ISProgram
SketchUp Orbinaut
The problem is, the basic structure of the first and upper stages are set in stone, so to speak. I could tweak their propellant capacity slightly, probably design different engines, but I really can't extensively modify the stage as it is.
I'm basically stuck trying to tease out as much performance as possible. Kind of like what NASA had to do with the Ares I. That's a bad omen.
Among the first things I'm doing at the moment is lengthening the second stage, by increasing the propellant tank length, but decreasing the forward skirt by the same amount, so the rocket doesn't get "taller". Drawback of this is that it takes up more space inside the fairing.
I'm also considering going with a J-2 derived engine (which weighs only 1,788 kg, compared to the 3,301 kg for the previous engine).
A common bulkhead for the first stage is also an option going through my mind right now.
A question I have to ask, though, is the 8mm and 6mm tank skin figures you used earlier in your calculations. How exactly do you come up with these numbers?
I ask this because if I can find a "thinner" tank skin figure that can still support its own weight, I would like to use that figure for dry mass calculations.
Also tried another simulation:
First stage flight. Pitched over 10 degrees beginning 11 seconds into flight. Gradually pitched over through flight, more so near the end of the first stage burn, until staging.
Second stage flight. Pitched over to near prograde attitude after staging. Maintained this attitude until cutoff, which resulted in a somewhat elliptical orbit.
It has consistently reached orbit, so I think the only real problem, barring any performance shortfalls, is a proper pitch program. Looking into that now. Still got a long way to go.
---------- Post added at 11:12 PM ---------- Previous post was at 08:23 PM ----------
Excerpt from Saturn V flight manual.
Due to this, I've decided to go with 4mm(?) and 3mm(?) for the tank skin thickness. Also, 2219-T87 is 2.84 g/cc. Another alloy used on the Saturn was 7075-T6, with a density of 2.81 g/cc, but it was only used on the intertank and skirt assemblies. These should be accounted for too.
So now calculations. Does anyone think 4mm and 3mm is too thin? Not looking for balloon tanks here.
I'm basically stuck trying to tease out as much performance as possible. Kind of like what NASA had to do with the Ares I. That's a bad omen.
Among the first things I'm doing at the moment is lengthening the second stage, by increasing the propellant tank length, but decreasing the forward skirt by the same amount, so the rocket doesn't get "taller". Drawback of this is that it takes up more space inside the fairing.
I'm also considering going with a J-2 derived engine (which weighs only 1,788 kg, compared to the 3,301 kg for the previous engine).
A common bulkhead for the first stage is also an option going through my mind right now.
A question I have to ask, though, is the 8mm and 6mm tank skin figures you used earlier in your calculations. How exactly do you come up with these numbers?
I ask this because if I can find a "thinner" tank skin figure that can still support its own weight, I would like to use that figure for dry mass calculations.
Also tried another simulation:
First stage flight. Pitched over 10 degrees beginning 11 seconds into flight. Gradually pitched over through flight, more so near the end of the first stage burn, until staging.
Second stage flight. Pitched over to near prograde attitude after staging. Maintained this attitude until cutoff, which resulted in a somewhat elliptical orbit.
It has consistently reached orbit, so I think the only real problem, barring any performance shortfalls, is a proper pitch program. Looking into that now. Still got a long way to go.
---------- Post added at 11:12 PM ---------- Previous post was at 08:23 PM ----------
Excerpt from Saturn V flight manual.
The 345,000 gallon lox tank is the structural link between the forward skirt and the intertank section. The cylindrical tank skin is stiffened by "integrally machined" T stiffeners. Ring baffles attached to the skin stiffeners stabilize the tank wall and sense to reduce lox sloshing. A cruciform baffle at the base of the tank series to reduce both slosh and vortex action. Support for four helium bottles is provided by the ring baffles. The tank is a 2219-T87 aluminum alloy cylinder with ellipsoidal upper and lower bulkheads. The skin thickness is decreased in eight steps from .254 inches at the aft section to .190 inches at the forward section.
Due to this, I've decided to go with 4mm(?) and 3mm(?) for the tank skin thickness. Also, 2219-T87 is 2.84 g/cc. Another alloy used on the Saturn was 7075-T6, with a density of 2.81 g/cc, but it was only used on the intertank and skirt assemblies. These should be accounted for too.
So now calculations. Does anyone think 4mm and 3mm is too thin? Not looking for balloon tanks here.