Modular Laser Launch Systems

BerntB writes "I don't think Jordin Kare's NIAC article has been covered? It's about using new laser tech to build modular laser launch systems. The modular nature makes it easier to test and build. The only other launch ideas as cool are the Orion Project and the space elevator."

Comments

Jerry Pournelle

[multiplexo]

used to write about these in his stories in the 1970s and also wrote about them in his book A Step Farther Out. You can probably go to his website, http://www.jerrypournelle.com, browse around and find more information, or send Dr. Pournelle an e-mail.

Went to a lecture on this by Jordin a while back

[WolfWithoutAClause]

There's a few 'gotchas':

a) the vehicle may blind by reflected light at a considerable distance (100m - 1km or more- think of the wildlife [handwring]).

b) it ideally uses pure liquid hydrogen fuel; this means that the fuel tank ends up pretty heavy relative to the fuel (heavier than the space shuttle, because the Space Shuttle tank also holds LOX, so the average propellent density is rather better.) The ratio of the vehicle weight full/empty is critical in a high performing rocket- so this rocket doesn't perform as well as you would hope- it's not a SSTO solution, not quite, so he has a drop tank or two.

c) got a few billion? The lasers are very expensive... note that conventional rockets can be designed for *well* under a billion if you don't do anything fancy (see SpaceX)

d) it works best when you are launching a lot, but then again, just about any launch system gets cheap real fast if you launch a lot; and this one is expensive up front, so you have to launch even more to offset this.

Still, it's a very cool idea, and he's still working on it. But I can't shake the feeling Jordin has missed something that will move the idea up one more notch.

Look at the numbers on this

[Animats]

Laser launch is a nice idea, but the power requirements are huge. The current altitude record is 71 meters (not kilometers), with a 51 gram (not Kg) craft and a 10 kilowatt laser.

Kare, who's been plugging this idea for decades, writes "A rule of thumb for laser launchers is that the unit payload is 1 kg per MW of laser power." The Apollo lunar module (all the stuff that went to the moon) massed about 6500 Kg, of which 2500Kg made the round trip. So we're going to need several gigawatts of laser power for a moon shot.

Kare is talking about using continuous diode lasers in the 1KW range. These don't exist, but 60W units are available, so this isn't totally unreasonable. Kare proposes to use maybe 150 of these future 1KW units in a prototype. That only launches a 150g craft.

Launching something the size of the Apollo lunar module would take six million such units, and about 12 gigawatts of electrical power for several minutes. This is twice the power output of Grand Coulee Dam, the biggest single power source in the US.

The power storage problem might be overcome using ultracapacitors. You can get 2600 farad capacitors (not ufd, farads) at 2.5V today, and you can take current out fast. Auto engines can be started with six of these things, weighing a total of about 3Kg. With a big budget, a laser launch system could have enough energy storage to do the job.

Six million lasers, though, is a bit much. The prototype doesn't put enough mass in orbit to be useful, and the real version is too big.

If you want to launch a microsat, you call Orbital Sciences Corporation, and they launch a Pegasus rocket from a L-1011 for you. The X-prize guys get all the press, but Orbital actually puts stuff in orbit. They've launched 45 payloads so far. Click here for their user manual.

Re:Look at the numbers on this

[pyrrhonist]

The power storage problem might be overcome using ultracapacitors. You can get 2600 farad capacitors (not ufd, farads) at 2.5V today, and you can take current out fast. Auto engines can be started with six of these things, weighing a total of about 3Kg. With a big budget, a laser launch system could have enough energy storage to do the job.

Actually, there's an easier way. I had a chance to tour the Princeton Plasma Physics Lab when they were still doing experiments with their big tokamak.

One of the things about doing plasma physics (i.e. attempting neclear fusion) is that you need an absolutely ginormous amount of energy to get the experiment started. What's more is that pulling all this energy off of the power grid at once and then dropping the load causes some, shall we say, "slight instabilites", with the power grid.

So, the way you get enough power is to slowly bleed power off of the grid and store it somewhere so that you can use it all at once at a later time. The way that they did this at the PPPL is with huge concrete discs encased in concrete bunkers that gradually spun up as more energy was applied. When enough energy was stored kinetically, they'd disconnect from the grid and apply the brakes to the discs to generate electricity for the experiment. At least this way, NJ was never blacked out, because of an experiment.

The amount of energy these things can store is amazing. One time, one of the discs broke. Most of the pieces embedded themselves in the bunkers, but one piece bounced around and flew out. The piece landed 40 miles away.

Re:Riding the Highways of Light

[rmayes100]

That is some really cool stuff. I had trouble with the link there, here's the article I think you are refering too:

Riding the Highways of Light