Rob Coppinger of Hyperbola blog points to a presentation (PDF) that explains why ESA and Roskosmos recently ended an 18-month study on whether to jointly build a new Crew Space Transportation System (CSTS).
The presentation by Marco Caporicci of ESA’s Human Spaceflight Directorate indicates the two sides were unable to agree on a division of work that allow them to get what they wanted out of the CSTS project.