Delta IV

Vehicle Configurations

Vehicle Components

Boeing developed Delta IV to compete for U.S. Air Force Evolved Expendable Launch Vehicle (EELV) launch contracts. Although it carries the "Delta" name, the big new rocket has little in common with with long running Douglas/NASA Thor-Delta series.

The United Launch Alliance consortium, a new company spun off by Boeing and Lockheed Martin, took over the Delta IV and Atlas V EELV programs in December 2006.

Several Delta IV models are available to loft 3 to 11 ton payloads into geosynchronous transfer orbit (GTO) or 8.4 to 22.5 ton payloads into low earth orbit (LEO). Planned versions include the Medium, Medium Plus (4,2), Medium Plus (5,2), Medium Plus (5,4), and the Heavy.

Delta IV is built around the 5.1 meter diameter Common Booster Core (CBC) first stage powered by a single 300 metric ton thrust Rocketdyne RS-68. The liquid hydrogen (LH2) and liquid oxygen (LOX) engine is the world's most powerful cryogenic engine and is the first new big liquid propellant rocket engine developed in the U.S. in more than 20 years.

RS-68 was designed to meet cost criteria. It operates at comparatively moderate chamber pressures using a basic gas generator cycle. The gas generator drives a turbopump. Turbine exhaust gases are vectored to provide first stage roll control. Rocketdyne borrowed some technology from the Space Shuttle Main Engine and from the Saturn J-2 engine, but much is new. The engine's part count was reduced through use of an ablative exhaust nozzle, for example. RS-68 engine testing began at Edwards Air Force Base, California in August 1998.

Delta IV is assembled at a purpose-built rocket plant in Decatur, Alabama, several miles west of Huntsville. When finished, the rockets are floated on a special self-propelled shipping vessel down the Tennessee River and Tombigbee Waterway (canal) to the Gulf of Mexico. From there they travel either to Cape Canaveral via the Intercostal Waterway or to Vandenberg Air Force Base via the Panama Canal.

The CBC is composed of four main structural subassemblies. These include the engine section, the aft LH2 tank, the intertank section, and the forward LOX tank, all 5.2 meters in diameter. Five aluminum isogrid skin panels are welded together to make the cylindrical tank sections. Interior stingers are added for reinforcement. An external feed pipe carries LOX around the LH2 tank. An external wiring tunnel runs the length of the booster. 

Two Delta IV LOX/LH2 second stages are available. The first is a stretched Delta III second stage with a 4 meter diameter forward LH2 tank. The second has a 5.1 meter diameter LH2 tank. Both use a 3 meter LOX tank suspended beneath the LH2 tank by an intertank truss. Mitsubishi Heavy Industries of Japan builds the LH2 tanks.

Both second stages are powered by a single Pratt and Whitney RL10B-2 engine. The engine has a French-built extendable exit cone, is restartable, and is capable of producing 11.23 tons of thrust. At one point, Mitsubishi and Boeing were jointly developing a new, more powerful engine, based on H-2A technology, that might eventually replace RL10, but this effort was apparently shelved after Boeing sold Rocketdyne to Pratt & Whitney in 2005.

The entire vehicle is controlled by an Allied Signal Redundant Inertial Flight Control Assembly (RIFCA) flight control system that is located on shelf below the second stage LOX tank.

Delta IV M (Medium) uses one CBC, a 4 meter diameter second stage, a stretched Delta 3 composite payload fairing, and a 5.1 meter to 4 meter tapered interstage. Two Alliant GEM 60-inch diameter solid rocket motors added to the base of the CBC turns the rocket into the Delta IV M+(4,2). A 5.1 meter diameter second stage, interstage, and payload fairing with two or four SRMs makes a Delta IV M+(5,2) and Delta IV M+(5,4), respectively. Delta IV H (Heavy) uses two CBC strap-on liquid rocket boosters and a 5 meter upper stage.
 

Delta IV is integrated horizontally in a Horizontal Integration Facility (HIF) and erected at the launch pad less than two weeks before launch. SRMs, if any, are then added to the vehicle. The encapsulated payload is mated to the vehicle at the pad a few days before launch. At Cape Canaveral, the long-dormant former Saturn 1/1B Pad 37B was rebuilt for Delta IV. The site includes a rail-mobile mobile service tower that is more 100 meters tall. At California's Vandenberg Air Force Base, Delta IV will be launched from Space Launch Complex (SLC) 6, a pad developed but never used for space shuttle launches. SLC 6 facilities include a mobile service tower and a mobile assembly shelter, massive enclosures that enclose the launcher from two directions like a clamshell.

The first Delta IV, an M+(4,2) model, successfully orbited Eutelsat W5 from SLC 37B on November 20, 2002. It was followed by two successful Delta IV M EELV flights during 2003. The first Delta IV Heavy lifted off from Cape Canaveral in 2004. The test flight achieved some objectives, but was marred when the first stage shut down several seconds too soon. The cause of the problem was a faulty first stage LOX depletion sensor signal that resulted when LOX cavitation occured in the LOX feedline.   The LOX feedline/sensor design was modified and the problem did not recur on subsequent Delta IV Heavy missions.

The first Vandenberg AFB Delta 4 launch took place on June 28, 2006 when a Delta IVM+(4,2) placed NRO L-22, a National Recconnaisance Office payload, into an elliptical 12 hour Molniya orbit.

A complete list of Delta 4 and Atlas 5 launches is provided on the EELV Launch Log page.

On Delta IV M missions, the CBC burns for more than four minutes, separating when the vehicle is more than 100 kilometers above the earth. On M+ flights, two to four GEM-60 SRMs burn during the first 90.8 seconds of flight. 

On Delta IV Heavy flights, all three CBCs ignite on the pad. The core CBC engine throttles down to 57% about 50 seconds after liftoff. The twin strap-on booster CBC units burn at full thrust until shortly before they complete their burns.  The strap-on units are jettisonned about 242 seconds after liftoff.  The core flies on for another 90-plus seconds, returning to full-throttle for more than 65 of those seconds. 

A program to upgrade the RS-68 engine to an "RS-68A" variant resulted in the first hot fire test of a prototype engine at Stennis Space Center in September 2008.  The first three production engines, Nos. 30003-300005, were delivered from Stennis to Decatur during March-April 2011 after completing their hot fire acceptance tests.  At the time, their first flight, on a Delta 4 Heavy, was expected to occur during 2012. 

RS-68A produces 319.79 tonnes of sea-level thrust with specific impulse improved by about 2 percent.  The engine should substantially increase Delta IV Heavy performance, especially on LEO missions.   

Vehicle Configurations

* GEO: Geosynchronous Earth Orbit

Vehicle Components

** Dry mass for Delta IV Medium version believed to include 5-4 meter interstage. Dry mass for Delta IV Medium 5-5 meter version interstage and for Delta IV Heavy versions with nose cones or 5 meter adapter are believed to weigh about one metric ton more than Medium CBC.

*** Propellant loadings for GTO missions shown. Propellant loadings would be less for LEO missions with heavy payloads.  Stage 2 masses do not include payload attachment fittings, which weigh 0.24 t to 0.4 t. 

References

Delta IV Payload Planners Guide, Boeing, October 2000
Delta IV Payload Planners Guide Update, Boeing, April 2002
Delta IV Payload Planners Guide Update, Boeing, November 2002
Delta IV Heavy Demosatration Flight Media Kit, Boeing, June 2005
Delta IV Payload Planners Guide, ULA, September 2007
ATK Space Propulsion Products Catalog, 2008
PWR Press Release, RS-68A Acceptance Testing, March 2011.

 Last Update:  January 24, 2012