https://ntrs.nasa.gov/search.jsp?R=20070021819 2019-03-28T12:41:18+00:00Z NASA/TM—2005-213610/REV1 The Effects of Lunar Dust on EVA Systems During the Apollo Missions James R. Gaier Glenn Research Center, Cleveland, Ohio April 2007 NASA STI Program . . . in Profile Since its founding, NASA has been dedicated to the • CONFERENCE PUBLICATION. Collected advancement of aeronautics and space science. The papers from scientific and technical NASA Scientific and Technical Information (STI) conferences, symposia, seminars, or other program plays a key part in helping NASA maintain meetings sponsored or cosponsored by NASA. this important role. • SPECIAL PUBLICATION. Scientific, The NASA STI Program operates under the auspices technical, or historical information from of the Agency Chief Information Officer. It collects, NASA programs, projects, and missions, often organizes, provides for archiving, and disseminates concerned with subjects having substantial NASA’s STI. 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NASA/TM—2005-213610/REV1 The Effects of Lunar Dust on EVA Systems During the Apollo Missions James R. Gaier Glenn Research Center, Cleveland, Ohio National Aeronautics and Space Administration Glenn Research Center Cleveland, Ohio 44135 April 2007 Acknowledgments The author would like to express his appreciation to Ron Creel, of Science Applications International Corporation (SAIC) for sharing his experience and expertise on the Apollo program, especially in the area of the thermal degradation of the LRV thermal radiators, for his helpful discussions, and his overall encouragement. Document Change History This printing, numbered as NASA/TM—2005-213610/REV1, April 2007, replaces the previous version, NASA/TM—2005- 213610, March 2005, in its entirety. It contains the following changes: Page 1, “Introduction,” paragraph 3, line 6: Extravehicular Mobility Units (EMU) replaces Extravehicular Mobility Suits (EMS). Page 5, “Abrasion,” paragraph 1, line 3: The sentence “One or two additional EVAs could have resulted in a pressure failure in the Apollo 12 EMS” has been deleted. Page 5, “Abrasion,” paragraph 1, line 6: Text has been deleted from sentence so that it reads “Harrison Schmitt’s sun shade on his face plate was so scratched that he could not see out in certain directions.” Page 7, “Conclusions and Recommendations,” paragraph 6, line 3: The word “its” replaces “it’s.” Page 11, Table II, “Mission” column, line 12: The word “Apollo” is aligned. Page 27, paragraph 1, line 1: “Neil” replaces “Niel.” Trade names and trademarks are used in this report for identification only. Their usage does not constitute an official endorsement, either expressed or implied, by the National Aeronautics and Space Administration. Level of Review: This material has been technically reviewed by technical management. Available from NASA Center for Aerospace Information National Technical Information Service 7115 Standard Drive 5285 Port Royal Road Hanover, MD 21076–1320 Springfield, VA 22161 Available electronically at http://gltrs.grc.nasa.gov The Effects of Lunar Dust on EVA Systems During the Apollo Missions James R. Gaier National Aeronautics and Space Administration Glenn Research Center Cleveland, Ohio 44135 Summary Mission documents from the six Apollo missions that landed on the lunar surface have been studied in order to catalog the effects of lunar dust on Extra-Vehicular Activity (EVA) systems, primarily the Apollo surface space suit. It was found that the effects could be sorted into nine categories: vision obscuration, false instrument readings, dust coating and contamination, loss of traction, clogging of mechanisms, abrasion, thermal control problems, seal failures, and inhalation and irritation. Although simple dust mitigation measures were sufficient to mitigate some of the problems (i.e., loss of traction) it was found that these measures were ineffective to mitigate many of the more serious problems (i.e., clogging, abrasion, diminished heat rejection). The severity of the dust problems were consistently underestimated by ground tests, indicating a need to develop better simulation facilities and procedures. Introduction NASA’s Vision for Space Exploration has as its fundamental goal the advancement of “…U.S. scientific, security, and economic interests through a robust space exploration program” (ref. 1). The Vision is based around a spiral development that extends “…human presence across the solar system, starting with a human return to the Moon by the year 2020…” The Advanced Extravehicular Activity (AEVA) program has been charged with developing both the technology and the flight hardware required for spacesuits, tools, and vehicular interfaces that will enable astronauts to work on the lunar surface. In the summer of 2004 the Advanced Integrated Matrix (AIM) Program undertook a study to identify systems on both the lunar and Martian surfaces that would be affected by dust, how they would be affected, the associated risks, the EVA system requirements that need to be developed, and knowledge gaps that need to be filled (ref. 2). The group generated a preliminary list of dust hazards in EVA systems that included those experienced by the Apollo astronauts plus possible electrical problems such as power drains and shorts caused by conductive paths of dust particles. It is essential that the lessons learned during the Apollo program be incorporated into the planning process. All experience with human EVA systems on the lunar surface comes from the six Apollo missions that landed two-man crews (Apollo 11, 12, 14, 15, 16, and 17) and occurred between 1969 and 1972 (see table I). The records of these missions are a valuable resource as NASA plans for a return to the moon with a more sustained human presence. One of the surprises of the Apollo experience was how troublesome the lunar dust turned out to be. It obscured their vision on landing, clogged mechanisms, abraded the Extravehicular Mobility Units (EMU), scratched the instrument covers, degraded the performance of radiators, compromised seals, irritated their eyes and lungs, and generally coated everything with surprising tenacity. Some of the EMU components were approaching failure at the end of these missions which ranged from 21 to 75 hr on the lunar surface. With the Vision for Space Exploration Spiral 2 missions being planned for the 2015 to 2020 time frame having a mission life of up to 14 days (336 hr), mitigation of the effects of lunar dust on EVA systems clearly must be improved. NASA/TM—2005-213610/REV1 1 This study constitutes a review of the mission documentation and experience with dust from those six Apollo missions. Original documentation such as the Mission Reports, the Technical Debriefings, and transcripts of the voice traffic between astronauts on the lunar surface and Mission Control make up the bulk of the resources that went into the review, though later interviews with some of the principals have also been included. The dust related hazards could be sorted into nine categories. These categories are: vision obscuration, false instrument readings, dust coating and contamination, loss of traction, clogging of mechanisms, abrasion, thermal control problems, seal failures, and inhalation and irritation. Table II catalogs the references to dust problems in the mission reports and the technical debriefings, sorted by hazard category. The relevant parts of each of the mission documents are reproduced in their entirety in the appendix. The full text of the mission reports and technical debriefings are available on line at http://www.hq.nasa.gov/alsj/. In some cases, because of differences in the amount of dust in the local area, problems were only experienced by some of the missions. In some cases later missions were able to lessen the problems by changing operational procedures and, where this was the case, it will be noted herein. But the global lesson is clear—more attention must be paid to the mitigation of the effects of lunar dust if EVA elements are to last through the 14-day nominal mission (ref. 3). Dust Transport Mechanisms In order for the dust to cause problems, it must be transferred to sensitive surfaces. A good first-level analysis of the relative importance of different dust transport mechanisms was given by Katzan et al. (ref. 4), and those results will be summarized here. There are two general classes of dust transport mechanisms, natural and anthropogenic. Natural transport mechanisms include secondary ejecta from meteor and micrometeoroid collisions with the surface, and electrostatic levitation of dust at the terminator. None of the natural mechanisms are expected to transport significant amounts of dust over a 14 day period. Three anthropogenic mechanisms were analyzed and are, in order of increasing importance; astronaut walking, rover wheels spinning up dust, and landing and take-off of spacecraft. By far the most dust is transported by the landing and take-off of spacecraft. Large amounts of dust were seen by the astronauts to be blown about both on landing and on take-off of the Lunar Module (LM). Additionally, parts of Surveyor III recovered by the Apollo 12 crew were totally covered with dust—most of which was probably deposited as the LM landed nearby. Significant dust, though much less than observed on landing, in the Apollo missions was elevated by the Lunar Roving Vehicle (LRV), especially when one or more of the fenders was damaged. Photographs were taken of “rooster tails” of dust thrown up by the rover during its “Grand Prix” performance trial. Dust was elevated by walking, as evidenced by how quickly the EMU around their feet and ankles became dirty. A fourth transport mechanism, not covered by Katzan, is falling. On several occasions astronauts lost their balance and tumbled to the surface, or intentionally went down on one knee to better observe the surface. In all cases, the result was dust adhering to the EMU which could not be brushed off. It should be noted that the moon has no appreciable atmosphere (∼10–12 Torr) and, as a result, even submicron particles do not stay suspended. All particles display ballistic motion, falling at the same rate regardless of their size. Thus, there was no enduring cloud of dust when the LM landed, just a racing of particles out radially from the thrust point which settled out almost immediately (ref. 5). This behavior limits the range of dust transport to a strictly local phenomenon. NASA/TM—2005-213610/REV1 2 Pre-Apollo Thermal Testing Northrop Space Laboratories performed a study sponsored by NASA MSFC in 1967 to try to determine the degradation effects of dust and to establish removal and prevention concepts (ref. 6). They considered the effects of dust on thermal control surfaces, including both a paint (S–13) and a second surface mirror (aluminized FEP Teflon (DuPont)). Sieved and sorted basaltic dust was used as the simulant. It was determined that neither the particle size distribution nor the total mass of the dust proved to be significant parameters and the increase in light absorption, so particle size distribution was not well controlled. However, it was observed that particles larger than 50 µm were easily removed by tapping or low velocity gas jets, so even though the optical properties were independent of particle size, the amount of residual dust contamination depended primarily on the initial amount of particles smaller than 2 µm. The infrared emittance of the dust (∼0.88) was similar to that of the thermal control surface (∼0.83), so it was found that the control surface emittance would not be highly affected by the dust. Thus, radiator performance is degraded primarily by increases in absorption in the UV and visible regions, which raise the temperature of the radiators. It was found that the effect of dust contamination on absorptance was non-linear, with only eleven percent dust coverage resulting in a doubling of the solar absorptance. Eight different strategies were considered to remove dust from radiator surfaces including brushing, an electrostatic curtain, an electrostatic surface, jet and shield, jet and surface, spinning shield, spinning surface, and vibrating surface. These were prioritized according to system factors and the three that were considered to be the most promising, vibrating surface, jet and shield, and brushing were tested. Preliminary testing was done to remove the dust by nitrogen jet, which proved almost totally ineffective with small particle sizes. Fine dust (<34 µm) with an initial dust coverage of 4.5 percent had an initial absorptance of 0.245. After blowing on the sample for 15 sec with 10 psi nitrogen, the absorptance was only reduced by two percent to 0.239. Use of an imcompressible fluid (water, benzene, or tricloroethane) did not improve the results much. The results of vibration tests were even worse. Vibration was most effective when the sample was tilted and the vibration was at the resonant frequency, but the fine particles were not substantially removed. Three different brush tests were also carried out, one with a bristle brush, one with styrofoam, and one with cheese cloth. Of these, the styrofoam brush was the most effective. Final evaluation was done using a functional test where the final temperature of a radiator surface was measured clean, dusted, and with the mitigation strategy employed. Of these trials the jet and plate was the most effective, followed by the mechanical brush, the jet and shield, and finally the vibrating plate. None were completely effective, and the mechanical bristle brush was eventually chosen to fly, primarily due to its lower weight. Ground-Based LRV Wheel Testing After Apollo 11 had landed on the moon, but before any LRV had been launched, testing was carried out to determine how the LRV wheels would perform on the moon. There was concern that if the fenders did not contain the dust, that it could cause problems both for the astronauts and for the LRV itself. There had been almost no study about how dust behaved in a vacuum environment under low gravity. In order to study LRV fender design and, indeed, whether they were even necessary, a test rig was constructed in which a LRV wheel could be propelled within a circular vacuum chamber over simulated lunar dust (LSS–4) while being flown on a C–135A aircraft in an arc which would result in a 1/6-g gravitational force (ref. 7). It was found that dust caused as many problems as the most pessimistic predictions, and established the absolute necessity of fenders. It also found that the more complete the coverage of the wheel by the fenders, the less dust was elevated. The vacuum in which the test apparatus operated was no better than a few Torr. Observation of the mechanics of the dust propelled by the wheel revealed that when the pressure dropped below about 5 Torr NASA/TM—2005-213610/REV1 3 the simulant started to exhibit extra cohesion, as a result of the “clean body effect”.1 Clumps of the simulant would be thrown up and remain intact until they hit a solid object such as the chamber wall. Under these partial vacuum conditions the dust appeared to travel ballistically, even under reduced gravity conditions, and no suspended particles were observed. Vision Obscuration The first dust-related problem experienced by the Apollo astronauts occurred when they landed the Lunar Module (LM). The Apollo 11 crew reported that “Surface obscuration caused by blowing dust was apparent at 100 ft and became increasingly severe as the altitude decreased” (ref. 8). This was even more of a problem for Apollo 12 where there was total obscuration in the last seconds before touchdown to the extent that there was concern that one of the landing feet could have landed on a boulder or in a small crater. In Apollo 14 the landing profile was adjusted to be more steep, and the astronauts reported little difficulty in seeing the landing site. However, this may have been due in part to the Apollo 14 landing site being intrinsically less dusty, because Apollo 15 and Apollo 16 also used the steeper landing profile, and both reported difficulties seeing the landing site in the critical last seconds. Apollo 17 experienced some vision obscuration in the landing of the LM, but they were able to see boulders and craters through the blowing dust all the way to touch down. The Apollo experience reveals that the extent that vision obscuration as a problem on landing is dependent on the amount of loose dust in the specific landing zone. The record has far fewer references to dust-related problems in Apollo 14 and 17, where there was little obscuration on landing, than in those of the other missions. Thus, it will probably remain a variable as long as spacecraft are landing in unexplored territory. Since vision obscuration is dependent on the depth of loose dust in a particular area, crews may use this as an indicator of how much difficulty they can expect to have with dust during EVA activities. A related observation is the discoloration of the Surveyor III spacecraft reported by the Apollo 12 crew. Apollo 12 landed about 163 m from Surveyor III with the intent of determining the degradation experienced by the spacecraft after being in the lunar environment for 31 months. The crew expected to find a white spacecraft, but found instead that is was a brown color. Further investigation revealed that the brown color could be wiped off, and was in fact a fine coating of dust. The source of the dust coating was later determined to be largely from the dust kicked up when the LM landed. In addition to vision obscuration on landing, the dust caused minor problems with photography. The Apollo 15 crew reported problems with a halo effect on the television camera transmission. This was remedied by brushing the dust off of the lens. False Instrument Readings In Apollo 12 the landing velocity trackers gave false readings when they locked onto moving dust and debris during descent. The Apollo 15 crew also noted that landing radar outputs were affected at an altitude of about 30 ft by moving dust and debris. But the Apollo 17 crew reported no lock-up onto moving dust or debris near the lunar surface. This again points out the differences in the amount of dust at the different landing sites, with it being high at the Apollo 12 and 15 sites, and low at the Apollo 17 site. 1When volatile surface films are removed from the surfaces of small particles, the result is stronger electrostatic and Van der Waals forces between the particles. NASA/TM—2005-213610/REV1 4 Dust Coating and Contamination Dust was found to quickly and effectively coat all surfaces it came into contact with, including boots, gloves, suit legs and hand tools. Consequences included the Apollo 11 astronauts repeatedly tripping over the dust covered TV cable, and a contrast chart on Apollo 12 becoming unusable after being dropped in the dust. This was particularly troublesome on Apollo 16 and 17 when rear fender extensions were knocked off of the LRV and dust “rooster tailed” and showered down on top of the astronauts. Dust coating is the precursor to other problems such as clogging of mechanisms, seal failures, abrasion, and the compromising of thermal control surfaces. In addition, valuable astronaut time was spent in ordinary housekeeping chores like brushing off and wiping down equipment—which often proved ineffective. Loss of Traction Neil Armstrong reported material adhering to his boot soles caused some tendency to slip on the ladder during ingress back to the LM. However, this slipperiness was not reported by any of the other crew members, and there are specific references in the Apollo 12 record that this was not a problem for them. It became standard practice for the astronauts to kick the excess dust off of their boots on the ladder before they re-entered the LM in an attempt to keep as much dust as possible out of the spacecraft, and it is likely that this measure was enough to keep slipping from happening. Although there was concern about the surface being slippery, there are no incidences in the mission record of falling due to slips, though some of the astronauts tripped and fell. In the Apollo experience, loss of foot traction was not a major concern, as long as simple precautions and care were used. Clogging of Mechanisms There were reports of equipment being clogged and mechanisms jammed in every Apollo mission. These included the equipment conveyor, lock buttons, camera equipment, and even the vacuum cleaner designed to clean off the dust. Dust made Velcro (Velcro Industries B.V.) fasteners inoperable, and was a particular problem with some LRV indicator mechanisms. The dust also clogged EMU mechanisms including zippers, wrist and hose locks, faceplates, and sunshades. This was particularly troublesome on Apollos 16 and 17 when fender extensions were knocked off of the LRV and showered dust down on top of the astronauts. The most alarming characteristic was how quickly and irreversibly this could happen. One short ride on the LRV with a missing fender extension, or standing where the equipment conveyor dumped dust on the EMU and difficulties began immediately. With Apollo EMU and equipment designs there was very little room for error. All of the astronauts experienced this to some degree, even those with the shortest stays on the surface. Several remarked that they could not have sustained surface activity much longer or clogged joints would have frozen up completely. Abrasion Lunar dust also proved to be particularly abrasive. Pete Conrad noted that the suits were more worn after 8 hr of surface activity that their training suits were after 100 hr and further reported that their EMU were worn through the outer layer and into the Mylar (DuPont) multi-layer insulation above the boot. Gauge dials were so scratched up during the Apollo 16 mission as to be unreadable. Harrison Schmitt’s sun shade on his face plate was so scratched that he could not see out in certain directions. Clearly, if the mission time is to be extended to fourteen days in Spiral 2, these abrasion problems must be solved. NASA/TM—2005-213610/REV1 5 Thermal Control Problems (ref. 9) An insulating layer of dust on radiator surfaces could not be removed and caused serious thermal control problems. On Apollo 12, temperatures measured at five different locations in the magnetometer were approximately 68 °F higher than expected because of lunar dust on the thermal control surfaces. Similarly, on Apollo 16 and 17 the LRV batteries exceeded operational temperature limits because of dust accumulation and the inability to effectively brush off the dust. John Young remarked that he regretted the amount of time spent during Apollo 16 trying to brush the dust off of the batteries—an effort that was largely ineffective. (This was contrary to ground-based tests which indicated that dusting the radiator surfaces would be highly effective.) This led him to recently remark that “Dust is the number one concern in returning to the moon.” In addition to difficulties with communications equipment and TV cameras, some of the instruments on both Apollo 16 and 17 had their performance degraded by overheating due to dust interfering with radiators. Seal Failures The ability of the EMU to be resealed after EVA was also compromised by dust on the suit seals. The Apollo 12 astronauts experienced higher than normal suit pressure decay due to dust in fittings. Pete Conrad’s suit, which was tight before the first EVA, developed a leak rate of 0.15 psi/min after it, and rose to 0.25 psi/min after the second EVA. Since the safety limit was set at 0.30 psi/min, it is doubtful whether a third EVA could have been performed, had it been scheduled. Another indicator is that all of the environmental sample and gas sample seals failed because of dust. By the time they reached earth the samples were so contaminated as to be worthless. This does not bode well for a long duration habitat where several astronauts will be passing through air locks and unsealing and resealing their EMU routinely. More attention must be directed at ways either to keep dust off of the seals, or to make more dust tolerant seals. Inhalation and Irritation Perhaps the most alarming possibility is the compromising of astronaut health by irritation and inhalation of lunar dust. The Apollo crews reported that the dust gave off a distinctive, pungent odor, (David Scott suggested it smelled a bit like gun powder) suggesting that there are reactive volatiles on the surface of the dust particles. Dust found its way into even the smallest openings, and when the Apollo 12 crew stripped off their clothes on the way back to earth, they found that they were covered with it. Dust was also transferred to the Command Module during Apollo 12 and was an eye and lung irritant during the entire trip back. Given the toxicity of particle sizes less than about 5 μm, this points out the need to monitor the concentrations of dust particles within the EMU, the airlock, the habitat, and the spacecraft. Later Apollo missions were more cognizant of the problem, and dust management strategies such as venting to space and using water to wash down the LM proved to be somewhat effective. But this experience points out that vigilant housekeeping will be required, and as crew sizes and mission durations increase, this will become more of a challenge. EMU Modifications for Dust Abatement (ref. 10) The principle concern early on was abrasion caused by sharp rocks. The “super beta cloth” outer covering was not very abrasion resistant, so Chromel-R was woven into the lunar boots and gloves, which NASA/TM—2005-213610/REV1 6