Venus Sample Return - A Hot Topic
Within th Solar System, Venus presents a set of unique challenges to obtaining samples and returning them to Earth.
Venus Sample Return Solar System samples Venus↗
Engineering topics
Chen, G. S.
Publications and source records attributed to Chen, G. S..
Venus Surface Sample Return: A Weighty High-Pressure Challenge
A mission to return a sample to Earth from the surface of Venus faces a multitude of challenges.
Venus↗
The Sciencecraft Process
In this paper, the authors propose a new process for the development and operation of inmanned vehicles for the exploration of space. We call the vehicle Sciencecraft to distinguish it from the more traditional vehicle Spacecraft. A Sciencecraft is an integrated unit that combines science instruments, electronics, telecommunications, power, and propulsion elements into a single system.
spacecraft↗
Kuiper Express: A Sciencecraft
The Kuiper Express is a mission to achieve the first reconnaissance of one of the primitive objects in the Kuiper Belt. The Kuiper Express is a sciencecraft mission. It will be launched using a Delta vehicle and will use solar electric propulsion to shape its trajectory in the inner Solar System, while executing two Earth gravity-assist flybys.
Kuiper↗
Planetary Integrated Camera-Spectrometer (PICS): A New Approach to Developing a Self-Sequencing, Integrated, Multiwavelength Instrument
The Planetary Integrated Camera-Spectrometer (PICS)is an highly integrated sensor system which performs the functions of three optical instruments:...
Planetary↗
Corrosion and corrosion fatigue of airframe aluminum alloys
Localized corrosion and corrosion fatigue crack nucleation and growth are recognized as degradation mechanisms that effect the durability and integrity of commercial transport aircraft. Mechanically based understanding is needed to aid the development of effective methodologies for assessing durability and integrity of airframe components. As a part of the methodology development, experiments on pitting corrosion, and on corrosion fatigue crack nucleation and early growth from these pits were conducted. Pitting was found to be associated with constituent particles in the alloys and pit growth often involved coalescence of individual particle-nucleated pits, both laterally and in depth. Fatigue cracks typically nucleated from one of the larger pits that formed by a cluster of particles. The size of pit at which fatigue crack nucleates is a function of stress level and fatigue loading frequency. The experimental results are summarized, and their implications on service performance and life prediction are discussed.
Chen, G. S.↗
Control of a slow-moving space crane as an adaptive structure
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Utku, S.↗
A mathematical basis for the design optimization of adaptive trusses in precision control
Optimal actuator placement schemes are presently studied for cases of adaptive truss precision control and prestressing control, with a view to the maximization of actuator efficiencies. In statically indeterminate truss structures, the optimal placement criteria and techniques differ, depending on whether the primary determinate structure is known. A suboptimal actuator-placement solution to the global optimization problem which combines displacement control and prestressing control is suggested, by combining the separate displacement control and prestressing control optimization results. Attention is given to the results obtained for the illustrative case of a two-bay, three-dimensional precision truss structure.
Das, S. K.↗
Dynamics of three-dimensional space crane - Motion requirements and computational considerations
Preliminary design requirements for a space crane are surveyed and some theoretical and computational issues that need to be addressed in support of the design activities are identified. Computational experiments conducted so far on rigid space crane models indicate that the sizing of joint actuators and operational constraints can be assessed by quasi-static rigid crane maneuvering simulations. Limited numerical experiments on flexible crane models raise several difficulties in developing control strategies, maneuvering speeds, maximum torque sustainable, and modeling detailed flexibility effects on the tip positioning accuracy. Computational algorithms development that will alleviate some of these difficulties are discussed and illustrated via example test runs.
Park, K. C.↗
Effect of joint imperfections on static control of adaptive structures as space cranes
Effect of imperfections in the joints of an adaptive structure on its slow (no inertia forces) motion along a prescribed trajectory as a space crane is studied. Two mathematical models to predict the effect of joint imperfections are proposed. The two models are used to obtain estimates of the deviations of the node of the space crane to which the end-effector is attached, from its prescribed trajectory. An application of the models to a two-section space crane is given.
Ramesh, A. V.↗
Adaptive structures in space
Future NASA missions will need large (20 to 100m) structural systems with precision position (few microns to submicron) requirements. Data are presented which indicate the technology deficiencies of previous programs and analyses in current state-of-the-art structural design approaches, analytical prediction capabilities, control of structure capabilities, and ground test technologies to meet the performance requirements of future large precision structural systems. Test results on laboratory truss structures that demonstrate static displacement control, active damping, and on-orbit system identification are described. It is shown that for large precision structures, adaptive structures provide not only a means to achieve the precision and characteristics required in space, but can also significantly alleviate the ground test requirements for flight-validating the hardware.
Wada, B. K.↗
Control of a slow moving space crane as an adaptive structure
Assuming that the space crane is an adaptive structure with length-adjustable bars and taking as controls the length-adjustments of these bars, the computation of the incremental controls corresponding to the motion of a payload along its minimum-energy trajectory is given in terms of the inverse-transpose of matrix B of the joint equilibrium equations Bs = p, where s lists the bar forces and p lists the nodal loads. The compensation of the controls for elastic deformations and support movements are shown. It is also shown that the computations may be done automatically and in real time by an attached processor once the characteristics of the crane's maneuver are keyed in.
Utku, S.↗
Effect of imperfections on static control of adaptive structures as a space crane
Effect of imperfections in the joints of an adaptive structure on its slow (no inertia forces) motion along a prescribed trajectory as a space crane is studied. Two mathematical models to predict the effect of joint imperfections are proposed. The two models are used to obtain estimates of the deviations of the node of the space crane to which the end-effector is attached, from its prescribed trajectory. An application of the models to a two-section space crane is given.
Ramesh, A. V.↗