The automated propellant-blending machine, a Johnson Space Center (JSC) innovation, refines the production processes of commercial rocket-propellant manufacturers by: (1) generating inert blends that contain particles of uniform size; (2) eliminating manual mixing, thereby speeding production and reducing the risk of injury or death; and (3) making it possible, with little or no modification, to produce a finer end-product for commercial and aerospace applications. These refinements are achieved by use of a nonproprietary technique — a significant departure in that commercial propellant manufacturers frequently use proprietary precipitation-drop techniques unavailable to other propellant manufacturers. One manufacturer has already expressed interest in the JSC automated propellant-blending machine.
Propellant-blending machines blend zirconium/potassium perchlorate (ZPP), titanium and titanium hydride propellants, and aluminum and magnesium compositions. Two commercial methods for blending ZPP are the evaporation method and precipitation blending. The disadvantages associated with the evaporation method are that the achievement of good blends depends upon, among other things, manual and frequent movement of mixtures, and production of the blends is dependent on the blender. Moreover, evaporation blending is dangerous; lives and limbs have been lost because of hazards associated with the blending process. The major disadvantage of precipitation blending is the unreliability of the process. The JSC automated propellant-blending machine overcomes the disadvantages of both evaporation and precipitation blending.
The JSC machine (see figure) includes a mixing container and a pouring container. An explosion-proof motor is connected by a shaft to an impeller (the blending actuator) in the mixing container.
In preparation for the blending process, a fluoroelastomer (Viton B or equivalent) is dissolved in acetone in proportions of 1:1, and the resulting solution is allowed to sit for a minimum of 24 hours. A required amount of hexane (which serves as a counter-solvent as explained below) is measured and put into a hexane fill container. The fluoroelastomer/acetone solution and the hexane are put into the mixing container. The active ingredients of the propellant mixture are placed in the pouring container. These ingredients include the following: (1) zirconium and graphite, which are placed on one side of the pouring container, and (2) potassium perchlorate, which is placed on the other side. At this juncture, personnel leave the machine, and the automated propellant-blending process begins.
During this process, the operation of the automated blending machine is controlled by a program executed on a personal computer. The program activates the explosion-proof motor, which rotates the shaft/impeller assembly. The program also activates a pneumatic actuator that tilts the pouring container to pour the active propellant materials into the acetone/hexane/fluoroelastomer solution in the mixing container.
A solenoid valve is opened to add hexane, and the amount of hexane added is measured. When the hexane-to-acetone ratio exceeds a certain value, the fluoroelastomer starts to precipitate from the solution and to coat the particles of the active propellant material. The desired amount of hexane to be added is the amount needed to precipitate the desired amount of the fluoroelastomer. Once the desired amount of hexane has been added, the solenoid valve is closed. After about 1 minute of mixing with the desired amount of hexane present, the computer tells the motor to stop. A ball valve opens, and the acetone/hexane solution is siphoned from the mixing container and deposited in an acetone/hexane disposal container. The ball valve is then closed.
The solenoid valve is opened and closed so that hexane can be added to the coated active ingredients. The computer orders the motor to rotate at a high speed for about 1 minute. The motor is then stopped and the ball valve is opened so that the hexane solution can be siphoned into the acetone/hexane disposal container. The mixing container is removed from the machine and the mixture is poured into a U.S. standard no. 30 sieve submerged in counter-solvent. The sieved particles are dried in air at room temperature, then sent to an oven for final drying.
The automated process as described above is superior to the evaporation method or to precipitation blending in the following respects:
- The human factor is removed; this means that the blend is uniform and consistent, time is saved, the cost of producing the propellant mixture is reduced.
- The automated part of the propellant-blending process can be controlled remotely; this makes the process a lot safer by limiting the exposure of personnel.
- The speed of production is increased. As a consequence, the product can be delivered in a more timely fashion. Excluding drying time, one station can produce 400 g/hr.
- The mixing step is safer because the materials are not taken to dryness.
- The end-product is a loose powder that is much finer; this reduces the screening requirement.
This work was done by Paul Kemp, Carl Hohmann, and Maureen Dutton of Johnson Space Center; Bill Tipton, Jr., of Lockheed Martin; and Jim Bacak of G. B. Tech. No further documentation is available. This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to
the Patent Counsel, Johnson Space Center, (281) 483-0837
Refer to MSC-22757.