The US National Aeronautics and Space Administration (Nasa) and giant US aerospace group Boeing hoped to launch the latter’s CST-100 Starliner spacecraft on its second uncrewed test flight on Thursday. This demonstration flight would see the CST-100 Starliner fly to and dock at the International Space Station (ISS).

For this mission, the craft would carry 800 lbs (about 363 kg) of cargo to the ISS, including some 500 lbs (around 227 kg) of Nasa freight and crew supplies. The capsule would spend five to ten days attached to the ISS, before undocking, re-entering the Earth’s atmosphere, and landing (and not, as usual with US space capsules, splashing down in the sea) in the western US. On its return, it would carry some 600 lbs (about 272 kg) of cargo.

Boeing developed the CST-100 Starliner under Nasa’s Commercial Crew Transportation (CCT) programme. Under this, astronauts would be flown from the Earth into low Earth orbit on a commercial basis, allowing Nasa to concentrate again on crewed exploration missions into deeper space. The CCT programme also saw the development of SpaceX’s Crew Dragon spacecraft, and Nasa’s intention was (and remained) to be able to contract flights from both SpaceX and Boeing, thereby ensuring competition and keeping costs down.

However, the Boeing project had been plagued by glitches, and was now running years behind the SpaceX programme. While Crew Dragon was now operating routinely, the Starliner had not yet completed a 100%-successful uncrewed demonstration flight.

This upcoming demonstration flight would employ the second Starliner so far built, which included improvements and other changes in comparison to the first example, which showed inadequacies during its original uncrewed demonstration flight. This second demonstration flight would test these changes and improvements.

This second test flight would also test the in-orbit functioning of the Starliner’s avionics, communications and telemetry systems, docking system, solar arrays and electrical power systems, propulsion systems and environmental control systems. Also to be tested were the guidance, navigation and control systems of both the Atlas V launch rocket and the Starliner, from launch, into orbit and re-entry. Vibration and acoustic levels would also be monitored, as would the loads across the Starliner, both externally and internally. Additionally, there would be monitoring of the launch escape trigger. Monitoring the operation of the Starliner system from the beginning to the end of the mission was another objective of the test flight.

Should this second demonstration flight prove successful, the next phase would be the review of all the data collected during the mission. Once this had been done, Nasa and Boeing would then set a date for the first crewed demonstration mission to the ISS.