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Orbit Determination Processes for the Navigation of the Cassini-Huygens Mission

Deep space navigation, particularly the Orbit Determination (OD) operations of Cassini at Saturn, cannot easily be automated due to the complex dynamical environment in which the spacecraft flies; however several sub-processes are automated. The Cassini OD operations are often faced with unique challenges that require more than routine procedures. The OD Team is staffed appropriately to meet the demanding schedules and allow some level of flexibility. This paper will discuss how the OD processes are developed and the seven-member OD team is scheduled to support efficient and accurate Cassini navigation operations. Also discussed will be the requirements of the radio-metric Doppler and range tracking data acquired via the Deep Space Network and the optical navigation images of the satellites to support the daily OD operations. Furthermore, the reliability of the OD solutions, which is ensured within the framework of the OD processes, will be explained.

Antreasian, P.G.↗

Completion of the Cassini-Huygens Prime Mission

The Cassini-Huygens mission is a joint endeavor between the United States and Europe to conduct an in-depth investigation of the Saturnian system. The agreement between the parties called for conducting operations in orbit at Saturn for a period of four years, and this was completed on July 1, 2008. The mission has been an unqualified success by any measure, and at the time of the completion of the four years, the spacecraft remained in excellent health and with sufficient consumables remaining that a decision has been reached to continue the endeavor for another two years at the same rate of data collection as in the four-year prime mission. This paper provides a high level overview of the mission's accomplishments in the four years, summarizes the current state of the spacecraft, and gives a summary of the plans and expectations for the two additional years of operations at Saturn.

Mitchell, Robert T.↗

A Surface Science Paradigm for a Post-Huygens Titan Mission

With the Cassini-Huygens atmospheric probe drop-off mission fast approaching, it is essential that scientists and engineers start scoping potential follow-on surface science missions. This paper provides a summary of the first year of a two year design study which examines in detail the desired surface science measurements and resolution, potential instrument suite, and complete payload delivery system. Also provided are design concepts for both an aerial inflatable mobility platform and deployable instrument sonde. The tethered deployable sonde provides the capability to sample nearsurface atmosphere, sub-surface liquid (if it exists), and surface solid material. Actual laboratory tests of the amphibious sonde prototype are also presented.

Cassini-Huygen↗

A Surface Science Paradigm for a Post-Huygens Titan Mission

With the Cassini-Huygens atmospheric probe drop-off mission fast approaching, it is essential that scientists and engineers start scoping potential follow-on surface science missions. This paper provides a summary of the first year of a two year design study which examines in detail the desired surface science measurements and resolution, potential instrument suite, and complete payload delivery system. Also provided are design concepts for both an aerial inflatable mobility platform and deployable instrument sonde. The tethered deployable sonde provides the capability to sample near surface atmosphere, sub-surface liquid (if it exists), and surface solid material. Actual laboratory tests of the amphibious sonde prototype are also presented.

Zimmerman, Wayne F.↗

NIAC Phase 1 Final Study Report on Titan Aerial Daughtercraft

Saturns giant moon Titan has become one of the most fascinating bodies in the Solar System. Even though it is a billion miles from Earth, data from the Cassini mission reveals that Titan has a very diverse, Earth-like surface, with mountains, fluvial channels, lakes, evaporite basins, plains, dunes, and seas [Lopes 2010] (Figure 1). But unlike Earth, Titans surface likely is composed of organic chemistry products derived from complex atmospheric photochemistry [Lorenz 2008]. In addition, Titan has an active meteorological system with observed storms and precipitation-induced surface darkening suggesting a hydrocarbon cycle analogous to Earths water cycle [Turtle 2011].Titan is the richest laboratory in the solar system for studying prebiotic chemistry, which makes studying its chemistry from the surface and in the atmosphere one of the most important objectives in planetary science [Decadal 2011]. The diversity of surface features on Titan related to organic solids and liquids makes long-range mobility with surface access important [Decadal 2011]. This has not been possible to date, because mission concepts have had either no mobility (landers), no surface access (balloons and airplanes), or low maturity, high risk, and/or high development costs for this environment (e,g. large, self-sufficient, long-duration helicopters). Enabling in situ mobility could revolutionize Titan exploration, similarly to the way rovers revolutionized Mars exploration. Recent progress on several fronts has suggested that small-scale rotorcraft deployed as daughtercraft from a lander or balloon mothercraft may be an effective, affordable approach to expanding Titan surface access. This includes rapid progress on autonomous navigation capabilities of such aircraft for terrestrial applications and on miniaturization, driven by the consumer mobile electronics market, of high performance of sensors, processors, and other avionics components needed for such aircraft. Chemical analysis, for example with a mass spectrometer, will be important to any Titan surface mission. Anticipating that it may be more practical to host chemical analysis instruments on a mothership than a daughtercraft, we defined system and mission concepts that deploy a small rotorcraft, termed a Titan Aerial Daughtercraft (TAD), from a lander or balloon to perform high-resolution imaging and mapping, potentially land to acquire microscopic images or other in situ measurements, and acquire samples to return to analytical instruments on the mothership. In principle, the ability to recharge batteries in TAD from a radioisotope or other long-lived power source on the mothership could enable multiple sorties. For a lander-based mission, a variety of landing sites is conceivable, including near lake margins, in dry lake beds, or in regions of plains, dunes, or putative cryovolanic or impact melt features. Such missions may require landing with greater precision than in previous missions (Huygens) and mission studies; this could also enhance the ability of TAD to reach interesting terrain from the landing site. Precision descent may also benefit balloon missions, with or without a daughtercraft, by increasing the probability that the balloon will drift over desired terrain early in its mission. Given these potential benefits, the overall concept studied here includes brief consideration of precision descent for landing or balloon deployment, followed by one or more sorties by a rotorcraft deployed from the mothership, with the ability to return to the mothership.

Saturn↗

Thermal Protection of the Huygens Probe During Titan Entry: Last Questions

CASSINI-HUYGENS mission is a cooperation between NASA and ESA, dedicated to the exploration of the Saturnian system. In the framework of this mission, the entry of the HUYGENS probe in the atmosphere of TITAN will be of major scientific interest. One of the essential points of the HUYGENS mission is therefore the good behavior of the thermal shield designed to maintain the aerodynamic shape and to protect the probe from excessive heating during the atmospheric entry on TITAN. The design and the qualification of this thermal shield were carried out between 1992 and 1995 (development phase). Currently, the final definition of mission parameters is being completed. As the performance of the thermal shield is one of all the parameters considered at system level, it is therefore necessary to reassess the thermal response of the TPS, taking into account some updated information that was not yet available during the development phase. After some recall of the results of 1992 to 1995, the paper will present a status of the current work on TPS.

Bouilly, Jean-Marc↗

The Saturn System Through the Eyes of Cassini

More than 400 years ago, Galileo Galilei trained his homemade telescope on the night sky and observed that Saturn had two objects closely related to the planet extending on either side. At the time, in 1610, Galileo declared them to be moons. A few decades later, Saturn moon science accelerated at a dizzying pace. Christiaan Huygens first observed Saturn's largest moon Titan in 1655 and was the first to describe the extended moon-like features at Saturn as a disk of material sounding the planet. From 1671 to 1674, Giovanni Cassini discovered the moons lapetus, Rhea, Dione and Tethys. In 1675, Cassini discovered the gap in Saturn's rings that we now know as the Cassini Division. In the space age, before the Cassini-Huygens mission, we had only hints of the discoveries awaiting us at Saturn. Pioneer 11 and Voyagers 1 and 2 conducted flybys decades ago. But these quick encounters didn't allow time for more extensive research. NASA and the European Space Agency created a partnership to orbit a Saturn orbiter (Cassini) and a lander (Huygens) on Titan. Like its namesakes, the Cassini-Huygens mission not only discovered previously unknown moons, but it also helped us understand the science behind their formation, their interactions with the rings, and how truly diverse they are. The Cassini-Huygens mission revolutionized what we know about the Saturn system. The rings of Saturn, the moons, and the planet itself offer irresistible and inexhaustible subjects for intense study, and Cassini-Huygens did not disappoint. The Saturnian system proved to be a rich ground for science exploration and discoveries, and Cassini has been nothing short of a discovery machine. At the time Cassini plunged into Saturn at the end of its mission, it had observed the planet for a little less than half of a Saturn year. But it also orbited the gas giant 293 times, forever changing our understanding of the Saturn system and yielding tremendous insight for understanding the entire Solar System.

Green, James↗

Cassini Engineering Operations at Saturn

These presentation viewgraphs shows the engineering operations that have contributed to the unprecedented scientific success of the Cassini and Huygens missions, and how engineering operations are planned and implemented in concert with the required sequence of science observations. Frequent Orbit Trim Maneuvers (OTM) keep Cassini on the correct trajectory to complete the planned Saturn Tour. Considerable effort has been invested in detailed planning of the complete set of science observations associated with this Tour, so a robust OTM strategy is necessary to protect this investment by ensuring the spacecraft keeps to the planned trajectory.

systems engineering↗

Distributed operations as applied in a large multi-instrument space mission: lessons learned from the Cassini-Huygens Program

Launched in 1997, the Cassini-Huygens Mission sent the largest interplanetary spacecraft ever built in the service of science. Carrying a suite of 12 scientific instruments and an atmospheric entry probe, this complex spacecraft to explore the Saturn system may not have gotten off the ground without undergoing significant design changes and cost reductions.

distributed↗

Preparing Cassini Uplink Operations for Extended Mission

The Cassini-Huygens Mission to Saturn and Titan, a joint venture between the National Aeronautics and Space Administration, the European Space Agency, and the Italian Space Agency, is conducting a four-year, prime mission exploring the Saturnian system, including its atmosphere, rings, magnetosphere, moons and icy satellites. Launched in 1997, Cassini began its prime mission in 2004. Cassini is now preparing for a new era, a two-year extended mission to revisit many of the highlights and new discoveries made during the prime mission. Because of the light time delay from Earth to Saturn, and the time needed to coordinate the complicated science and engineering activities that take place on the spacecraft, commanding on Cassini is done in approximately 40-day intervals known as sequences. The Cassini Uplink Operations team is responsible for the final development and validation of the pointing profile and instrument and spacecraft commands that are contained in a sequence. During this final analysis prior to uplink to the spacecraft, thorough and exact evaluation is necessary to ensure there are no mistakes during commanding. In order to perform this evaluation, complete and refined processes and procedures are fundamental. The Uplink Operations team is also responsible for anomaly response during sequence execution, a process in which critical decisions often are made in real-time. Recent anomalies on other spacecraft missions have highlighted two major risks in the operations process: (1) personnel turnover and the retirement of critical knowledge and (2) aging, outdated operations procedures. If other missions are a good barometer, the Cassini extended mission will be presented with a high personnel turnover of the Cassini flight team, which could lead to a loss of expertise that has been essential to the success of the prime mission. In order to prepare the Cassini Uplink Operations Team for this possibility and to continue to develop and operate safe science and engineering sequences, a review and major update of the current documentation and operations procedures was needed. This paper will address the changes made to extended mission sequence generation processes primarily due to new restrictions in spacecraft operating capability and lessons learned from prime mission. In addition, it will address the state of the prime mission operations procedures, the philosophy changes and updates that were made to those procedures in response to process improvement, and the validation of those new procedures through the training of current and new personnel. And lastly, it will address the lessons learned throughout prime mission and how the Uplink Operations team chose to incorporate those lessons into the working documentation and team knowledge. This incorporation was necessary to facilitate the success of the extended mission with potentially all new personnel at some point prior to the end of the mission.

Maxwell, Jennifer L.↗

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↗

The Origin of Planetary Nitrogen

The nitrogen found today in planetary atmospheres appears to come from two sources: N2 and condensed, nitrogen-containing compounds. On Jupiter and thus presumably on the other giant planets, the nitrogen is present mainly as ammonia but was apparently delivered primarily in the form of N2, whereas on the inner planets and Titan, the nitrogen is present as N2 but was delivered as condensed compounds, dominated by ammonia. This analysis is consistent with abundance data from the Interstellar Medium and models for the solar nebula. For Jupiter and the inner planets, it is substantiated by measurements of N-l5/N-14 and is supported by investigations of comets and meteorites, soon to be supplemented by solar wind data from the Genesis Mission. The Cassini-Huygens Mission may be able to constrain models for Saturn s ammonia abundance that could test the proportion of N2 captured by the planet. The Titan story is less direct, depending on studies of noble gases. These studies in turn suggest an evolutionary stage of the early Earth s atmosphere that included the ammonia and methane postulated by S. L. Miller (1953) in his classical experiments on the production of biogenic compounds.

Owen, T.↗

Cassini-Huygens Engineering Operations at Saturn

On 30th June 2004 the Cassini spacecraft fired its main engine to maneuver into orbit around Saturn. This paper describes the engineering operations that have contributed to the unprecedented scientific success of the Cassini and Huygens missions, and how engineering operations are planned and implemented in concert with the required sequence of science observations.

Huygens↗

Mission Summary of Cassini Spacecraft Guidance and Control Hardware Health and Performance

The Cassini-Huygens mission ended on September 15, 2017, after nearly two decades in ight. The well-designed Cassini spacecraft had robust hardware that permitted two extended missions, lasting nine years longer than the expected prime mission. At the end of the mission, the Attitude and Articulation Control Subsystem (AACS) was using two pieces of redundant back-up of hardware, one reaction wheel and the hydrazine thruster branch, due to hardware anomalies earlier in the mission. The back-up hardware performed nominally through the rest of mission. The prime reaction wheels at the end of the mission had reached more than 130% of the consumable limit for number of revolutions. No thruster on either thruster branch accumulated more than 45% of the consumable limits. The inertial reference unit slightly exceeded the pre-launch requirements on bias error, but as the software continuously estimated this value in ight, the attitude estimation was not adversely a ected. The star trackers performed nominally, and though there was a spacecraft anomaly in 1998 related to the star trackers, the origin was not in hardware itself. The Sun sensors and accelerometer both performed as expected and met all requirements throughout the mission. Ultimately, the lifetime of the Cassini spacecraft was not limited by hardware performance. Planetary protection requirements necessitated the end of the mission as the spacecraft's propellant reserves depleted, and Cassini plunged into Saturn's atmosphere with a healthy attitude control system.

Stupik, Joan↗