SpaceX founder and CEO Elon Musk gave the first detailed reason for the failed Falcon 9 landing last Tuesday.

In a tweet Saturday afternoon, Musk said, “Cause of hard rocket landing confirmed as due to slower than expected throttle valve response.”

Musk added that SpaceX will attempt another launch and landing of the reusable Falcon 9 rocket in two months.

Of course, the rocket is only reusable if it survives its landing. So far, SpaceX has made three attempts at a successful return to Earth after a launch, and each has missed the mark for one reason or another.

The first attempt, in January, ended in a spectacular explosion as it hit the platform askew and out of control. The second, in February, came close, but the rocket splashed down a mere 10 meters away from the drone ship in heavy seas. On Tuesday, the rocket almost made it, but ended up tipping over and exploding, as was famously seen in the above video and in another video, released days later.

In a tweet on Tuesday, Musk said, “Rocket landed on droneship, but too hard for survival” and followed quickly with a second tweet adding, “Looks like Falcon landed fine, but excess lateral velocity caused it to tip over post-landing.”

Despite the near-miss on the landing, the other half of the SpaceX mission — to deliver scientific cargo to the International Space Station aboard the company’s Dragon capsule — went just as planned.

Being able to successfully return a Falcon 9 to Earth is a major step for SpaceX, because it will allow the company to reuse the rockets for future launches. That would be significant because it would slash the cost of future missions, SpaceX said:

SpaceX believes a fully and rapidly reusable rocket is the pivotal breakthrough needed to substantially reduce the cost of space access. 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.

According to DefenseNews, SpaceX is expected to make its next attempt at a landing of the Falcon 9 on terra firma, instead of at sea. But Musk did not address that in his tweet.

Also this afternoon, Musk tweeted a video showing that returning a rocket to Earth is possible, despite it looking “tall and tippy.”