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Atlas – A Successful Launcher

Published by spacecowboy on Thu Jan 26, 2006 6:50 pm
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By Klaus Schmidt and reviewed by Stephen Deisher, The Space Fellowship.

With another successful maiden launch of a new Atlas variant putting NASA’s New Horizons probe on a nine year journey to Pluto, it’s time to review the history of the Atlas launcher family.

Developed in the 1950s as an ICBM, the Atlas soon came into the focus of NASA for their manned Mercury project. As staging was considered technically difficult, mainly because of in-flight ignition of an upper stage engine, the Atlas rocket was designed a bit different than today’s rockets. Also called a one-and-a-half stage rocket, it was powered by a central main engine, supported at liftoff with two booster engines, that were jettisoned after 135 seconds. To maximize the payload capacity, the structure was built so light that the rocket had to be kept filled with fuel in order to maintain structural integrity. The Atlas was powered by kerosene and liquid oxygen.

The first “commercial” use of the Atlas occurred at Christmas 1958, as an Atlas B broadcasted a Christmas message from, then US President, Eisenhower down to earth. After several more flight test models, the Atlas D was used for the manned space program Mercury and carried the first US astronauts into space.

After staging of rockets became mature, the Atlas launcher was upgraded with an added upper stage, the Agena. The Atlas-Agena was able to lift 2 tonnes into LEO and was used for example to orbit the rendezvous stages for the Gemini manned missions. In November 1963 the Atlas-Centaur had its maiden launch and this combination was later used in the Apollo program to put the Surveyor landers onto the moon.

In 1964 the Atlas ICBM (models D, E and F) were decommissioned and put into storage. They were later modified and used to put payloads into orbit. After the phase-out, the Atlas was solely used as a space launcher.

As the Agena upper stage wasn’t strong enough for the emerging market of geostationary satellites, the Centaur was the only upper stage used from 1967 on. Both, the first stage with its main and booster engines, as well as the RL-10 engine of the Centaur experienced constant upgrades so the Atlas could keep pace with the steady increasing satellite masses.
As even the most powerful Atlas, the Atlas-Centaur, could put only 2.3 tonnes into geosynchronous transfer orbit (GTO) and Martin Marietta got an Air Force launch contract over ten heavy satellites for launch from 1992 on, the Atlas II was developed. It had an uprated MA-5A main engine and the booster engines were replaced with RS-27 engines. As the launcher then needed more fuel, it got a stretched tank. Additionally the Centaur upper staged was lengthened, so that the Atlas II was capable of putting 2.8 tonnes into GTO. The maiden launch took place in December 1991 and was as all Atlas maiden launches successful.

Further improvement saw an uprated engine on the Centaur (Atlas IIA). As the 3 tonnes capacity of this launcher was still not enough for the new communication satellites the Atlas IIA was reinforced with four solid rocket strap-on boosters, made by Thiokol. This Atlas IIAS successfully lifted off for the first time in December 1993.
With the fall of the Soviet Union, an attractive option became available to further improve the Atlas rocket. The owner of the Atlas launcher family, meanwhile Lockheed-Martin, replaced the first stage main and booster engines with a single Russian-made RD-180. This two-chamber engine is a derivative of the RD-170, which was originally developed and used on the Energia heavy lift launcher. With this new main engine the first stage was further stretched and the Centaur upper stage got a new RL-10A-4-1 engine, used as a single motor in the Atlas IIIA and uses in a dual configuration in the most powerful Atlas IIIB.

As the US Air Force searched new launch vehicles, with its Evolved Expandable Launch Vehicle (EELV) program initiated in 1994, it became clear, that this would be the chance for Lockheed Martin to completely redesign the Atlas launcher. The new vehicle was called Atlas V.

A main change was the switch from a pressure-stabilized tank design to a structurally stable propellant tank. The launcher is powered by the same RD-180 engine of the Atlas III series. To increase the payload capacity the central stage, the Common Core Booster, is enclosed with up to five solid propellant strap-on boosters. The Centaur upper stage is the same as with the Atlas IIIB and is, depending on the payload mass, equipped with one or two RL-10 engines. The Atlas V 400 series features a 4 m diameter payload fairing, while the 500 series uses a 5 m diameter large fairing to engulf the largest satellites.

A heavy lift version with three Common Core Boosters was also considered but as the US Air Force decided to use the Delta 4 Heavy as a heavy lift carrier, the development is currently frozen but would be finishable in 30 months from order. The maiden launch of the Atlas V occurred in 2002 and was as usual for Atlas launches successful.

Using a different number of strap-on boosters and different-motorized upper stages, the Atlas V family offers a great flexibility and even more important today, with more and more complex and expensive satellites, the reliability is most significant. Since the introduction of the Atlas II in 1991, the Atlas launcher family produced an impressive record of 100% success. The only problem is, in comparison to other launchers like the Proton, Zenit or Ariane, the higher launch cost as that is the problem with all US-build rockets.

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