James Dean

FLORIDA TODAY

Update, 1:53 a.m. Saturday:

NASA and SpaceX hope the weather cooperates early Sunday for their second attempt to launch an International Space Station resupply mission from Cape Canaveral Air Force Station.

Thick clouds and rain scrubbed a planned liftoff at 2:14 a.m. Saturday, with conditions showing no sign of improving with about 30 minutes left in the countdown.

Sunday's launch time is 1:52 a.m., but the forecast remains iffy, with a 40 percent chance of acceptable weather.

If there's another scrub, a third attempt may be possible early Tuesday.

The mission is SpaceX's fourth of 12 under a $1.6 billion NASA Commercial Resupply Services (CRS) contract.

The Dragon spacecraft is carrying more than 5,000 pounds of cargo including astronaut food and supplies, a mouse habitat, a 3-D printer and a climate science instrument.

Original story:

Last-minute cargo including a habitat holding 20 mice is being loaded into a SpaceX Dragon capsule for a late-night launch to the International Space Station.

The Dragon is targeting a 2:14 a.m. Saturday liftoff from Cape Canaveral Air Force Station atop a Falcon 9 rocket. Falcon 9/Dragon stand 208 feet tall.

There's a 50-50 chance of acceptable weather during an instantaneous window at Launch Complex 40, with thick clouds and rain showers potential concerns.

Aside from weather, NASA and SpaceX said their systems in space and on the ground are ready for the mission.

"We're in great shape," said Dan Hartman, NASA's space station deputy program manager, during a prelaunch briefing this morning at Kennedy Space Center. "(Station) systems are ready. The crew is ready to go with robotic (operations), and so we're really look forward to the launch early tomorrow morning."

"We are also ready to go," said Hans Koenigsmann, SpaceX vice president of mission assurance. "This is a very challenging mission in terms of cargo and in terms of experiments on board up and down, so I'm really looking forward to the mission."

The mission is SpaceX's fourth of at least 12 under a $1.6 billion NASA commercial resupply contract.

The Dragon is packed with more than 5,000 pounds of food, supplies and experiments, including the first mice flown on a Dragon, for which SpaceX designed a special life support system. They are flying in a new habitat NASA is flying as the start of a new program expanding rodent research on the orbiting research complex.

Other interesting payloads include a 3-D printer that will practice making replacement parts in space, an ocean winds sensor for improved weather and climate forecasts, a materials experiment operated by a golf company, IMAX cameras and spacesuit batteries.

With an on-time launch, the Dragon would be expected to berth at the station early Monday to start a month-long stay.

If necessary, the mission has another launch attempt early Sunday, when there's a 70 percent chance of favorable weather, then possibly another try Tuesday. Then the mission would wait until at least Sept. 28, a few days after the planned launch of three more ISS crew members from Kazakhstan in a Russian Soyuz spacecraft.

After the launch, SpaceX will again command its Falcon 9 rocket booster to perform a series of engine firings in an effort to land it softly in the Atlantic Ocean, though the company does not expect to recover it intact. Due to the mission's timing, this booster is not equipped with landing legs that could improve aerodynamic control of the returning rocket stage before hitting the water.

Koenigsmann stressed that the booster flyback remains an experimental effort to advance development of a reusable rocket, and is secondary to the primary mission to deliver the Dragon safely to orbit.

The 13th launch by a Falcon 9 is planned just 13 days after SpaceX's last launch from the same pad, the company's fastest turnaround time yet and close to a record at the Cape, Koenigsmann said.

"I think the fastest one was in '65 or '67," he said. "In the future, actually, I anticipate this will be the norm. We are ramping up for that launch rate and actually even more than that."

Asked about SpaceX this week winning a NASA contract to fly astronauts to the station by 2017, Koenigsmann said his reaction was "a big smile."

"It's obviously a huge responsibility for SpaceX and our team," he said. "It's a lot of work, but we are obviously totally delighted to be on that team and to provide the human spaceflight capability back to America.