Dr. Samuel E. Hetherington Profile

Dr. Samuel E. Hetherington

at NASA Goddard Space Flight Ctr

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Author

Publications (4)

Proceedings Article | 20 October 2016 Presentation + Paper

A toolbox of metrology-based techniques for optical system alignment

Phillip Coulter, Raymond Ohl, Peter Blake, Brent Bos, Victor Chambers, William Eichhorn, Jeffrey Gum, Theodore Hadjimichael, John Hagopian, Joseph Hayden, Samuel Hetherington, David Kubalak, Kyle Mclean, Joseph McMann, Kevin Redman, Henry Sampler, Greg Wenzel, Jerrod Young

Proceedings Volume 9951, 995108 (2016) https://doi.org/10.1117/12.2239070

KEYWORDS: Optical alignment, Metrology, Optical components, James Webb Space Telescope, Mirrors, Telescopes, Lawrencium, Sensors, Spherical lenses, Optical benches

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Proceedings Article | 19 September 2016 Presentation + Paper

Advanced topographic laser altimeter system (ATLAS) receiver telescope assembly (RTA) and transmitter alignment and test

John Hagopian, Matthew Bolcar, John Chambers, Allen Crane, Bente Eegholm, Tyler Evans, Samuel Hetherington, Eric Mentzell, Patrick Thompson, Luis Ramos-Izquierdo, David Vaughnn

Proceedings Volume 9972, 997207 (2016) https://doi.org/10.1117/12.2240241

KEYWORDS: Space telescopes, Telescopes, Optical fibers, Receivers, Transmitters, Diffractive optical elements, Collimators, Wavefronts, Mirrors, Interferometers

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The sole instrument on NASA’s ICESat-2 spacecraft shown in Figure 1 will be the Advanced Topographic Laser Altimeter System (ATLAS)¹. The ATLAS is a Light Detection and Ranging (LIDAR) instrument; it measures the time of flight of the six transmitted laser beams to the Earth and back to determine altitude for geospatial mapping of global ice. The ATLAS laser beam is split into 6 main beams by a Diffractive Optical Element (DOE) that are reflected off of the earth and imaged by an 800 mm diameter Receiver Telescope Assembly (RTA). The RTA is composed of a 2-mirror telescope and Aft Optics Assembly (AOA) that collects and focuses the light from the 6 probe beams into 6 science fibers. Each fiber optic has a field of view on the earth that subtends 83 micro Radians. The light collected by each fiber is detected by a photomultiplier and timing related to a master clock to determine time of flight and therefore distance. The collection of the light from the 6 laser spots projected to the ground allows for dense cross track sampling to provide for slope measurements of ice fields. NASA LIDAR instruments typically utilize telescopes that are not diffraction limited since they function as a light collector rather than imaging function. The more challenging requirements of the ATLAS instrument require better performance of the telescope at the ¼ wave level to provide for improved sampling and signal to noise. NASA Goddard Space Flight Center (GSFC) contracted the build of the telescope to General Dynamics (GD). GD fabricated and tested the flight and flight spare telescope and then integrated the government supplied AOA for testing of the RTA before and after vibration qualification. The RTA was then delivered to GSFC for independent verification and testing over expected thermal vacuum conditions. The testing at GSFC included a measurement of the RTA wavefront error and encircled energy in several orientations to determine the expected zero gravity figure, encircled energy, back focal length and plate scale. In addition, the science fibers had to be aligned to within 10 micro Radians of the projected laser spots to provide adequate margin for operations on-orbit. This paper summarizes the independent testing and alignment of the fibers performed at the GSFC.

Proceedings Article | 10 September 2013 Paper

Optical alignment of the Global Precipitation Measurements (GPM) star trackers

Samuel Hetherington, Dean Osgood, Joe McMann, Viki Roberts, James Gill, Kyle McLean

Proceedings Volume 8844, 884406 (2013) https://doi.org/10.1117/12.2024558

KEYWORDS: Optical alignment, Stars, Mirrors, Relays, Optical tracking, Autocollimation, Space operations, Data analysis, Neodymium, Magnetorheological finishing

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Proceedings Article | 11 February 2003 Paper

The COR1 inner coronagraph for STEREO-SECCHI

William Thompson, Joseph Davila, Richard Fisher, Larry Orwig, John Mentzell, Samuel Hetherington, Rebecca Derro, Robert Federline, David Clark, Philip Chen, June Tveekrem, Anthony Martino, Joseph Novello, Richard Wesenberg, Orville StCyr, Nelson Reginald, Russell Howard, Kimberly Mehalick, Michael Hersh, Miles Newman, Debbie Thomas, Gregory Card, David Elmore

Proceedings Volume 4853, (2003) https://doi.org/10.1117/12.460267

KEYWORDS: Coronagraphy, Objectives, Sensors, Sun, Light scattering, Space operations, Charge-coupled devices, Stray light, Calibration, Imaging systems

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