Engineering topics

Niedner, Malcolm B.

Publications and source records attributed to Niedner, Malcolm B..

6 records

NASA NTRS2017

Model-Based Thermal System Design Optimization for the James Webb Space Telescope

Spacecraft thermal model validation is normally performed by comparing model predictions with thermal test data and reducing their discrepancies to meet the mission requirements. Based on thermal engineering expertise, the model input parameters are adjusted to tune the model output response to the test data. The end result is not guaranteed to be the best solution in terms of reduced discrepancy and the process requires months to complete. A model-based methodology was developed to perform the validation process in a fully automated fashion and provide mathematical bases to the search for the optimal parameter set that minimizes the discrepancies between model and data. The methodology was successfully applied to several thermal subsystems of the James Webb Space Telescope (JWST). Global or quasiglobal optimal solutions were found and the total execution time of the model validation process was reduced to about two weeks. The model sensitivities to the parameters, which are required to solve the optimization problem, can be calculated automatically before the test begins and provide a library for sensitivity studies. This methodology represents a crucial commodity when testing complex, large-scale systems under time and budget constraints. Here, results for the JWST Core thermal system will be presented in detail.

Cataldo, Giuseppe↗

NASA NTRS2017

JWST Point Spread Function Quality and Stability: Ground Testing, Integrated Modeling, and Space Validation

The James Webb Space Telescope (JWST) is a large (6.5 m) cryogenic segmented aperture telescope with science instruments that cover the near- and mid-infrared from 0.6-27 microns. The large aperture not only provides high photometric sensitivity, but it also enables high angular resolution across the bandpass, with a diffraction limited point spread function (PSF) at wavelengths longer than 2 microns. The JWST PSF quality and stability are intimately tied to the science capabilities as it is convolved with the astrophysical scene. However, the PSF evolves at a variety of timescales based on telescope jitter and thermal distortion as the observatory attitude is varied. We present the image quality and stability requirements, recent predictions from integrated modeling, measurements made during ground-based testing, and performance characterization activities that will be carried out as part of the commissioning process.

McElwain, Michael↗

NASA NTRS2010

Early Scientific Results and Future Prospects for the Rejuvenated Hubble Space Telescope

Following the extraordinarily successful Servicing Mission 4 (SM4) of Hubble Space Telescope (HST) in May of 2009, the Observatory is now fully equipped with a broad array of powerful science instruments that put it at the pinnacle of its scientific power. Relevant to the subject matter of the Beyond 2010 Conference, HST will be well-placed over the next five-plus years to advance our knowledge of the formation of high-redshift galaxies and their growth with cosmic time; the emergence of structure in the early universe via Dark Matter-driven gravitational instability; and the universe's expansion history and any resulting implications for the temporal character of Dark Energy. These are fitting projects for the iconic facility now celebrating its 20th anniversary in orbit.

Niedner, Malcolm B.↗

NASA NTRS1991

Comet Halley remote plasma tail observations and in situ solar wind properties - Vega-1/2 IMF/plasma observations and ground-based optical observations from 1 December 1985 to 1 May 1986

General features of the solar wind plasma and the interplanetary magnetic field (IMF) are studied for the time period of December 1, 1985 - May 1, 1986. Characteristics studied include corotating events, shocks, and sector boundaries in the IMF. For the same period, Comet Halley was near its perihelion and many ground-based observations of the plasma tail were made. They show interesting events such as tail substorms and disconnection events where the whole distant plasma tail seems to be disrupted from the part that is still attached to the cometary head. Several mechanisms have been produced to explain the cause of these events. The correlation between the IMF sector boundaries measured by Vega and the observed disconnection events are studied, noting that such a correlation would support the dayside reconnection explanation. It is found that only in 50 percent of the considered events does a correlation between these two phenomena exist. For the other cases, a sector boundary of the IMF sweeping over the comet cannot explain the occurrence of disruptions of the main plasma tail.

Delva, Magda↗

NASA NTRS1990

A tail-wagging event in comet Austin

On the morning of 21 May 1990, a sequence of images of Comet Austin was obtained in the light of H2O+. The filter was centered at 602.5 nm with FWHM of 5.0 nm. At least two waves were followed out through the main ion tail structure. During the course of the observations, 2.5 hours, two new tail rays were seen to form and undergo similar wave motion. Several condensations, possibly representing disconnected material, were seen to develop and move out along the tail ray with a velocity of about 60 km/sec.

Klinglesmith, Daniel A.↗

NASA NTRS1987

Ultraviolet spectrophotometry of Comet Giacobini-Zinner during the ICE encounter

The IUE's UV spectrophotometer was used to monitor Comet Giacobini-Zinner's H2O production rate from June to October, 1985, in support of the International Cometary Explorer (ICE) mission. Observation results for the spatial and temporal variation and the abundance or upper limits of C, CO, CO(+), CO2(+), CS, H, Mg(+), O, OH, and S, between September 9 and 12, included the time of the ICE encounter: at this time, the H2O production rate obtained was consistent with a number of gas production rates derived indirectly from the ICE experiments. A comparison of the CO2(+) ion abundance with the total electron density measured by the plasma electron and radio science experiments on ICE implies an ion deficiency relative to electrons, so that the satisfaction of charge balance criteria requires the presence of a major ion population not detected by remote sensing.

Mcfadden, Lucy A.↗