Engineering topics

Cheng, Edward S.

Publications and source records attributed to Cheng, Edward S..

8 records

NASA NTRS2008

Technical Aspects of the Advanced Camera For Surveys Repair (ACS-R)

The ACS Repair (ACS-R) team includes contributors from NASA's Goddard Space Flight Center, Ball Aerospace, and Teledyne Imaging Sensors; It determined that all of the capabilities of the ACS could be restored and created a concept for the ACS-R component of SN4. ACSR will restore the WFC of ACS by replacing the existing CCD Electronics Box (CEB) with the CEB-Replacement (CEB-R) and providing power from a new Low Voltage Power Supply Replacement (LVPS-8). The new LVPS-R will also attempt to restore the HRC function by providing power through the original power bus. In this presentation, we faeus on the concept and technical aspects of the ACS-R.

Rinehart, Stephen↗

NASA NTRS2006

Exo-atmospheric telescopes for deep space optical communications

For deep space optical communications, optical telescopes located above the Earth's atmosphere would have significant performance advantages over telescopes mounted on the Earth's surface. Link outages due to could cover would be eliminated, atmospheric attenuation would be eliminated, and signal degradation due to stray light would be reduced.

orbiting optical terminal↗

NASA NTRS2006

Exo-atmospheric telescopes for Deep Space Optical Communications

For deep space optical communications, optical telescopes located above the Earth's atmosphere would have significant performance advantages over telescopes mounted on the Earth's surface. Link outages due to cloud cover would be eliminated, atmospheric attenuation would be eliminated, and signal degradation due to stray light would be reduced. A study has been conducted to compare various exo-atmospheric platforms for the Earth end of the optical link.

orbiting optical terminal↗

NASA NTRS2002

Charge-coupled device for low background observations

A charge-coupled device with a low-emissivity metal layer located between a sensing layer and a substrate provides reduction in ghost images. In a typical charge-coupled device of a silicon sensing layer, a silicon dioxide insulating layer, with a glass substrate and a metal carrier layer, a near-infrared photon, not absorbed in the first pass, enters the glass substrate, reflects from the metal carrier, thereby returning far from the original pixel in its entry path. The placement of a low-emissivity metal layer between the glass substrate and the sensing layer reflects near infrared photons before they reach the substrate so that they may be absorbed in the silicon nearer the pixel of their points of entry so that the reflected ghost image is coincident with the primary image for a sharper, brighter image.

Loh, Edwin D.↗

NASA NTRS1992

Resonant cryogenic chopper

An account is given of the design features, construction, and performance of a both mechanically and thermally robust, resonant cryogenic chopper operating at 4.2 K. The chopper can occult a 2.54-cm aperture at 4.5 Hz, with approximately 1-mW dissipation. The controllability of the stator and rotor magnetic fields facilitates performance optimization and the determination of any possible interference effects. Attention is given to long-term amplitude stability determinations.

Page, Lyman A.↗

NASA NTRS1991

A measurement of the large-scale cosmic microwave background anisotropy at 1.8 millimeter wavelength

This measurement of the large-scale cosmic microwave background radiation (CMBR) anisotropy places the most stringent constraints to date on fluctuations in the CMBR on angular scales greater than about 4 deg. Using a four-channel bolometric radiometer operating at 1.8, 1.1, 0.63, and 0.44 mm, the diffuse sky brightness over half of the northern hemisphere has been mapped with an angular resolution of 3.8 deg. Analysis of the sky map at the longest wavelength for Galactic latitudes of 15 deg or more yields a 95-percent confidence level upper limit on fluctuations of the CMBR at Delta T/T of 1.6 x 10 to the -5th with a statistical power of 92 percent for Gaussian fluctuations at a correlation angle of 13 deg. Between 3 deg and 22 deg, the upper limit of fluctuations is 4.0 x 10 to the -5th . An anisotropy is detected in the map, but it cannot yet be attributed to primordial sources. The ultimate sensitivity for this experiment is 7 x 10 to the -6th over this angular range for Gaussian fluctuations.

Meyer, Stephan S.↗

NASA NTRS1991

Early results from the MIT millimeter and sub-millimeter balloon-borne anisotropy measurement

The MIT balloon-borne bolometric search for Cosmic Microwave Background Radiation (CMBR) anisotropies places the most stringent constraints to date on fluctuations in the CMBR. Four maps of half of the Northern Hemisphere at 1.8, 1.1, 0.63 and 0.44 mm wavelength, have a beam size of 3.8 deg with a 1 sigma sensitivity of less than 0.1 mK (thermodynamic) per FOV in each of the first two channels. Analysis of the sky map at 1.8 mm wavelength using a likelihood ratio test for galactic latitudes of 15 deg and greater yields a 95 percent confidence level (CL) upper limit on fluctuations of the CMBR at DeltaT/T less than or equal to 1.6 x 10 exp -5 with a statistical power of 92 percent for Gaussian fluctuations at a correlation angle of 13 deg. Between 3 deg and 22 deg, the upper limit for fluctuations is DeltaT/T less than or equal to 4.0 x 10 exp -5 (95 percent CL).

Meyer, Stephan S.↗

NASA NTRS1990

A large-scale cosmic microwave background anisotropy measurement at millimeter and submillimeter wavelengths

A balloon-borne experiment to measure the anisotropy of the cosmic microwave background radiation at angular scales of 4 deg or greater is reported. The instrument simultaneously measures in four spectral bands centered on 5.6, 8.7, 15.8, and 22.5/cm. Three results are presented: (1) the 95-percent confidence limit for monochromatic anisotropies is 0.0001 or less on angular scales of 10 deg; (2) the Galactic plane dust emission at l = 42 deg is consistent with a nu-squared emissivity law at frequencies above 15/cm, with excess emission below 15/cm; and (3) atmospheric ozone at an altitude of 35 km may form clumps as large as Delta emissivity/emissivity = 0.002.

Page, Lyman A.↗