Suddenly, everybody and his brother wants to go to space -- then come back home and go again.

You've probably heard that Elon Musk is hard at work at SpaceX, tinkering with a new version of his Falcon 9 space rocket to make it "reusable." After launching a satellite into space, the new Falcon 9R will descend back to Earth, land gently on its jets, and be ready to go again in a few days. By reusing the rocket, Musk believes he can save U.S. taxpayers as much as $50 billion on the cost of our satellite launches.

SpaceX's search for a reusable spacecraft began with Grasshopper. Photo: SpaceX

Meanwhile at DARPA, they've hired Boeing (NYSE:BA), Northrop Grumman (NYSE:NOC) -- and several other firms besides -- to help build a new "space plane." A 21st century space shuttle, DARPA's XS-1 would fly to the edge of space, toss a rocket-boosted small satellite into orbit, then turn back to Earth and land like an airplane.

The proposed DARPA XS-1 "space plane." Photo: DARPA

You may even have heard about start-up space firm Stratolaunch Systems, which has a DARPA-like space plane in the works. Dubbed "Eagles Launch," this plane would also fly as high as it can get (but not quite as high as DARPA is aiming), before boosting an even bigger satellite the rest of the way aboard a three-stage rocket.

Stratolaunch's "carrier" aircraft. Source: Stratolaunch Systems

Now, it's time to meet the newest entrant into the reusable space launch game. But to do so, we'll first need to take a short trip to Britain...

Ye olde (actually newe) space plane
As reported on CNN earlier this month, British space firm Reaction Engines has developed a new liquid-fueled rocket engine that it calls SABRE (for "Synergistic Air-Breathing Rocket Engine") to power a hypersonic aircraft (think "Concorde on steroids") to be dubbed SKYLON.

Here's how it works: SKYLON takes off like an ordinary airplane. It's propelled by a rocket engine using liquid hydrogen and oxygen as fuel. That's pretty ordinary stuff for space launch. SKYLON's twist is that the SABRE engine also scoops up extra oxygen from the atmosphere as it rockets along, cooling and compressing the gas into liquid form and then combining it with liquid hydrogen to burn as fuel. Thus, SKYLON replenishes its own fuel tanks as it moves. (At higher altitudes where the atmosphere is thinner, SKYLON relies entirely upon stored fuel).

Flying at extreme altitudes (28 kilometers and up), SKYLON is expected to hit speeds five times the speed of sound. That will be enough, the company thinks to permit commercial hypersonic passenger flights between the U.K. and Australia to be completed in as little as four hours. The space plane could go even faster, as much as Mach 25, once it breaks above atmosphere.

What's good about SKYLON?
Well, there's the name, right? When you're dealing in science fiction level technology, it helps to have a name that resonates with the sci-fi crowd. But SKYLON has other factors working in its favor, too. For one thing, SKYLON already has advanced past the concept stage of DARPA's space plane. The European Space Agency already has tested and approved the basic mechanisms that will power Reaction Engines' space plane.

In fact, according to CNN, SKYLON could be ready to begin flight tests as early as 2018, and if all goes well, could be running commercial flights to the International Space Station four years later.

The cost is another attraction. Reaction Engines believes it can build SKYLON for about $94 million per unit. And because the space plane will be reusable, and not require building new planes from scratch for each launch (the current practice with rocket launches), the cost per flight would be little more than the cost of refueling and performing routine maintenance the plane after each launch.

What's bad about SKYLON?
In a word: history. For all SKYLON's promise, after hearing all of the above, investors can be forgiven for wondering, "Haven't we heard all this before?"

After all, when NASA was first bandying the "Space Shuttle" idea about, enthusiasts said it would be able to fly a mission a week, and cost about $10.5 million per launch. (In 1972 dollars. After inflation, the cost would have been closer to $60 million in today's dollars.)

In practice, the shuttle actually required about three months on average to recondition between flights, limiting it to only about four missions per year. Conservative estimates put the shuttle's cost per launch at anywhere from $200 million-$450 million (three to six times initial estimates). Harsher critics point out that if you factor in all costs of the shuttle program, the cost of replacing disposable external fuel tanks (which the shuttle routinely jettisoned), replacing antique parts as they broke down, and the inability to amortize fixed costs across the anticipated number of missions, the real cost per launch of the 135 shuttle missions was closer to $1.5 billion per launch.

Maybe SKYLON will avoid this fate. To keep costs down, and fulfill the promise of its proponents, though, the company must dodge a hail of bullets that doomed the space shuttle program. It will need to overcome technological hurdles, and prove it can fly, of course. But it will also need to ensure that all its parts are fully reusable, and easily replaceable when the break down. And of course, it will need to maintain a truly frenetic flight schedule.

If SKYLON can fly as few as 100 missions per year, British Interplanetary Society spokesman David Baker says the cost of each incremental space flight "would fall through the floor." But if the best SKYLON manages is closer to a space shuttle-like four missions per year -- it's the SKYLON program itself that will fall, just like so many pie in the sky programs before it.

Last flight of the space shuttle Atlantis -- and of the American space shuttle program. Photo: NASA

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.