Spacelab Mission D2 Research Articles

Floating-zone growth of GaAs

Te-doped and undoped GaAs single crystals of 6–7 mm diameter and up to 20 mm length have been grown by the floating-zone method. In addition, a Te-doped GaAs single crystal of 20 mm diameter and 20 mm length was successfully grown during the 2nd German Spacelab mission D2. It could be shown that growth rates up to 240 mm/h are possible without losing single crystallinity. Dopant striations due to Marangoni convection have been found, as well as a reduction of the etch pit density compared with that of the starting material.

Long‐term Crystal Growth under Microgravity during the EURECA‐1 Mission (II) THM Growth of Sulphur‐doped InP

AbstractLong‐term crystal growth experiments were successfully performed under microgravity conditions during the first flight of the unmanned EURECA‐1 mission in the automatic mirror furnace (AMF). Two crystals of sulphur‐doped InP with [001] and [111] orientation respectively were grown from indium solution by the travelling heater method (THM). The absence of time dependent buoyancy‐driven convection is documented by the lack of type I striations in the space‐grown crystals. The sulphur concentration is measured by spatially resolved photoluminescence. As expected, the macrosegregation can be described by a pure diffusion‐controlled model which is in good agreement with the findings from the first German spacelab mission D1. Compared to the earth‐grown reference samples, both of the space‐grown InP crystals show strong disturbances such as inclusions and type II striations. The morphological instabilities are similar to growth disturbances already known from the space‐grown MD‐ELI‐01 from the D1 mission.

Microgravity and hypergravity effects on collagen biosynthesis of human dermal fibroblasts.

Astronauts experiencing long periods of space flight suffer from severe loss of bone tissue, particularly in those bones that carry the body weight under normal gravity. It is assumed that the lack of mechanical load decreases connective tissue biosynthesis in bone-forming cells. To test this assumption, quantitative and qualitative aspects of collagen synthesis under microgravity, normal gravity, and hypergravity conditions were investigated by incubating human fibroblast cultures with [3H]-proline for 4, 7, 10, and 20 h during the Spacelab D2-mission in 1993. Quantitative analysis revealed an increase of collagen synthesis under microgravity conditions, being up to 143% higher than in 1 g controls. In contrast, hypergravity samples showed a decrease in collagen synthesis with increasing g, being at the 13% level at 10 g. The relative proportion of collagen in total synthesized protein showed a slight decrease with increasing g. The secretion of collagen by the cells, proline hydroxylation of individual collagen alpha-chains, and the relative proportions of synthesized collagens I, III, and V were not affected under any of the applied conditions.

The process of heat and mass transport at the critical point of pure fluids

The effects of fast isentropic temperature propagation, called the “piston effect,” or “critical speeding up,” and slow mass diffusion, called “critical slowing down,” are investigated. A temperature propagation experiment in a spherical cell filled with pure SF6 at critical density was performed during the Second German Spacelab Mission D2 in 1993. The results evidently confirm the presence of the piston effect both in the one-phase region and in the two-phase region. The numerical simulations are in remarkable good quantitative agreement with the experimental results.

Measurements of the isochoric heatc v at the critical point of SF6 under microgravity: Results of the German Spacelab Mission D2

During the Second German Spacelab Mission D2 (April 26 to May 6, 1993) the isochoric specific heatcv of SF6 was measured along the critical isochore under microgravity conditions with a newly developed scanning radiation calorimeter. This calorimeter provided the possibility to perform comparable heating and cooling runs with variable ramp rates since the spherical sample cell was heated and cooled only by radiation. During the experimental time of 220 h, 11 heating and cooling runs with different ramp rates were performed in a temperature range ofT–Tc=±6 K. ApproachingTc by cooling from the homogeneous one-phase region avoided significant temperature and density gradients in the fluid, which would have distorted the integral measurement ofcv. The inhomogenities introduced by a finite ramp rate were greatly reduced by the fast dynamic temperature propagation (“critical speeding up”). Thecv data achieved with slow cooling runs are in remarkably good agreement with the theoretical prediction more than one order of magnitude closer to the critical point than anycv measurements done so far. The preliminary value for the critical exponentα is 0.107±0.02, and for the amplitude ratio we obtainedA−/A+=1.94±0.07. In contrast to the cooling runs, the heating runs showed a strong hysteresis ofcv. A comparison to 1g measurements is provided.

Role of the astronaut in operating the Advanced Fluid Physics Module

The role of man in space is investigated in the operation of the Advanced Fluid Physics Module (AFPM), a scientific instrument dedicated to fluid physics research in a microgravity environment and flown on the Spacelab D2 mission. The astronaut involvement is addressed by applying the criteria of the THURIS study, conducted by NASA for the optimization of future manned space flights. Outcomes of the THURIS study are first summarized. The AFPM characteristics and interfaces are briefly presented. The five experiments performed on board Spacelab D2 are introduced and the involvement of the astronaut is described. Finally, THURIS criteria are applied to an AFPM experiment scenario. Results show that, of all the activities involved in the AFPM nominal operation, two thirds are related to hardware manipulation and to procedure following, while the last third uses the unique astronaut intellectual capabilities, making his presence in orbit mandatory for successful experiment completion.

Measurements of the isochoric heat c v at the critical point of SF 6 under microgravity — Results of the German Spacelab Mission D2

During the Second German Spacelab Mission D2 (April 26 to May 6, 1993) the specific isochoric heat c v of SF 6 was measured along the critical isochore under microgravity conditions with a newly developed scanning radiation calorimeter. This calorimeter provided the possibility to perform comparable heating and cooling runs with variable ramp rates since the spherical sample cell was heated and cooled only by radiation. During the experimental time of 220 hours, 11 heating and cooling runs with different ramp rates were performed in a temperature range of T − T c = ±5 K. Approaching T c by cooling from the homogeneous 1-phase region avoided significant temperature and density gradients in the fluid, which would have distorted the integral measurement of c v. The inhomogenities introduced by a finite ramp rate were greatly reduced by the fast dynamic temperature propagation (“critical speeding up”). The c v data achieved with slow cooling runs are in remarkably good agreement with the theoretical prediction more than one order of magnitude closer to the critical point than any c v-measurements done so far. The preliminary value for the critical exponent α is 0.107 ±0.02 and for the amplitude ratio we obtained A − A + =1.94 ±0.07 .

MOMS-02/D2: First results and future applications

Abstract The Modular Opto-electronic Multi-spectral Stereo Scanner MOMS-02 experimental data acquired during the German Spacelab D2 mission will be used for a broad range of geoscientific objectives. The simultaneous acquisition of high spatial resolution, multi-spectral and stereo scenic data enables a real combination of thematic and topographic information, thus considerably improving the verification and interpretation of dynamic changes of the Earth's surface by means of remote sensing. This paper gives a first assessment of the MOMS-02/D2 mission, the data quality and an overview on the planned methodological and application-oriented investigations for various test sites. On the basis of a few examples the possibilities of this system for future thematic applications is shown.

Visual grasping with long delay time of a free floating object in orbit

In the US-German Spacelab mission D2 (April/May 1993) a new level of automation capabilities has been achieved with the ROTEX-‘freeflyer’-experiment of DLR. For the first time, a combined human/robotic task force on the ground succeeded in visually controlled tele-grasping of a free floating object on board the Space Shuttle Columbia within a working cell of the German Space-lab by a remotely controlled robot arm. The contributions of UniBwM in the fields of monocular motion-stereo vision, state prediction and fully automatic grasping under long delay times (5 to 7 seconds) are presented and discussed.The successful team jointly consisted of scientists from DLR and UniBwM for decision taking and remote manual control as well as a network of computers representing a robot specialist for visual motion interpretation and prediction including the expertise for delayed feedback, which is hard for humans.

Spaceborne autoranging infrared viewing system for thermal mapping of fluids in a microgravity condition

The European Space Research and Technology Centre (ESTEC) has developed a small, space qualified and TV compatible IR viewing system able to visualize thermal flows in fluids in microgravity. This instrument is a part of the diagnostics of a Spacelab facility, namely the Autonomous Fluid Physics Module (AFPM) flown on the last Spacelab D2 mission (April to May 1993). One of the main objectives of the research is to enable monitoring changes in the surface temperature of a fluid following the application of different stimuli. The only way to achieve this without disturbing the fluid under test is to use nonintrusive infrared measurement techniques. Starting from a basic commercial item, the Agema 870 scanner, ESTEC designed and built a thermal mapping diagnostic system provided with an autoranging capability that allows real-time temperature measurement in the range from 0 to 80°C and with a frame rate of 6 images/s. The geometrical resolution is 70 x 70 pixels in a field of view of 130 x 1 30 mm, which maps out the full temperature distribution of a typical fluid column experiment. An automatic compensation of the background noise at room temperature keeps the minimum resolvable temperature difference (MRTD) figure below 0.2°C. Therefore, the overall accuracy of the system allows one to follow the evolution of the complex phenomena related to the heat convection and mass transport effects at the surface of fluids in a weightlessness environment. The general design of the thermal mapping diagnostic (TMD) system is described and the technical solutions adopted to achieve the scientific goals of the investigation carried out with the AFPM are presented.

Floating‐zone growth of GaAs under microgravity during the D2‐mission

AbstractA Te‐doped GaAs (100) single crystal of 20 mm diameter and 20 mm length was successfully grown by the floating‐zone method during the 2nd German Spacelab mission D2. Dopant striations due to Marangoni convection as well as a reduction of the etch pit density compared to te starting material have been found. The last part of the crystal, grown with the quite high translation rate of 120 mm/h, showed no sign of unstable growth and exhibited properties similar to the parts grown with 3 and 6 mm/h.

Visual grasping with long delay time of a free floating object in orbit

In the US-German Spacelab mission D2 (April/May 1993) a new level of automation capabilities has been achieved with the ROTEX-‘freeflyer’-experiment of DLR. For the first time, a combined human/robotic task force on the ground succeeded in visually controlled tele-grasping of a free floating object on board the Space Shuttle Columbia within a working cell of the German Spacelab by a remotely controlled robot arm. The contributions of UniBwM in the fields of monocular motion-stereo vision, state prediction and fully automatic grasping under long delay times (5 to 7 seconds) are discussed in detail.

Characterization of the directionally solidified lamellar eutectic LiF-LiBaF 3

Directionally solidified samples of the lamellar LiF-LiBaF 3 eutectic have been examined by light microscopy and quantitative image analysis. When performing investigations of the influence of the growth parameters on the eutectic texture, it is necessary to use sensitive characterization methods to determine its quality. We have developed a new quantitative method for characterizing this lamellar eutectic, using a normalized length of the lamellae. We have also studied the correlation between the growth velocity v and the lamellar spacing γ for the eutectic system LiF-LiBaF3. These investigations were made in the course of preparing an experiment under microgravity conditions during the second German Spacelab Mission D2.

Isochoric heat capacity Cv at the critical point of SF6 under micro- and earth-gravity

Abstract As a consequence of the diverging compressibility, earth-bound experiments near the gas-liquid critical point suffer extremely from the strong influence of gravity. Caloric measurements, in particular of the heat capacity Cv, are inevitably affected by local changes of the density throughout the volume. Experimental results thus rather represent some integral average over all density and temperature variations than a thermodynamic point of state. The first measurements of Cv under micro-gravity conditions for the fluid SF6 near the critical state conducted during the German Spacelab Mission D1 in Oct./Nov. 1985 are reported here. Due to the surprising μg-results, the influence of gravity and equilibration have subsequently been investigated. By numerical simulation of the equilibration process, it became evident that the flattening of the Cv-curves observed could be caused by a non-uniform mass distribution and the slow mass diffusion process.

Crystal growth under reduced gravity

During the German Spacelab mission D1 various Crystal Growth Experiments have been successfully performed. The aim of this article is to review those growth studies which have been carried out in ellipsoidal mirror furnace systems. A Floating Zone Technique has been applied to Si whereas GaSb, InP, CdTe and (Pb, Sn) Te have been grown in quartz ampoules by the Travelling Heater Method (THM). One CdTe-growth run used a vapour zone instead of a metallic solution zone. As a main result of all experiments it could be demonstrated that semiconductor crystals may be grown under reduced gravity conditions in a nearly diffusive growth regime.

Telescience with MARCO/HOLOP on board the spacelab D2-mission as a preparation for Columbus

The implementation of the telescience concept and its test in precursor missions is mandatory for experiment operations in the Columbus era with respect to enhancements in science quality and quantity. During the German D2 Spacelab mission, scheduled for spring 1993, a fluid physics experiment (MARCO, MARangoni COnvection in an open boat) will be performed in the telescience mode, using the HOLOP-D2 (HOLographic OPtics laboratory) experiment facility. MARCO will be remotely operated by the experimenter from a USOC (User Support and Operations Center). DLR/MUSC (Microgravity User Support Center, located at Cologne, Germany) will play the role of this USOC, being connected to DLR/GSOC (German Space Operations Center, located in Oberpfaffenhofen, Germany) via remote data, voice and video lines. Telescience with MARCO/HOLOP is a joint effort between DARA GmbH (Deutsche Agentur für Raumfahrt-Angelegenheiten), DLR (Deutsche Forschungsanstalt für Luft- und Raumfahrt e.V.) and ESA (European Space Agency).

Directional solidification of the LiF - LiBaF 3 eutectic

The lamellar eutectic LiF - LiBaF 3 has been directionally solidified in different furnaces and special designed cartridges with growth rates between 3 and 60 mm/h and temperature gradients from 1.5 to 7°C/mm. The growth rates have been calculated from temperature measurements in the melt. The critical ratio G/v for interface stability avoiding eutectic cells has been determined. These experiments have been made in preparing experiments under μg(microgravity)-conditions during the second German Spacelab Mission D2 in spring 1993.

Possible actions of gravity on the cellular machinery.

Since the first flight of the ESA Biorack on the German Spacelab Mission D1 in 1985 evidence has been obtained that biological cells and small unicellular organisms function differently under conditions of microgravity. However, there is still lack of scientific proof that these effects are caused by a direct influence on the cells in the weightlessness condition. The question how normal gravity may play a role in cellular activity is being addressed and the results show that gravity may provide important signals during certain state transitions in the cell. These would be gravity-sensitive windows in the biological process. Also, by amplification mechanisms inside the cell, the cell may assume a state that is typical for normal gravity conditions and would change in microgravity. Experimental tools are discussed that would provide the conditions to obtain evidence for direct action of gravity and for the possible existence of gravity-sensitive windows.

The advanced fluid physics module: A technical description

The Advanced Fluid Physics Module (AFPM) is a multi-purpose, multi-user instrument for investigations on fundamental behaviour of liquid zones in a microgravity environment. The AFPM instrument is presently in its final development phase and is intended to fly on the second German Spacelab D2 mission in 1992. The technical features of the AFPM instrument and its accommodation for the D2 mission are described. The five fluid physics experiments selected to be performed with AFPM on D2 are also addressed.

Progress in early detection and follow up of glaucoma

The importance of Hans Goldmann's contributions to clinical tonometry is discussed in detail. One example is the principle of an applanation diameter of 3.06 mm, which was established by him and is still the basis for the various methods of clinical tonometry today. Therefore, further advances in this field can only be concerned with facilitating the application of this principle. An instrument which can be used by both physician and patient is described. By facilitating more frequent tonometric examinations it would ensure much better glaucoma control than is at present possible. A further application of a self-test tonometer of this kind, which is not affected by gravity, is space medicine. It is planned to use the instrument in the German Spacelab D2 mission in 1991.