Having missed the sci-fi reading frenzy when I was a teen, I've recently have been "catching up." The book "the moon is a harsh mistress" really opens up some possiibilties for nearer term space flight. Of course, the Ender series really argues for super light speed or a hibernation mode during flight. In any event, none of any of this is conceivable with out nuclear power. I haven't seen much of that in space flight, as of yet...
I saw a Discovery Channel program of X-Prise projects several years ago. There were many interesting ideas of cheap-and-safe re-entry methods, instead of proven but expensive burn-out heat shield. I don't remember them all, but I recall one used parachute, one use autorotating blade (powerless hellicopter). I understand Rutan's method is also utilizing atmosphre drag. The idea is not new - there is striking similarities between SpaceShipOne and NASA's X-20 Dyna-Soar lifting body re-entry vehicle back in 1960s.
I think navigation issue is not very difficult until enter to atmosphere. Unless we have enough thrust to launch the vehicle to circular orbit, the flight path is actually ballistic trajectory (like extremely powerful cannon shell) so the entry point is deterministic at launch. We have no control to choose entry point at all.
Once in atomosphere, we have to navigate the fast-decending, powerless vehicle to landing spot safely. In the case of parachute or autorotating method, they have very little (if ever) control so they have to choose ocean or dessert as anding location. Not very convenient destination for traveling :-)
Rutan's glider method have some control and it lands on conventional runway, but FAA (or any air-safety authority) will not easily allow such vehicle entering busy commercial airport traffic. I don't think it is good idea neither - the spaceship might have to execute forced landing (or worse, crash) when it missed the landing spot by any reasons, and there are not many place you can crash spaceship around commercial airport.
@Y-sasaki: I don't spend near as much time in a plane as say, Junko, here. But' I've spent enough to know ow cool it would be to get to Asia or Europe from Silicon Valley in an hour or so--and maybe get a view of space on the short trip.
Question: How do we cost effectively handle the navigation needs and the heat of re-entry of such a flight?
I think that astroid mining will be something that will really be a viable thing, though there are things that could fall out from it that are not expected. There arer technologies that will fall out of this that will advance other areas. Already they have been working to get high temperature composite advanced for re entry control surfaces. This will find applications in turbine engines and other high speed aircraft. Already it has brought about the fabrication of the largest single composite piece ever manufactured.
As to other things that have been invested in, but had no apparent value might be understanding the atom. For many, this was a waste of time and money, and yet this very research is what allows us to use many of the electronics we have today. There are many other examples of things that were "rich peoples" play things that today are common place items.
Only half said in jest, Junko. Striving for the unknown is essential to being human. It would be a crying shame if the human race were ever to give that up. IMO, this is what Adam eating the apple is all about. The quest for knowledge defines us, risks and all. The ancients even wrote a story about it.
Back to the warp drive. Assume you're a tiny mite, crawling along a curtain. It would be a really long journey to travel the width of that curtain. In your mite's mind, the world is this flat and wide surface, and you can only reach the other end so fast.
On the other hand, if you can get beyond this 2-D representation of your space, and hop between the folds in the curtain, your journey would be way shorter.
We need a way to jump between those folds in space. What we perceive as our 3-D space (plus time) is not all there is to it. So, warp drive, finding wormholes, call it what you will, we need to get moving faster than the effective 3E8 meters/sec in our perceived 3-D space.
Math has no problem whatever dealing with multiple dimensions. Albert Einstein worked his theories of relativity based only on math and intuition. Some of his predictions were only demonstrated decades later. So, who's to say?
Exploration is just that: you don't really know what's out there unless you go out and look. Bert speaks upstream about warp drives. Who knows, maybe someone left an old teleporter on the far side of the Moon and if we set up a Moon colony and started doing some serious exporation we'd find it. More practically, maybe there are huge stockpiles of minerals on the Moon that are hard to get on Earth because of various factors. We just don't know, and won't know unless we act like mongooses and "run and find out" [Kipling].
y_sasaki mentions the high cost of getting things into Earth orbit or worse, escaping it. Well, many people have proposed a self-sustaining Moon colony as solving this problem by taking advantage of the Moon's weaker gravity to blast payloads of useful stuff to Earth and to act as a platform for exploring the cosmos. Unfortunately, after that terrible accident in 1999 there's been no political will to continue with a Moon colony :-) Maybe the Chinese will do it.
Bottom line: Every time humans try to solve hard technical problems they always learn useful things that can be applied elsewhere. Sometimes the useful things are misused -- it's unfortunately that the social advancement of humankind is so much slower than technological advancement.