WASHINGTON, June 11 (Reuters) - NASA and Boeing ( BA )

said they expect to bring Starliner and its first astronaut crew

back to Earth from the International Space Station as soon as

June 18, later than previously scheduled as mission analysts

examine issues that could affect its return.

Boeing's ( BA ) CST-100 Starliner spacecraft was originally

expected to undock on Friday and return to Earth after launching

its inaugural crew of two NASA astronauts from Florida on June

5. The mission is a crucial test before the U.S. space agency

can certify Starliner for routine flights.

In scheduling Starliner's return, NASA officials in Houston

are juggling various factors: fixes to faulty components on

Starliner, weather conditions, and ISS scheduling matters such

as spacewalks by other astronauts aboard the station. More

changes to Starliner's return date could be announced during its

mission.

But as of Tuesday, mission officials were targeting June 18

for Starliner's undocking from the station. Roughly six hours

later the spacecraft would land in the desert of White Sands

Missile Range in New Mexico, Willcox Playa in Arizona or other

similar pre-determined locations, pending weather conditions.

Dina Contella, NASA's deputy program manager for the ISS,

told reporters on Tuesday that NASA had detected a new issue on

Starliner while it remained docked to the station - a "sticky"

oxidizer valve.

A NASA blog posted on Monday mentioned an additional helium

leak on Starliner's propulsion system, on top of four already

identified during its 24-hour trek to the space station last

week.

During that flight, five of its 28 maneuvering thrusters

went dead, but NASA and Boeing ( BA ) were able to regain four of them

before docking to the orbital laboratory.

Starliner can stay docked to the ISS for a maximum of 45

days, NASA officials have said.