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SpaceX Hopes Third Time's a Charm for Rocket Landing Attempt

SpaceX stands ready to launch a much-needed load of supplies to the International Space Station and attempt another rocket landing on a drone ship.

SpaceX stands ready to launch a much-needed load of supplies to the International Space Station this weekend on the heels of a failed supply run by Russia. The company will also try again to pull off a feat it's failed at twice beore: land the first stage of its Falcon 9 rocket on a floating ocean platform.

The weather forecast is 90 percent favorable for the scheduled 10:21 a.m. EDT Sunday launch at Cape Canaveral, Florida, mission officials said in a Friday afternoon briefing.

The Falcon 9 rocket will carry a Dragon spacecraft loaded with more than 4,000 pounds of food, equipment, experiments and other supplies destined for the ISS, including a new docking port, or parking place, for future commercial crew capsules.

Engineers in the Space Station Processing Facility at the Kennedy Space Center in Cape Canaveral, Fla., check measurements on the International Docking Adapter. On Sunday, SpaceX is scheduled to launch a much-needed load of supplies and this new docking port to the International Space Station.Cory Huston / AP

This shipment is especially critical because the space station has lost two deliveries since fall. A Russian supply ship spun out of control shortly after liftoff in April and burned up on re-entry with all its contents. In October, an Orbital Sciences Corp. cargo carrier was destroyed in a Virginia launch explosion.

Minutes after Sunday's liftoff, SpaceX will make another attempt to vertically land the Falcon 9's discarded first-stage booster on an ocean platform off the north Florida coast. Two of the previous efforts — aimed at demonstrating rocket reusability — ended in flames. SpaceX said it has pinpointed and fixed the cause of those failures: lack of hydraulic fluid for the stabilizing "grid fins" in the first attempt in January, and a non-responsive throttle valve in a try in April.

Hans Koenigsmann, SpaceX vice president of mission assurance, said innovative companies learn from their mistakes. "This is an experimental trial to some extent," he said. "You look at the data, you evaluate this and then you make corrections, and that’s ultimately how you succeed."

SpaceX founder Elon Musk had pegged the odds of a successful landing for the previous mission at 50/50. Koenigsmann was reluctant to give numbers this time around. "There is always going to be some uncertainty about the outcome. But I feel a little bit better," he said.

Related: SpaceX: Odds of Successful Falcon 9 Rocket Landing on Barge Are 'Uncertain'

Meanwhile,the Russian Space Agency plans to take another stab at a station shipment from Kazakhstan next Friday. Russian space officials want to see how that goes before launching a new three-man crew to the station on July 22, two months late because of the April cargo ship mishap.

Three men currently are living at the space station, three persons fewer than usual because of the recent hold in Russian Soyuz launches. Two of them are one-quarter of the way through a one-year mission: American Scott Kelly and Russian Mikhail Kornienko. The third, Russia's Gennady Padalka, will become the world's most experienced spaceman this weekend. He's set to break the world record for most accumulated time in space, surpassing the 803-day mark held by former cosmonaut Sergei Krikalev, now a Russian space program official. By the time Padalka returns to Earth in September, he will have spent 2½ years in orbit.