The flight, a final test before Starliner takes up regular service for the space agency, is critical for Boeing, whose reputation has suffered of late due to safety issues with its passenger jets.

For NASA, the stakes are also high: Having a second option for human space flight in addition to SpaceX's Dragon vehicles is "really important," said Dana Weigel, manager of the agency's International Space Station program.

Astronauts Butch Wilmore and Suni Williams are set to take off from Cape Canaveral at 10:34 pm Monday (0234 GMT Tuesday), if favorable weather predicted for the launch continues to hold.

Starliner will be propelled into orbit by an Atlas V rocket made by United Launch Alliance, a Boeing-Lockheed Martin joint venture.

Once in space, one of Wilmore and Williams's tasks will be to temporarily pilot the craft manually, in a test.

The astronauts, both Navy-trained space program veterans, have each been to the ISS twice, traveling once on a shuttle and then aboard a Russian Soyuz vessel.

"It's going to be like going back home," Williams said ahead of the launch.

As for the Boeing spacecraft, Wilmore said: "Everything is new."

- Hiccups expected -

Starliner is scheduled to arrive at the ISS at about 0500 GMT Wednesday, and remain there for a little over a week. Tests will be performed to check it is working properly, and then Williams and Wilmore will reboard the capsule to return home.

A successful mission would help dispel the bitter taste left by the numerous setbacks in the Starliner program.

In 2019, during a first uncrewed test flight, the capsule was not placed on the right trajectory and returned without reaching the ISS.

Then in 2021, with the rocket on the launchpad for a new flight, blocked valves forced another postponement.

The empty vessel finally reached the ISS in May 2022. But problems since then have delayed Monday's crewed test flight, necessary for the capsule to be certified for NASA's use on regular ISS missions.

NASA associate administrator Jim Free had predicted the mission would not be hiccup-free.

"We certainly have some unknowns in this mission, things we expect to learn, being a test mission. We may encounter things we don't expect," Free said, noting that Starliner is just the sixth US-built class of vessel for NASA astronauts.

SpaceX's Dragon capsule joined that exclusive club in 2020, following the Mercury, Gemini, Apollo and space shuttle programs.

In 2014, the agency awarded fixed-price contracts of $4.2 billion to Boeing and $2.6 billion to SpaceX to develop the capsules.

Once Starliner is fully operational, NASA hopes to alternate between SpaceX and Boeing vessels to ferry astronauts to the ISS.

Even though the ISS is due to be mothballed in 2030, both Starliner and Dragon could be used to taxi humans to future private space stations, which several companies are planning to build.

Boeing's Starliner joins select club of crewed US spaceships
Washington (AFP) May 4, 2024 - Throughout the annals of American space exploration, a select few spacecraft have had the distinction of carrying human beings beyond Earth.

Next week, Boeing is poised to join this elite group with the long-awaited launch of its Starliner capsule, just the sixth class of vessel built in the United States for NASA astronauts.

Here's a recap of their storied past, marked by groundbreaking triumphs and some devastating setbacks.

- Mercury -

Known as America's "man-in-space" program, Project Mercury was born just days after NASA itself was formed in 1958, and officials settled on the term "astronauts" for its space explorers.

On May 5, 1961, Alan Shepard became the first American to fly in space during a 15-minute suborbital flight in the one-man, cone-shaped capsule -- about a month after the Soviet Union's Yuri Gagarin became the first human to achieve the feat.

Another first came in February 1962 when Mercury astronaut John Glenn became the first American to orbit the Earth.

Black mathematician Katherine Johnson, whose story was immortalized in the book and film "Hidden Figures," was among those working tirelessly from the ground to ensure the program's success.

- Gemini -

While Mercury was about getting people up to space, Gemini was focused on extending their mission time and developing critical maneuvers -- such as mastering precise orbital velocity matching for spacecraft docking and safe spacewalk procedures.

The Gemini spaceship resembled an enlarged Mercury capsule, designed for a two-person crew. A significant innovation was the introduction of onboard computers, primitive by today's standards but capable of assisting with the complexities of space rendezvous.

- Apollo -

Apollo was NASA's response to President John F. Kennedy's challenge to land a man on the Moon before the end of the 1960s.

Achieving the goal required three key pieces of technology.

The first was the giant Saturn V rocket. Designed under ex-Nazi Wernher von Braun, it remained the most powerful rocket for five decades.

The second piece was the command module -- whose interior was as roomy as a big car -- and the third was the lunar descent vehicle.

While Apollo 11 achieved humanity's first crewed touchdown on July 20, 1969, the program was also marked by tragedy. A fire during a preflight test for Apollo 1 killed all three crew members, highlighting the risks and sacrifices made in pursuit of space exploration.

- Space Shuttle -

NASA's space shuttle program, which spanned from 1981 to 2011, took a revolutionary approach by combining rocket launch, capsule re-entry, and glider-like runway landings.

The era marked significant milestones, including the first space flights by American women and minorities, the launch of the Hubble Space Telescope on the shuttle Discovery, and the construction of the International Space Station in the late 1990s.

However, it was also marred by two devastating tragedies: the 1986 Challenger disaster, which occurred just after launch, and the 2003 Columbia disaster, which happened during re-entry.

Both incidents resulted in the loss of all crew members, totaling 14 lives.

Despite these setbacks, former astronaut Tom Jones, author of "Space Shuttle Stories," argued the shuttle was far ahead of its time and was "an iconic symbol of America's presence in space."

- Crew Dragon and Starliner -

After the space shuttle was retired, the United States was left without a homegrown capacity to launch its astronauts and was forced to rely on Russian Soyuz rockets.

NASA decided to shift from a model where it owned the hardware, to instead hiring services from the commercial industry in multibillion dollar contracts.

Elon Musk's SpaceX, which was derided in its startup phase as reckless, beat heavily-favored aerospace giant Boeing in flying its first crew to the ISS in 2020.

Since then, it has flown 49 people on its Dragon vehicles, in missions for NASA and private clients.

Meanwhile, Boeing has struggled with technical issues, echoing wider organizational problems that have plagued its aviation division.

Both companies have adopted the classic gumdrop-shaped capsule design, but with modern twists: sleek displays, autonomous flight, and full reusability.

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