Washington, Mar 30 (IANS): The first crewed flight of Boeing's CST-100 Starliner has been again pushed till July, NASA has announced.

This comes after Boeing and NASA, last month, said Starliner's astronaut debut, a mission to the International Space Station (ISS) called Crew Flight Test (CFT), was on track to launch in April.

Kathy Lueders, NASA Associate Administrator of Space Operations, last week announced on Twitter that the date has again been pushed to May.

But May liftoff for CFT is now off the table, and liftoff is now targeted for July 21 at the earliest, agency officials announced at a press conference on Tuesday.

"We've deliberated and decided that the best launch attempt is no earlier than July 21 for CFT," Steve Stich, manager of NASA's Commercial Crew Programme, said during a press conference today.

Considerable traffic at the ISS with Ax-2 lifting off in May and SpaceX's next robotic cargo mission targeted for June was stated as the reason for the delay, Space.com reported.

Further, CFT's launch site, Cape Canaveral Space Force Station in Florida, will be busy over the coming months.

United Launch Alliance (ULA) plans to fly a mission for the US Space Force from Cape Canaveral with an Atlas V rocket this spring, and the first-ever liftoff of the company's new Vulcan Centaur vehicle is targeted for May from the site. (CFT will employ an Atlas V as well.)

In addition, NASA wants a bit more time to analyse data about Starliner's various components, such as its parachute system, before putting astronauts on the vehicle, Stich said.

Together with Boeing, the agency also plans to conduct one more ground test of a parachute subsystem -- the chute that pulls off Starliner's forward heat shield. That trial is targeted for May, Stich said.

"At this time, there's really no issues or concerns with the parachute system," Stich said.

"The parachutes are installed in the vehicle; they're in good shape. It's just a matter of going through all that data and looking at the data and making sure we're really ready to go fly safely."

CFT aims to send NASA astronauts Butch Wilmore and Sunita Williams to the ISS for a roughly eight-day stay.

Boeing had signed a contract with NASA's Commercial Crew Programme to fly operational missions to and from the space station with Starliner in 2014. It had last year conducted two test uncrewed flights to space.

If all goes well with the upcoming test flight, NASA will likely certify Starliner for operational astronaut missions to the orbiting lab.