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Ehlers, H. K. F.

Publications and source records attributed to Ehlers, H. K. F..

14 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Spacecraft external molecular contamination analysis

Control of contamination on and around spacecraft is required to avoid adverse effects on the performance of instruments and spacecraft systems. Recent work in this area is reviewed and discussed. Specific issues and limitations to be considered as part of the effort to predict contamination effects using modeling techniques are addressed. Significant results of Space Shuttle missions in the field of molecule/surface interactions as well as their implications for space station design and operation are reviewed.

Ehlers, H. K. F.↗
NASA NTRS1985

The Space Shuttle Orbiter molecular environment induced by the supplemental flash evaporator system

The water vapor environment of the Space Shuttle Orbiter induced by the supplemental flash evaporator during the on-orbit flight phase has been analyzed based on Space II model predictions and orbital flight measurements. Model data of local density, column density, and return flux are presented. Results of return flux measurements with a mass spectrometer during STS-2 and of direct flux measurements during STS-4 are discussed and compared with model predictions.

Ehlers, H. K. F.↗
NASA NTRS1985

Shuttle on-orbit contamination and environmental effects

Ensuring the compatibility of the space shuttle system with payloads and payload measurements is discussed. An extensive set of quantitative requirements and goals was developed and implemented by the space shuttle program management. The performance of the Shuttle system as measured by these requirements and goals was assessed partly through the use of the induced environment contamination monitor on Shuttle flights 2, 3, and 4. Contamination levels are low and generally within the requirements and goals established. Additional data from near-term payloads and already planned contamination measurements will complete the environment definition and allow for the development of contamination avoidance procedures as necessary for any payload.

Leger, L. J.↗
NASA NTRS1984

An analysis of return flux from the Space Shuttle Orbiter RCS engines

The return flux from the Space Shuttle Orbiter reaction control system (RCS) engines to sensors in the open payload bay has been analyzed on the basis of Shuttle/Payload Contamination Evaluation (SPACE II) model predictions and orbital flight measurements. Model data are presented showing the variations of molecular return flux values with Orbiter orientation and instrument direction. The effects of multiple molecular collisions within RCS engine plumes and in their vicinity are discussed. These collisions significantly influence the amount of plume molecules returning to payload instruments and, therefore, the amount of contaminants received.

Ehlers, H. K. F.↗
NASA NTRS1983

Modeling correlation with flight data

The molecular contamination flow model (space 2 program) predicts the induced environment of the space shuttle orbiter/payload on orbit as well as the induced gas flow between the orbiter and payload surfaces. This computer program relates the input parameters which characterize the time dependent status of the orbiter/payload to the required output parameters. An application of the model to data from space transportation system flights 1, 2, and 3 shows that the model correlates well for direct flow and for return flux (STS-2/H2O). Correlation for return flux from other molecular sources/species appears to be within expectations but more analysis is required. The space 2 model seems to be an adequate predictive tool.

Ehlers, H. K. F.↗
NASA NTRS1983

Space Shuttle contamination measurements from flights STS-1 through STS-4

Results of contamination measurements performed on the initial four flights of the Space Shuttle Orbiter are summarized and compared with requirements contained in the Space Shuttle Flight and Ground System Specifications and those formulated by the Contamination Requirements Definition Group. In general, the results of measurements carried out with the induced environment contamination monitor indicate that molecular fluxes, deposition rates, and average counts of particulates are within the requirements and close to predicted values. Among the exceptions, were such special circumstances as water dumps, payload bay door closures, and RCS engine, APU, and flash evaporator operations which led to molecular and particulate contamination levels exceeding the limits. In cases where these circumstances would interfere with sensitive payload operations, careful mission planning to preclude a contamination source by operational limitation should be done to avoid losses.

Ehlers, H. K. F.↗
NASA NTRS1982

Space Shuttle preliminary. Contamination assessment from STS-1 and STS-2

A preliminary assessment of the space shuttle contamination environment was made using data from the first two orbital flight tests, STS-1 and STS-2. Data sources consisted of crew observations during flight, postflight vehicle inspection, and the induced environment contamination monitor which was used on STS-2 and consists of 10 instruments. These instruments are used to measure gas phase contaminants, particle population, humidity, and molecular deposition in the orbiter payload bay during ascent and descent and particle population, molecular deposition, and gas cloud during orbital flight. Results of the measurements described are presented in summary form and indicate low molecular deposition rates for both pressurized and orbital flight.

Leger, L. J.↗
NASA NTRS1982

Shuttle payload integration - Contamination aspects

As part of the development of the Space Shuttle, a payload integration system has been established. This integration system or process encompasses several technical disciplines, one of which is concerned with the control of molecular and particulate contamination. Specific integration procedures and documentation have evolved that reflect the incorporation of payload/Space Transportation System contamination requirements and capabilities. Of the 38 payloads in the payload integration system currently, about 20% are considered sensitive to contamination in that special precautions must be taken to ensure that contamination from the Space Shuttle Orbiter does not impair payload function. Most of these payload requirements have been satisfied by the incorporation of controlled ground operations discipline and installation of a payload bay liner, which isolates the payload from the Orbiter systems. Some payloads, however, provide covers for sensitive payload instrumentation.

Jacobs, S.↗
NASA NTRS1978

Space Shuttle contamination overview

Consideration is given to particle and gaseous contamination associated with Shuttle payload orbital delivery. An approach to control contamination is discussed which consists of analytical environment assessment, vehicle design optimization, and flight environment measurement. The analytical assessment of orbital contamination source characteristics and their effects on the Shuttle orbital environment has resulted in vehicle design changes and a detailed understanding of system operational flexibility. Verification of resulting Shuttle contamination performance will be made by the Induced Environment Contamination Monitor.

Leger, L.↗
NASA NTRS1972

Directional molecular flow analysis and leak detection with a rotatable gas analyzer in a large space simulation chamber

A system was developed and applied at the NASA Manned Spacecraft Center for measuring and analyzing directional molecular flows in a large thermal vacuum chamber in order to verify molecular environment and identify characteristic and abnormal test article and chamber conditions. The system is described, and some results obtained in over 1200 hours of operation are given.

Ehlers, H. K. F.↗