| CAPE CANAVERAL, Florida
CAPE CANAVERAL, Florida A Space Exploration Technologies' cargo ship parked at the International Space Station for three weeks returns to Earth on Tuesday and will ferry back experiment samples key to ongoing science research.
The Dragon spaceship, built and operated by the privately owned company known as SpaceX, is due to depart the orbital outpost at 7:06 a.m. EDT and parachute down into the Pacific Ocean west of Mexico's Baja California about 5-1/2 hours later.
A skeleton crew of three astronauts and cosmonauts aboard the space station will oversee Dragon's release. Three new crew members are due to launch to the orbital complex, a $100 billion project of 15 nations, on Thursday and, for the first time, arrive the same day.
The Dragon cargo ship reached the station on March 3 with more than 2,300 pounds (1,043 kg) of science equipment, spare parts, food and supplies. It was the second of 12 planned cargo runs for NASA under a $1.6 billion contract. A second freighter, built and operated by Orbital Sciences Corp is expected to debut this year.
The U.S. space agency hired both firms to fill the gap left by the retirement of its space shuttle fleet in 2011.
Dragon's arrival was delayed a day while SpaceX engineers grappled with a thruster pod problem that had threatened to derail the mission.
"I don't want to go through that again. That was hard-core," SpaceX founder and chief executive Elon Musk said during a keynote speech at the popular South by Southwest conference in Austin, Texas, earlier this month.
Engineers believe the glitch was caused by a blockage in a pressurization line or a stuck valve. It was cleared and the capsule made a precision rendezvous with the station with no problems.
Dragon is due to return to Earth with 2,668 (1,210 kg) of cargo, including a freezer filled with biological samples from the crew for medical research.
While Russian, European and Japanese freighters also service the station, only the SpaceX vessel is designed to return cargo to Earth, a critical transportation link that had been lost with the retirement of the shuttles.
SpaceX is working to upgrade the Dragon capsule to fly people as well. A test flight with company astronauts is targeted for 2016.
In addition to enhancing the Dragon capsules, SpaceX is working on an upgraded Falcon 9 rocket. Last week, the rocket's new Merlin engines completed a 28th and final test run, certifying it for flight, said SpaceX spokeswoman Christina Ra.
The company plans to debut its upgraded Falcon 9 rocket on a science satellite-delivery mission for the Canadian Space Agency in June. That rocket also will be the first flight from SpaceX's new launch pad at Vandenberg Air Force Base in California. Five previous Falcon 9 flights have launched from Cape Canaveral Air Force Station in Florida.
Dragon's return initially was scheduled for Monday, but it remained docked an extra day due to high seas in the Pacific. Splashdown now is targeted for 12:34 p.m. EDT on Tuesday about 246 miles off the coast of Baja California.
A recovery ship will retrieve the capsule and ferry it back to the Port of Los Angeles, a journey expected to take about 30 hours.
Meanwhile, Orbital Sciences Corp, which holds an eight-flight, $1.9 billion NASA contract for station resupply flights, plans to test launch its new Antares rocket as early as April 16 from the commercial Mid-Atlantic Regional Spaceport at NASA's Wallops Flight Facility in Virginia.
Orbital's Cygnus cargo capsule is targeted to make a demonstration run to the space station later in the year.
(Editing by Tom Brown and Cynthia Osterman)