Delta III History

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exoscientist

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Thanks for that. Perhaps you could answer a question for me. SpaceX has noted that its Falcon 9 first stage has reached a milestone in achieving a better than 20 to 1 mass ratio:

SPACEX ACHIEVES ORBITAL BULLSEYE WITH INAUGURAL FLIGHT OF FALCON 9 ROCKET.
Cape Canaveral, Florida – June 7, 2010
"The Merlin engine is one of only two orbit class rocket engines developed in
the United States in the last decade (SpaceX’s Kestrel is the other), and is
the highest efficiency American hydrocarbon engine ever built. The Falcon 9
first stage, with a fully fueled to dry weight ratio of over 20, has the
world's best structural efficiency, despite being designed to higher human
rated factors of safety."
http://www.spacex.com/press.php?page=20100607

The early versions of the Atlas rocket also reached comparably high mass ratios using both "balloon" tank and common bulkhead design, though the latest version, the Atlas 5 first stage, has a poorer mass ratio in not using either of these methods.
As described in SpaceX news releases, the Falcon launchers are able to get their high mass ratios because they use both common bulkheads and lightweight aluminum-lithium alloys.
But then I was startled to see that some early Delta rocket first stages also had better than 20 to 1 mass ratios, particularly ones using an extra long tank:

Delta 1914.
http://www.friends-partners.org/partner ... la1914.htm

Astronautix is sometimes inaccurate but this is probably about right since on your page on the Delta II you give its first stage a mass ratio of about 18 to 1:

Delta II Data Sheet.
http://www.spacelaunchreport.com/delta2.html

My question is how were these Delta rocket first stages able to achieve these high mass ratios without using balloon tanks or common bulkheads? Note that the Atlas 5 first stage in not using common bulkheads or balloon tanks has a much poorer first stage mass ratio.
In any case we have three different rocket versions that have a better than 20 to 1 first stage: the early Atlas's, the early Delta's, and the Falcon 9's. And we also have ground-launch kerosene engines that get better than 330 s vacuum Isp, such as the NK-33 and the RD-180. Put those two factors together and we have several options for kerosene-fueled SSTO's.


Bob Clark
 
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edkyle99

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exoscientist":15lj29dc said:
My question is how were these Delta rocket first stages able to achieve these high mass ratios without using balloon tanks or common bulkheads?

Keep in mind that the Delta first stage does not have sufficient thrust to lift itself. It depends on the solids for most of its liftoff thrust. If the Delta first stage was able to lift itself like Atlas, it would have a higher dry mass because it would need more, or bigger, engines.

Even so, the Delta first stage *was* very mass efficient. It used isogrids machined as triangular patterns in the tank wall aluminum sheets. Of course, this methodology cost more too.

As for Atlas 5, it is heavier by design. The Atlas 5 core needs to be strong to handle the big monolithic solid motors and the heavy payloads. In addition, the idea with EELV was to reduce cost. Lockheed Martin chose not to go to the extreme when it came to production steps meant to cut dry mass from the core stage.

- Ed Kyle
 
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