- #1
- 1,109
- 1
You are called into the office of Wernher von Braun on a fine summer day in 1940. He tells you he has been working with an engineering team on the early design phase for what will be “a very large sounding rocket, the A-4, which will be used for peaceful purposes to investigate the upper atmosphere. This rocket will be capable of carrying one metric ton of, um, some meteorological equipment known as a ’gonkulator,’ to an altitude of 90 kilometers.” The fuel tank will hold ethanol, and the oxidizer tank will hold liquid oxygen. The issue at hand is the placement of the propellant tanks inside the fuselage of the rocket. Von Braun tells you that the team looked at, and discarded the idea of making single cylinder with a vertical septum to separate the two liquids from one another. Instead, one cylindrical tank will be immediately above the other, which will in turn be immediately above the turbo pump, which in turn is above the thrust chamber. Once that decision was made, this idea was considered but ultimately discarded: run a pipe from the bottom of the upper tank down on the exterior of the fuselage to the position of the turbo pump inside the fuselage, where the pipe re-enters the fuselage to feed the pump. Instead, it has been decided that the liquid in the upper tank, in order to get to the pump, will pass through a lagged pipe running down through the lower tank close to its centerline. He asks you to determine whether the upper tank ought to be the one holding the oxidizer or the fuel.
Here is a cutaway view of the pipe running through the lower tank:
http://www.v2rocket.com/start/others/003-a-tank_017-b-delivery_pipe.jpg
A view of region between the two tanks:
http://www.v2rocket.com/start/others/004-ab_tank-010.jpg
Von Braun tells you, “Your decision should balance the objectives of rocket performance, reliability, and the safety of the launch crew. It is intended that the rocket will be stored at the launch site with the ethanol fuel in its tank at ambient temperatures prevailing in the Fatherland--or perhaps temperatures prevailing along the coast of the North Sea, since we are anticipating that authorities might wish to launch our research rocket out over that body of water, in order to meet certain objectives that I am unfortunately not at liberty to discuss with you.“
The liquid oxygen will be transferred to the oxidizer tank from a tank truck a few minutes prior to launch. The oxidizer tank will of course be vented at its top to allow the evaporating oxygen to escape so that the tank does not burst under pressure. The fuel tank (but not the oxidizer tank) will be kept under pressure during the rocket’s ascent by nitrogen gas, in order to assure consistent feed of fuel to the pump inlet. The turbo pump is powered by its own monopropellant, and is in that sense independent of the rocket engine’s propellant tanks. Some physical parameters that you might wish to make use of in deciding how to arrange the tanks are:
Height of rocket: 46 feet
Diameter: 5 feet 5 inches
Thrust: 52,000 pounds
Burn time: 65 sec
LOX loaded onboard: 4900 kg
Ethanol loaded onboard: 3710 kg
Boiling point LOX: -297.3 deg. F
Freezing point ethanol: -227 F
Specific gravity LOX: 1.105
Specific gravity ethanol: 0.789
{Actually a 75/25 mixture of ethanol and water was used in the fuel tank, so the freezing point and specific gravity of the fuel were somewhat different than the numbers for pure ethanol given above.}
I know the answer as to which way the German design team went, but I do not know their motivations for making the choice, and I am curious to see what ideas people here can come up with.
Here is a cutaway view of the pipe running through the lower tank:
http://www.v2rocket.com/start/others/003-a-tank_017-b-delivery_pipe.jpg
A view of region between the two tanks:
http://www.v2rocket.com/start/others/004-ab_tank-010.jpg
Von Braun tells you, “Your decision should balance the objectives of rocket performance, reliability, and the safety of the launch crew. It is intended that the rocket will be stored at the launch site with the ethanol fuel in its tank at ambient temperatures prevailing in the Fatherland--or perhaps temperatures prevailing along the coast of the North Sea, since we are anticipating that authorities might wish to launch our research rocket out over that body of water, in order to meet certain objectives that I am unfortunately not at liberty to discuss with you.“
The liquid oxygen will be transferred to the oxidizer tank from a tank truck a few minutes prior to launch. The oxidizer tank will of course be vented at its top to allow the evaporating oxygen to escape so that the tank does not burst under pressure. The fuel tank (but not the oxidizer tank) will be kept under pressure during the rocket’s ascent by nitrogen gas, in order to assure consistent feed of fuel to the pump inlet. The turbo pump is powered by its own monopropellant, and is in that sense independent of the rocket engine’s propellant tanks. Some physical parameters that you might wish to make use of in deciding how to arrange the tanks are:
Height of rocket: 46 feet
Diameter: 5 feet 5 inches
Thrust: 52,000 pounds
Burn time: 65 sec
LOX loaded onboard: 4900 kg
Ethanol loaded onboard: 3710 kg
Boiling point LOX: -297.3 deg. F
Freezing point ethanol: -227 F
Specific gravity LOX: 1.105
Specific gravity ethanol: 0.789
{Actually a 75/25 mixture of ethanol and water was used in the fuel tank, so the freezing point and specific gravity of the fuel were somewhat different than the numbers for pure ethanol given above.}
I know the answer as to which way the German design team went, but I do not know their motivations for making the choice, and I am curious to see what ideas people here can come up with.
Last edited: