Laser propulsion

[SiberianTiger]

After watching the video

And reading about similar experiments carried out by Russian physicists in Prokhorov General Physics Institute (of Russian Academy of Sciences) - they have an abstract in Russian - I wondered, if it's a real possibility that we may see transition of rocket to laser space vehicles in our lifetime?

How realistic do you think is that?

 

[Wishbone]

I'd rather go for laser-ignited fusion...

 

[Pyromaniac605]

I couldn't imagine this being used as any sort of launch vehicle or manned spacecraft, but I can imagine it being implemented into some sort of probe or satellite.

 

[jedidia]

Well, that's some badass laser they're using to shoot that ultralight model 40 feet into the air... I think this doesn't look too good for scaling.

 

[SiberianTiger]

Well, that's some badass laser they're using to shoot that ultralight model 40 feet into the air... I think this doesn't look too good for scaling.

I wish I could translate V.V. Apollonov's article where he describes his vision of powerful ground-based laser boosters, among all things, but that would be lengthy. In essence, he proposed clustering many considerable sized lasers into big round battery.

 

[Sky Captain]

You would need lasers with total sustained beam power in gigawatt range to launch any meaningful payload. Currently such laser battery would cost many many billions of $$$. Then it needs electrical power, lots of it, so you would need to build dedicated high voltage transmisson lines from several very large powerstations to supply enough electricity and I have no idea what effect it would make on the electrical grid when suddenly such enormous load is turned on.

Anyway this would be viable only if there is continous demand for launches to LEO, there is no point of building such hugely expensive facility if you launch few dozen sattelites per year.

 

[SiberianTiger]

You would need lasers with total sustained beam power in gigawatt range to launch any meaningful payload. Currently such laser battery would cost many many billions of $$$. Then it needs electrical power, lots of it, so you would need to build dedicated high voltage transmisson lines from several very large powerstations to supply enough electricity and I have no idea what effect it would make on the electrical grid when suddenly such enormous load is turned on.

Anyway this would be viable only if there is continous demand for launches to LEO, there is no point of building such hugely expensive facility if you launch few dozen sattelites per year.

But then, you save on expendable (or reusable) rockets, their launch pads, manufacturing and all the associated things.

And also, tell the guys in olive uniforms you want to build a number of laser facilities that can launch things into space with ease, or, if you need, take them out in quite a wide volume of space, and your you've got your billions of $$$.

 

[T.Neo]

But then, you save on expendable (or reusable) rockets, their launch pads, manufacturing and all the associated things.

But those (in all probability) end up being cheaper to operate anyway...

And also, tell the guys in olive uniforms you want to build a number of laser facilities that can launch things into space with ease, or, if you need, take them out in quite a wide volume of space, and your you've got your billions of $$$.

That actually backfires on them, because such a device would be enormously controversial both worldwide and back home...

 

[SiberianTiger]

That actually backfires on them, because such a device would be enormously controversial both worldwide and back home...

Military laser installations did and do exist. They aren't paid much attention to, because they can't be used as a strategic weapon. For instance, here are remnants of Terra-3 mammoth sat-killer laser at former Soviet Balkhash test range (unconfirmed rumors are, it was once tested on a US Space Shuttle - at low volume):

It's only a matter of scaling them up.

 

[Wishbone]

The scaling up part hurls itself against blooming. Non-linearity at its best. Either scale up ABL or put lasers into space, or find out some way to create a low-loss channel through the air. Atmosphere is the enemy...

 

[Urwumpe]

The main problem will be effectivity and duration - so the problems are mostly of technical nature.

First problem: There is no perfect reflector. Even in the best thinkable really existing mirror, a small portion of the laser light is not reflected, but absorbed. No problem in a laboratory, with maximal a kW power laser (which is already very powerful). But a Gigawatt laser for hauling a small spacecraft into space is already a different topic, such a thing needs protection from its own laser.

Next problem: Lasers turn only a small part of the energy fed into them into light. So, for firing a GW laser for the duration of an ascent, you need serious cooling. Military lasers today solve this problem by being expendable. They are chemical lasers, that dump the excess heat of a shot away in the form of toxic waste. a single shot does not last longer than a few seconds, so no problem there. But for 10 minutes acceleration (so you don't need to build artillery shell kind of spacecraft), you would need 600 such shots at the same low intensity as such a laser does have. And such a laser is not propulsive on the target, it just ablates parts of the weak skin away.

We would be thinking in terms of laser technology, in completely new dimensions. We would be feeding more energy into a laser, need to convert much more of this energy into light and do that for a longer period of time than we can currently even just dream of.

 

[SiberianTiger]

The scaling up part hurls itself against blooming. Non-linearity at its best. Either scale up ABL or put lasers into space, or find out some way to create a low-loss channel through the air. Atmosphere is the enemy...

I believe the idea is that laser beam with high enough pulse frequency creates a low-loss channel though atmosphere itself, similar to main stream of a lightning bolt. The abstract I linked does not cover the topic, but I've read article of the same scientist, in which he does not only propose laser-driven launch engine, but use of head-on working lasers for effective beaming energy from space to a receiver on Earth through formed plasma channel. I'll try to find this text.

 

[Urwumpe]

Not sure that this works like that, AFAIR you use laser pulses for not loosing as much energy to absorption as you do if the air becomes ionized and opaque for laser light.

It does not make things better, it just makes the stuff less bad.

One application of such ion channels is for example for ground based particle accelerator cannons in various star wars projects, since you can easier transmit ions through such a channel then.

 

[tori]

Also, isn't anyone bothered by the fact that this would only work in atmosphere with its power proportional to local density? The guy in the video talks about going to the moon and beyond... did I miss something? Also, how does one go about calculating the (finite) Isp of this if it has zero mass flow? It just don't add up.

 

[SiberianTiger]

Also, isn't anyone bothered by the fact that this would only work in atmosphere with its power proportional to local density? The guy in the video talks about going to the moon and beyond... did I miss something? Also, how does one go about calculating the (finite) Isp of this if it has zero mass flow? It just don't add up.

Saying again from top of my memory, the Russian version would work on atmospheric air as long as its density is enough, and then start to ablate special compound which is fed into focal area of the reflector. Some calculations provided that ablating compound reserve required for reaching orbit is really small for a craft weighing ~100 kg. Or at least, such is the idea.

 

[N_Molson]

[ame="http://en.wikipedia.org/wiki/Specific_impulse"]ISP[/ame] applies only to rocket and jet engines.

Here it's different : you apply a force generated elsewhere on the object. Much more like a solar sail. Or even a sail on a sailboat.

 

[tori]

SiberianTiger, thanks, makes sense.

N_Molson, yes, exactly, that's why it struck me as odd when the guy in the video said something about 3000 s Isp. Or was that about the ablative mode?

 

[N_Molson]

Maybe this could be used if you build it on the Moon (to avoid atmosphere nuisance), target a Probe launched by a rocket and accelerate it to let's say Proxima Centauri or Oort cloud objects... If you manage to cover a significant surface of the Moon with solar panels, maybe you would get enough power from the Sun. With a mirror of ultra-high quality and cooling devices on the probe and on the laser-generating device, then maybe this could work.

Yeah, we'll probably have mastered nuclear fusion far before all those "if" happen

 

[tori]

I'd also be a little worried about reflections off of that thing when full scale. I mean, if one millionth of that megawatt ray hits someone, then that's a coupe retinas worth of damage right there

Re lasers on the Moon - there's something I find unnerving about beaming large volumes of power from space. Miss the ship by this much, intentionally or not... there goes the neighborhood.

 

[Sky Captain]

ISP applies only to rocket and jet engines.

Here it's different : you apply a force generated elsewhere on the object. Much more like a solar sail. Or even a sail on a sailboat.

In this case it was meant to use laser light to heat up air and later at higher altitudes onboard propellant. Using only light for propulsion would be super ineficient, It would get only 1 N of thrust per 300 MW of laser beam power.