WASHINGTON — On the company’s 20th mission of the year and second within 48 hours, SpaceX successfully launched a Dragon cargo spacecraft to the International Space Station Dec. 5, but suffered a rare failed landing of the rocket’s first stage.

The Falcon 9 lifted off from Space Launch Complex 40 at Cape Canaveral Air Force Station in Florida at 1:16 p.m. Eastern. The Falcon 9’s upper stage released the Dragon into orbit 10 minutes later.

The rocket’s first stage, making its first flight, attempted to land at Landing Zone 1 several kilometers south of the launch pad. However, the stage splashed down into the ocean just offshore instead, shortly after video from the stage showed it to be spinning as it descended.

“Grid fin hydraulic pump stalled, so Falcon landed just out to sea,” SpaceX Chief Executive Elon Musk tweeted shortly after the failed land landing. “Appears to be undamaged & is transmitting data. Recovery ship dispatched.”

Engines stabilized rocket spin just in time, enabling an intact landing in water! Ships en route to rescue Falcon. pic.twitter.com/O3h8eCgGJ7 — Elon Musk (@elonmusk) December 5, 2018

The failed landing is the first for SpaceX on a launch where it attempted a booster landing since February, when the center booster on the inaugural Falcon Heavy launch was unable to land on a droneship downrange from the launch site in the Atlantic Ocean. The last failure of a Falcon 9 first stage landing was on the June 2016 launch of the ABS-2A and Eutelsat 117 West B satellites.

The Dragon, flying a mission designated CRS-16, is carrying 2,573 kilograms of cargo for the International Space Station, primarily in the form of research payloads. That includes two payloads, weighing 975 kilograms, in the Dragon’s unpressurized trunk: the Robotic Refueling Mission 3 investigation and the Global Ecosystem Dynamics Investigation, or GEDI, instrument that will be mounted on the station’s exterior.

More than 2,000 kilograms of the cargo on the Dragon is in the form of science investigations and payloads. The remaining cargo consists of crew supplies and other hardware. The Dragon is scheduled to arrive at and berth with the station Dec. 8.

The mission is the 20th launch this year for SpaceX, a new company record. It also comes less than 48 hours after another Falcon 9 launched from Vandenberg Air Force Base, placing 64 smallsats into low Earth orbit on the SSO-A mission for Spaceflight Industries.

The two launches would have been 24 hours apart under earlier plans, but the Dragon launch was postponed a day to replace rodent food for one experiment on the Dragon that was contaminated with mold. That separation is about as close as SpaceX is willing to conduct two launches in order to give the company enough time to examine data. “Twenty-four hours is, approximately, my comfort zone for reviewing data,” said Hans Koenigsmann, vice president of build and flight reliability at SpaceX, said at a Dec. 3 briefing.

On the horizon for SpaceX is the first test flight of its Crew Dragon spacecraft for NASA’s Commercial Crew program. NASA announced Nov. 21 that it had set a Jan. 7 target date for the launch of that “Demo-1” mission, which will fly to the ISS but not carry a crew.

However, NASA Administrator Jim Bridenstine said days later that the Jan. 7 date was contingent on the completion of several reviews, as well as approvals of ISS partners and planning for other activities on the station. In a roundtable with a small group of reporters Nov. 29, he suggested that the mission might slip until the spring because of testing issues with the spacecraft’s parachutes.

Koenigsmann said at the Dec. 3 briefing that SpaceX was still planning a January launch, with all the elements of the spacecraft currently in Florida undergoing final testing and integration. “The whole company’s focus is certainly, after CRS-16, back on Demo-1,” he said, noting specifically that the parachutes on Crew Dragon are upgraded versions of those used on the current cargo version of the spacecraft.

“What I could see is a couple days [delay] because of traffic,” he said, referring to the arrivals and departures of other vehicles at the ISS. “Our target is, at this point in time, mid-January, and we’re pushing as hard and as diligently as we can for this particular launch.”

In addition to preparations for Demo-1, SpaceX has up to two more Falcon 9 missions scheduled before the end of the year. A Falcon 9 is scheduled to launch the first GPS 3 satellite from Cape Canaveral no earlier than Dec. 18, while another Falcon 9 will launch the final batch of 10 Iridium Next satellites from Vandenberg no earlier than Dec. 30.