The fourth commercial flight of Jeff Bezos' space tourism venture Blue Origin, offering short suborbital joyrides to well-heeled thrill-seekers and celebrity guests, was due for liftoff on Tuesday from the company's launch site in rural west Texas.

Blue Origin's New Shepard spacecraft was slated for launch at 8:30 a.m. CDT (1330 GMT) with six would-be citizen astronauts strapped into the crew cabin atop the fully autonomous launch vehicle, standing nearly six stories tall, outside Van Horn, Texas.

But unlike Blue Origin's first three commercial flights, with passenger rosters including "Star Trek" actor William Shatner, morning TV host Michael Strahan and even Bezos himself, nobody among the latest group of customers even comes close to being famous.

The most recent household name confirmed as a non-paying promotional guest, "Saturday Night Live" comic Pete Davidson, dropped out earlier this month when the planned launch was postponed for six days from its original March 23 date to allow time for additional pre-flight tests.

Days later the company announced that Davidson, 28, the boyfriend of reality TV star Kim Kardashian, had been replaced on the latest "crew" manifest by veteran Blue Origin designer Gary Lai, architect of the New Shepard reusable launch system.

Lai is flying for free. He joins five previously announced paying customers - angel investor Marty Allen, real estate veteran Marc Hagle and his wife Sharon Hagle, entrepreneur and University of North Carolina professor Jim Kitchen and George Nield, founder-president of Commercial Space Technologies.

Kitchen's journey to the final frontier caps a lifelong dedication to travel that has taken him to all 193 U.N.-recognized countries, according to biographical material from Blue Origin.

Tuesday's entire flight, from liftoff to touchdown, is expected to last just over 10 minutes. The crew will experience a few minutes of weightlessness at the very apex of their suborbital ride, some 350,000 feet (106,680 metres) high, before their capsule falls back to Earth for a parachute landing on the desert floor.

Bezos, the billionaire founder of online retail giant Amazon, tagged along himself on Blue Origin's inaugural crewed flight to the edge of space last July.

He accompanied his brother, Mark Bezos, trailblazing octogenarian female aviator Wally Funk and an 18-year-old Dutch high school graduate.

Later passengers included Shatner, who became the oldest person to fly to space at age 90, "Good Morning America" co-host and retired NFL star Strahan, and the eldest daughter of pioneering astronaut Alan Shepard, for whom Blue Origin's spacecraft is named.

(Reporting by Steve Gorman in Los Angeles; Editing by Sam Holmes)