Author Topic: Laser assisted launch?  (Read 5323 times)

Offline vda

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Laser assisted launch?
« on: 02/18/2007 01:56 PM »
A few years ago I came across idea of "laser launch". Basically idea is to vaporize material, which then forms the exhaust and creates thrust.

http://en.wikipedia.org/wiki/Laser_propulsion
http://yarchive.net/space/exotic/laser_launch.html

Pros: porpellant can be basically anything (e.g. water); no big 1 stage booster engine on LV; performance is not limited by amount of energy stored in propellant -> can surpass chemical engine performance.

If I get it right, there are no unsurmountable technical problems preventing this from working, "only" lack of interest -> lack of R&D money.

Does it make sense to "piggyback" R&D of such a system on current ELV launches. Something like:

1. Build low-lower laser and teach it to be able to precisely point into nozzle of ELV in boost phase. With laser beam too feeble to do any kind of damage it is safe & cheap. The goal is to perfect laser beam aiming, measure athmospheric effects on the beam etc...

2. Build bigger laser and shoot laser beam into nozzle/combustion chamber of ELV on a small part of ascent trajectory, say ~5 seconds. The goal is to get small measurable effect on vehicle performance. At this stage of R&D ELV is still not modified and flies it's usual trajectory.

3. Laser assist. Bigger laser, longer duration of laser "firing", ELV trajectory possibly adapted to make geomentry more favorable for aiming. At this stage we want to noticeably improve ELV's performance.

Offline Tom Ligon

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RE: Laser assisted launch?
« Reply #1 on: 02/18/2007 04:27 PM »
I've seen a demo video in which they launch an object that looks rather like a styrofoam cup, and it really is impressive to watch the sucker delta V.

The array of lasers to do this for practical spacecraft would be awesome, and very expensive.  It would probably be an effective launch system, but the economics would be daunting.  At some scale it probaby is practical, but the up-front costs are going to make folks choke and squirm until a payback is in sight.  But that's a general trend in everything worthwhile, isn't it?

There's also the matter of powering human flight.  These lasers go well beyond what would qualify as an anti-aircraft weapon.  I wonder how many folks would pay to be on their receiving end?

Offline publiusr

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Re: Laser assisted launch?
« Reply #2 on: 02/18/2007 08:50 PM »
I think Leik Myrabo was to do a book for Apogee on the subject--but he has taken forever.

It would probably take a nuclear reactor and a laser both in a building a mile on a side to place a Vostok mass craft up there--and it would be molten by the time it reached orbit.

I wish people would forget all this talk about doing away with rockets--embrace them--and increase their size and capability over time as we have done with all other forms of transportation.

Offline khallow

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Re: Laser assisted launch?
« Reply #3 on: 02/19/2007 04:53 AM »
Quote
publiusr - 18/2/2007  1:50 PM

I think Leik Myrabo was to do a book for Apogee on the subject--but he has taken forever.

It would probably take a nuclear reactor and a laser both in a building a mile on a side to place a Vostok mass craft up there--and it would be molten by the time it reached orbit.

I wish people would forget all this talk about doing away with rockets--embrace them--and increase their size and capability over time as we have done with all other forms of transportation.

Why would it be molten? Remember that most of the heat can be drawn off by the reaction mass and the rest of the vehicle can be highly reflective to the laser.

There are obvious limitations with rockets. My take is that there're fundamental problems with any mode of transportation that requires the energy of a small nuclear bomb inserted inside the vehicle at the start and operates on narrow engineering/safety margins. There's little "let's make it twice as strong as it needs to be" because that would result in a heavy vehicle that couldn't achieve its job. Concepts like laser assisted launch or space tethers are attempts to get around some of these problems.

With an infrared laser and frozen water as the payload, here's some benefits. No cryonics on the first stage of the vehicle, there's no need to have the ice well below the freezing point of water. That part also won't be an explosive hazard. With the energy source applied remotely and a single propellant type, the vehicle probably would save some weight on plumbing too.
Karl Hallowell

Offline vda

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Re: Laser assisted launch?
« Reply #4 on: 02/19/2007 08:11 AM »
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publiusr - 17/2/2007  10:50 PM
It would probably take a nuclear reactor and a laser both in a building a mile on a side to place a Vostok mass craft up there

We already have nuclear reactors (and other forms of electricity generation) which are totally adequate for this kind of task. R&D stage 2 laser would be in 1-10MW range - big, but not nearly THAT big. Such lasers already exist, even in mobile variants (THEL).

Quote
--and it would be molten by the time it reached orbit.

I doubt laser beam will be able to even _reach_ the wall of combustion chamber of e.g. working RS-68 engine if you fire laser from the ground. It has to penetrate air, exhaust plume and very hot and dense gases in combustion chamber. If it was unclear, the goal is to arrange for laser beam to be absorbed mostly by the chamber gas, raising its temperature and resulting Isp.

Offline vda

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RE: Laser assisted launch?
« Reply #5 on: 02/19/2007 08:21 AM »
Quote
Tom Ligon - 17/2/2007  6:27 PM
The array of lasers to do this for practical spacecraft would be awesome, and very expensive.  It would probably be an effective launch system, but the economics would be daunting.  At some scale it probaby is practical, but the up-front costs are going to make folks choke and squirm until a payback is in sight.  But that's a general trend in everything worthwhile, isn't it?

Full-fledged laser launch system - yes, building it is expensive. I am saying that maybe trying something simpler first is much cheaper - basically, it's little more than bringing THEL to Delta IV launch and firing it precisely into the nozzle from the back while Delta IV is ascending.

If THEL can hit a flying mortar round, it shouldn't need any further improvement in accuracy of targeting machinery or beam width to track RS-68's nozzle?

Offline stargazer777

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RE: Laser assisted launch?
« Reply #6 on: 02/19/2007 09:31 AM »
Full-fledged laser launch system - yes, building it is expensive. I am saying that maybe trying something simpler first is much cheaper - basically, it's little more than bringing THEL to Delta IV launch and firing it precisely into the nozzle from the back while Delta IV is ascending.

 If THEL can hit a flying mortar round, it shouldn't need any further improvement in accuracy of targeting machinery or beam width to track RS-68's nozzle?
I understand that there is continuing research on this topic.  However, tracking a missile (or whatever you want to call it) and maintaining constant contact by laser through the atmosphere may be more difficult than you imagine.  Remember it doesn't take much cloud cover to completely disperse a laser.  In fact, I understand that this is one of the reasons the ABL (Airborne Laser project designed to target and destroy enemy missiles in their boost phase) -- which seems like a much simpler project -- has run into so many delays.  Atmospheric moisture, light clouds, all can diminish the laser's effectiveness.  The concept of a laser assisted launch is attractive, but I fear we will be using rockets (of some kind) for a very long time to come -- at least until we build a space elevator.

Offline vda

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RE: Laser assisted launch?
« Reply #7 on: 02/19/2007 10:00 AM »
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stargazer777 - 18/2/2007  11:31 AM
If THEL can hit a flying mortar round, it shouldn't need any further improvement in accuracy of targeting machinery or beam width to track RS-68's nozzle?

I understand that there is continuing research on this topic.  However, tracking a missile (or whatever you want to call it) and maintaining constant contact by laser through the atmosphere may be more difficult than you imagine.  Remember it doesn't take much cloud cover to completely disperse a laser.

Thank NASA for placing space launch complex on Cape Canaveral. Wet swampy terrain near the ocean. Not just wet, but wet with sea salts! Oh yeah, just about right to spend billions of $s on corrosion protection for vehicles and buildings. You cannot even properly dig flame trenches underground in this swamp, need to build huge ramps instead, which in turn lead to "cannot use rail tracks for transportation, ramps are too steep for trains", and now suddenly you can't have 4-SRB rockets "because crawlers can't support the load". Just wonderful...

Maybe we just should launch rockets from places with much drier climate and atmosphere, like deserts?

Offline Jim

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RE: Laser assisted launch?
« Reply #8 on: 02/19/2007 12:21 PM »
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vda - 19/2/2007  6:00 AM

Thank NASA for placing space launch complex on Cape Canaveral. Wet swampy terrain near the ocean. Not just wet, but wet with sea salts! Oh yeah, just about right to spend billions of $s on corrosion protection for vehicles and buildings. You cannot even properly dig flame trenches underground in this swamp, need to build huge ramps instead, which in turn lead to "cannot use rail tracks for transportation, ramps are too steep for trains", and now suddenly you can't have 4-SRB rockets "because crawlers can't support the load". Just wonderful...


What is this rant all about?  Totally nonsense.   There is reasons why KSC and CCAFS are where they are

Trains couldn't handle 4 SRB's neither

Offline TyMoore

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RE: Laser assisted launch?
« Reply #9 on: 02/19/2007 12:45 PM »
It is just about the most southerly part of the US that is part of the continental US. Corpus Christi, Texas is also possible, but can get whacked with a storm surge (I'm not sure how high Cape Canaveral is, but probably no more than a few feet above sea level too.) Only a Florida --Easterly-- launch site has thousands of miles of clear open ocean to dump hardware if something goes wrong. A Easterly launch corridor from Corpus Christi would involve hundreds of miles of the Gulf (with all kinds of oil platforms to hit,) and Florida Keys, not to mention Cuba. Overflight of populations by heavy, supersonic, and flammable hardware would probably give any respectable RSO heartfailure all the way...

Seems like the only other reasonable alternative would be a Hawaii launch site which I think Dr. Werhner Von Braun first proposed for his big rocket. But moving that much hardware across that much ocean...it's no wonder that NASA launches from Cape Canaveral! The logistics is much, much simpler I think.

Offline tom nackid

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Re: Laser assisted launch?
« Reply #10 on: 02/22/2007 09:08 PM »
Florida:

* Close to equator to take advantage of Earth's spin.
* Heavy hardware can be shipped in by barge already assembled. Having to build large rocket stages onsite was partly to blame for the Soviet's N1 disasters.
* Open, uninhabited ocean to the east for dumping stages. Russia dumps spent stages containing of toxic fuel remnants on nomadic herders to the east.

Seems to be a fair trade off.

Offline Joffan

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Re: Laser assisted launch?
« Reply #11 on: 02/22/2007 11:36 PM »
I hijacked the last four remarks here and opened a new thread to pursue the topic of launch site choice...

ETA: the link doesn't want to format so here it is nekkid:

http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=6787&posts=2&start=1
Max Q for humanity becoming spacefaring

Offline publiusr

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Re: Laser assisted launch?
« Reply #12 on: 03/02/2007 07:15 PM »
I seem to remember a program where a laser was pulsed in order to cut through some metal, in that a single beam encountered stagnant gases coming off--reducing the effect of the beam. This doesn't seem to be the case when cutting metal up close.

But the plume coming off the rocket may itself weaken/distort the beam...

Offline TyMoore

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Re: Laser assisted launch?
« Reply #13 on: 03/02/2007 08:27 PM »
Pulsing the beam allows the plume to dissipate slighly--otherwise most of the lasing energy goes into heating the plume and forming a plasma and thus dissipating energy away from the 'work.' A large industrial laser avoids this problem by using a cutting head through which a jet of gas blows vaporized material away from the work.


Offline stargazer777

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Re: Laser assisted launch?
« Reply #14 on: 03/02/2007 09:02 PM »
Would there be any advantage to having one or more lasers on the rocket itself?  Solid state lasers might be light weight enough -- the question would seem to me to be whether you would gain more in thrust than you would lose in additional weight -- of course conventional rocket engines aren't exactly light weight either.  You may gain quite a bit if you can bypass complex and heavy machinery of a regular liquid fuel or even solid fuel booster.  

Offline kevin-rf

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Re: Laser assisted launch?
« Reply #15 on: 03/03/2007 12:55 PM »
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stargazer777 - 2/3/2007  4:02 PM

Would there be any advantage to having one or more lasers on the rocket itself?  Solid state lasers might be light weight enough -- the question would seem to me to be whether you would gain more in thrust than you would lose in additional weight -- of course conventional rocket engines aren't exactly light weight either.  You may gain quite a bit if you can bypass complex and heavy machinery of a regular liquid fuel or even solid fuel booster.  

The laser may be "lite" but the power supply would not be, you would first have to convert fuel to electricity and then the electricity to light. Call it a wild guess but a rocket engine would be a more efficent way to go for a launch vehicle. Lasers are not the most energy efficent devices in the world...
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Offline BarryKirk

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Re: Laser assisted launch?
« Reply #16 on: 03/03/2007 04:19 PM »
Rocket engines have a surprisingly high thrust to weight ratio.  They are also fairly efficient at converting the energy content of the fuel into thrust.

The advantage of a ground based laser is that it doesn't matter how heavy the laser, fuel, or power supply are since they stay on the ground.

The only mass that counts is the mass on the part that leaves the ground.

One of the biggest problems with a conventional rocket is the limitation of the ISP of chemical fuels.  The higher ISP fuels can be difficult to deal with for one or more of the following reasons.

1) Low density, so large volumes required. ( Mostly with Hydrogen )
2) Low ISP.
3) Some of the fuels are cryogenic which makes them harder to work with and store.

With a laser heating up the reaction mass there are more choices available for what to use for the reaction mass, since that mass doesn't also have to provide the energy.  Also, the temperature and therefore the ISP can be raised to arbitrarily high levels.

Offline publiusr

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Re: Laser assisted launch?
« Reply #17 on: 03/30/2007 07:53 PM »
Now if you chilled propellants for maximum density, and heated the rocket body right as the engine started to ignite---you might get both the benefits of higher density from chilled propellants and higher energy from their heating.

To prevent the tanks from bursting, you would have to heat it up at the moment the engine fires up to reduce pressure on the tanks. By heating the propellants hotter as more of the propellant load's mass is 'staged' as thrust--you keep pressure up in the body of the rocket and you don't have to fire up thru the plume.


I don't know as I'd try it---and its probably more trouble than what its worth.

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