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NASA NTRS1980

SPIRIT - A high resolution cosmic ray isotope spectrometer for Spacelab

An instrument to measure the isotopic abundances of cosmic ray nuclei with Z in the range 20-30 and A in the range 40-70 has been conceived. The instrument, named SPIRIT (Superconducting Passive Iron Isotope Telescope), will have the mass resolution (sigma less than 0.15 amu) and collecting power (151 sq m ster h for a 10 day flight) to detect and convincingly resolve isotopes as rare as 0.5% of the total abundance of each element. Both range and magnetic rigidity are measured by following tracks through an array of sheets of CR-39, a sensitive new track-recording plastic, which had been kept in fixed position at uniform temperature within the uniform field region of a large superconducting magnet.

Tarle, G.↗

NASA NTRS1989

High resolution analysis of satellite gradiometry

Satellite gravity gradiometry is a technique now under development which, by the middle of the next decade, may be used for the high resolution charting from space of the gravity field of the earth and, afterwards, of other planets. Some data analysis schemes are reviewed for getting detailed gravity maps from gradiometry on both a global and a local basis. It also presents estimates of the likely accuracies of such maps, in terms of normalized spherical harmonics expansions, both using gradiometry alone and in combination with data from a Global Positioning System (GPS) receiver carried on the same spacecraft. It compares these accuracies with those of current and future maps obtained from other data (conventional tracking, satellite-satellite tracking, etc.), and also with the spectra of various signals of geophysical interest.

Colombo, O. L.↗

NASA NTRS2007

SIMBOL-X: A Formation Flying Mission on HEO for Exploring the Universe

SIMBOL-X is a high energy new generation telescope covering by a single instrument a continuous energy range starting at classical X-rays and extending to hard X-rays, i.e. from 0.5 to 80 keV. It is using in this field a focalizing payload which until now was used for energy below 10 keV only, via the construction of a telescope distributed on two satellites flying in formation. SIMBOL-X permits a gain of two orders of magnitude in sensibility and spatial resolution in comparison to state of the art hard X-rays instruments. The mirror satellite will be in free flight on a high elliptical orbit and will target the object to observe very precisely, thus focusing the hard X-ray emission thanks to this mirror module. At the focal point area which is situated 20 meters behind the mirror satellite, the detector satellite maintains its position on a forced orbit thanks to a radio link with the mirror satellite and a lateral displacement sensor using a beam emitted onboard the mirror satellite. This configuration is said "formation flying". The location of the detector satellite shall be very finely tuned as it carries the focal plane of this distributed telescope. To provide science measurements, the Simbol-X orbit has been chosen High elliptic (HEO), which means elliptical orbit with a high perigee altitude. Preliminary studies where made with an orbit with an altitude of the perigee of 44000km and altitude of the apogee of 253000km. The orbit was seven days ground track repeated in order to maintain a perigee pass over the Malindi ground station to download scientific telemetry. But as studies went on, difficulties in mass budget, link budget, perigee maintenance and formation flying maintenance were raised. This was mainly due to the vicinity of the Moon and its disturbing effect on the satellites orbits. Alternative orbits have been proposed in order to demonstrate the feasibility of the mission. The problematic of bringing the two satellites from their injection orbit to their operational orbit 20 m apart from each other and then maintain this configuration is very challenging. It requires theoretical development of the relative motion between two satellites in high eccentric orbit with large differential disturbance on the two bodies. This paper will present the mission analysis for the Simbol-X satellites with the complex problematic of doing formation flying in high elliptic orbit.

Gamet, Philippe↗

NASA NTRS2009

3D Lunar Terrain Reconstruction from Apollo Images

Generating accurate three dimensional planetary models is becoming increasingly important as NASA plans manned missions to return to the Moon in the next decade. This paper describes a 3D surface reconstruction system called the Ames Stereo Pipeline that is designed to produce such models automatically by processing orbital stereo imagery. We discuss two important core aspects of this system: (1) refinement of satellite station positions and pose estimates through least squares bundle adjustment; and (2) a stochastic plane fitting algorithm that generalizes the Lucas-Kanade method for optimal matching between stereo pair images.. These techniques allow us to automatically produce seamless, highly accurate digital elevation models from multiple stereo image pairs while significantly reducing the influence of image noise. Our technique is demonstrated on a set of 71 high resolution scanned images from the Apollo 15 mission

Broxton, Michael J.↗

NASA NTRS2010

Global Estimates of Average Ground-Level Fine Particulate Matter Concentrations from Satellite-Based Aerosol Optical Depth

Exposure to airborne particles can cause acute or chronic respiratory disease and can exacerbate heart disease, some cancers, and other conditions in susceptible populations. Ground stations that monitor fine particulate matter in the air (smaller than 2.5 microns, called PM2.5) are positioned primarily to observe severe pollution events in areas of high population density; coverage is very limited, even in developed countries, and is not well designed to capture long-term, lower-level exposure that is increasingly linked to chronic health effects. In many parts of the developing world, air quality observation is absent entirely. Instruments aboard NASA Earth Observing System satellites, such as the MODerate resolution Imaging Spectroradiometer (MODIS) and the Multi-angle Imaging SpectroRadiometer (MISR), monitor aerosols from space, providing once daily and about once-weekly coverage, respectively. However, these data are only rarely used for health applications, in part because the can retrieve the amount of aerosols only summed over the entire atmospheric column, rather than focusing just on the near-surface component, in the airspace humans actually breathe. In addition, air quality monitoring often includes detailed analysis of particle chemical composition, impossible from space. In this paper, near-surface aerosol concentrations are derived globally from the total-column aerosol amounts retrieved by MODIS and MISR. Here a computer aerosol simulation is used to determine how much of the satellite-retrieved total column aerosol amount is near the surface. The five-year average (2001-2006) global near-surface aerosol concentration shows that World Health Organization Air Quality standards are exceeded over parts of central and eastern Asia for nearly half the year.

Van Donkelaar, A.↗

NASA NTRS2012

The Proper Motion of the Central Compact Object RX J0822-4300 in the Supernova Remnant Puppis A

Using the High Resolution Camera (HRC) aboard the Chandra X-ray Observatory, we have re-examined the proper motion of the central compact object RX J0822-4300 in the supernova remnant Puppis A. New data from 2010 August, combined with three archival data sets from as early as 1999 December, provide a baseline of 3886 days (more than 10 1/2 years) to perform the measurement. Correlating the four positions of RX J0822-4300 measured in each data set implies a projected proper motion of mu = 71 +/- 12 mas/yr. For a distance of 2 kpc this proper motion is equivalent to a recoil velocity of 672 +/- 115 km/s. The position angle is found to be 244 +/- 11 degrees. Both the magnitude and direction of the proper motion are in agreement with RX J0822-4300 originating near the optical expansion center of the supernova remnant. For a displacement of 371 +/- 31 arcsec between its birth place and today's position we deduce an age of (5.2 +/- 1.0) 10(exp 3) yrs for RX J0822-4300. The age inferred from the neutron star proper motion and filament motions can be considered as two independent measurements of the same quantity. They average to 4450 +/- 750 yrs for the age of the supernova remnant Puppis A.

Becker, Werner↗

NASA NTRS2020

Sensitive Probing of Exoplanetary Oxygen via Mid-Infrared Collisional Absorption

The collision-induced fundamental vibration–rotation band at 6.4 μm is the strongest absorption feature from O2 in the infrared, yet it has not been previously incorporated into exoplanet spectral analyses for several reasons. Either collision-induced absorptions (CIAs) were not included or incomplete/obsolete CIA databases were used. Also, the current version of HITRAN does not include CIAs at 6.4 μm with other collision partners (O2–X). We include O2–X CIA features in our transmission spectroscopy simulations by parameterizing the 6.4-μm O2–N2 CIA based on ref. 3 and the O2–CO2 CIA based on ref. 4. Here we report that the O2–X CIA may be the most detectable O2 feature for transit observations. For a potential TRAPPIST-1 e analogue system within 5 pc of the Sun, it could be the only O2 signature detectable with the James Webb Space Telescope (JWST) (using MIRI LRS (Mid-Infrared Instrument low-resolution spectrometer)) for a modern Earth-like cloudy atmosphere with biological quantities of O2. Also, we show that the 6.4-μm O2–X CIA would be prominent for O2-rich desiccated atmospheres and could be detectable with JWST in just a few transits. For systems beyond 5 pc, this feature could therefore be a powerful discriminator of uninhabited planets with non-biological ‘false-positive’ O2 in their atmospheres, as they would only be detectable at these higher O2 pressures.

Thomas J Fauchez↗

NASA NTRS2020

Sensitive Probing of Exoplanetary Oxygen via Mid-Infrared Collisional Absorption

The collision-induced fundamental vibration–rotation band at 6.4 μm is the strongest absorption feature from O2 in the infrared1,2,3, yet it has not been previously incorporated into exoplanet spectral analyses for several reasons. Either collision-induced absorptions (CIAs) were not included or incomplete/obsolete CIA databases were used. Also, the current version of HITRAN does not include CIAs at 6.4 μm with other collision partners (O2–X). We include O2–X CIA features in our transmission spectroscopy simulations by parameterizing the 6.4-μm O2–N2 CIA based on ref. 3 and the O2–CO2 CIA based on ref. 4. Here we report that the O2–X CIA may be the most detectable O2 feature for transit observations. For a potential TRAPPIST-1 e analogue system within 5 pc of the Sun, it could be the only O2 signature detectable with the James Webb Space Telescope (JWST) (using MIRI LRS (Mid-Infrared Instrument low-resolution spectrometer)) for a modern Earth-like cloudy atmosphere with biological quantities of O2. Also, we show that the 6.4-μm O2–X CIA would be prominent for O2-rich desiccated atmospheres5 and could be detectable with JWST in just a few transits. For systems beyond 5 pc, this feature could therefore be a powerful discriminator of uninhabited planets with non-biological ‘false-positive’ O2 in their atmospheres, as they would only be detectable at these higher O2 pressures.

Thomas Fauchez↗

NASA NTRS2026

Petermann Glacier on the Brink: Progress, Challenges and Insights

Petermann Glacier, the largest marine-terminating glacier in northern Greenland based on catchment area and ice discharge, plays a key role in regulating ice discharge from the Greenland Ice Sheet into the Arctic Ocean. With an upstream catchment connected to the ice sheet interior via a deep subglacial canyon, its future stability has major implications for sea level rise. In this review, we synthesize recent advances in understanding Petermann’s dynamics across three critical interfaces: the ice–ocean, ice–atmosphere, and ice–bed boundaries. At the surface, observations show that reanalysis products underestimate air temperatures and melt, while regional climate models diverge significantly in their estimates of surface mass balance, underscoring the need for improved in situ data and models. At the ocean boundary, enhanced basal melting driven by both subglacial runoff and Atlantic water intrusions is identified as the dominant driver of recent mass loss of Petermann Glacier, with continued warming posing a serious threat to the stability of the floating tongue. At the bed, new geophysical synthesis reveals complex geology, likely spatial variability in geothermal heat flux, and the influence of the megacanyon on seasonal hydrology and velocity fluctuations. Petermann’s mass balance has been negative in recent decades without corresponding flow acceleration. However, the glacier has undergone significant calving events, and the current rifting that began in September 2025 highlights its vulnerability. This upcoming calving event underscores the timeliness of this review, as it will put Petermann Glacier’s terminus at its most retreated position since records began in 1923. The anticipated retreat of the ice tongue also reduces buttressing and brings the terminus closer to the grounding zone, and modeling studies suggest that calving within 12 km of the grounding zone could potentially trigger dynamic retreat, accelerating ice discharge, and a doubling of flow speeds. We conclude that improved observations, sustained monitoring of oceanographic and atmospheric properties, and high-resolution modeling are critical to constraining projections of Petermann Glacier’s future and its role in the stability of the Greenland Ice Sheet.

Dominik Fahrner↗

NASA NTRS2015

Effects of Mesoscale Eddies in the Active Mixed Layer: Test of the Parametrisation in Eddy Resolving Simulations

In eddy resolving simulations, we test a mixed layer mesoscale parametrisation, developed recently by Canuto and Dubovikov [Ocean Model., 2011, 39, 200-207]. With no adjustable parameters, the parametrisation yields the horizontal and vertical mesoscale fluxes in terms of coarse-resolution fields and eddy kinetic energy (EKE). We compare terms of the parametrisation diagnosed from coarse-grained fields with the eddy mesoscale fluxes diagnosed directly from the high resolution model. An expression for the EKE in terms of mean fields has also been found to get a closed parametrisation in terms of the mean fields only. In 40 numerical experiments we simulated two types of flows: idealised flows driven by baroclinic instabilities only, and more realistic flows, driven by wind and surface fluxes as well as by inflow-outflow. The diagnosed quasi-instantaneous horizontal and vertical mesoscale buoyancy fluxes (averaged over 1-2 degrees and 10 days) demonstrate a strong scatter typical for turbulent flows, however, the fluxes are positively correlated with the parametrisation with higher (0.5-0.74) correlations at the experiments with larger baroclinic radius Rossby. After being averaged over 3-4 months, diffusivities diagnosed from the eddy resolving simulations are consistent with the parametrisation for a broad range of parameters. Diagnosed vertical mesoscale fluxes restratify mixed layer and are in a good agreement with the parametrisation unless vertical turbulent mixing in the upper layer becomes strong enough in comparison with mesoscale advection. In the latter case, numerical simulations demonstrate that the deviation of the fluxes from the parametrisation is controlled by dimensionless parameter estimating the ratio of vertical turbulent mixing term to mesoscale advection. An analysis using a modified omega-equation reveals that the effects of the vertical mixing of vorticity is responsible for the two-three fold amplification of vertical mesoscale flux. Possible physical mechanisms, responsible for the amplification of vertical mesoscale flux are discussed.

simulation↗

NASA NTRS1988

Martian sample sites: Examples based on a global geologic perspective

Ten areas were selected that each include several rock units of varying lithology and age. These areas were chosen to optimize the geologic and chronologic data return from Mars. Geologic mapping and stratigraphic studies identify stratigraphic ages, rock types, and information on Martian geologic history that samples of a given site may yield. Volcanic rocks occur over much of the planet and in virtually all stratigraphic positions, and they are amenable to radioisotopic dating. Therefore, a reasonable and essential goal for a sample return mission is to return datable rocks from widely varying strata. Generally, about three or four major geologic units can be sampled at any of the given sites, most of which can probably be dated. The Mars Observer mission will aid greatly in interpreting lithology and defining contacts at the high resolution required to actually pinpoint good sample acquisition sites within these areas.

Scott, D. H.↗

NASA NTRS1990

Intergalactic HI in the NGC5018 group

The cold interstellar and intergalactic medium is in the small group of galaxies whose brightest member is the elliptical galaxy NGC5018. Researchers' attention was first drawn to this galaxy as possibly containing cold interstellar gas by the detection by the Infrared Astronomy Satellite (IRAS) of emission at lambda 60 microns and lambda 100 microns at an intensity of about 1 Jy (Knapp et al. 1989), which is relatively strong for an elliptical (Jura et al. 1987). These data showed that the temperature of the infrared emission is less than 30K and that its likely source is therefore interstellar dust. A preliminary search for neutral hydrogen (HI) emission from this galaxy using the Very Large Array (VLA) showed that there appears to be HI flowing between NGC5018 and the nearby Sc galaxy NGC5022 (Kim et al. 1988). Since NGC5018 has a well-developed system of optical shells (cf. Malin and Carter 1983; Schweizer 1987) this observation suggests that NGC5018 may be in the process of forming its shell system by the merger of a cold stellar system with the elliptical, as suggested by Quinn (1984). Researchers describe follow-up HI observations of improved sensitivity and spatial resolution, and confirm that HI is flowing between NCG5022 and NGC5018, and around NGC5018. The data show, however, that the HI bridge actually connects NGC5022 and another spiral in the group, MCG03-34-013, both spatially and in radial velocity, and that in doing so it flows through and around NGC5018, which lies between the spiral galaxies. This is shown by the total HI map, with the optical positions of the above three galaxies labelled.

Guhathakurta, P.↗

NASA NTRS1994

New composite reflectance spectra of Mars from 0.4 to 3.14 micron

To verify the quality and accuracy of Phobos-2 Imaging Spectrometer for Mars (ISM) spectra of Mars, we have performed comparisons with telescopic data obtained contemporaneously and which have spatial and spectral overlap with the ISM measurements. We find general agreement between the independently-calibrated data sets in terms of spectral shape and absorption band strength and position in the 0.77 to 0.93 micron overlap region. The telescopic data were scaled to the ISM reflectance values in this overlap region to yield new bright and dark region composite reflectance spectra from 0.40 to 3.14 microns. We ascribe the increase in band depth and overall spectral heterogeneity of the ISM data relative to previous telescopic observations to the more than order of magnitude increase in spatial resolution achieved by ISM from Martian orbit. Further increases in spatial resolution from future orbital imaging spectroscopic instruments can be expected to reveal even greater degrees of compositional and mineralogic diversity on Mars.

Mustard, John F.↗

NASA NTRS2000

Fine-Scale Comparison of TOMS Total Ozone Data with Model Analysis of an Intense Midwestern Cyclone

High-resolution (approx. 40 km) along-track total column ozone data from the Total Ozone Mapping Spectrometer (TOMS) instrument are compared with a high-resolution mesoscale numerical model analysis of an intense cyclone in the Midwestern United States. Total ozone increased by 100 DU (nearly 38%) as the TOMS instrument passed over the associated tropopause fold region. Complex structure is seen in the meteorological fields and compares well with the total ozone observations. Ozone data support the meteorological analysis showing that stratospheric descent was confined to levels above approx. 600 hPa; significant positive potential vorticity at lower levels is attributable to diabetic processes. Likewise, meteorological fields show that two pronounced ozone streamers extending north and northeastward into Canada at high levels are not bands of stratospheric air feeding into the cyclone; one is a channel of exhaust downstream from the system, and the other apparently previously connected the main cyclonic circulation to a southward intrusion of polar stratospheric air and advected eastward as the cut-off cyclone evolved. Good agreement between small-scale features in the model output and total ozone data underscores the latter's potential usefulness in diagnosing upper tropospheric/lower stratospheric dynamics and kinematics.

Olsen, Mark A.↗

NASA NTRS2003

Research on Spectroscopy, Opacity, and Atmospheres

For planetary and telluric atmosphere projects the solar irradiance spectrum is required as the input at the top of the atmosphere. It has never been observed. People ask me to compute it. I can compute it theoretically using both known and predicted lines and get agreement averaged over a nanometer but there is no way to predict the resolved spectrum when only half the lines are known. In other stars the situation is worse because the signal-to-noise and resolution of the observations are worse. Logically one has to know a priori what is in the spectrum in order to interpret it; there is not enough information in the observed spectrum itself (qualifiers are given). Basically we need a list of all the energy levels of all atoms and molecules that matter. From that list can be generated all the lines. With the energy levels and line positions known, one can measure gf values, lifetimes, damping, or one can determine a theoretical or semiempirical Hamiltonian whose eigenvalues and eigenvectors produce a good match to the observed data, and that can then be used to generate additional radiative and collisional data for atoms or molecules.

Kurucz, Robert L.↗

NASA NTRS1996

Orbiter Aerodynamic Acceleration Flight Measurements in the Rarefied-Flow Transition Regime

Acceleration data taken from the Orbital Acceleration Research Experiment (OARE) during reentry on STS-62 have been analyzed using calibration factors taken on orbit. This is the first Orbiter mission which collected OARE data during the Orbiter reentry phase. The data examined include the flight regime from orbital altitudes down to about 90 km which covers the free-molecule-flow regime and the upper altitude fringes of the rarefied-flow transition into the hypersonic continuum. Ancillary flight data on Orbiter position, orientation, velocity, and rotation rates have been used in models to transform the measured accelerations to the Orbiter center-of-gravity, from which aerodynamic accelerations along the Orbiter body axes have been calculated. Residual offsets introduced in the measurements by unmodeled Orbiter forces are identified and discussed. Direct comparisons are made between the OARE flight data and an independent micro-gravity accelerometer experiment, the High Resolution Accelerometer Package (HiRAP), which also obtained flight data on reentry during the mission down to about 95 km. The resulting OARE aerodynamic acceleration measurements along the Orbiter's body axis, aid the normal to axial acceleration ratio in the free-molecule-flow and transition-flow regimes are presented and compared with numerical simulations from three direct simulation Monte Carlo codes.

Blanchard, Robert C.↗

NASA NTRS2010

A Controller-in-the Loop Simulation of Ground-Based Automated Separation Assurance in a NextGen Environment

A controller-in-the-loop simulation was conducted in the Airspace Operations Laboratory (AOL) at the NASA Ames Research Center to investigate the functional allocation aspects associated with ground-based automated separation assurance in a far-term NextGen environment. In this concept, ground-based automation handled the detection and resolution of strategic and tactical conflicts and alerted the controller to deferred situations. The controller was responsible for monitoring the automation and managing situations by exception. This was done in conditions both with and without arrival time constraints across two levels of traffic density. Results showed that although workload increased with an increase in traffic density, it was still manageable in most situations. The number of conflicts increased similarly with a related increase in the issuance of resolution clearances. Although over 99% of conflicts were resolved, operational errors did occur but were tied to local sector complexities. Feedback from the participants revealed that they thought they maintained reasonable situation awareness in this environment, felt that operations were highly acceptable at the lower traffic density level but were less so as it increased, and felt overall that the concept as it was introduced here was a positive step forward to accommodating the more complex environment envisioned as part of NextGen.

Homola, J.↗

NASA NTRS2020

Comprehensive Investigation of Mars Methane and Organics with ExoMars/NOMAD

Methane (CH4) on Mars has attracted a great deal of attention since it was first detected in January 2003. As methane is considered a potential marker for past/present biological or geological activity, any possible detection would require evidence with strong statistical significance. Ethane (C2H6) and ethylene (C2H4) are also relevant chemical species as their shorter lifetimes in the Martian atmosphere make them excellent tracers for recent and ongoing releases. If detected, a CH4/C2Hn ratio could aid in constraining the potential source of organic production. Here we present the results of an extensive search for hydrocarbons in the Martian atmosphere in 240,000 solar occultation measurements performed by the ExoMars Trace Gas Orbiter/NOMAD instrument from April 2018 to April 2019. The observations are global, covering all longitudes and latitudes from 85°N to 85°S, and sampled from 6-100 km altitude with a typical vertical resolution of 2km. There were no statistically significant detections of organics and new stringent upper limits for global ethane and ethylene were set at 0.1 ppbv and 130.7 ppbv, respectively. No global background level of methane was observed, obtaining an upper limit of 0.06 ppbv, in agreement with early results from ExoMars (Korablev et al., 2019). Dedicated searches for localized plumes at more than 2000 locations provided no positive detections, implying that if methane were released in strong and rapid events, the process would have to be sporadic.

Elise W Knutsen↗