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Wagner, Sean

Publications and source records attributed to Wagner, Sean.

33 records · Page 2

Cassini In-Flight Navigation Adaptations

In the nearly two decades of Cassini flight, adaptations to navigation processes were applied as characteristics unique to Cassini were identified and spacecraft configuration changes were implemented. Additionally, operational experience was leveraged into more efficient processes, better modeling, and more robust contingency strategies. Trajectory adjustments were implemented to allow further investigation of surprising science discoveries meriting more attention. Unique analyses were performed to determine how to best accomplish atypical science observations while maintaining acceptable risk levels. Descriptions of the most significant adaptations are organized according to the affected navigation subsystems: trajectory design, orbit determination, optical navigation, and maneuver design.

Wagner, Sean

The Cassini Mission: Reconstructing Thirteen Years of the Most Complex Gravity-Assist Trajectory Flown to Date

Cassini launched in 1997 and completed its prime mission, its Equinox first extended mission, and its Solstice second extended mission. Since its arrival at Saturn in 2004, Cassini completed almost 300 orbits around the planet. Over the span of the mission, significant improvements were made to all the major satellites ephemeris, and to Saturn gravitational and pole models. These improvements have enabled better trajectory reconstructions throughout the timeframe of the mission, although using about one hundred different models of the Saturn system. Now that the mission is over, the paper reports on the uniform reconstruction of the entire Cassini orbital mission, which uses one consistent Saturn system model and satellite ephemerides throughout. We discuss the challenges of undertaking this task, and comparison strategies for choosing the best and greatest Cassini trajectory for its very final delivery.

Wagner, Sean

Flying Cassini Through the Grand Finale Orbits: Prediction vs. Reality

After twenty years of successful mission operations and invaluable scientific discoveries, the Cassini orbiter completed its tour around the Saturnian system on the most complex gravity-assist trajectory ever flown. The end-of-mission target of September 15, 2017 was achieved by preserving propellant at the expense of minimizing maneuver cycles. A navigation a strategy that incorporated orbit trim maneuvers was developed years in advance to maintain position dispersions below 250 km (1σ) at three specific periapses. This paper reports on the actual maneuver performance and overall trajectory control to maintain the Grand Finale orbits, highlighting the differences between predicted and implemented values.

Roth, Duane

50,000 Laps Around Mars: Navigating the Mars Reconnaissance Orbiter Through the Extended Missions (January 2009 - March 2017)

Orbiting Mars since March 2006, the Mars Reconnaissance Orbiter (MRO) spacecraft continues to perform valuable science observations, provide telecommunication relay for surface assets, and characterize landing sites for future missions. Previous papers reported on the navigation of MRO from interplanetary cruise through the end of the Primary Science Phase (PSP) in December 2008 and on maneuvers performed through November 2016. This paper highlights the navigation of MRO from January 2009 through its 50,000th orbit around Mars on March 27, 2017, an eight-year period covering the Extended Science Phase, the first three extended missions, and a portion of the fourth extended mission which began on October 1, 2016. Since the beginning of the PSP in November 2006, MRO’s navigation performance has continued to exceed expectations. Over that period of time, the mission has returned over 300 terabytes of data.

Schulze, William

Mars Reconnaissance Orbiter Navigation Strategy for the ExoMars Schiaparelli EDM Lander Mission

The Mars Reconnaissance Orbiter (MRO) had planned to provide surface relay support for the brief mission of the ExoMars Schiaparelli EDM lander on Mars in October 2016. Launched with the Trace Gas Orbiter (TGO) in March 2016, Schiaparelli and TGO composed the first part of the ExoMars program. To place MRO directly overhead on its third overflight of the Schiaparelli landing site, two propulsive maneuvers were performed starting three months prior to Shiaparelli’s arrival at Mars. This paper documents the maneuver strategy employed by the MRO Navigation Team to support the Schiaparelli overflight campaign.

Schulze, William B.

Cassini Maneuver Experience for the Fourth Year of the Solstice Mission

After sixteen years of successful mission operations and invaluable scientific discoveries, the Cassini orbiter continues to tour Saturn on the most complex gravity-assist trajectory ever flown. To ensure that the end-of-mission target of September 2017 is achieved, propellant preservation is highly prioritized over maneuver cycle minimization. Thus, the maneuver decision process, which includes determining whether a maneuver is performed or canceled, designing a targeting strategy and selecting the engine for execution, is being continuously re-evaluated. This paper summarizes the maneuver experience throughout the fourth year of the Solstice Mission highlighting 27 maneuvers targeted to nine Titan flybys.

Maneuver Design

The Double Flybys of the Cassini Mission: Navigation Challenges and Lessons Learned

Since 2004, the Cassini spacecraft has flown by Titan and other Saturn moons numerous times, successfully accomplishing its 100th targeted encounter of Titan in March 2014. The navigation of Cassini is challenging, even more so with "double flybys," two encounters separated by at most a few days. Because of this tight spacing, there is not enough time for a maneuver in between. Additionally, maneuvers prior to a double flyby only target one of the two encounters. This paper discusses the challenges faced by the Cassini Navigation Team with each double flyby, as well as lessons learned during operational support of each dual encounter. The strengths and weaknesses of the targeting strategies considered for each double flyby are also detailed, by comparing downstream ?V costs and changes to the non-targeted flyby conditions.

maneuver

Maneuver Performance Assessment of the Cassini Spacecraft Through Execution-Error Modeling and Analysis

The Cassini spacecraft has executed nearly 300 maneuvers since 1997, providing ample data for execution-error model updates. With maneuvers through 2017, opportunities remain to improve on the models and remove biases identified in maneuver executions. This manuscript focuses on how execution-error models can be used to judge maneuver performance, while providing a means for detecting performance degradation. Additionally, this paper describes Cassini's execution-error model updates in August 2012. An assessment of Cassini's maneuver performance through OTM-368 on January 5, 2014 is also presented.

Wagner, Sean

Cassini-Huygens maneuver automation for navigation

Many times during the Cassini-Huygens mission to Saturn, propulsive maneuvers must be spaced so closely together that there isn't enough time or workforce to execute the maneuver-related software manually, one subsystem at a time. Automation is required. Automating the maneuver design process has involved close cooperation between teams. We present the contribution from the Navigation system. In scope, this includes trajectory propagation and search, generation of ephemerides, general tasks such as email notification and file transfer, and presentation materials. The software has been used to help understand maneuver optimization results, Huygens probe delivery statistics, and Saturn ring-plane crossing geometry. The Maneuver Automation Software (MAS), developed for the Cassini-Huygens program enables frequent maneuvers by handling mundane tasks such as creation of deliverable files, file delivery, generation and transmission of email announcements, generation of presentation material and other supporting documentation. By hand, these tasks took up hours, if not days, of work for each maneuver. Automated, these tasks may be completed in under an hour. During the cruise trajectory the spacing of maneuvers was such that development of a maneuver design could span about a month, involving several other processes in addition to that described, above. Often, about the last five days of this process covered the generation of a final design using an updated orbit-determination estimate. To support the tour trajectory, the orbit determination data cut-off of five days before the maneuver needed to be reduced to approximately one day and the whole maneuver development process needed to be reduced to less than a week..

propulsion maneuvers

Cassini - Huygens maneuver experience : cruise and arrival at Saturn

The Cassini-Huygens mission to Saturn and Titan was launched in 1997. It is an international effort to study the Saturnian system. Cassini-Huygens' interplanetary cruise delivered the spacecraft to Saturn in 2004. It also made use of many propulsive maneuvers, both statistical and deterministic. Maneuver-related analysis and performance for latter half of cruise is reported. The system has performed more accurately than the pre-launch expectations and requirements. Additionally, some maneuvers have already been skipped, saving propellant and flight team effort. Analysis of historical execution error data is presented.

Huygens

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

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