On Saturday, two NASA astronauts, Robert L. Behnken and Douglas G. Hurley, were launched into orbit atop a SpaceX rocket. It was the first time the private company, founded by the billionaire Elon Musk, had ever launched humans into space. It was also the first time since 2011, when NASA retired its space shuttles, that astronauts had lifted off for the International Space Station from American soil.

Mr. Behnken and Mr. Hurley’s trip required a 19-hour trip around the planet as the spacecraft they were traveling in steadily caught up with the orbital outpost. Their capsule, the SpaceX Crew Dragon, is scheduled to dock at the space station at 10:29 a.m. Eastern time on Sunday. NASA Television is providing ongoing coverage of the trip to the space station.

The space station, at an altitude of about 250 miles, zips around Earth at more than 17,000 miles per hour. The fundamental principle of orbital dynamics is that objects in lower orbits move faster, and those in higher orbits move slower.

At launch, the Crew Dragon started out trailing the space station. But traveling in an orbit below the space station, it was moving faster and catching up. Through a series of maneuvers, the capsule raised its orbit, allowing the capsule to approach the station at a lower speed.

While the astronauts could dock with the station manually in an emergency, the Crew Dragon’s computers will automatically begin the capsule’s close approach to the space station at about 8:27 a.m., when it is about 4.5 miles away.

At a series of predetermined points along the approach, the spacecraft stops so that mission controllers on Earth can make sure everything is working as planned. At one point, when the Crew Dragon is about 720 feet in front of the space station, the astronauts will try out the manual control of the spacecraft as they continue to approach. This mission is a test flight, and NASA wants to make sure that astronauts would be able to successfully dock the capsule in case of a computer malfunction.

The computer will take over again for the final approach. Once docked, Mr. Hurley and Mr. Behnken will still have to wait a couple of hours for the completion of tests needed to ensure that the seals between the spacecraft and the space station are airtight.

Not at the International Space Station. The chances of a damaging collision are small because visiting spacecraft approach the station at very low speeds. But there have been a couple of instances in which the approach systems of spacecraft have malfunctioned.

SpaceX sent Dragon, its crewless capsule that carries cargo, to the space station for the first time in 2012. During that mission, the vessel’s navigation system encountered problems because of stray reflections off one of the station modules. SpaceX engineers reconfigured the system from the ground, and the Dragon made a final approach that allowed it to be grabbed by one of the station’s robotic arms.

In 2017, another cargo Dragon aborted an approach because of a problem with its GPS system. It successfully approached the station the next day.

In 2019, an uncrewed Russian Soyuz spacecraft on a test flight similarly called off a docking problem because of a problem with its automated system. But it successfully docked on the second try.

SpaceX’s new Crew Dragon capsule made its first test flight to the space station last year with no astronauts aboard. After that visit, Russian space officials raised concerns that a possible sequence of malfunctions could put the spacecraft on a collision course with the station. Although the series of events that could cause such an error was unlikely, SpaceX’s engineers made changes to eliminate that possibility for this mission.

While the International Space Station has been spared, unintended collisions have occurred at earlier outposts. In 1997, a Russian Progress cargo ship crashed into Mir, the former Russian space station, during a test of the vessel’s manual docking system. That punched a hole in a laboratory module, knocked out power and caused an air leak. With makeshift repairs, the station’s crew was able to keep Mir operating.

Crew Dragon has never gone to space with humans aboard. That means SpaceX and NASA have a great deal to learn from this trip to orbit.

One of the most important goals of this trip was for the astronauts to get their first try at flying the spacecraft manually when they were still far away from the space station — essentially taking the spacecraft out for a test drive and seeing how it handles to the commands.

They also took a pause during the trip to give the public a tour of the capsule’s interior.

Mr. Behnken and Mr. Hurley also had time to change out of their fancy new spacesuits, eat a meal and sleep. They also promised they’d try out the bathroom.

source: nytimes.com

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