Ready for a ride on a space elevator?

A NASA rendering for a space elevator of the future.
Bruce Irving | Flickr
A NASA rendering for a space elevator of the future.

To push the envelope of transportation technology, you need to think big.

And as globalization continues to drive advances in ways to move people and goods around the world faster and cheaper, there's no shortage of ideas.

Some of them may never fly. But others that seemed futuristic just 25 years ago may be commonplace by 2039.

Major carmakers, for example, are hard at work developing autonomous cars that will put computers in charge of braking, steering and avoiding crashes—allowing drivers to text message and surf the Web while on their way to work.

Battlefield advances in unmanned drones are spawning a new generation of flying vehicles able to deliver freight to soldiers in remote locations. The ongoing spread of online shopping makes civilian applications of the technology all but inevitable.

But sometimes even the best ideas never leave the drawing board. Some are derailed by a wide range of forces—from advances in competing technologies to changes in the cost of materials or fuel.

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For engineers working on the cutting edge, that can be a delicate balancing act.

"It's sort of like, how do you write a song—do the lyrics come first or the music?" said Robert Boyd, a program manager at Lockheed's Skunk Works unit, devoted to advanced aircraft technologies. "Sometimes it goes both ways. What we create are products at the intersection of what's possible with what's needed."

Nine big ideas that may soon take off

Photo credit: NASA

Space Elevators

Imagine deploying a giant cable vertically from ground to space, perfectly balanced between the gravity pulling it down and the Earth's centrifugal force holding it up.

It may sound far-fetched, but it is based on the same principle that keeps geosynchronous communications satellites moored serenely in stationary orbit.

Once in place, vehicles tethered to the massive cable could haul payloads into space—resupplying orbital and long distance missions with fuel, water, food, oxygen and other critical supplies.

The only sticking point: No material has been developed yet that's strong enough to support its own weight thousands of miles into space.

Photo credit: Wikimedia

Jet Packs

The '60s-era Rocket Belt captures the imagination of a generation of rocket-addled Americans—but never got off the ground as a commercial product.

Today a handful of seaside resorts offer joyrides on a water-propelled jet pack tethered to a fire hose, and Dallas-based Rocketman stages demonstration flights.

But if you're looking to pilot one yourself, a Mexican company, Tecnologia Aeroespacial Mexicana, claims to be "the first and only company in the world" to offer a custom-designed Rocket Belt.

"Price and sale conditions" are available on request, according to the company's website.

Photo credit: Terrafugia

Flying Cars

Ever since George Jetson and his flying station wagon introduced cartoon fans to the idea of personal space travel, traffic-bound commuters have longed for a car that would fly.

Massachusetts-based Terrafugia claims it's getting close to offering a mass-produced "street-legal airplane that converts between flying and driving modes in under a minute."

The two-seater Transition cruises at 100 mph (in the air), runs on premium unleaded gas and has a 400-mile range. Expected base purchase price: $279,000. (Available with optional "full vehicle" parachute.)

Photo credit: Terrafugia

Autonomous Flying Cars

Major carmakers are hard at work developing autonomous cars that will put computers in charge of breaking, steering and avoiding crashes, allowing drivers to text-message and surf the Web on their way to work or the mall.

Terrafugia wants to apply those technologies to a flying car with a 500-mile range that would take off and land vertically and pilot itself to your destination.

You'll need a clear space 100 feet in diameter to take off and land, the company said, but the vehicle will fit in a "standard-construction single-car garage."

So far, the TF-X is a concept vehicle only. Don't look for it before 2021.

Photo credit: NASA

Solar-Powered Flying Wing

Fuel has long presented the biggest challenge to engineers seeking breakthroughs in transportation technologies. Fortunately, photovoltaics has opened new possibilities for solar-powered flight, but early advances have been halting.

In 1999, NASA flew its first experimental solar-power unmanned aircraft, the HELIOS. Two years later the prototype reached an altitude of nearly 100,000 feet and set a world record for sustained horizontal flight by a winged aircraft.

But in 2003, on a flight off Hawaii, the vehicle encountered heavy turbulence, broke apart in flight and crashed into the Pacific Ocean.

Photo credit: Boeing

Cargo Wide-Body

Intermodal transportation was revolutionized decades ago by the roll-on/roll-off concept that allows shippers to move fully-loaded trucks and cargo containers directly from ocean to highway. Why not apply the same concept to air freight?

Boeing tried the idea in the early 1970s with the 754—a wide-body cargo plane with a hold that included five side-by-side cargo bays 90 feet long.

But by 1974, with fuel prices soaring and development costs estimated at $2 billion to $3 billion, Boeing's partner in the project, International Husky, couldn't find enough customers for the 754, and the project was canceled.

Photo credit: Lockheed Martin

Freighter Drones

As unmanned aircraft play an increasingly critical role in combat, a new generation of drones may soon be pressed in service to deliver supplies to the battlefield.

Operated by a remote-controlled "militarized iPad," Lockheed's Martin Aerial Reconfigurable Embedded System (ARES) uses two giant fan engines to power vertical takeoff and landing.

The aircraft is designed to fly to remote forward bases to resupply soldiers and evacuate casualties—at a cost per vehicle of "less than a small helicopter," according to a Lockheed Martin official. Following successful test flights, a prototype is expected to be completed in 2015.

Photo credit: Lockheed Martin

Hybrid Airships

Since manned hot-air balloons first lifted off the ground more than two centuries ago, aerospace engineers have known that lighter-than-air vehicles provide a relatively cheap, efficient way of getting off the ground. But these airships have played only a marginal role in commercial aviation.

Developers of a new generation, known as hybrid airships, are hoping to change that. Combining the powerful lift of a helium-filled shell with propellers and controls found on fixed-wing aircraft, hybrid airships can operate in remote parts of the world not serviced by costly airport infrastructure.

Lockheed Martin's P-791 also includes a hovercraft landing system, which lets it touch down on sand or water.

Photo credit: Lockheed Martin

Second Generation SST

Grounded by high fuel costs and noise restrictions in 2003, supersonic transportation could make a comeback if cheaper, quieter planes overcome those obstacles. Boeing and Lockheed Martin (whose "N Plus" SST concept is shown here) are among the companies hoping to revive supersonic flight with a new generation of plans that burn fuel much more efficiently and create much less noise.

One of the biggest hurdles: eliminating the sonic boom created when these aircraft break the sound barrier. That meant the first generation of SSTs were banned from flying at supersonic speed over land, which greatly reduced the appeal of supersonic aircraft.

Sometimes new technologies give older ideas a second chance. Boyd's team is working on a hybrid airship that harks back to century-old dirigibles. These lighter-than-air flying ships are being designed to deliver heavy freight loads to remote parts of the developing world that aren't served by conventional air service—and can't afford the costly infrastructure required to provide it.

The idea sounds simple—which is a good sign to Boyd.

"You know you're getting close when it's getting simpler," he said. "That means you've brought it from the technology realm down to the useful military or commercial product realm."

Then again, some simple ideas turn out to be devilishly difficult to pull off—like flying cars. Terrafugia, a Massachusetts-based private company, said it's getting close to offering a mass-produced "street-legal airplane that converts between flying and driving modes in under a minute."

Read MoreFlying cars may no longer be just science fiction

Bold predictions of flying cars have captured the imagination of Earth-bound travelers since Kitty Hawk—some of them bolder than others. And those "failed" early visions can arouse powerful skepticism about the next Big Idea that comes along.

"We call that the giggle factor—when you talk about a flying car, you have to kind of smile a little bit," said Kevin Renshaw, another program manager at Lockheed Skunk Works. "But a lot of things have evolved in unmanned aircraft in the last 10 years. Sometimes you just have to get the right pieces to come together at the right time."

Renshaw's team is working on an idea most people won't have a hard time with—a freight drone. (Officially known as the Aerial Reconfigurable Embedded System, or ARES.)

The vehicle—under development for the Defense Advanced Research Projects Agency—is intended to resupply small groups of soldiers in remote, hostile terrain. Controlled by a "militarized iPad," the system would be based with the field unit, available on a moment's notice to return to base for supplies or evacuate casualities—with far less cost or risk than a manned helicopter.

"We want to be the FedEx or Postal Service going door to door for these small groups of soldiers out there in the field," Renshaw said.

Making deliveries in harsh battlefield conditions is one thing. Delivering payloads 1,000 miles into space is another.

Dozens of private companies have now taken up where government space programs—and the public funding behind them—left off.

Some are specializing in unmanned systems to delivery payloads like satellites into orbit. Others are taking reservations on an emerging market for space tourism.

All of them face the same challenge: to lower the cost of overcoming gravity's pricey pull on people or cargo headed for space. Today it costs roughly $10,000 to put a pound of payload in Earth orbit, according to NASA. To develop commercial spaceflight, that cost will have to come down to hundreds or even tens of dollars per pound.

That's the goal of the International Space Elevator Consortium, a group of scientists, aerospace engineers and other big thinkers devoted to the development of "inexpensive, safe, routine and efficient access to space."

They believe the answer lies in suspending a very long—and very strong—elevator cable from the surface of the Earth to a point thousands of miles in space.

Read MoreTransportation investors skip jet packs

To be sure, the idea seems far-fetched. But when first proposed, so did the idea of setting a 5-ton communications satellite in place 25,000 miles above Earth in a geosynchronous orbit.

Proponents of the space elevator concept point out that the same physics would apply: The pull of gravity on an elevator cable would be offset by Earth's centrifugal force holding it up. Properly designed and built, the cable would hang in place, ready to guide a reusable, electromagnetically propelled payload vehicle up and down as efficiently as the elevator in a modern high-rise building.

Much of the work needed to prove the concept has already been done, according to the consortium's president, Peter Swan.

"The only thing we haven't done is make a material that will go 100,000 kilometers and be strong enough to hold itself," he said. "The material question is the main issue with space elevators."

That issue is closer to resolution, thanks to a new generation of light, high-strength materials being developed in the emerging nanotechnology field.

Swan believes that if production challenges can be overcome, the development of a space elevator would open up a new era in commercial space—from asteroid mining to manned, interplanetary missions.

"We have a lot of challenges, no question," Swan said. "But holy Toledo—if you looked at the San Francisco [Bay] in 1800, you'd have said, 'Ah, there's no way you can build a bridge across there.' It's the way you look at things. The future is there."

—By CNBC's John W. Schoen

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