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NASA NTRS1984

Helium and Hydrogen of the Local Interstellar Mdium Observed in the Vicinity of the Sun

The Sun illuminates the hydrogen and helium atoms of the interstellar medium through which it travels. As a result, the Sun and the whole solar system are imbedded in a glow of the resonance lines of hydrogen (H Lyman alpha; 121.6nm) and helium (58.4nm). From the intensity distribution of the glow in the solar system, the density of H and He in the local interstellar medium (LISM) and the direction of the relative motion between the Sun and the LISM in the vicinity of the Sun are derived. The velocity module and the LISM temperature are more adequately found from a measurement of the Lyman alpha line shape, which is an image of the velocity distribution of H atoms. The result is summarized and together the methods of interpretation and difficulties are dicusssed.

Bertaux, J. L.↗

NASA NTRS2024

Interstellar Propulsion

As you read this, humanity’s first interstellar probe has left our solar system and is moving at nearly 17 km/s on its journey through interstellar space. Launched in 1977 and carrying a message from Earth on an inscribed golden disk, Voyager 1 completed its grand tour of the outer planets and has since travelled more than 24 billion km on its outward journey; it’s twin probe, Voyager 2, has also left the heliopause and entered interstellar space, traveling over 20 billion km from Earth. Yet even at these speeds and distances, our intrepid Voyagers have barely moved beyond the influence of our local star. If the distance between our Sun and the closest neighboring star system, Alpha Centauri, were scaled to the size of a meter stick, Voyager 1 would be located just over the ½-mm mark, having traveled 0.06% of the way to the next star (assuming it was pointed in the right direction, which it isn’t). At this rate it will take the probe nearly 75 thousand years to cover the equivalent distance to Alpha Centauri.

Interstellar↗

NASA NTRS1994

Gasdynamic models of the solar wind/interstellar medium interaction

The interaction between the solar wind and the interstellar medium is modeled self-consistently using numerical solutions of the time-dependent gasdynamic equations in spherical and cylindrical coordinates. For the results presented here it is assumed that the solar system moves through the surrounding medium with a supersonic velocity. After an initial (nonequilibrium) state has been specified, the numerical solution follows the evolution in time until the interaction relaxes to a dynamic equilibrium. As would be expected, the solutions show the formation of a bow shock upstream of the traveling solar system to deflect the interstellar plasma around the cavity created by the solar wind. A terminiation shock also forms to slow and compress the solar wind plasma. For the simulation in spherical coordinates, the downstream portion of the termination shock reaches equilibrium more than three times further from the Sun than the equilibrium distance to the termination shock on the upstream side.

Steinolfson, R. S.↗

NASA NTRS1991

The composition of the cosmic rays - An update

The relative abundances of elements and/or isotopes in the cosmic radiation are the source of information on both the sites of cosmic ray origin and acceleration and the conditions in the interstellar medium through which the particles travel. Recent (1988-90) measurements and interpretations have provided new information on cosmic ray composition and source abundances. These new results are described and compared to previous work.

Wefel, John P.↗

NASA NTRS2019

Helical Engine

A new concept for in-space propulsion is proposed in which propellant is not ejected from the engine, but instead is captured to create a nearly infinite specific impulse. The engine accelerates ions confined in a closed loop to relativistic speeds, and slightly varies their velocity to change their momentum. The engine then moves the ions back and forth along the direction of travel to produce thrust. This in-space engine is intended to be used for long-term satellite station-keeping without refueling or to propel spacecraft across interstellar distances. The engine has no moving parts other than ions traveling in a closed-loop vacuum line, trapped inside electric and magnetic fields.

Burns, David M.↗

NASA NTRS2000

The Propulsion Center at MSFC

The Propulsion Research Center at MSFC serves as a national resource for research of advanced, revolutionary propulsion technologies. Our mission is to move the nation's capabilities beyond the confines of conventional chemical propulsion into an era of aircraft like access to earth-orbit, rapid travel throughout the solar system, and exploration of interstellar space. Current efforts cover a wide range of exciting areas, including high-energy plasma thrusters, advanced fission and fusion engines, antimatter propulsion systems, beamed energy rockets and sails, and fundamental motive physics. Activities involve concept investigation, proof-of-concept demonstration, and breadboard validation of new propulsion systems. The Propulsion Research Center at MSFC provides an environment where NASA, national laboratories, universities, and industry researchers can pool their skills together to perform landmark propulsion achievements. We offer excellent educational opportunities to students and young researchers-fostering a wellspring of innovation that will revolutionize space transportation.

Gerrish, Harold↗

NASA NTRS2005

Assessing Potential Propulsion Breakthroughs

The term, propulsion breakthrough, refers to concepts like propellantless space drives and faster-than-light travel, the kind of breakthroughs that would make interstellar exploration practical. Although no such breakthroughs appear imminent, a variety of investigations into these goals have begun. From 1996 to 2002, NASA supported the Breakthrough Propulsion Physics Project to examine physics in the context of breakthrough spaceflight. Three facets of these assessments are now reported: (1) predicting benefits, (2) selecting research, and (3) recent technical progress. Predicting benefits is challenging since the breakthroughs are still only notional concepts, but kinetic energy can serve as a basis for comparison. In terms of kinetic energy, a hypothetical space drive could require many orders of magnitude less energy than a rocket for journeys to our nearest neighboring star. Assessing research options is challenging when the goals are beyond known physics and when the implications of success are profound. To mitigate the challenges, a selection process is described where: (a) research tasks are constrained to only address the immediate unknowns, curious effects or critical issues, (b) reliability of assertions is more important than their implications, and (c) reviewers judge credibility rather than feasibility. The recent findings of a number of tasks, some selected using this process, are discussed. Of the 14 tasks included, six reached null conclusions, four remain unresolved, and four have opportunities for sequels. A dominant theme with the sequels is research about the properties of space, inertial frames, and the quantum vacuum.

Millis, Marc G.↗

NASA NTRS2000

Propulsion Options For Interstellar Exploration

NASA is considering missions to explore near-interstellar space (40 - 250 Astronomical Units) early in the next decade as the first step toward a vigorous interstellar exploration program. A key enabling technology for such an ambitious science and exploration effort is a propulsion system capable of providing fast trip times, yet which has low enough mass to allow for the use of inexpensive launch vehicles. Advanced propulsion technologies that might support the First interstellar precursor mission by the end of the first decade of the new millennium include solar sails and nuclear electric propulsion. Solar sails and electric propulsion are two technology areas that may hold promise for the next generation of interstellar precursor missions as well - perhaps a thousand astronomical units traveled in a professional lifetime. Future missions to far beyond the Heliosphere will require the development of propulsion technologies that are only at the conceptual stage today. For years, the scientific community has been interested in solar sail and electric propulsion technologies to support robotic exploration of the solar system. Progress in thin-film materials fabrication and handling, and advancement in technologies that may enable the deployment of large sails in space are only now maturing to the point where ambitious interstellar precursor missions using sails can be considered. Xenon ion propulsion is now being demonstrated for planetary exploration by the Deep Space 1 mission. The primary issues for the adaptation of electric propulsion to interstellar precursor applications include the development of low specific mass nuclear power systems, engine lifetime, and high power operation. Recent studies of interstellar precursor mission scenarios that use these propulsion systems will be described, and the range of application of each technology will be explored.

Johnson, Les↗

NASA NTRS1992

Ulysses probes solar wind, interstellar gas

The ESA-NASA Ulysses mission will furnish high-latitude observations which may deepen current understanding of the outward flow of gases from the magnetically open regions of the sun. Also furnished will be a clearer view of the processes in the Galaxy that create cosmic rays, and how cosmic rays enter the solar system. The Ulysses mission has already achieved important new results during its travel in the ecliptic plane; the density and temperature of the interstellar neutral He flowing into the solar system has been directly measured.

Goldstein, Bruce↗

NASA NTRS2018

Developed AprilNav, an Indoor Navigation and Localization System for Autonomous Testing of Electric Sail Dynamics

An electrostatic sail (E-sail) is a new type of propulsion which harnesses the Sun's solar wind to propel a spacecraft. Voyager I took about 40 years to reach interstellar space using solid rocket propellant, whereas electrostatic sails can travel the same distance in 6-10 years by using small but constant acceleration. As part of Marshall Space Flight Center's (MSFC) Space Systems Dept. and Advanced Concepts Office, we are continuing research for the HERTS (Heliopause Electrostatic Rapid Transit System) E-sail project. Previous researchers developed a Nano Air-bearing Simulator (NAS) prototype for initial testing of E-sails; this prototype was properly documented in CAD (Computer-Aided Drafting) in order to build a second improved NAS. MSFC's Robotic Lab (Flat Floor) allows for 2-dimensional simulations of spacecraft dynamics by attaching air bearings to a system. An indoor navigation system AprilNav, was developed and has been implemented on the ceiling of the flat floor for localization and autonomous testing of the two bearing-equipped NAS. With two NAS, tether dynamics between the two simulators as well as steering control algorithms are being tested on the flat floor using AprilNav.

Schuler, Tristan↗

NASA NTRS1995

The Honeycomb supernova remnant

At 2.5 min southeast of SN 1987A, the Honeycomb Nebula Supernova remnant (SNR) is named after its interesting morphology, which consists of over ten loops with sizes of 2-3 pc. High-dispersion spectra of these loops show hemispheres expanding toward the observer at 100-300 km/s. Using archival data X-ray data and a combination of new and archival radio data, we find bright X-ray and nonthermal radio emisssion associated with the Honeycomb Nebula. New CCD images further show enhanced (S II) H-alpha ratios. These results confirm a model in which the Honeycomb Nebula is due to a supernova shock front, traveling toward the observer, encountering an intervening sheet of dense, but porous, interstellar gas. The bulk of the supernova remnant resides in a low-density cavity, and is not otherwise visible. The situation is similar to the hidden supernova remnants postulated for the X-ray bright superbubbles. The Honeycomb Nebula has an unusually steep radio spectral index (S(sub nu) is proportional to nu(exp -1.2)), normally associated with young SNRs.

Chu, You-Hua↗

NASA NTRS1973

Do interstellar gas clouds exist between spiral arms.

This paper discusses what can happen to clouds as they move from arm regions to interarm regions, through a density-wave shock, and back to arm regions again. Shu et al. (1972) have taken the viewpoint that interstellar clouds will survive the trip between arms. Biermann et al. (1972) have taken the viewpoint that they will not. We shall point out that cloud-cloud collisions and other processes may lead to the destruction of interstellar clouds in less time than the 100 m.y. it takes clouds to travel across arms. A possible observational test is suggested to distinguish between the two possibilities.

Quirk, W. J.↗

NASA NTRS1976

Search for radiation from the 2 pi 1/2, J = 5/2 state of interstellar CH

The note reports results of an unsuccessful search for the four hyperfine transitions in the cited rotational state of interstellar CH, which was performed using a 25.6-m radio telescope equipped with a traveling-wave maser radiometer. The frequency interval covered ranged from 4677 to 4850 MHz; the sources observed were W3 Cont, W51, Orion A, and IRC+10216. It is shown that the lines in the present excited state cannot be expected to be observed if the state is populated according to thermodynamic equilibrium at the kinetic temperature of the medium. The possibility is considered of detecting thermally excited CH in a more compact region and of detecting excited-state CH maser lines. It is concluded that no strong CH maser lines exist for the frequencies and sources covered.

Sume, A.↗

NASA NTRS1988

Laboratory investigations

Laboratory studies related to cometary grains and the nuclei of comets can be broken down into three areas which relate to understanding the spectral properties, the formation mechanisms, and the evolution of grains and nuclei: (1) Spectral studies to be used in the interpretation of cometary spectra; (2) Sample preparation experiments which may shed light on the physical nature and history of cometary grains and nuclei by exploring the effects on grain emissivities resulting from the ways in which the samples are created; and (3) Grain processing experiments which should provide insight on the interaction of cometary grains with the environment in the immediate vicinity of the cometary nucleus as the comet travels from the Oort cloud through perihelion, and perhaps even suggestions regarding the relationship between interstellar grains and cometary matter. A summary is presented with a different view of lab experiments than is found in the literature, concentrating on measurement techniques and sample preparations especially relevant to cometary dust.

Russell, Ray W.↗

NASA NTRS2003

Generation and Scattering of Radiation Observed by Voyager in the Outer Heliosphere

Excellent progress was made under this grant on the generation and scattering of the 2-3 kHz radio emissions observed by the Voyager spacecraft in the outer heliosphere. These are the most powerful radio emissions produced in our solar system, surpassing even those of Jupiter and the Sun. The widely-held hypothesis pursued is that the radiation is generated near the electron plasma frequency f(sub p) or near 2f(sub p) as a shock wave traverses the heliosheath regions and/or heliopause predicted in the interaction region between the solar wind and the local interstellar medium. (Note that f (sup 2) (sub p) is proportional to the plasma density.) The traveling shock wave is plausibly associated with a global merged interaction region (GMIR). Accordingly, this so-called GMIR model is strongly analogous to the common interpretation of type II solar radio bursts and to radio emissions associated with Earth's bow shock, with coronal mass ejections (CMEs) and Earth's magnetosphere playing the role of a GMIR, respectively. Accordingly, Dr Cairns work on type II bursts, Earth's foreshock, and stochastic growth theory (not described in detail) strongly aided and complemented the research progress on the 2-3 kHz emissions described.

Spangler, Steven R.↗

NASA NTRS1973

Solar wind heating beyond 1 AU

The effect of an interplanetary atomic hydrogen gas on solar wind proton, electron and alpha-particle temperatures beyond 1 AU is considered. It is shown that the proton temperature (and probably also the alpha-particle temperature) reaches a minimum between 2 AU and 4 AU, depending on values chosen for solar wind and interstellar gas parameters. Heating of the electron gas depends primarily on the thermal coupling of the protons and electrons. For strong coupling, the electron temperature reaches a minimum between 4 AU and 8 AU, but for weak coupling (Coulomb collisions only), the electron temperature continues to decrease throughout the inner solar system. A spacecraft travelling to Jupiter should be able to observe the heating effect of the solar wind-interplanetary hydrogen interaction, and from such observations it may be possible of infer some properties of the interstellar neutral gas.

Holzer, T. E.↗

NASA NTRS2000

JSC Stardust Curation Team

STARDUST, a NASA Discovery-class mission, is the first to return samples from a comet. Grains from comet Wild 2's coma-the gas and dust envelope that surrounds the nucleus-will be collected as well as interstellar dust. The mission which launched on February 7, 1999 will encounter the comet on January 10, 2004. As the spacecraft passes through the coma, a tray of silica aerogel will be exposed, and coma grains will impact there and become captured. Following the collection, the aerogel tray is closed for return to Earth in 2006. A dust impact mass spectrometer on board the STARDUST spacecraft will be used to gather spectra. of dust during the entire mission, including the coma passage. This instrument will be the best chance to obtain data on volatile grains, which will not be well-collected in the aerogel. The dust impact mass spectrometer will also be used to study the composition of interstellar grains. In the past 5 years, analysis of data from dust detectors aboard the Ulysses and Galileo spacecraft have revealed that there is a stream of interstellar dust flowing through our solar system. These grains will be captured during the cruise phase of the STARDUST mission, as the spacecraft travels toward the comet. The sample return capsule will parachute to Earth in February 2006, and will land in western Utah. Once on y the ground, the sample return capsule will be placed into a dry nitrogen environment and flown to the curation lab at JSC.

Zolensky, Michael E.↗

NASA NTRS1995

Determining large-scale heliospheric structure using ultraviolet resonance line observations

Currently the Pioneer 10 and Voyager 1 and 2 spacecraft are beyond the orbit of Pluto, traveling outward from the Sun. Each is capable of detecting ultraviolet radiation resonantly scattered from hydrogen and helium atoms in the heliosphere and local interstellar medium. These observations are particularly well suited for the investigation of the large-scale heliospheric H and He distributions because the Voyager spacecraft are heading upstream, into the direction of local interstellar flow, whereas Pioneer 10 is heading downstream. Observations of the brightest resonance line, H Lyman-alpha, reveals that beyond about 20 AU from the Sun, upstream intensities decrease less quickly as a function of solar distance than downstream intensities. This implies that the heliospheric H distributions in the upstream and downstream directions are significantly different. Heliospheric H atoms originate in the local interstellar flow, and must penetrate through the heliospheric interface, where they are subject to charge exchange collisions with solar wind and interstellar protons. Models indicate that this process is probably responsible for the upstream/downstream difference in H Lyman-alpha. In addition, a recent spectroscopic determination of the H atom velocity distribution in the inner heliosphere implies a significant deceleration in the bulk flow speed of the heliospheric hydrogen gas relative to the helium flow, an effect that is also likely due to H-p charge exchange occurring in the upstream heliospheric interface region. In this presentation, recent heliospheric resonance line observations and their interpretations will be reviewed, focusing on their sensitivity to large-scale heliospheric structure.

Hall, Doyle T.↗