1. Field of the Invention (Technical Field)
The present invention relates generally to liquid transfer, measurement and temperature control of fluid loading using minimum ullage loading techniques. One application is the propellant loading of reusable launch vehicles.
2. Background Art
Liquids are transferred in many industries. The space launch industry offers a unique set of liquid loading challenges and requires innovative techniques to accomplish safe and cost effective transfer.
Originally, supercooled liquids used in expendable launch vehicles (ELVs) took days to transfer from storage to the launch vehicles prior to launch. The process depended on pumps, which broke down periodically further complicating the problems and the cost.
The transportation of cargo to space is expensive. Part of the problem is the high cost of the individual operations required for the transport of cargo to orbit. One of these individual operations is the liquid propellant transfer performed on the surface of the earth from the ground facility into the launch vehicle. The problem is further increased by the potential of a launch delay requiring the transfer of propellants back into the ground storage tanks and the related loss of pressurant gases, contamination of the liquids including cryogenic propellants and potential of equipment failures.
This liquid transfer problem has been partly addressed by various minor changes and patch like improvements to the thirty-year-old facilities used to launch early expendable launch vehicles (ELV's). Future generations of launch vehicles called the reusable launch vehicles (RLVs) are fully reusable and need an integrated liquid propellant loading process that is more cost effective, faster, safer and more reliable than existing liquid transfer methods. In future reusable space launch systems, the launch vehicle hardware, the ground liquid handling facilities, individual propellant liquids and some of the pressurant gas recovery procedures and techniques will all be designed, refined, enhanced and optimize to work together in an integrated manner with recovery of the liquids and gasses in a cost effective manner.
Previous propellant loading operations use cryogenic and other liquid mechanical pumps that are subject to breakdown and special re-circulating liquid cooling methods in the flight tanks due to the length of the wait on the launch pad. These systems use complicated liquid shut off instrumentation inside the tanks. These solutions are complicated and subject to breakdown at safety critical times in the propellant loading operation, which is already full of very critical tasks, instrumentation that is subject to failure and time sensitive problems. The pumps are also used in the de-tanking of the propellants, if an abort of the launch process on the launch pad is required. De-tanking usually wastes the pressurant gases and at times contaminates the propellant liquid. The propellant pumps are expensive and are a critical part of the propellant handling operations. Each critical component of hardware and instrumentation is usually duplicated to provide redundancy, if failure occurs.
Ullage is a small pressurant gas volume at the top of the tank and includes the region of interface between the uncontaminated liquid and the pressurant gas. Ullage is defined as the volume of a tank not used for useful propellant transport. This total of unused propellant volume for whatever reason is also called ullage and is a combination unused propellant and unused propellant volume in the tank. The objective of the liquid transfer process is to decrease the ullage to a practical minimum, but not to zero. The ullage volume goal is approximately 1% of the tank volume.
U.S. Pat. No. 4,023,717 to Schultz, et, al. entitled “Pressure-Operated Container for Viscous Products” discloses a piston and container used for unloading a food container using simple pressure and a slippery piston to expel viscous foods from a container. The '717 Patent is a limited temperature range, non-integrated transfer system focused on one industry. Gravity or pump feed is not mentioned in the '717 Patent and it is limited to non-cryogenic piston driven transfer of food using a single pressurant.
U.S. Pat. No. 5,499,339 to Rosen, et. al., and Whittmann, entitled “Apparatus and Method for Transporting a Spacecraft and a Fluid Propellant from the Earth to a Substantially Low Gravity Environment Above The Earth,” discloses the transfer of bi-propellants from a stronger second tank into the lighter weight tanks of satellite payloads on orbit. The liquid transfer is only in microgravity and is not an integrated transfer system in one gravity focused on reusable vehicles. Gravity, pressure or pump feed is not mentioned and the '339 Patent is limited to bi-propellants.
U.S. Pat. No. 5,479,959 to Stotelmeyer, et. al., entitled “Integrated Storage and Transfer System and Method for Spacecraft Propulsion Systems” discloses a portable propellant loading cart for the ground loading of bi-propellants into satellites and focuses on the load cell measurement of bi-propellants loading into satellite payloads. The '959 Patent system is not an integrated transfer system focused on reusable vehicles. Gravity or pump feed is not mentioned and the process is limited to bi-propellants using a single pressurant. This invention appears to have reduced the loading process for a small amount of bi-propellant to about 17 days for the small satellite, where the present invention allows loading approximately ¾ of a million pounds of propellant in 2 to 14 hours. The '959, '656 and the '402 patents never mention gravity, pumps, or the recovery of consumable fluids or gasses.
U.S. Pat. No. 5,499,656 to inventors Stotelmeyer, et. al., entitled “Integrated Storage and Transfer System and Method for Spacecraft Propulsion Systems” discloses a later version of the portable propellant loading cart for the ground loading of propellants into satellites and focuses on the same load cell measurement of bi-propellants loading into satellite payloads as the '959 patent. The '656 Patent system is not an integrated transfer system focused on reusable vehicles, but a slower bi-propellant limited transfer process. Gravity or pump feed is not mentioned and the process is limited to bi-propellants using a single pressurant.
U.S. Pat. No. 5,749,402 to Stotelmeyer, et. al., entitled “Integrated Storage and Transfer System and Method for Spacecraft Propulsion Systems” discloses a later revision of the portable propellant loading cart for the ground loading of propellants into satellites and focuses on the same load cell measurement of bi-propellants loading into satellite payloads as the '959 and '656 Patents. This is a slower system bi-propellant limited transfer process. This is still not an integrated transfer system. The '402 Patent does add limited temperature conditioning focused on the spacecraft rather than reusable vehicles, but is limited to small spacecraft rather than launch vehicles. Gravity or pump feed is not mentioned and is limited to bi-propellants using a single pressurant.
Examples of cryogenic liquid transfer from other industries include the optical coating industry and methane tank service industry. U.S. Pat. No. 3,938,347 to Riedel, et. al., assigned to Optical Coating Lab, entitled “Level Control Apparatus and Method for Cryogenic Liquids” discloses cryogenic tanks, with level sensing means in the form of thermocouples and resistors inside the tank. Cryogenic temperatures in this Patent mean that everything put into the tank must be compatible with the cryogenic liquids.
Mixing instruments and LOX is a big compatibility issue and forces complicated expensive solutions. The thermocouples and resistors inside the tank also add weight to the tank. The thermocouples and resistors add complexity and another source of failure. An instrument subject to failure forces the designer to add a second sensor to increase the reliability of the system to detect an instrument failure versus an actual change. This modification generally solves the problem, but adds to the complexity, weight and cost of the vehicle.
The cryogenic liquid filling and ullage in other industries such as the methane industry is accomplished by placing instrumentation in the tank. For example, U.S. Pat. No. 4,334,410 to Drumare, entitled “Tank Designed to Contain a Liquefied Gas” discloses a system that uses methane tanks, which work at minus 160 degrees C. and typically get 98% full or 2% ullage. In filling methane tanks the heat responding device and the temperature responding element are placed inside the tank and are a source of extra expense. Each element of complexity is a source of failure.
Sometimes the cryogenic propellants are cooled as they are loaded into the launch vehicle, but the vehicle tanks are not usually efficient cryogenic containers and the temperature of the cryogenic propellants in the flight tanks at launch is elevated due to the heat and propellant loading waiting time. For this reason most launch vehicles solve the need for re-circulating cryogenic cooling systems in the flight tanks, because the propellant loading takes several days. This increases weight and makes the launch vehicle less efficient. The objective of the liquid loading or more accurate transfer of liquids in either direction is to accomplish the transfer with a minimum of time and delay with maximum safety. These new commercial launch vehicles are reusable and the propellant loading time is reduced, in this reduced duration propellant loading operation.
U.S. Pat. No. 5,644,920 to Lak, et. al, entitled “Liquid Propellant Densification” discloses super cooling of cryogenic liquid propellant, but not non-cryogenic propellants, such as Rocket Propellant One (RP-1). The '920 Patent system cools the propellant in the flight tanks and not in the storage tanks. The heat rejection from the liquid bulk fluid in the less temperature-efficient flight tanks and cooling is a relatively slow process. Cooling the propellant only in the thermally less inefficient flight tank as suggested in the '920 Patent means a slow ineffective fluid cooling process, use of significant re-circulation lines and an “in the tank Re-circulation Manifold.” The tank hardware also includes the return line near the bottom of the flight tank. The “in the tank Re-circulation Manifold” requires support hardware and hangers inside the tank to support the extra hardware. All the hardware in board from the umbilical disconnect fitting interface actually increases the weight of the flight vehicle and reduces the payload weight of the vehicle. This is not an integrated transfer system using transfer, cooling and flow/level controls in an integrated process to reduce time, reduce cost, minimize hardware weight and increased safety on commercial reusable vehicles. Gravity or pump feeds are not mentioned and the '920 Patent system limits the propellants to the cooling of liquid oxygen and liquid hydrogen. The '920 Patent says little about pressurant gases. This system appears to add significant weight to the flight tank and does little to shorten the loading process, which increases the need for in the tank re-circulation cooling. The Rockwell '920 Patent never mentions gravity, pumps, or the recovery of consumable fluids in the de-tanking process.
Cryogenic propellant tanks typically have three volumes within the tank and each is a different temperature: First, the coldest cryogenic liquid is usually in the bottom of the tank; second, the liquid-gas interface region between the cryogenic liquid and the pressurant gas used to pressure feed or pressurize the propellant; and third, the actual pressurant gas. The reason for the pressurant gas under pressure is to force a propellant from storage to the flight tanks and later into a utilization location at the rocket engines.
Typically, the ground operations include the handling, monitoring, and effective use of all the liquids required for the transportation cycle to orbit. The total cost of the transportation cycle is in part the result of the ground operations, the cost-effective transfer of vehicle propellants at the ground facility, and the efficient use of the reusable vehicle and its propellants.
A number of other industries use cryogenic liquids and require transfer, pre-cooling and control systems for the liquid utilization. For example, the Methane Tank Liquefied Gas Filling uses systems that would benefit as would the Optical Coating Industry Cryogenic Systems.
In contrast, the present invention transfers liquid by three methods, cools it and controls the shut-off of the liquid filling without instruments in the cryogenic tank to measure the liquid levels.
Accordingly, several objects and advantages are the cost effective, reliable and safe liquid transfer using a combined or integrated operation containing three alternatives for a successful completion of the tasks.