When it comes to getting into space, traditional rocketry is the pits. Gigantic tanks that cost millions of dollars, massive fuel requirements, trajectories that fight against the atmosphere instead of using it to their advantage. Out of the five space shuttles built, two have gone boom. If you're going to build a Lifeboat in orbit, deploy solar power satellites, or visit space hotels, you're going to need a better way to get into space.
Luckily, there are numerous ideas, including rocket planes, orbital airships, the space elevator, and the space pier. 3/4 of these ideas already have companies putting serious resources towards their realization. Let's take a look at the details, shall we?
The rocket plane is currently the idea getting the most attention and funding. All current rocket planes are only capable of taking people to the edge of space and back, rather than going into orbit. Thus, trips on rocket planes are called suborbital space flights. The typical rocket plane launch consists of a larger plane that helps a smaller unit ascend to about 14km, where the air is several times thinner than at ground level, then releasing it.
The first rocket plane to reach space, as defined by 100km altitude, was the North American X-15, which was flown almost two hundred times throughout the 60s. Today, we have SpaceshipOne, with SpaceShipTwo on the way by 2008. Virgin Galactic, the company largely funding the present effort, has stated that if SpaceShipTwo is successful, it will follow up with a craft capable of making it into orbit, SpaceShipThree:
In general, craft that suck material directly from the atmosphere to use for oxidation offer superior specific impulse to traditional chemical rockets:
Earlier this year, Virgin Galactic started constructing the world's first purpose-built commerical spaceport, SpacePortAmerica, in southwest New Mexico. Space Adventures Ltd. is partnering with the people behind the Ansari X Prize to plan and eventually build the Ras Al Khaimah spaceport in the United Arab Emirates, and the Singapore Spaceport in Singapore. Here's what they would look like upon completion:
So what is an orbital airship? Proposed by JP Aerospace, the orbital airship concept is a three-staged process which includes a conventional airship, a permanent sky base, followed by a helium-filled, solar-powered ascender unit that slowly accelerates horizontally until it reaches escape velocity. Here's a look into the crotch of the Y-shaped ascender unit:
Here's a look at the inside:
The JP Aerospace website has several videos of both real flights and CG mockups. Problem is, engineers on the sci.space newsgroup confirmed that their plan is physically impossible. You can't gather enough energy with solar cells to overcome the atmospheric drag on the ascender unit. Interesting idea, but seems as if it will require major breakthroughs to be feasible, if ever. Time to move on to the space elevator...
The space elevator is a concept being championed by the Liftport Group. It's one of the older alternative space ideas, dating back several decades. The proposed contruction method, as I understand it, is to guide an asteroid into geostationary orbit, launch a series of rockets filled with carbon nanotube fiber to it, and lower a thin "seed elevator" to the earth's surface. From this point on, the elevator could be strengthened by using robotic climbers to add additional material to the initial thread.
The space elevator concept is very popular, in no small part due to its common presence in sci-fi, Tower of Babel-esque connotations, and the numerous CG mockups floating around on the net. I used to be a big space elevator advocate, but I've started to think that in the short term, it is not the ideal means of getting to space. To quote extropy list veteran Eugen Leitl:
I have problems with terrestrial space elevators (much less so with lunar elevators), largely because of need of actively moving the ribbon to avoid perforation by debris, because the tensile strenth required is borderline to what physics gives you, with not much safety margin, and if you fail only once you've wrapped all your infrastructure around the equator.
Forming a continuous rigid strand from earth to space, a space elevator would interfere with all sorts of low earth orbits, and also be an ideal target for terrorists of the future. Once that cable snaps, it would practically take the power of a god to grab the two ends and reconnect them without imminent disaster. My preferred alternative is the Space Pier:
The Space Pier is an idea from J. Storrs Hall, a pioneer in the field of nanotechnology and my colleague on the CRN Global Task Force. His site explaining the idea can be found here. Essentially, it's a 100km-tall, 300km-structure topped with an electromagnetic linear accelerator. Air resistance at this altitude is lessened by a factor of one million, and the plan is less cumbersome and catastrophe-prone than a taut string that reaches six earth radii from the surface. It would be a compressive tower, that is, standing under its own weight rather than using a geosyncronous counterweight. If one of the legs were K.O.ed by a nuclear terrorist attack, the structure as a whole would still stand. Utility fog distributed around the legs would provide yet another failsafe. The trip to the top is much shorter than climbing up a 36,000 km space elevator, and the way to low earth orbit is fast and easy. Once in LEO, one could employ ion drives or other techniques to get to GEO or out of the earth's gravity well.
Well, that's my summary... dozens of other exotic earth-to-orbit schemes can be found on this site. Happy flying. ;)