Virgin Galactic has fired back at Boeing’s accusations that it failed to pay $25 million for Aurora Flight Sciences Corp. engineering services by claiming Boeing “substantially underdelivered” in the process, according to a federal countersuit in the U.S. District Court for the Central District of California last week.

While Boeing and its subsidiary Aurora Flight Sciences claimed Virgin Galactic failed to cover costs for the design of a new mothership, the human spaceflight company alleged Boeing’s repeated failures to deliver on its promises compelled them to end the partnership.