SpaceX the Alan Notes

SpaceX succeeded on Tuesday in launching a Falcon 9 rocket to carry supplies up to the International Space Station — and though the company's second attempt to land the used-up rocket stage on a floating barge was a failure, they're definitely getting closer:

The rocket landed vertically and on target, but lateral motion caused it to tip over at the last second. Compare that to the last attempt, in January, when the rocket became destabilized and exploded as it hit the barge because of a shortage of hydraulic fluid:

The fact that the rocket was on target and landed vertically Tuesday was a sign of progress — and could lead to something big.

Normally, rockets are simply allowed to break up into pieces or sink into the ocean after each use. But controlled landings could allow SpaceX to reuse rocket stages on future flights — and reusing these multimillion-dollar pieces of equipment, rather than throwing them out after every launch, could dramatically drive down the cost of space travel.

What SpaceX was trying to do

(SpaceX)

The company launched a Falcon 9 rocket in order to send a Dragon capsule, packed with 4, 300 pounds of supplies (including materials for 40 different scientific experiments and an espresso machine for the astronauts), up to the space station — the sixth of 12 resupply missions SpaceX is carrying out for NASA. The capsule will arrive there on Thursday, and return with waste and other cargo in about five weeks. Here's video of the launch:

The Falcon 9 is made up of two parts: a 138-foot-tall first stage, which burns for the first few minutes of flight, lifting the craft up to an altitude of about 50 miles before separating and falling back to Earth; and a smaller, 49-foot-tall second stage, which burns for another six minutes, carrying the Dragon into orbit before disconnecting and falling back down to Earth, as well.

Normally, both of these stages — as well as the stages that make up other rockets in general — break up into pieces as they plummet downward, eventually sinking into the ocean and becoming unusable. But on Tuesday, as the first stage fell back to Earth, SpaceX fired its engines in order to stabilize and guide it in for a controlled landing.