Today, in the eternal war between SpaceX’s reusable rockets and SpaceX’s robot boat, the rockets lost again. Elon Musk's company loaded up a Dragon capsule full of supplies this morning in what would have been its seventh mission to the International Space Station—and its third attempt to salvage the capsule's rocket, Falcon 9, by landing on an autonomous barge. But the poor thing didn't even get the chance to try. Less than three minutes into flight, the rocket and its cargo exploded, their disintegrating parts cloaked by a huge cloud of smoke.

Astronaut Scott Kelly, watching the catastrophic failure from his perch in the ISS above, said it right: "Space is hard."

It's not clear yet what caused the rocket to break up. At the time of "launch vehicle failure," in NASA-speak, Falcon was still firing all of its nine first-stage engines, with the Dragon capsule and second stage Merlin vacuum engine attached. Right now, the NASA mishap and anomaly teams are trying to piece together video analysis of the flight path with the two minutes or so of data sent from the craft before it exploded. Canadian astronaut Chris Hadfield speculated that the failure might have started at the front of the craft—near the second stage engine and the Dragon capsule.

In a NASA press conference today, SpaceX president and COO Gwynne Shotwell confirmed that a problem occurred in that general location, noting an overpressurization event in the liquid oxygen tank in the second stage of the rocket. But SpaceX doesn't know yet what caused it. Even the typically speculation-happy Musk can't say more yet, tweeting only that their "data suggests [a] counterintuitive cause."

The Dragon capsule was carrying more than 4,000 pounds of supplies for the ISS. This is the third resupply mission to fail in the last eight months; at the end of April, a Russian Progress spacecraft and its Soyuz rocket similarly failed early in their launch, and last October, an Antares rocket from Orbital Sciences blew up right on the launch pad. While that might seem to indicate a troubling trend, "there’s no commonality across these three events other than that it’s space and it’s difficult to fly," says NASA's associate administrator for Human Exploration and Operations William Gerstenmaier.

The multiple failed missions shouldn't be a problem for the astronauts aboard the ISS; NASA confirmed that they have enough to live on for the next several months, and multiple launches will make it to the ISS before supplies run out. Another Progress craft is set to launch on July 3, a Japanese HTV flight is scheduled for August, and another commercial US outfit, Orbital ATK, has plans for a launch later this year.

But the loss of this cargo in particular is still a huge a blow to the ISS. On board the Dragon was a new docking station and a space suit that will take time to rebuild and replace. The cargo also included a multi-filtration bed that would have allowed the astronauts to continue processing water for reuse (though they don't need the extra water, it's certainly good to have the filter as a backup), and more than 30 student science projects.

Thousands of people were watching the failure live this morning, in anticipation of a potential historic landing of the rocket on SpaceX's drone barge after two failed attempts. (You can see the moment in the video below, with the launch starting at 21:15 and trouble starting around 23:30.) SpaceX and many of its competitors are in hot pursuit of a reusable rocket, hoping to lower the costs of space travel. A Falcon 9 costs as much a jumbo jet, so it’d obviously be preferable if SpaceX could use it multiple times instead of driving its investment into the ground...or water.

Landing a rocket that travels ten times the speed of sound is no easy feat, and SpaceX had prepared this Falcon 9 in an attempt to learn from its previous failures. This time around, the rocket was stocked with extra hydraulic fluid—it ran out of that sweet sweet juice used to steer the rocket’s landing in January—and they’ve made improvements to a sluggish throttle valve which caused the rocket fall over during an attempted landing in April.

But those changes will have to wait until another launch to get tested. More updates to come on what caused the explosion, and what it means for SpaceX's next planned launches.