RS-68 Propulsion System SPECIFICATIONS
The RS-68 engine is one of two new rocket engines Rocketdyne is developing the first new American engines in more than 25 years. Designed for the McDonnell Douglas Delta IV Evolved Expendable Launch Vehicle (EELV), the bell nozzle RS-68 is a liquid hydrogen - liquid oxygen booster engine that develops 650,000 lb. of sea level thrust. The RS-68 utilizes a simplified design philosophy resulting in a drastic reduction in parts compared to current cryogenic engines. This design approach results in lower development and production costs.
'''December 13, 2004'''

CAPE CANAVERAL, Florida - The first new heavy lift space vehicle in a generation is cleared to launch from Cape Canaveral Air Force Station. The Boeing '''Delta IV Heavy''' has missed launch opportunities three days in a row (starting Friday, December 12) due to minor technical difficulties. It is now scheduled to launch Dec. 20 or 21 from pad SLC-37B.

The '''Delta 4''' was developed as part of the U.S Air Force's ''Evolved Expendable Launch Vehicle'' program to reduce costs and improve reliability.  The basic design is a two stage, cryogenic LOx/LH2 rocket.  Strap-on boosters may be added to increase lift capacity.  

Two major obstacles have plagued the project in recent years; a bidding scandal which cost Boeing a large portion of the military satellite launch business for which it was competing, and a downturn in commercial satellite launches in 2001.

The ''Heavy'' variant of the Delta 4 rocket can place 13,100 kg (28,950 Lb) into geostationary transfer orbit, greater than any other current rocket. Two additional first stage cores are used as strap-on boosters for this configuration. Their rated thrust is 2,900,000 N (656,000 lb) each. 

Delta 4's main engine, the RS68, is the most powerful hydrogen/liquid oxygen engine in the world, approximately three times as powerful as the Ariane 5 Vulcain HM60. Its design sacrifices efficiency for increased reliability and lower cost: rated specific impulse is 365s at sea level and 410s in a vacuum. The second stage engine, Pratt and Whitney's RL-10B-2, has a specific impulse of 462s.

The primary market for this launcher will be classified spy satellites for the US intelligence community. Most of these satellites were previously launched on the Titan 4, which has since been retired. The Delta 4 Heavy's published launch cost is $170 million, compared to the Titan 4's $400 million (1999 dollars).

Delta 4 Heavy's maiden launch is a demonstration and will carry a dummy load and two nano-satellites. The main payload, dubbed ''DemoSat'' is a 6020 kg (13271 lb) mass designed to simulate the dynamic and initial properties of a real satellite.  Its design consists of large brass rods, intended to fully burn up on reentry.

The two nano-satellites are part of the US Department of Defense ''Nanosat-2 Program'', and built by students from New Mexico State University, Arizona State University, and the University of Colorado at Boulder.