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Ionasescu, Rodica

Publications and source records attributed to Ionasescu, Rodica.

34 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2008

Navigational Use of Cassini Delta V Telemetry

Telemetry data are used to improve navigation of the Saturn orbiting Cassini spacecraft. Thrust induced delta V's are computed on-board the spacecraft, recorded in telemetry, and downlinked to Earth. This paper discusses how and why the Cassini Navigation team utilizes spacecraft delta V telemetry. Operational changes making this information attractive to the Navigation Team will be briefly discussed, as will spacecraft hardware and software algorithms responsible for the on-board computation. An analysis of past delta V telemetry, providing calibrations and accuracies that can be applied to the estimation of future delta V activity, is described.

Roth, Duane C.↗
NASA NTRS2005

Preparing for the Huygens Probe Mission, Cassini orbit determination results for the first and second targeted Titan encounters

Dynamic modeling of the spacecraft and Saturn system, tracking data, including radio-metric and optical navigation data, and measurement modeling associated with the final trajectory analysis are described. Navigation predictions produced during the operational phase are compared with the final trajectory in order to gain insight into navigation performance and maneuver execution errors. Special attention is given to refinement of the dynamical environment of Saturn, particularly Titan, during the first two orbits.

navigation↗
NASA NTRS2005

Addition of a low altitude Tethys flyby to the nominal Cassini tour

Of the eight Saturnian icy satellites. all but Mimas and Tethys had low altitude targeted flybys during the 4-year primary Cassini spacecraft tour. In November 2004, the existence of a potential low-altitude Tethys flyby was discovered; this low-altitude flyby, added to the nominal tour in March 2005, corresponded to a 1500 km non-targeted periapsis altitude on September 24, 2005 with an associated (delta)v cost of approximately 8 mis. This memo details the methods used to determine the Rev-15 non-targeted Tethys flyby altitude, driven by navigational requirements and operational constraints, in addition to several trajectory modifications implemented to reduce total (delta)v costs, and in some cases. render simultaneous increases in scientific return.

Cassini↗
NASA NTRS2005

Addition of a Low Altitude Tethys Flyby to the Nominal Cassini Tour

Of the eight Saturnian icy satellites, all but Mimas and Tethys have low altitude targeted flybys during the 4-year nominal Cassini spacecraft tour. In November 2004, the existence of a potential low-altitude Tethys flyby was discovered; this low-altitude Tethys flyby, added to the nominal tour in March 2005, corresponds to a 1500 km nontargeted periapsis altitude on September 24, 2005 and requires a Av cost of 8 mls. This paper details the methods used to determine the Tethys non-targeted flyby altitude, driven by navigational requirements and operational constraints, in addition to several trajectory modifications implemented to reduce total Av costs, and in some cases, simultaneous increases in scientific return.

Cassini↗
NASA NTRS2005

Orbit determination results and trajectory reconstruction for the Cassini/Huygens Mission

During Cassini's third orbit around Saturn, the Huygens Probe was successfully released on a trajectory that resulted in the probe entering Titan's atmosphere on January 14, 2005, making it both the most distant spacecraft landing and the first spacecraft to successfully land on the moon of another planet. This paper documents the reconstruction of both the orbiter and probe trajectoriespanning the Titan-B and Titan-C encounters.

reconstruction↗
NASA NTRS2003

Cassini tour navigation strategy

The Cassini-Huygens spacecraft was launched on October 15, 1997 as a joint NASA/ESA mission to explore Saturn. After a 7 year cruise the spacecraft will enter orbit around Saturn on 1 July 2004 for a 4 year investigation of the Saturnian system. The Cassini Navigation Team is responsible for designing the reference trajectory and conducting operations to realize this design. This paper describes the strategy for achieving project requirements, the characteristics of the Cassini navigation challenge, and the underlying assumptions.

Saturn↗
NASA NTRS2003

Cassini tour navigation strategy

This paper describes the strategy for achieving project requirements, the characteristics of the Cassini navigation challenge, and the underlying assumptions.

Cassini↗
NASA NTRS1993

Asteroid approach covariance analysis for the Clementine mission

The Clementine mission is designed to test Strategic Defense Initiative Organization (SDIO) technology, the Brilliant Pebbles and Brilliant Eyes sensors, by mapping the moon surface and flying by the asteroid Geographos. The capability of two of the instruments available on board the spacecraft, the lidar (laser radar) and the UV/Visible camera is used in the covariance analysis to obtain the spacecraft delivery uncertainties at the asteroid. These uncertainties are due primarily to asteroid ephemeris uncertainties. On board optical navigation reduces the uncertainty in the knowledge of the spacecraft position in the direction perpendicular to the incoming asymptote to a one-sigma value of under 1 km, at the closest approach distance of 100 km. The uncertainty in the knowledge of the encounter time is about 0.1 seconds for a flyby velocity of 10.85 km/s. The magnitude of these uncertainties is due largely to Center Finding Errors (CFE). These systematic errors represent the accuracy expected in locating the center of the asteroid in the optical navigation images, in the absence of a topographic model for the asteroid. The direction of the incoming asymptote cannot be estimated accurately until minutes before the asteroid flyby, and correcting for it would require autonomous navigation. Orbit determination errors dominate over maneuver execution errors, and the final delivery accuracy attained is basically the orbit determination uncertainty before the final maneuver.

Ionasescu, Rodica↗
NASA NTRS1990

To explore a comet - The Comet Rendezvous Asteroid Flyby mission at Comet Kopff

The Comet Rendezvous Asteroid Flyby (CRAF) mission has the primary goal of determining the composition and physical characteristics of a comet. To achieve this goal, a spacecraft will rendezvous with Comet Kopff and spend 2.5 years near the comet to study it with a variety of instruments. A penetrator will also be released by the spacecraft and propel itself into the nucleus of the comet for direct measurements. This paper presents a typical scenario for orbiting the comet, which provides for meeting all major scientific objectives.

Cheng, Jeannie T.↗
NASA NTRS1989

Design options and analysis of variable gravity systems in space

Design options for tethered systems which can produce a variable gravity living environment in space are discussed. Parameters of rotating systems are reviewed, and early studies of rotating systems are recalled. Artificial gravity configurations are shown and their individual advantages and disadvantages are examined.

Penzo, Paul A.↗
NASA NTRS1989

Coma and tail trajectory design for the CRAF mission

The design of the trajectory for the proposed Comet Rendezvous Asteroid Flyby (CRAF) mission to study comet coma and tail development is examined. A two part trajectory is planned for the CRAF mission to study comet Kopff. It is proposed that, during the 213 day perihelion phase of the trajectory, CRAF should perform multiple petallike flybys at 50-5000 km from the comet's nucleus. Nine days after the perihelion, the spacecraft would transition into the comet tail in the antisun direction to a maximum distance of 50,000 km. The objectives of these two phases of exploration are discussed.

Ionasescu, Rodica↗
NASA NTRS1988

Innovative uses of tethers in space

Potential uses of tethers in the fields of science, transportation, electrodynamics, and space exploration are discussed. Special attention is given to the use of tethers for scientific and planetary application, with descriptions of the type of measurements to be performed in a given science field or a planetary body and the particular method of tether use. Experiments proposed regarding the use of tethers will address some of the pending issues regarding the use of tethers, such as the tether deployment and control laws, the recoil, electrodynamic effects, the strength and survivability of tethers in the lower atmosphere, the stability of a tethered platform, and the propulsion through momentum exchange.

Ionasescu, Rodica↗