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A brief control technology overview is given in Control Structures Interaction (CSI) by illustrating that many future NASA mission present significant challenges as represented by missions having a significantly increased number of important system states which may require control and by identifying key CSI technology needs. The JPL CSI related technology developments are discussed to illustrate that some of the identified control needs are being pursued. Since experimental confirmation of the assumptions inherent in the CSI technology is critically important to establishing its readiness for space program applications, the areas of ground and flight validation require high priority.

Future missions is space will require controlling spacecraft which are both large and flexible. The limited inherent damping and the uncertain and changing dynamic characteristics of many of these vehicles, such as manned space stations and large antennas, will revolutionize spacecraft control requirements. In preparation for the time that such control systems are required, considerable research and technology development is necessary. A program is in place at NASA for the development of active control technology to support major initiatives for space station and advanced spacecraft. A number of key control technology program needs are cited in the paper as required for these and other future NASA missions together with an integrated controls/structures technology flight experiment to demonstrate and validate technology for large flexible structures.

It is noted that the large space systems deployable by means of the Space Shuttle will have increased flexibility, and therefore unprecedented interaction between control and other subsystems. Open loop performance in such systems would be grossly inadequate, prompting active control method development to achieve the required performance levels. The structures in question encompass those of projected science and communications platforms, interplanetary space transportation systems, and manned permanent space stations.

Landsat-D and the Large Space Telescope represent current state-of-the-art systems with precise requirements placed on attitude control. Future systems for planetary stations, high precision earth monitoring and large precision deployable and erectable platforms project still more severe constraints and requirements on attitude control, including the requirement for many enabling and highly enhanced technologies beyond current state of the art. Two trend projections are identified for the areas of (1) precision pointing systems for earth orbiters and planetary spacecraft and (2) onboard high-capacity fast controllers for distributed control systems.

Future automated space missions present challenging opportunities in the pointing-and-control technology disciplines. The enabling pointing-and-control system technologies for missions from 1985 to the year 2000 were identified and assessed. A generic mission set including Earth orbiter, planetary, and other missions which predominantly drive the pointing-and-control requirements was selected for detailed evaluation. Technology candidates identified were prioritized as planning options for future NASA-OAST advanced development programs. The primary technology thrusts in each candidate program were cited, and advanced development programs in pointing-and-control were recommended for the FY 80 to FY 87 period, based on these technology thrusts.

Future automated space missions present challenging opportunities in the pointing and control technology disciplines. A NASA-OAST sponsored study at JPL, identified and assessed the enabling pointing and control system technologies for missions from 1985 to year 2000. A generic mission set including earth orbiter, planetary, and other missions which predominantly drive the pointing and control requirements was selected for detailed evaluation. Technology candidates identified in the study are discussed.

Problems associated with controlling a large diameter (200 - 300 m) spaceborne antenna and microwave system operating at frequencies in the range from 20 GHz to at least 300 GHz are addressed. Such large structures must point to any new target and settle in one hour, and have control surface accuracy to 50 microns rms. Critical technologies required to enable system development by 1990 to 2000 for radio/ radar astronomy, orbiting Deep Space rela satellite, SETI, very long base interferometry, and earth looking radiometry applications are discussed.

Performance characteristics of the LES-6 pulsed plasma thruster over a range of input conditions were investigated by means of a torsion pendulum system. Parameters of particular interest included the impulse bit and time average thrust (and their repeatability), specific impulse, mass ablated per discharge, specific thrust, energy per unit area, efficiency, and variation of performance with ignition command rate. Intermittency of the thruster as affected by input energy and igniter resistance were also investigated. Comparative experimental data correlation with the data presented. The results of these tests indicate that the LES-6 thruster, with some identifiable design improvements, represents an attractive reaction control thruster for attitude contol applications on long-life spacecraft requiring small metered impulse bits for precise pointing control of science instruments.

Because of the low thrust characteristics of solid-propellant pulsed plasma thrusters and their operational requirement to operate in a vacuum environment, unique and sensitive test techniques are required. A technique evolved for testing and evaluating pulsed plasma thrusters in an open- or closed-loop system mode employs a unique air bearing platform as a single-axis simulator on which the thruster is mounted. The simulator described was developed to evaluate pulsed plasma thrusters in the low micropound range; however, the simulator can be extended to cover the operational range of currently developed millipound thrusters.

The design of the thruster described incorporates a coaxial four-segment trigger assembly to discharge a high-energy capacitor. The discharge ablates a waxy perfluorocarbon from the surface of porous annular metal ring, and the resulting plasma is electromagnetically accelerated to ambient producing thrust. Tests revealed a thruster performance well in excess of the major design goals.