Delta IV rocket

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Image:Delta rocket evolution.png The Delta IV is a family of rockets built by Boeing IDS in a purpose-built facility in Decatur, Alabama. The rockets were designed for the United States Air Force Evolved Expendable Launch Vehicle (EELV) program. 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 U.S. military market.

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Vehicle Description

The first stage of a Delta IV consists of one, or in the Heavy variety three, Common Booster Cores (CBC) 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 methods of the upper stage tanks originally developed for the Delta III, but enlarged to five meters diameter. As the name implies, the CBC is used across the entire Delta IV range, allowing the launch vehicle to accommodate different payloads with minimal changes.

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 sacrifice in chamber pressure was made, hurting efficiency; however, development time, part count, and assembly labor were reduced to a fraction of the SSME, despite the RS-68 being a noticeably larger engine. The RS-68 uses channel-wall construction in the thrust chamber and upper 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, which burns away as the engine runs to dissipate heat. This method is heavier, but is much simpler to construct. The RS-68 is also capable of deep throttling like its competitors. Typically, the RS-68 runs at 102% rated thrust for the first few minutes of flight, and then throttles down to 58% rated thrust before main engine cutoff.[1]

The Redundant Inertial Flight Control Assembly (RIFCA) guidance system used on the Delta IV is common to that carried on the Delta II, although the software is different because of the differences between the Delta II and Delta IV.

Image:Delta IV Medium Rocket DSCS.jpg Image:Second stage of a Delta IV Medium rocket.jpg The upper stage of the Delta IV is nearly identical to that of the Delta III. It is powered by a Pratt & Whitney RL-10B2 engine.

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Variants

The Delta IV Medium is the most basic Delta IV. It features a single CBC and the Delta III second stage, with 4-meter liquid hydrogen and liquid oxygen tanks and a 4-meter payload fairing derived from the Delta III 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 Alliant-built 1.5-m (60-in) diameter solid rocket strap-on graphite epoxy motors (GEM-60s) to increase its payload capacity to 5,845 kg (12,890 lb) to GTO.

The Delta IV Medium+ (5,2) is similar to the Medium+ (4,2), but has a 5-m–diameter payload fairing for larger payloads and a modified second stage with a 5-meter liquid hydrogen tank and stretched liquid oxygen tank. The Medium+ (5,2) can launch 4,640 kg (10,230 lb) to GTO.

The Delta IV Medium+ (5,4) is similar to the Medium+ (5,2), but uses four GEM-60s instead of two, enabling it to lift 6,565 kg (14,475 lb) to GTO.

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. The Delta IV Heavy also features a stretched 5-meter composite payload fairing, although an aluminum fairing derived from the Titan IV is also available. [2]

Capacity (separated spacecraft mass) of the Delta IV Heavy:

The total mass at launch is 733,000 kg, much less than that of the Space Shuttle (2,040,000 kg).

Image:Delta IV Heavy rocket on launch pad.jpg

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 has had difficulty finding a market in commercial launches. The first launches have been paid for by the U.S. Military, with a cost of between $140 million and $170 million.1.

Comparable rockets: Atlas V - Ariane 5 - Chang Zheng 5 - Angara

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Launch sites

The Delta IV booster utilizes Space Launch Complex 37 (SLC-37) at the Cape Canaveral Air Force Station, site of several unmanned Saturn-1 and -1B launches. Polar-orbit launches are planned for SLC-6 at Vandenberg Air Force Base, which was originally intended for the cancelled Air Force MOL space station, and later for polar orbit Space Shuttle flights (neither mission ever actually launched from SLC-6).

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Launch history

  • The third launch was 29 August 2003. A Delta IV Medium lifted DSCS III-B6, the last of the DSCS satellites, into GTO from Cape Canaveral.
  • The first launch of the Heavy variant was on 21 December 2004 after significant delays due to bad weather. Due to cavitation in the propellant lines, sensors registered depletion of propellant. The booster, and later core engines shut down prematurely, even though sufficient propellant remained to continue the burn as scheduled. The second stage attempted to compensate for the under-burn, until it ran out of propellant. This flight was a test launch carrying a payload consisting of:
    • DemoSat — 6020 kg; an alumunum cylinder filled with 60 brass rods — 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.
    • NanoSat-2, carried to low Earth orbit (LEO) — a set of two very small satellites of 24 and 21 kg, nicknamed Sparky and Ralphie — planned to orbit for one day. Given the under-burn, it is unlikely the two reached a stable orbit.
  • The first launch of a valuable payload aboard the Delta IV Heavy is scheduled for fall 2005, a U.S. Defense Support Program missile warning satellite, and the second will be a classified U.S. National Reconnaissance Office reconnaissance satellite. NASA may have plans to use the Delta IV Heavy for the Crew Exploration Vehicle, the replacement for the Space Shuttle.
  • GOES-N, a weather satellite for NOAA, will be launched no earlier than May 2006 aboard a Delta IV Medium+ (4,2). The launch has been delayed several times due to technical issues and a union strike. However, as the union has voted to end the strike, the launch has been scheduled for late spring. [3]
  • NROL-22, launching a classified satellite for the U.S. National Reconnaissance Office, will be launched aboard a Delta IV Medium+ (4,2). This will be the first Delta IV launched from SLC-6 at Vandenberg Air Force Base. The launch date is to be announced; however Boeing has stated that NROL-22 could launch by late April. [4]

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List Date: August 14 2005

Date Type Serial-No. Startplace Payload Kind of Payload Outcome
November 20 2002 Delta-4M+(4,2) D-293 CC LC37B Eutelsat W5 Commercial communications satellite Success
March 11 2003 Delta-4M D-296 CC LC37B DSCS-3 A3 (USA 167) Military communications satellite Success
August 29 2003 Delta-4M D-301 CC LC37B DSCS-3 B6 (USA 170) Military communications satellite Success
December 21 2004 Delta-4H D-310 CC LC37B DemoSat / 3CS 1 / 3CS 2 Demonstration payload Partial success
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Upgrade options

Possible future upgrades for the Delta IV include adding extra strap-on solid motors to boost capacity, higher-thrust main engines, lighter materials, higher-thrust second stages, and more (up to six) strap-on CBCs. [6]

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External links

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