Nerdy Notes: Supersonic After All

Despite their advantages, vactrains woul require rather unsightly tubes to be built between destinations. (source:

In the 1960s and ‘70s, the common assumption among the traveling public was that supersonic transportation would become a significant reality some day.  After all, it was only the next, logical step beyond ordinary, sub-sonic jetliners.  Aviation seemed to be advancing at an incredible rate.  The transition from propeller-driven aircraft to jetliners had only taken a few decades.  With the technology to travel above the speed of sound and the tremendous advantages of being able to cross the Atlantic, for example, in under three hours, few barriers seemed to stand in the way of flight above mach one.

Although that seems not to have taken place, that thinking may actually have been correct.  The technology does exist to travel faster than the speed of sound—much faster.  Unfortunately, developing that technology would work against the world of aviation, and it is likely that that is one reason for which it has not come about.  Ultimately, the fastest, most efficient, and—surprisingly—quietest methods of transport would be those without wings and which never left the ground.  The technology spoken of is the vacuum train.

Vacuum trains were first conceptualized over a century ago.  At that time, however, the technology to develop them did not exist, at least not with any degree of financial viability.  That is no longer the case.

Vacuum trains work on some very simple principles of physics.  Specifically: it is easier to move an object through a vacuum than it is through a medium, such as air.  That’s why airplanes fly at high altitudes—the air is thinner, so there is less resistance.

To take this explanation to an extreme, let’s consider space stations and space shuttles.  When these objects orbit the Earth, they do so at about 17,000 miles per hour—much, much faster than a bullet flies.  The International Space Station, and any other low-orbit spacecraft, will fly all the way around the world several times a day, experiencing multiple sunrises and sunsets.  This is significant because, at first glance, one rather imagines it must take a lot of engine power to maintain such incredible velocity.  Actually, though, it takes just about none whatsoever—spacecraft in Earth orbit float freely.  Once they’ve been given a boost up to that phenomenal speed, they keep going with little assistance (actually, Earth’s gravity and drag induced by trace elements of the exosphere do cause orbiting spacecraft to decelerate and lose altitude, so they require occasional bursts of thrust to keep themselves up and running).

As Sir Isaac Newton famously noted, an object in motion tends to remain in motion.  That’s why spacecraft don’t need much to keep going.  In space—in a vacuum—there’s nothing (or almost nothing) to slow them down.

A vacuum train would work on the same principle.  A tube would be built—between two cities, for example—and all the atmosphere would be sucked out of it by pumps.  Once the atmosphere was evacuated, any object moving through that tube would encounter the same level of resistance as experienced in outer space—none whatsoever.  Well, almost.

Traveling through a vacuum tube would still pose the problem of friction with the tube itself.  A train, for example, would presumably run on rails, and therefore lose energy through its wheels.  That said, a train on traditional wheels would be able to move many times faster in a vacuum than the same train pushing through thick, ground-level air.  But vacuum trains propose to eliminate this problem altogether by having the trains make no contact at all with the tube.

You may have heard of “maglev” trains.  Maglev—short for magnetic levitation—is the science of using electromagnets to elevate objects (trains, namely) into the air.  With this technology, there is no physical contact between a train and its track.  It floats on a magnetic force field the same way any two household magnets might oppose each other.

By combining maglev technology with the described vacuum tube idea, proponents of “vactrains” have a pretty solid argument.  They describe a technology in which a train floats on electromagnetic forces in a tube with no atmosphere.  Thus, there is zero resistance experienced.  Because there is no air to push aside, the train would be able to accelerate and move quickly and easily.

Just how quickly and easily is somewhat startling.  According to various nerds who sit about thinking up these things, a vactrain would be able to hum along at a gentle 3,000 to 4,000 miles per hour.  That means crossing the United States of America—say from New York to Los Angeles—in about an hour.  Of course, extra time would be needed to accelerate to and slow down from that high speed.  The energy needed to move at these speeds would not be as great as you might imagine.  In terms of overall energy needed, it would take about one fourth as much energy to move a vactrain with 250 people at 3,000 miles an hour as it does to move a similarly sized jetliner at one sixth that speed.  Plus, because vactrains run entirely on electricity, there would be no environmental output or carbon footprint whatsoever, aside from that of the power stations generating the electricity in the first place.  Additionally, because vactrains travel in a vacuum, they would produce no sound—at all.  Sound cannot travel through a vacuum, so even if you pressed your ear to the outside of the vactrain’s tube as it flashed past at 3,000 miles per hour, you wouldn’t even hear so much as a whisper.

In addition, vactrains would be arguably safer than planes.  If a vactrain broke down in transit, it wouldn’t plummet thousands of feet to Earth; it would just stop in its tube and sit there idly.  In a real emergency, air could be released into the vacuum tube, slowing the train and providing breathable atmosphere in the event of decompression of the passenger cars.  Plus, with propulsion provided by the electromagnetic rails rather than any onboard engine, the system could be linked to any number of power stations and have enormous levels of redundancy.  On top of all this, vactrains would operate—obviously—in at atmosphere-free environment, so no sort of inclement weather would affect them.  The most hellish of blizzards going on outside the vacuum tube would have no impact on operations within it.  Thick fog can ground airplanes; vactrains wouldn’t even take notice.

Naturally, the question has to be asked: if all this is true, why aren’t we using these machines?

There are a lot of reasons.  Firstly, vactrains would be anathemas to the airlines.  A huge, highly respected, and proud industry which is renowned for safety would be utterly unable to compete.  The airlines would do—and indirectly, are doing—everything possible to keep vactrains from becoming a reality.

Second, vactrains would be a burden on existing power grids.  In the United States, new power plants are not constructed very often, especially now that we have awoken to an age of environmental awareness.  Creating any sizeable network of electromagnetically propelled trains would require new sources of power.  Although there are clean, green ways to do this, the fact remains that building the trains would have to be accompanied by building new power stations.

Third, there’s no way to slowly integrate vactrains into people’s comfort zones.  Unlike airplanes, which grew very gradually through stages of experimentation over many decades, a vactrain would go from nothing to everything almost overnight.  There would be no puttering around in an experimental, beginning mode.  Rather, people would simply be asked to trust that this new technology was safe and sound in its fully-developed form.  Only time could truly prove that, and as with anything big and new, it would take lots of time for people to get accustomed to the technology.

And of course, there’s politics.  Whose districts and states would these trains pass through?  Who would give up land to the potentially unsightly metallic tubes laced about?  What agreements would have to be worked out with landowners to compensate them for the trains’ passage through their property?  Would there be areas which were so averse to the idea that the trains would have to be routed awkwardly out of the way (and if so, would this make the entire route impossible, since vactrain tubes could not bend or turn sharply, owing to the high speed at which the trains would operate within them)?

Ultimately, it is likely that some day, we will see vactrains in use (the Chinese—not surprisingly—are currently working on a small-scale version of the concept, which would move at about 600mph).  Airplanes generally have to run on fossil fuels or artificial substitutes for such fuels.  Electricity is a cleaner means of propulsion, but it’s proving very difficult to make aircraft which use electrical engines and move with any appreciable speed.  As many nations have proven, electrically powered trains—which the US has had for over a century—can move at very high speed and with great safety and efficiency.  When fossil fuels become scarce, and as electricity generation becomes greener and more widely utilized for a greater variety of applications (e.g. automobiles) it is likely that someone, somewhere, will finally concede to the fact that we do know how to build these vacuum trains, and that they would be a more efficient way of getting people and property from point A to point B.

On a nitpicking note, vactrains—despite moving at thousands of miles an hour—would not be supersonic.  Because sound cannot travel through a vacuum, a vactrain would never exceed the speed of sound—there would be no such speed in their tubes, just as there is no such speed in space.  A vactrain would not produce a sonic boom as it accelerated, and would not—technically—be moving supersonically.  It would just be moving very, very fast.

Editor’s Note: This post was written by Mark Jacobs, an editor at The Jet Fuel Review.  He is an Aviation major, but the left side of his brain is an avid writer.  Mark is a sophomore and will be working a few hours as a tutor in the Writing Center in the 2011-2012 school year.

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