If that first test of the unpiloted SpaceX Falcon 9 rocket and Crew Dragon spacecraft goes well, a second test will fly astronauts Robert Behnken and Douglas Hurley to the International Space Station in June.
The Falcon 9 rocket lifted off successfully at 1:16 pm Eastern Standard Time from Florida's Cape Canaveral Air Force Station, carrying 2,500 kilos of supplies, including science experiments and food for six astronauts now on board the ISS.
Musk also tweeted a video from on board the booster, showing the rocket spinning uncontrollably until it regained stability at the last moment, but missed the landing pad. The first-stage rockets have a 84 percent recovery rate, according to the company.
The rocket engines compensated somewhat for the spin, and by the time the rocket hit the water, its fin had emerged.
The rocket was initially meant to take off Tuesday but was delayed for a day after engineers discovered moldy mouse food in one of the science investigations created to study the effect of microgravity on the immune system.
"The first stage did land in the water", SpaceX spokesperson John Insprucker said during a live webcast.
The Falcon rocket used for Wednesday's launch was not used in any prior mission.
The mission lifted off at 10:16 am PST (01:16 p.m. EST), from Space Launch Complex 40 (SLC-40) at Cape Canaveral Air Force Station.
The Dragon is carrying more than 56-hundred pounds of supplies and payloads to the International Space Station, including critical materials to directly support more than 250 science and research investigations. The mice and their habitat were loaded into spacecraft shortly before launch, but the spoiled food had to be replaced ahead of launch.