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The purpose of the 1997 NASA Microgravity Technology Report is to update the Microgravity Research Program's technology development policy and to present and assess current technology related activities and requirements identified within its research and technology disciplines.
Calcium loss and muscle atrophy are two of the main metabolic changes experienced by astronauts and crew members during exposure to microgravity in space. For long-term exposure to space it is crucial to understand the underlying mechanisms for altered physiological functions. Fundamental occurrences in cell biology which are likely to depend on gravity include cytoskeletal dynamics, chromatin and centrosome cycling, and ion immobilization. These events can be studied during fertilization and embryogenesis within invertebrate systems. We have chosen the sea urchin system to study the effects of microgravity on cytoskeletal processes and calcium metabolism during fertilization, cell division, development, and embryogenesis. Experiments during an aircraft parabolic flight (KC-135) demonstrated: (1) the viability of sea urchin eggs prior to fertilization, (2) the suitability of our specimen containment system, (3) the feasibility of fertilization in a reduced gravity environment (which was achieved during 25 seconds of reduced gravity under parabolic flight conditions). Two newly developed pieces of spaceflight hardware made further investigations possible on a spaceflight (STS-77); (1) the Aquatic Research Facility (ARF), and (2) the Fertilization Syringe Unit (FSU). The Canadian Space Agency developed ARF to conduct aquatic spaceflight experiments requiring controlled conditions of temperature, humidity, illumination, and fixation at predetermined time points. It contained a control centrifuge which simulated the 1 g environment of earth during spaceflight. The FSU was developed at the Kennedy Space Center (KSC) by the Bionetics Corporation specifically to enable the crew to perform sea urchin fertilization operations in space.
Fires still remain as one of the most important safety risks in manned spacecraft. This problem will become even more important in long endurance non orbital flights in which maintenance will be non existing or very difficult. The basic process of a fire is the combustion of a solid at microgravity conditions in O2/N2 mixtures. Although a large number of research programs have been carried out on this problem, especially on flame spreading, several aspects of these processes are not yet well understood. It may be mentioned, for example, the temperature and characteristic of low emissivity flames in the visual range that take place in some conditions at microgravity; and there exists a lack of knowledge on the influence of key parameters, such as convective flow velocities of the order of magnitude of typical oxygen diffusion velocities. The "Departamento de Motopropulsion y Termofluidodinamica" of the "Universidad Politecnica de Madrid, Escuela Tecnica Superior de Ingenieros Aeronauticos" is conducting a research program on the combustion of solids at reduced gravity conditions within O2/N2 mixtures. The material utilized has been polymethylmethacrylate (PMMA) in the form of rectangular slabs and hollow cylinders. The main parameters of the process have been small convective flow velocities (including velocity angle with the direction of the spreading flame) and oxygen concentration. Some results have also been obtained on the influence of material thickness and gas pressure.
The use of water mists (very fine water sprays) for fire suppression is currently receiving increased attention as a replacement technology for halogen-based chemical agents-such as Halon 1301 (CF3Br)--the manufacturing of which has been banned by the Montreal Protocol due to their high ozone depletion potential. Water mist technology has been found effective for a wide range of applications such as Class B pool fires, shipboard machinery, aircraft cabins, computers, and electronic equipment. There are five distinct mechanisms by which water droplets may interact with a flame. First, the high enthalpy of vaporization of water (2450 kJ/kg) leads to heat removal from the flame front as the liquid droplets turn to steam. Second, as water vaporizes its volume increases approximately three orders of magnitude, which leads to the dilution of the oxygen and vaporized fuel required to maintain the flame. The third effect is the recombination of H-atoms and other radicals on the droplet surface. A fourth effect of water mists in fires is the retardation of surface propagation rates due to the wetting of walls and surfaces. The last potential impact of fine water mists affects the radiative propagation of the fire by forming an optically thick barrier to infrared radiation which prevents ignition of the unburned regions. Unfortunately, little fundamental information exists on the interaction of a flame with a water mist. To date, there is no widely accepted interpretation of the critical concentration of droplets required to suppress a flame or of the fundamental mechanisms involved in flame extinguishment by water mists. One of the main obstacles to obtaining such understanding is the difficulty of providing a simple, well-defined experimental setup for the flame front/water mist interaction. Some of the difficulty stems from the problem of generating, distributing and maintaining a homogeneous concentration of droplets throughout a chamber while gravity depletes the concentration and alters the droplet size by coalescence and agglomeration mechanisms. Experiments conducted in the absence of gravity provide an ideal environment to study the interaction of water mists and flames by eliminating these distorting effects. In addition, microgravity eliminates the complex flow patterns induced between the flame front and the water droplets. The long duration and quality of microgravity in space flights provide the required conditions to perform the setup and monitoring of flame suppression experiments. Consequently, a series of experiments have been identified to be performed on the Combustion Module (CM-2) in the Space Shuttle. These consist of measuring the extinguishing capability of a water mist on a premixed flame propagating along a tube. These experiments should provide the necessary data to obtain further understanding of the water mist suppression phenomena that can be later used to design and manufacture appropriate fire suppression systems. In preparation for the orbital flights, experiments have been conducted on low-gravity ground facilities to obtain the preliminary data necessary to define the scientific objectives and technical issues of the spacecraft experiments.
Many thermoplastic materials in common use for a wide range of applications, including spacecraft, develop bubbles internally as they burn due to chemical reactions taking place within the bulk. These bubbles grow and migrate until they burst at the surface, forceably ejecting volatile gases and, occasionally, molten fuel. In experiments in normal gravity, Kashiwagi and Ohlemiller observed vapor jets extending a few centimeters from the surface of a radiatively heated polymethylmethacrylate (PMMA) sample, with some molten material ejected into the gas phase. These physical phenomena complicated the combustion process considerably. In addition to the non-steady release of volatiles, the depth of the surface layer affected by oxygen was increased, attributed to the roughening of the surface by bursting events. The ejection of burning droplets in random directions presents a potential fire hazard unique to microgravity. In microgravity combustion experiments on nylon Velcro fasteners and on polyethylene wire insulation, the presence of bursting fuel vapor bubbles was associated with the ejection of small particles of molten fuel as well as pulsations of the flame. For the nylon fasteners, particle velocities were higher than 30 cm/sec. The droplets burned robustly until all fuel was consumed, demonstrating the potential for the spread of fire in random directions over an extended distance. The sequence of events for a bursting bubble has been photographed by Newitt et al.. As the bubble reaches the fluid surface, the outer surface forms a dome while the internal bubble pressure maintains a depression at the inner interface. Liquid drains from the dome until it breaks into a cloud of droplets on the order of a few microns in size. The bubble gases are released rapidly, generating vortices in the quiescent surroundings and transporting the tiny droplets. The depression left by the escaping gases collapses into a central jet, which rises with a high velocity and may break up, releasing one or more relatively large drops (on the order of a millimeter in these experiments). A better understanding of bubble development and bursting processes, the effects of bursting behavior on burning rate of the bulk material, and the circumstances under which large droplets are expelled, as well as their trajectories, sizes, and burning rates, is sought through computer modeling compared with experiment.
A unique flame-vortex interaction experiment is being operated in microgravity in order to obtain fundamental data to assess the Theory of Flame Stretch which will be used to improve models of turbulent combustion. The experiment provides visual images of the physical process by which an individual eddy in a turbulent flow increases the flame surface area, changes the local flame propagation speed, and can extinguish the reaction. The high quality microgravity images provide benchmark data that are free from buoyancy effects. Results are used to assess Direct Numerical Simulations of Dr. K. Kailasanath at NRL, which were run for the same conditions.
Ground based (normal gravity) combustion studies can provide important information on the processes by which monopropellants and composite systems burn. The effects of gravitational forces, however, can often complicate the interpretation of the models and the implementation of experiments designed to help elucidate complex issues. We propose to utilize a combined computational/experimental approach in a microgravity environment to understand the interaction of oxidizer-binder diffusion flames in composite propellants. By operating under microgravity conditions we will be able to increase the length scales and suppress the gravitational forces on melting binders such that increased resolution of both major and minor species will be possible thus reducing the demands placed on both the computational and diagnostic tools. Results of a detailed transport/finite rate chemistry model will be compared with nonintrusive optical diagnostic measurements of the structure and extinction of diffusion flames in which oxidizers such as ammonium perchlorate (AP) and ammonium dinitramide (ADN) are counterflowed against realistic binders such as hydroxyl-terminated polybutadiene (HTPB) and 3,3-bis(azidomethyl)oxetane (BAMO). The work proposed herein represents a collaborative effort among the research groups at Yale University, Princeton University and the Combustion Diagnostics Laboratory at the Naval Air Warfare Center in China Lake, CA.
The growth of protein crystals suitable for X-ray crystal structure analysis is an important topic. The methods of protein crystal growth are under increasing study whereby different methods are being compared via diagnostic monitoring including Charge Coupled Device (CCD) video and interferometry. The quality (perfection) of protein crystals is now being evaluated by mosaicity analysis (rocking curves) and X-ray topographic images as well as the diffraction resolution limit and overall data quality. Choice of a liquid-liquid linear crystal growth geometry and microgravity can yield a spatial stability of growing crystals and fluid, as seen in protein crystallization experiments on the unmanned platform EURICA. A review is given here of existing results and experience over several microgravity missions. The results include CCD video as well as interferometry during the mission, followed, on return to earth, by rocking curve experiments and full X-ray data collection on LMS and earth control lysozyme crystals. Diffraction data recorded from LMS and ground control apocrustacyanin C(sub 1) crystals are also described.
The use of the microgravity environment of space to expand scientific knowledge and to enable the commercial development of space for enhancing the quality of life on Earth is particularly suitable to the field of combustion. This document reviews the current status of microgravity combustion research and derived information. It is the fourth in a series of timely surveys, all published as NASA Technical Memoranda, and it covers largely the period from 1995 to early 1999. The scope of the review covers three program areas: fundamental studies, applications to fire safety and other fields. and general measurements and diagnostics. The document also describes the opportunities for Principal Investigator participation through the NASA Research Announcement program and the NASA Glenn Research Center low-gravity facilities available to researchers.
Microgravity science studies the influences of gravity on phenomena in fluids, materials processes, combustion, and human cell growth in the low acceleration environment of space flight. During the last decade, the accomplishment of the flight research in the field has evolved into an effective cooperation between the flight crew in the Shuttle and the ground-based investigator using real-time communication via voice and video links. This team structure has led to interactive operations in which the crew performs the experimentation while guided, as necessary, by the science investigator who formulated the investigation and who will subsequently interpret and analyze the data. One of the primary challenges to implementing this interactive research has been the necessity of structuring a means of handling fluids, gases, and hazardous materials in a manned laboratory that exhibits the novelty of weightlessness. Developing clever means of designing experiments in closed vessels is part of the solution- but the space flight requirement for one and two failure-tolerant containment systems leads to serious complications in the physical handling of sample materials. In response to the conflict between the clear advantage of human operation and judgment, versus the necessity to isolate the experiment from the crewmember and the spacecraft environment, the Microgravity Research Program has initiated a series of Gloveboxes in the various manned experiment carriers. These units provide a sealed containment vessel whose interior is under a negative pressure with respect to the ambient environment but is accessible to a crewmember through the glove ports.
The viscosity of a liquid metal was successfully measured for the first time by a containerless method, the oscillating drop technique. This method also provides a means to obtain a precise, non-contact measurement of the surface tension of the droplet. This technique involves exciting the surface of the molten sample and then measuring the resulting oscillations; the natural frequency of the oscillating sample is determined by its surface tension, and the damping of the oscillations by the viscosity. These measurements were performed in TEMPUS, a microgravity electromagnetic levitator (EML), on the Space Shuttle as a part of the First Microgravity Science Laboratory (MSL-1), which flew in April and July 1997 (STS-83 and STS-94). Some results of the surface tension and viscosity measurements are presented for Pd82Si18. Some observations of the fluid dynamic characteristics (dominant flow patterns, turbulent transition, cavitation, etc.) of levitated droplets are presented and discussed together with magnetohydrodynamic calculations, which were performed to justify these findings.
alpha-Crustacyanin, the lobster carapace astaxanthin-protein, was crystallized using the European Space Agency's (ESA) automated Protein Crystallization Facility (PCF) which flew onboard the unmanned EUropean REtrievable CArrier (EURECA). A free interface linear, liquid - liquid diffusion, method was used. Crystals grew larger and thicker in the microgravity case compared to the biggest crystals grown on earth. Video observation on EURECA revealed variations in crystal sizes through-out the reactor neatly correlated with depletion of this coloured protein from the solution. The video observations most importantly revealed no visible movement of crystals over the initial 7 weeks of the experiment, although an obvious temperature induced jump occurred at that time in a mission spanning 11 months. An important observation from this mission, over the first 7 weeks, of completely stationary crystal growth contrasts with crystal motions viewed on manned microgravity missions, even using linear liquid - liquid geometries, and much shorter flights (eg. 12 to 16 days).
Materials Science research programs are funded by NASA through the Microgravity Research Division. Such programs are normally designated as flight definition or ground based and can be awarded initially for up to four years. Selection is through a peer review process in response to a biennial NASA Research Announcement (NRA). The next announcement is due in November 1998 with proposals due in March 1999. Topics of special interest to NASA are described in the guidelines for proposal writing within the NRA. NASA's interest in materials is wide and covers a range which includes metals and alloys, ceramics, glasses, polymers, non-linear optics, aerogels and nanostructures. With increasing interest in the Human Exploration and Development of Space (HEDS) program, the materials research funded will not be exclusively devoted to processes dependent on microgravity, but will also support materials of strategic interest in meeting NASA's long range plans of interplanetary travel.
Numerical modeling was undertaken to analyze the influence of radial thermal gradient on solid/liquid interface shape and convection patterns during solidification of pure Al and Al-4 wt. % Cu alloy. Steady state calculations were performed for different gravity levels and orientations. Furthermore, transient modeling was undertaken to investigate effect of the solidification velocity. The furnace configuration used in this analysis is the proposed International Space Station Furnace. Results from a thermal model of the furnace core were used as initial boundary conditions for solidification modeling. The Solidification model was adopted from previous work and was based on the finite element code FIDAP. Thermocouple data and quenched interface shape from a pure Al sample flown on the Life Sciences and Microgravity Spacelab (LMS) mission, July 1996 was used for model validation. Good agreement was obtained between the predicted interface shape and that measured from the quenched LMS sample. It was found that the imposed temperature boundary condition must be sufficiently smooth for the heat fluxes in the model to be self-consistent. The model predicted that alloy sample Al-Cu is more sensitive to variations in the gravity level compared to pure Al. For Al-Cu alloy, solute diffusivity is approximately 10(exp 4) times smaller than thermal diffusivity of pure Al. Hence, in a microgravity environment the weak convection has no measurable effect on the heat fluxes, but is still strong enough to affect concentration distribution. Since the alloy melting temperature is determined by concentration the interface shape depends on the level of convection. This was found not to be the case for pure metal.
This document reports the one year science results for the Fourth United States Microgravity Payload (USMP-4). The USMP-4 major experiments were on a support structure in the Space Shuttle's payload bay and operated almost completely by the Principal Investigators through telescience. The mission included a Glovebox where the crew performed additional experiments for the investigators. Together about eight major scientific experiments were performed, advancing the state of knowledge in fields such as low temperature physics, solidification, and combustion. The results demonstrate the range of quality science that can be conducted utilizing orbital laboratories in microgravity and provide a look forward to a highly productive Space Station era.
Ten pregnant Sprague Dawley rat dams were exposed to spaceflight aboard the Space Shuttle (STS-70) for gestational days 11-20 (G 11-20; FILT group). Control dams were maintained in either a flight-like (FIDS group) or vivarium cage environment (VIV group) on earth. All dams had ad lib access to food and water and were exposed to a light-dark cycle consisting of 12 hours of light (- 30 lux) followed by 12 hours of darkness. The dams were closely monitored from G 22 until parturition. All pups were cross-fostered at birth; each foster dam had a litter of 10 pups. Pups remained with their foster dam until post-natal day 21 (PN 21). Pup body mass was measured twice weekly. At PN14 FILT pups had a smaller body mass than did the VIV pups (p < 0.01). Circadian rhythms of body temperature and activity of pups from two FILT dams (n = 8), two FIDS dams (n = 9) and two VIV dams (n = 7) were studied starting from age PN 21. All pups had circadian rhythms of temperature and activity at this age. There were no significant differences in rhythms between groups that could be attributed to microgravity exposure. We also examined the development of neural structures involved in circadian rhythmicity: the retina, the intergeniculate leaflet (IGL) and the circadian pacemaker, the suprachiasmatic nucleus (SCN). There were small differences between the flight and control groups at very early stages of development (G 20 and PN3) which indicated that the development of both the SCN and the IGL. These results indicate that exposure to the microgravity environment of spaceflight during this embryonic development period does not affect the development of the circadian rhythms of body temperature and activity, but may affect the early development of the neural structures involved in circadian timing.
The paper reviews historical aspects of solidification processing and the detrimental attributes associated with gravity-driven flow phenomena. Benefits of and avenues toward conducting experiments in a microgravity environment are presented and illustrated with relevant examples. Finally, some comments regarding the role of microgravity experimentation are given.
Exercise in microgravity is one of the most promising countermeasures to the dual problems of space flight-induced bone loss and muscle atrophy. Although exercise in microgravity has been studied extensively from a metabolic standpoint, little research has focused on the efficacy of different forms of exercise for maintaining musculoskeletal integrity. Exercise protocols have not been effective in preventing muscle atrophy and bone loss during space flight, especially in the lower extremities. In 1-G, however, animal experiments have clearly indicated that: (1) certain bone strains and strain rates do stimulate bone deposition, and (2) repetitive loading of the lower extremity can increase osteonal bone formation even as proximally as the vertebral column. Such studies have also indicated that a relatively small number of appropriate loading cycles may lead to bone deposition. This suggests that an optimal exercise regimen might be able to maintain bone and muscle integrity during space flight. Since there is evidence that the bones and muscles of the lower limbs are particularly affected by space flight, the present study addressed two major aims: (1) quantify externally applied impact loads and rates of loading under the feet during tethered jumping exercises, and (2) determine the amount of eccentric and concentric whole-muscle activity during these jumping exercises in true and in simulated zero-gravity.