The term "Molecular-Sieve Type 3Å" denotes a clay-based, zeolite material that revolutionizes a fluid-purification process by removing trace water and iron from nitrogen tetroxide/nitric oxide (MON-3) mixtures used as oxidizer components of spacecraft propellants. Older processes of this type removed only water or iron effectively, but never both. Because contamination of nitrogen tetroxide by trace amounts of water elevates the corrosion level of spacecraft hardware, the reduction of such contamination decreases the cost of facility maintenance and increases propellant-storage time. Consequent further benefits include increases in the usable lifetimes of rocket engines, flight components, deep-space probes, and satellites, along with reductions in their failure rates. All this is achieved by a process that involves the use of a revolutionary material and that supplants less-effective, energy-intensive distillation process.

In the past, trace amounts of water were distilled from MON-3 mixtures. While distillation effectively removes iron, it removes trace water only poorly. Applications that involve two types of molecular sieves remove water but remove iron only poorly, thus excessively increasing system temperatures — something Molecular-Sieve Type 3Å never does. Only Molecular-Sieve Type 3Å can remove both water and iron equally well, and without any deleterious side effects.

Molecular-Sieve Type 3Å is a zeolite material with a nominal pore size of 3 Å. Zeolites are used in many industrial applications because they can selectively remove chemicals from fluid systems on the basis of molecular sizes. Water and iron, with molecular diameters less than 3 Å, are adsorbed by Molecular-Sieve Type 3Å. But because MON-3 molecules are larger than those of either water or iron, MON-3 is not adsorbed by Molecular-Sieve Type 3Å.

In the U.S. space program, water and iron must be removed from MON-3 mixtures to reduce the risk of failure of primary reaction control system (PRCS) valves in the space shuttle. Molecular-Sieve Type 3Å does this completely, with out deteriorating and without polluting the nitrogen tetroxide. Reduction of the amount of water in MON-3 reduces corrosion; reduced corrosion rates reduce PRCS failures. Not only do reduced corrosion rates increase the usable lifetimes of the space shuttle PRCS valves; they also increase the usable lifetimes of rocket engines, flight components, deep-space probes, and satellites while reducing failure rates. All of this naturally leads to significant reductions of costs.

Significant cost savings are already being realized at Kennedy Space Center, White Sands Test Facility, and Vandenberg Air Force Base, where Molecular-Sieve Type 3Å is in use. This revolutionary molecular-sieve material could also be put to use by the manufacturer of MON-3 oxidizers to satisfy procurement specifications; moreover, it could be transferred to a commercial line in its existing form, or with minor modification, for use in removing impurities from other industrial fluids.

Molecular-Sieve Type 3Å embodies a major improvement of the state of the art. Production of highly purified MON-3 would increase orbital times for satellites and deep-space probes. Reduction of system weights owing to better protection against corrosion would increase payloads and profits. The largest single benefit that can be attributed to the use of Molecular-Sieve Type 3Å is reduction of corrosion with consequent increases in reliability of affected systems. Not only will increased reliability significantly affect the U.S. space program, but its effects will be felt in other government industries and in the commercial world as well — indeed, in any industry in which MON-3 oxidizers are used and system reliability is important.

This work was done by Ari Ben Swartz and Louis A. Dee of the Rockwell Space Operations Company for Johnson Space Center. MSC-22763

NASA Tech Briefs Magazine

This article first appeared in the March, 2000 issue of NASA Tech Briefs Magazine.

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