Delta IV rocket
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The Delta IV family of rockets are EELVs (evolved expendable launch vehicles) built by Boeing IDS in a purpose-built facility in Decatur, Alabama. They come in five versions: medium, medium+ (4,2), medium+ (5,2), medium+ (5,4), and heavy. These vehicles are primarily designed to satisfy the needs of the US military market.
The first stage of a Delta IV consists of one, or in the Heavy variety three, CBCs (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 first-stage tanks are based on the construction of the upper stage, originally developed for the Delta III, but enlarged to 5 meters diameter.
The RS-68 is the first large, liquid-fueled rocket engine designed in the US since the Space Shuttle Main Engine SSME in the '70s. The primary goal was to reduce cost versus the SSME. Some sacrifice in thrust-chamber pressure was made, hurting efficiency. However, development time, part count, and assembly labor were reduced to a fraction of the SSME, despite being a noticeably-larger engine. The RS-68 uses channel-wall construction in the thrust chamber and upper expansion nozzle. This method, pioneered in the Soviet Union, uses inner and outer skins brazed to a middle separator to form cooling channels. This is much simpler than tube-walled nozzles, in which hundreds of tubes are bent and brazed together. The lower nozzle, where heat transfer is lower, uses an ablative layer to dissipate heat. This method is heavier, but much simpler to construct. The RS-68 is also capable of deep throttling like its competitors.
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The upper stage and payload fairing of the Delta IV medium are nearly identical to that of the Delta III. The upper stage is powered by a Pratt & Whitney RL-10B2 engine. In the medium variety it is 4 m in diameter, with a 4-m–diameter payload fairing. The Delta IV medium is capable of launching 4,210 kg (9,285 lb.) to geosynchronous transfer orbit (GTO).
The Delta IV medium+ (4,2) is similar to the medium, but uses two 1.5-m (60-in.) diameter solid rocket strap-on graphite epoxy motors (GEMs) to increase its payload capacity.
The Delta IV medium+ (5,2) is similar to the medium+ (4,2), but has a 5-m–diameter payload fairing and upper stage enlarged to 5 m diameter, like the first stage.
The Delta IV medium+ (5,4) is similar to the medium+ (5,2), but it uses four GEMs instead of two.
The Delta IV Heavy is similar to the medium+ (5,2), except that it uses two additional CBCs instead of using GEMs. These are strap-on boosters which are separated earlier in the flight than the center CBC.
Capacity (separated spacecraft mass) of the Delta IV Heavy:
- geosynchronous transfer orbit (GTO) 13,130 kg (28,950 lb.), more than any other currently available launch vehicle
- geosynchronous orbit (GEO) 6275 kg
- escape orbit 9306 kg
- C3 performance of 30 km2s-2: 5228 kg
- C3 performance of 60 km2s-2: 2521 kg
The total mass at launch is 733 000 kg, much less than that of the Space Shuttle (2 040 000 kg).
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The Delta IV entered the space launch market at a period when global capacity was already much higher than demand. Furthermore, as an unproven design it would have difficulty finding a market in commercial launches. The first launches have been paid for by the US Military involving a cost of between $140 million and $170 million.1.
Launch History
- The first launch of a Delta IV occured on 20 Nov 2002, from Cape Canaveral. The Delta IV medium+ (4,2) placed the Eutelsat W5 communications satellite into Geosynchronous Transfer Orbit (GTO).
- The second launch, also from Cape Canaveral, was 10 Mar 2003. The Delta IV medium placed the US Air Force DSCS A3 (Defense Satellite Communications System) into GTO.
- The third launch was 29 Aug 2003. A Delta IV medium lifted DSCS B3 into GTO from Cape Canaveral.
- The first launch of the heavy rocket was on December 21 2004 after significant delays due to bad weather. Due to bubbles in the propellant lines, sensors registered depletion of propellant. The booster, and later core engines shut down prematurely. The second stage attempted to compensate for the under-burn, until it ran out of propellant. This was a test launch carrying a payload consisting of:
- NanoSat-2 carried to LEO - a set of two very small satellites of 24 and 21 kg - planned to orbit for one day. Given the under-burn, it is unlikely the two reached a stable orbit.
- DummySat - 5900 kg; planned to be carried to GEO, but due to lower than expected performance from the first stage, this payload fell short of its intended orbit.
The first launch of a valuable payload is scheduled for fall 2005, a US Defense Support Program missile warning satellite, and the second will be a classified US National Reconnaissance Office reconnaissance satellite.
External links
- Boeing's Delta Rocket page
- http://www.skyrocket.de/space/doc_lau/delta-4.htm
- Comparison of Delta IV Heavy with Spaceshuttle
- Boeing's Delta IV Heavy Gets Ready for its Close-Up, Space News, 2004-12-06.
- Weather Delays Delta IV Heavy Launch Mission, Media Release, U.S. Air Force, 2004-12-09
