Space Station lubrication considerations

Future activities in space will require the use of large structures and high power availability in order to fully exploit opportunities in Earth and stellar observations, space manufacturing and the development of optimum space transportation vehicles. Although these large systems will have increased capabilities, the associated development costs will be high, and will dictate long life with minimum maintenance. The Space Station provides a concrete example of such a system; it is approximately one hundred meters in major dimensions and has a life requirement of thirty years. Numerous mechanical components will be associated with these systems, a portion of which will be exposed to the space environment. If the long life and low maintenance goals are to be satisfied, lubricants and lubrication concepts will have to be carefully selected. Current lubrication practices are reviewed with the intent of determining acceptability for the long life requirements. The effects of exposure of lubricants and lubricant binders to the space environment are generally discussed. Potential interaction of MoS2 with atomic oxygen, a component of the low Earth orbit environment, appears to be significant

Atomic oxygen

The effects of atomic oxygen (AO) on materials in aerospace environments are examined. Materials are categorized according to their susceptibility to AO. The degradation effects of AO are examined to determine which materials are most vulnerable. Classes of spacecraft materials are listed and correlated with a performance category. The spacecraft orbits sensitive to AO interactions are also listed. Correlations are presented of AO effects on materials and of spacecraft glow effects

Material interactions with the Low Earth Orbital (LEO) environment: Accurate reaction rate measurements

To resolve uncertainties in estimated LEO atomic oxygen fluence and provide reaction product composition data for comparison to data obtained in ground-based simulation laboratories, a flight experiment has been proposed for the space shuttle which utilizes an ion-neutral mass spectrometer to obtain in-situ ambient density measurements and identify reaction products from modeled polymers exposed to the atomic oxygen environment. An overview of this experiment is presented and the methodology of calibrating the flight mass spectrometer in a neutral beam facility prior to its use on the space shuttle is established. The experiment, designated EOIM-3 (Evaluation of Oxygen Interactions with Materials, third series), will provide a reliable materials interaction data base for future spacecraft design and will furnish insight into the basic chemical mechanisms leading to atomic oxygen interactions with surfaces

Working group written presentation: Atomic oxygen

Earlier Shuttle flight experiments have shown NASA and SDIO spacecraft designed for operation in low-Earth orbit (LEO) must take into consideration the highly oxidative characteristics of the ambient flight environment. Materials most adversely affected by atomic oxygen interactions include organic films, advanced (carbon-based) composites, thermal control coatings, organic-based paints, optical coatings, and thermal control blankets commonly used in spacecraft applications. Earlier results of NASA flight experiments have shown prolonged exposure of sensitive spacecraft materials to the LEO environment will result in degraded systems performance or, more importantly, lead to requirements for excessive on-orbit maintenance, with both conditions contributing significantly to increased mission costs and reduced mission objectives. Flight data obtained from previous Space Shuttle missions and results of the Solar Max recovery mission are limited in terms of atomic oxygen exposure and accuracy of fluence estimates. The results of laboratory studies to investigate the long-term (15 to 30 yrs) effects of AO exposure on spacecraft surfaces are only recently available, and qualitative correlations of laboratory results with flight results have been obtained for only a limited number of materials. The working group recommended the most promising ground-based laboratories now under development be made operational as soon as possible to study the full-life effects of atomic oxygen exposure on spacecraft systems

Tilt

In poker, everybody loses sooner or later. Sometimes it’s just a few hands, and sometimes you lose for the whole night (or longer). Sometimes the losses are your own fault, and sometimes you can play perfectly and still go broke. The point is that losing is part of the game. No one is immune from it, and even the most skilled players cannot avoid it. In the long run, of course, there is no luck in poker, and the best players will eventually win. But as the card player and poet A. Alvarez explained, there is plenty of luck, both good and bad, in the short run, and “the short run is longer than most people know.” Managing losses, therefore, is one of the most important parts of the game. It is essential to keep them in perspective and, most of all, to prevent bad beats from influencing the way you play the next hand. It may seem counterintuitive, and it is certainly counterproductive, but there is a nearly universal tendency to play loosely in a misguided attempt to “get even” following a series of losses. Card players call it “going on tilt” or “steaming,” and journalist Andy Bellin describes it like this: “After losing a big hand, a player bets and raises with garbage because he is steamed over the last game. Then he loses more, and a cycle begins. Once you tilt, there’s almost no hope for recovery.” If anything, lawyers are even more susceptible to steaming when things go wrong and more likely to rationalize bad behavior. Losing your temper in negotiation, berating a judge for a bad ruling, snarling at a surprisingly unhelpful witness—these are all examples of going on tilt, turning a momentary disadvantage into a potential debacle. Needless to say, most decent lawyers understand the need to maintain their composure, especially in court. Nonetheless, even the calmest among us will occasionally snap, and the less disciplined will throw outright tantrums, later rationalized (though never excused) with the self-justification that “it had to be said.” Well, it almost certainly did not have to be said, especially if it was disrespectful, rude, crude, loud, or inconsiderate. Loutish outbursts might feel good (just like betting heavily on rag hands), but they almost never accomplish anything positive. But all of that is obvious. No one (well, almost no one) thinks it useful for lawyers to lose their tempers or behave badly. But there is also a more subtle lesson to be learned about steaming. Serious mistakes are more likely to happen when things are going wrong. Judgment becomes clouded when frustration sets in, and foolish temptations seem somehow irresistible

On Some Recent Applications of the Coanda Effect

Over the last quarter century or so, the Coanda principle has become increasingly used in a wide variety of applications, including industrial, medical, maritime technology, and aerodynamics. In addition, its effect has been increasingly observed in the natural world. Devices employing this principle usually offer substantial flow deflection, and enhanced turbulence levels and entrainment compared with conventional jet flows. However, these prospective advantages are generally accompanied by other significant disadvantages such as jet flow detachment, and a considerable increase in associated noise levels. Much of the time, the reasons for this are not well understood. Consequently, in many cases, the full potential offered by the Coanda effect is yet to be completely realized. This paper discusses a variety of recent applications of the principle and describes attempts to understand some of the difficulties associated with it, particularly those related to increased acoustic radiation

On Some Recent Experimental Results Concerning Turbulent Coanda Wall Jets

The Coanda effect is the tendency of a stream of fluid to stay attached to a convex surface, rather than follow a straight line in its original direction. As a result, in such jets mixing takes place between the jet and the ambient air as soon as the jet issues from its exit nozzle, causing air to be entrained. This air-jet mixture adheres to the nearby surface. Whilst devices employing the Coanda effect usually offer substantial flow deflection, and enhanced turbulence levels and entrainment compared with conventional jet flows, these prospective advantages are generally accompanied by significant disadvantages including a considerable increase in associated noise levels and jet breakaway. Generally, the reasons for these issues are not well understood and thus the full potential offered by the Coanda effect is yet to be realized. The development of a model for predicting the noise emitted by three-dimensional flows over Coanda surfaces would suggest ways in which this noise could be reduced or attenuated. In this paper, the results of recent modelling and experiments on a 3-D turbulent Coanda wall jet are presented. They include the relationship of SPL, shock cell distribution and breakaway to various flow parameters, and predictions of the jet boundary. The potential application of these results to important problems of practical interest such as launch noise is also discussed, and recent data pertaining to rocket launch noise sources is presented

Slip events and dilatancy in a sheared fine noncohesive powder

International audienceWe present experimental results of the transition from steady-state sliding to oscillatory motion for a fine noncohesive powder, sheared in an annular cell. The onset of instability is compared to the Dieterich-Ruina model for solid friction. We present data showing that at low velocity and close to the transition, the major sliding jumps are preceded by a short or long period of unstable plastic yielding of the granular matter. This ambivalent behavior suggests that the jumps are initiated when the sliding overcomes a critical velocity. During the stick-slip motion, the dilatancy of the powder bed has been also observed: the slippage is associated with a compaction whose value increases with the jump in the friction coefficient