Delta II 7920H

The Delta II Rocket has been flying since 1989 and is operated by United Launch Alliance. Delta II was originally built by McDonnell Douglas. The workhorse of the expandable launch vehicle fleet has flown nearly 150 times (149 as of August 2011) and has proven its reliability. In total, the program has logged only one failure and one partial failure. This record makes the launcher the most reliable active launch vehicle. Delta II rockets can be launched from Space Launch Complex 17 at the Cape Canaveral Air Force Station, Florida and from SLC-2 at Vandenberg Air Force Base, California.

Delta II uses a Delta XLT-C core stage that is being powered by a flight proven RS-27 engine that is built by Rocketdyne. Rocket Propellant 1 (ultra purified Kerosine) and liquid Oxygen are used as propellants. Strapped onto the core stage are a number of Solid Rocket Boosters. For the 7920 variant, GEM-46 Motors that are 45 inches in diameter are being used. 6 are ignited at liftoff. When those have burned out, the remaining three SRBs are being fired. The second stage is using Nitrogen Tetroxide and Aerozine as propellants. A restartable Aerojet AJ-10-118K engine places the stack in the desired orbit. The fuels that are used in the second stage require a launch within 37 days following tanking because those propellants are highly corrosive and can cause damage to the rocket that leads to major malfunctions.

Also part of stage 2 are all important flight control systems like on-board computers and guidance&navigation control. Those instruments control the flight from the moment of blastoff until spacecraft separation. Delta II can support a third stage. This is optional and not included in a 7920 stack. UlA provides three different payload fairing designs. GRAIL uses the standard 10 feet enclosure. The fairing protects the payloads from thermal loads during atmospheric flight and separates as soon as the vehicle has left the atmosphere to increase capabilities of the rocket.

GRAIL is the final planned launch of the Delta II rocket before the system is retired. However, there is talk about continuing to fly the launcher for chosen missions.

~ Spaceflight 101