May 6 (Reuters) - Two years after its initial unmanned journey to the International Space Station (ISS), Boeing's new Starliner astronaut capsule is set for its first crewed test flight on Monday night, following numerous delays.

Boeing's Crew Space Transportation (CST)-100 Starliner spacecraft, developed in collaboration with NASA's Commercial Crew Program, is engineered to carry up to seven passengers, or a combination of crew and cargo, for journeys to low-Earth orbit.

Riding aboard the Starliner are NASA astronauts Barry "Butch" Wilmore, 61, a retired U.S. Navy captain, and Sunita "Sunni" Williams, 58, a former Navy aviator and test pilot.

Here's a quick rundown of key events over the past few years:

Sept. 4, 2015 - Boeing takes the wraps off an assembly plant for its first line of commercial spaceships, which NASA plans to use to fly crews to the ISS.

Nov. 4, 2019 - Boeing says one of three parachutes failed to open during a crucial unmanned test of the CST-100 Starliner.

Dec. 20, 2019 - Boeing successfully launches its new astronaut capsule on an unmanned debut journey to the ISS.

Dec. 22, 2019 - The spacecraft makes a "bull's-eye" landing in the New Mexico desert.

Jan. 7, 2020 - NASA and Boeing probe software glitch that stopped the capsule from reaching the ISS.

Feb. 6, 2020 - Boeing narrowly misses a "catastrophic failure" during its December flight test of an unmanned space taxi that was cut short by an unrelated problem.

Aug. 25, 2020 - The first Starliner crewed mission is tentatively slated for 2021

Oct. 7, 2020 - The chief astronaut for Starliner crewed flight to the ISS, Chris Ferguson, steps down from the job, citing family priorities

July 29, 2021 - Space station mishap prompts NASA to postpone launch of Boeing Starliner

Aug. 3, 2021 - Boeing postpones Starliner launch after new glitch

Aug. 13, 2021 - Boeing to return the spacecraft to the factory to resolve a valve issue, delaying the launch date

May 19, 2022 - The Starliner capsule launches on a do-over uncrewed test flight bound for the International Space Station

May 20, 2022 - The new Starliner crew capsule docked for the first time with the International Space Station

Aug 25, 2022 - Boeing targets early 2023 for the first Starliner mission carrying astronauts

June 1, 2023 - Boeing says it is standing down from late preparations for its first crewed Starliner test flight to space that was planned for July 2023 after it discovered two safety-critical issues with the spacecraft. (Reporting by Nathan Gomes and Shivansh Tiwary in Bengaluru; Editing by Anil D'Silva)