Scaling of Two-Phase Flows to Partial-Earth Gravity

A report presents a method of scaling, to partial-Earth gravity, of parameters that describe pressure drops and other characteristics of two-phase (liquid/ vapor) flows. The development of the method was prompted by the need for a means of designing two-phase flow systems to operate on the Moon and on Mars, using fluid-properties and flow data from terrestrial two-phase-flow experiments, thus eliminating the need for partial-gravity testing. The report presents an explicit procedure for designing an Earth-based test bed that can provide hydrodynamic similarity with two-phase fluids flowing in partial-gravity systems. The procedure does not require prior knowledge of the flow regime (i.e., the spatial orientation of the phases). The method also provides for determination of pressure drops in two-phase partial-gravity flows by use of a generalization of the classical Moody chart (previously applicable to single-phase flow only). The report presents experimental data from Mars- and Moon-activity experiments that appear to demonstrate the validity of this method

Lightweight, Rack-Mountable Composite Cold Plate/Shelves

Rack-mountable composite-material structural components that would serve as both shelves and cold plates for removing heat from electronic or other equipment mounted on the shelves have been proposed as lightweight alternatives to all-metal cold plate/shelves now in use. A proposed cold plate/shelf would include a highly thermally conductive face sheet containing oriented graphite fibers bonded to an aluminum honeycomb core, plus an extruded stainless-steel substructure containing optimized flow passages for a cooling fluid, and an inlet and outlet that could be connected to standard manifold sections. To maximize heat-transfer efficiency, the extruded stainless-steel substructure would be connected directly to the face sheet. On the basis of a tentative design, the proposed composite cold plate/shelf would weigh about 38 percent less than does an all-aluminum cold plate in use or planned for use in some spacecraft and possibly aircraft. Although weight is a primary consideration, the tentative design offers the additional benefit of reduction of thickness to half that of the all-aluminum version

100-LBF LO2/LCH4 - Reaction Control Engine Technology Development for Future Space Vehicles

The National Aeronautics and Space Administration (NASA) has identified liquid oxygen (LO2)/liquid methane (LCH4) propulsion systems as promising options for some future space vehicles. NASA issued a contract to Aerojet to develop a 100-lbf (445 N) LO2/LCH4 Reaction Control Engine (RCE) aimed at reducing the risk of utilizing a cryogenic reaction control system (RCS) on a space vehicle. Aerojet utilized innovative design solutions to develop an RCE that can ignite reliably over a broad range of inlet temperatures, perform short minimum impulse bits (MIB) at small electrical pulse widths (EPW), and produce excellent specific impulse (Isp) across a range of engine mixture ratios (MR). These design innovations also provide a start transient with a benign MR, ensuring good thrust chamber compatibility and long life. In addition, this RCE can successfully operate at MRs associated with main engines, enabling the RCE to provide emergency backup propulsion to minimize vehicle propellant load and overall system mass

Cold Helium Pressurization for Liquid Oxygen / Liquid Methane Propulsion Systems: Fully-Integrated Initial Hot-Fire Test Results

A prototype cold helium active pressurization system was incorporated into an existing liquid oxygen (LOX) / liquid methane (LCH4) prototype planetary lander and hot-fire tested to collect vehicle-level performance data. Results from this hot-fire test series were used to validate integrated models of the vehicle helium and propulsion systems and demonstrate system effectiveness for a throttling lander. Pressurization systems vary greatly in complexity and efficiency between vehicles, so a pressurization performance metric was also developed as a means to compare different active pressurization schemes. This implementation of an active repress system is an initial sizing draft. Refined implementations will be tested in the future, improving the general knowledge base for a cryogenic lander-based cold helium system

Chromatic Illumination Discrimination Ability Reveals that Human Colour Constancy Is Optimised for Blue Daylight Illuminations

The phenomenon of colour constancy in human visual perception keeps surface colours constant, despite changes in their reflected light due to changing illumination. Although colour constancy has evolved under a constrained subset of illuminations, it is unknown whether its underlying mechanisms, thought to involve multiple components from retina to cortex, are optimised for particular environmental variations. Here we demonstrate a new method for investigating colour constancy using illumination matching in real scenes which, unlike previous methods using surface matching and simulated scenes, allows testing of multiple, real illuminations. We use real scenes consisting of solid familiar or unfamiliar objects against uniform or variegated backgrounds and compare discrimination performance for typical illuminations from the daylight chromaticity locus (approximately blue-yellow) and atypical spectra from an orthogonal locus (approximately red-green, at correlated colour temperature 6700 K), all produced in real time by a 10-channel LED illuminator. We find that discrimination of illumination changes is poorer along the daylight locus than the atypical locus, and is poorest particularly for bluer illumination changes, demonstrating conversely that surface colour constancy is best for blue daylight illuminations. Illumination discrimination is also enhanced, and therefore colour constancy diminished, for uniform backgrounds, irrespective of the object type. These results are not explained by statistical properties of the scene signal changes at the retinal level. We conclude that high-level mechanisms of colour constancy are biased for the blue daylight illuminations and variegated backgrounds to which the human visual system has typically been exposed