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#131
02-07-2018, 03:58 PM
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I agree it does look counter to reason the way they have shown the S-IC stage floating "engines up". It is (I think) a very interesting question (maths story). I think it is quite a complicated problem and depends on a number of things. If it tries to turn up the other way one factor is all the mass of the engines and their distance from the centre of gravity of the stage. That "turning motion" will try to be resisted by the water that the stage will have to push out of the way in order to spin around. In reality this is not an easy calculation. Then there is the "buoyancy effect" of any air trapped inside the stage (which moves and changes as the stage tries to turn). Overall as the stage hits the water (and it depends in what position the stage is in when that happens) it depends which of that competing forces is the greater as to how the stage will look when floating. I think (and I hasten to add I am no expert) under some circumstances it could look like in the picture. Yes that does look weird (impossible some might say). I mention this because this question was very important for another part of the space craft, namely the command module. For those who do not know I want to point out that the command module actually has two ways it can sit in the water and will stay in that position (relatively) stable. There is the way we are used to seeing, pointy bit up (or apex up to be a bit more posh sounding) but it could also float apex down and would be "stable" in that position. Indeed the two positions were called "Stable I" and "Stable II" by NASA. (Here is a picture, source quora)  If anyone has watched the film Apollo 13, (slight spoiler) when they slpash down you hear Tom Hanks (playing Jim Lovell) saying to mission control "We are at stable one this is Odyssey signing off" (I have probably got the exact quote wrong, so good excuse to watch it again!) In fact all 3 dimensional objects have a number of "stable" balance points and a number of "unstable" balance points (they are positions where the object will balance but the slightest deviation from that position and it will "topple" to a stable balance point (roughly speaking). For example the point of a pyramid is an unstable balance point. For a long time it was thought that it was impossible for a 3d object to have only one stable and one unstable balance point but eventually two mathematicians proved there is such an object and eventually were able to make one (it has to be made very precisely). It is called a GOMBOC. It has the almost magical property that no matter how you put it on a table it will move by itself to the same position. This is NOT happening because of some weight (like in a weeble toy) it is down purely to the shape of the gomboc. Here is a couple of youtubes (there are others) There is a connection with a type of turtle and (more interestingly for NASA) pebbles. In fact one of the mathematicians who discovered the gomboc, Gabor Domokos, gives a very accessible talk about these things in the youtube below. The maths is minimal and you don't have to follow the maths at all to understand this (very visual) talk. Now what has this got to do with NASA. Well, it is thought that possibly 3 billion years ago Mars looked a lot like the earth (with or without life is a hot topic). Crucially there were flowing rivers of water there. But how could you try and prove this? One way (it turns out) to try and decide this is send a rover to mars (Curiosity) and look at pebbles and do some mathematics. But how does that help? Well if you want to know watch the youtube below and Gabor Domokos will explain.... So whether the S-IC will turn over is connected to whether there was ever water on mars. This is why I find maths, space and science fascinating and fun. Sorry for going off on one! 
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#132
02-07-2018, 04:00 PM
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#133
02-07-2018, 04:01 PM
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#134
02-07-2018, 04:03 PM
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#135
02-07-2018, 04:06 PM
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Glad you are enjoying the thread. I am really enjoying everything about doing this build (well, maybe not about how to move the model when finished!) Kevin
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#136
02-07-2018, 04:08 PM
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You're welcome. Thanks for the support Kevin
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#137
02-07-2018, 04:10 PM
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#138
02-07-2018, 08:37 PM
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The plans for recovery of the S-IC were designed around this conundrum... The F-1's, as mentioned, are very heavy and at the aft end, and they present about an 11 foot wide open "face" at the bell end of the nozzle which will impact the ocean surface first in a tail-first landing, which will compress the air trapped inside the nozzle to high pressure from the impact itself, which could damage the engine. Also, if the stage sat "upright" in the ocean after splashdown, the engines would actually be probably 20-30 feet underwater, as the source of buoyancy would be the trapped gases in the empty kerosene and oxygen tank, as the base area below the kerosene tank and the intertank area between the kerosene tank and LOX tank above it would be open to the sea and would flood with seawater, depending on how low in the water the stage would settle before it achieved buoyancy. (The empty oxygen tank would also have trapped vapor in it and provide buoyancy as well, but whatever is sticking up out of the water has to be supported by buoyancy forces from below.) Flooding the aft thrust structure, the engines, etc. would GREATLY complicate their reuse. SO, floating "engines up" would make reuse considerably easier. NASA had done tests where they test fired a Saturn IB H-1 kerosene engine, shut it down, then dunked it in seawater, retrieved it, refurbished it, and fired it again, successfully. Doing it with an entire cluster or stage would be more difficult, however. SO, *if* the engines and thrust structure could be made to float UP above the ocean surface, and thus prevent the engines and thrust structure from being submerged and flooded with seawater, refurbishment and reuse would be considerably easier. It was also important that the engines not be dropped into the ocean "nozzle end first" in order to prevent damage to the nozzles and combustion chambers at impact as well (which is why the shuttle SRB's explosively severed the nozzle skirts off the bottom of the SRB shortly before they touched down under parachute... some seawater is "shoved" up into the open nozzle end and floods the lower part of the SRB after splashdown, but having the hnvbbcbcvbv b uge "funnel end" of the nozzle remain on the SRB during splashdown created problems, so they chose to use a linear shaped charge fired a couple hundred feet before splashdown to cut the nozzle off and drop it into the ocean before splashdown, so only the nozzle "stub" and flexible joint with the nozzle throat opening was hitting the water. In order to make the S-IC float upright, the center of buoyancy force of the stage would have to be shifted "below" the stage's floating center of gravity (in the direction of flight, since the center of buoyancy is above the center of gravity in stable floating condition). Plus, when you have something as massive as an S-IC stage dropping into the ocean, even under parachute, it's GOING to hit hard and that impact force *needs* to be softened somewhat. The solution was to use a linear shaped charge to sever the forward LOX dome "Y-ring" where the dome, tank wall, and forward skirt of the stage all join together. This would "blow off" the forward dome of the oxygen tank at the front of the stage, which would fall into the ocean and sink along with the forward skirt ring. The parachutes would deploy out the back, slowing the stage, which would splash down "open end of the LOX tank first" into the water. The 33 foot diameter open end of the LOX tank would impact the ocean, and the air trapped inside the tank would compress to "soften the blow" of splashdown. The tank walls would likely crumple, buckle and rupture, absorbing the energy of the impact and allowing the compressed air from impact to escape. The stage would then settle into the water, the now-flooded LOX tank and intertank region between the upper LOX tank and lower kerosene tank would flood from the drainage vents and access hatches, which were not airtight. The kerosene tank would provide buoyancy, as it settled into the water. The weight of the flooded oxygen tank and intertank band and equipment would then sink below the air-filled kerosene tank, which was providing the buoyancy, keeping the F-1 engines and thrust structure hopefully pointing more or less "straight up" as the stage floated stably "front end down". The stage could then be secured and towed back for refurbishment and reuse. Obviously it would be lifted out of the water, and the explosively severed/crushed/ruptured oxygen tank would quite obviously be scrap metal. It would be separated from the intertank band between it and the kerosene tank, and would be discarded. I'm not sure what would happen to the intertank band-- due to the fact it was unpressurized in flight and had access hatches for crews to enter and work in there on the equipment between the two tanks, and it had a series of small "drains" or "vents" in pairs in four places around the periphery of the kerosene tank's upper "Y-ring" where the intertank band and the kerosene tank joined together, (the intertank band also was joined to the oxygen tank above it by another Y-ring on the bottom of the LOX tank), the intertank would doubtlessly flood and would surely be submerged completely while the stage floated at sea. Whether the intertank was to be scrapped and replaced with a new one, by separating it from the kerosene tank along its joint at the kerosene tank upper Y-ring, I don't know. Maybe they'd inspect it for damage and reuse it, maybe replace it. The kerosene tank, assuming it was undamaged, could be reused, with either a refurbished intertank or new intertank, and a new LOX tank bolted on to the front of it. The F-1's and thrust structure, which would have remained above the water line, would presumably be refurbished and verification test-fired, which would require their return to Stennis Space Center in Mississippi. I've not read anything on the exact methods of the "reuse" planned for the S-IC... I think that part of the plan wasn't well fleshed out. It was, after all, merely a proposal, and one that never got adopted anyway. I think that the reason the stage's fate after recovery was so "hazy" is because the focus at the time was to see if a *feasible* method of recovering the S-IC was even possible. *IF* they ever got approval to try it, they'd just have to see how extensive the damage was once the first stages were recovered and towed back to land. Perhaps the entire stage would be scrapped and merely the F-1 engines removed from it, refurbished and recertified, and sent to the Michoud Assembly Facility to be incorporated on a brand-new S-IC stage, with the remainder of the recovered stage being scrapped, kerosene tank, thrust structure, intertank, and of course the severed/crumpled LOX tank. There was also the "Saturn S-ID" stage proposal, which would have created a "single stage to orbit" vehicle from a modified S-IC Saturn V first stage. This vehicle would have used the Atlas's "stage-and-a-half" method to drop the outer four F-1 engines and their thrust structure after about 2-2.5 minutes of flight, and then fly on to orbit using the remaining F-1 engine. This required a redesign of the thrust structure of the S-IC, removing the "X" bracing from the center of the thrust structure ring that supported the center engine within the ring of the outer four F-1 engines, and making that ring "separable" from the rest of the stage at the appropriate time in flight, along with incorporating valves to shut off the fuel and oxidizer lines to those engines, and severing the lines explosively with shaped charges or using mechanical couplers when the engine ring separated from the stage. It would mean replacing the center engine's "X" mount with an inverted conical thrust structure to transfer the engine thrust into the stage/vehicle during flight, and putting the center engine on a gimbal instead of having it fixed (bolted solid) during flight as it was on Saturn V. The ring of F-1's would provide thrust for liftoff, but once sufficient fuel was burned off and velocity/altitude gained that they were no longer needed, they would be shut down and dropped off along with their heavy thrust structure and gimbals, fairings, and other associated equipment. The center F-1 would continue to power and control the vehicle and insert it into LEO, with a payload comparable to a space shuttle. The outer four F-1 engines would of course fall back into the ocean, as they did after Atlas staged in the same way. Unlike Atlas, there were plans to recover and reuse the F-1 engines, by deploying a series of parachutes and inflating "flotation devices" (airbags) to keep the ring of engines afloat nozzles-up and permit their recovery and reuse. There were even proposals for recovery of the S-IC stage via a gigantic, specially built helicopter designed to "snatch it in midair" under its parachutes BEFORE it splashed down into the ocean, eliminating the damage to the stage from splashdown altogether, but it was a rather fanciful proposal that never went any further. Recovery of the ring of F-1 engines by similar means would have at least "theoretically" have been possible, snatching them out of mid-air under parachute by a specially-built or equipped helicopter vehicle (though the weight and technical challenge would be substantial!) Interestingly enough, Elon Musk mentioned during his press conference yesterday following the successful Falcon Heavy maiden launch, inserting his Tesla Roadster and "Starman" into interplanetary space, that in working on the problem of fairing recovery, which had proven significantly more difficult than first anticipated, due to the fact that a HUGE fairing disrupts the airflow quite a bit, and this disrupted airflow does "bad things" to the parachutes/parafoils designed to recover the fairing, like twist them all up badly... Anyway, he said they were close to solving those problems, and in fact have built a new drone recovery ship specifically to recover the fairings at sea... Basically it's a "catcher's mitt on pontoons" as he described it... basically an enormous contraption designed to get under the fairing halves descending under their parachutes/parafoils as they descend, so they land in this "catcher's mitt" rather than splashing down into the ocean. They will have the speed and maneuverability to get under the fairings before they splash down. (Presumably there will be two of these ships operating close by, since there are 2 fairing halves coming down fairly close together but far enough apart I don't see how 1 ship could catch BOTH before the other splashed down, besides the fact how the second one could land without crushing the first one already "on deck"...) Such a recovery method would also be "feasible" for recovering rocket engines descending under parachute, particularly if they were in a thrust structure or suitably equipped with various strategically placed "landing bags" to cushion their landing (or landing on a deck equipped with enormous "air bags"... Later! OL J R 
__________________
The X-87B Cruise Basselope-- THE ultimate weapon in the arsenal of Homeland Defence and only $52 million per round!
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#140
02-08-2018, 06:17 PM
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lol
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