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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 631 records · Page 35
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NASA NTRS2004

Atmospheric Models for Aerocapture Systems Studies

Aerocapture uses atmospheric drag to decelerate into captured orbit from interplanetary transfer orbit. This includes capture into Earth orbit from, for example, Lunar-return or Mars-return orbit. Eight Solar System destinations have sufficient atmosphere for aerocapture to be applicable - three of the rocky planets (Venus, Earth, and Mars), four gas giants (Jupiter, Saturn, Uranus, and Neptune), and Saturn's moon Titan. These destinations fall into two groups: (1) The rocky planets, which have warm surface temperatures (approx. 200 to 750 K) and rapid decrease of density with altitude, and (2) the gas giants and Titan, which have cold temperatures (approx. 70 to 170 K) at the surface or 1-bar pressure level, and slow rate of decrease of density with altitude. The height variation of average density with altitude above 1-bar pressure level for the gas giant planets is shown. The periapsis density required for aerocapture of spacecraft having typical values of ballistic coefficient (a measure of mass per unit cross-sectional area) is also shown. The aerocapture altitudes at the gas giants would typically range from approx. 150 to 300 km. Density profiles are compared for the rocky planets with those for Titan and Neptune. Aerocapture at the rocky planets would occur at heights of approx. 50 to 100 km. For comparison, typical density and altitudes for aerobraking operations (circularizing a highly elliptical capture orbit, using multiple atmospheric passes) are also indicated.

Justus, C. G.↗
NASA NTRS2003

Impacts and evolution: future prospects

The discipline of astrobiology includes the dynamics of biological evolution. One of the major ways that the cosmos influences life is through the catastrophic environmental disruptions caused when comets and asteroids collide with a planet. We now recognize that such impacts have caused mass extinctions and played a major role in determining the evolution of life on Earth. The time-averaged impact flux as a function of projectile energy can be derived from lunar cratering statistics as well as the current population of near Earth asteroids (NEAs). Effects of impacts of various energies can be modeled, using data from historic impacts [such as the Cretaceous-Tertiary (KT) impactor 65 million years ago] and the observed 1994 bombardment of Jupiter by fragments of Comet Shoemaker-Levy 9. It is of particular interest to find from such models that the terrestrial environment is highly vulnerable to perturbation from impacts, so that even such a small event as the KT impact (by a projectile 10-15 km in diameter) can lead to a mass extinction. Similar considerations allow us to model the effects of still smaller (and much more likely) impacts, down to the size of the asteroid that exploded over Tunguska in 1908 (energy approximately 10 megatons). Combining the impact flux with estimates of environmental and ecological effects reveals that the greatest contemporary hazard is associated with impactors near 1 million megatons in energy (approximately 2 km in diameter for an asteroid). The current impact hazard is significant relative to other natural hazards, and arguments can be developed to illuminate a variety of public policy issues. The first priority in any plan for defense against impactors is to survey the population of Earth-crossing NEAs and project their orbits forward in time. This is the purpose of the Spaceguard Survey, which has already found more than half of the NEAs >1 km in diameter. If there is an NEA on a collision course with Earth, it can be discovered and the impact predicted with decades or more of warning. It is then possible to consider how to deflect or disrupt the NEA. Unlike other natural hazards, the impact risk can be largely eliminated, given sufficient advanced knowledge to take action against the threatening projectile.

Directed Molecular Evolution↗
NASA NTRS2002

Captain Cook, the Terrestrial Planet Finder and the search for extraterrestrial intelligence

A recently completed NASA study has concluded that a Terrestrial Planet Finder could be launched within a decade to detect terrestrial planets around nearby stars. Such a mission, complemented by projects (Kepler and Eddington) that will provide statistical information on the frequency of Earth-sized planets in the habitable zone, will determine key terms in the Drake equation that describes the number of intelligent civilizations in the Universe.

Terrestrial Planet Finder TPF↗
NASA NTRS2010

Modern Exploration of Galileo's New Worlds

Four hundred years ago Galileo turned his telescope to the heavens and changed the way we view the cosmos forever. Among his discoveries in January of 1610 were four new 'stars', following Jupiter in the sky but changing their positions with respect to the giant planet every night. Galileo showed that these 'Medicean stars', as he named them, were moons orbiting Jupiter in the same manner that the Earth and planets revolve about the Sun in the Copernican theory of the solar system. Over the next three centuries these moons, now collectively named the Galilean satellites after their discoverer, remained tiny dots of light in astronomers' telescopes. In the latter portion of the twentieth century Galileo's new worlds became important targets of exploration by robotic spacecraft. This paper reviews the history of this exploration through the discoveries made by the Galileo mission from 1995 to 2003, setting the stage for on-going exploration in the new century.

space vehicles↗
NASA NTRS2001

Meteoric Ions in Planetary Ionospheres

Solar system debris, in the form of meteoroids, impacts every planet. The flux, relative composition and speed of the debris at each planet depends on the planet's size and location in the solar system. Ablation in the atmosphere evaporates the meteoric material and leaves behind metal atoms. During the ablation process metallic ions are formed by impact ionization. For small inner solar system planets, including Earth, this source of ionization is typically small compared to either photoionization or charge exchange with ambient molecular ions. For Earth, the atmosphere above the main deposition region absorbs the spectral lines capable of ionizing the major metallic atoms (Fe and Mg) so that charge exchange with ambient ions is the dominant source. Within the carbon dioxide atmosphere of Mars (and possibly Venus), photoionization is important in determining the ion density. For a heavy planet like Jupiter, far from the sun, impact ionization of ablated neutral atoms by impacts with molecules becomes a prominent source of ionization due to the gravitational acceleration to high incident speeds. We will describe the processes and location and extent of metal ion layers for Mars, Earth and Jupiter, concentrating on flagging the uncertainties in the models at the present time. This is an important problem, because low altitude ionosphere layers for the planets, particularly at night, probably consist predominantly of metallic ions. Comparisons with Earth will be used to illustrate the differing processes in the three planetary atmospheres.

Pesnell, W. D.↗
NASA NTRS2003

Plans for living on a restless planet sets NASA's solid Earth agenda

What are the most important challenges facing solid Earth science today and over the next two decades? And what is the best approach for NASA, in partnership with other agencies, to address these challenges? A new report, living on a restless planet, provides a blueprint for answering these questions. The top priority for a new spacecraft mission in the area of solid earth science over the next 5 years, according to this report, is a satellite dedicated to interferometric synthetic aperture radar(inSAR).

Earth magnetic field imaging spectroscopy solid ea↗
NASA NTRS1983

Missions to the asteroid Anteros and the space of true anomalies

Three opportunities for missions to rendezvous ballistically with the earth-crossing asteroid Anteros are studied to illustrate the requirements for a trip to a near-earth minor planet. The rationale, sample payload, spacecraft requirements and trajectory characteristics of these opportunities are typical of a rendezvous mission to an accessible near-earth object. Round trip ballistic trajectories to return small samples of the asteroid with launch dates between 1985 and 2000 are also presented. Contours of minimum total delta drawn in the space of launch and arrival true anomalies, given the designation Prime Rib curves, are introduced as a useful tool for mission design.

Hulkower, N. D.↗
NASA NTRS2001

NASA/USGS US Digital Landsat Moasaics

The Earth Satellite Corporation (EarthSat) has been providing orthorectified Landsat data to NASA.Also included are 5 degree by 6 degree mosaics for most of the planet. The Earth Science Applications Directorate developed a specialized viewer application to view and navigate these individual tiles. It is the intent of NASA to make this publicly available and useable through the distribution of the U.S. Digital Landsat Mosaic Product.

Stanley, Thomas M.↗
NASA NTRS2012

On Advanced Estimation Techniques for Exoplanet Detection and Characterization using Ground-based Coronagraphs

The direct imaging of planets around nearby stars is exceedingly difficult. Only about 14 exoplanets have been imaged to date that have masses less than 13 times that of Jupiter. The next generation of planet-finding coronagraphs, including VLT-SPHERE, the Gemini Planet Imager, Palomar P1640, and Subaru HiCIAO have predicted contrast performance of roughly a thousand times less than would be needed to detect Earth-like planets. In this paper we review the state of the art in exoplanet imaging, most notably the method of Locally Optimized Combination of Images (LOCI), and we investigate the potential of improving the detectability of faint exoplanets through the use of advanced statistical methods based on the concepts of the ideal observer and the Hotelling observer. We propose a formal comparison of techniques using a blind data challenge with an evaluation of performance using the Receiver Operating Characteristic (ROC) and Localization ROC (LROC) curves. We place particular emphasis on the understanding and modeling of realistic sources of measurement noise in ground-based AO-corrected coronagraphs. The work reported in this paper is the result of interactions between the co-authors during a week-long workshop on exoplanet imaging that was held in Squaw Valley, California, in March of 2012

coronagraphs↗
NASA NTRS2012

On Advanced Estimation Techniques for Exoplanet Detection and Characterization using Ground-Based Coronagraphs

The direct imaging of planets around nearby stars is exceedingly difficult. Only about 14 exoplanets have been imaged to date that have masses less than 13 times that of Jupiter. The next generation of planet-finding coronagraphs, including VLT-SPHERE, the Gemini Planet Imager, Palomar P1640, and Subaru HiCIAO have predicted contrast performance of roughly a thousand times less than would be needed to detect Earth-like planets. In this paper we review the state of the art in exoplanet imaging, most notably the method of Locally Optimized Combination of Images (LOCI), and we investigate the potential of improving the detectability of faint exoplanets through the use of advanced statistical methods based on the concepts of the ideal observer and the Hotelling observer. We provide a formal comparison of techniques through a blind data challenge and evaluate performance using the Receiver Operating Characteristic (ROC) and Localization ROC (LROC) curves. We place particular emphasis on the understanding and modeling of realistic sources of measurement noise in ground-based AO-corrected coronagraphs. The work reported in this paper is the result of interactions between the co-authors during a week-long workshop on exoplanet imaging that was held in Squaw Valley, California, in March of 2012.

instrumentation↗
NASA NTRS2008

Terrestrial Planet Finder Interferometer: 2007-2008 Progress and Plans

This paper provides an overview of technology development for the Terrestrial Planet Finder Interferometer (TPF-I). TPF-I is a mid-infrared space interferometer being designed with the capability of detecting Earth-like planets in the habitable zones around nearby stars. The overall technology roadmap is presented and progress with each of the testbeds is summarized. The current interferometer architecture, design trades, and the viability of possible reduced-scope mission concepts are also presented.

formation flying↗
NASA NTRS2017

Spontaneous Hot Flow Anomalies at Mars and Venus

We report the first observations of Spontaneous Hot Flow Anomalies (SHFAs) at Venus and Mars, demonstrating their existence in the foreshocks of other planets beyond Earth. Using data from the ESA Venus Express and the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, we present magnetic and plasma observations from events at both planets, exhibiting properties similar to “classical” Hot Flow Anomalies, with bounding shock-like compressive regions and a hot and diffuse core. However, these explosive foreshock transients were observed without any attendant interplanetary magnetic field discontinuity, consistent with SHFAs observed at Earth and our hybrid simulations.

Collinson, Glyn A.↗
NASA NTRS2018

The Large Ultraviolet/Optical/Infrared Surveyor

Astronomy crossed a threshold three decades ago with the discovery of planets around other stars. Compared to scientists' previous expectations set by the Solar System, exoplanets are wonderfully abundant and varied. Indirect planet discovery techniques have shown that small rocky planets residing in stellar habitable zones, where such planets may have liquid water on their surfaces, are not rare. This revelation drives us to ask more ambitious and fundamental questions, that fascinate scientists and the public alike: are there other truly Earth-like planets out there and do any of them harbour life? Today, exoplanets are largely ‘small black shadows' to us, with measurements of orbits, sizes and masses (all three in the best cases).The upcoming James Webb Space Telescope and future 30-m-class ground-based telescopes will characterize the atmospheres of habitable planet candidates orbit in glow-mass M dwarf stars. However, deeply probing atmospheres of the exoplanets most similar to the Earth, those around Sun-like stars, remains out of reach for currently planned observatories. Bringing them within our grasp is a primary motivation for the Large UV/Optical/Infrared Surveyor(LUVOIR) mission concept, currently the focus of a three-year NASA study.

exoplanets↗
NASA NTRS2004

Relative Sensor with 4Pi Coverage for Formation Flying Missions

The Terrestrial Planet Finder (TPF) pre-project, an element of NASA s Origins program, is currently developing two architectures for a mission to search for earth-like planets around nearby stars. One of the architectures being developed is the Formation Flying Interferometer (FFI). The FFI is envisioned to consist of up to seven spacecraft (as many as six "collectors" with IR telescopes, and a "combiner") flying in precise formation within +/-1 cm of pre-determined trajectories for synchronized observations. The spacecraft-to-spacecraft separations are variable between 20 m and 100 m or more during observations to support various configurations of the interferometer in the planet-finding mode. The challenges involved with TPF autonomous operations, ranging from formation acquisition and formation maneuvering to high precision formation control during science observations, are unprecedented. In this paper we discuss the development of the formation acquisition sensor, which uses novel modulation and duplexing schemes to enable fast signal acquisition, multiple-spacecraft operation, and mitigation of inherent jamming conditions, while providing precise formation sensing and integrated radar capability. This approach performs delay synthesis and carrier cycle ambiguity resolution to improve range measurement, and uses differential carrier cycle ambiguity resolution to make precise bearing angle measurements without calibration maneuvers.

Tien, Jeffrey Y.↗
NASA NTRS2004

Relative Sensor with 4(pi) Coverage for Formation Flying Missions

The Terrestrial Planet Finder (TPF) pre-project, an element of NASA's Origins program, is currently developing two architectures for a mission to search for earth-like planets around nearby stars. One of the architectures being developed is the Formation Flying Interferometer (FFI). The FFI is envisioned to consist of up to seven spacecraft (as many as six 'collectors' with IR telescopes, and a 'combiner') flying in precise formation within f 1 cm of pre-determined trajectories for synchronized observations. The spacecraft-to-spacecraft separations are variable between 20 m and 100 m or more during observations to support various configurations of the interferometer in the planet-finding mode. The challenges involved with TPF autonomous operations, ranging from formation acquisition and formation maneuvering to high precision formation control during science observations, are unprecedented. In this paper we discuss the development of the formation acquisition sensor, which uses novel modulation and duplexing schemes to enable fast signal acquisition, multiple-spacecraft operation, and mitigation of inherent jamming conditions, while providing precise formation sensing and integrated radar capability. This approach performs delay synthesis and carrier cycle ambiguity resolution to improve range measurement, and uses differential carrier cycle ambiguity resolution to make precise bearing angle measurements without calibration maneuvers.

formation flying sensors↗
NASA NTRS2008

Recent Results of the Guide-2 Telescope Testbed for the SIM-Lite Mission

The Space Interferometry Mission Planet QuestLite (SIM-Lite) is a new mission concept to perform microarcsecond narrow-angle astrometry to search approximately 50 nearby stars for Earth-like planets, and also to perform a global astrometry. The SIM-Lite consists of two Michelson interferometers and one telescope. The main six-meter baseline science interferometer observes a target star and a set of reference stars. The four-meter baseline interferometer (Guide-1) monitors the attitude of the instrument in the direction of a target star. A new Guide-2telescope (G2T) tracks a bright star to monitor the attitude of the instrument in the other two orthogonal directions. In the current mission concept, the G2T consists of a 30 cm siderostat and a 30 cm confocal telescope, similar to other four telescopes used in the science and Guide-1interferometers. A testbed has been built to demonstrate the G2T feasibility for SIM-Lite mission. Recent results show that field-independent, star-tracking capability of the system is less than 30 (mu)as after the SIM narrow angle analysis.

Guide-2 Telescope↗
DOE OSTI2020

Atmospheric Escape From TOI-700 d: Venus versus Earth Analogs

The recent discovery of an Earth-sized planet (TOI-700 d) in the habitable zone of an early-type M-dwarf by the Transiting Exoplanet Survey Satellite constitutes an important advance. In this Letter, we assess the feasibility of this planet to retain an atmosphere – one of the chief ingredients for surface habitability – over long timescales by employing state-of-the-art magnetohydrodynamic models to simulate the stellar wind and the associated rates of atmospheric escape. We take two major factors into consideration, namely, the planetary atmospheric composition and magnetic field. In all cases, we determine that the atmospheric ion escape rates are potentially a few orders of magnitude higher than the inner Solar system planets, but TOI-700 d is nevertheless capable of retaining a 1 bar atmosphere over gigayear timescales for certain regions of the parameter space. The simulations show that the unmagnetized TOI-700 d with a 1 bar Earth-like atmosphere could be stripped away rather quickly (< 1 gigayear), while the unmagnetized TOI-700 d with a 1 bar CO 2 -dominated atmosphere could persist for many billions of years; we find that the magnetized Earth-like case falls in between these two scenarios. We also discuss the prospects for detecting radio emission of the planet (thereby constraining its magnetic field) and discerning the presence of an atmosphere.

79 ASTRONOMY AND ASTROPHYSICS↗