Monday, December 7, 2009

Like a Virgin ...

Virgin Galactic's SpaceShipTwo was officially rolled out today, bringing suborbital space tourism one step closer to really happening.

Future generations may have their share of mirth over the choice of name, particularly in our current less than chaste era. They can also ponder the iconography of the logo, a young woman in a tastefully impractical spacesuit. I hope they have a good laugh, because that will mean that SpaceShipTwo did well enough to be remembered.

I've had mixed feelings in the past about suborbital tourism, which is in some ways a gimmick, less demanding by an order of magnitude (at least!) than getting into orbit, the real ticket to Space. On the other hand it can't hurt, and may be a proving ground for technologies and streamlined operating procedures that will in time allow cheaper orbital flight.

Here's to a wonderful first time!


Anonymous said...

That logo looks a lot like Second World War era nosecone art. And I suspect SpaceShip Two will be remembered in the same way that people remember pre-WWII airplane travel: Gimmicky, expensive, and somehow more elegant than today's rushed commercial travel.

It's also interesting to see that after decades of over-promising and under-delivering, from government and private-sector alike, someone seems to be building a launch-craft that does exactly what it says in the brochure.

"Virgin Galactic: Taking rich people for a ride since 2011."


Z said...

It's not orbit, but it does represent a return to a build-a-little, fix-a-little, fly-a-little, development of a technology base. Sure, the propulsion and TPS requirement are something like an order of magnitude easier, but the day Virgin Galactic turns a profit, there will be a real, honest-to-goodness no-funky-military-accounting for more and more reliable and powerful rockets, RCS and TPS systems- delivering longer and longer flights more and more often to a market of more and more people with smaller and smaller incomes. Sure, it might stall out, and certainly won't "run to completion," but it might just be the kind of environment where the simple facts of rocketry- that the equation, while cold, are certainly not unmanageable- gets turned into an economic reality.

Citizen Joe said...

I noticed an article on a space elevator tower that uses an electron cloud to provide pressure instead of air. There's already theoretical models for 100 km, GEO and something further out. While such an elevator would be great for cargo, nobody is gonna want to ride an elevator for a month to get to orbit. So, you could take the Virgin ship up instead. The tower could then catch the ship while passengers disembarked for the remainder of their trip.

Of course, that doesn't really help much as far as the rest of the trip goes. As a matter of scale , the edge of space is 100 km. At that altitude, gravity (net apparent, centripetal force accounted for) is still about 9.4 m/s/s. At 500 km (the ISS) gravity is about 8.4 m/s/s. At 4500 km, gravity is about the same as Mars surface. At one Earth radius, gravity is about 2.4 m/s/s. Lunar gravity is available at about 8500 km. At 1 Earth diameter (12700km), it is about 1 m/s/s. At about three times that distance you have GEOstationary orbit.

I'm not sure at what point you say close enough and use boosters for the remainder of the trip.

Jean Remy said...

Unless you're an aviation nut, the name Tony Jannus will mean little, and the Benoist XIV flying boat even less and Percival Fansler nothing at all.

But Percival Fansler wanted to create an airline to link the cities of St. Petersburg and Tampa, which, though in sight of one another, required hours by train or automobile. Even more with horse and buggy. After signing a contract with Benoist and hiring several pilots, including Tony Jannus, everything was ready.

On January 1st, 1914, carrying passenger (and mayor of St. Petersburg FL.) Abram C. Pheil, Jannus left St. Petersburg at 10 a.m, flew over Tampa bay, and arrived twenty-three minutes later in Tampa. The average altitude of the flight was 15 meters above the bay. The seaplane reached the astounding speed of 121 km/h (75 mph).

It was the first scheduled commercial airline route ever implemented. And it cost $5.00 a ticket.

What does this tell us?

Well first, in 1914, city mayors had balls of tungsten-steel, because, DAMN.

Secondly, well, next time you are at an airport, look around, really look, and think about more than the technology. Think about the infrastructure, the complexity, the sheer momentum of the power of industry applied to a dream that started with a wooden seaplane flying at highway speeds fifteen meters above water.

I suggest you sit down for this. You might get dizzy.

I also have to add, this is a stunningly beautiful machine they've built there.

Thucydides said...

For at least a generation, craft like SpaceShip Two will be to transport what cars or airplanes were to (really) rich enthusiasts in the early part of the last century: expensive toys.

This isn't a bad thing, actually. Rich people can afford to hire servents and mechanics to tinker with their toys, and these people take their knowledge to the toymakers for better and better models.

Of course, you might get weird digressions like super powered roadsters with V-16 engines, or aviation companies which produce little more than one race plane per year (Bee-Gee race planes), but even these show which are technological or economic dead ends for everyone else.

Finally, the knowledge base is big enough and enough people are entering the market looking for customers that niches that you or I could afford become filled with products and services that we actually want!

By this sort of progression (and assuming technology isn't forced by war the way aviation technology was boosted by WW II), we will probably see some sort of spacegoing Model T or Piper Cub by @ 2030.

Of course if Global warming fraudsters manage to destabilize the economy with their schemes, things will slow down (perhaps considerably), but there is no reason to believe that Tata or some Chinese firm can't do the job...

Jean Remy said...

2030 seems like an overly optimistic timeline.

IF SS2 is a success, or even partially so, we might have, before the end of the century, a Cessna Citation equivalent in a similar design. They can fly in a few hours to the ends of the world, and ferry a CEO from New York to Tokyo for a luncheon, and be back for dinner. If Hugh Hefner is still alive after having his brain transplanted in a clone body, he will have one.

By 2130 we might have a high-performance vehicle that ferry passengers, mostly lower level businessmen on expense accounts, in suborbital ballistic hops across the globe in 90 minutes. Said ballistic hopper might carry with it a cargo pod with its own engine able to boost a micro satellite to LEO or a high-altitude weather balloon. This ballistic Concorde would be a marvel of (over-)engineering, probably run at a deficit by an airline company that maintains it for the prestige, and might eventually be a commercial failure if it was engineering marvel.

To really get a Piper Club IN SPACE we would need to discover some drastically new technology that will change the way we get to orbit. Rick mentioned in a previous post a sort of anti-gravity or gravity-reversing engine. Short of any semi-miraculous thing like that, suborbital and orbital access vehicles will remain the purview of the military, corporations, and multinational scientific expeditions. And a select few super-rich.

Anonymous said...

To be honest, it's probably a good idea that we won't be getting cheap surface-to-orbit crafts anytime soon. If 9/11 was bad, imagine crashing a space-Cessna into downtown Manhattan.


Jean Remy said...

Really, probably not that bad. If they come in steep to conserve maximum kinetic energy they'd suffer burn-though. If they came in at an ideal angle the friction would slow them down and they would arrive with no greater speed that a Cessna, and most likely empty tanks, and would be built at least as lightly as a Citation if not more.

It's one thing to drop a rod of solid tungsten straight through the atmosphere, it's another to do the same with a complex, fragile shuttle, especially if you want to pilot it at arrival.

Rick said...

I had no idea that someone did a commercial airline route in 1914!

A while back I suggested that technologies typically take ~50 years to mature. But when do you set the clock? Does it start with the X-15 and end with SS2, or start with SS1 and end with a 'space Citation' sometime around midcentury.

But the tougher question is whether robustness and simple operation, the key to cheap, can be combined at all with the extreme performance needed to reach orbit.

On the other hand, it was about 150 years from the Stockton & Darlington to the TGV (or a mere 125 years to the Shinkansen). On that timetable we could expect practical human orbital flight around 2075-2100.

Citizen Joe said...

How does the saying go? Cheap, Fast, Good... pick one.

I suppose for cheap, you just assume that a meteor will impact Earth eventually and eject matter into orbit...

Fast could include the Pegasus booster system.

Good... I'm not entirely convinced that we've come up with a good means of getting something into orbit. Right now, all the methods involve riding a bomb into space...

Jim Baerg said...

"Of course if Global warming fraudsters manage to destabilize the economy with their schemes,"

It seems rather fraudulent to suggest that moving away from fossil fuels will wreck the economy. Replacing fossil fuels with nuclear can be done for many applications at no greater expense.
Eg: electricity generation, ocean shipping, rail travel (by electrifying the rail lines) are ones that come to my mind.

It will benefit some while damaging the prosperity of those invested in fossil fuels (which is why there is well funded opposition to nuclear power).

Jean Remy said...

Going to pick a few nits.

Is the TGV the maturity of the rail? No, it is the ultimate expression of the technology. It is the very best we can do at this time, and so there will always be something better in the horizon.

The first steam rail line was opened in 1804. I would advance maturity for steam rail as the Orient Express, opened in 1883. By that time most European countries had railroad systems that could be linked together (implying a shared technology, and shared gauge, therefore implying standardization) The Orient Express cemented the train into the consciousness. It became synonymous with a sort of casual luxury for travel. It's still 80 years, rather than fifty, but railroad and steam power also harkened the age of industrialization, without which the maturity time for a technology is far far greater than 50 years anyway.

Maturity therefore is not the "current ultimate expression of the technology" but "at what point did it become a common cheap and reliable form of itself that can be applied on a widespread level. I think we're nearing that point in terms of standard rocketry. The launch of an R-7 rocket carrying a small be-antennaed spherical radio transmitter shook the world. Badly. In 1957. Do we even twitch at the news of yet ANOTHER TV sat going up on an Ariane IV? Yawn. It doesn't even make CNN. That's maturity.

Is SS2 a mature X-15? Probably not yet. We're not jaded enough for that. It's a step in the process though

Rick said...

Good point about the distinction between 'maturity' and 'ultimate expression.' To make a pre-industrial comparison, the TGV is the clipper ship of trains, pushing the technology to a level no one in the age of classical maturity thought was necessary or practical.

The difference between them is interesting too. Both were challenged by a fundamentally later and more 'advanced' tech.

The clippers fought back against steam, but in the end steamers could outperform them in all trades. In contrast, while fast trains are superior to jetliners for trips up to several hundred km, and there's no longer any credible prospect that VTOL or the like will change this.

On global warming. I'm hesitant to wade into contentious political issues here, but this one has its roots in planetary science. I'll make four observations:

1) Scientists, being human, are as prone as anyone else to think that they alone can Save the World.

2) Science is always more complicated and nuanced than the version that gets into the mass media, and thence into political debate.

3) Environmentalists can be really annoying and self righteous (again, common behaviors of H. sapiens), and the movement readily becomes a stalking horse for vegetarianism, Henry David Thoreau wannabees, et al.

4) All of that said, if you dump a lot of CO2 into a planetary atmosphere, other things being equal you will warm up its surface. This is pretty much Planetary Science 101.

Planetary atmospheres are complex, especially Earth's biogenic atmosphere, so a lot of other mechanisms MAY cancel out the projected linear effects of increased CO2. But this is no given, and for now we pretty much have to go with the planetary science we've got.

Which gives us considerable reason to take global warming seriously, and none to dismiss it.

Jean Remy said...

I think a better comparison to the clipper v steamship comparison is the electric v steam train competition, since they operate in the same medium utilizing (mostly) existing infrastructure (railroads and ports)

The first electric rail line opened in 1881, yet there were some streamlined steam engines that were built as late as 1950. Eventually the electric (or diesel-electric for the US on the non-electrified lines) would win over and supplant the steam engine.

The reason I feel the comparison is more valid than the electric-jetliner you seem to imply is that we're talking about complementary rather than supplementary technologies. We currently move 2 billion metric tonnes of crude a year, this would not be possible by airline. Similarly, however, passenger and mail delivery being far less bulky and far more time sensitive benefits hugely from air travel.

In the end, really, the transportation advances never really mesh up between the various mediums (land, sea, air) because of the various challenges posed by each medium. Space is a fourth medium, the difficulty being compounded by the fact you need a form of transportation that links both mediums. Basically SS2 is neither clipper nor TGV but a Hovercraft, which introduces a great many more design problems into the mix (not the least the blunt/streamline issue we discussed in another post) and unlike the Chunnel, which thretens to obsolete the channel hovercrafts, there is no way to dig a tunnel to space...

or, is there? *dun dun duuuun*

Rick said...

You could say in a way that an elevator is a 'tunnel to space.' Or at any rate an el train to space. It has no similarity to either an airplane or spaceship, but in fact basically IS a form of railway.

My comparison of TGVs to clipper ships is along a different dimension. Both embody techs that were not only mature, but thought to have reached their practical limits of refinement until they faced challenges from entirely new techs.

You are right that air travel never challenged freight railroading - its challenge came from trucks.

Jean Remy said...

Actually I was referring to the elevator when I said "or is there? dun dun dunnn".

It was a little obscure.

Kind of in the way the Andromeda Galaxy is a little far.

Jean Remy said...

Oh and I hadn't thought about trucks as being a challenge to the trains but of course!

Thucydides said...

WRT to the technological development of light launch vehicles and the timeline, there are a few developments on the horizon that make me think the 2030 timeline is indeed possible.

Carbon nanotubes and graphine materials promise super light and super strong structures which would allow orbital flight using modest rocket engines and far less fuel than we use today. If the space shuttle orbiter only weighed five tons, the entire stack would become far smaller in proportion and absolute size as well. SpaceShip two might be capable of orbital insertion with its current rocket engine if it was made of featherweight graphine materials.

Removing the engines and fuel entirely and launching with beamed power is another breakthrough, and the convergence of propulsion science by Lyek Myrabo and the development of high energy lasers should come very soon. Myrabo has been waiting for suitable lasers since the 1990's, and demonstration flights using subscale models and modest lasers have taken place. Military laser technology has advanced to the point that rugged 100 kW lasers can now be mounted on aircraft, ships and armoured vehicles for tests, and megawatt lasers are not far behind (sized to fit a Boeing 747 carrier plane).

The real wild card is fusion energy using unconventional methods. Small fusion devices have been developed using diverse techniques like magnetized target fusion, dense focus fusion and Inertial Electrostatic Confinement, all of which (if practical) are far smaller and have higher power densities than conventional devices like laser driven inertial confinement. If they are successful, they can also be fueled with aneutronic fuels like 3He or proton-Boron, which means direct harvesting of electrical energy from the charged fusion products is possible; another order of magnitude reduction in size and cost.

Where politics intrudes can be seen in the current push for economic controls and political rent seeking (Cap and Trade and Carbon Taxes). Given the proponents of "Global Warming" and "Climate Change" have been discovered to have been doctoring data, stonewalling attempts to see raw data, methodology and algorithems; the same data used to support the need for such economic controls as Cap and Trade or Carbon Taxes, then yes there is reason to be concerned.

Since the proponents of man made climate change have tweaked their models to hide or diminish events such as the Medieval Warm Period and the Little Ice Age, I think fraud is certainly a very good word to describe their actions. We can agree that the Earth's climate has changed without resorting to man made causes.

Anonymous said...

I have to say, I don't see any of those technologies having massive impact on launch operations in 20 years time.

Featherlight carbon-composites are incredibly useful. But the types of carbon-composites that would be particularly useful in space operations are still hard to produce and not cost-effective compared to current aerospace materials. We know how to make graphine materials, but we don't know how to make them in large amounts. Twenty years from now, we'll probably just be starting to see experimental launch-vehicles made from these materials as opposed to cheaper aerospace aluminum or titanium steels.

I'm a big proponent of laser-launch technologies, but as far as I can tell they're only useful for small packages. Beyond that the more traditional lift technologies are more cost-effective.

Fusion. Yeah, sure. Anytime real soon now. Wait for it, wa-a-i-i-t...

The people working in the fusion industry have developed a bad habit of over-promising and under-delivering. If you want a real analysis of their claimed results, the rule of thumb from investors is to knock 30% off the claimed outputs and add 30% to the inputs.


Jean Remy said...

1/ Carbon nanotubes: right now we can barely make a few strands. We have no idea how to mass produce them or to effectively "weave" them into, say, giant cables. They are not a magical material either. They have good tensile strength, yes, but are also brittle and non malleable, as metals are. They are also non-conducting. And they do a bad job at contracting and expanding. You can't build an entire engine out of carbon materials. Coat them, yes, but you still need a metal structure. and metal components, and metal electrical systems, especially for power generation. Even more if you want to use fusion, which require magnetic fields, which require a lot of metal, not least of which steel to absorb neutrons, which brings us to

2/ Fusion. Even D-He3 fusion is not truly aneutronic. It will emit free neutrons, in smaller percentages than, say D-T fusion, granted. But it doesn't take a lot of neutrons to ruin your day. So you'll need shielding. Luckily steel and hydrogen make good proton shields, so really you get free shielding just building one. Proton-Boron is aneutronic, but proton-Boron has so many more disadvantages few scientists think it can ever become a viable fusion pair. It gives off very little energy (especially compared to D-T, but even less than D-He3) thus reducing the net power creation. By the way, so far, both Magnetic and Inertial confinements systems have yielded rather the same results. So far net power generation is 65%, that is: 65% of the input power is generated back. For the foreseeable future, fusion generators are energy sinks, not generators. It could change, but to get fro 65% today to a viable source of commercial power, 20 years seems.... actually, unsafe.

3/ ground laser-based delivery systems have been explored. They have several issues. First it would need to be very powerful. Now, lasers of that power are possible, and are being used (ironically the most powerful lasers are used to research inertial confinement systems. Another issue with lasers shooting through the atmosphere is diffraction, which not only lowers their power but might divert part of the beam at unintended targets, notably eyes. There is a multinational treaty, which even the Chinese signed, that forbids the use of laser weapons in a blinding manner.

4/ It is difficult to quantify exactly the impact of one factor on an extremely complex system like the biosphere. However, fudged as some numbers might be, there isn't a world-wide conspiracy of scientists aimed at toppling the US economy. Even if some of the more extreme projections are exaggerated, the consensus across the board is that yes, indeed, man has altered his environment in the past 100 years far more than any other factor naturally occurring could have. We are looking at C02 and CO levels in ice cores from the poles which do not appear in the history of the world's natural climate changes. Ever. One need only take a picture of LA to realize pollution has gone out of hands and needs to be regulated, or that new sources of power need to be sought out and developed. Refusing to develop new clean technologies by threatening it would ruin our economy is to refuse to look at the evidence that it is *because* in the past we have sought out new sources of energy that our economy is even feasible.

Anonymous said...

Does anyone here know the historical rate of increase in Q (The net energy gain factor in fusion)? That is, in 1950 researchers could achieve a Q of ?, in 1965 they achieved a Q of ?, in 1975 ?, in 1990 ?, etc.

I'm curious about the historical rate of progress in fusion research, but can't find the information. I suspect I'm not using the right search terms.


Jean Remy said...

I am actually having to correct my own numbers after further research as prompted by Ian.

The record is Q=1.25 at Japan's JT-60, achieved in 1998

Other than that I can't report much success getting a Q timeline.

Projections for the ITER (an international collaboration, based in France) say they might achieve Q=20 (necessary to even consider a commercially viable generator) by 2030. They expect a fully functional prototype generator to be in place in 2050, and global adoption of fusion power plants no sooner than 2080. Since project backer include the European Union, the Russian Federation, the United States and the People's Republic of China (ie: anyone who has a chance of developing fusion power at all) we can safely guess that unless an unexpected breakthrough happens, these are best case estimates.

ITER is a D-T cycle magnetic confinement reactor.

Citizen Joe said...

Part of the problem, and inherent to D-T fusion, is that the primary energy produced is by means of high energy neutrons. These must first be caught (typically in water) and then converted to heat. That heat then needs to be converted to electricity by means of turbines. Each of those steps adds inefficiencies. If it were applied to a project where heat was required, like a rocket, then you can pick up efficiency from direct usage.

D-He3 throws protons, but you've got mixed reactants. The Deuterium (outside a specific temperature range) will preferentially fuse to itself, which in turn creates He3 and Tritium. The tritium then reacts and throws neutrons. He3-He3 fusion is completely aneutronic, and only throws protons. Protonic fusion can be efficiently converted to electricity due to its charge. It does take a tremendous amount of energy and confinement to get it to work though.

Anonymous said...

So to get from JT-60's 1998 record of Q=1.25 to a goal of Q=20 in 2030, we need a sustainable increase in Q of >53% per year. Doable, if we're in the right part of the development curve.

Now we just need to find out of Q=20 really is the right point for fusion to be competitive with other power sources. If it is, then based on historical rates of uptake for new power sources we could expect fusion to provide 1% of global power needs around the turn of the century.

On the other hand, pyroelectric fusion is already useful in areas other than power generation. By 2030 we may discover that economically-viable fusion power is a pipe dream, but the pure physics pay off in other areas.


Rick said...

Fusion is like AI; they've both been 20 years away for about 50 years now.

Fusion propulsion has considerably different requirements than electric power production, though no easier. You only have to recover enough power to maintain the cycle, and don't have to be cost competitive in power output. On the other hand there's a stringent power density requirement, which power plants don't have.

Jean Remy said...

"Fusion is like AI; they've both been 20 years away for about 50 years now."

But once it is implemented someone twenty years before will have been right that it was 20 years away.

Also, fusion is a simple process and we know how it works. Like the director of the CNRS said once: "It's putting the sun in a box. We just don't know how to make the box yet."

Consciousness? We don't even know what that IS.

Citizen Joe said...

But we do know how to make AI's. Dolly the cloned sheep was artificial and it was intelligent. Actually, you might apply the same logic to in-vitro fertilization, which makes those children artificial intelligences with biological support systems.

I think that just about all of humanity's inventions have come from the observation of nature. Hey! Look at that bird flap its wings, that must be how it flies... no... wait... its the SHAPE of the wing... Fusion has to be possible, because the Sun does it.

Now if we side step our crude efforts to thrust two nuclei together and instead figure out a way to either make gravity (like the Sun) or eliminate the electrostatic force of two like particles, then fusion would be as simple as pouring reagents into a cup.

Luke said...

Jean: There is an important distinction between peak laser power and time averaged laser power. The fusion lasers have very high peak laser powers, but poor time averaged powers. For laser launch, you want a high time averaged power. For this, the current research on military laser weapons seems the most appropriate.

Atmospheric propagation does not cause much diffraction in the usual sense. You will get scattering from the beam path (including some caused by diffraction around particulates), but this in itself is not likely to be a health hazard. You will need good air traffic control, to prevent the lasers from frying commercial and private aircraft.

The anti-blinding laser treaty only forbids lasers specifically designed to cause permanent blindness. It does not address lasers that may incidentally cause blindness as a normal part of their non-blinding duties. It also applies to the use of lasers in warfare - the treaty has no bearing on civilian applications.

That said, we are still a long way from laser launch. A 1 MW continuous laser producing a 5 km/s exhaust velocity would produce a thrust of 400 newtons. That's enough to levitate a 40 kg object against the Earth's gravity.

Anonymous said...

Citizen Joe: "Fusion has to be possible, because the Sun does it."

But that doesn't mean it has to be easy. Fission turned out to be easy - It's happened under Earth-normal conditions at least sixteen times. Google 'natural fission reactor'. On the other hand, fusion has never occurred spontaneously on Earth (Excluding rare high-energy cosmic ray collisions with the atmosphere, because that process has the entire freakin' galaxy powering it).

Fusion-for-energy may be something like lead-into-gold. Possible, but not worth the effort.


Citizen Joe said...

I thought the laser launch technique focuses the laser in a combustion chamber. The intake air then expands to create thrust. The mass reduction for no power plant, no thruster and no remass makes it very light. However, once you get above the atmosphere you lose your thrust.

Anonymous said...

CJ: "I thought the laser launch technique focuses the laser in a combustion chamber. The intake air then expands to create thrust. The mass reduction for no power plant, no thruster and no remass makes it very light. However, once you get above the atmosphere you lose your thrust."
Yes...but if you bring a small amount of propellent on board with you, you can still use the laser to power the long as you are in line-of-sight of the laser.

I'm wondering if a variant of the beamed power launch could be used? Have a solid disk of propellent (like a ceramic, plastic, or composite material), under the bell; use a laser or particle beam to vapourize this material, propelling the craft into orbit; not exactly like the air-breathing lightcraft, but it can be used above the atmosphere by redirecting the beamed power to where the craft is...even if it is in orbit.


Thucydides said...

Better late than never I guess:

Newer fusion schemes like MTF, IEC and Focus Fusion use totally different means to achieve fusion, and if (big if) they work as described they use much smaller, cheaper machinery to create the plasma and achieve fusion. IEC is an outgrowth of the Farnsworth Fusor, and high school kids make these from time to time for science fair projects. If Polywell IEC is feasable, then fusion reactors can be made cheaply by the same people who make your car, not highly trained scientists and engineers.

WRT laser propulsion, using the laser to vaporize propellent blocks was one of the first schemes devised, Lyek Myrabo has refined this idea to use the atmosphere for reaction mass (heated by the laser) to boost to near space altitude. Like I said, the sticking point right now is getting the right laser, his tests shut down while waiting for funding to refurbish a former "SDI" laser, which never seems to have happened.

Read this for a good introduction:

Rick said...

I don't think that laser launch is very well suited to human traffic, for the reason Luke implies - the beam power requirements get hefty, and VERY hefty if you are sending up something heavy like passenger capsules. It is best suited to a steady flow of small freight payloads.

Anonymous said...

What a great resource!