Aeronautics and astronautics – Aircraft structure – Fuel supply
Reexamination Certificate
1999-03-09
2001-05-15
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Aircraft structure
Fuel supply
C244S13500B, C244S158700, C244S172200
Reexamination Certificate
active
06231008
ABSTRACT:
PRIORITY CLAIM
This application is based on and claims the priority under 35 U.S.C. §119 of German Patent Application 198 10 638.6, filed on Mar. 12, 1998, the entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to a storage container or tank for storing a liquid medium and a gaseous pressure medium separated from each other, whereby the gaseous pressure medium pressurizes and causes the liquid medium to be expelled out of the tank. The invention especially relates to a tank for storing rocket fuels or oxidizers for operating the rocket engines of spacecraft, having at least one separating membrane that separates the interior space of the tank into two partial chambers.
BACKGROUND INFORMATION
In order to adjust the position and the attitude, and to stabilize the orbital motion, of satellites and orbital space stations, such orbital spacecraft typically include rocket thrusters that effectuate the required corrective movements of the spacecraft by relatively small, exactly dosed or controlled thrust impulses. In order to operate these rocket thrusters, the spacecraft carry along appropriate propellant fuels which are usually stored in liquid form in suitable fuel tanks, as well as oxidizers if necessary, which are also stored in suitable tanks. In order to expel the liquid fuel and oxidizer out of the respective tanks in a positive-feed manner, it is generally known to use pressurized gases introduced into the tanks. However, this gives rise to the problem that the gaseous pressure medium can become mixed with the liquid fuel or oxidizer.
In order to allow the gaseous pressure medium to be separated from the liquid fuel or oxidizer, it is also known to separate the interior space of the fuel tank or oxidizer tank into two or more partial chambers by means of one or more flexible membranes. One of these partial chambers on one side of the membrane contains the liquid fuel or oxidizer, while the other partial chamber on the other side of the membrane is filled with and pressurized by the gaseous pressure medium. When the pressure medium is supplied into the respective partial chamber and pressurized, it flexibly deflects the dividing membrane and thus exerts a corresponding supply pressure onto the liquid fuel or oxidizer so as to push the liquid fuel or oxidizer out of the tank.
Especially when the tank is to be used to store a rocket or satellite fuel based on hydrazine, or an oxidizer based on nitrogen tetroxide, the membrane for separating these liquid media from the gaseous pressurizing medium is typically a polymeric membrane, because the polymer materials provide relatively good separation, resistance to chemical attack by the media being stored, and long term durability even under the repeated flexing conditions that come into play.
However, such polymeric membranes cannot completely prevent the permeation of vapors of the liquid fuel or oxidizer through the membrane and into the partial chamber containing the gaseous pressure medium. Such a permeation process is especially caused or enhanced due to the temperature variations that are unavoidable in every technical system of this type, and the influence of these temperature variations on the differing thermal capacities of the liquid fuel or oxidizer relative to the gaseous pressure medium. As a result, the fuel or oxidizer vapors that permeate through the membrane ultimately condense in the partial chamber containing the gaseous pressure medium. The condensed liquid then becomes trapped, so to speak, in the gas-containing partial chamber and cannot be supplied to the associated rocket engine. Since this permeation and condensation can occur continuously, the result can be a considerable loss of useable fuel or oxidizer.
The above described problem of permeation of the fuel or oxidizer through the membrane could be prevented by using a membrane of a non-permeable material rather than the permeable polymers that are conventionally used. The requirements of non-permeability would essentially only be satisfied by providing metal membranes, but such metal membranes are mechanically not suitable for this application because they would suffer metal fatigue and crack formation as a result of the substantial repetitious deformation or deflection processes with a great extent of deformation, to which such dividing membranes are subjected during operation.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the invention to provide a container and particularly a fuel tank or an oxidizer tank of the above mentioned general type that is improved in such a manner so as to reduce or absolutely minimize the permeation and then condensation of fuel or oxidizer vapors into the partial chamber of the tank containing the gaseous pressure medium. It is also an object of the invention to provide a method for minimizing such permeation and condensation of the liquid vapors. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages, as apparent from the present specification.
The above objects have been achieved in an apparatus according to the invention including a container, at least one membrane separating the inner space of the container into at least a first partial chamber adapted to receive a liquid medium therein and a second partial chamber adapted to receive a gaseous pressure medium therein, and a temperature regulating arrangement provided especially on the side of the tank in which the second partial chamber is formed. The temperature regulating arrangement is adapted to achieve and maintain a second temperature in the second partial chamber containing the gaseous pressure medium that his higher than the first temperature of the liquid medium received in the first partial chamber.
The temperature regulating arrangement, for example, includes thermal insulation around at least a portion of the tank enclosing the second partial chamber containing the gaseous pressure medium and a heater such as an electrical resistance heater, radiant heater or thermoelectric heater, or a heat pipe or other heat conveying device that carries waste heat from any onboard system of the spacecraft into the temperature regulating arrangement. The temperature regulating arrangement may further include at least one temperature sensor of any known type connected to a control circuit, whereby the provision of heat by the heater can be controlled to achieve a precisely controlled or regulated temperature difference between the second temperature of the second partial chamber containing the gaseous pressure medium and the first temperature of the first partial chamber containing the liquid fuel or oxidizer.
The inventive combination of a temperature regulating arrangement and a membrane-divided liquid storage tank serves to constantly maintain the second partial chamber containing the gaseous pressure medium at a temperature that is higher than the temperature of the liquid medium in the first partial chamber. In this manner, the possibility of condensation of fuel or oxidizer vapors in this second partial chamber is reliably prevented. Namely, any fuel or oxidizer vapor that permeates through the membrane and thus comes into the second partial chamber is maintained in a gaseous state until an equilibrium condition is reached, and further permeation through the membrane is thereby prevented. The higher temperature in the second chamber prevents condensation of the fuel or oxidizer vapor and also establishes an advantageous vapor partial pressure equilibrium as will be described further below.
The apparatus according to the invention is especially suitable for use as a fuel tank or an oxidizer tank in a rocket or a satellite or other spacecraft. However, in principle, the inventive liquid storage tank can be used in all situations or all applications in which a liquid medium is to be stored in the tank and then caused to flow out of the tank in a pressure controlled manner by means of a gaseous pressure medium, while reliably pre
Barefoot Galen L.
DaimlerChrysler Aerospace AG
Fasse W. F.
Fasse W. G.
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