Live coverage: Proton blasts off on return-to-flight mission

Bulking up NASA’s constellation of tracking stations in the sky that provides critical links between orbiting spacecraft and ground control, a United Launch Alliance Atlas 5 rocket successfully deployed a new communications hub in space today.

A pair of innovative satellites for ViaSat and Eutelsat, valued at approximately $800 million, are scheduled to lift off Thursday on an Ariane 5 rocket from French Guiana, hauling the heaviest and costliest commercial payload ever launched.

SpaceX’s launch director halted a countdown Tuesday to replace a sensor on the upper stage of a Falcon 9 rocket set to blast off with the GovSat 1 communications craft, the product of a joint venture between the commercial satellite operator SES and the government of Luxembourg.