NASA Scientific and Technical Aerospace Reports

X-Ray Timing Explorer Proportional Counter Array observations covering two outbursts in 2002 and early 2003. At the onset
of the first outburst, the source was found in a spectrally low/hard state lasting for approx.40 days, followed by a 3 day long
transition to the high/soft state. The source flux (in 2- 10 keV) reached approx.100 mcrab on 2002 April 6, then decayed
rapidly. In power spectra, we detect strong band-limited noise and varying low- frequency quasi-periodic oscillations that
evolved from approx.0.5 to approx.5 Hz during the initial low/hard state of the source. We find that the second outburst closely
resembled the spectral evolution of the first. The X-ray transient s overall outburst characteristics led us to classify XTE
J1908+094 as a black hole candidate. Here we also derive precise X-ray position of the source using Chandra observations
that were performed during the decay phase of the first outburst and following the second outburst.
Author
Black Holes (Astronomy); Accretion Disks; X Ray Timing Explorer; Low Frequencies; Oscillations
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LUNAR AND PLANETARY SCIENCE AND EXPLORATION
Includes planetology; selenology; meteorites; comets; and manned and unmanned planetary and lunar flights. For spacecraft design or
space stations see 18 Spacecraft Design, Testing and Performance.
20040111080 Escuela Tecnica Superior de Ingenieros Aeronauticos, Madrid, Spain
A ‘Free Lunch’ Tour of the Jovian System
Sanmartin, J. R.; Lorenzini, E. C.; 8th Spacecraft Charging Technology Conference; March 2004; 7 pp.; In English; See also
20040111031; No Copyright; Avail: CASI; A02, Hardcopy
An ED-tether mission to Jupiter is presented. A bare tether carrying cathodic devices at both ends but no power supply,
and using no propellant, could move ‘freely’ among Jupiter’s 4 great moons. The tour scheme would have current naturally
driven throughout by the motional electric field, the Lorentz force switching direction with current around a ‘drag’ radius of
160,00 kms, where the speed of the jovian ionosphere equals the speed of a spacecraft in circular orbit. With plasma density
and magnetic field decreasing rapidly with distance from Jupiter, drag/thrust would only be operated in the inner
plasmasphere, current being near shut off conveniently in orbit by disconnecting cathodes or plugging in a very large
resistance; the tether could serve as its own power supply by plugging in an electric load where convenient, with just some
reduction in thrust or drag. The periapsis of the spacecraft in a heliocentric transfer orbit from Earth would lie inside the drag
sphere; with tether deployed and current on around periapsis, magnetic drag allows Jupiter to capture the spacecraft into an
elliptic orbit of high eccentricity. Current would be on at successive perijove passes and off elsewhere, reducing the
eccentricity by lowering the apoapsis progressively to allow visits of the giant moons. In a second phase, current is on around
apoapsis outside the drag sphere, rising the periapsis until the full orbit lies outside that sphere. In a third phase, current is on
at periapsis, increasing the eccentricity until a last push makes the orbit hyperbolic to escape Jupiter. Dynamical issues such
as low gravity-gradient at Jupiter and tether orientation in elliptic orbits of high eccentricity are discussed.
Author
Jupiter (Planet); Electrodynamics; Tethering; Space Missions
20040111218 NASA Langley Research Center, Hampton, VA, USA
Aerocapture Performance Analysis for a Neptune-Triton Exploration Mission
Starr, Brett R.; Westhelle, Carlos H.; Masciarelli, James P.; [2004]; 11 pp.; In English; AIAA Atmospheric Flight Mechanics
Conference and Exhibit, 16-19 Aug. 2004, Providence, RI, USA
Contract(s)/Grant(s): 23-800-90-50
Report No.(s): AIAA Paper 2004-4955; No Copyright; Avail: CASI; A03, Hardcopy
A systems analysis has been conducted for a Neptune-Triton Exploration Mission in which aerocapture is used to capture
a spacecraft at Neptune. Aerocapture uses aerodynamic drag instead of propulsion to decelerate from the interplanetary
approach trajectory to a captured orbit during a single pass through the atmosphere. After capture, propulsion is used to move
the spacecraft from the initial captured orbit to the desired science orbit. A preliminary assessment identified that a spacecraft
with a lift to drag ratio of 0.8 was required for aerocapture. Performance analyses of the 0.8 L/D vehicle were performed using
a high fidelity flight simulation within a Monte Carlo executive to determine mission success statistics. The simulation was
the Program to Optimize Simulated Trajectories (POST) modified to include Neptune specific atmospheric and planet models,
spacecraft aerodynamic characteristics, and interplanetary trajectory models. To these were added autonomous guidance and
pseudo flight controller models. The Monte Carlo analyses incorporated approach trajectory delivery errors, aerodynamic
characteristics uncertainties, and atmospheric density variations. Monte Carlo analyses were performed for a reference set of
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