Update 2:08 p.m.: SpaceX reports that the rocket first stage successfully navigated to the drone ship, but it was a hard landing that broke one of the rocket's landing legs.
Update 10:34 p.m.: SpaceX CEO Elon Musk posted video this evening showing the rocket's landing attempt. In a tweet, he wrote, "Falcon lands on drone ship, but the lockout collet doesn't latch on one the four legs, causing it" to topple and explode.
Update 3:30 p.m: In two tweets afterwards, SpaceX CEO Elon Musk wrote that it's "Definitely harder to land on a ship. Similar to an aircraft carrier vs land: much smaller target area, that's also translating & rotating. However, that was not what prevented it being good. Touchdown speed was ok, but a leg lockout didn't latch, so it tipped over after landing."
Today, at 1:42 p.m. EST, SpaceX will make its fourth attempt to launch, and then land, its Falcon 9 rocket on an at-sea platform.
The launch will take place at Vandenberg Air Force Base, California. The goal is to land the rocket's first stage on a so-called "drone ship" known as "Just Read the Instructions."
Each of the company’s three previous planned attempts to land the rocket at sea had failed, some in spectacular explosions, some in oh-so-close misses, and one when the rocket exploded before it could be brought back for landing.
Last month, for the first time, SpaceX successfully landed the Falcon 9 after launch, returning it to terra firma.
About 10 minutes after liftoff, the rocket will attempt to land itself upright on the deck of a 100-foot-by-300-foot, unmanned floating platform, about 200 miles from Vandenberg, off the coast of Southern California. The rocket is meant to guide itself to the barge using GPS. Today's landing could be complicated by 12-foot to 15-foot waves.
For Musk’s company, successfully reusing a rocket—and demonstrating that last month’s performance wasn’t a fluke—is a key element of a future of affordable launches.
"SpaceX believes a fully and rapidly reusable rocket is the pivotal breakthrough needed to substantially reduce the cost of space access," the company says on its website. "The majority of the launch cost comes from building the rocket, which flies only once. Compare that to a commercial airliner—each new plane costs about the same as Falcon 9, but can fly multiple times per day, and conduct tens of thousands of flights over its lifetime. Following the commercial model, a rapidly reusable space launch vehicle could reduce the cost of traveling to space by a hundredfold."
Today's mission also had a scientific purpose beyond returning the rocket home. The launch was meant to "deliver the Jason-3 satellite to low-Earth orbit for the U.S. National Oceanic and Atmospheric Administration (NOAA), National Aeronautics and Space Administration (NASA), French space agency Centre National d'Etudes Spatiales (CNES) and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT)," SpaceX said on its site (PDF). "If all goes as planned, the Jason-3 satellite will be deployed approximately an hour after launch."
Watch a live stream of the satellite launch above. We will update this article with news of the ocean landing attempt.