Cassini Reaction Wheel Momentum Bias Optimization Tool

Lee, Clifford C.; Lee, Allan Y.

doi:10.2514/6.2005-6271

Cited by 19 publications

(11 citation statements)

References 1 publication

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“…Also, in preparation for the prime science mission, the operations team began to develop and use a ground software tool named the reaction wheel bias optimization tool (RBOT) to select an optimal set of RWA bias rates so that the total RWA dwell time inside the problematic low-rpm region can be minimized. Details on RBOT are given in [15] and Sec. VI.…”

Section: Cassini Rwa Bearing Cage Instabilitymentioning

confidence: 99%

“…RWA Bias Optimization Tool [15] In preparation for the extensive use of reaction wheels in the prime science mission (which started on July 2004), the operations team began to develop and use a ground software tool named RBOT in early 2001. This software tool is used by the operation team to select an optimal set of RWA bias rates so that the total RWA dwell time inside the problematic sub-EHD region can be minimized.…”

Section: Cassini Rwa Drag Torque Spikesmentioning

confidence: 99%

“…The RBOT software allows the users to make changes to any of the set of key system parameters (e.g., 300 rpm, 1850 rpm, environmental torques, etc.). A graphical illustration of the gain function G is given in [15]. The formulated nonlinear optimization problem is solved numerically using the Nelder-Mead simplex method [10].…”

Section: Lee and Wangmentioning

confidence: 99%

“…To protect Cassini against an accidental violation of any of these constraints, the ground software tool RBOT was developed by the Cassini operations team for the management of the Cassini RWA [15]. Given the time histories of the spacecraft's attitude and attitude rate commands (to meet science observation needs), from the start to the end of an RWA biasing time segment, RBOT will select a set of optimal biasing rates for the three prime RWA that minimizes a cost functional J.…”

Section: Cassini Rwa Drag Torque Spikesmentioning

confidence: 99%

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In-Flight Performance of Cassini Reaction Wheel Bearing Drag in 1997–2013

Lee

Wang

2015

Journal of Spacecraft and Rockets

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As the first spacecraft to achieve orbit at Saturn in 2004, Cassini has collected science data throughout its four year prime mission (2004)(2005)(2006)(2007)(2008) and has since been approved for a first and second extended mission through September 2017. Cassini uses reaction wheels to achieve the spacecraft pointing stability that is needed during imaging operations of several science instruments. The Cassini flight software makes in-flight estimates of reaction wheel bearing drag torque and made them available to the mission operations team. In trending these telemetry data (for the purpose of monitoring the long-term health of the reaction wheel bearings), anomalous drag torque signatures have been observed over the past 15 years. One of these anomalous drag conditions is bearing cage instability that appeared (and disappeared) spontaneously and unpredictably. Cage instability is an uncontrolled vibratory motion of the bearing cage that can produce high-impact forces internal to the bearing, which will cause intermittent and erratic torque transients. Characteristics of the observed cage instabilities and other drag torque "spikes" are described in this paper. In day-to-day operations, the reaction wheels' rates must be neither too high nor too low. To protect against operating the wheels in any undesirable conditions (such as prolonged low spin rate operations), a ground software tool named a reaction wheel bias optimization tool was developed for the management of the wheels. Flight experience on the use of this ground software tool, as well as other lessons learned on the management of Cassini reaction wheels, is given in this paper.Nomenclatures c = viscous coefficient of wheel bearing lubrication system, N · m · s∕rad Gω = function of wheel spin rate ω defined in Eq. (5) I RWA = moment of inertia of reaction wheel rotor, kg · m 2 K I = integrator gain of reaction wheel assembly drag torque estimator, kg · m 2 ∕s 2 K P = proportional gain of reaction wheel assembly drag torque estimator, kg · m 2 ∕s L −1 = inverse Laplace operator s = Laplace variable, rad∕s T D = Dahl drag torque of reaction wheel bearing system, N · m T Drag = total drag torque of reaction wheel bearing system, N · m ξ D = damping ratio of reaction wheel assembly drag torque estimator τ = time constant of wheel speed decay [see Eq. (4)], s Ω 0 = initial wheel spin rate of coast-down test, rad∕s ω = angular rate of the reaction wheel, rad∕s ω D = bandwidth of the reaction wheel assembly drag torque estimator, rad∕s

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Section: Cassini Rwa Bearing Cage Instabilitymentioning

confidence: 99%

Section: Cassini Rwa Drag Torque Spikesmentioning

confidence: 99%

Section: Lee and Wangmentioning

confidence: 99%

Section: Cassini Rwa Drag Torque Spikesmentioning

confidence: 99%

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In-Flight Performance of Cassini Reaction Wheel Bearing Drag in 1997–2013

Lee

Wang

2015

Journal of Spacecraft and Rockets

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“…This section will identify the sources of future propellant consumption, describe the propellant usage predictor (PUP), and the Monte Carlo simulation used to predict the end-of-mission propellant margins at various confidence levels. Reaction Wheel Biases-Reaction wheel biases are used to maintain the health of the reaction wheels by avoiding extreme wheel speeds (both high and low) and limiting revolutions [7]. The RCS thrusters are used to counteract the change in angular momentum created by changing the wheel speeds.…”

Section: Propellant Usage Predictionmentioning

confidence: 99%

Ensuring Cassini's end-of-mission propellant margins

Sturm

Barber

Roth

2015

2015 IEEE Aerospace Conference

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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 sevenyear, 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-ofmission 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%.

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