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Burncycle Burncycle is offline
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Default Sea Dragon
by Burncycle 02-03-2018, 03:11 AM

Hello,

I am starting a Sea Dragon project, primarily for 3d printing purposes but may try and get a version in Orbiter too. The more I look at the available schematics, the more I realize the drawings are very preliminary and the actual look (especially where the payload goes) would probably have changed quite a bit depending on if they were lofting fuel or oversized cargo. One example is the Apollo CSM that is often seen in the drawings -- it wouldn't fit as it stands, because there's a tank wall just below. My plans is to create a "classic" Sea Dragon (as per drawings found online) and then a possible evolution of the design with different uppers to accommodate various payloads such as fuel, oversized probes and station pieces, etc


This is the reference image I am using:





As well as this one:




I am fleshing out a rough shape, some inner tanks are not modeled since they won't be visible, but have some specific questions about some of the parts so that I get it right overall.

This first picture is an overall cross section of what I have so far. As you can see the small rocket motors sticking out from the sides on the 2nd stage have not yet been modeled, because this is an area where I have some questions.







As you can see, there doesn't seem to be any sort of interstage section that falls away between stage one and stage two, and if there was one and the drawings just don't indicate it, then it may be an issue due to the positions of the small side rockets (not modeled here yet but visible in the reference images above). But that means there's almost ZERO detail visible from the outside with regards to the 2nd stage engine, and no room for the 2nd stage engine to expand at all like the 1st stage. Is that correct? If so, while it makes it easy to model (I can get rid of a lot of that interior actually) it is rather boring to look at... I wonder if a production version would have had an interstage of some sort.





This is a view of the first stage from below. The reference pictures indicate that the first stage engine bell is capable of 3 degrees of movement off center, and I assume all the bits and bobs drawn in the cross sectional view are actuators to move the main engine bell. The problem is, I'm having trouble visualizing what those parts look like in 3d so I can replicate them. Are they spheres or flat sided cylinders of some sort? They would partially fill the void at the narrow part of the cone here.






Finally, below is a cutaway of the structure near the top. For 3d printing purposes, I have holes in the Apollo CSM so that small neodymium magnets can be glued in order to keep the capsule on the service module for display purposes, though for Orbiter purposes I can simplify it further. But this shows how the reference drawings don't necessarily match up to what is possible; if the CSM was buried about halfway in as in the drawings, the engine bell and the upper portion of the internal tank would conflict. It's just about perfect sticking out like it does on the Saturn V though.


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Old 02-03-2018, 08:23 AM   #2
Urwumpe
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Great to get it finally.

Quote:
Originally Posted by Burncycle View Post
 This first picture is an overall cross section of what I have so far. As you can see the small rocket motors sticking out from the sides on the 2nd stage have not yet been modeled, because this is an area where I have some questions.


As you can see, there doesn't seem to be any sort of interstage section that falls away between stage one and stage two, and if there was one and the drawings just don't indicate it, then it may be an issue due to the positions of the small side rockets (not modeled here yet but visible in the reference images above). But that means there's almost ZERO detail visible from the outside with regards to the 2nd stage engine, and no room for the 2nd stage engine to expand at all like the 1st stage. Is that correct? If so, while it makes it easy to model (I can get rid of a lot of that interior actually) it is rather boring to look at... I wonder if a production version would have had an interstage of some sort.
If you look at the other drawings in the NASA report, you can get some clues there: There is no interstage because the first stage sticks into the second stage engine - the cylindrical top of the first stage engine fits into a cylindrical hole in the second stage chamber. The second stage engine uses an expanding nozzle, that is covering the first stage engine during launch (The darker textured region on the first stage in the outside drawing, with the retainer bands that wrap around it). It starts cylindrically, but when the retainer bands are pyrotechnically cut, the tension inside it expands the end of the nozzle into a truncated conical shape.

Quote:
Originally Posted by Burncycle View Post
 This is a view of the first stage from below. The reference pictures indicate that the first stage engine bell is capable of 3 degrees of movement off center, and I assume all the bits and bobs drawn in the cross sectional view are actuators to move the main engine bell. The problem is, I'm having trouble visualizing what those parts look like in 3d so I can replicate them. Are they spheres or flat sided cylinders of some sort? They would partially fill the void at the narrow part of the cone here.
Well, they are hydraulic actuators at station 450, so they should be rather cylinders, with ball joints connecting the actuator to first stage and engine. The rest you can see there is piping and valves. For allowing the engine to gimbal, the propellant lines must be flexible, by means of bellows (as you can see in the drawing "View looking aft with tankage removed for purposes of clarity"). The circle above the actuator in the cross section is a cross section of the propellant line.

Quote:
Originally Posted by Burncycle View Post
 Finally, below is a cutaway of the structure near the top. For 3d printing purposes, I have holes in the Apollo CSM so that small neodymium magnets can be glued in order to keep the capsule on the service module for display purposes, though for Orbiter purposes I can simplify it further. But this shows how the reference drawings don't necessarily match up to what is possible; if the CSM was buried about halfway in as in the drawings, the engine bell and the upper portion of the internal tank would conflict. It's just about perfect sticking out like it does on the Saturn V though.
Well, read here from the summary of the study about the command module:

Quote:
An abort propulsion system is also provided. If the only function of the command module is to ensure attainment of orbit by the LH2 payload, a considerably smaller and simpler module similiar to Mercury or Gemini could be utilized.
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Old 02-04-2018, 01:59 AM   #3
Burncycle
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Quote:
Originally Posted by Urwumpe View Post
 Great to get it finally.

If you look at the other drawings in the NASA report, you can get some clues there: There is no interstage because the first stage sticks into the second stage engine - the cylindrical top of the first stage engine fits into a cylindrical hole in the second stage chamber. The second stage engine uses an expanding nozzle, that is covering the first stage engine during launch (The darker textured region on the first stage in the outside drawing, with the retainer bands that wrap around it). It starts cylindrically, but when the retainer bands are pyrotechnically cut, the tension inside it expands the end of the nozzle into a truncated conical shape.
Oh wow, so the circled area is actually the bell that expands out like so? (I just moved the 1st stage down so the retaining bands are still on)









Quote:
Well, they are hydraulic actuators at station 450, so they should be rather cylinders, with ball joints connecting the actuator to first stage and engine. The rest you can see there is piping and valves. For allowing the engine to gimbal, the propellant lines must be flexible, by means of bellows (as you can see in the drawing "View looking aft with tankage removed for purposes of clarity"). The circle above the actuator in the cross section is a cross section of the propellant line.
That makes perfect sense now, thanks, as does the command module size issue

Regards
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