Tim Furniss/LONDON

Boeing is to introduce three new versions of a Delta IV Medium Plus class Evolved Expendable Launch Vehicle (EELV) booster to compete in the commercial market and to complement the standard Delta Medium EELV to be built for the US Air Force. The developments will give Boeing new capabilities to rival Arianespace's Ariane 5 booster.

EELV contracts are expected to be awarded to Boeing and Lockheed Martin shortly, as part of a USAF attempt to cut its satellite launch costs by rationalising the present line-up of Titan, Delta and Atlas boosters to two low cost versions of the Delta and Atlas. Three basic EELV models, small, medium and heavy, are destined to be built, each based on a Common Core Booster (CCB).

The Delta IV Medium booster on which the variants will be based will have an upper stage powered by a single Pratt & Whitney-built powerplant based on those used on the Atlas Centaur upper stage.

To become the Delta IV Medium Plus, Boeing plans to augment the launcher's CCB with combinations of two or four enlarged Alliant TechSystems solid rocket boosters, based on those already used for the Delta III. The two new variants will be equipped with different payload fairings.

The Delta IV Medium Plus 4.2, with two boosters and a small payload fairing, will have the capability to place payloads of up to 5,760kg into geostationary transfer orbit (GTO). The Medium Plus 5.2, with a large fairing, will be able to hoist up to 4,856kg into GTO. The final, and heaviest variant, the Medium Plus 5.4, will feature a larger fairing and the capability to place 6,667kg payloads into GTO.

The Medium Plus 4.2 and the 5.4 will be pitched into the top end of the commercial launcher market being competed for by rivals such as Arianespace, with the Ariane 5, and the Boeing-led Sea Launch consortium, which uses the Russian built Zenit.

The current Boeing Delta III, which failed on its maiden flight on 26 August, can place 3,810kg into GTO. The payload carrying range for the three USAF EELVs, the Delta IV Small, Medium and Large, is 2,175kg to 13,200kg to GTO. These are not being proposed for commercial launches.

Source: Flight International