Author Topic: SDLV/CEV - Extra comparison info from January AIAA Joint Propulsion Conference  (Read 20416 times)

Offline kraisee

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There was comment in the other thread that all these images originated from a PDF file somewhere...   Is there any way to get hold of that document?   While this is a wonderful resource here, saving the web page just isn't as efficient as having a PDF.

Nice site BTW. I only just found it this week, but there's a great deal of valuable comment and information here, so I know I'll be a regular here from now on.

Ross B Tierney
www.launchcomplexmodels.com
"The meek shall inherit the Earth -- the rest of us will go to the stars"
-Robert A. Heinlein

Offline SRBseparama

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If you mail Chris - he'll have it.

Offline publiusr

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I just hope we can get HLLV going.

Offline UK Shuttle Clan

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Having looked through that document again with the images, what's the status of the Longfellow? Kraisee and people tend to be saying the Magnum when they talk about serious heavy lift, but I've not really seen anything by way of mentions for the Longfellow. Any help?

Offline kraisee

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Quote
UK Shuttle Clan - 24/11/2005  2:23 PM

Having looked through that document again with the images, what's the status of the Longfellow? Kraisee and people tend to be saying the Magnum when they talk about serious heavy lift, but I've not really seen anything by way of mentions for the Longfellow. Any help?

Longfellow isn't actually dead.   Some of the features of that design got merged into the Magnum base which was eventually announced by Griffin.

The primary difference was purely in the main engines under the Main ET-derived First Stage.

Magnum's main engines were SSME, Longfellow used RS-68.   As the final design uses SSME, it is a Magnum derivative.

"But what about the difference in size of the upper stage?" I hear you cry!   That is not actually specific to Longfellow. It is a necessity of any moon-bound rocket, and was a feature last seen on the mighty Saturn-V even.   I'll explain...

The Magnum can lift about 106 Metric Tons (MT) to LEO with no upper stage at all, and I'd expect to see variants fly like that early on.

With a small upper stage on top (30MT plus 25MT fuel), you increase useful payload capacity to LEO to about 130MT.

That configuration would be useful for launching heavy LEO payloads, sure enough, but the SDLV's primary purpose is for moon-shots and that's a whole different animal.

By simply stretching the tubular parts of the upper stage so it can physically contain more fuel, and by having engines which can be re-started, you can save an awful lot of mass for going to the moon.

You need engines, fuel and a fuel tank to get you into orbit.   You also need engines, fuel and a fuel tank to go from orbit to the moon.   If you could use the same engines and fuel tank for both parts of the mission, you don't have to carry a duplicate set of everything up during launch - and that means you can take additional useful payload instead.

All you do is just put your TLI-burn propellant in a stretched upper stage at the start.   You end up increasing the weight of the upper stage marginally, to about 35MT instead of 30MT.   But you can then put an extra 80MT of fuel in there for the burn needed to send you to the moon.

The 80MT of fuel needed to get you to the moon comes out of your 125MT payload limit, leaving you about 45MT of useful payload launched by the SDLV to the moon.   In addition, you have the 20MT CEV attached too, so you've got quite a bit heading to the moon.

Ultimately that upper stage on Magnum will do exactly the same job as the upper stage of the Saturn-V, the S-IVB. But this stage will have two engines instead of just one, and a larger fuel capacity able to send more mass to the moon.

So, the design we are getting is Magnum, but with the upper stage sized for moon flights.   It just so happens that we first *saw* that on the Longfellow design.   Whichever LV was chosen for moon missions was always going to get that big upper stage, I guarantee you.

Ross.
www.launchcomplexmodels.com
"The meek shall inherit the Earth -- the rest of us will go to the stars"
-Robert A. Heinlein

Offline British NASA

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I've copied and pasted that post and saved it in my PC, because you just answered about 10 questions I've not fully understood! Thanks.

Offline UK Shuttle Clan

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Brilliant. Thanks for a great explanation.

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