Wednesday night, weather permitting (there have already been two delays), SpaceX will take a second shot at what would be a rocketeering first: After its Falcon 9 rocket blasts the DSCOVR spacecraft into orbit, SpaceX will try to land the first stage of that rocket on a platform at sea:

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By now this might not be news to you. You might know that SpaceX came close to success with its first try, when the rocket reached the platform but a last-minute error cause a fiery crash. You might know that the company's success could open the floodgates to making space travel significantly cheaper. But what you might not know is just how unbelievably hard this mission is, even for people who do rocket science for a living.

SpaceX has publicly compared the engineering challenge of stabilizing their 14-story rocket as it falls from the sky to "trying to balance a rubber broomstick on your hand in the middle of a wind storm." In fact, the Falcon-9's delicate 9-minute balancing act consists of multiple tricky steps that must go off without a mistake. Each is unquestionably vital for success, and even minute error can cascade catastrophically.

It's like trying to balance a rubber broomstick on your hand in the middle of a wind storm.

The first hurdle for Falcon 9 is simply surviving atmospheric re-entry—a goal that's the opposite of just about every other rocket used to launch things into space, which are designed to burn up as they fall back to Earth. Having successfully flung its payload and next rocket stages into space, the heavily shielded first stage must flip 180 degrees so that it's pointed back toward the planet, and then adjust to the correct angle before it can arrow back through the atmosphere.

This is the point at which the Falcon-9 would re-fire its engines in what will be the first of three self-adjusting burns, called the boostback burn. However, that's the best-case scenario. For today's launch, SpaceX already knows that the Falcon 9 won't have enough leftover fuel to attempt the boostback because it has to launch its payload fairly deep into space, burning extra. That means Falcon 9 will be coming in extra hot, which means this attempt will actually be harder than the first.

As the rocket rips through Earth's atmosphere, aerodynamic drag helpfully will slow it down some. But the atmosphere will also be doing its best to knock the pencil-diving rocket off course and send it tumbling to instant death. This is because the jostling forces of the fall are inherently chaotic—and no amount of aerodynamic design will completely eliminate this concern.

Falcon 9 will be coming in extra hot—this attempt will actually be harder than the first

To stay steady and on track, the Falcon 9 will then deploy four lattice fins that are programmed to constantly adjust the rocket. These fins act like fletching on an arrow, but in this case you're talking about a hulking metal arrow flying faster than 3,000 miles per hour. Fins and engines are working like crazy to stabilize the rocket, as are the computers calculating all the right moves.

The next burn—for today, the first—now fires to slow the diving rocket to a little over 500 miles per hour. This is called the supersonic retro propulsion burn. Something to keep in mind here: As they execute split-second changes to keep the Falcon 9's trajectory true, the steering fins are using up a finite amount of hydraulic fluid to lubricate their machinery. The rocket ran out of this fluid during SpaceX's first attempt, which caused the crash. This time around, the company added an extra reservoir so as not to repeat the same mistake.

If all goes to plan, then the supersonic burn will have left the falling rocket at a speed (approximately 550 mph) at which it can safely extend its four carbon fiber and aluminum landing legs. As it approaches its destination—the small, unanchored floating SpaceX barge—the Falcon 9 continues the delicate dance of balancing itself, maintain control of its final landing burn, and navigating toward the ship.

It's a tense juggling act, where any one of thousands of moving parts can push the entire system into mayhem. If the rocket does land softly on the barge, it's because of millions of insanely detailed self-adjustments have kept the Falcon 9's composure as it dove through chaos. Just like last time, SpaceX is giving the odds of success at 50/50, though that sounds a lot more impressive when you realize what goes into the attempt.

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