Logic of the NASA/MSFC Simulant Development Technical Approach
At the simplest level of expression, NASA/MSFC has been asked to define requirements for simulants and to "make some stuff." Past experiences by multiple individuals and organizations have repeatedly shown that to just make simulants is not a simple task. Nor is it quick, cheap or easily reproducible. The approach created by the MSFC team addresses both the mandates to create requirements and produce simulants. MSFC's approach also positions the Agency to obtain better simulants, with rigorous specifications and performance, and at lower expense.
Requirements and Measurements - Logically, one can only express requirements in terms defined by standards accepted by a community of subject matter experts. Useful standards must have several elements, such as defined terminology, fixed methods of measurement and an established framework in which to understand the measurements. Such standards have never been defined for lunar simulants. Therefore, to write the necessary simulant requirements, standards must be created.
As indicated the creation of standards has several elements. In this case the decision has been made that:
This decision permits the definition of a series of required tasks:
- Standards for lunar simulant will mandate comparison, via a defined procedure, to actual lunar material.
- The comparison will use specified measurements using specified analytical techniques.
For the Figures of Merit to work properly three subtasks tasks are identified:
- Material comparison using a defined procedure will use an algorithm that produces numerically indices referred to as Figures of Merit.
a. Creation of the necessary algorithm(s)
b. Measurements of a reference material (Apollo samples)
c. Measurements of a simulant
The FoM algorithm requirement to measure simulants is a task shared by the work required to make a simulant and is discussed further below.
Feedstocks and Production - An ability to make simulant has serious technical challenges in material handling and material synthesis. The technologies for grinding and mixing materials are both notorious for illusory simplicity. Material synthesis on the scales needed for a true simulant is never trivial when flexibility is needed. In such work it is often easy to achieve a result once. The greater challenge is achieve the same result repeatability, in the face of variations in feedstocks, machinery wear, and other uncontrollable variables. Therefore, one additional required task is the development and demonstration of such a process control. This effort is termed the prototyping task.
Process control requires measurement of the simulant. The Figure of Merit algorithm also requires measurements of the simulant. The two needs though not exactly identical, share enough similarities that they can be combined into one effort to save resources. Given the intimate need for the process control task, the MSFC plan has placed this work within the prototyping task.
Terrestrial materials can readily be discriminated from lunar materials by experts. There are many features at many scales that permit this. Some of the features will have considerable engineering significance to NASA's return to the Moon. Other features are almost certainly irrelevant. Examples of the former are the presence of agglutinates containing nano-phase iron and the presence of the mineral troilite. Both are common on the Moon but non-existent or extremely rare on Earth. On the other hand the relative abundances of certain trace elements are of no practical significance at this time. Examples of unknown significance are the crystallographic position of Fe in the mineral ilmenite or the exact abundance of calcium in plagioclase. Such considerations have substantial impacts on the selection of appropriate feedstocks to be used in making simulants. This is especially true because minimal simulant consumption will be measured in 10's to hundreds of tons. Use of feedstocks on this scale can only be achieved by mining. Given the worldwide restrictions on mining this means feedstocks must come from existing, licensed operations. In total this makes selection of suitable feedstocks difficult.
Summary - As illustrated the technical approach that MSFC has taken requires five (5) specific, independent tasks to be completed. Those tasks are:
- Development of the necessary simulant requirements based on the appropriate standards
- Development of a method by which to compare simulants to a reference
- Selection and measurement of the appropriate reference materials.
- Development and demonstration of simulant development and process control techniques
- Selection of suitable simulant feed stocks
These five tasks are recognized as the minimum number of basic tasks needed to begin making the range of simulant products already requested. Each task is substantial and demands specialized knowledge. Therefore work on the tasks is being done by many organizations. Johnson Space Center is leading the effort to characterize the Apollo samples. In this they are being assisted by other NASA Centers. Also involved in the characterization is the United States Geological Survey, who is leading the prototyping effort. The Survey is also leading the effort to identify source materials for feedstocks. The development of the Figure of Merit algorithm is being led by Teledyne Brown Engineering.
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