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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Low noise 1.2 THz SIS receiver

We prevent the development of a low noise SIS mixer for the 1.1-1.25 THz heterodyne receiver of FIRST space radiotelescope.

superconductor↗
NASA NTRS2019

Fabrication of Phononic Filter Structures for Far-IR/sub-mm Detector Applications

A photon noise limited sub-mm/far-IR cold telescope in space will require detectors with noise equivalent power (NEP) less than 1x10-19W/Hz1/2for imaging applications and at least an order of magnitude lower for spectroscopic studies. The detector NEP can be reduced by lowering the operation temperature and improving the thermal isolation between the bolometer and a heat bath. We report on the fabrication of membrane isolated transition edge sensor bolometers incorporating compact (<50 μm) thermal isolation beams based on phononic filters. Phononic filters are created by etching quasi-periodic nanoscale structures into supporting thermo-mechanical beams. The cross-sectional dimensions of the etched features are less than the thermal wavelength at the operating temperature, enabling coherent phonon transport to take place in one dimension. The phonon stop-band can be tuned by adjusting the scale of the quasi-periodic structures. Cascading multiple filter stages can increase bandwidth and provide improved thermal isolation similar to the function of a multi-stage electrical filter. We describe the fabrication of AlMn based transition edge sensor bolometers on silicon and silicon nitride membranes isolated by one-and two-dimensional phononic filters. The phononic filters are patterned through electron beam lithography and isolated with deep reactive ion etching.

Phononic↗
NASA NTRSDate not supplied

Risk Reduction Testing of Superconducting Coils for the High Efficiency Megawatt Motor

Second generation high temperature superconducting coils provide a very attractive level of performance for use in the field winding of electric machines for aircraft. Aside from maintaining these coils at cryogenic temperatures, much care must be taken to prevent damaging these relatively fragile materials due to excessive stress. Thermal stresses due to temperature cycling and mechanical stresses due to centrifugal forces are the most critical for the High Efficiency Megawatt Motor. This paper summarizes two test campaigns that were undertaken to reduce the risks posed by these loads. In one campaign, several superconducting coils were fabricated, thermally cycled up to 50~times, and electrically tested in liquid nitrogen to assess the change in superconductivity metrics throughout thermal cycling. In the other campaign, a full-scale superconducting coil was fabricated, a test article was designed to produce a representative stress environment in the coil, the test article and coil were rotated at room temperature up to a speed of 11,800~rpm, and the superconductivity metrics were measured in liquid nitrogen before and after each rotation. The experimental results demonstrate that the superconducting coils manufactured in house can survive both thermal cycling and high speed rotation with no appreciable degradation in superconducting performance.

partially superconducting electric machine↗
NASA NTRSDate not supplied

DC Performance Testing of MgB2 Superconducting Straight Wire Samples

To enable turboelectric aircraft that utilize fully superconducting motors and generators, testing of high-current, low-AC-loss superconducting wires and coils must be performed. A preliminary investigation was conducted on the critical current capabilityof a magnesium diboride sample and on the complications that arise from testing the sample with a cryocooler. While a cryocooler provides the benefit of a wide and continuous operating temperature range, cooling a sample by conduction through solid media without a heat-exchange gas is difficult. This paper outlines the hardware and software used to conduct the first DC performance tests on magnesium diboride superconducting samples, along with several check-out tests and mitigation steps needed to produce quality superconducting data using a cryocooler rather than a cryogen

Superconductor↗
NASA NTRSDate not supplied

Thermal Vacuum Chamber Demonstration of a Cryocooled, HTS Rotor for a 1.4 MW Electric Machine for Electrified Aircraft Propulsion

Aircraft with electrified propulsion systems require electric machines that are very lightweight and highly efficient. Advancements to the state of the art are required to meet this demand. This is particularly true for large transport aircraft with more than about 150 passengers, which will require electric machines with power ratings in the 1 to 30+ MW range. At this scale of power, superconducting technology becomes attractive for electrified aircraft propulsion to increase efficiency and reduce mass [1]. A mass reduction relative to non-superconducting machines can result from an increase in the specific power of the machine and indirectly through a significant reduction in the amount of waste heat generated on the aircraft, which reduces the mass of the thermal management system [2]. NASA’s high efficiency megawatt motor (HEMM) is a 1.4 MW partially superconducting machine that is being developed to achieve an efficiency greater than 98% and electromagnetic specific power greater than 16 kW/kg. HEMM contains a copper stator operating at an average temperature around 423 K and a superconducting rotor composed of no-insulation 2nd generation high temperature superconducting (HTS) coils that operates around 60 K. The superconducting coils are conductively cooled by a pulse tube cryocooler embedded inside and rotating with the rotor shaft. This paper presents a full-scale demonstration of the rotor in a thermal vacuum chamber at the designed operating temperature. The test was designed to validate the design of HEMM’s rotor, namely the ability to operate the 2G HTS coils at their rated direct current in a relevant thermal environment while being conductively cooled.

high temperature superconductors↗
NASA NTRS2023

Superconducting Notch Filter for RFI Mitigation in Ground-Based Radio Telescope

This paper presents a high-rejection, thin-film HTS, microstrip bandstop filter to prevent a local and high-power RFI source from interfering with NASA GGAO’s VGOS cryogenic receiver. This filter has an excellent 2.7%, 50-dB-fractionalbandwidth and a center stop-band frequency of 9.41 GHz. It does not contain any narrow or interdigital features as found in some designs, which reduces the fringing electric fields and improves its power handling capability. The YBCO films were grown on 435-µm-thick R-plane sapphire substrate and the anisotropic behavior was modeled and simulated with a high degree of accuracy. The device was tested while cooled to 77 K and the measurements agree well with simulation.

high-temperature superconductors↗
NASA NTRS2023

Static Testing of A Conductively-Cooled, High Temperature Superconducting Rotor for A 1.4 MW Electric Machine in a Thermal Vacuum Chamber

NASA’s high efficiency megawatt motor (HEMM) is a partially superconducting, 1.4 MW electric machine designed for electrified aircraft propulsion. HEMM’s high performance is enabled by a field winding composed of 2nd generation high temperature superconducting (HTS) coils that are designed to operate at temperatures below 62 K. The superconducting rotor is conductively cooled to cryogenic temperatures using a rotating cryocooler embedded inside the machine’s shaft. This paper presents a static test of the full-scale superconducting rotor in a thermal vacuum chamber. The experimental setup is described in detail. Thermal and electromagnetic 3D finite element analyses of the experimental setup are shown along with a comparison of the model results to model results for HEMM. The thermal response during cool down from room temperature is discussed. Electrical measurements are presented for operation at different dc current excitations up to the rated current of the rotor (57.2 A) and temperature limit of the HEMM design (62 K). The results suggest that minor damage to one superconducting coil occurred at 50 A and 61.2 K, causing increased resistance in the system, but that the system could still be stably operated at 57.2 A and 62 K when conductively cooled by a cryocooler.

electrified aircraft propulsion↗
NASA NTRS2024

Thermal Cycling of Stationary Superconducting Rotor Coils for the High Efficiency Megawatt Motor

The self-cooled, superconducting rotor included in the design of the High Efficiency Megawatt Motor (HEMM) can produce magnetic field strengths far higher than those produced using conventional approaches. However, the superconductivity properties of high-temperature superconducting coils can degrade as the coil is repeatedly thermally cycled, significantly impacting the HEMM’s performance. To explore ways to reduce this risk, NASA researchers fabricated and tested several coils of increasing complexity. The results of the testing campaign indicate that NASA can fabricate and test full-scale superconducting coils for the rotor of the HEMM that can reliably survive repeated thermal cycling with no or acceptably slow degradation.

Electrified Aircraft Propulsion↗
NASA NTRS2024

Effect of High-Speed Rotation on High-Temperature Superconducting Coils for High Efficiency Megawatt Motor

The use of a superconducting rotor in the High Efficiency Megawatt Motor (HEMM) comes with a number of challenges. The HEMM’s rotor must be designed so that the superconducting coil can tolerate the forces it will encounter during operation. These forces introduce considerable risk to the design of the HEMM. Because this risk cannot be adequately addressed through refined analysis, a set of experiments was deemed necessary to demonstrate that the HEMM’s superconducting coils can survive the stresses imparted by the centrifugal forces acting on the coil during full-speed operation of the machine. These experiments required spin testing a full-scale HEMM coil on a representative rotor structure at room temperature and sequentially higher rotation speeds and measuring the superconductivity response of the coil in liquid nitrogen (LN2) before and after each spin test. Tests were carried out to the full centripetal loading of a recent HEMM design. According to finite element analysis, this load produced stress components in the coil that exceed their design limit by a factor of 1 to 7.4. Although not yet confirmed, the current HEMM design is expected to produce even smaller stresses in the coil due to a 20 percent reduction in the coil’s mass and an increased volume of structural material. The only degradation of the coil that occurred during this testing resulted from a test rig failure and from the voltage taps, which are not part of the final coil design.

Electrified Aircraft Propulsion↗