Francis C. Wessling

Consort 1 sounding rocket flight

This paper describes a payload of six experiments developed for a 7-min microgravity flight aboard a sounding rocket Consort 1, in order to investigate the effects of low gravity on certain material processes. The experiments in question were designed to test the effect of microgravity on the demixing of aqueous polymer two-phase systems, the electrodeposition process, the production of elastomer-modified epoxy resins, the foam formation process and the characteristics of foam, the material dispersion, and metal sintering. The apparatuses designed for these experiments are examined, and the rocket-payload integration and operations are discussed.

Consort 1 flight results: A synopsis☆

Consort 1 was the first low gravity materials processing payload to be launched by a commercially licensed rocket in the U.S.A. It carried six experiments which operated as planned during approx. 7 min of suborbital, low gravity flight (10(-5) g) and were returned in excellent condition to the investigators within 4 h of launch. Nearly 150 physical samples supported by measurements and photographs made during the flight were obtained for analysis. In addition to the experimental data returned, the success of Consort 1 demonstrated the ability of industry, working with university centers and government agencies, to rapidly prepare and launch payloads. A brief description of the rocket flight and payload configuration is given. Experiment objectives and methods are described and preliminary results and conclusions are presented.

Foam formation in low gravity

An apparatus that produced the first polyurethane foam in low gravity has been described. The chemicals were mixed together in an apparatus designed for operation in low gravity. Mixing was by means of stirring the chemicals with an electric motor and propeller in a mixing chamber. The apparatus was flown on Consort 1, the first low-gravity materials payload launched by a commercial rocket launch team. The sounding rocket flight produced over 7 min of low gravity during which a polyurethane spheroidal foam of approximately 2300 cu cm was formed. Photographs of the formation of the foam during the flight show the development of the spheroidal form. This begins as a small sphere and grows to approximately a 17-cm-diam spheroid. The apparatus will be flown again on subsequent low-gravity flights.

Vapor deposited organic thin film in microgravity

Organic thin films have been grown in space by effusive ampoule physical vapor transport technique with different growth parameters for the source temperature, transport flux, substrate, seeding, and backfilling. Results described in this paper are based on data from the two United States Space Shuttle Endeavour flights, STS (Space Transportation System)-59 and STS-69, using the moderate temperature facility (MTF) for materials processing in space. The facility consists primarily of the effusive ampoule, in which the thin film growth process takes place, encased in two concentric aluminum cylinders with a vacuum space between them. The MTF has produced thin films of variable quality and thickness across 12 mm diameter substrates. The results are discussed with reference to the growth parameters.

Design of thermal initial and boundary conditions to control the expansion of water-based phase-change materials in low gravity

ABSTRACT A passive carrier employing water-based phase-change materials is designed to return temperature-critical payloads from the International Space Station. These materials expand by 9% when frozen, which can cause rupture of freezers and/or an inability to fit inside the carrier. To solve this problem a method is devised that decouples the thermodynamic and physical expansion characteristics. Solutions are found simultaneously to the two independent problems by coupling them through pressure. The final numerical models are used to devise a freezing method to ensure desirable final shapes. Finally, ground-based experiments are conducted, adding validity to the model and freezing method.

Determination of thermal diffusivity in a disk shaped sample using edge heating applications to Stainless Steel

We describe a methodology for determining thermal diffusivities in real time by using temperature measurements at only two locations in a cylindrical sample. The technique is based on an analytical solution of heat transfer in a circular cylinder. This methodology does not require knowing the initial temperature increase or any timing between the applied and measured response. Starting with a cylinder heated on the outer surface and unique temperature measurement locations, the analytical solution for temperature at two specific radii can be approximated, after an initial transient, by a constant plus a single term that decreases exponentially with time. There are two special radii that fulfill the required condition. The data are analyzed by taking logarithms of the differences of the temperature versus time at these two radii, resulting in lines having slopes that are proportional to the thermal diffusivity. Surprisingly, other choices of the measurement locations lead to similar results, except with lo...

Subtle Issues in the Measurement of the Thermal Conductivity of Vacuum Insulation Panels

Vacuum insulation panels have values of thermal conductivity that are extremely low (∼4 mW/m.K) compared to the thermal conductivity of most common insulations. Typical ASTM test methods are not designed for testing these very low thermal conductivity materials. An apparatus has been built and tested that uses a thin foil heater and vacuum chamber to test vacuum insulation panels. Several different measurement configurations are studied to determine the effects of the parasitic heat losses. The differences between the ASTM standards and this technique are described and the rationale explained. A new ASTM technique for vacuum panels appears to be needed

Real-time determination of thermal diffusivity in a disk-shaped sample: Applications to graphite and boron nitride

We describe a methodology for determining thermal diffusivities in real time by using temperature measurements at only two locations in a cylindrical sample. The technique is based on an analytical solution of heat transfer in a circular cylinder. This methodology does not require knowing the initial temperature increase or any timing between the applied and measured response. Starting with a heated cylindrical region having a unique fraction of the sample radius, and unique temperature measurement locations, the analytical solution for temperature at three specific radii can be approximated, after an initial transient, by a constant plus a single term that decreases exponentially with time. There are three special radii that fulfill the required condition. The data are analyzed by taking logarithms of the differences of the temperature versus time at these three radii, resulting in lines having slopes at large times that are proportional to the thermal diffusivity. Surprisingly, other choices of the size of the heated region and the measurement locations lead to similar results, except with longer transients. Experimental results for graphite and boron nitride agree with our numerical simulations and with the manufacturer’s data. This technique is applicable to solids and to liquids if heat transport due to convection is negligible.

Ground and space processing of single-crystalline organic thin films

Physical vapor transport (PVT) crystal growth experiments are being conducted with nonlinear optical organic materials in semi-closed ampoules which allow a vacuum to penetrate into the growth chamber, removing impurities and decomposition products from the growth interface. One material being grown is N,N-dimethyl-p-(2,2-dicyanovinyl) aniline (DCVA). Two samples of DCVA were flown in separate, seeded PVT chambers on Space Shuttle mission STS-59 in April 1994. The growth parameters were set to reproduce laboratory experiments that yielded small, bulk crystals. Surprisingly, however, the results from the STS experiment were, for both samples, the production of single-crystalline thin films. A second set of 8 PVT cells with DCVA was flown on STS-69 in September 1995. Several parameters were changed to study their influences on the film growth process and, in summary, the film growth process was found to be very robust. Films were obtained in all cases, albeit with varying quality. An evaluation of the flight- and ground-test data revealed a slower heat-up rate than was typical of the laboratory experiments. No background pressure measurements were made, but the temperature profile is an indication of a much higher background nitrogen pressure than the millitorr range used in the laboratory. A 4-year research grant has been obtained to study this film-growth phenomenon. Ground-based experiments are beginning to be carried out involving the varying of source and substrate temperatures, nitrogen background pressure, and the substrate material.

Gravitational Effects on Closed-Cellular-Foam Microstructure

Polyurethane foam has been produced in low gravity for the first time. The cause and distribution of different void or pore sizes are elucidated from direct comparison of unit-gravity and low-gravity samples. Low gravity is found to increase the pore roundness by 17% and reduce the void size by 50%. The standard deviation for pores becomes narrower (a more homogeneous foam is produced) in low gravity. Both a Gaussian and a Weibull model fail to describe the statistical distribution of void areas, and hence the governing dynamics do not combine small voids in either a uniform or a dependent fashion to make larger voids. Instead, the void areas follow an exponential law, which effectively randomizes the production of void sizes in a nondependent fashion consistent more with single nucleation than with multiple or combining events.