What If We Get Unlimited Supercheap Natural Gas (Methane)?

A guest post by Joseph Friedlander   

In a reader comment I shall always treasure, I got this: What’s next, the economics of importing methane by wormhole from Titan?  

  

Well, actually that would not be a bad business to be in– but if you had access to a wormhole that itself would become the overwhelming fact about the business. (If velocities are not automatically cancelled out that itself becomes an energy source–think about it) Not to mention the military implications (the equivalent of a transporter for assault teams, H-bombs, you name it)  and the literally dozens of other story complications that occur when you introduce a costless method of joining two points in space that sometimes can be very costly indeed. But if we had that, why bother, open a hole to the core of the Sun and get free power that way. (Not a very wide one please and that hole better not spread under radiation pressure or you have just found a new solution for Fermi’s Paradox.)

Or maybe space super-tankers are more your style.

There is always the economics of landing an immersible cubic kilometer capacity sphere ship into the methane/ethane lakes of Titan and scooping up a cubic kilometer of Titanian LNG –456 megatons –with a suitable gas core engine the payload might make it home but really the energy squandered is far more than the mere combustion of methane could provide(that incoming tanker would have far over a gigaton explosive yield if deliberately crashed) 

The actual configuration of such a super-super tanker might be, very durable outside hull deorbits with thin membrane bag within, fills it up, boosts to Titan orbit at 1900 m/sec or so (EV 2.639 km/s)  and rendevous with dump station, dump bag and crew, new crew and bag in, bag gets added to tow string, expensive gas core tanker goes back to Titan, ideally three times a day. Dump station would be better in LOQ Titan orbit, at a lower delta V, but the main point is you want to amortize that huge tanker. ideally a thousand trips a year, and the tanker itself might have a dumb frame and switch outable maintenence intensive tug section including the engines and well-shielded crew compartment. (unlike most designs mass for shielding is DEFINITELY not a problem on this baby) .

Although my first thought was a gas core reactor, such as I postulated for the speculative Aldebaran 2 spacecraft  https://www.nextbigfuture.com/2013/08/in-praise-of-large-payloads-for-space.html actually a Zuppero style ordinary low temperature solid core reactor would work for the boost, so low is the delta V.
https://www.nextbigfuture.com/2012/03/friedlanders-idea-for-nuclear-hopper.html  
 For me the definitive approach to the problem of a robust and buildable solid core thermal rocket reactor is Zuppero et al’s 1998 paper on a Lunar South Pole Space Water Extraction and Trucking System.


There, Zuppero et al postulate easily sublimed lunar volatiles that can be captured near the lunar poles and then trucked to lunar orbit 20 tons at a time (throwing away 92.6 tons propellant water per flight, part of which (75.7 tons) gets them liftoff to orbit, part of which (16.9 tons) retros them and enables landing back on the Moon. The dry ship weighs 10.4 tons including a 292 thermal megawatt reactor deliberately engineered for many many cycles for robustness, durability and low maintenance—keys, as it happens—to economical reuse.


The Zuppero et al paper says,

The nuclear reactor mass of 1818 kg (4000 lbs) is considered 50% more than minimum. The reactor must deliver 292 megawatts to the steam at a mixed mean outlet temperature of 1100 K with propellant flow of 155 kg/s. A rocket nozzle area ratio of 200:1 will deliver a specific impulse of 198 seconds.

Unlike there however on a Moon mission you need to boost to orbit  with lunar water and retro down, here on Titan you get the priceless gifts of aerobraking and free liquid cryogens which changes the picture beyond recognition.

 In fact so favorable is the aviation environment in Titan’s atmosphere that a nuclear ramjet ascent might well allow something close to flying into orbit without anything but around 25% of the propellant loadings (at some altitude scooping thin air tends to add more drag than the collected gas gives boost so you need to go back to rocket power).

This article discusses the aviation paradise of Titan, http://www.centauri-dreams.org/?p=22445
In an environment where gravity is seven times less than on Earth, we’re dealing with an atmospheric pressure one and a half times greater than Earth’s. It was Robert Zubrin who suggested, back in the 1990s, that humans with wings strapped to their arms would be able to fly in this thick and soupy environment. We’ve already seen evidence of this atmosphere’s effect on the Huygens probe, which took fully two and a half hours to descend to the surface in early 2005. 

The paper quoted in the article notes that the same vehicle power and wing configuration will lift 28 times more on Titan than Earth, and 1000 times more on Titan than Mars.  A 250 ton capacity https://en.wikipedia.org/wiki/Antonov_An-225_Mriya An 225 on Earth if could fly on Titan could lift 7000 tons.

  I am not depending on that here though you can easily imagine a hybrid mode– seaplane/spaceplane reenters, buoyantly lands in Kraken Mare (levitated by a cubic kilometer of vacuum),  splashdown, crack the valves open and get to siphoning.
Remember Zuppero’s 1st gen reactor was designed for 1100 K. Nerva nuclear tests showed 2800 K to be a reasonable target.  If 2800 K can be achieved and coking can be avoided liquid methane can give an exhaust velocity of 5942.8299 m/sec (606 seconds of impulse) vs 4.5 for hydrogen oxygen chemical fuels.(See Zubrin’s table below) 

 I hope no one will object to the cost because remember liquid methane is nearly free FOB Kraken Mare.  I am giving figures for a gigaton class  tanker but I don’t really think our first exporting station will use gigaton tankers, just trying to get a feel for the ultimate scale possible even if there were 1000 x the official 9000 cubic kilometers of LNG available.  3 flights a day is half a teraton a year of natural gas. For one shuttle.  So dense is the Titanian atmosphere that a very small ascent rocket might need to use a balloon to get high enough to successfully ascend; a very large ship can neglect (within reason) atmospheric resistance.


Robert Zubrin’s Wonderful NIMF paper on exploring Mars with nuclear rockets and compressors from1990 gives nuclear exhaust velocities on common chemicals run through a nuclear rocket:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19910012833.pdf

A cubic kilometer 456 megaton ton cargo of Titanian LNG would need around 300 million tons of structure in the ship to also contain the propellant. (If that sounds high it’s not given you want a very robust ship and are also carrying another 500 megatons of LNG as propellant both for ascent and terminal pre splashdown use. My instinct is you could get away with a third that amount of structure but I am thinking of a ship as reusable as an Earthly tugboat (I guarantee the engines will need massive switching out and maintenance in the orbital port) 
Liftoff mass 1300 megatons,  cargo 500 megatons, (includes 40 megatons retro propellant allowance) structure 300 megatons, exhaust velocity 5942 m/sec, (methane) propellant 500 megatons  delta v 2885 m/sec (part of this pays for drag and gravity losses)  Mission delta-v to low Titan Orbit 1900-2700 m/sec (Titan escape velocity  2.639 km/s) 
Zubrin gives 2.4 gigawatts 2400 mw as needed for lifting 330 tons at 2800 K engine temperature. 
~9600 terawatts (9600 thousand gigawatts) thermal are needed for a 1.3 gigaton liftoff from Titan at 2800 K engine temperature. 
Remember the Liberty ship engine discussed in my article here 
https://www.nextbigfuture.com/2013/08/in-praise-of-large-payloads-for-space.html
which had 80 gigawatts each. (Much higher exhaust velocity, less propellant  throughput)  You would need the power of 120,000 of them.  The Phoebus 2A engine fired in 1968 by NASA  put out 4000 megawatts. (4 gigawatts)

  The final 2A test in June 1968 ran for over 12 minutes at 4,000 MW,
https://en.wikipedia.org/wiki/Nuclear_thermal_rocket#Test_firings

 You would instead need 2.4 million of those engines putting out 9600 terawatts
Roughly modeling the fuel loadings, assume 80 kilo of U-235 or U-233,  talking 192000 tons of U-235. Realistically we have plenty of weight to play with and luxurious margins and plenty of cryogenic coolant available. My feeling is a Phoebus clone engine putting out 80,000 MW is doable, using 80 kilo of U-235.  to keep the ship loading down to 20 tons of U-235. But if not it under 200 tons is comparable to many reactor loadings today (albeit with far more 235)

• 0.9664 gram U235 second burned (needs full critical mass to function) derived from Atomic Rockets website  table below http://www.projectrho.com/public_html/rocket/atomicfuel.php

Fuel	MeV/fission	TJ/kg	1000 MW burn
235U	202.5 MeV	83.14 TJ/kg	0.01208 gram/sec
233U	197.9 MeV	81.95 TJ/kg	0.01220 gram/sec
239Pu	207.1 MeV	83.61 TJ/kg	0.01196 gram/sec

Regarding active thrusting time– assuming 10 minutes will do it, implying fuel throughflow of a million tons a second of propellant methane. Wow.  Also implying

Once  achieving Titan orbit– A second tug tows the bags to a depot where it waits for a Earth transfer opportunity.
   Interplanetary transfer can be by Hohmann boost with a string of pearls, each kilometer sized bag (now in a chilled micrometeor proof shield) is pushed during the once a Earth year transfer season, arriving 6 years later at Earth (time value of money ticking all the way but not undoable).

 Possibly an Orion type tug might push, a Medusa might pull or a wide variety of other tether systems tricks including rotary spin and release (but there is only one launch opportunity for a Hohmann transfer per Earth year at minimum delta v so that’s why the nuclear option, to push the most cargo throughput).  The economics feel reasonable for a far future economy at $100 a ton a cubic kilometer of LNG would then be 45.6 billion dollars but as we’ll see below there is a catch.

Readers new to Next Big Future might ask, why methane from Titan?
2000 plus known  cubic miles of LNG liquid methane and ethane. 
Youve heard of a cubic mile of oil? (of which in proven reserves there are around 50)  https://en.wikipedia.org/wiki/Cubic_mile_of_oil
= 1,300 billion barrels (210×109 m3).
 This corresponds to roughly 43 cubic miles, or 43 CMO.
Natural gas reserves total 42 CMOs (69 years at current consumption)
Coal reserves total 121 CMOs (150 years at current consumption)

CMO, meet CMLNG —Cubic Mile of Oil–Meet a cubic mile of LNG.  We use about 1.25 CMLNGs.
https://en.wikipedia.org/wiki/Liquefied_natural_gas

World total production


Year Capacity (Mtpa)
1990 50
2014 246


LNG achieves a higher reduction in volume than compressed natural gas (CNG) so that the (volumetric) energy density of LNG is 2.4 times greater than that of CNG or 60 percent that of diesel fuel…
The range of heating value can span +/- 10 to 15 percent. A typical value of the higher heating value of LNG is approximately 50 MJ/kg or 21,500 Btu/lb A typical value of the lower heating value of LNG is 45 MJ/kg or 19,350 BTU/lb.


For the purpose of comparison of different fuels the heating value may be expressed in terms of energy per volume which is known as the energy density expressed in MJ/liter. The density of LNG is roughly 0.41 kg/liter to 0.5 kg/liter, depending on temperature, pressure, and composition compared to water at 1.0 kg/liter. Using the median value of 0.45 kg/liter, the typical energy density values are 22.5 MJ/liter (based on higher heating value) or 20.3 MJ/liter (based on lower heating value).


The (volume-based) energy density of LNG is approximately 2.4 times greater than that of CNG which makes it economical to transport natural gas by ship in the form of LNG. The energy density of LNG is comparable to propane and ethanol but is only 60 percent that of diesel and 70 percent that of gasoline


1 billion meters cubic of natural gas is 35.315 billion cubic feet of natural gas or 760 
kilotons of of LNG or 38.847 trillion BTU


Source: DOE Office of Fossil Energy * Based on a volume conversion of 600:1, LNG density of 456 kg per cubic meter of LNG, and 1,100 gross dry Btu per cubic feet of gas.
Liquefied Natural Gas – U.S. Department of Energy

energy.gov/sites/prod/files/2013/04/f0/LNG_primerupd.pdf


So playing with those numbers, a cubic kilometer of LNG is 456 megatons which is the equivalent of  600 cubic kilometers (600 billion cubic meters) of natural gas.
https://en.wikipedia.org/wiki/Billion_cubic_metres_of_natural_gas
 BP uses standard which is equivalent to 41.87 petajoules (1.163×10e10 kWh) per billion cubic metres


And remember Titan has visible surface lakes of 9000 cubic kilometers which is the equivalent of 456 megatons of LNG x 9000 or  4 104 000 megatons of  LNG like liquids. In other words 4.104 teratons or more than the volume of Phobos
5783.61 km3; 

https://en.wikipedia.org/wiki/Phobos_(moon)
and nearly 3 times the mass of Deimos
1.4762×10e12 tons

Current market price LNG per ton around $400 in Japan  383 at 7.90 million btus
USA natural gas prices around a quarter of that or $100 a ton. A cubic kilometer of LNG would then be 45.6 billion dollars. Times 9000 that is 410400 billion dollars. $410 trillion.  

 According to the World Bank, the 2013 nominal  gross world product was ~US$75.59 trillion.

So get your Texas petroleum hydrocarbons hat on under your bubble helmet and let’s ride out to the Titan Lake Country mining boom.

New Views of Titan’s Lake Country
Paul Gilster at Centauri Dreams –
Titan has about 9000 cubic kilometers of liquid hydrocarbon, some forty times more than in all the proven oil reservoirs on Eart
hhttp://www.centauri-dreams.org/?p=29692

by Paul Gilster on December 17, 2013

NASA/JPL-Caltech/ASI/USGS
Titan has about 9000 cubic kilometers of liquid hydrocarbon, some forty times more than in all the proven oil reservoirs on Earth. That’s just one of the findings of scientists working over the data from recent Cassini flybys of the Saturnian moon. …That’s part of Titan’s fascination, of course, because it’s similar to the Earth in terms of basic interactions between liquids, solids and gases but completely alien in terms of temperatures.

Just how extensive are those seas and lakes we’ve found in Titan’s northern hemisphere?…. Kraken Mare, Titan’s largest sea, and Ligeia Mare, the second largest, appear along with nearby lakes. We learn not only that Kraken Mare is more extensive than first thought, but that almost all the lakes on Titan are in an area some 900 kilometers by 1800 kilometers. A mere three percent of the liquid on Titan is found outside this region. Cassini radar team member Randolph Kirk explains:

    “Scientists have been wondering why Titan’s lakes are where they are. These images show us that the bedrock and geology must be creating a particularly inviting environment for lakes in this box. We think it may be something like the formation of the prehistoric lake called Lake Lahontan near Lake Tahoe in Nevada and California, where deformation of the crust created fissures that could be filled up with liquid….  Because the liquid methane of Ligeia Mare is very pure, Cassini’s radar signal passes through it easily and can detect a signal from the sea floor. The lake turns out to be about 170 meters deep, and in at least one place is deeper than the average depth of Lake Michigan…”

Incidentially I used to live not far from Lake Michigan and  am a little puzzled by that last comment since the average depth is  85 m). Maybe they meant greatest depth? Which is 281 m.  Perfect depth to land dry and then fill the tanker up. In any case since Lake Michigan contains a volume of 1,180 cubic miles (4,918 km³) of water. We are talking about 2 lake Michigans  volume of liquid natural gas.  And my take on the evidence is that this is a drainage sump, a low place on Titan’s surface where the ‘water table’ is poking up. I would not exclude millions of cubic kilometers of the stuff lying deep, though as we see later it hardly matter if your goal is to burn it on Earth.

https://youtu.be/RrGPtCdItBw
The importance of Titan’s methane is that is basically proves that abiotic methane is not only possible in the Cosmos but probable.
Unless you believe in Titanian dinosaurs in which case do I have a kid’s TV show pitch for you.

From say 1744 and early studies of oil 
https://books.google.co.il/books?id=eckUAAAAIAAJ&pg=PA34


https://en.wikipedia.org/wiki/Timeline_of_geology 

Until 1944 when Gerard Kuiper detected an atmosphere around Titan containing methane https://en.wikipedia.org/wiki/Gerard_Kuiper#Discoveries  the biological origin of methane was a reasonable hypothesis but frankly since then pathetic to watch purely biotic origin being pushed as the ONLY source of natural gas.
Methane-CH4– is the most stable hydrocarbon IIRC, it is generated by breakdown of more complex ones.  And built up from simpler ones in an abundance of available hydrogen. That alone is a powerful argument for chemistry, not biology being the origin of most of it.

 It may be that geology and astrophysics don’t talk together as often as they should; it could be in my view a historical paradigm that is very hard to get out of because early advocates of evolution really liked the idea of fossil fuel as opposed to abiotic chemistry dominating things in the depths of the earth. It was part of the mental wardrobe they were fashioning to redress the past and although you can understand why they were forceful advocates for their ideas about petroleum and NG geology–really–science is about accepting evidence when it becomes overwhelming.
Is Petroleum abiotic? Dunno, not the discussion here. 

Is methane? Provably.  Titan, dude. Kraken Mare alone is comparable to the Caspian Sea. Of LNG.

The one killer objection to importing the known vast reserves of Titanian methane is not the abundance of methane there but the shortage of oxygen here?
Shortage? Oxygen? Earth? Get real!
But as a cycle its infinite. Once in once out; not so much. When you burn lunar silicon (link below) that’s what happens.
As I point out in https://www.nextbigfuture.com/2012/03/lunar-silicon-vs-helium-3.html 
the atmosphere of the Earth masses around 5 milion gigatons. 21% oxygen is around a million gigatons of oxygen.  
So since methane has 1 carbon  (12 gigatons uses up 32 gigatons of oxygen and makes 44 gigatons of CO2) and 4 hydrogens (4 gigatons H uses up 32 gigatons of oxygen and makes 36 gigatons of H2O )

 So 16 gigatons of methane uses up 64 gigatons of oxygen to make 80 gigatons of products: 44 gigatons of CO2 + 36 gigatons of H2O.

Since 64 gigatons of oxygen  is used up if there is no recycling (you send CO2 through the wormhole to Titan for disposal or up the rotovator
https://en.wikipedia.org/wiki/Momentum_exchange_tether
 that exchanges momentum from space to earth transport  in one scenario (if you can mine the incoming from Saturn momentum that is many times the power of the combustion of the LNG) then burning LNG can’t go on for long. 

If you keep the reaction products on Earth of course you have a 36000 new cubic kilometers of water (negligable against the 1.37 billion or so in the ocean)  and a CO2 disposal problem.

But let’s assume it’s once in once out. 1 million gt oxygen / 4,104 such gigatons in the known 9000 km3 of Titanian LNG is 1 part in 243 or so of oxygen burned or .41 percent.  of the 21 percent.  Hm. Looks like a rounding error And I could use a spare $410 trillion for pocket change…


Well you can see where that dynamic leads.  And then of course the full millions of cubic kilometers of LNG is confirmed on Titan…If the biosphere is allowed to recycle the carbon by definition we are headed for a new level of carbon sequestration.


But wait.   There are other uses for methane gas. Suppose we just import it but don’t burn it?  First of all the energy coming in at minimum escape velocity is on the order of 63 mj kg
1562atmosphere earth 5 million gt so 1million gt oxygen so 10000 gt lunar silicon uses up 1% 30 gt for how many years 333
Atmosphere of Earth – Wikipedia, the free encyclopedia

all 2,795 gigatons of carbon dioxide now scheduled for release into the atmosphere would likely warm the Earth to an astonishing 11 degrees Celsius.rtf
Liquid CO2 has a density of1.1470km3.rtf
km ab mtns 400k km3 plus 45-900tw freeze ice.rtf

For the whole Earth, with a cross section of 127,400,000 km2, the total energy rate is 174 petawatts (1.740×1017 W), plus or minus 3.5%. This value is the total rate of solar energy received by the planet; about half, 89 PW, reaches the Earth’s surface.[citation needed]
http://en.wikipedia.org/wiki/World_energy_consumptionPrimary energyWorld energy and power supply (TWh)[15]
Energy Power
1990 102 569 11 821
2000 117 687 15 395
2005 133 602 18 258
2008 143 851 20 181  2.28 tw full time mine
Source: IEA/OECD

Other RE* 15 284 10.6%
Others 241 0.2%
Total 143 851 100%
Source: IEA *`=solar, wind, geothermal and biofuels

Another use for massive areas of film– aerostat construction! (Giant balloons to support huge masses in the atmosphere like mile wide artificial clouds—notice the small size of huge airliners next to fluffy cumulus masses)


Keith Henson’s estimates (simplifying greatly) show that 120 mw of constant electric power for the hydrogen and 2 mw constant power for the CO2 capture can produce the materials needed from air and water for 1000 barrels of oil equivalent a day.(Synthetic oil through a gas shift reaction using 1/3 of the H to reduce the CO2 to CO, then using the mixture of CO and the remaining H to make the hydrocarbon liquids. So a gigawatt of constant power can synthesize 8000 barrels of oil a day, and in a year that is equivalent to about 2.9 million barrels of oil a year. A terawatt of constant electric power would give 2.9 billion barrels a year. The cost at 10c a kilowatt-hour (today) would be, per barrel, around $240-300 (insurance against absolute civilization-breaking price increases if we used thorium molten-salt reactors or space solar power at that 10c a kilowatt-hour price because those are scalable to more than the entire needs of all the world (15 TW today) or even at USA levels of consumption–(say 75 TW for an all USA standard world. Many other power sources like conventional hydro top out at a terawatt or two real potential—24/7 output.) For that 75 terawatt world, of course I am thinking in terms of a USA standard world of huge cars like a vintage Chrysler Imperial of 1961 or 1970, or the full sized finned Cadillac of 1959 or 1967 but there is no reason to be intentionally wasteful! Even with limitless wealth, all places (think Tokyo) do not have limitless room.


Slides by Keith Henson


The prospect of $300 a barrel oil would basically end business as usual. Carpooling would be an economic neccessity, deliveries might be limited to full truckloads– but there would be unlimited availability at that price, and we would not go back to a horse and buggy economy (locally, quite possible at those prices) or lose the ability to fight wars, travel by air, etc.


There is however, every prospect of nearly unlimited 2c per kilowatt-hour power, or even 1c per kilowatt-hour power or even less from those two sources, Thorium and space solar. At that price, nearly unlimited oil and plastics at $30 a barrel (directly drawing down the greenhouse gas surplus WITHOUT the cap and trade Big Brother nightmare) become profitable and so we may eventually hear whining about Peak Atmospheric Carbon Dioxide instead!


What is interesting is that with such a capability to generate massive amounts of hydrogen, and say hydrogen-rich linings of pressure vessels (balloon-shaped) to enable massive lift, we may be able to build massive aerostats using synthetic methane, ammonia, hydrogen, or even (insulated steam) water vapor—(after all, clouds visibly float). By massive I mean cubic kilometer-scale. Considering that a cubic kilometer of air at STP weighs 1.29 million tons, and a cubic kilometer of hydrogen at STP weighs around 90,000 tons, you can see that with a 200,000 ton envelope we could support a million tons of weight– with 5 tons of cabin per inhabitant, and 5 tons of machinery/support stuff, we could trail a hose (really a plastic film kilometer-wide perimeter) like a jellyfish to suck up moist lower air and supply the water needs of the floating 100,000 person city! 


The walls of the gas envelope –even if say quartz cloth from the asteroids–might be lined with hydrogen containing plastics to avoid hydrogen embrittlement in metal components http://en.wikipedia.org/wiki/Hydrogen_embrittlement


To generate by electrical means starting with water 90,000 tons of hydrogen (at 48kwh/kg, 48mwh/ton, 48gwhr/kiloton) will take 4320 gigawatt-hours– over half a gigawatt year. At a single penny a kilowatt-hour it would cost $10,000 a gigawatt hour or $43.2 million. That is for just a single 90 kilotons of hydrogen aerostat. But barring leaks (and hydrogen WANTS to escape-) this would be a capital cost. Imagine a 30 terawatt world, with 3 terawatts dedicated solely to hydrogen production for hydrogen aerostats. 


That is 6083 cubic kilometer capacity aerostats filled (1.4 kilometers diameter). At 100,000 people each in a decade 6 billion people could be living in aerial cities. It would certainly cut urban sprawl. One imagines it would cut transportation costs as well—since in principal at 12 miles an hour net groundspeed no location on Earth would be more than a month away.


On board gardens could produce fresh vegetables embedded in Styrofoam, and of course imports of food or other goods from ship is only a cable raise away from a ship or a transportation terminal or even jungle site just the way our current cities are supported. In fact one of the great advantages of this would be the ability of literally moving your float city within view of a great
sight– say Angel Falls http://en.wikipedia.org/wiki/Angel_Falls or the Himalayas or Manhattan. (Obviously they could see you too, but a big floating city cluster might, like a balloon festival, be a wonderful multicolored sight—a feature, not a bug)


If they are going to be fixed, however, having them in a straight line would enable very rapid transportation (vacuum levitation tube) literally world wide at near-orbital speeds (At 100,000 people within 1 kilometer of the station, the density is certainly there to support a one-city effect). And there are other transport modes possible—If 10 kilometers apart, and artfully arranged, the levitated cities and pipelines would enable the kind of Cape of Good Horn to Bering Strait to South Africa rapid transit that has long been a dream of vacuum subway advocates. However, an aerial version may actually be more practical than undersea and underground tubes because of lack of continental drift and earthquakes (and sea bottom quakes) Having such vacuum subways available in the high stratosphere (30 km up at a 99% lift penalty ie 10,000 tons lifted instead of a million with hydrogen) would enable a switching track to orbit, where the exiting vacuum levitation vehicle would punch through the Martian thickness atmosphere at that altitude and be in space within seconds (going for example at escape velocity already)


One interesting application for aerostat cities would be supporting yet another huge user of asteroidal industry produced films and fabrics– the ‘atmospheric skyway industry’ (as yet nonexistent!) Consider a chain of aerostat cities over the Atlantic on a straight line or great circle route. Now imagine each supporting its’ section of a ‘pipeline’ or ‘skyway’ with a hydrogen atmosphere inside.


Assuming a design could be found that could resist the sonic boom, it would be a great way to get hypersonic travel with unique advantages. First of all, a ramjet like craft could fly in it (ramjets top out at about 2 kilometers per second = 4 473.87258 miles per hour) but scramjets could take over above that. (Ramjets would need accelerated start up at the start of the tunnel.) Getting up to speed, it enters the hydrogen skyway and burns—oxygen, liquid oxygen http://en.wikipedia.org/wiki/Liquid_oxygen from tanks inside http://upload.wikimedia.org/wikipedia/commons/8/82/Liquid_Oxygen.gif (Typically in a 8:1 ratio (the real-life 6:1 ratio in some hydrogen-oxygen rocket engines is to make sure no precious hydrogen goes unburned– but here oxygen is scarce and hydrogen is plentiful). Although massively disadvantaged by burn ratio, the oxygen is much easier to store on board, very compactly and at high density (liquid hydrogen has a density of .07, (67.8 kg·m-3 ) liquid oxygen 1.14) So although the oxygen weighs 8 times more than the hydrogen, the tank holding it (which can be much less insulated) can be 16 times smaller. 


From Wikipedia SSTO article http://en.wikipedia.org/wiki/SSTO
While kerosene tanks can be 1% of the weight of their contents, hydrogen tanks often must weigh 10% of their contents. This is because of both the low density and the additional insulation required to minimize boiloff (a problem which does not occur with kerosene and many other fuels). The low density of hydrogen further affects the design of the rest of the vehicle — pumps and pipework need to be much larger in order to pump the fuel to the engine. The end result is the thrust/weight ratio of hydrogen-fueled engines is 30–50% lower than comparable engines using denser fuels.


Hydrogen has nearly 30% higher specific impulse (about 450 seconds vs. 350 seconds) than most dense fuels.




This tankage weight problem would be greatly reduced with just having to carry LOX tanks and scooping hydrogen from the skyway tunnel..


Assuming free hydrogen to burn, a surprisingly small (read normal) sized craft can carry a surprisingly large (read normal) size payload to near-orbital speeds. There are also other huge advantages– the atmosphere is reducing, not oxidizing, so little char will occur to heat shielding– hydrogen conducts heat well, and the speed of sound is far higher in hydrogen than in air (at 27 °C 1310 meters per second against dry air at 20 °C (68 °F), the speed of sound rate of 343.2 meters per second)


Mach 7 in air would then be equivalent to Mach 25 in hydrogen. This suggests a certain reduction in stresses (and increase in re-usability) in a craft making its speed run in a hydrogen atmosphere.


A possible advantage would be confining the sonic boom to the tunnel. http://en.wikipedia.org/wiki/Oklahoma_City_sonic_boom_tests This has kept supersonic travel from being welcomed world wide (and basically killed the Concorde’s overland markets) http://en.wikipedia.org/wiki/Concorde that and the fuel consumption)
Even if only enabling 4500 mile per hour transoceanic travel (1 hour St. Louis to Paris, 3 hours, London to Australia or anywhere to its antipode if a skyway existed) this would be very interesting in terms of a smaller world effect but higher speeds probably are possible as well (not to mention a Single Stage To Orbit reusable craft being practical if it rode on the back of one of them (I am personally skeptical of launches off the back of other craft; accidents have happened that way–


SR71 Sistership, The MD21 Blackbird Accident
4 min – 14 Nov 2007
Uploaded by Blackbird101
http://www.youtube.com/watch?v=GMyC2urCl_4


a better strategy might be rearward ejection from the mother craft as was done with bomb ejection from the A-5A Vigilante, or in the T-Space air launch tests. Or as was actually done with a Minuteman I air launched after drop from the rear of a C-5 http://www.youtube.com/watch?v=It7SQ546xRk


At subsonic C-5 like speeds, the delta V savings are not much.


The t/Space version of air launch provided only modest performance gains compared to a ground launch (savings of 335 m/s to 550 m/s in booster delta-V …
www.astronautix.com/craft/cxv.htm From Mark Wade’s Astronautix site




But we can imagine the equivalent of a pop up vehicle– it goes on a ballistic track out of the tunnel, and in space discharges a vacuum-optimized space booster (that need not be streamlined– like a version of the LM Ascent Module that is (neglecting the ramjet/scramjet) A single-stage to orbit vehicle, one engine, already lit before release, very few failure modes.




Discussion of optimum staging velocity– remember ramjets peak at 2 km/sec, scramjets can easily reach 5-6 km sec. A small amount of rocket power would be necessary for reaction control.
http://en.wikipedia.org/wiki/SSTO


Analysis shows the optimum staging velocity (the speed at which the first stage is dropped) is very high — possibly 3.65 km/s (12,000 feet per second). This means after separation, the large first stage is at high altitude and headed downrange very fast, which makes it difficult to turn around and get back to the launch point


A scramjet that wished to actually fly to orbit could reach the needed staging velocity and more, and could actually approach close enough to orbital velocity that the last bit could be by rocket.




As actual orbital speed (Mach 25 in air) is approached the thing will pull upward, so the actual ballistic path of the tunnel would be constrained as would top speed– but one can imagine a ‘switching track’ where space-bound craft go sharply upward before using a final kilometer or two a second of rocket delta V from on-board fuel before assuming orbit. As several hydrogen oxygen craft (Saturn 5 second and third stages and Space Shuttle engines pod (not whole Orbiter) with external tank) are theoretically capable of reaching orbit single stage with reduced payloads, and as neither the hydrogen nor the tankage for it need be carried in a hydrogen skyway, that may be a possibility here too.





One can also imagine a nuclear ramjet/scramjet reaching orbit in the tunnel without burning liquid oxygen at all … 3000 degrees Kelvin hydrogen exhausts at 9.8 km/sec and theoretically one could reach orbital speed in the tunnel itself (which presumably would make for interesting stresses on the tunnel walls!–Not to mention the bad 5 seconds when it leaves the tunnel and punches its way through the remaining atmosphere—) The mass ratio would be basically like an ordinary plane. However the nuclear fuel could have no contact with the hydrogen– we don’t want ablating flakes of it cast throughout the long tunnel…