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[bulldogtrekker]

How Humanity Will Conquer Space Without Rockets

George Dvorsky, I09


* Britain's Skylon Spaceplane.

Getting out of Earth's gravity well is hard. Conventional rockets are expensive, wasteful, and as we're frequently reminded, very dangerous. Thankfully, there are alternative ways of getting ourselves and all our stuff off this rock. Here's how we'll get from Earth to space in the future.

Make no mistake, chemically-driven rockets are critical to human spaceflight and they'll continue to stay that way well into the future. But that doesn't mean they'll always be our only option.

Without a doubt, it's critical that we develop other methods of getting into space; humanity's long term future may very well depend on it. But as it stands, rockets are prohibitively expensive, inefficient, and dangerous. NASA's new Space Launch System will cost about $500 million per launch, while SpaceX's Falcon Heavy will be considerably better at an estimated (but still very expensive) $83 million per launch. And as we know, rockets aren't the most environmentally friendly of things.

Scientists and engineers have been proposing alternative launch systems for years, with some of them having the potential to become technologically feasible within a few decades. Most can be divided into the following broad categories: (1) alternative propulsion schemes, (2) fixed, tensile, and dynamic transportation structures, and (3) projectile launch systems. There are more proposals than I could possibly describe in a short article, but here's a sampling of the most promising.
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Alternative Propulsion Schemes

Laser propulsion

Conventional rockets require a hideous amount of solid or liquid fuel, and their range and power is limited by the amount of fuel they can carry. But there's an interesting idea that could help us get around this limitation — the use of ground-based lasers to propel rockets into space. Russian scientists Yuri Rezunkov and Alexander Schmidt recently described the process of "laser ablation" where a pulsed laser beam would hit a receiving surface, heat it up, and burn off material to create a plasma plume — a column of charged particles that flow off the surface. The resulting exhaust would generate considerable additional thrust capable of pushing aircraft beyond ten times the speed of sound.

Stratolaunches and space planes



Less conceptually, there are plans in the works to send aircraft into space through high altitude air launches or directly via powerful space planes. (image: Virgin Galactic)

Indeed, air launches are not just for space tourists. By 2016, it's hoped that Virgin Galactic's proposed LauncherOne will deliver "smallsat" payloads reaching 220 pounds (100 kg) into Earth's orbit....

The ongoing miniaturization revolution is starting to pay some serious dividends as far as satellite technologies go; they're becoming more smarter and powerful than ever before — but they're also getting easier to send into space. LauncherOne will borrow from the SpaceShipTwo concept to further drive down the costs of getting small objects into orbit.





Other examples of stratolaunchers include XCOR Aerospace Lynx Mark III (above) and Orbital Sciences Pegasus II (below).





One of the primary advantages of air launches is that rockets won't have to fly through the low, high-density atmosphere on their way to space. Thus, they won't be subject to extra drag and high ambient pressure. Also, carrier aircraft are easier to launch, are less subject to inclement weather, and are highly scalable.





Spaceplanes are another option. These reusable launch vehicles are similar to the retired Space Shuttle, but they won't require an array of rockets to get them into orbit. One of the more developed programs in this area is the British Skylon spaceplane (pictured above), a single-stage-to-orbit launch vehicle. Once built, it will be powered by a two-in-one air-breathing rocket engine that will boost the plane to five times the speed of sound as it climbs to an altitude of nearly 19 miles (30 km). But that's only 20% of the speed and altitude required to get into space, so the spaceplane will then have to switch to rocket mode.

Unfortunately, there are still many technological hurdles to overcome. It's expected that spaceplanes will be exposed to a depressed trajectory resulting in high dynamic pressure, excessive heat, and heat flow loads on some of the more sensitive parts of the plane. These aircraft could be quite dangerous.

Fixed, Tensile, and Dynamic Structures

Or, we could build massive structures that extend to extreme heights — or even into space itself.

For example, scifi author and engineer Geoff Landis has envisioned a fixed tower with a top that reaches past the Earth's atmosphere. At a height of 60 miles (~100 km), the tip could be used as a launch site for a conventional rocket. At such a height, rockets won't have to endure any atmospheric drag.

Another proposed static structure that has received a lot of attention over the years is the space elevator. Conceived as early as the late 19th century, it would involve a 22,000 mile (35,400 km) cable extending from the surface of the Earth to geosynchronous orbit (which is beyond where most communications satellites reside). After being anchored and counterbalanced at a fixed location (probably in the ocean), laser-powered climbers would ascend the cable, delivering cargo into space. To get into orbit or all the way to GEO, however, a person would have to board a rocket or other vehicle. Beyond that, an astronaut or space tourist could be flung into higher orbits, or even all the way to escape velocity at sufficient heights . . .






Want to read more? Click here:
http://io9.com/how-humanity-will-conquer-space-without-rockets-1676441431

[Pye-Rate]

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Another possibility for fixed structures is a rail launcher.

Miles long maglev track climb up a mountain about two miles and away you go.

Compromise for shorter track; aeroblade engines good to 20 miles high, mach 5 ignition, mach 12 max, noise dispersal about 300 miles.

[Bud Brewster]

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I presume you meant something like this, Pye-rate?

Except that these things apparently aren't more efficient if the rail goes down a mountain slope, because the spacecraft ends up sort of heading in the wrong direction.

And the down-and-then-up method we saw in When Worlds Collide isn't as good as it seems either, because the spacecraft looses momentum at the low end of the track when the spacecraft's direction is changed from down to up.

So, apparently a straight run like in the picture from the article below is the best method.


Railway to the Sky? NASA Ponders New Launch System



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Is there no man on Earth who has the wisdom and innocence of a child?
~ The Space Children (1958)