Delta IV Heavy
United Launch Alliance’s Delta IV Heavy is a heavy-lift launch vehicle, the largest type of the Delta IV family and one of the world’s most powerful rockets. The Delta IV Heavy configuration is comprised of a common booster core (CBC), a cryogenic upper stage and a 5-meter diameter payload fairing (PLF). The Delta IV Heavy employs two additional CBCs as liquid rocket boosters to augment the first-stage CBC. The Delta IV Heavy can lift 28,370 kg (62,540 lbs) to low Earth orbit and 13,810 kg (30,440 lbs) to geostationary transfer orbit. It is an all liquid-fueled rocket, consisting of an upper stage, one main booster and two strap-on boosters.
Payload Fairing (PLF)
The PLF encapsulates the spacecraft to protect it from the launch environment on ascent. The 19.2-m (63-ft) long PLF makes the vehicle’s height approximately 71.0 m (233 ft).
Delta Cryogenic Second Stage (DCSS)
The DCSS is a cryogenic liquid hydrogen/liquid oxygen fueled vehicle, with a single RL10C-2-1 engine that produces 110.1 kilo-Newtons (24,750 lbs) of thrust.
The Delta IV booster propulsion is provided by three liquid hydrogen and liquid oxygen-burning RS-68A engines. Each RS-68A engine produces 312.3 kilo-Newtons (705,250 lbs) of thrust for a combined total liftoff thrust of more than 2.1 million pounds.
NROL-91 has launched from Space Launch Complex 6 (SLC-6) at Vandenberg Space Force Base, California. The first launch from SLC-6 was on an Athena I rocket in August 1995. In 2000, United Launch Alliance took over SLC-6 and re-fitted it to serve as the west coast home for the Delta IV launch vehicle family with modifications to the Assembly Building, Mobile Service Tower, Launch Tower, and other support structures.