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The Cassini spacecraft has been in orbit around Saturn since July 1, 2004. To remain on the planned trajectory which maximizes science data return, Cassini must perform orbit trim maneuvers using either its main engine or its reaction control system thrusters. Over 200 maneuvers have been executed on the spacecraft since arrival at Saturn. To impro...
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... standard product for each OTM is the current estimated total spacecraft mass, center-of-mass, and inertia matrix, based on this analytical summation of elements as a function of propellant remaining. Figure 11 plots the spacecraft body X-axis and Y-axis components of the pre-aim unit vector history since late 2004 and the equivalent components of a unit vector from the main engine gimbal center to the estimated center-of- mass (computed for that OTM). Although they have similar trends, there is a 11 to 15 mrad difference between the two vectors at any given time. ...
Citations
... The associate editor coordinating the review of this manuscript and approving it for publication was Jianyong Yao . residence time and much more liquid fuel are needed for the spacecraft [16], [17]. However, due to the sloshing of the liquid fuel, the maneuverability of spacecraft is inevitably influenced, which causes the bad control performance and even the failure task [18], [19]. ...
... The diagram of LFS-FS is shown in Figure 1. The dynamic equations can be described by [16], [47] ...
... Theorem 1: Consider the (9) and the FDO (13). If the adaptive law of the parameter vectorθ is chosen as (16), and the parameters κ 0 > 0, γ 0 > 0, then e is uniformly stable converging to a small region. ...
This paper investigates a fuzzy disturbance observer (FDO)-based terminal sliding mode control (TSMC) strategy for the liquid-filled spacecraft with flexible structure(LFS-FS) under control saturation. Firstly, a novel FDO is designed to estimate the lumped uncertainty, including the inertia uncertainty, external disturbance, the coupling of liquid slosh and flexible structure(LF), as well as the parts that exceed control saturation. The merits of the FDO lie in that estimation error can be arbitrarily small by adjusting the designed parameters and the prior information is not required. Then, based on the estimation of FDO, a finite-time TSMC is designed, which has more satisfactory control performance, such as chattering reduction and fast convergence speed. The stability of the closed-loop system is proved strictly by Lyapunov theory. Finally, numerical simulations are presented to demonstrate the effectiveness of the proposed method.
... Smaller ∆V's were performed using four Z-facing thrusters (each with a 1-N thrust). [13][14][15][16] During the Cruise phase, thrusters were used to roll and yaw the spacecraft attitude so as to align the pre-aimed rocket engine with the target ∆V vector. "Settling" times on the order of 5 minutes were "inserted" in between the roll and yaw turns, and in between the end of the yaw turn and the start of the burn. ...
... Details on the design of the TVC algorithm are given in Reference 17. Flight performance of the TVC algorithm has been excellent and is given in Refs. [14][15]. See also the section entitled "Engine-based ∆V Control and Operational Issues". ...
The attitude maneuver control problem for a liquid-filled spacecraft system is investigated in the presence of attitude and angular velocity constraints and external disturbance in this paper. First, the attitude dynamics model is constructed for the spacecraft with sloshing liquid. Second, during attitude maneuver, large amplitude of angular velocity is easy to stimulate the liquid slosh and even lead to instability of the system, and in the process of spacecraft maneuver, there will be constraints on the transient and steady attitude performance. Therefore, it is necessary to take attitude and angular velocity constraints into account simultaneously during attitude maneuver control. A time-varying barrier Lyapunov function and a logarithmic barrier Lyapunov function are proposed correspondingly, and a finite-time maneuver control law is designed from the barrier Lyapunov functions. Furthermore, an adaptive estimation law is designed to compensate the unknown disturbance and uncertainties in the system. Finally, simulation results are provided to show the effectiveness of the proposed control algorithms and estimation algorithms.
A sophisticated interplanetary spacecraft, Cassini–Huygens was launched on 15 October 1997. After achieving orbit at Saturn in 2004, Cassini collected science data throughout its four-year prime mission (2004–2008) and nine-year extended mission (2008–2017). The Cassini Attitude and Articulation Control Subsystem (AACS) is perhaps the spacecraft subsystem that must satisfy the most mission and science pointing requirements. The performance of the Cassini AACS design was superb from launch through end of mission. All key mission and science requirements were met with significant margins. Overviews of the Cassini attitude control system design and flight performance (in 1997–2017) are given in this paper. Processes taken by the attitude control operations team to guard against human errors are also outlined. Cassini flight experience and many lessons learned are equally applicable to the safe operations of other interplanetary missions.
The Cassini spacecraft has executed nearly 300 maneuvers since 1997, providing ample data for execution-error modeling and analysis. With maneuvers through 2017, opportunities remain to update the execution-error 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 January 2014 is also presented.
The Cassini spacecraft is in its final years. On September 15, 2017, Cassini will plunge deep into Saturn's atmosphere never to reemerge; thus concluding its second extended mission and 13 years in orbit around the ringed planet. As of October 2014, the spacecraft is four years in to its seven-year, second extended mission, the Cassini Solstice Mission (CSM). With three years left and only 2.5% of its loaded bipropellant and 37% of its loaded monopropellant remaining, the Cassini project actively manages the predicted end-of-mission propellant margins to maintain a high confidence in the spacecraft's ability to complete the CSM as designed. Accurate spacecraft navigation, rigorous remaining-propellant estimation, and frequent future propellant consumption prediction have resulted in efficient propellant use and a probability of sufficient propellant margin greater than 99%.
The Cassini mission at Saturn will come to an end in the spring and summer of 2017 with a series of 22 orbits that will dip inside the rings of Saturn. These are called proximal orbits and will conclude with spacecraft disposal into the atmosphere of the ringed world on September 15, 2017. These unique orbits that cross the ring plane only a few thousand kilometers above the cloud tops of the planet present new attitude control challenges for the Cassini operations team. Crossing the ring plane so close to the inner edge of the rings means that the Cassini orientation during the crossing will be tailored to protect the sensitive electronics bus of the spacecraft. This orientation will put the sun sensors at some extra risk so this paper discusses how the team prepares for dust hazards. Periapsis is so close to the planet that spacecraft controllability with RCS thrusters needs to be evaluated because of the predicted atmospheric torque near closest approach to Saturn. Radiation during the ring plane crossings will likely trigger single event transients in some attitude control sensors. This paper discusses how the attitude control team deals with radiation hazards. The angular size and unique geometry of the rings and Saturn near periapsis means that star identification will be interrupted and this paper discusses how the safe mode attitude is selected to best deal with these large bright bodies during the proximal orbits.
