Spacecraft utilizing cryogenic propellants need accurate microgravity liquid mass gauging capability. In this paper we describe the spatial regularization method for providing estimations of liquid mass fraction for any liquid configuration in a propellant tank using capacitance measurements among electrodes surrounding the tank volume. The capacitance measurements, which interrogate the entire fluid volume, are weighted and summed to spatially regularize the capacitance sensitivity in the tank volume and to minimize the influence of the fluid configuration on the liquid mass fraction measurement. We begin by developing the mathematical foundation for the spatial regularization method for arbitrary tank geometries with continuous electrode distributions, including the theoretical limit on liquid mass fraction accuracy achievable with the method. We then discretize the mathematics, and we provide the solution for a cylindrical volume with 16 discrete electrodes that depends on self-capacitances. Finally, we demonstrate how to apply the discrete solution in a manner that uses only mutual capacitances. For both the continuous and discrete cases, accuracy predictions are made using finite element modeling and a variety of fluid configurations. Our analyses indicate that the spatial regularization method yields liquid mass fractions with mean accuracy greater than 98% for a cylindrical volume using 16 electrodes.

Urine is processed on the International Space Station using pretreat, a highly acidic compound. The dilution ratio of this compound in water is important; too little will inhibit the recovery of water from the urine, and too much is both corrosive and wasteful. Recently, a feasibility study concluded that a sensor based on optical absorption should meet the system requirements to monitor the concentration of pretreat in water before mixing with urine. This paper presents a design for that sensor, based on looking through the walls of a semitransparent perfluoroalkoxy tube carrying the diluted pretreat. The result is an accurate, completely nonintrusive, rapid-response pretreat concentration sensor. A theoretical model of the sensor is developed, yielding an analytic relationship between optical measurements and concentration that can be used to compensate for the nonlinear output of the optical sensor. Experiments demonstrate that the assembled device has adequate sensitivity and response time to monitor flowing diluted pretreat such that the total dose administered per use can be monitored.

The sensitivity matrix, used in electrical capacitance tomography to connect capacitance readings to a dielectric distribution, is derived without assumptions on the magnitude of the relative permittivity and without dropping higher order terms. Deriving this matrix may provide a means to improve the performance of the various published electrical capacitance tomography algorithms and extend their applicability to a wider range of dielectric materials.

A lab-scale experimental apparatus that mimics the solar-thermal environment of space has recently been developed and tested at NASA Kennedy Space Center in support of novel materials research for future space science and exploration applications. The Space Irradiance Simulator (SIRS) apparatus exposes specimens up to roughly 61 mm in diameter to a similar thermal environment that exists at distances as close as 0.4 AU from the Sun. This includes a high vacuum environment, access to a deep cryogenic background temperature with optical properties that closely imitate a blackbody, and irradiance from a broadband solar “point” source at fluxes as high as 9300 W/m2. Cooling is provided by a Gifford-McMahon cryocooler capable of 25 W of cooling power at 20 K, with a base temperature of 14 K. A commercially available Xenon lamp acts as the solar source, creating broadband electromagnetic radiation with a spectrum similar to that of the Sun. Light is beamed through the vacuum chamber and onto a sample suspended within the cold-mass via a flexible quartz fiber bundle in conjunction with a custom vacuum feedthrough. The system design, fabrication, and operation are discussed; and results from the initial checkout testing of the system are presented.

As NASA endeavors to extend the human presence in space beyond low Earth orbit, methods to efficiently store cryogenic propellants in space are required. Current state of the art rigid thermal control coatings absorb approximate 6% of the total solar irradiance, while state of the art thermal control paints absorb approximately 10% of the total solar irradiance. Consequently, radiative heat transfer a lone makes passive storage of cryogens in space impossible. A new rigid thermal control coating is in development and has achieved solar absorption values as low as -0.6 % (compared to a NIST standard) while maintaining high emissivity. This negative value for a rigid tile of pure yttria has required a new testing method be developed. Rigid tiles are very high performance but have more mass than paints and paper-th in coatings. Tiles must have a metallic substrate and create application challenges. While some use cases may necessarily address the challenges associated with rigid tiles in order to achieve required performance, a similar paint-like coating was also developed. The spray-on version of the new thermal control coating is easily applied to large complex surfaces and is very low mass. This version is also primarily yttria but includes a potassium bromide binder. Application to various substrates shows solar absorption values consistently below 5%, with a minimum of 2.8% achieved. Details of each version of this coating, along with test data is discussed.

Results are presented for the reflectivity of spray on foam insulation (SOFI) samples coated with a new high solar reflectivity coating. Reflectance spectra are presented comparing bare SOFI to samples with one, two, or three layers of the new coating as well as one sample with white paint. Samples were coated on the front side of the SOFI, where the surface height varies significantly, as well as on the flatter back surface. Predicted solar absorbance values are provided for a few select cases.

The 2019 Center Innovation Fund Annual Report contains FY18 completed reports. Attached is the executive summary/abstract section of the reports.

Modeling the interaction between a non-uniform magnetic field and a rotating conductive object provides insight into the drag force, which is used in applications such as eddy current braking and linear induction motors, as well as the transition to a repulsive force, which is the basis for magnetic levitation systems. Here, we study the interaction between a non-uniform field generated by a cylindrical magnet and a rotating conductive sphere. Each eddy current in the sphere generates a magnetic field which in turn generates another eddy current, eventually feeding back on itself. A two-step mathematical process is developed to find a closed-form solution in terms of only three eddy currents. However, the complete solution requires decomposition of the magnetic field into a summation of spherical harmonics, making it more suitable for a graduate-level electromagnetism lecture or lab. Finally, the forces associated with these currents are calculated and then verified experimentally.

The Sun sustains life on Earth and NASA has made its study one of the four pillars of the Science Mission Directorate. A specific area of study, the coronal heating problem, has been of significant concern for nearly 80years; namely how does the 5800 K surface of the Sun heat the nearby corona to over 1,000,000 K. Differing theories have been proposed to explain this process, but verification by actual measurement would not only resolve this issue, it would provide close-up measurements of the Sun never before obtained. However, this requires the development of a solar shield that can protect a satellite located less than 10,000 km from the Sun's surface. Steps towards that capability are the goal of this NIAC project. The current state-of-the-art in solar shielding is best shown by the upcoming Parker Solar Probe Mission, so the approach taken by that satellite is discussed and used as a starting point; allowing a distance of 9.5 solar radii from the Sun's center to be reached. It is then shown that state-of-the-art solar reflectors do not improve this performance. Next, we review the use of pressed powder as a better solar reflector and show that there is some improvement, but not sufficient to reach the Sun's surface. We spend some time on this architecture because the Parker Solar Probe has a thin scattering layer on its solar shield and it is important to discuss the advantages and disadvantages of this feature.

Modeling the interaction between a moving conductor and a static magnetic field is critical to understanding the operation of induction motors, eddy current braking, and the dynamics of satellites moving through Earth's magnetic field. Here, we develop the case of a thick-walled sphere rotating in a uniform magnetic field, which is the simplest, non-trivial, magneto-statics problem that leads to complete closed-form expressions for the resulting potentials, fields, and currents. This solution requires knowledge of all of Maxwell's time independent equations, scalar and vector potential equations, and the Lorentz force law. The paper presents four cases and their associated experimental results, making this topic appropriate for an advanced student lab project.

This paper describes a thermal control coating that should allow non-heat-generating objects, such as cryogenic tanks and superconductors, to reach and maintain cryogenic temperatures in deep space locations far from the infrared (IR) emission of a planet and at least 1 astronomical unit from the Sun. This new coating is designed to reflect nearly all of the Sun's irradiance, while still permitting far-IR emission, allowing steady-state temperatures as low as 50 K to be achieved. A brief background on currently available thermal control coatings is given, followed by a discussion on how this new coating circumvents the limitations of the state-of-the-art approaches. The theory behind these new coatings is reviewed, followed by models yielding predicted emissivities over broad spectral ranges. From this, the predicted steady-state temperatures for different coating thicknesses, materials, geometries, and environments are obtained. Experimental data are provided on two versions of this coating in a low-fidelity deep space environment, substantiating the predicted performance. The final section presents a straw-man model showing how these coatings could be used to facilitate the transport of liquid oxygen to Mars.

Large liquid hydrogen (LH2) storage tanks are vital infrastructure for NASA, the DOD, and industrial users. Over time, air may leak into the evacuated, perlite filled annular region of these tanks. Once inside, the extremely low temperatures will cause most of the air to freeze. If a significant mass of air is allowed to accumulate, severe damage can result from nominal draining operations. Collection of liquid air on the outer shell may chill it below its ductility range, resulting in fracture. Testing and analysis to quantify the thermal conductivity of perlite that has nitrogen frozen into its interstitial spaces and to determine the void fraction of frozen nitrogen within a perlite/frozen nitrogen mixture is presented. General equations to evaluate methods for removing frozen air, while avoiding fracture, are developed. A hypothetical leak is imposed on an existing tank geometry and a full analysis of that leak is detailed. This analysis includes a thermal model of the tank and a time-to-failure calculation. Approaches to safely remove the frozen air are analyzed, leading to the conclusion that the most feasible approach is to allow the frozen air to melt and to use a water stream to prevent the outer shell from chilling.

There is a current need to develop coatings that can reject more than 99% of the sun's irradiance to enable cryogenic storage and superconductor operation in space. Such a coating is proposed, composed of broadband scatterers on a metallic reflecting layer, yielding a surface that backscatters most of the solar spectrum yet still emits far-IR radiation. A model is presented with results, showing that a properly designed coating may potentially backscatter more than 99.9% of the sun's energy and allowing temperatures below 50 K to be achieved.

Modeling the interaction of a slowly rotating hollow conducting sphere in a magnetic field provided an understanding of the dynamics of orbiting space objects moving through the Earth's magnetic field. This analysis, performed in the late 1950s and limited to uniform magnetic fields, was innovative and acknowledged the pioneers who first observed rotary magnetism, in particular, the seminal work of Hertz in 1880. Now, there is interest in using a magnetic field produced by one space object to stop the spin of a second object so that docking can occur. In this paper, we consider, yet again, the interaction of a rotating hollow sphere in a magnetic field. We show that the predicted results can be tested experimentally, making this an interesting advanced student project. This analysis also sheds light on a rich set of previously unaddressed behaviors involving eddy currents.

JSC 66320, Revision A, Optical Property Requirements for Glasses, Ceramics, and Plastics in Spacecraft Window Systems, lists several quantitative requirements that spacecraft windowpanes must meet. Recently, we were asked to establish a capability at the Kennedy Space Center to perform these measurements on category B plastic panes, i.e., plastic panes that could be used on a spacecraft for long-focal-length photography and piloting. Two of the criteria, normal wavefront and 30-degree wavefront attributes, can be measured with existing equipment and processes (see NASA TM NESC-RP-14-00951, April 2016) and are not discussed in this document. However, the other six criteria-haze, wedge angle, birefringence, reflectance, transmittance, and color balance-required substantial development and are the subject of this document. In this document, we do not discuss the rationale behind the requirements, but we did engage in discussions with the authors of JSC 66320 in order to better understand the requirements and the verifications being imposed on windows and their testing. Accordingly, this document presents our best understanding of the requested requirements and verifications. We also present our methodology for performing each of the six measurements, along with applicable mathematics and a description, with photos, of the hardware used. In addition, we supply the results of a test on a low-quality in-house plastic window as an example of the system operation. Only requirements that can be met by acceptance test and analysis, as opposed to optical inspection, are considered in this document.

A magnetic field approach is presented whereby a large number of closely located satellites can be positioned and oriented relative to each other, but can also be tracked in six degrees of freedom. This is accomplished by using frequency-multiplexed magnetic fields where coils are placed on each satellite to allow them to generate magnetic fields, to interact with the magnetic fields from other satellites, and to sample the surrounding magnetic fields. By doing this, a satellite can choose which alternating field to push or pull against, to provide torque about, or to sample in order to determine its location and orientation relative to the other satellites. Theory is provided demonstrating the capability of this approach along with its advantages and limitations. An experimental system allowing 3 degrees-of-freedom was constructed and used to demonstrate a feedback and control system where a satellite is told to move to a location and it does this by interacting with the surrounding satellites to both generate forces and torques and to track its position and orientation.

Under our NASA Innovative Advanced Concepts (NIAC) project we have theoretically demonstrated a novel selective surface that reflects roughly 100 times more solar radiation than any other known coating. If this prediction holds up under experimental tests it will allow cryogenic temperatures to be reached in deep space even in the presence of the sun. It may allow LOX to be carried to the Moon and Mars. It may allow superconductors to be used in deep space without a refrigeration system.

Selective surfaces have wavelength dependent emissivitya bsorption. These surfaces can be designed to reflect solar radiation, while maximizing infrared emittance, yielding a cooling effect even in sunlight. On earth cooling to -50 C below ambient has been achieved, but in space, outside of the atmosphere, theory using ideal materials has predicted a maximum cooling to 40 K! If this result holds up for real world materials and conditions, then superconducting systems and cryogenic storage can be achieved in space without active cooling. Such a result would enable long term cryogenic storage in deep space and the use of large scale superconducting systems for such applications as galactic cosmic radiation (GCR) shielding and large scale energy storage.

Gas sensors have been demonstrated based on the conductivity changes in ultrathin films. These sensors operate in a regime where three different physical phenomena determine the total resistivity of the film; quantum mechanical coupling between metallic islands, bulk material conductivity of the islands, and network resistivity. We present a lumped parameter model that simulates thin-film growth and calculates the total film resistance during the growth process accounting for these three phenomena. The model contains four free parameters and yields a good agreement with experimental data presented for palladium, titanium, and gold. The primary benefit of this model is that it shows the relative contribution of each source of conductivity during the growth process providing insight into the operation of ultrathin films as gas sensors. We then model an ultrathin-film palladium-based hydrogen sensor and show that the sensing mechanism is primarily due to variations in quantum tunneling.