What is it?: The Delta IV is part of a family of Delta rockets that were designed for the United States Air Force Evolved Expendable Launch Vehicle (EELV) program and commercial satellite business, and are intended to reduce the cost and effort needed to launch payloads into orbit. The Delta IV is available in five versions: Medium, Medium+ (4,2), Medium+ (5,2), Medium+ (5,4), and Heavy, which are tailored to suit specific payload size and weight ranges. Delta IV launch vehicles can accommodate single or multiple payloads on the same mission. The rockets can launch payloads to polar orbits, sun-synchronous orbits, geosynchronous and geosynchronous transfer orbits (GTO), and low Earth orbit (LEO). Delta IV vehicles can launch payloads weighing from 4,300 kg to 12,980 kg to GTO, and can lift over 23,000 kg to LEO.
The first stage of a Delta IV consists of one, or in the Heavy variety three, Common Booster Cores powered by a Rocketdyne RS-68 engine. Unlike most first-stage rocket engines, which use solid fuel or kerosene, the RS-68 engines burn liquid hydrogen and liquid oxygen.
The RS-68 is the first large, liquid-fueled rocket engine designed in the U.S. since the Space Shuttle Main Engine (SSME) in the 1970s. The primary goal for the RS-68 was to reduce cost versus the SSME. Some sacrifices were made in its design hurting its efficiency; however, development time, part count, total cost, and assembly labor were reduced to a fraction of the SSME. The second stage is powered by a Pratt & Whitney RL-10B2 engine, which features an extendable carbon-carbon nozzle to improve specific impulse.
The Delta IV was designed by Boeing and built in Decatur, Alabama by United Launch Alliance (co-owned by Lockheed Martin and Boeing) with final assembly at the launch site (LC-37B at Cape Canaveral or SLC-6 at Vandenberg AFB.) by United Launch Alliance. Each Delta IV rocket is assembled horizontally, erected vertically on the launch pad, integrated with its satellite payload, fueled and launched. This process reduces on-pad time to less than 10 days and the amount of time a vehicle is at the launch site to less than 30 days upon arrival from the factory.
The Delta IV entered the space launch market at a period when global capacity was already much higher than demand. It has had difficulty finding a market in commercial launches, and the cost to launch a Delta IV is somewhat higher than that for competing vehicles. In 2003, Boeing pulled the Delta IV from the commercial market, citing low demand and high costs. All but one of the first launches have been paid for by the U.S. Government, with a cost of between $140 million and $170 million.
NASA originally had plans to use the Delta IV Heavy for the Crew Exploration Vehicle, the replacement for the Space Shuttle. But these plans changed and the only component from the Delta IV that NASA has adopted is the RS-68 engine that will be used to power part of the Ares V rocket first stage (there are now talks that the RS-68 will be replaced by the Shuttle's SSME engines for the Ares V first stage).
The first payload launched with a Delta IV was the Eutelsat W5 communications satellite. The launch vehicle was a Medium+ (4,2) variant, launched from Cape Canaveral. It carried the communications satellite into geostationary transfer orbit (GTO) on November 20, 2002.
Delta IV launch on January 18th (17:26):
News on this launch
Sources:
Wikipedia
Boeing's Delta IV Site
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