Railroads don't scrap their locomotives after every trip. Airports don't junk their jets with each flight. Yet for all their space-age know-how, aerospace scientists have long struggled with how to recommission spent booster rockets that cost tens of millions of dollars to build.
That could change after today, if SpaceX's test launch of its Falcon 9 succeeds in sending a rocket into orbit and returning it to Earth, intact and primed for another launch.
"It would be utterly revolutionary," says Boston-based space analyst Charles Lurio, a former aerospace engineer who publishes the Lurio Report, a newsletter about the commercial space industry.
"Reusability means you don't want to throw away a multimillion-dollar vehicle on every flight. This would break this vicious cycle we've had since the '60s."
With each of SpaceX's resupply rockets so far costing in the ballpark of $60 million, the prospect of wasting a booster after each launch is not to be taken lightly.
'Close, but no cigar'
The last failed attempt in January was — as billionaire SpaceX CEO Elon Musk put it — "close, but no cigar."
Approaching its targeted ocean barge in January, the Falcon 9's booster rocket headed toward the landing pad, but its steering fan ran out of hydraulic fluid. The rocket struck the barge at an angle, smashing its legs and engine before exploding.
John Logsdon, professor emeritus at the Space Policy Institute at George Washington University, remembers the attempt as a near-success.
"It got back, but it didn't slow down enough and bounced off the platform," he said. "But it did get all the way back to the platform."
That was as promising a start as any Logsdon has seen.
"Reusability has been the holy grail in the space business for a long time," Logsdon said. "The space shuttle developed in 1969 was supposed to be fully reusable until it was discovered that was too hard."
Conventional launching systems are designed to separate into subsets, or "stages," after the rocket lifts off, shedding fuel tanks and engines that essentially become dead weight after their fuel is spent.
This allows the vehicle to ascend more efficiently, hauling its payload containing science experiments or supplies toward its destination.
Expendable rockets ditch their first stage, or bottom portion of the launch vehicle, into the ocean. By that point, the first stage is a virtual wreck, having been damaged by heat upon re-entering Earth's atmosphere.
An uncompromising equation
Building a beefier rocket isn't the answer, however.
A primary problem with reusability has been an uncompromising principle in rocket design known as the Tsiolkovksy equation, which concerns how much cargo a rocket can carry.
"It's the core equation in all of rocket design. All rockets that need to get up into orbit have to be built as light as possible," said Kieran Carroll, chief technology officer at Gedex, a Toronto aerospace instruments company funded by the Canadian Space Agency.
A typical launch vehicle only dedicates about five per cent of its total mass to payload.
Devices such as landing gear add weight, putting even more of a squeeze on room for the payload capacity.
"So you strip out everything non-essential. Shave off mass so you don't take away from the payload capacity," Carroll said.
That slimmed-down design, however, means the rocket won't last.
Until recent years, Carroll said, the thinking was that "maybe you could build a more robust reusable rocket, but you wouldn't be able to carry any payload."
Carroll said SpaceX designers have since taken advantage of progress in material science. A lighter yet stronger aluminum-lithium alloy, for example, has replaced aerospace-grade aluminum for propellant tanks.
Mars a future target
Commercial space expert Paul Kostek, former president of the IEEE Aerospace and Electronic Systems Society, also points to advances in navigation systems, noting they have allowed for unmanned GPS-guided steering of booster rockets.
Once the Falcon 9 heads back to its football field-sized barge in the Atlantic Ocean, pop-out steering fins will deploy for aerodynamic guidance.
Kostek said landing legs will unfurl as the first stage of the rocket touches down.
Musk, who has stated his wish "to die on Mars, just not on impact," expresses a wider public desire for futuristic manned missions to other planets, via rockets that would land and ferry people between Earth and the moon or the Red Planet.
Reusable rockets would be essential for that to happen.
But SpaceX's mission to pull off a vertical landing manoeuvre is more than a mere flight of aerospace fancy for those dreaming of lunar colonies.
"Bringing materials up to a space station, to the moon, becomes a much quicker turnaround activity," said Kostek.
"You turn around missions faster, costs drop, and for businesses putting satellites in space, they now have a cheaper means of doing it," he said.
Check back later today for CBCNews.ca's full coverage of SpaceX's Falcon 9 liftoff at 4:33 p.m. ET.Suggest a correction