The Delta II family of rockets has a lengthy and successful flight history. NASA has relied on various configurations of the Delta II for a number of high-profile missions, such as the Earth-observing Aquarius and Orbiting Carbon Observatory-2, telescopes such as Kepler and WISE, and several Mars missions, including Mars Pathfinder and the Spirit and Opportunity rovers.
On the launch pad this morning is a Delta II-7320. This code tells us this is a rocket from the 7000 series with three solid rocket motors on the first stage, with a second stage, but no third stage required.
The rocket’s first-stage engine, also called the main engine, is the Aerojet Rocketdyne RS-27A. It burns a highly refined kerosene fuel called RP-1 in addition to cryogenic liquid oxygen. The second stage is powered by a restartable Aerojet Rocketdyne AJ10-118K engine that runs on the propellants Aerozine 50 and nitrogen tetroxide. The rocket is topped by a fairing that protects the payload.
RP-1 was loaded into the first stage yesterday evening, and first-stage liquid oxygen loading is planned to begin around 7:35 a.m.