The problem for NASA and Boeing is that the Starliner’s service module, which houses the helium lines, thrusters and other critical systems, is discarded before re-entry and burns up in the atmosphere. Engineers will not be able to study the hardware after the fact and as a result, they want to collect as much data as possible before NASA astronauts Butch Wilmore and Sunita Williams head home.

Astronauts Jeff Williams and Kate Rubins ventured outside the lab complex Friday for a long-awaited spacewalk to attach a new docking mechanism, the first of two that will be used by U.S. crew ferry ships being built by Boeing and SpaceX to carry astronauts to and from the outpost, ending NASA’s sole reliance on Russian Soyuz spacecraft.

Delays have set up the possibility of up to three rocket launches this weekend from different pads along Florida’s Space Coast, including two SpaceX missions on Sunday that could set a company record for the shortest span between two Falcon 9 rocket launches. But in the world of ever-changing launch schedules, numerous factors such as weather and technical issues could thwart launch plans this weekend.