Engineering topics

Jones, J. B.

Publications and source records attributed to Jones, J. B..

At least 19 records

NASA NTRS2010

Resilience of Alaska's Boreal Forest to Climatic Change

This paper assesses the resilience of Alaska s boreal forest system to rapid climatic change. Recent warming is associated with reduced growth of dominant tree species, plant disease and insect outbreaks, warming and thawing of permafrost, drying of lakes, increased wildfire extent, increased postfire recruitment of deciduous trees, and reduced safety of hunters traveling on river ice. These changes have modified key structural features, feedbacks, and interactions in the boreal forest, including reduced effects of upland permafrost on regional hydrology, expansion of boreal forest into tundra, and amplification of climate warming because of reduced albedo (shorter winter season) and carbon release from wildfires. Other temperature-sensitive processes for which no trends have been detected include composition of plant and microbial communities, long-term landscape-scale change in carbon stocks, stream discharge, mammalian population dynamics, and river access and subsistence opportunities for rural indigenous communities. Projections of continued warming suggest that Alaska s boreal forest will undergo significant functional and structural changes within the next few decades that are unprecedented in the last 6000 years. The impact of these social ecological changes will depend in part on the extent of landscape reorganization between uplands and lowlands and on policies regulating subsistence opportunities for rural communities.

Chapin, F. S., III↗

NASA NTRS2008

Cassini Orbit Determination Results: January 2006 - End of Prime Mission

After the forty-fifth flyby of Titan, the Cassini spacecraft has successfully completed the planned four-year prime mission tour of the Saturnian system. This paper reports on the orbit determination performance of the Cassini spacecraft over two years spanning 2006 - 2008. In this time span, Cassini's orbit progressed through the magnetotail and pi-transfer phases of the mission. Thirty-four accurate close encounters of Titan, one close flyby of Iapetus and one 50 km flyby of Enceladus were performed during this period. The Iapetus and Enceladus flybys were especially challenging and so the orbit determination supporting these encounters will be discussed in more detail. This paper will show that in most cases orbit determination has exceeded the navigation requirements for targeting flybys and predicting science instrument pointing during these encounters.

Lapetus↗

NASA NTRS2008

Navigation Ground Data System Engineering for the Cassini/Huygens Mission

The launch of the Cassini/Huygens mission on October 15, 1997, began a seven year journey across the solar system that culminated in the entry of the spacecraft into Saturnian orbit on June 30, 2004. Cassini/Huygens Spacecraft Navigation is the result of a complex interplay between several teams within the Cassini Project, performed on the Ground Data System. The work of Spacecraft Navigation involves rigorous requirements for accuracy and completeness carried out often under uncompromising critical time pressures. To support the Navigation function, a fault-tolerant, high-reliability/high-availability computational environment was necessary to support data processing. Configuration Management (CM) was integrated with fault tolerant design and security engineering, according to the cornerstone principles of Confidentiality, Integrity, and Availability. Integrated with this approach are security benchmarks and validation to meet strict confidence levels. In addition, similar approaches to CM were applied in consideration of the staffing and training of the system administration team supporting this effort. As a result, the current configuration of this computational environment incorporates a secure, modular system, that provides for almost no downtime during tour operations.

Beswick, R. M.↗

NASA NTRS2007

Cassini Orbit Determination Performance during Saturn Satellite Tour: August 2005 - January 2006

During the period spanning the second Enceladus flyby in July 2005 through the eleventh Titan encounter in January 2006, the Cassini spacecraft was successfully navigated through eight close-targeted satellite encounters. Three of these encounters included the 500 km flybys of the icy satellites Hyperion, Dione and Rhea and five targeted flybys of Saturn's largest moon, Titan. This paper will show how our refinements to Saturn's satellite ephemerides have improved orbit determination predictions. These refinements include the mass estimates of Saturn and its satellites by better than 0.5%. Also, it will be shown how this better orbit determination performance has helped to eliminate several statistical maneuvers that were scheduled to clean-up orbit determination and/or maneuver-execution errors.

Rhea↗

NASA NTRS2005

Cassini orbit determination performance during the first eight orbits of the Saturn satellite tour

From June 2004 through July 2005, the Cassini/Huygens spacecraft has executed nine successful close-targeted encounters by three major satellites of the Saturnian system. Current results show that orbit determination has met design requirements for targeting encounters, Hugens descent, and predicting science instrument pointing for targetd satellite encounters. This paper compares actual target dispersion against, the predicte tour covariance analyses.

navigation↗

NASA NTRS1987

Comparative aspects of hematological responses in animal and human models in simulations of weightlessness and space flight

This paper reviews some human and animal responses to space flight as well as in control models in simulations of weightlessness. Astronauts after space flight have been found to have a decreased red blood cell mass and plasma volume. The reason for these changes is unknown but appears to be caused primarily by a decrease in the need of red blood cells in the weightless condition. Similar though more moderate changes have been found in human subjects subjected to prolonged bed rest or water immersion. What happens to the red cell mass of laboratory rats flown in microgravity is not known but rats have shown an increase in the rate of random red cell loss in flight suggesting a probable decrease. Rat models subjected to either head-down suspension or restraint alone have shown a decrease in red blood cell masses and a decrease in their plasma volume.

Lange, R. D.↗

NASA NTRS1987

Hematological measurements in rats flown on Spacelab shuttle, SL-3

Previous studies have shown that a decrease in red cell mass occurs in astronauts, and some studies indicate a leukocytosis occurs. A life science module housing young and mature rats was flown on shuttle mission Spacelab 3 (SL-3), and the results of hematology studies of flight and control rats are presented. Statistically significant increases in the hematocrit, red blood cell counts, and hemoglobin determinations, together with a mild neutrophilia and lymphopenia, were found in flight animals. No significant changes were found in bone marrow and spleen cell differentials or erythropoietin determinations. Clonal assays demonstrated an increased erythroid colony formation of flight animal bone marrow cells at erythropoietin doses of 0.02 and 1.0 U/ml but not 0.20 U/ml. These results agree with some but vary from other previously published studies. Erythropoietin assays and clonal studies were performed for the first time.

NASA Experiment Number SL3-26↗

NASA NTRS1984

Autonomous navigation - The ARMMS concept

A conceptual design is outlined for the navigation subsystem of the Autonomous Redundancy and Maintenance Management Subsystem (ARMMS). The principal function of this navigation subsystem is to maintain the spacecraft over a specified equatorial longitude to within + or - 3 deg. In addition, the navigation subsystem must detect and correct internal faults. It comprises elements for a navigation executive and for orbit determination, trajectory, maneuver planning, and maneuver command. Each of these elements is described. The navigation subsystem is to be used in the DSCS III spacecraft.

Wood, L. J.↗

NASA NTRS1981

Small velocity changes using a SEP spacecraft

The Solar Electric Propulsion (SEP) system is designed to deliver large payloads using extended thrusting periods. However, for certain classes of missions, it would be desirable to also use the low thrust propulsion system to impart the small velocity changes typically required to control an orbit in the vicinity of the target body. This paper examines the characteristics and capabilities of using an example SEP system to apply small velocity changes in arbitrary directions. Formulas are developed and examples presented for the rotation and translation which results when the ion thrusters are used to make large turns about all three of the spacecraft axes. This data is then used to propose various techniques for achieving arbitrary velocity changes. While still in a formative stage, the results may be useful in both the design of SEP spacecraft and formulation of future missions.

Jones, J. B.↗

NASA NTRS1980

A solution of the variational equations for elliptic orbits in rotating coordinates

For elliptic reference orbits, formulas are given for the perturbation state transition matrix of the two-body problem. The formulas relate perturbations expressed in a local vertical rotating coordinate system and are valid for motion in the linear neighborhood of reference orbits with e in the range of 0 to 1. The elements of the state transition matrix are expressed in terms of natural parameters (horizontal and radial velocity, radius, eccentricity, true anomaly, etc.) at the initial and final points. In addition to the general form, a simplified version, valid for small eccentricity orbits, is given.

Jones, J. B.↗

NASA NTRS1980

Near-comet trajectory design

The Halley Flyby/Tempel 2 Rendezvous mission requires not only a new spacecraft design and a new propulsion system (the Solar Electric Propulsion System), but it also requires new approaches to the trajectory and the mission design. Because of the feebleness of Tempel 2 gravitation and because of the presence of various other competing forces, a realization and/or preservation of a spacecraft trajectory about the comet is characteristically different from that about a more massive body. This paper surveys, compares, and evaluates the significance of various forces acting on the spacecraft in the vicinity of the comet. The range of variations and uncertainties inherent in modeling of these forces are also discussed. Then, a number of different types of trajectories relevant to the design of the Tempel 2 exploration are depicted and examined. These include short-arc trajectories, near-comet short- and long-term orbits, and comet-landing trajectories.

Jones, J. B.↗

NASA NTRS1977

Voyager navigation strategy and accuracy

The paper presents the results of the prelaunch navigation studies conducted for the Mariner spacecraft launched toward encounters with the giant planets. The navigation system and the strategy for using this system are described. The requirements on the navigation system demanded by the goals of the project are mentioned, and the predicted navigational capability relative to each of the requirements is discussed. Baseline navigation results for three possible trajectories are analyzed.

Jones, J. B.↗

NASA NTRS1977

Operational utilization of remotely sensed data

The use of data from environmental satellites and other remote sensing platforms in some of NOAA's operational services are described. Topics discussed include: hurricanes; severe local storms and tornadoes; forest guidance; weather forecasting; hydrology; space program support; oceanography; search and rescue; and wildlife management. Applications which have become routine, and those which are in advanced field test are included. Some applications yield a clear cut economic benefit. In other cases, benefits -- if any -- are obscure. In yet other cases, benefits in one sector may be offset by detriments in another. Illustrative examples are given.

Jones, J. B.↗

NASA NTRS1976

Optimal rendezvous in the neighborhood of a circular orbit

The minimum velocity-change rendezvous solutions, when the motion may be linearized about a circular orbit, fall into two separate regions; the phase-for-free region and the general region. Phase-for-free solutions are derived from the optimum transfer solutions, require the same velocity-change expenditure, but may not be unique. Analytic solutions are presented in two of the three subregions. An algorithm is presented for determining the unique solutions in the general region. Various sources of initial conditions are discussed and three examples are presented.

Jones, J. B.↗

NASA NTRS1975

Optimal rendezvous in the neighborhood of a circular orbit

The minimum velocity change rendezvous solutions, when the motion may be linearized about a circular orbit, fall into two separate regions; the phase-for-free region and the general region. Phase-for-free solutions are derived from the optimum transfer solutions, require the same velocity change expenditure, but may not be unique. Analytic solutions are presented in two of the three subregions. An algorithm is presented for determining the unique solutions in the general region. Various sources of initial conditions are discussed and three examples presented.

Jones, J. B.↗

NASA NTRS1975

The navigation of a satellite re-encounter in a Jupiter Orbiter mission

Very often in the course of the Jupiter Orbiter-Satellite Tour mission it is desired to have the spacecraft re-encounter a satellite after one complete Jovicentric orbit whose period is resonant with that of the satellite for the purposes of orbit 'cranking' or 'pumping'. This paper develops the deterministic guidance strategy necessary for the implementation of such re-encounters (360 deg transfers). Both single impulse and fuel optimal multiple impulse guidance strategies are developed on the basis of which an estimate of the total navigational fuel cost for the mission is made.

Sherman, G. N.↗

NASA NTRS1975

Navigation results of the Mariner Venus/Mercury 1973 mission

The navigation aspects of the Mariner Venus/Mercury 1973 mission are presented. Principal emphasis is on the maneuver strategy employed, propellant costs and the results of the navigation performance relating to the accomplishment of the mission objectives including an extended mission for a second Mercury encounter. Key error sources and mission constraints are discussed. Of particular interest is the impact of in-flight adaptation of the pre-launch maneuver strategy (due to spacecraft anomalies) on propellant cost and the delivery achieved at the first Mercury encounter. The maneuver strategy and propellant cost for the extended mission are shown to be heavily influenced by the delivery achieved at the first Mercury encounter and the science objectives at the second Mercury encounter.

Bantell, M. H., Jr.↗

NASA NTRS1973

Mariner Venus/Mercury 1973 navigation strategy

This paper presents the navigational aspects of the Mariner Venus/Mercury 1973 mission. Principal emphasis is on the development of the trajectory correction strategy, propellant costs, and delivery accuracies at Venus and Mercury. Key error sources and mission constraints are discussed. Of particular interest are the statistics of the first, post-Venus, maneuver which must correct for the magnification of errors in the Venus encounter. Finally, although not a primary objective of the mission, the analysis is extended to include a second Mercury encounter.

Mckinley, E. L.↗