Dynamic Simulation of Controls & Structure (Goddard, 1970s-1990s)

Another important area of spacecraft structural modeling is in the inter­action of control systems with flexible multibody structural systems. In a general sense, this is the spacecraft counterpart to aeroservoelasticity, although the driving mechanisms are very different. Dynamic Simulation of Controls & Structure (DISCOS) was developed in the late 1970s to perform this type of analysis. "The physical system undergoing analy­sis may be generally described as a cluster of contiguous flexible struc­tures (bodies) that comprise a mechanical system, such as a spacecraft. The entire system (spacecraft) or portions thereof may be either spin­ning or nonspinning. Member bodies of the system may undergo large relative excursions, such as those of appendage deployment or rotor/ stator motion. The general system of bodies is, by its inherent nature, a feedback system in which inertial forces (such as those due to centrifu­gal and Coriolis acceleration) and the restoring and damping forces are motion-dependent. . . . The DISCOS program can be used to obtain non­linear and linearized time response of the system, interaction constant forces in the system, total system resonance properties, and frequency domain response and stability information for the system. DISCOS is probably the most powerful computational tool to date for the computer simulation of actively controlled coupled multi-flexible-body systems,” according to the computer program abstract. The program was made available to approved licensees (for $1,000, in 1994) with the caveat that DISCOS " . . . is not easy to understand and effectively apply, but is not

intended for simple problems. The DISCOS user is expected to have extensive working knowledge of rigid-body and flexible-body dynamics, finite-element techniques, numerical methods, and frequency-domain analysis.” DISCOS was used extensively at least into the 1990s for spacecraft modeling.[989] In 1983, a program for bridging DISCOS, NASTRAN, and SAMSAN—a large order control system design program—was also publicly released.[990] A 1987 NASA-funded study by Honeywell (Space and Strategic Avionics Division) out­lined some limitations of DISCOS and other contemporary multi­body dynamics programs and made recommendations for future work in the field.[991] Also in the late 1980s, GSFC began collaborat­ing with a research group at the University of Iowa that was devel­oping similar multibody modeling capabilities for mechanical engineering applications. The National Science Foundation (NSF), U. S. Army Tank Automotive Command, and about 30 other Government and industry laboratories were involved in this project through the Industry/University Cooperative Research Center (I/UCRC) at the University of Iowa. Goals of the I/UCRC were to achieve mutual enhance­ment of capabilities in the modeling, simulation, and control of complex mechanical systems, including man/machine interactions applicable to manufacturing processes.[992]