A pipelauncher is a pipe with one end capped. It floats vertical. In deep water, it can launch a rocket and add some speed to this rocket.
Here's my lastest idea for a piplauncher:
1000' tall plus the height of structure that houses the rocket.
Accelerates at 1 gee for 7 seconds for an vertical distance of about 790' for blast off speed of about 150 mph
Decelerates at *about* -1 gee for *about* a distance of 300'.
Launch sequence:
The base of rocket is about 200' above waterline. The air temperature inside the pipe is about 80 degrees. Air temperature is lowered inside the pipe and/or air is released from this central chamber. The air temperature wouldn't need to go below freezing, you want to adjust the volume of air so that instead of floating 200' above the water it would float around 75'. The air is cooled rapidly or simply vented so that that pipelauncher falls past the 75' level, then bounces up again. Once it begins to bounce, the air is heated, say burning natural gas. And also compress air is added. How much the air is heated and compressed air is added controls the acceleration. At about 1000' above the water, the rocket blasts off and pressure inside pipe is decreased by venting and possibly cooling the air.
Some construction details:
12 steel pipes 2' in diameter with 1/2" wall thickness, form a larger pipe; each 2' pipe is separated by a spacer which is 2 foot wide and 1/2" of inch thick steel plate which is welded to the 2' diameter pipe.
Has total circumference at weld of 48' or 576" and diameter of 15.2' or 183.3"
Steel pipe with outside diameter of 2' with 1/2" walls weighs 125.5 lb per 1' length & 2" wide spacer would weigh about 1/3 the weight of a 2' pipe: 41 lbs. 125.5 lb times 12 = 1506 lb and 41 times 12 = 492 lb.
This totals 1998 lbs or 906.3 kg. In order to roughly fiqure displacement I'll convert to metric: the the diameter of 15.2' is 465.7 cm and 2' pipe is 60.96 cm in diameter. And 1' length is
30.88 cm (.3048 meters) and is also the radius. Each 2' diameter pipe 1' long has the volume of .3048 sq times pi times .3048 which equals .08896 cubic meters.
Volume at weld point is 4.657 meters in diameter 2.3285 meters in radius squared times pi times .3048 which equals 5.19179 cubic meters. Half of the 12 pipe are outside of weld circumference, so times .08896 cubic meters by 6 which equals .53376 cubic meters; add this to 5.19179 and get total displacement of 5.7255 cubic meters. Divide by 906.3 kg (pipe's weight) and get 6.32. Which means for every 6.32 inches/feet/meters of pipe length needs 1 inch/feet/meter to float the weight of the structure in fresh water.
If 2' diameter pipe & spacers are made of average strength steel, 40,000 psi yield strength.
stress = ( pressure * diameter ) / ( 2 * wall thickness )
1666 psi * 24" /1 = 40,000
218.2 psi * 183.3" /1 = 40,000
218.2 psi * 183.3" /2 = 20,000
Assuming the central chamber has max operation pressure of 120 psi & the 2' pipes have max operation of 300 psi:
120 psi * 183.3" /2 = 10998
300 psi * 24" /1 = 7200
Giving combine stress of 18,198- slightly more than a safety factor of 2, and the spacer at 120 psi has 21,996- slightly less than two safety factor.
The 2' pipe & spacer fabricated pipe will only be part of the overall length of the pipelauncher (600'), a large single wall pipe will be used for 300' below* and 100' above the "pipe & spacer fabricated pipe" section. These pipe sections will be 15.2' diameter pipe with 1/2' thick wall; per foot of length they will weigh about 1/2 of the "pipe & spacer fabricated pipe's" weight. The primary purpose of these sections is to add to the overall length of the pipelauncher at a lower cost and reducing the overall weight as compared to making the entire length from the "pipe & spacer fabricated pipe". Now, the next obvious question is why not make the entire length of pipelauncher from large single walled pipe. For me, it's a tough question- for a trained engineer it might an easy question- I simply will admit that I'm slightly worried about the rigidity of the 100' top section and 300' bottom section- I would make these longer but I'm simply not *comfortable* doing so. There are also "other reasons" such as safety- the pipelauncher will float even if central chamber can't hold air pressure (barely). And pipes will allow a pipelauncher to pump it's own compressed air.
All this steel would weigh:
600' of the pipe & spacer fabricated pipe: 906.3 kg times 600 = 543,780 kg.
400' of single wall pipe: 906 kg times 400 times about 1/2 = 181,200 kg, so about 725 metric tons plus about another 100 tonnes for support stuctures and other things.
The total weigh including a rocket (Zenit-3SL Total Mass: 471,000 kg) would be somewhere around 1500 metric tonnes. Since each foot of large pipe section displaces about 5.7255 cubic meters that requires 262 ft of pipe length to float which is about 1/4 of entire length of pipelauncher.
Yikes, I got much tighter margins than I thought, with total weight at 1500 metric tonnes that give about 120 psi in center chamber which is it's max pressure.
Hmm, if total weight is 1200 metric tonnes it requires 209.6' pipe to float and 93.4 psi- which still looks like too much.
Hmm, hmm, hmm. Going to have to axe the total length to 800' by taking off 200' off the pipe & spacer section , so that's 400' of length = 362,520 kg. And limit rocket size to 500 metric tonnes and only have 50 metric tonnes for support structure & misc. So, 362,520 + 50,000 + 181,200 + 500,000 = 1,093,720 kg. Which means when the pipelauncher is "at rest" with 500 tonne rocket, the pressure in center chamber is 85 psi.
That still sucks. But you should notice that even though I chop off 500 metric tonnes it didn't change the psi very much, which also means I don't need to add much psi to center chamber to get acceleration- but it looks like I need to have the center chamber hold more pressure than 120 psi. Which means I *could* have it operate at lower safety margins: with 1.5 safety margin the max pressure in center chamber could 145 psi or a 1.2 safety margin gives 181 psi max pressure. OR it means I would need to use steel with higher psi yield strength than 40,000. And/or slightly increase the spacer's strenght (which are currently the "weakest link").
The problem (for me) in using higher psi yield strength steel is I'm uncertain as to how difficult it would make the welding- and a major element of the construction of this design of a pipe launcher is the welding. Not only would you need to weld the spacer to the pipe, you also would need to make the large single walled pipe from sections. Plus you will have a restriction on the lenght of each piece- probably somewhere around 40' long- though depending on where you build a pipelauncher could have a significant affect on the size of the pieces which are manufactured (and need to be shipped). Though the spacer are a fairly insignificant in terms of overall weight, they *might* provide an easy way of incorporating higher yeild str steel- thereby increasing their strenght and lower their overall weight.
In summary you *might* be able to make a pipelauncher 1000 ft long and get a max speed of 175 but this is close to the envelop of using steel which would have to use somewhat stronger than 40,000 psi str steel and using tight safety factor. A pipelauncher around 800' would be slightly easier and lower construction cost, though of course, a lower maximum speed. I suspect that if a pipelauncher is ever built it will be built because it's a cheaper way of getting a launchpad and the added speed seen as a small bonus.
I still think launch assist speeds of near the speed of sound are possible, just a bit further along and more complicated than I orginally thought- it's about the same as envisioning a car going 300 mph at the beginning of 20th century.