able to launch anything even very small payloads"

NASA has already done some basic testing. With standard ablative launching (without the amplification effect discussed here by Bae) a 1MW CW (continuous-wave) laser would be sufficient to launch a 1 kg payload. NIF is building a 700 terawatt laser (700M times as powerful) but it fires only extremely short pulses, so thats not a fair comparison. It might be possible to use a bank of pulsed lasers instead of a CW, but its certainly safe to say we're a considerable ways away from being able to launch non-trivial payloads.


RE: small correction
By McTwist on 9/21/2007 4:44:27 PM , Rating: 2
Can you share the source you have for the NASA tests? I was only able to find some anecdotal references to it.
Are you really proposing that we use an NIF laser? That would most likely shoot a hole through anything we put in its way. It would be cool to see though.


RE: small correction
By Darkmatterx76 on 9/22/2007 2:46:39 AM , Rating: 2
Couldn't an object (craft) be launched normally and then fly to its destination using this method by having the laser in space?


RE: small correction
By TomZ on 9/21/2007 3:32:06 PM , Rating: 2
quote:
35µN may seem small. But note that this is a constant force If you can scale it to say 35N

Sure, and if you took my bank account balance and scaled it up by the same factor, I'd be the richest man in the world by far. :o)


RE: small correction
By Spoelie on 9/22/2007 9:29:36 AM , Rating: 2
If scaling it was such a problem, then Bae wouldn't be able to claim it would cut the time needed to travel to mars in half.


RE: small correction
By PrinceGaz on 9/22/2007 1:18:04 PM , Rating: 2
quote:
It seems like this thing will be confined to the formation flying missions that the linked articles mention. But even then spacecraft could only push off from each other. Once they push off, how do they stop from drifting further apart?

There will be a (tiny) gravitational attraction between each satellite which causes them to come back together. Periodic use of some method to repel them from each other will in fact be necessary just to prevent them coming together completely.


RE: small correction
By Gneisenau on 9/22/2007 8:36:44 PM , Rating: 2
Not to mention removing those pesky birds that fly into the beam.

Seriously, I wonder what would happen to the payload if something like a flock of birds flew into the beam during accention


RE: small correction
By jak3676 on 9/21/2007 11:40:30 AM , Rating: 2
Yeah, I think something is missing (or maybe I just don't get it). He bounces a laser beam in between two points thousands of times to create a force driving them apart. In terms of space flight, you'd have to have something to push off from.

Keeping the laser on Earth makes sense, but there are obviously severe limitations on a passivly propelled spacecraft.


RE: small correction
By cochy on 9/21/2007 1:24:50 PM , Rating: 2
hmm such as the Earth rotating perhaps...


RE: small correction
By npoe1 on 9/21/2007 1:54:05 PM , Rating: 2
The lack of atmosphere makes the moon a good place for a launching device, more missions anyone?


RE: small correction
By Treckin on 9/21/2007 2:07:36 PM , Rating: 2
Or the atmosphere...

The idea here is an orbital laser, which could propel a craft quite fast...

And by thousands, I hope you mean billions... Light does move quite fast you know.


RE: small correction
By Treckin on 9/21/2007 2:10:35 PM , Rating: 2
As to slowing down... Ideally, an orbiting laser+reflector at both ends of the trip makes both a moot point, allowing for controlled deceleration. It would be a very convenient way to travel, and quick.


RE: small correction
By masher2 (blog) on 9/21/2007 2:23:19 PM , Rating: 3
> "And by thousands, I hope you mean billions... Light does move quite fast you know."

You can't bounce a laser between two mirror "billions" of times. Even the best mirrors are not perfectly reflective. A high-grade metallic mirror would allow for maybe 10K bounces, whereas an exotic dielectric type might reflect enough to allow for 100K round-trips.


RE: small correction
By HercDriver on 9/21/2007 11:43:10 AM , Rating: 2
If that's really how the system works, it would seem more feasible to launch the spacecraft from Earth, using conventional rockets. Once in orbit, the LASER site (perhaps in orbit, itself) would propel the craft towards Mars. There would have to be another LASER on or orbiting Mars, to slow the spacecraft down, as it's velocity would be much to great for aerobraking to work. This could still be a cost-effective means for interplanetary travel, provided they are able to maintain precise beam alignment long enough to reach the proposed 100km/sec speed. An orbiting LASER would not have to make corrections for atmospheric distortions, and could have a HUGE solar array to generate the power required.


RE: small correction
By Spivonious on 9/21/2007 11:54:09 AM , Rating: 2
Yeah but then the object generating the laser would receive the same amount of force, pushing it away from the object it's pushing. Assuming Newton's Third Law is still valid.


RE: small correction
By Oregonian2 on 9/21/2007 1:24:42 PM , Rating: 2
The article in EE Times a few days ago about this had a bit more detail and it was talking about perhaps using conventional rockets to keep the "stationary" portion of this thing still. I dunno though, I suspect this is a physics pyramid scheme. :-)


RE: small correction
By masher2 (blog) on 9/21/2007 11:56:26 AM , Rating: 2
An orbiting laser has a couple serious disadvantages though. For one, you have to pay to lift all that mass (lasers, power source, etc) in the first place. And every time you use it, the thrust you impart to the launched vehicle you receive in reverse, forcing you to continually re-pay via chemical propulsion to maintain atitude.

The beauty of laser launch systems is that you get to keep your rocket motor and fuel "at home", so to speak. Only the payload gets launched, and the reverse thrust is cancelled out by the mass of the planet you're launching from.

> "..."as it's velocity would be much to great for aerobraking to work"

Technically, you'd have to use an aerocapture if you're coming in with a hyperbolic orbit. Admittedly, thats much trickier than a simple aerobrake, but its not impossible.


RE: small correction
By jak3676 on 9/21/2007 12:16:46 PM , Rating: 2
Putting it in space does have some serious disadvantages, but the question would be if its worth it to avoid atmospheric interference.

I could see a system of multiple laser bases (propulsion points) that would start in several locations on earth and later in orbit. The terrestrial lasers would be used to get the payload into orbit, 2/3 of the energy required to make it to mars (or the moon, etc). The orbiting systems could them be used to provide the propulsion for everything else. The earth based systems would also provide the counter force for the orbiting systems.

By setting up a system of propulsion points you would simplify the geometry of trying to direct your payload where you want it. I'm assuming that a single propulsion point can only propel an object linearly. If you want the ability to steer - you'll need multiple points.

Big picture wise, you could eventually end up with an entire grid of propulsion points throughout the galaxy or further.


RE: small correction
By masher2 (blog) on 9/21/2007 12:38:28 PM , Rating: 2
> "you could eventually end up with an entire grid of propulsion points throughout the galaxy"

TAANSTAFL. Such a system wouldn't work for the same reason two satellites can't gravitionally slingshot off each other forever, continually gaining velocity for free.

The 'free' momentum gained from bouncing the beam is really just stolen from another source. If you bounce off a planet, its technically free. But if you bounce off another orbital system, you have to pay that momentum back.


RE: small correction
By jak3676 on 9/21/2007 12:43:16 PM , Rating: 2
roger - so you have to fix these points to planets/moons. I'm not suggesting other points in orbit (except probably near earth as noted above)


RE: small correction
By augiem on 9/21/2007 1:30:00 PM , Rating: 2
I don't see the problem in using orbiting laser systems. You don't have to ALWAYS be firing laser at the payload. What's wrong with alternating firing bursts at the payload, then other bursts in the opposite direction to correct for drift? Or, just fire in both directions at all times in you have to keep it on 24/7.

(Moon-based probably still would be better, but)...


RE: small correction
By augiem on 9/21/2007 1:31:38 PM , Rating: 2
Addition:
The orbiting laser could always use the earth or the sun or whatever as its anchor for laser-based "push" for compensation.


RE: small correction
By masher2 (blog) on 9/21/2007 1:56:00 PM , Rating: 2
> "The orbiting laser could always use the earth or the sun or whatever as its anchor for laser-based "push" for compensation"

In that case, why have the orbiting platform at all? Far more efficient to just let the payload itself push off the earth directly.

Technically, you could envision some sort of massive "relay" scheme, where you use multiple platforms to keep beam round-trips shorter, and thus cut your worries about correction and focusing. But such a Rube Goldberg implementation would be stymied by the losses incurred by each stage. Laser beams are an incredibly wasteful way of generating power, so this would mean pyramidal losses in efficiency.


RE: small correction
By nrb on 9/21/2007 5:55:29 PM , Rating: 2
quote:
In that case, why have the orbiting platform at all? Far more efficient to just let the payload itself push off the earth directly.
The advantage of doing it this way comes when you think about refueling. Once a spaceship is travelling rapidly away from Earth at high speeds you can't catch up with it to refuel it. But a large platform in Earth orbit could have fresh fuel supplies on a regular basis. That way you can keep supplying more and more fuel throughout the mission and keep accelerating the spacecraft without actually having to get the fuel to it.

You could perhaps combine this idea with a space elevator. :-) That would be a relatively efficient way of getting the payload into orbit to begin with. The laser platform could take it from there; no need for any conventional rockets to be attached to the payload at any point. You could also use the elevator to transport fuel most of the way to the laser platform.


RE: small correction
By nrb on 9/21/2007 5:57:04 PM , Rating: 2
Or, of course, you could forget about the platform, and just build your spaceships in pairs, with one half containing nothing but the laser, then send the two halves off in opposite directions.


RE: small correction
By skd911 on 9/29/2007 1:16:14 PM , Rating: 2
OK but there is a small correction. You can just have 2 lasers on that platform it don't have to be massive. That lasers will fire in opposite direction, and you don't even need earth or whatever planet, you can dump that platform in the middle of nowhere one beam straight and one beam in opposite direction, and that way you can push 2 satellites simultaneously. You can reach two destinations.

Sorry for my English but it was so simple that even a little child will understand it right away without knowing about Newton laws. Because when you push in two opposite directions with even force you will stay in the middle.


RE: small correction
By phattyboombatty on 9/21/2007 12:42:55 PM , Rating: 5
I do not believe that you are correct that this is planned to be an earth-based launch propulsion system. Besides the site saying nothing whatsever about the propulsion being earth based, and nothing about launch propulsion, the tip-off is the following quote from the site:

quote:
Although built on a shoestring budget, the maximum photon thrust was demonstrated to be 35 µN, which is already close to, or sufficient power for many envisioned space missions.


I doubt 35 uN would be enough propulsion to defeat the earth's gravitional pull on a feather, much less any feasible launch vehicle. Additionally, the article indicates that the power requirements are well within the limits of today's space power budgets, further indicating that the propulsion system will be located on the spacecraft itself, not located on Earth.

Even if the plan was to use an Earth-based laser, the laser would definitely not be used to launch any vehicles into space, but would only be used to propel space-based objects that have been already been transported to space from Earth by the normal fuel-based rocket approach.


RE: small correction
By phattyboombatty on 9/21/2007 1:13:06 PM , Rating: 2
It's so heartening to see that masher2's original post has been rated up to 5, even though its flat-out wrong.


RE: small correction
By masher2 (blog) on 9/21/2007 2:29:51 PM , Rating: 2
I'm sorry you feel that way, but the physics here are really very simple. Bae hasn't invented perpetual motion. As a self-contained system, this is useful for attitude control of satellites (just as Bae himself states), but to propel a craft to alternate destinations, you need the Earth (or other large body) as a platform.


RE: small correction
By phattyboombatty on 9/21/2007 3:04:27 PM , Rating: 2
The irony of your statement is that the entire breakthrough made by Bae (and the reason its newsworthy and currently being discussed) is that he figured out a plausible, alternative method of laser propulsion that did not require an Earth-based laser. Now you are continuously harping about an Earth-based laser being required, which, in effect, means that you are completely disputing Bae's research.


RE: small correction
By masher2 (blog) on 9/21/2007 3:17:48 PM , Rating: 2
Err, orbital-based laser propulsion systems have been discussed for decades. Bae didn't come up with the idea, he merely created a more efficient manner for them to transfer momentum.


RE: small correction
By phattyboombatty on 9/21/2007 3:40:32 PM , Rating: 3
Which is why I said plausible alternative. The idea of orbital based propulsion has been around for a while, but until Bae came up with a way to decrease the power requirements enough to house the propulsion system on a satellite, it wasn't a plausible idea. That's why I can't figure out why you aren't getting this. The whole point of his research is to put the damn laser on a satellite in orbit.


RE: small correction
By masher2 (blog) on 9/21/2007 3:59:59 PM , Rating: 2
I think you're misunderstanding what I'm saying. Of course you can base it upon a satellite. You just can't do so as a means of propelling conventional payloads to a destination.

For attitude control of conventional payloads, or for launching micropayloads, it works fine. But if you want a "rocket motor" that will get a heavy spacecraft to the moon or another planet-- you need a terrestrial platform.


RE: small correction
By phattyboombatty on 9/21/2007 4:18:02 PM , Rating: 2
masher2 wrote in original post:
quote:
As I read it, its feasible only for surface launching of micro-payloads.


I guess I misunderstood "surface" in your statement above to mean the surface of the Earth. I'm such an idiot. You clearly meant the surface of outerspace. I apologize for my misunderstanding.

Seriously though, your argument is shifting so quickly that I can't keep up to pin you down on anything.


RE: small correction
By TSS on 9/21/2007 4:23:39 PM , Rating: 2
*ahem*

"Using a photonic laser and a sophisticated photon beam amplification system, Dr. Bae demonstrated that photonic energy could generate amplified thrust between two spacecraft by bouncing photons many thousands of times between them."

if i interpet this correctly, he's basicly shooting a laser between 2 spacecraft to get one moving. thus, it would be possible to put it in space, and a land system would be possible though a hell of alot more trickier to aim.

it would be possible to propel conventional payloads with this. afterall, if you had a planet to stand on that would not move, and you could push something in 0 G with no G's of itself, you could move anything independant of mass. more power just makes it go faster. there are spacecraft flying to distant planets in our system right now, which do not generate more then a newton or 2 constant thrust at best (one beeing a ion engine). the thrust generated by the laser will be like the engine is in the spacecraft itself. it's not perpetual motion however, since here, the energy that is needed to propel the spacecraft is the energy generated by a diesel generator connected to the power grid, thus electricity. no more diesel, no more electricity, no more power, no more increase in velocity.

anyways if you base it on a sattelite, your going to spend extra energy keeping it in its place since the laser beam going forward will want to push the laser backwards. if you put the thing on earth, you have the refraction of the atmosphere to consider, plus extra distance to keep the beam focussed. stopping will be a problem, because if you put a reflector at the other end then shoot the beam to it to reflect off and stop the spacecraft, the reflector will be pushed away as well. if you put the relector on the target planet, then there's a 2nd atmosphere to consider, twice, not to mention the weather on the ground.

however if i had a choice though i'd put the laser on the earth. afterall if you calculate through the atmosphere interference and put the laser somewhere with constant weather (say a desert), then your done with it. with sattelite's, you'd have to keep burning fuel to keep the thing in orbit. tough, there's still the rotation of the earth to consider. once that thing is free of our orbit, we couldn't power it constantly with the laser since it'd be out of view. but another laser on the other end of the planet helps. but costs even more.

the question is efficiency gentlemen. how good it can do what it does, not what it does.


RE: small correction
By lco45 on 9/24/2007 8:02:17 AM , Rating: 2
Basically everyone (mainly masher2) seems to be saying that you need an infinitely (relatively) massive base to fire the laser from (ie earth or a moon).

Instead you could have a sacrificial heavy space craft that fires at the small payload craft.

So, you launch the base-craft (1000kg) and the payload craft (10kg) at say 20,000 miles per hour.
The the base craft fires the laser at the payload craft until the base craft is slowed to a stop (or even starts falling back to earth).

The payload craft would the be able to be accelerated to 100 times the original speed of both craft together, in this example that would be 2,000,000 miles per hour.

Another option (which I'm not sure about, maybe someone can correct me or add something) is that you could have a single craft which collects sunlight using solar cells, charges a battery and uses the battery power to beam a laser backwards. Would that cause constant acceleration without the need for onboard fuel? I know it would get much weaker as the distance from the sun increased, but for interstellar flight it might pass a series of stars, slingshotting each time and also getting more solar power each time.

My 2c.

Luke


RE: small correction
By ksundara20 on 9/21/2007 1:14:11 PM , Rating: 2
quote:
The beam is generated here on Earth, then bounces back and forth between the launch site and the payload, generating additional thrust each time.
quote:


I am not an expert in Space flight propulsion systems but
only a crackpot with a PhD in smoking weed will assume that the thrust comes from a Earth based station. When the paper is talking about amplifying by reflecting the photons, it is between 2 mirrors that are a few centimeters apart. The amplified laser is then used to propel the whole spacecraft while the PLT would remain inside the spacecraft. This is a STANDALONE propulsion system. The rest of the mechanics is beyond me but I know this much.

By your theory, the amplification will never happen because as the spacecraft moves away from the Earth, the thrust would decrease since the photons will have to travel more distance in every reflection. What an idea!!!


RE: small correction
By masher2 (blog) on 9/21/2007 2:03:31 PM , Rating: 2
quote:
By your theory, the amplification will never happen because as the spacecraft moves away from the Earth, the thrust would decrease since the photons will have to travel more distance in every reflection. What an idea!!!
You have a rather basic misunderstanding of the mechanics of momentum transfer here. It doesn't matter how far a photon travel, its going to impart a fixed amount of momentum when it strikes a surface. Absorption vs. reflection will affect the amount, but travel time does not.


RE: small correction
By Spoelie on 9/22/2007 9:51:30 AM , Rating: 2
yes and no, it is the amount of photons that matter. And the further a target gets, the less photons it will receive, either through absorbation (space is not empty) or 'mis'shooting. Normally, the farther a target gets, the less photons it will receive. I have no hard numbers on how much less this would be tho, so I do not know how significant it all is


RE: small correction
By Spoelie on 9/22/2007 9:53:11 AM , Rating: 2
with the yes and no, I meant that what you said was right, but that there would still be less thrust the further a target gets, only not because of what the original poster said


RE: small correction
By FrankM on 9/21/2007 1:23:00 PM , Rating: 2
I'm not sure if that is really the way they plan on using it, but if it is, then I wouldn't call it 'out of the box', as the article claims it. Experiments with laser propulsion have been going on for years. One that made it to real-life testing for example involved a concave mirror on the bottom of the small payload, and high-energy pulses from a land-based laser. The object was driven more by the collision and explosion of photons in the mirror's focal point, so it is a bit different, but is was tested and working.


RE: small correction
By Terberculosis on 9/21/2007 4:29:16 PM , Rating: 2
Hmm, I beleive a similar lazer based on mars (probably flown there in a chemical rocket years before the manned launch) would work just fine as a braking mechanism.


RE: small correction
By UsernameX on 9/21/2007 4:29:27 PM , Rating: 2
If we can build an accelerator point on the moon, that might make it more feasible for us to reach Mars. But still the braking issue is a problem.


No More Misinformation
By phattyboombatty on 9/21/2007 1:07:23 PM , Rating: 5
Despite the repeated misinformation given by various comments in this thread (mostly masher2), please read the following quote which accurately describes how this propulsion system is designed to work:

quote:
Originally, PLP designers imagined using large ground-based lasers to generate enough intensity and to provide a backstop for pushing against, later moving to passive optical cavities located in space. Unfortunately, none of these designs was able to demonstrate enough thrust. In contrast, Bae's active optical cavity was demonstrated to supply milliNewtons (mN) of power using small, cheap lasers that can be operated from space so they don't have to suffer the distortion of cutting through the Earth's atmosphere. Rather than using the Earth as a backstop, the space-based laser platforms would send beams to push against spacecraft while keeping the central laser stationary with a balancing beam in the opposite direction, or with a conventional thruster attached to the laser platform.
http://www.eetimes.com/showArticle.jhtml?articleID...

Please, please stop saying this is an Earth-based propulsion system.




By Master Kenobi (blog) on 9/21/2007 1:44:22 PM , Rating: 3
Yea, I read the article in question and your right. I'm not sure why masher2 is harping on the laser being earth based.


RE: No More Misinformation
By masher2 (blog) on 9/21/2007 1:47:32 PM , Rating: 1
You've totally misunderstood the context. The "space based platforms" pushing against other spacecraft is indeed useful for attitude control during formation flight. But that doesn't allow propulsion to other destinations. It merely allows the satellite formation to trade momentum. In oversimplified terms, if one needs to move a little left, and the other right, they can do so for free in such a system, rather than both wasting propellant.

To use this as a launch platform or a means to propel a craft to another point in the solar system, you'll need to base your platform off the earth or some other sufficiently massive "neutral" platform. You can't generate momemtum out of thin air, or else perpetual motion machines would be possible.


RE: No More Misinformation
By phattyboombatty on 9/21/2007 2:47:41 PM , Rating: 3
Please read the EE Times article linked in my post. The satellite that is being pushed off of using a conventional thruster (i.e. fuel based) to counteract the propulsion.


RE: No More Misinformation
By phattyboombatty on 9/21/2007 2:52:49 PM , Rating: 2
The article also gives a neat little diagram to show how it would work.


RE: No More Misinformation
By masher2 (blog) on 9/21/2007 3:14:55 PM , Rating: 2
I see. Now look at the 'conventional thruster' used to balance the platform. A little thought should convince you that, if that thruster develops a force of 1000N, then you can't apply a force stronger than that to the payload. So there's no "amplification" occurring in this case.

In fact, you're actually losing ground, as you not only need the energy to run the thruster, but also the laser (which is typically only a few percent efficient) plus losses in the mirrors themselves.

So the system is a losing proposition from a perspective of total energy or total momentum transferred. Its only useful in one special case-- where the mass ratio of the payload compared to the launch platform is very small. In that case, even though you're losing energy and momentum, you're gaining more velocity than you'd get from directly powering the payload with that thruster. A factor of 10,000 would definitely work...with good lasers and mirrors, a factor of 1000:1 might be feasible.

That means to launch a 10kg microsatellite, a launch platform of between 10-100 metric tons would be required. That's feasible. But to launch a 100 ton spacecraft, you'd need a platform in the 100K-1M ton range. Clearly infeasible.

All this is born out by Bae's own words. This is useful for satellite attitude control and micro payloads. But if you want to launch any massive object, you're going to need an anchored platform.


RE: No More Misinformation
By phattyboombatty on 9/21/2007 3:27:27 PM , Rating: 2
Assuming the propulsion force is a constant 35uN, like the example from the article, the stationary satellite would only have to counteract the 35uN force, which would require an extremely small amount of fuel to generate.

Are you still thinking this has something to do with launching satellites into space from Earth? It's pretty clear to me that this system is used to transport payloads after they have already been placed into orbit by conventional fuel-based rockets.


RE: No More Misinformation
By masher2 (blog) on 9/21/2007 3:45:33 PM , Rating: 2
> "the stationary satellite would only have to counteract the 35uN force, which would require an extremely small amount of fuel to generate."

You're missing the point. Say you've got that 35uN thruster in space already. Why wouldn't you simply attach it directly to the payload? Why put in this complicated system of mirrors and lasers? And waste the energy needed to power it all? Since you're only going to get a total thrust of 35uN anyway, its far more efficient to leave all that junk on the ground, and just drive the payload directly.

As I said in the previous post, it only pays off if there's a huge mass ratio differential between platform and payload. In that case that ratio imbalance translates to an acceleration imbalance. The payload receives the same thrust, but a much higher acceleration. That translates to higher velocities. But again, this is possibly only for micropayloads.

> "It's pretty clear to me that this system is used to transport payloads after they have already been placed into orbit "

Its not intended for any fixed purpose. Its useful in the following cases:

- attitude control of satellite constellations.
- Orbital-based launch of micro-payloads (assuming more powerful lasers)
- Terrestrial-based launch of conventional payloads (assuming much more powerful lasers)


RE: No More Misinformation
By phattyboombatty on 9/21/2007 4:09:20 PM , Rating: 4
The point of the mirrors and lasers is to take a lot of weight off of the payload and stick it on the stationary satellite instead. I never disputed that the payloads are micro-payloads. I never disputed that there would be a large mass difference between the payload and the stationary satellite. My only dispute has focused from the start on your original assertion that Bae's research (discussed in the article) involved Earth-based lasers. I've come to the conclusion that you're so in love with yourself that you'll never admit you were wrong, so its hopeless to try to debate you anymore on this.


RE: No More Misinformation
By masher2 (blog) on 9/21/2007 9:59:16 PM , Rating: 2
> "My only dispute has focused from the start on your original assertion that Bae's research...involved Earth-based lasers. "

My original assertion was related to the article itself. The title is "laser engine may revolutionize space travel".

To most people "space travel" implies moving something at least slightly more substantial than a 5 kg ball. I was merely trying to get people to understand that moving around nontrivial payloads is going to require terrestrial launch facilities. I didn't mean to imply they were feasible at present (quite the opposite) or that Bae intended this to be the primary use of the system. I merely wanted to clear up any misconceptions about the system's potential.

If you feel my original post was misleading, I can accept that. The important part is that we both agree this system is not useful for orbital-based launches of nontrivial payloads.


RE: No More Misinformation
By guwd1 on 9/22/2007 1:49:33 PM , Rating: 2
Regarding 'out of the box thinking' I don't really see the problem with countering the force exerted on say a laser-firing satellite/platform. Why do you have to counter the force exerted on the platform (if the laser is reflected off / being fired from that platform) with another force at the same time? Why not counter it later? Think about all the possibilities we might have if we can simply postpone the need to correct the platforms speed/position enough to make use of this energy.

Not sure I'm explaining this well but here's a try:
Remember that 'a straight line' in space is not so straight. I'm not talking about relativity here just the massive objects (planets including moons and the sun) and their associated gravity which prevents you from traveling straight without active correction. Use this to your advantage and you can store the energy exerted on the platform for later use (back and forth changes in the platforms kinetic and potential energy).

Example: Firing towards the spacecraft/probe/whatever will push the platform a bit in the opposite direction, but this is not necessarily a problem, if you've planed for this maybe you can create a scenario where the platform will (given time) turn around (big U-turn half way round a planet, say... earth) due to gravitational pull from some massive object.
So after some waiting time, during which the platform will not be able to fire at the spacecraft/probe, the platform will once again be in a 'firing position', only this time it's traveling towards the spacecraft/probe with the extra speed it received earlier
(Or the opposite: traveling away from the spacecraft with less speed than it originally had, it doesn't matter).
Once again firing against the spacecraft and taking into account the current direction of gravitational pull and the likely increase in offset you've recived during the waiting time, you should be able to calculate a way to make the force that the laser beam exerts on the platform in this second firing interval cancel out the 'effect' (speed/depositioning) that the first firing interval has caused on the platform.

So what you need is basically a platform positioned relative to earth (or any suitable planet-sized or bigger object in space) in such a way that the force exerted on it by the laser doesn't put it more out of course then what is later correctable: It has to be able to remain in orbit despite being slightly off-course long enough (until the next laser-firing interval).
For example if the platform is positioned so that it follows earths rotation (located in the same part of the sky all the time, there is a word for this of course but I don't remember it) this waiting time would be approx 12 hours, allowing you to fire for (I'm guessing) 1-2 hours starting every twelfth hour.

You are basically using the planet as a buffer that allows you to store the energy a small amount of time (if you wait too long the platform will leave orbit, one way or the other ;) ).
Having multiple stations like this would allow for continuous laser-firing at the target. But then again it's basically as simple as: the more laser platforms the better propulsion power/time ratio you get, continuous / multiple simultaneous beams or whatever.


RE: No More Misinformation
By Ajax9000 on 9/23/2007 9:18:52 PM , Rating: 2
quote:
Regarding 'out of the box thinking' I don't really see the problem with countering the force exerted on say a laser-firing satellite/platform. Why do you have to counter the force exerted on the platform (if the laser is reflected off / being fired from that platform) with another force at the same time? Why not counter it later?


I agree with you guwd1, but I think a delayed counterforce is unnecessary.

Everyone seems to have forgotten that there is a relatively simple (for space operations :-) fuel-less technique that can be used to stationkeep an orbiting launch platform for this system -- an electrodynamic tether operating in propulsion mode (http://www.google.com.au/search?q=electrodynamic+t... ). This uses the Earths' magnetic field to absorb the counterthrust. Importantly, prototype tether missions have already flown (with mixed success).

BTW, thanks for the EE Times link phattyboombatty, I was wondering how the system was going to cope with the problem of laser beam divergence (http://www.google.com.au/search?q=laser+Beam+Diver... ) and the picture in the link gave the answer. Beam divergence is a significant issue at interplanetary distances. IIRC for Earth-Moon distance measurements an optical telescope was used to create a bigger beam waist -- and even then only a few photons would make it back from the round-trip (old SciAm article I read once).


RE: No More Misinformation
By masher2 (blog) on 9/24/2007 8:59:26 AM , Rating: 2
quote:
there is a relatively simple ... technique that can be used to stationkeep an orbiting launch platform for this system -- an electrodynamic tether
An interesting idea, but it won't work for stationkeeping in this particular case. A force acting against the Earth's magnetic field will act to reduce orbital velocity, thus bringing the launch platform into a lower orbit. But any probe launched from such a platform is going to want to escape orbit, meaning it will force its launch platform into a lower orbit as well. So the two forces can't counteract each other; they sum, not negate.

Simply put, an ED drag tether can counteract a force only in one particular direction...and that direction is pointed square at the Earth itself.


RE: No More Misinformation
By Ajax9000 on 9/24/2007 8:08:19 PM , Rating: 2
There are two types of EDTs. You referred to a drag EDT, I specifically referred to a propulsion EDT.

Compare paragraph two and paragraph three at http://www.tethers.com/EDTethers.html .


RE: No More Misinformation
By masher2 (blog) on 9/25/2007 10:35:40 AM , Rating: 2
> "You referred to a drag EDT, I specifically referred to a propulsion EDT."

Right, but a propulsion tether isn't "fuel-less". It doesn't require reaction mass, but it does need energy of some sort, in fact as much as is imparted to the launched payload, plus losses. Meaning this still isn't practical for launching anything but micropayloads from very massive platforms.


RE: No More Misinformation
By Ajax9000 on 9/25/2007 8:23:26 PM , Rating: 2
quote:
Right, but a propulsion tether isn't "fuel-less".

Very true. Many designs I have seen use solar panels as the energy source. E.g. from the EDTethers page: "Tethers Unlimited, Inc. has helped NASA to explore the potential for using electrodynamic tether propulsion to maintain the orbit of the ISS. By using excess power generated by the ISS's solar panels to drive current through a conducting tether, a tether reboost system could counteract the drag forces or even raise the station's orbit."

Unless the solar array is huge this makes for a low thrust solution of course. But as the laser system is a low thrust system as well, the two should fit together fairly neatly.

I'd hope that scaling up shouldn't be any harder :-) than scaling up any other space-based system.


RE: No More Misinformation
By werepossum on 9/21/2007 7:08:49 PM , Rating: 1
quote:
Say you've got that 35uN thruster in space already. Why wouldn't you simply attach it directly to the payload? Why put in this complicated system of mirrors and lasers? And waste the energy needed to power it all? Since you're only going to get a total thrust of 35uN anyway, its far more efficient to leave all that junk on the ground, and just drive the payload directly.


ROFLMAO!

Asher, just so you don't feel so bad, not everyone here is incapable of understanding basic physics. I think you'd better give up explaining it though, before your rating goes negative! Now I think I'll go home and look for that special structure of forces that gives me a free unpaired vector.

And now I'm running for home, so anyone flaming me is just rattling an empty cage. LOL


RE: No More Misinformation
By evildorf on 9/21/2007 7:52:10 PM , Rating: 2
You do realize that people with an understanding of basic physics can disagree with the quote you included in your reply, right? If you're going to insult the intelligence of the commenting public, you should at least quote one of them saying something stupid. Instead, you quote a debatable point, roll all over your floor removing your ass by the force of your laughing, and then kiss Masher2's ass a bit. Classic.


RE: No More Misinformation
By augiem on 9/21/2007 1:48:18 PM , Rating: 2
Ahh, yes this makes sense. Exactly what I was envisioning when in my post above to masher2 about how orbiting lasers would work by using an additional beam(s) in the opposite direction of the payload craft for balance.

The confusion has ended.

Thanks!


RE: No More Misinformation
By augiem on 9/21/2007 1:51:06 PM , Rating: 2
just so there is no confusion in the above statement: ASSUMING there's a planet beind the laser somewhere


RE: No More Misinformation
By Mgz on 9/25/2007 8:50:27 PM , Rating: 2
Beam me up, scotty


How much power?
By jak3676 on 9/21/2007 11:30:33 AM , Rating: 3
This all looks great, my only question is how much power (electricity) does it take to accomplish this? i.e. what is the return rates. Is the power envelop required within the scale that we can get from solar panels or would this take a massive generator to provide the electricity required? The article states that it can provide constant thrust, but doesn't mention what the requirement is to provide this constant output. Reguardless its a great leap forward - I'll go look for some more information.




RE: How much power?
By JasonMick (blog) on 9/21/2007 12:03:49 PM , Rating: 4
The Bae Institute, claims that the laser operates well within the current limits of space power budgets (I think I mention this in the article somewhere). I don't know enough about the shuttle/satellite's power systems to know exactly how many watts/etc. they mean, but it seems like it must not be unreasonably high, if their claims are true.

The continuous output is a problem for long term travel, but if you are talking about only a week, it might be doable on a generator's power.

Hopefully Dr. Young Bae's paper will mention the power rates and efficiency of the engine when it is published.


RE: How much power?
By masher2 (blog) on 9/21/2007 12:06:42 PM , Rating: 2