Engineering topics

Smith, Scott

Publications and source records attributed to Smith, Scott.

25 records · Page 2

NASA NTRS2007

TRL-6 for JWST Wavefront Sensing and Control

NASA's Technology Readiness Level (TRL)-6 is documented for the James Webb Space Telescope (JWST) Wavefront Sensing and Control (WFSC) subsystem. The WFSC subsystem is needed to align the Optical Telescope Element (OTE) after all deployments have occurred, and achieves that requirement through a robust commissioning sequence consisting of unique commissioning algorithms, all of which are part of the WFSC algorithm suite. This paper identifies the technology need, algorithm heritage, describes the finished TRL-6 design platform, and summarizes the TRL-6 test results and compliance. Additionally, the performance requirements needed to satisfy JWST science goals as well as the criterion that relate to the TRL-6 Testbed Telescope (TBT) performance requirements are discussed

Feinberg, Lee↗

NASA NTRS2007

Coadding Techniques for Image-based Wavefront Sensing for Segmented-mirror Telescopes

Image-based wavefront sensing algorithms are being used to characterize optical performance for a variety of current and planned astronomical telescopes. Phase retrieval recovers the optical wavefront that correlates to a series of diversity-defocused point-spread functions (PSFs), where multiple frames can be acquired at each defocus setting. Multiple frames of data can be coadded in different ways; two extremes are in "image-plane space," to average the frames for each defocused PSF and use phase retrieval once on the averaged images, or in "pupil-plane space," to use phase retrieval on every set of PSFs individually and average the resulting wavefronts. The choice of coadd methodology is particularly noteworthy for segmented-mirror telescopes that are subject to noise that causes uncorrelated motions between groups of segments. Using data collected on and simulations of the James Webb Space Telescope Testbed Telescope (TBT) commissioned at Ball Aerospace, we show how different sources of noise (uncorrelated segment jitter, turbulence, and common-mode noise) and different parts of the optical wavefront, segment and global aberrations, contribute to choosing the coadd method. Of particular interest, segment piston is more accurately recovered in "image-plane space" coadding, while segment tip/tilt is recovered in "pupil-plane space" coadding.

Smith, Scott↗

NASA NTRS2007

Status on Iterative Transform Phase Retrieval Applied to the GBT Data

This slide presentation reviews the use of iterative transform phase retrieval in the analysis of the Green Bank Radio Telescope (GBT) Data. It reviews the NASA projects that have used phase retrieval, and the testbed for the algorithm to be used for the James Webb Space Telescope. It shows the comparison of phase retrieval with an interferometer, and reviews the two approaches used for phase retrieval, iterative transform (ITA) or parametric (non-linear least squares model fitting). The concept of ITA Phase Retrieval is reviewed, and the application to Radio Antennas is reviewed. The presentation also examines the National Radio Astronomy Observatory (NRAO) data from the GBT, and the Fourier model that NRAO uses to analyze the data. The challenge for ITA phase retrieval is reviewed, and the coherent approximation for incoherent data is shown. The validity of the approximation is good for a large tilt. There is a review of the proof of concept of the Phase Review simulation using the input wavefront, and the initial sampling parameters estimate from the focused GBT data.

Dean, Bruce↗

NASA NTRS2006

Nutrition Issues for Space Exploration

Optimal nutrition will be critical for crew members who embark on space exploration missions. Nutritional assessment provides an opportunity to ensure that crew members begin their missions in optimal nutritional status, to document changes in status during a mission, and to assess changes after landing to facilitate return of the crew to their normal status as soon as possible after landing. Nutritional assessment provides the basis for intervention, if it is necessary, to maintain optimal status throughout the mission. We report here our nutritional assessment of the US astronauts who participated in the first twelve International Space Station missions.

Smith, Scott↗

NASA NTRS2006

Interactions between Artificial Gravity, the Affected Physiological Systems, and Nutrition

Malnutrition, either by insufficient supply of some nutrients or by overfeeding, has a profound effect on the health of an organism. Therefore, optimal nutrition is a necessity in normal gravity on Earth, in microgravity, and when applying artificial gravity to the human system. Reduced physical activity, such as observed in microgravity or bed rest, has an effect on many physiological systems, such as the cardiovascular, musculoskeletal, immune, and body fluids regulation systems. There is currently no countermeasure that is effective to counteract both the cardiovascular and musculoskeletal deconditioning when applied for a short duration (see Chapter 1). Artificial gravity therefore seems the simplest physiological approach to keep these systems intact. The application of intermittent daily dose of artificial gravity by means of centrifugation has often been proposed as a potential countermeasure against the physiological deconditioning induced by spaceflight. However, neither the optimal gravity level, nor its optimal duration of exposure have been enough studied to recommend a validated, effective, and efficient artificial gravity application. As discussed in previous chapters, artificial gravity has a very high potential to counteract any changes caused by reduced physical activity. The nutrient supply, which ideally should match the actual needs, will interact with these changes and therefore has also to be taken into account. This chapter reviews the potential interactions between these nutrients (energy intake, vitamins, minerals) and the other physiological systems affected by artificial gravity generated by an on-board short-radius centrifuge.

Heer, Martina↗

NASA NTRS2004

Wavefront Sensing Using a Multi-Object Spectrograph (NIRSpec)

An analysis is presented that illustrates how the James Webb Space Telescope (JWST) fine-phasing process can be carried out using the Near-Infrared Spectrograph (NIRSpec) data collected at the science focal plane. The analysis considers a multi-plane diffraction model which properly accounts for the microshutter diffractive element placed at the first relay position of the spectrograph. Wavefront sensing results are presented based on data collected from the NASA Goddard Microshutter Testbed.

Dean, Bruce H.↗

NASA NTRS1993

Preliminary analysis of the benefits derived to US Air Force spacecraft from on-orbit refueling

This analysis was undertaken during FY-91 as a preliminary step to identify potential benefits from refueling Air Force satellites on orbit. Both economic and operational benefits were included. Operational benefits were related in economic terms to allow evaluation. All economic comparisons were made using FY-91 costs. An additional purpose of the effort was to identify the preferred mission parameters, for an on-orbit refueling system. A companion study was being concurrently conducted by SSD/XRP and NASA/JPL to develop a hardware concept for an on-orbit refueling system. The mass estimates for refueling missions obtained from the companion study were used in conducting the economic analyses of this benefits study. For this study, on-orbit refueling was based on the concept developed in the companion JPL study. The concept involves launching an S/C carrying fuel that would be transferred to another 'target' S/C which is already in orbit. The two S/C would then rendezvous, dock, and transfer fuel. Another fluid, such as a cryogenic, might be included if needed by the target S/C. The hardware concept for refueling was intended to minimize costs. The re-fueler S/C was designated to be expendable and would contain only the minimal capabilities. It would be launched into the orbit plane and altitude of the target S/C(s). The re-fueler S/C would rendezvous and dock with the target S/C and the fluid transfer would occur. When the refueling mission was completed, the re-fueler S/C would be ejected from the orbit. In order to optimize launch costs, some missions involved launching two re-fueler S/C on the LV. In this case the second re-fueler S/C would be placed in a storage orbit until needed.

Smith, Scott↗