Ryan L. Kobrick

Three-Body Abrasion Testing Using Lunar Dust Simulants to Evaluate Surface System Materials

Numerous unexpected operational issues relating to the abrasive nature of lunar dust, such as scratched visors and spacesuit pressure seal leaks, were encountered during the Apollo missions. To avoid reoccurrence of these unexpected detrimental equipment problems on future missions to the Moon, a series of two- and three-body abrasion tests were developed and conducted in order to begin rigorously characterizing the effect of lunar dust abrasiveness on candidate surface system materials. Two-body scratch tests were initially performed to examine fundamental interactions of a single particle on a flat surface. These simple and robust tests were used to establish standardized measurement techniques for quantifying controlled volumetric wear. Subsequent efforts described in the paper involved three-body abrasion testing designed to be more representative of actual lunar interactions. For these tests, a new tribotester was developed to expose samples to a variety of industrial abrasives and lunar simulants. The work discussed in this paper describes the three-body hardware setup consisting of a rotating rubber wheel that applies a load on a specimen as a loose abrasive is fed into the system. The test methodology is based on ASTM International (ASTM) B611, except it does not mix water with the abrasive. All tests were run under identical conditions. Abraded material specimens included poly(methyl methacrylate) (PMMA), hardened 1045 steel, 6061-T6 aluminum (Al) and 1018 steel. Abrasives included lunar mare simulant JSC- 1A-F (nominal size distribution), sieved JSC-1A-F (<25 m particle diameter), lunar highland simulant NU-LHT-2M, alumina (average diameter of 50 m used per ASTM G76), and silica (50/70 mesh used per ASTM G65). The measured mass loss from each specimen was converted using standard densities to determine total wear volume in cm3. Abrasion was dominated by the alumina and the simulants were only similar to the silica (i.e., sand) on the softer materials of aluminum and PMMA. The nominal JSC- 1A-F consistently showed more abrasion wear than the sieved version of the simulant. The lunar dust displayed abrasivity to all of the test materials, which are likely to be used in lunar landing equipment. Based on this test experience and pilot results obtained, recommendations are made for systematic abrasion testing of candidate materials intended for use in lunar exploration systems and in other environments with similar dust challenges.

Robotic Joint Torque Testing: A Critical Tool in the Development of Pressure Suit Mobility Elements

Pressure suits allow pilots and astronauts to survive in extreme environments at the edge of Earth’s atmosphere and in the vacuum of space. One obstacle that pilots and astronauts face is that gas-pressurized suits stiffen when pressurized and greatly limit user mobility. As a result, a critical need exists to quantify and improve the mobility characteristics of pressure suits. A historical survey and critique of pressure-suit testing methodologies is first presented, followed by the results of recent pressure suit testing conducted at the MIT Man-Vehicle Laboratory (MVL). MVL researchers, in cooperation with the David Clark Company (Worcester, MA), used an anthropometrically-realistic robotic space suit tester to quantify pressure suit mobility characteristics of the S1034 Pilot Protective Assembly (PPA), a pressure suit worn by U-2 pilots. This suit was evaluated unpressurized, at a vent pressure of 5.5 kPa (0.8 psi), and at an emergency gauge pressure of 20.7 kPa (3 psi). Joint torque data was collected for elbow flexion/extension, shoulder flexion/extension, shoulder abduction/adduction, and knee flexion/extension motions. The aim of this study was to generate a robust baseline mobility database for the S1034 PPA to serve as a point of comparison for future pressure suit designs, and to provide recommendations for future pressure garment testing.

Developing Abrasion Test Standards for Evaluating Lunar Construction Materials

Operational issues encountered by Apollo astronauts relating to lunar dust were catalogued, including material abrasion that resulted in scratches and wear on spacesuit components, ultimately impacting visibility, joint mobility and pressure retention. Standard methods are being developed to measure abrasive wear on candidate construction materials to be used for spacesuits, spacecraft, and robotics. Calibration tests were conducted using a standard diamond stylus scratch tip on the common spacecraft structure aluminum, Al 6061-T6. Custom tips were fabricated from terrestrial counterparts of lunar minerals for scratching Al 6061-T6 and comparing to standard diamond scratches. Considerations are offered for how to apply standards when selecting materials and developing dust mitigation strategies for lunar architecture elements.

Evaluation of a Surface Exploration Traverse Analysis and Navigation Tool

SEXTANT is an extravehicular activity (EVA) mission planner tool developed in MATLAB, which computes the most efficient path between waypoints across a planetary surface. The traverse efficiency can be optimized around path distance, time, or explorer energy consumption. The user can select waypoints and the time spent at each, and can visualize a 3D map of the optimal path. Once the optimal path is generated, the thermal load on suited astronauts or solar power generation of rovers is displayed, along with the total traverse time and distance traveled. A field study was conducted at the Mars Desert Research Station (MDRS) in Utah to see if there was a statistical difference between the SEXTANT-determined energy consumption, time, or distance of EVA traverses and the actual output values. Actual traverse time was significantly longer than SEXTANTpredicted EVA traverse time (n=6, p<0.01), traverse distance was not significantly different than SEXTANT-predicted distance, and explorer energy consumption was significantly greater than SEXTANT-predicted energy consumption (n=5, p<0.01). A second study was done to see if mission re-planning, or contingency planning, was faster and less work when using SEXTANT in the habitat or in the field using an iPad. Time and workload measurements were collected for each subject under both conditions. Contingency planning in the habitat was not significantly different than contingency planning in the field. There was no significant workload difference when contingency planning in either location, however there was a trend that suggested contingency planning was faster in the habitat (n=3, p=0.07). Every subject commented that it was a hassle to carry the mission planner in the field and it was difficult to see the screen in the sunlight. To determine if gloves were a factor in the difference between mission re-planning time, subjects were asked to plan a contingency indoors with and without gloves. Performance and workload were not significantly different when re-planning with and without the gloves. The SEXTANT mission planner will continue to be improved according to the results and the recommendations of subjects in this study.

Expedition Mars: A Mars Analogue Program Dedicated to Advancing Competency in Human Planetary Surface Exploration

Mars analogue research facilities are excellent tools for advancing comparative planetology scientific research and exploration methodologies, as well as for investigating and devising countermeasures for the challenges astronauts may encounter while exploring the Martian surface. Analogue studies, and more specifically human mission simulations, also play an important role by training the future leaders in space exploration. With this in mind, the Mars Society of Canada (MSC) established the Expedition Mars program to advance the competence (knowledge, expertise and leadership) needed for human exploration of Mars. The program is divided into two distinct, but complementary, Mars analogue expedition series: Expedition Mars Analogue Training Series (ExMATS) and Expedition Mars Analogue Research Series (ExMARS). The ExMATS missions are designed to train and certify researchers, engineers and commanding officers for ExMARS missions which are dedicated to conducting extended Mars analogue research missions for maximum return on scientific research. Through the two series, Expedition Mars has established a systematic and sustainable method of developing and transferring competence within the program, and to the space community.

Custom Scratch Tips for Evaluation of Two-Body Abrasion on Lunar Surface Spacecraft Materials

During the Apollo missions to the surface of the Moon, numerous hardware issues were encountered due to the abrasive nature of lunar dust, which is formed from micrometeorite bombardment resulting in jagged particle geometries in the absence of weathering. Mineralogy of lunar minerals is characterized in order to predict regolith particle abrasive behavior by properties such as toughness, hardness, cleavage or fracture, and distribution. An investigation was conducted to study the abrasive nature of these particles using twobody scratch testing. The standard two-body abrasion test, ASTM G 171, uses a diamond stylus tip. However, we are also interested in the behavior of the abrasive material itself, which is not possible with the standard method since it does not allow evaluation of specific interaction between lunar minerals on spacecraft materials, and vice versa, as would occur on the Moon. Therefore, in an attempt to better model single particle interactions with typical engineering materials, custom scratch tips were fabricated out of analogous terrestrial minerals including anorthosite, olivine, enstatite and ruby spinel. The ASTM scratch methodology was then used to test these minerals against aluminum 6061-T6, a common spacecraft structural material. Observations of volume removal showed variability due to the friable tips and resultant fracturing that occurred during testing. We also included a diamond tip to relate our studies to established theory and to serve as a baseline for comparing the custom mineral tip data of interest to the large body of available data for interactions of diamond on various materials. Key spinel data are presented for scratch penetration depth and compared to two standard diamond tips, and recommendations for future testing are outlined.