Live coverage: Atlas 5 countdown and launch journal

After prepping their patient — a $2 billion cosmic ray detector — during two earlier spacewalks, two space station astronauts ventured back outside for a third outing Monday to carry out what amounted to transplant surgery, installing replacement coolant pumps in a bid to revive the costly instrument and extend its life.

United Launch Alliance has selected Orbital ATK to provide solid rocket boosters for the company’s next-generation Vulcan launcher, and will switch the workhorse Atlas 5 to the new booster supplier by the end of 2018, officials said Tuesday.

An Air Force missile detection spacecraft will, effectively, lose its position in the Atlas 5 rocket’s cramped manifest over the next few months after the flight-worthiness of a thruster on the satellite was called into question and delayed its Oct. 3 liftoff date.