The Multi-user Droplet Combustion Apparatus (MDCA) is a multi-user facility designed to accommodate different droplet combustion science experiments.  The MDCA will conduct experiments using the Combustion Integrated Rack (CIR) of the NASA Glenn Research Center’s Fluids and Combustion Facility (FCF).  The payload is planned for the International Space Station.  The MDCA, in conjunction with the CIR, will allow for cost effective extended access to the microgravity environment, not possible on previous space flights.  It is currently in the Engineering Model build phase with a planned flight launch with CIR in 2007.   

The MDCA contains the hardware and software required to conduct unique droplet combustion experiments in space.  It consists of a Chamber Insert Assembly (CIA), an Avionics Package, and a multiple array of diagnostics.  Its modular approach permits on-orbit changes for accommodating different fuels, fuel flow rates, soot sampling mechanisms, and varying droplet support and translation mechanisms to accommodate multiple investigations.  Unique diagnostic measurement capabilities for each investigation are also provided.  Additional hardware provided by the CIR facility includes the structural support, a combustion chamber, utilities for the avionics and diagnostic packages, and the fuel mixing capability for PI specific combustion chamber environments.  Common diagnostics provided by the CIR will also be utilized by the MDCA.  Single combustible fuel droplets of varying sizes, freely deployed or supported by a tether are planned for study using the MDCA.  Such research supports how liquid-fuel-droplets ignite, spread, and extinguish under quiescent microgravity conditions.  This understanding will help us develop more efficient energy production and propulsion systems on Earth and in space, deal better with combustion generated pollution, and address fire hazards associated with using liquid combustibles on Earth and inspace.

Flame Extinguishment Experiment (FLEX)

The MDCA hardware will be launch as stowed hardware on the same incremental flight launch as the CIR.  This hardware will include the MDCA common hardware and experiment unique hardware for the first droplet investigation, Flame Extinguishment Experiment (FLEX).  The Chamber Insert Assembly, MDCA Avionics Package, and experiment unique hardware will be separate stowed items.  Once on-orbit, the CIA and Avionics Package will be removed from stowage.  The avionics package will be installed on the CIR rack and the CIA will be inserted into the CIR combustion chamber.  Experiment unique diagnostics for the first experiment will be installed on the CIR optics bench.

The Light Microscopy Module (LMM) is planned as a remotely controllable on-orbit microscope subrack facility, allowing flexible scheduling and control of physical science and biological science experiments within the GRC Fluids Integrated Rack (FIR) on the International Space Station.

Within the FIR, an initial complement of four fluid physics experiments will utilize an instrument built around a lightmicroscope. These experiments are the "Constrained Vapor Bubble" experiment (Peter C. Wayner of Rensselaer Polytechnic Institute), the "Physics of Hard Spheres Experiment–2" (Paul M. Chaikin of Princeton University), the "Physics of Colloids in Space–2" experiment (David A. Weitz of Harvard University), and the "Low Volume Fraction Entropically Driven Colloidal Assembly" experiment (Arjun G. Yodh of the University of Pennsylvania). The first experiment investigates heat conductance in microgravity as a function of liquid volume and heat flow rate to determine, in detail, the transport process characteristics in a curved liquid film. The other three experiments investigate various complementary aspects of the nucleation, growth, structure, and properties of colloidal crystals in microgravity and theeffects of micromanipulation upon their properties. Key diagnostic capabilities include video microscopy to observe sample features including basic structures and dynamics, thin film interferometry, laser tweezers for colloidal particle manipulation and patterning, confocal microscopy to provide enhanced three-dimensional visualization of colloidal crystal structures, and spectrophotometry to measure colloidal crystal photonic properties. In addition to using the confocal system, biological experiments can conduct fluorescence imaging by using the fiber-coupled output of the Nd:YAG laser operating at 532-nm, the 437-nm line of a mercury arc, or appropriate narrow-band filtering of the FIR provided metal halide white light source.

Constrained Vapor Bubble (CVB)

The use of interfacial free energy gradients to control fluid flow naturally leads to simpler and lighter heat transfer systems because of the absence of mechanical pumps. Therefore, “passive” engineering systems based on this principle are ideal candidates for the space program. In this context, “passive” refers to the natural pressure field for fluid flow due to changes in the intermolecular force field under an imposed nonisothermal temperature field. This force field is a function of the shape, temperature, and composition of the system. For example, heat pipes which rely on these forces have been proposed frequently to optimize heat transfer under microgravity conditions. However, the basic thermophysical principles controlling these systems are not well understood and, as a result, they have under performed. In general, the full potential of interfacial forces has not been realized in transport phenomena.

Therefore, the basic experimental and theoretical studies of the constrained vapor bubble (CVB) under microgravity conditions to help remedy this undesirable situation. The proposed use of a transparent glass cell and related optical measurements will increase the understanding of transport systems controlled by interfacial phenomena because the system is viewed directly. Relatively large systems with high heat fluxes and small capillary pressure levels set in the condenser will be emphasized.