Photos: More Delta 4 launch shots

The last unflown variant of United Launch Alliance’s Atlas 5 launcher — fitted with a five-meter fairing and a single strap-on solid rocket booster — will carry a pair of U.S. military space surveillance satellites toward geosynchronous orbit from Cape Canaveral late this year, according to a Space Force spokesperson.

Lockheed Martin, the largest U.S. defense contractor, announced late Sunday that it has reached a deal valued at $4.4 billion to acquire Aerojet Rocketdyne, a supplier of engines to NASA’s Space Launch System moon rocket and United Launch Alliance’s Atlas, Delta, and Vulcan rockets.

A rocket-transporting railroad car ferried a Proton rocket to its launch pad Friday at the Baikonur Cosmodrome in Kazakhstan for final checkouts and testing before the vehicle’s scheduled June 21 liftoff with the Russian-German Spektr-RG X-ray telescope.