Delta IV rocket

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The Delta IV is a family of Delta rockets designed by Boeing's Integrated Defense Systems division and built in its purpose-built facility in Decatur, Alabama with final assembly at the launch site. The rockets 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. The Delta IV is primarily designed to satisfy the needs of the U.S. military.

The rockets are launched from LC-37B at Cape Canaveral, and SLC-6 at Vandenberg AFB.

[edit] 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 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 and specific impulse was made, hurting efficiency; however, development time, part count, total cost, and assembly labor were reduced to a fraction of the SSME, despite the RS-68's significantly greater size. 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.<ref>Delta IV GOES-N Launch Timeline</ref> On the Heavy variant, the core CBC's engine throttles down to 58% rated thrust around 50 seconds after liftoff, while the strap-on CBCs remain at 102%. This allows the core CBC to conserve propellant and burn longer. After the strap-on CBCs separate, the core CBC's engine throttles back up to 102%, until main engine cutoff, before which it throttles back down to 58%.<ref>Delta IV Heavy Demo Launch Timeline</ref>

The RS-68 engine is mounted to the lower thrust structure of the vehicle by a four-legged (quadrapod) thrust frame, and enclosed in a protective composite conical thermal shield. Above the thrust structure is an aluminum isogrid (a grid pattern machined out of the inside of the tank to reduce weight) liquid hydrogen tank, followed by a composite cylinder called the centerbody, an aluminum isogrid liquid oxygen tank, and a forward skirt. Along the back of the CBC is a cable tunnel to hold electrical and signal lines, and a tube to carry the liquid oxygen to the RS-68 from the tank. The CBC is of a constant, 5-meter, diameter.

The L3 Communications 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. The RIFCA features six ring laser gyroscopes and accelerometers each, to provide a higher degree of reliability.<ref>L-3 Space & Navigation's RIFCA Trihex</ref>

The upper stage of the Delta IV is nearly identical to that of the Delta III, however the tanks are either stretched (in 4-meter variants), or have a larger diameter (5-meter variants). The second stage is powered by a Pratt & Whitney RL-10B2 engine, which features an extendible carbon-carbon nozzle to improve specific impulse. Depending on variant, two different interstages are used to mate the first and second stages. A tapering interstage which narrows down from 5-meters to 4-meters in diameter is used on 4-meter variants, where a cylindrical interstage is used on 5-meter variants. Both interstages are built from composites.

To encapsulate the satellite payload, a variety of different payload fairings are available. A stretched Delta III 4-meter payload fairing is used on 4-meter variants, where an enlarged, 5-meter fairing is used on 5-meter variants. A longer version of the latter is standard on the Heavy variant, and a 5-meter, aluminum isogrid payload fairing is also available for the Heavy.

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, 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. In 2005, Boeing stated that it may return the Delta IV to commercial service; however as of 2006 no further announcements have been made regarding this.<ref>Delta IV may return to commercial launches</ref> 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.

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

[edit] Variants

The Delta IV Medium (Delta 9040) is the most basic Delta IV. It features a single CBC and a modified 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) (Delta 9240) 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 payload capacity to 5,845 kg (12,890 lb) to GTO.

The Delta IV Medium+ (5,2) (Delta 9250) 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. Because of the extra weight of the larger payload fairing and second stage, the Medium+ (5,2) can launch 4,640 kg (10,230 lb) to GTO, less than the Medium+ (4,2).

The Delta IV Medium+ (5,4) (Delta 9450) 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 (Delta 9250H) 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.<ref name="Growth">Delta IV Heavy Growth Options</ref>

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) 6,275 kg
• escape orbit 9,306 kg
• C₃ performance of 30 km²s⁻²: 5,228 kg
• C₃ performance of 60 km²s⁻²: 2,521 kg

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

During the Delta IV's development, a Small variant was considered. This would have featured the Delta II second stage, an optional Thiokol Star 48B third stage, and the Delta II payload fairing, all atop a single CBC.<ref>Delta IV Small on Astronautix.com</ref> The Small variant was dropped by 1999.<ref>Gunter's Space page - Delta IV</ref><ref>Boeing Signs agreement for Delta IV Integration Facility</ref> This was probably due to the fact that the Delta II has a similar payload capability.

[edit] Launch sites

The Delta IV utilizes both East and West Coast launch sites. Space Launch Complex 37 (SLC-37) at the Cape Canaveral Air Force Station, site of several unmanned Saturn I and -IB launches is used in the East. Polar-orbit and high-inclination launches use Vandenberg Air Force Base's SLC-6 pad, 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).

Launch facilities at both sites are similar. At the pad is a Mobile Service Tower (MST), which provides service access to the rocket and protection from the weather. There is a crane at the top of the MST, which allows the payload and GEM-60 solid motors to be attached to the vehicle. The MST is rolled away from the rocket several hours before launch. At Vandenberg, the launch pad also has a Mobile Assembly Shelter (MAS), which completely encloses the vehicle; at CCAFS, the vehicle is partly exposed near its bottom.

Beside the vehicle is a Fixed Umbilical Tower (FUT), which has two (VAFB) or three (CCAFS) swing arms. These arms carry electrical, hydraulic, environmental control, and other support functions to the vehicle through umbilical lines. The swing arms retract at T-0 seconds to prevent them from hitting the vehicle.

Under the vehicle is a Launch Table, with six Tail Service Masts (TSMs), two for each CBC. The Launch Table supports the vehicle on the pad, and the TSMs provide further support and fueling functions for the CBCs. The vehicle is mounted to the Launch Table by a Launch Mate Unit (LMU), which is attached to the vehicle by bolts that sever at launch. Behind the Launch Table is a Fixed Pad Erector (FPE), which uses two long-stroke hydraulic pistons to raise the vehicle to the vertical position after being rolled to the pad from the Horizontal Integration Facility (HIF). Beneath the Launch Table is a flame duct, which deflects the rocket's exhaust away from the rocket or facilities.

The Horizontal Integration Facility (HIF) is situated some distance from the pad. It is a large building that allows the Delta IV CBCs and second stages to be mated and tested before they are moved to the pad.

Movement of the Delta IVs among the various facilities at the pad is facilitated by Elevating Platform Transporters (EPTs). These rubber-tired vehicles can be powered by either diesel engines or electric power. Diesel EPTs are used for moving the vehicles from the HIF to the pad, while electric EPTs are used in the HIF, where precision of movement is important.<ref>Delta IV Launch Facilities</ref>

[edit] Vehicle processing

The Delta IVs are assembled using a process that Boeing claims reduces cost and expensive on-pad time. The CBCs are built in Boeing's factory in Decatur, Alabama. They are then loaded onto the M/V Delta Mariner, a roll-on/roll-off cargo vessel, and shipped to either launch pad. There, they are offloaded and rolled into the HIF, where they are mated with the second stages, which were shipped separately to the pad on the Delta Mariner. Also, in the HIF, the three CBCs of Heavy variant are mated to each other.

Various tests are performed, and then the vehicle is rolled horizontally to the pad, where the Fixed Pad Erector (FPE) is used to raise the vehicle to the vertical position, inside the MST. At this time, the GEM-60 solid motors, if any are required, are rolled to the pad and attached to the vehicle. After further testing, the payload (which has already been enclosed in its fairing) is transported to the pad, hoisted into the MST by a crane, and attached to the vehicle. Finally, on launch day, the MST is rolled away from the vehicle, and the vehicle is ready for launch.<ref>Delta IV prelaunch assembly</ref>

[edit] Delta IV launches

[edit] Past launches

• The Eutelsat W5 communications satellite was first launch of a Delta IV using the Medium+ (4,2) variant. The rocket launched from Cape Canaveral carrying the communications satellite was placed into geostationary transfer orbit (GTO) in 2002.

• DSCS III-A3 was the second launch, also from Cape Canaveral in 2003. The Medium placed the U.S. Air Force's Defense Satellite Communications System (DSCS) satellite into GTO.

• DSCS III-B6 was a Medium variant launched from Cape Canaveral in 2003, carrying the last of the DSCS satellites into GTO.

• Heavy Demo was the first launch of the Heavy variant in Dec. 2004 after significant delays due to bad weather. Due to cavitation in the propellant lines, sensors registered depletion of propellant. The strap-on, and later core CBC 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 aluminum cylinder filled with 60 brass rods — planned to be carried to GEO; however due to the sensor faults, the satellite did not reach this 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, the two most likely did not reach a stable orbit. [1]

• GOES-N, a weather satellite for NOAA and NASA, was launched aboard a Medium+ (4,2) from Cape Canaveral in May 2006. The launch had been delayed several times due to technical issues and a union strike.

• NROL-22, a classified satellite for the U.S. National Reconnaissance Office (NRO) was launched aboard a Medium+ (4,2) in June 2006. This was the first Delta IV launched from SLC-6 at Vandenberg Air Force Base (VAFB).

• DMSP 17, a United States Defense Meteorological Satellite Program satellite, was launched on 4 November 2006 aboard a Medium rocket. This launch was the second from SLC-6 at VAFB.

• DSP-23 is the first launch of a valuable payload aboard a Heavy vehicle. The main payload is the 23rd and final Defense Support Program missile-warning satellite. Launch will take place from Cape Canaveral and is curently scheduled for early 2007.

• NROL-26 will carry a classified U.S. NRO satellite on a Heavy. Launch date is currently for June 2007.

• NROL-25 will carry a classified U.S. NRO reconnaissance satellite on a Medium+ (5,2). Launch date is currently to be determined.

List updated: 4 November 2006.

[edit] Planned launches

List Date: 4 November, 2006

[edit] 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.<ref name="Growth" />

NASA originally had plans to use the Delta IV Heavy for the Crew Exploration Vehicle, the replacement for the Space Shuttle. But with the change of the CEV from a winged or lifting body spacecraft to an Apollo-like capsule and a new launch vehicle based on Space Shuttle components, the only component from the Delta IV that NASA would adopt is the RS-68 engine that would be used to power the new cryogenically-fueled Ares V rocket.

[edit] External links

• Boeing's Delta IV Rocket page
• Gunter's Space page - Delta IV
• Comparison of Delta IV Heavy with Space Shuttle
• Boeing's Delta IV Heavy Gets Ready for its Close-Up, Space News, 2004-12-06.
• Astronautix.com links for:
  • Delta IV Heavy
  • Delta IV Medium (5,4)
  • Delta IV Medium (5,2)
  • Delta IV Medium (4,2)
  • Delta IV Medium

[edit] References

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