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

This is the only orbital platform technology...

[Anonymous Coward]

...that offers a built-in light show and 1600x DVD burning.

Yeah but...

[pyrrhonist]

Can it launch other things besides lasers?

Oh. Nevermind...

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.

How Ironic...

[Baldrson]

The only other launch ideas as cool are the Orion Project and the space elevator.

Since the prior story is about Carnegie Mellon its rather ironic that the most intriguing launch technology was left off entirely -- and it is out of the robotics department of CM: the Rotovar(tm) by Hans Moravec.

We investigate a cheaper system. A satellite in low circular equatorial orbit has two long cables extending in opposite directions. It rotates in the orbital plane, and the cables touch the planet each rotation, with the rotational velocity canceling the orbital velocity. The system acts like two spokes of a giant wheel rolling on the equator.

The orbit is stable, and the taper is minimized when the satellite's diameter is one third the planet's. On Earth it is 4000 km long and touches down every 20 minutes, every 2 hours at six points. Cable motion near the ground is vertical and uniformly accelerated at 1.4 g. The maximum velocity in the atmosphere is 2 km/sec. One eighth the strength of graphite gives it a taper of 10:1, and it can lift 1/54 of its own mass at each contact.

The central idea in this paper, of a satellite that rolls like a wheel, was originated and suggested to me by John McCarthy of Stanford. He also encouraged the work and provided many of the resources for it. The symbolic mathematics was done with the MACSYMA system being developed at MIT. This program behaves like a programmable desk calculator that deals with algebraic expressions instead of simply numbers. It is capable of solving equations, integrating formulas, taking limits and much more.

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:Look at the numbers on this

[Jordin]

You've made a few pessemistic assumptions. The required lasers are available -- 60 watts is the power from a single laser diode "bar" but that's irrelevant; 1 kW is already available from a single diode pumped fiber laser.

One would not (initially) try to launch multi-ton payloads; the baseline concept is to start with roughly 100 kg payloads and let the system grow as investment is available. Contrary to your comment, 100 kg is a useful payload for many applications, especially at a marginal launch cost of perhaps $20,000, as compared to $15 million for a Pegasus. However, a laser launcher would not immediately replace all other launch systems; at least to start with, rockets would still be preferred for heavy single payloads.

When and if we do build a big launcher, 12 GW would be a large power load, but not terribly hard to supply. At the moment, the least expensive storage medium is truck batteries (!) at somewhere around 1 cent/watt, but flywheels or superconducting magnetic storage would probably be preferable for an operational system. Ultracapacitors tend to be better for shorter-duration loads than the few hundred seconds required for a laser launch.

-- Jordin Kare

Riding the Highways of Light

[s_p_oneil]

Here's a similar, but more interesting article: http://science.nasa.gov/newhome/headlines/prop16ap r99%5F1.htm

Now that's cool. ;-) A flying saucer that flies straight up by creating a vacuum above it that literally sucks it upward. Plus, it uses no propellant at all, which means significantly less weight to lift.

Quote:
"You could go halfway around the world in 45 minutes, or from the Earth to the Moon in about 5-1/2 hours."

If NASA wants to build a base on the moon, they need something similar to this. Even if technical problems make it difficult to lift people this way (i.e. excessive heat, microwave radiation, or G-forces), it sounds perfect for lifting heavy cargo and supplies into orbit or to the moon.

Of course, I like the candle-based rocket fuel as well:
http://science.nasa.gov/headlines/y2003/29j an%5Fen virorocket.htm

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

X Prize Proof Of Concept

[SEWilco]

Everyone bring two laser pointers to the Las Vegas water tower on August 1st for an X Prize attempt.

Make sure you bring enough extra batteries for the landing, rewelding the tower, and the second required flight.