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EELV: NEW LAUNCHERS FOR THE US AIR FORCE

by Christopher Hess

One name, two rockets. The US Air Force is trying to adapt its launcher fleet to the requirements of the next century with the Evolved Expandable Launch Vehicles (EELV). In a new strategy, where two manufacturers are involved, Boeing Expendable Launch Systems in Huntington Beach, California, and Lockhhed Martin Astronautics, Denver, are currently working on their own concepts for the EELV. It is expected that the US Air Force will sign contracts worth 500 million US-Dollars in the fourth quarter of 1998. This sum covers about a third to a half of the amount the manufacturers have invested themselves in this project.

The aim of this program is to replace today's Titan rockets for heavy payloads as well as the Delta and Atlas rockets, which are used for medium payloads. The new rockets are expected to reduce launch costs by 25 to 50 per cent. This is another reason why the US Air Force gave the job to two companies: They will try to undercut each other's prices.

Both proposed EELV families comprise three different basic classes: with small, medium and heavy load capacity. Each of the first stages is identical and is adapted to the mission in question with the help of modular additional boosters or other top stages. The EELVs of both manufacturers look similar from their outward appearance, however, there are distinct differences in their design, because both versions use components of their predecessors.

Boeing's EELV also trades under the name Delta IV. A modified first stage is used here. To power the first stage, Rocketdyne is currently developing the RS-68 engine (thrust at sea level: 650,000 lbs), which uses a mixture of liquid oxygen/liquid hydrogen as fuel. The central point of this development is a drastic simplification of the gas generator. This will lower development and production costs and increase reliability at the same time. The first engine will start a series of tests soon.

In the Delta IV version "Small" the top stage and payload cover of Delta II is used. "Medium" uses the corresponding parts of the Delta III and the heavy load carrier is fitted with a modified Delta III top stage and a big payload cover currently used on Titan. Two additional first stages that serve as extra boosters in the "Heavy" version are used. They are called "common core boosters".

The launch site for the EELV will either be Cape Canaveral, Florida or Vandenberg, California. In order to increase the efficiency of the launch preparations further, Boeing intends to assemble the bigger Delta IV components in a hangar. The rocket will be in a horizontal position and not in a vertical position at the pad as is commonly the case.

Lockheed's EELV will also use the two established launching sites in California and Florida. Just like Boeing's Delta IV Lockheed Martin's EELV concept is based on a "common core booster". The engine of the Lockheed EELV is a RD-180, which is being developed in co-operation of Pratt & Whitney and NPO Energomash. The two chamber drive is based on the RD-170 Zenith launcher and works on liquid oxygen/kerosene.

Like the versions of the competitor Lockheed's EELV will be adapted to the required payloads and the target orbit by a combination of various modules. A stage with storable fuel and a further developed Agena engine or the cryogen Centaur Stage will be used as the top stage.

As well as the smallest version MLV-D (payload: 1,842 kg into GTO), Lockheed Martin have also planned the medium version MLV-A (payload: 3,856 kg into GTO). As heavy load carrier the HLV-L (1,897 kg into GEO) or the HLV-G (6,124 kg into a geosynchronous orbit) are under consideration. The two "Heavies" will, like Boeing's heavy load version consist of three "common core boosters".

The payload capacity of Boeing's EELV version (into GTO) ranges from 2,200 kg (Delta IV "Small"), 3,800 kg and 4,200 kg ("Medium") to 13,200 kg ("Heavy").

During the Farnborough Air Show Boeing also announced that it was planning three further commercial variations of Delta IV. These will be known as "Medium plus". The reason for this is the expected weight increase of communications satellites to 5 tons and more, which cannot be launched into GTO without additional boosters by the medium versions of the EELV suppliers.

The three variations of the Delta IV "Medium plus" differ by the use of Alliant Techsystems small additional solid-fuel boosters, upper stages which differ in size and different payload fairings.

The following are all members of the "Medium plus" family; the Delta IV M+ (4.2) with a GTO capacity of 5,800 kg, the M+ (5.2) with 4,700 kg into the GTO (but with a wider payload fairing) and the M+ (5.4) with a payload capacity of 6.700 kg also with a wider cover.

Apparently Lockheed is receiving offers from booster manufacturers in order to increase the payload capacity of its EELV as well.

From page 42 of FLUG REVUE 11/98