Description of Three Candidate Cassini Satellite Tours
This paper describes three candidate Cassini satellite tours which are indicative of tours currently under consideration.
Cassini↗
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Galileo Jupiter encounter and satellite tour trajectory design
The trajectory design process for the Galilean satellite probe, expected to be launched in January 1982, is examined and its interplanetary path, emphasizing arrival dates and the Mars flyby, is presented. The Galileo spacecraft is of dual spin design, combining features of Pioneer, a spinning craft, and Voyager which was 3-axis stabilized. The design of the initial orbit from Orbiter deflection through Jupiter to the beginning of the satellite tour is discussed as well as the use of an Io gravity assist flyby to achieve Jupiter orbit insertion, and the effects of solar perturbation on the initial orbit. Detail is given to the entire satellite tour trajectory design process, starting from the requirements and constraints placed on the tour through the conic design to the final numerically integrated trajectories.
Diehl, R. E.↗
Satellite tour design for the Cassini mission
The mission design for the Cassini satellite tour of Saturn is described. The use of Titan encounters for gravity-assisted trajectory shaping to satisfy atmosphere, magnetosphere, and satellite science requirements is discussed. Three candidate satellite tours that illustrate the tradeoffs between different strategies to satisfy the science objectives are presented. Tour characteristics for a 4yr mission include at least 30 Titan encounters to provide a minimum of 90 deg orbit rotation for either a magnetotail petal orbit or noon petal orbit; evenly distributed Titan ground tracks for radar mapping coverage; at least 2 Iapetus and 1 Enceladus close flybys; inclined orbits during the first 3 yr to provide Earth and Sun occultations by Saturn and its rings; and Polar orbits during the fourth year.
Diehl, R. E.↗
Satellite tour design for the Galileo mission
The design of Galileo's tour of Jupiter's Galilean satellites is discussed. The Galileo mission is reviewed, and the gravity-assist trajectory design is described. Attention is given to mission constraints and science requirements, several tour design strategies, and a strawman satellite tour. The software used to design a satellite tour is examined.
Diehl, R. E.↗
Design of the Galileo Satellite Tour
Concepts, strategies, and techniques developed in the 1970s and 1980s, which were used in designing the satellite tour for the 1986 launch opportunity were employed and extended for this effort.
satellite tour↗
Galileo Satellite Tour: Orbit Determination
This paper discusses orbit determination results for the Galileo satellite tour. Lacking a high gain antenna, the mission will use a low gain antenna for communication and tracking. This change implies far less navigation data will be available than previously expected. A baseline orbit analysis was completed assuming this decreased data schedule. Variations on this baseline were studied to determine sensitivity to data loss. Results indicate that the probability of completing the tour is less than 90 percent, although future improvements in orbit determination promise to raise the probability of completion above 90 percent.
Haw, R. J.↗
Galilean satellite tour orbit determination assessment
Results are given which demonstrate the ability of the orbit determination system to satisfy accuracy requirements in support of the Galileo Project's planned tour of Jupiter's satellites. The results are derived through the application of mission operation strategies and assumptions. It is shown that the achievement of the requisite orbit determination accuracies is predicated on the availability of optical navigation data. It is further demonstrated that the unavailability of tour optical navigation data yields not only degraded orbit determination accuracies which fail to meet propellant budget and science instrument pointing requirements, but also produces, for the planned 200 km flyby of Europa, an approximate 0.02 risk of having the spacecraft collide with the satellite.
Moultrie, B.↗
Galileo satellite tour maneuver strategies
In January of 1982 the United States will launch Galileo, the first space mission designed to perform an intensive tour of the Galilean satellites of Jupiter. This paper discusses the results of preliminary maneuver strategy studies for typical interplanetary and orbital phases of the Galileo mission. These studies include the effects of maneuver placement and various linear control algorithms on propellant consumption as determined by Monte Carlo analysis. Estimates of total propellant required for various probabilities of mission success are also given.
Miller, L. J.↗
The Gem Extension Satellite Tour: Galileo's Mission Across the Millennium
A one year follow-on to the Galileo Europa Mission (GEM) has been proposed. This extension to GEM begins in October 1999 and consists of six encounters, the first two overlapping with the last two encounters in GEM.
Galileo↗
The Jupiter orbiter satellite tour mission
Consideration of the problem of exploring the Jupiter-Galilean satellite system by a spacecraft in orbit about the planet. A simple patched conic algorithm is developed which identifies Jupiter orbiter trajectories that utilize gravity assist flybys of the Galilean satellites. A detailed reference mission is designed against specific science criteria for satellite exploration to demonstrate the possible science return of utilizing close satellite encounters. A navigation strategy is developed, including both planet and satellite relative orbit determination and a maneuver analysis; spacecraft delivery statistics are determined in the barycentric Jupiter-Galilean satellite coordinate system and mapped to the satellite target planes to determine feasibility. A simple maneuver sequence is employed which yields acceptable velocity requirements.
Beckman, J. C.↗
Galileo Icy Satellite Tour
Galileo's orbital tour at Jupiter will involve multiple close passes by the Galilean satellites, typically 10-100 times closer than Voyager encounters.
Galileo↗
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↗
Post Galileo-Europa-Mission Satellite Tour Design
The Galileo orbiter mission as originally envisioned would orbit Jupiter eleven times, closely encountering either Europa, Ganymede, or Callisto on ten of those orbits. This nominal or prime mission began with Jupiter orbit insertion on December 7, 1995 and ended as designed ten encounters later on December 1, 1997. An extension to this nominal mission was proposed, developed and accepted in 1997 and was designed to continue orbital operations through an additional two years until December 31, 1999. This follow- on mission, labelled the Galileo Europa Mission, visits Europa eight times, Callisto four times, and ends with two visits to Io. It augments the prime mission by offering many attractive additional opportunities for science, especially remote sensing. The opportunities include increased scrutiny of Europa, a world with a possible global ocean hidden beneath the surface ice-cap, and the first high resolution images of Io (the only major satellite not encountered during the nominal tour). In 1998 a new effort was begun to investigate a possible extension to GEM. Remote sensing observations will continue to be important but moreover, valuable unique in situ fields and particles measurements will be a high priority motivation in the design and selection of any post-GEM tour. A significant design feature of a possible post-GEM tour would be the extension of the mission through the December 2000 timeframe. This would permit the possibility of simultaneous fields and particles experiments coordinated with the Cassini spacecraft as it swings by the Jupiter system for the final gravity assist enroute to Saturn.
Wilson, M. G.↗
Galileo Satellite Tour: Orbit Determination Performance
The Galileo mission is an ambitious attempt to explore the Jovian system by spacecraft. This voyage of exploration is a logical successor to the reconnaissance voyages of Pioneers 10 and 11, Voyagers 1 and 2, and Ulysses. These spacecraft merely flew past Jupiter, spending relatively little time in its system. Galileo differs from these earlier spacecraft in that it will remain within the Jovian system, studying the planet and its four major satellites for a period of two years. Insertion into orbit around Jupiter will occur on December 7, 1995. The portion of the mission encompassing observations of Jupiter and the major and minor satellites, and magnetospheric mapping, has become known as the Jovian tour. During this period Galileo will encounter each of Europa, Ganymede, and Callisto at least three times on trajectories that will bring it to altitudes from 200 to 3100 kilometers.
Haw, R. J.↗
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↗