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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 271 records · Page 15
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NASA NTRS1976

Trajectories and orbits from the NASA-NMSU meteor observatory. I

Reduced trajectory data and orbital elements are reported for 20 double-station meteors photographed at the NASA-NMSU meteor observatory during the winter of 1974/75. The objects photographed include 10 sporadic meteors and 10 members of the Geminid shower. The data for the sporadic meteors indicate that their magnitudes range from 0 to -4, all have eccentricities greater than 0.4, all but three are in direct orbits, and one is probably a member of the Coma Berenicid shower. The elements for the Geminids are obtained using times of appearance chosen by adopting 34.6 km/s as the heliocentric velocity of the shower. The results are compared with previous orbital determinations, and it is concluded that there is no evidence for significant evolution of the Geminid-stream orbit over a period of several decades.

Tedesco, E. F.↗
NASA NTRS1990

The CRAF mission and Earth-based comet observations

The Comet Rendezvous Asteroid Flyby (CRAF) mission is now being designed and planned to perform detailed studies of a typical short period comet as it moves around its orbit, building on the data gained from the Giotto, Vega, and Suisei fast flybys of Comet Halley in 1986. CRAF will be launched in Aug. 1995 and will match orbits with short period Comet Kopff in July 2000, 850 days before perihelion at a heliocentric distance of 5.05 AU. After a series of close, slow flybys, the spacecraft will be placed in orbit around the nucleus for a better than 1 m/line-pair imaging resolution on the nucleus surface. Earth based observations of the target comet, either by ground based facilities or Earth orbiting satellites, can provide essential data for CRAF mission planning, and are needed in support of the rendezvous mission. Estimates of the nucleus size, albedo, shape, rotation period, and rotation pole orientation are needed for preliminary mission planning, resource allocation, and sequence design.

Weissman, Paul R.↗
NASA NTRSDate not supplied

Maneuver Reconstruction, Tracking Scheduling, and Bias Estimation in the Near Rectilinear Halo Orbit (NRHO)

NASA’s Gateway program will build a crew-tended station in an Earth-Moon Near Rectilinear Halo Orbit (NRHO) to support deep space missions to the lunar surface and heliocentric space. The station in the NRHO will be tracked by the Deep Space Network (DSN) with 2-way radiometric tracking data to produce an estimated state that is utilized to target Orbit Maintenance Maneuvers (OMMs). However, the tracking data is corrupted with measurement noise and range bias, which results in state estimation error and OMM execution error. This paper reports on analysis performed to improve the geometry of the tracking data problem with the inclusion of cross-hemispheric partner sites and explores the performance impact of handovers between partner sites and DSN sites. The OMM execution error is estimated directly using a Batch Least Squares (BLS) process, and the range bias estimation is analyzed among both original DSN sites and a combined DSN + partner sites scenario.

Clark P Newman↗
NASA NTRS2019

OSIRIS-REx Orbit Determination Performance During the Navigation Campaign

The OSIRIS-REx mission Navigation Campaign consists of three sub-phases: Approach,Preliminary Survey, and Orbital A. Approach was designed for initial characterization ofBennu while matching Bennu's heliocentric velocity. Preliminary Survey provided the firstspacecraft-based estimate of Bennu's mass. This phase consisted of five target flybys witha close approach distance of about 7 km. Orbital A was a two-month phase devoted to theNavigation Team learning the close proximity operations dynamics and environment aroundBennu and transitioning from center-finding optical navigation to landmark feature-basednavigation. This paper provides a detailed summary of the orbit determination performancethroughout the Navigation Campaign.

Leonard, Jason M.↗
NASA NTRS1990

One year variations in the near earth solar wind ion density and bulk flow velocity

One-year periodic variations in the near earth solar wind ion density and bulk flow velocity are reported. The variations show an inverse relationship between the ion velocity and density. The peak strength of the observed density variation ranges from 50-100 percent over the background. These variations imply either large scale mass loading inside the earth's orbit or intrinsic solar modulations. Analyses of both near earth and Pioneer Venus Orbiter spacecraft data provide a comparison at two different heliocentric distances. Several explanations for these variations are discussed.

Bolton, Scott J.↗
NASA NTRS2002

Clementine Observations of the Zodiacal Light and the Dust Content of the Inner Solar System

Using the Moon to occult the Sun, the Clementine spacecraft used its navigation cameras to map the inner zodiacal light at optical wavelengths over elongations of 3 approx. less than epsilon approx. less than 30 deg from the Sun. This surface brightness map is then used to infer the spatial distribution of interplanetary dust over heliocentric distances of about 10 solar radii to the orbit of Venus. The averaged ecliptic surface brightness of the zodiacal light falls off as Z(epsilon) is a member of epsilon(sup -2.45 +/- 0.05), which suggests that the dust cross-sectional density nominally falls off as sigma(r) is a member of r(sup - 1.45 +/- 0.05). The interplanetary dust also has an albedo of alpha approx. = 0.1 that is uncertain by a factor of approx. 2. Asymmetries of approx. 10% are seen in directions east-west and north-south of the Sun, and these may be due the giant planets' secular gravitational perturbations. We apply a simple model that attributes the zodiacal light as due to three dust populations having distinct inclination distributions, namely, dust from asteroids and Jupiter-family comets (JFCs) having characteristic inclinations of i approx. 7 deg, dust from Halley-type comets having i approx. 33 deg, and an isotropic cloud of dust from Oort Cloud comets. The best-fitting scenario indicates that asteroids + JFCs are the source of about 45% of the optical dust cross section seen in the ecliptic at 1 AU but that at least 89% of the dust cross section enclosed by a 1-AU-radius sphere is of a cometary origin. Each population's radial density variations can also deviate somewhat from the nominal sigma(r) is a member of r(sup -1.45). When these results are extrapolated out to the asteroid belt, we find an upper limit on the mass of the light-reflecting asteroidal dust that is equivalent to a 12-km asteroid, and a similar extrapolation of the isotropic dust cloud out to Oort Cloud distances yields a mass equivalent to a 30-km comet, although the latter mass is uncertain by orders of magnitude.

Hahn, Joseph M.↗
NASA NTRS1981

Low cost transfer into useful sun-synchronous orbits at Mars

Mars oblateness has been found to provide sun-synchronous orbits, including orbits with stationary apsides, similar to those used at earth. A low mass and low data rate complement of scientific instruments placed in such orbits can provide exciting planetary investigations such as the Mars Orbiter Water Mission described herein. Use of a modest Shuttle kickstage (PAM-A) and existing spacecraft hardware makes this mission low-cost. A preliminary mission and spacecraft design is described. The major emphasis of the paper is on the mechanics of heliocentric transfer for the 1986 and 1988 launch opportunities, Martian sun-synchronous orbit geometries, injectable mass capabilities, and methods of achieving these scientifically useful orbits.

Glickman, R. E.↗
NASA NTRS1974

Small bodies and the outer planets and Appendices 1 and 2

Correlations of asteroid spectral reflectivity characteristics with orbital parameters have been sought. Asteroid proper elements and extreme heliocentric distance were examined. Only general trends were noted, primarily red asteroids and asteroids with IR (.95 micron) absorption bands are concentrated toward the inner part of the belt. Also, asteroids with the pyroxene band tend to have larger proper eccentricities relative to non-banded asteroids.

Davis, D. R.↗
NASA NTRS1995

Estimates of Comet Fragment Masses from Impact Crater Chains on Callisto and Ganymede

Chains of impact craters, or catenae, have been identified in Voyager images of Callisto and Ganymede. Although these resemble in some respects secondary crater chains, the source craters and basins for the catenae cannot be identified. The best explanation is a phenomenon similar to that displayed by former comet Shoemaker-Levy 9; tidal (or other) breakup close to Jupiter followed by gradual orbital separation of the fragments and collision with a Galilean satellite on the outbound leg of the trajectory. Because the trajectories must pass close to Jupiter, this constrains the impact geometry (velocity and impact angle) of the individual fragments. For the dominant classes of impactors, short period Jupiter-family comets and asteroids, velocities at Callisto and Ganymede are dominated by Jovian gravity and a satellite's orbital motion, and are insensitive to the pre-fragmentation heliocentric velocity; velocities are insensitive to satellite gravity for all impactor classes. Complex crater shapes on Callisto and Ganymede are determined from Voyager images and Schmidt-Holsapple scaling is used to back out individual fragment masses. We find that comet fragment radii are generally less than about 500 m (for ice densities) but can be larger. These estimates can be compared with those for the Shoemaker-Levy 9 impactors.

McKinnon, William B.↗
NASA NTRS1995

Fine-Scale Filamentary Structure in Coronal Streamers

Doppler scintillation measurements of a coronal streamer lasting several solar rotations have been conducted by Ulysses in 1991 over a heliocentric distance range of 14-77 R(sub 0). By showing that the solar corona is filamentary, and that Doppler frequency is the radio counterpart of white-light eclipse pictures processed to enhance spatial gradients, it is demonstrated that Doppler scintillation measurements provide the high spatial resolution that has long eluded white-light coronagraph measurements. The region of enhanced scintillation, spanning an angular extent of 1.8 deg in heliographic longitude, coincides with the radially expanding streamer stalk and represents filamentary structure with scale sizes at least as small as 340 km (0.5 sec) when extrapolated to the Sun. Within the stalk of the streamer, the fine-scale structure corresponding to scale sizes in the range of 20-340 km at the Sun and associated with closed magnetic fields amounts to a few percent of the mean density, while outside the stalk, the fine-scale structure associated with open fields is an order of magnitude lower. Clustering of filamentary structure that takes place within the stalk of the streamer is suggestive of multiple current sheets. Comparison with ISEE 3 in situ plasma measurements shows that significant evolution resulting from dynamic interaction with increasing heliocentric distance takes place by the time streamers reach Earth orbit.

Woo, Richard↗
NASA NTRS2009

Orbital Effects on Mercury's Escaping Sodium Exosphere

We present results from coronagraphic imaging of Mercury's sodium tail over a 7 deg field of view. Several sets of observations made at the McDonald Observatory since May 2007 show a tail of neutral sodium atoms stretching more than 1000 Mercury radii (R(sub m)) in length, or a full degree of sky. However, no tail was observed extending beyond 120 R(sub m) during the January 2008 MESSENGER Fly-by period, or during a similar orbital phase of Mercury in July 2008. Large changes in Mercury's heliocentric radial velocity cause Doppler shifts about the Fraunhofer absorption features; the resultant change in solar flux and radiation pressure is the primary cause of the observed variation in tail brightness. Smaller fluctuations in brightness may exist due to changing source rates at the surface, but we have no explicit evidence for such changes in this data set. The effects of radiation pressure on Mercury's escaping atmosphere are investigated using seven observations spanning different orbital phases. Total escape rates of atmospheric sodium are estimated to be between 5 and 13 x 10(exp 23) atoms/s and show a correlation to radiation pressure. Candidate sources of Mercury's sodium exosphere include desorption by UV sunlight, thermal desorption, solar wind channeled along Mercury's magnetic field lines, and micro-meteor impacts. Wide-angle observations of the full extent of Mercury's sodium tail offer opportunities to enhance our understanding of the time histories of these source rates.

Schmidt, Carl A.↗
NASA NTRS2022

Patches of Magnetic Switchbacks and Their Origins

Parker Solar Probe (PSP) has shown that the solar wind in the inner heliosphere is characterized by the quasi omnipresence of magnetic switchbacks ("switchback" hereinafter), local backward bends of magnetic field lines. Switchbacks also tend to come in patches, with a large-scale modulation that appears to have a spatial scale size comparable to supergranulation on the Sun. Here we inspect data from the first 10 encounters of PSP focusing on different time intervals when clear switchback patches were observed by PSP. We show that the switchbacks modulation, on a timescale of several hours, seems to be independent of whether PSP is near perihelion, when it rapidly traverses large swaths of longitude remaining at the same heliocentric distance, or near the radial-scan part of its orbit, when PSP hovers over the same longitude on the Sun while rapidly moving radially inwards or outwards. This implies that switchback patches must also have an intrinsically temporal modulation most probably originating at the Sun. Between two consecutive patches, the magnetic field is usually very quiescent with weak fluctuations. We compare various parameters between the quiescent intervals and the switchback intervals. The results show that the quiescent intervals are typically less Alfvénic than switchback intervals, and the magnetic power spectrum is usually shallower in quiescent intervals. We propose that the temporal modulation of switchback patches may be related to the "breathing" of emerging flux that appears in images as the formation of "bubbles" below prominences in the Hinode/SOT observations.

Solar wind↗
NASA NTRS1985

On reflecting boundary behind the Earth's orbit at propagation of fast particles from solar flares

The flares of solar cosmic rays (SCR) associated with the presence of shocks in interplanetary magnetic field and with their propagation at significant heliocentric distances were always of great interest. Some events and problems concerning the peculiarities of propagation of flare CR in the interplanetary medium are considered. The distinguishing feature of such events is the presence of shock front behind the Earth's orbit having formed either directly in the process of shock generation on the Sun or at large heliocentric distances as a result of the interaction of fast and slow quasistationary recurrent solar wind (SW) streams. Based on the experimental material it is shown that the significant nonlinear disturbances in IMF behind the Earth's orbit can yield the occurrence of the additional SCR flux from shock front region as a result of the interaction of flare flux with shock and a partial reflection from it.

Nishkovskikh, A. S.↗
NASA NTRS1989

Feasibility study of a single, elliptical heliocentric Earth-Mars trajectory

The initial intent of this design project was to evaluate the existence and feasibility of a single elliptical heliocentric Earth/Mars trajectory. This trajectory was constrained to encounter Mars twice in its orbit, within a time interval of 15 to 180 Earth days between encounters. The single ellipse restriction was soon found to be prohibitive for reasons shown later. Therefore, the approach taken in the design of the round-trip mission to Mars was to construct single-leg trajectories which connected two planets on two prescribed dates. Three methods of trajectory design were developed. Method 1 is an eclectic approach and employs Gaussian Orbit Determination (Method 1A) and Lambert-Euler Preliminary Orbit Determination (Method 1B) in conjunction with each other. Method 2 is an additional version of Lambert's Solution to orbit determination, and both a coplanar and a noncoplanar solution were developed within Method 2. In each of these methods, the fundamental variables are two position vectors and the time between the position vectors. In all methods, the motion was considered Keplerian motion and the reference frame origin was located at the sun. Perturbative effects were not considered in Method 1. The feasibility study of round-trip Earth/Mars trajectories maintains generality by considering only heliocentric trajectory parameters and planetary approach conditions. The coordinates and velocity components of the planets, for the standard epoch J2000, were computed from an approximate set of osculating elements by the procedure outlined in an ephemeris of coordinates.

Blake, M.↗
NASA NTRS1991

Chiron: Evidence for historic cometary activity

The non-asteroidal brightening of (2060) Chiron, first noted by Tholen in 1988 is now ascribed to cometary activity. Photometry since 1988 has revealed a broad surge in brightness that peaked in 1989 about 1.0 mag above the brightness in the mid-1980s. The surge is evidently due to sporatic formation of dust coma, which is itself driven by the presence of extremely volatile ices at or near the surface. CN emission was recently reported. Since Chiron is now nearing perihelion, there is interest in determining whether it has exhibited anomalous brightening in the past, particularly at greater heliocentric distances. Photographic plates dating back to 1895 are known to contain images of Chiron. Using some of these archival material, the initial results are presented for a project to determine Chiron's brightness history over orbital timescales. A particularly homogeneous and high-quality set of plates taken prior to and around the time of Chiron's discovery in Oct. 1977 at the 1.2 m Oschin Schmidt telescope at Mt. Palomar Observatory were examined. Images of Chiron were identified and digitized using a PDS microdensitometer, and images of field stars around Chiron were both similarly digitized and photometrically calibrated using recently acquired B and V band CCD frames. As a result of the present work, eleven new data, including estimated errors, were added between 1969 and 1977. The implications that Chiron can be active at any heliocentric distance in its present orbit suggest that the active volatile is either N2, CH4, or CO, and that a substantial degree of mantling may have developed. Further historical data is presented, the error bars discussed, and possible mechanisms suggested for the observed activity.

Bus, Schelte J.↗
NASA NTRSDate not supplied

Perturbation Modeling and Navigation Tuning for a Crewed Station in Near Rectilinear Halo Orbit

NASA's Gateway program will build a crew-tended station in an Earth-Moon Near Rectilinear Halo Orbit (NRHO) to support deep space missions to the lunar surface and heliocentric space. The station in the NRHO will be visited by crewed vehicles including lunar landers that are high mass relative to Gateway. Docking events with large vehicles induce significant thruster plume and docking contact velocity perturbations. Crewed vehicles induce significant venting perturbations that can stress the navigation filter's ability to remain converged about an estimated state. The torques that arise from venting and lunar gravity gradient require reaction control system (RCS) thruster intervention, which themselves induce a velocity perturbation. The best method to model RCS thruster perturbations is currently in development. This paper simulates different RCS perturbation models, schedules, and an increasing magnitude to investigate the navigation sensitivity to different RCS perturbation models. From the RCS perturbation models simulated, a worst-case scenario is chosen for further scrutiny. The navigation filter is further tuned to handle the most disruptive perturbation modeling and the resulting performance is analyzed.

Navigation↗
NASA NTRS1995

Dynamic behavior of solar wind as revealed by a correlation study of magnetic fields observed at the Venus and Earth orbits

Correlations between interplanetary magnetic fields (IMFs) at 0.72 AU and 1.0 AU have been examined using data sets obtained from the Pioneer Venus orbiter and Earth-orbiting spacecraft. While the two-sector structures are evident in long-term variations at these two heliocentric distances, the corresponding auto-correlation coefficients are consistently smaller at 1.0 AU than at 0.72 AU. This suggests that the IMF structures become less persistent at 1.0 AU due to the effects of changing solar wind dynamics between the Venus and Earth orbits. Short-term variations exhibit generally poor correlations between IMFs near Venus and those near Earth, though good correlations are sometimes obtained for well-defined structures when the Sun, Venus, and Earth are closely aligned. The rather poor correlations in the background streams indicate that the IMFs are still changing between the Venus and Earth orbits under the strong influence of solar wind dynamics.

Marubashi, K.↗