Search NASA⌕ Search

Engineering topics

MacDonnell, David

Publications and source records attributed to MacDonnell, David.

Rapid Generation of Large Dimension Photon Sieve Designs

A photon sieve is a revolutionary optical instrument that provides high resolution imaging at a fraction of the weight of typical telescopes (areal density of 0.3 kg/m2 compared to 25 kg/m2 for the James Webb Space Telescope). The photon sieve is a variation of a Fresnel Zone Plate consisting of many small holes spread out in a ring-like pattern, which focuses light of a specific wavelength by diffraction. The team at NASA Langley Research Center has produced a variety of small photon sieves for testing. However, it is necessary to increase both the scale and rate of production, as a single sieve previously took multiple weeks to design and fabricate. This report details the different methods used in producing photon sieve designs in two file formats: CIF and DXF. The difference between these methods, and the two file formats were compared, to determine the most efficient design process. Finally, a step-by-step sieve design and fabrication process was described. The design files can be generated in both formats using an editing tool such as Microsoft Excel. However, an approach using a MATLAB program reduced the computing time of the designs and increased the ability of the user to generate large photon sieve designs. Although the CIF generation process was deemed the most efficient, the design techniques for both file types have been proven to generate complete photon sieves that can be used for scientific applications

Hariharan, Shravan↗

An Innovative Concept for Spacebased Lidar Measurement of Ocean Carbon Biomass

Beam attenuation coefficient, c, provides an important optical index of plankton standing stocks, such as phytoplankton biomass and total particulate carbon concentration. Unfortunately, c has proven difficult to quantify through remote sensing. Here, we introduce an innovative approach for estimating c using lidar depolarization measurements and diffuse attenuation coefficients from ocean color products or lidar measurements of Brillouin scattering. The new approach is based on a theoretical formula established from Monte Carlo simulations that links the depolarization ratio of sea water to the ratio of diffuse attenuation Kd and beam attenuation C (i.e., a multiple scattering factor). On July 17, 2014, the CALIPSO satellite was tilted 30Âdeg off-nadir for one nighttime orbit in order to minimize ocean surface backscatter and demonstrate the lidar ocean subsurface measurement concept from space. Depolarization ratios of ocean subsurface backscatter are measured accurately. Beam attenuation coefficients computed from the depolarization ratio measurements compare well with empirical estimates from ocean color measurements. We further verify the beam attenuation coefficient retrievals using aircraft-based high spectral resolution lidar (HSRL) data that are collocated with in-water optical measurements.

Hu, Yongxiang↗

CALIPSO Mission Status Update: Payload Status

The CALIPSO mission payload status update is presented. The contents include: 1) Wide Field Camera Overview; 2) WFC Temperatures; 3) WFC Voltages; 4) Imaging Infrared Radiometer (IIR) Health; 5) IIR Voltages; 6) Payload Control (PLC) Voltages; 7) PLC Temperatures; 8) Low Voltage Power Supply (LVPS) (CALOPS0025N); 9) PLC Radiation Effects; 10) SDS Status (CALOPS0020N); 11) CALIOP LIDAR; 12) Laser Energy Trends; 13) Laser Energy Zoom; 14) Laser Management Approach; 15) Green / Red Ratio; 16) Pedestal @ SHG Temperature Trends; 17) LOM Heater Duty Cycle Trends; 18) LOM Pressure Trends; 19) Boresight Trend; 20) 1064 Dark Noise Trend; 21) 532 SNR Trend; 22) Spike Trends; 23) LIDAR Highlights; 24) Backup Laser Status; and 25) Future Plans.

Verhappen, Ron↗

The Preliminary Design of a Universal Martian Lander

As part of the NASA/USRA program, nineteen West Virginia University students conducted a preliminary design of a manned Universal Martian Lander (UML). The WVU design considers descent to Mars from polar orbit, a six month surface stay, and ascent for rendezvous. The design begins with an unmanned UML landing at Elysium Mons followed by the manned UML landing nearby. During the six month surface stay, the eight modules are assembled to form a Martian base where scientific experiments are performed. The mission also incorporates hydroponic plant growth into a Controlled Ecological Life Support System (CELSS) for water recycling, food production, and to counteract psycho-logical effects of living on Mars. In situ fuel production for the Martian Ascent and Rendezvous Vehicle (MARV) is produced From gases in the Martian atmosphere. Following surface operations, the eight member crew uses the MARV to return to the Martian Transfer Vehicle (MTV) for the journey home to Earth.

Norman, Timothy L.↗