The Delta IV family of rockets are EELVs (evolved expendable launch vehicles) built by Boeing IDS. 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 upper stage of the Delta IV is powered by a Pratt & Whitney RL-10B2 engine. In the medium variety it has a 4-m–diameter payload fairing. It 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 increased upper-stage fuel capacity.

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).

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. The first launch of the heavy rocket was on December 21 2004 after a delay due to bad weather. It is 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
• 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