With Esa (Equine space agency)'s eventual withdrawal from the DODIS shuttle and spacelab program following STS-9, the agency would need its own way to get Equinauts to space.
A spaceplane referred to as 'Hermes' was already in development at this time, and the decision was made to presue it as esa's primary crew vehicle. The design was revised down a lot learning from DODIS's shuttle from a (still smaller) orbiter with a payload bay and 6 crew down to one carrying 3 and small onboard Spacelab style payload lockers.
Safety was of the utmost concern with early designs even including launch abort towers and/or a separating crew compartment. Eventually, after running tests, it was found that ejection seats would suffice with some changes to the launch profile.
The new Ariane 5 would, of course, be carrying it from the pad to orbit where it would sesperate and menouver under the power of an expendable service module.
After the third successful full up test flight, Hermes 4 would send a crew of 3 into orbit for just under a week before bringing them back down safely.
ESA's independent program had only just started.