Author Topic: NESTED propellant tanks.  (Read 1006 times)

NESTED propellant tanks.
« on: 11/13/2017 02:02 PM »
The nested configuration of the propellant tanks with the upper tank dome inverted seems to have a better advantage in terms of mass saving. How many launch vehicles have been using such tank configurations? I knew about ares-V that never flew. Why is such a configuration neglected? or am i missing something?

Offline e of pi

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Re: NESTED propellant tanks.
« Reply #1 on: 11/13/2017 02:26 PM »
Can you elaborate more on what you mean, perhaps with a sketch of a tank that does use this vs one that does?

It sounds like you're asking about common bulkhead tankage. Are you asking about why a stage would use separate tanks with their own forward/aft domes instead of a common bulkhead, or why the common bulkhead "points" the way it does in a given stage or group of stages, or something else?

Re: NESTED propellant tanks.
« Reply #2 on: 11/13/2017 03:16 PM »
Thanks for the reply.No ,this configuration is slightly different from common Bulkhead
if you look closer you can see the domes are slighty separated by some distance. In this case both the tanks are having Fore-end and aftend domes unlike common bulkhead.
The inverted dome of the fuel tank and the dome of the oxidizer tank are connected using a ring as shown in the fig.

Online zhangmdev

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Re: NESTED propellant tanks.
« Reply #3 on: 11/13/2017 03:28 PM »
Is the volume between "the inverted dome of the fuel tank and the dome of the oxidizer tank" pressurized? empty? or filled with some insulation material?

Re: NESTED propellant tanks.
« Reply #4 on: 11/13/2017 03:31 PM »
it will be filled with insulated material.

Offline e of pi

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Re: NESTED propellant tanks.
« Reply #5 on: 11/13/2017 03:38 PM »
That's actually the standard layout for a common bulkhead, at least one with a substantial temperature difference between the propellants (cryo LOX/RP-1 or hard cryo LH2/LOX). There's a dome on each tank, with insulation in the middle to stop heat flow.

If you look at the first diagram you'll see the labels "CB FWD Dome' ("Common Bulkhead FWD Dome"), "CB AFT Dome" ("Common Bulkhead AFT Dome") for the domes, and then on the second diagram there's the  "CB Core Volume" and "CB Inside Volume" for the insulated and remaining space between the two domes. The benefit is that since the two domes are under lower stress between the two tanks, they can be lighter as well as being more compact and avoiding the additional weight of an intertank section between two convex domes.

Doing some reading, it seems like if there's much difference at all it's to do with the "connecting ring" configuration and what's bonded to what on the domes and insulation--a variant on common bulkead, not a whole different thing. The two domes with insulation between them pretty typical layout for a hydrolox common bulkhead, it's just a nice detail diagram of the engineering of implementing what's often shown on stage-level diagrams as a single dome between two tanks. 
« Last Edit: 11/13/2017 03:45 PM by e of pi »

Online zhangmdev

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Re: NESTED propellant tanks.
« Reply #6 on: 11/13/2017 03:45 PM »
it will be filled with insulated material.

So basically it is common bulkhead. Search "common bulkhead insulation S-II stage". There are 2 sheets of domes with insulation in between.

Offline DarkenedOne

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Re: NESTED propellant tanks.
« Reply #7 on: 11/13/2017 03:48 PM »
The nested configuration of the propellant tanks with the upper tank dome inverted seems to have a better advantage in terms of mass saving. How many launch vehicles have been using such tank configurations? I knew about ares-V that never flew. Why is such a configuration neglected? or am i missing something?

Consider the added complexity.  Such nested tanks would definitely have advantages in mass savings, which would translate into cost savings.  On the other hand nested tanks increase the manufacturing complexity immensely, which directly increases cost.   My guess is that for most applications the cost from the increase in complexity is more than savings that come from decreased mass.

Offline e of pi

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Re: NESTED propellant tanks.
« Reply #8 on: 11/13/2017 03:49 PM »
it will be filled with insulated material.

So basically it is common bulkhead. Search "common bulkhead insulation S-II stage". There are 2 sheets of domes with insulation in between.
There's also some good images of S-IVB common bulkead domes being assembled into the common bulkhead in Stages to Saturn, which is online, including this one:



EDIT: And a good detail of the common bulkhead on S-IV:

« Last Edit: 11/13/2017 03:53 PM by e of pi »

Re: NESTED propellant tanks.
« Reply #9 on: 11/13/2017 03:56 PM »
it will be filled with insulated material.

So basically it is common bulkhead. Search "common bulkhead insulation S-II stage". There are 2 sheets of domes with insulation in between.
https://www.google.co.in/patents/US5085343
I'm not sure if both nested tanks and common bulkhead tanks meant the same. The above paper refers it as a nested construction. How are the the propellant tanks generally connected together in Common BH constuction??

Online zhangmdev

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Re: NESTED propellant tanks.
« Reply #10 on: 11/13/2017 04:07 PM »
Sorry, can't access google or any ntrs papers :( I am sure there are a lot related material on this site.

https://forum.nasaspaceflight.com/index.php?topic=4329.80

Edit: dig up TITAN IIIE/CENTAUR D- I T SYSTEMS SUMMARY on my hard drive

Intermediate Bulkhead.

is a doublewalled, ellipsoidal structure  consisting of a structural bulkhead and an insulation bulkhead, separated by plastic mesh and fiberglass matt insulation. The volume between the bulkheads is filled with gaseous nitrogen prior to tanking. When the cryogenic fuel (LH2) is loaded, the trapped nitrogen condenses and a vacuum is formed by cryopumping effect.

The structural bulkhead is welded to the fuel tank sidewall. The insulation bulkhead is welded in a similar manner to the oxidizer tank.

The attached image gives some idea about how it is assembled.
« Last Edit: 11/13/2017 04:33 PM by zhangmdev »

Offline e of pi

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Re: NESTED propellant tanks.
« Reply #11 on: 11/13/2017 04:18 PM »
Normally in common bulkhead, as I understand it (some people on here with actual personal experience may be able to comment) the domes and honeycomb are all bonded together. This appears to differ by only bonding the honeycomb to the forward dome, reading the description and looking at the diagrams on the patent, then letting the tank pressure squeeze the aft dome into the forward one. Apparently the idea is that you can more effectively bond the one dome to the honeycomb if you only have to bond on one side, and then the pressure will automatically press-seal the other dome against the honeycomb in spite of a lack of mechanical bond, to reduce risks of insufficiently bonded areas and ease manufacture.

So it's a variant of common bulkhead, just with a twist on assembly aiming for ease of manufacturing. Not sure if it's ever actually flown, or if it's just sat on a shelf. It looks like Lockheed's filed some subsequent patents since which reference it. It may have some relevance for ULA's latest Centaurs on Atlas V or for Centaur 5/ACES on Vulcan, or it might not.
« Last Edit: 11/13/2017 06:27 PM by e of pi »

Offline brickmack

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Re: NESTED propellant tanks.
« Reply #12 on: 11/13/2017 05:28 PM »
or for Centaur 5/ACES on Vulcan, or it might not.

ACES has the common bulkhead inverted compared to previous designs, so I dunno if it'd work quite so well in that orientation. Centaur 5 probably has a similar structure

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