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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,549 records · Page 86
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Extracting ocean surface information from altimeter returns - The deconvolution method

An evaluation of the deconvolution method for estimating ocean surface parameters from ocean altimeter waveforms is presented. It is shown that this method presents a fast, accurate way of determining the ocean surface parameters from noisy altimeter data. Three parameters may be estimated by using this method, including the altimeter-height error, the ocean-surface standard deviation, and the ocean-surface skewness. By means of a Monte Carlo experiment, an 'optimum' deconvolution algorithm and the accuracies with which the above parameters may be estimated using this algorithm are determined. Then the influence of instrument effects, such as errors in calibration and pointing-angle estimation, on the estimated parameters is examined. Finally, the deconvolution algorithm is used to estimate height and ocean-surface parameters from Seasat data.

Rodriguez, Ernesto↗
NASA NTRS1988

Space Shuttle solid rocket motor testing for return to flight

Significant design changes made to major components of the NASA Space Shuttle SRM are summarized. The extent of changes made in the nozzle-to-case joint to better protect the joint O-ring seals is indicated schematically as are changes made to the motor nozzle. It is noted that the use of subscale, full scale/short duration burn hardware tests to provide data for structural and thermal analytical models was necessary.

Coates, Keith D.↗
NASA NTRS1989

Prompt Gamma Activation Analysis (PGAA): Technique of choice for nondestructive bulk analysis of returned comet samples

Prompt gamma activation analysis (PGAA) is a well-developed analytical technique. The technique involves irradiation of samples in an external neutron beam from a nuclear reactor, with simultaneous counting of gamma rays produced in the sample by neutron capture. Capture of neutrons leads to excited nuclei which decay immediately with the emission of energetic gamma rays to the ground state. PGAA has several advantages over other techniques for the analysis of cometary materials: (1) It is nondestructive; (2) It can be used to determine abundances of a wide variety of elements, including most major and minor elements (Na, Mg, Al, Si, P, K, Ca, Ti, Cr, Mn, Fe, Co, Ni), volatiles (H, C, N, F, Cl, S), and some trace elements (those with high neutron capture cross sections, including B, Cd, Nd, Sm, and Gd); and (3) It is a true bulk analysis technique. Recent developments should improve the technique's sensitivity and accuracy considerably.

Lindstrom, David J.↗
NASA NTRS1989

Measurements of long-lived cosmogenic nuclides in returned comet nucleus samples

Measurements of long lived cosmic ray produced radionuclides have given much information on the histories and rates of surface evolution for meteorites, the Moon and the Earth. These nuclides can be equally useful in studying cometary histories and post nebular processing of cometary surfaces. The concentration of these nuclides depends on the orbit of the comet (cosmic ray intensity changes with distance from the sun), the depth of the sampling site in the comet surface, and the rate of continuous evolution of the surface (erosion rate of surface materials). If the orbital parameters and the sampling depth are known, production rates of cosmogenic nuclides can be fairly accurately calculated by theoretical models normalized to measurement on lunar surface materials and meteoritic samples. Due to the continuous evaporation of surface materials, it is expected that the long lived radioactivities will be undersaturated. Accurate measurements of the degree of undersaturation in nuclides of different half-lives allows for the determination of the rate of surface material loss over the last few million years.

Nishiizumi, K.↗
NASA NTRS1989

America's shuttle returns to space

The Shuttle management structure, streamlined since the Challenger accident, is outlined. The associate administrators for space flight are identified and their responsibilities clearly spelled out. The NASA policy of assigning astronauts to management positions is described. A spaceflight safety panel is described. Non-managerial safety enhancement programs are outlined. These include: solid rocker booster changes, shuttle crew escape systems, and landing improvements.

Moorehead, Robert W.↗
NASA NTRS1990

Return to the moon - The Lunar Observer mission

The Lunar Observer mission seeks to understand the moon in its global context. Motivation for this project comes from scientific interest and the need for robotic precursor missions in the proposed Space Exploration Initiative. The multiple roles to be performed by this mission mean that the trajectory design process promises to be quite complex and unique. The choice of launch vehicle, launch opportunity and daily launch window are affected by the selection of the translunar transfer trajectory, as well as the arrival conditions desired at lunar orbit insertion. The length of the mission and the tight lunar orbit control requirements determine the design of the circumlunar portions of the Lunar Observer mission.

Cook, Richard A.↗
NASA NTRS1990

The SPICE concept - An approach to providing geometric and other ancillary information needed for interpretation of data returned from space science instruments

The Navigation Ancillary Information Facility (NAIF), acting under the direction of NASA's Office of Space Science and Applications, and with substantial participation of the planetary science community, is designing and implementing an ancillary data system - called SPICE - to assist scientists in planning and interpreting scientific observations taken from spaceborne instruments. The principal objective of the implemented SPICE system is that it will hold the essential geometric and related ancillary information needed to recover the full value of science instrument data, and that it will facilitate correlations of individual instrument datasets with data obtained from other instruments on the same or other spacecraft.

Acton, Charles H., Jr.↗
NASA NTRS1990

Telescience - Optimizing aerospace science return through geographically distributed operations

The paper examines the objectives and requirements of teleoperations, defined as the means and process for scientists, NASA operations personnel, and astronauts to conduct payload operations as if these were colocated. This process is described in terms of Space Station era platforms. Some of the enabling technologies are discussed, including open architecture workstations, distributed computing, transaction management, expert systems, and high-speed networks. Recent testbedding experiments are surveyed to highlight some of the human factors requirements.

Rasmussen, Daryl N.↗
NASA NTRS1991

Earth return aerocapture for manned Mars missions

Lift to drag ratio (L/D) requirements and stagnation point heating have been examined for a variety of probable entry conditions and vehicle configurations. It is found that vehicles with an L/D of 0.5 or more provide a corridor width of at least 0.7 degrees while keeping the peak deceleration load below 5 g for approach velocities up to 14.5 km/s. It is shown that stagnation point peak heating rates and integrated heat load critically depend on both entry velocity and ballistic coefficient. For the most severe cases under consideration, peak heating and integrated heat load are five times greater than those encountered by Apollo but within the range of experience for unmanned vehicles.

Tauber, M. E.↗
NASA NTRS1992

Remote Sensing by Spaceborne Lidar Aided by Surface Returns

Spaceborne lidar offers the possibility of global mapping of clouds and atmospheric aerosols. Mapping of cloud-top heights, multiple layers of thin clouds and the depth of the planetary boundary layer (PBL), given sufficient aerosols, are applications that should be fairly easy to accomplish from space with even a modest lidar system. However, the constraints imposed on spaceborne lidar by large ranging distances, limited available power/weight, and fast moving platforms present significant challenges to achieving more quantitative retrievals such as extracting aerosol extinction profiles, PBL optical depths and cloud optical depths. Ways to take advantage of the strong signals available from ground/sea reflections to improve upon atmospheric aerosol and cloud retrievals as well as to distinguish certain surface types are explored.

Reagan, J. A.↗
NASA NTRS1992

A variable phase function approach for the inversion of lidar return signals

A variable phase function is developed. This function may be used for the inversion of lidar data in an iterative process. Numerical simulations of this method were performed successfully, demonstrating fast convergence of the particulate phase function. The method will be used in the future to evaluate extinction and backscattering corrections for an Ultra-Violet Differential Absorption Lidar (UV-DIAL) system measuring tropospheric ozone concentrations.

Kovalev, V. A.↗
NASA NTRS1991

Magnetic radiation shielding - An idea whose time has returned?

One solution to the problem of shielding crew from particulate radiation in space is to use active electromagnetic shielding. Practical types of shield include the magnetic shield, in which a strong magnetic field diverts charged particles from the crew region, and the magnetic/electrostatic plasma shield, in which an electrostatic field shields the crew from positively charged particles, while a magnetic field confines electrons from the space plasma to provide charge neutrality. Advances in technology include high-strength composite materials, high-temperature superconductors, numerical computational solutions to particle transport in electromagnetic fields, and a technology base for construction and operation of large superconducting magnets. These advances make electromagnetic shielding a practical alternative for near-term future missions.

Landis, Geoffrey A.↗