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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 379 records · Page 21
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NASA NTRS1972

Comparison of advanced propulsion concepts for deep space exploration

Equations and charts are presented that permit rapid estimation of propulsion-system performance requirements for some typical deep-space missions. A number of advanced propulsion concepts for which performance estimates are available are compared with respect to their capability for flyby, rendezvous, and roundtrip planetary missions. Based on these estimates, the gas-core nuclear fission rocket and the pulsed fusion rocket yield the fastest trip times to the near planets. For round trips to Jupiter and beyond, the controlled fusion rocket shows progressively superior capabilities. Several propulsion concepts based on use of impinging laser beams are found to be noncompetitive with the other advanced concepts for deep space missions. Requirements for attainment of interstellar distances within a human lifetime are found to be some orders of magnitude beyond the capabilities of any propulsion concepts for which performance estimates are now possible.

Moeckel, W. E.↗
NASA NTRS1972

The oscillator strengths of the SO /A 3Pi/-/X 3Sigma-/ band systems.

The oscillator strengths for these SO transition band systems are calculated using RKR Franck-Condon factors and the radiative lifetime previously derived from electron-beam phase-shift measurements by Smith (1971). The SO transition concerned is of considerable astrophysical importance in the search for SO in the interstellar medium by means of space-based telescopes with monochromators since the transition probability is concentrated, as shown, in relatively few transitions from the ground state.

Smith, W. H.↗
NASA NTRS1993

(abstract) Infrared Cirrus and Future Space Based Astronomy

A review of the known properties of the distribution of infrared cirrus is followed by a discussion of the implications of cirrus on observations from space. Probable limitations on space observations due to IR cirrus.

cirrus infrared space observations astronomy inter↗
NASA NTRS2020

A Modified Algorithm and Open-Source Computational Package for the Determination of Infrared Optical Constants Relevant to Astrophysics

Infrared (IR) telescopes, such as Spitzer and SOFIA, have revealed a rich variety of chemical species trapped in interstellar ices. The most fundamental parameters to be derived from observed IR spectra are the identity and abundance of each component. Several compounds have been conclusively or tentatively identified, but the band strengths and optical constants needed to derive accurate abundances for many of these are poorly constrained. We have developed a modified approach to the extraction of the real and imaginary parts of the refractive index (optical constants) of a thin film from a single transmission spectrum measured in the IR spectral range. Our algorithm is similar to those implemented by previous authors, with some major changes that yield results for strong absorptions where previous approaches fail: (1) an adaptive k-correction step size, (2) the use of a root-finding algorithm to obtain a more accurate k-correction at each iteration, and (3) a k-correction step that prevents non-physical results such as negative n-values that prevent convergence in the calculation algorithm. The algorithm is presented and described, with examples to show agreement with some existing results and improvements upon others. New optical-constants calculations for CH3OH, CO2, N2O, and CH4 are presented, and potential implications for the modeling of interstellar and planetary ice data from space telescopes are discussed. With the objective of being open-source and transparent, the full source code in the free Python programming language is made available along with the compiled version and the laboratory data used to produce the results shown.

Perry A. Gerakines↗
NASA NTRS2017

The Detection of 6.9 µm Emission Features in the Infrared Spectra of IRAS 04296+3429, IRAS 05341+0852, IRAS 22272+5435: Evidence for the Presence of Hn-PAHs in Post AGB Stars

Polycyclic aromatic hydrocarbons (PAHs) are generally believed to be ubiquitous in space and responsible for numerous telltale interstellar infrared emission bands. In Sandford et al., (2013), we suggested that polycyclic aromatic hydrocarbons with excess hydrogenation at their periphery (Hn-PAHs) may be an important subclass of these molecules in some astrophysical environments. These molecules are candidates to explain objects with anomalously large 3.4 μm features, which are presumed to be associated with the aliphatic C—H stretching vibrations of the excess hydrogen. In that work, we suggest that for Hn-PAHs to be a viable candidate as the source for this 3.4 μm feature, we must also expect to observe methylene scissoring modes at 6.9 μm. In this work, we continue to develop the Hn-PAH hypothesis with a focus on the 6.9 μm feature. We also present some new observations of three post-asymptotic giant branch (post- AGB) objects with abnormally large 3.4 μm features, IRAS 04296+3429, IRAS 05341+0852, IRAS 22272+5435, in addition to one post-AGB object with normal PAH emissions, IRAS 20000+3239. These observations were made using the FORCAST instrument in grism mode on the Stratospheric Observatory for Infrared Astronomy (SOFIA) aircraft (Adams et al. 2010) and demonstrate the presence of a 6.9 μm feature for the three objects with abnormally large 3.4 μm features and no detectable 6.9 μm feature for the normal PAH emitter. These results are consistent with the hypothesis that Hn-PAHs are a possible source of these infrared emission bands.

ISM↗
NASA NTRS2026

Isotopic Signature of Organic Molecules from Beyond the Solar System: An Enriched Methane D/H Ratio in the Interstellar Object 3I/ATLAS

Interstellar objects are interlopers from other planetary systems, and their volatile compositions provide a glimpse into planet formation around their host star. We present near-infrared spectra of the coma of interstellar object 3I/ATLAS measured with the James Webb Space Telescope. Our results demonstrate an unexpectedly high D/H = (3.31 ± 0.34)% for methane and represent an exceedingly rare detection of deuterated organic molecules in an interstellar object. This D/H ratio is a factor of 14 ± 2 higher than that measured in comet 67P/Churyumov-Gerasimenko by the Rosetta spacecraft, the only other comet for which CH3D has been detected, yet the ratio of deuteration in methane compared with water is consistent for both comets within 1.2σ. The D/H ratio in methane is observationally unconstrained in extrasolar sources to date, but the enriched ratio in 3I/ATLAS is most similar to those measured in other organic molecules toward primitive environments. The high D/H ratios of water and methane in 3I/ATLAS are a natural consequence of formation in a high D/H elemental ratio environment as a result of locally cold conditions in the protoplanetary disk and prior interstellar cloud. Thus, 3I/ATLAS formed in an environment very different from that in which our Sun and planets originated.

Interstellar Object 3I/ATLAS↗
NASA NTRS1998

X-Ray Emission from Protostellar Jets

The goals of this program were to identify the termination shocks in several parsec-scale protostellar jets through the thermal soft X-rays emitted by the high-velocity terminal shock waves, and to assess the impact these outflows have on the surrounding interstellar and intercloud medium. The terminal shock waves that plow into the undisturbed interstellar medium may have shock velocities commensurate with the observed space motions of several hundred km s(exp -1). Such shocks will heat and ionize the interstellar medium, perhaps creating large ovoid bubbles of hot gas. Identifying the location of the terminal shocks in these outflows would also allow us to place constraints on the ages of these outflows, and hence the duration of the mass-loss phase that accompanies the formation of a star. We targeted four outflows where the outer optical shock waves are projected against low-extinction backgrounds. From the two dozen or so parsec-scale flows known, we chose those that have the highest velocities, brightest optical counterparts, and/or the richest concentration of shock waves in a small area on the sky. Four giant HH flows have been observed with the ROSAT HRI at Priority A for 30 ksec each. Results: Unfortunately, we failed to detect X-ray emission from the terminal bow shocks of the giant HH flows using the ROSAT HRI. The reasons are likely to be: (1) The shock velocities may be too low to emit in the soft X-rays. (2) The sensitivity of the HRI is too low to detect the diffuse emission. The fields that we observed were chosen to be low extinction sight-lines, with the consequence that the tenuous media into which the outer bow shocks are propagating produce low fluxes. Despite the failure to achieve the primary science goals, we have identified in each image a half a dozen or so point-source young stellar objects. The HRI images have been very useful for discerning potential outflow sources and are being combined with optical, near-IR, and radio imaging data of each outflow field. The first paper on L1551 NE is currently in preparation.

Morse, Jon A.↗
NASA NTRS1990

Use of magnetic sails for advanced exploration missions

The magnetic sail, or magsail, is a field effect device which interacts with the ambient solar wind or interstellar medium over a considerable volume of space to generate drag and lift forces. Two theories describing the method of thrust generation are analyzed and data results are presented. The techniques for maintaining superconductor temperatures in interplanetary space are analyzed and low risk options presented. Comparisons are presented showing mission performance differences between currently proposed spacecraft using chemical and electric propulsion systems, and a Magsail propelled spacecraft capable of generating an average thrust of 250 Newtons at a radius of one A.U. The magsail also provides unique capabilities for interstellar missions, in that at relativistic speeds the magnetic field would ionize and deflect the interstellar medium producing a large drag force. This would make it an ideal brake for decelerating a spacecraft from relativistic speeds and then maneuvering within the target star system.

Andrews, Dana G.↗
NASA NTRS2005

PAHs and the Diffuse Interstellar Bands. What have we Learned from the New Generation of Laboratory and Observational Studies?

Polycyclic Aromatic Hydrocarbons (PAHs) are an important and ubiquitous component of carbon-bearing materials in space. PAHs are the best-known candidates to account for the IR emission bands (UIR bands) and PAH spectral features are now being used as new probes of the ISM. PAHs are also thought to be among the carriers of the diffuse interstellar absorption bands (DIBs). In the model dealing with the interstellar spectral features, PAHs are present as a mixture of radicals, ions and neutral species. PAH ionization states reflect the ionization balance of the medium while PAH size, composition, and structure reflect the energetic and chemical history of the medium. A major challenge for laboratory astrophysics is to reproduce (in a realistic way) the physical conditions that exist in the emission and/or absorption interstellar zones, An extensive laboratory program has been developed at NASA Ames to characterize the physical and chemical properties of PAHs in astrophysical environments and to describe how they influence the radiation and energy balance in space and the interstellar chemistry. In particular, laboratory experiments provide measurements of the spectral characteristics of interstellar PAH analogs from the ultraviolet and visible range to the infrared range for comparison with astronomical data. This paper will focus on the recent progress made in the laboratory to measure the direct absorption spectra of neutral and ionized PAHs in the gas phase in the near-W and visible range in astrophysically relevant environments. These measurements provide data on PAHs and nanometer-sized particles that can now be directly compared to astronomical observations. The harsh physical conditions of the IS medium - characterized by a low temperature, an absence of collisions and strong V W radiation fields - are simulated in the laboratory by associating a molecular beam with an ionizing discharge to generate a cold plasma expansion. PAH ions are formed from the neutral precursors in an isolated environment at low temperature (of the order of 100 K). The spectra of neutral and ionized PAHs are measured using the high sensitivity methods of cavity ring down spectroscopy (CRDS). These experiments provide unique information on the spectra of free, cold large carbon molecules and ions in the gas phase. Intrinsic band profiles and band positions of cold gas-phase PAHs can now be measured with high- sensitivity spectroscopy and directly compared to the astronomical data. The electronic bands measured for ionized PAH are found to be intrinsically broad (about 20/cm) while the bands associated with the neutral precursors are narrower (of the order of 2 - 10/cm).

Salama, Farid↗
NASA NTRS1994

A rare gas optics-free absolute photon flux and energy analyzer to provide absolute photoionization rates of inflowing interstellar neutrals

A prototype spectrometer has been developed for space applications requiring long term absolute EUV photon flux measurements. The energy spectrum of the incoming photons is transformed directly into an electron energy spectrum by taking advantage of the photoelectric effect in one of several rare gases at low pressures. Using an electron energy spectrometer, followed by an electron multiplier detector, pulses due to individual electrons are counted. The overall efficiency of this process can be made essentially independent of gain drifts in the signal path, and the secular degradation of optical components which is often a problem in other techniques is avoided. A very important feature of this approach is its freedom from the problem of overlapping spectral orders that plagues grating EUV spectrometers. An instrument with these features has not been flown before, but is essential to further advances in our understanding of solar EUV flux dynamics, and the coupled dynamics of terrestrial and planetary atmospheres. The detailed characteristics of this optics-free spectrometer are presented in the publications section.

Judge, Darrell L.↗
NASA NTRS1995

Atomic Physics with the Goddard High-Resolution Spectrograph on the Hubble Space Telescope: Oscillator Strengths for Neutral Sulfur - No. 1

Interstellar spectra toward zeta Oph acquired with the Goddard High-Resolution Spectrograph were used to obtain oscillator strengths for approximately two dozen S I lines. This analysis was possible because precisely determined experimental oscillator strengths are available for several multiplets, including one with a weak interstellar line. The self-consistent set of oscillator strengths then was obtained from a curve of growth based on line strengths spanning a range of a factor of 100. The derived f-values for a number of multiplets differ from values quoted by Morton (1991) but are generally consistent with the suite of available experimental and theoretical results.

Federman, S. R.↗
NASA NTRS2019

Electric Sail Propulsion for Deep Space Missions

Electrostatic Sail (E-sail) propulsion extracts momentum from the solar wind, which has minimal speeds of 400 km/sec, through electrostatic repulsion of the positively charged solar wind ions. This momentum exchange is accomplished by an array of multi-kilometer-length charged tethers biased to a high positive voltage, producing an electric field around the tethers that deflect the positively charged solar wind particles. This electric field grows in diameter as the spacecraft moves away from the sun, increasing the E-sail effective area. The growth of the E-sail effective area allows the created propulsive force to decrease at a rate closer to 1/r out to distances from the sun of up to 20 Astronomical Units (AU). This is unlike solar sail propulsion, where the thrust decreases at a rate of 1/r2 and is only effective out to distances of ~5 AU. The propulsive force is applied without expending any propellant. Although the thrust generated by an E-Sail is low, it can be applied continuously over a period of years (depending on the mission type), and can push a 500 kg spacecraft to tremendous velocities—as high as 12 AU per year—making the voyage to 600 AU in as few as 50 years after launch. The NASA Marshall Space Flight Center recently completed a NASA Innovative Advanced Concept (NIAC) study in which all of the major system- and subsystem-level aspects of an E-Sail-propelled vehicle were assessed and a maturation plan developed. If implemented, E-Sail propulsion could be realized and deployed as a viable option for space missions within a decade.

Interstellar Probe↗
NASA NTRS2004

Vibrational Spectroscopy of Ions and Radicals Present in the Interstellar Medium and in Planetary Atmospheres: A Theoretical Study

Anharmonic vibrational frequencies and intensities are calculated for OH(H2O)n and H(H2O)n radicals (that form on icy particles of the interstellar medium), HCO radical (the main intermediate in the synthesis of organic molecules in space), NH2(-) and C2H(-) anions, H5(+) cation, and other systems relevant to interstellar chemistry. In addition to pure ions and radicals, their complexes with water are studied to assess the effects of water environment on infrared spectra. The calculations are performed using the correlation-corrected vibrational self-consistent field (CC-VSCF) method with ab initio potential surfaces at the MP2 and CCSD(T) levels. Fundamental, overtone, and combination excitations are computed. The results are in good agreement with available experimental data and provide reliable predictions for vibrational excitations not yet measured in laboratory experiments. The data should be useful for interpretation of astronomically observed spectra and identification of ions and radicals present in the interstellar medium and in planetary atmospheres.

Chaban, Galina M.↗
NASA NTRS2012

Submillimeter Measurements of Photolysis Products in Interstellar Ice Analogs: A New Experimental Technique

Over 150 molecular species have been confirmed in space, primarily by their rotational spectra at millimeter/submillimeter wavelengths, which yield an unambiguous identification. Many of the known interstellar organic molecules cannot be explained by gas-phase chemistry. It is now presumed that they are produced by surface reactions of the simple ices and/or grains observed and released into the gas phase by sublimation, sputtering, etc. Additionally, the chemical complexity found in meteorites and samples returned from comets far surpasses that of the remote detections for the interstellar medium (ISM), comets, and planetary atmospheres. Laboratory simulations of interstellar/cometary ices have found, from the analysis of the remnant residue of the warmed laboratory sample, that such molecules are readily formed; however, it has yet to be determined if they are formed during the warm phase or within the ice during processing. Most analysis of the ice during processing reveals molecular changes, though the exact quantities and species formed are highly uncertain with current techniques due to overwhelming features of simple ices. Remote sensing with high resolution spectroscopy is currently the only method to detect trace species in the ISM and the primary method for comets and icy bodies in the Solar System due to limitations of sample return. We have recently designed an experiment to simulate interstellar/cometary/planetary ices and detect trace species employing the same techniques used for remote observations. Preliminary results will be presented.

Milam, Stefanie N.↗
NASA NTRS2002

The Laboratory Production of Complex Organic Molecules in Simulated Interstellar Ices

Much of the volatiles in interstellar dense clouds exist in ices surrounding dust grains. Their low temperatures preclude most chemical reactions, but ionizing radiation can drive reactions that produce a suite of new species, many of which are complex organics. The Astrochemistry Lab at NASA-Ames studies the UV radiation processing of interstellar ice analogs to better identify the resulting products and establish links between interstellar chemistry, the organics in meteorites, and the origin of life on Earth. Once identified, the spectral properties of the products can be quantified to assist with the search for these species in space. Of particular interest are findings that UV irradiation of interstellar ice analogs produces molecules of importance in current living organisms, including quiriones, amphiphiles, and amino acids. Quinones play a variety of roles including electron transport and are used by all organisms. Studies show that quinones should be made wherever polycyclic aromatic hydrocarbons are irradiated in interstellar ices (Bernstein et al. 2001). Amphiphiles are also made when mixed molecular ices are irradiated. These amphiphiles self-assemble into membrane-walled vesicles when put in liquid water (Dworkin et al. 2001). Ice irradiation can also produce (Bernstein et al. 2002) and destroy amino acids (Ehrenfreund et al. 2001). Many of the same processes thought to make organics in space should yield products highly enriched in deuterium (D) (Sandford et al. 2001). The high D/H ratios in some interstellar species, and the knowledge that many of the organics in primitive meteorites are D-enriched, suggests that such linkages do exist. By using D as a tracer, we expect to learn more about the different chemical processes occurring in space and their relative importance in the production of different organic compounds and delivery to planetary surfaces.

Dworkin, Jason P.↗