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This paper addresses the problem of self-excited vibration in power steering racks -- an instability that results in a vibration that the driver can feel at the steering wheel. A coupled mathematical model is used to express the interaction between the rack's opposed hydraulic actuators and the shimmy vibration of the steering mechanism. It is found that igh steering control valve gain causes an unstable self-excited vibration of the modeled system, and The system's susceptibility to instability depends upon the position of the rack in its stroke. Adjustments to the system parameters significantly reduce this instability.

The International Space Station (ISS) will have, upon completion, a large suite of international facilities that can be utilized for plant research from cell and tissue culture to intact plants. Characteristics and capabilities of the various plant related facilities being developed in the United States and by our international partners will be described in the order of their current launch sequence. An overview will also be presented of support equipment and facilities such as the life science glove box and 2.5 meter centrifuge. A critical feature of plant research on ISS will be the ability to have controls as well as conduct long term and repetitive experiments.

Space Station Freedom will provide an opportunity to conduct long duration life sciences research on plants and animals in a microgravity environment. Studies will be able to determine the rate of change of various processes in animals, e.g., calcium loss from bones, muscle atrophy, etc., determine the effect of microgravity on plant respiration and transpiration, and assess the impact of the microgravity environment over multiple generations for both plants and animals. However, all of these processes may also be affected by the 5.3 mm Hg partial pressure of CO2 (7000 ppm) currently specified for Space Station Freedom. The specifications for the plant and animal habitats to be developed as part of the Centrifuge Facility require that the CO2 level for plants be controlled over the range of 0.23 -2.3 mm Hg (300 to 3000 ppm ± 10-50 ppm) and that the atmospheric composition (CO2 level) for rodents be ± 1 % of the cabin composition.

The U.S. Laboratory (USL) module on Space Station will house a biological research facility for multidisciplinary research using living plant and animal specimens. The science community requires that the specimen environment remain biologically isolated from the rest of the Station environment. Environmentally closed chambers isolate the specimen habitats, but specimens must be removed from these chambers during research procedures as well as while the chambers are being cleaned. An enclosed, sealed Life Science Glovebox (LSG) is the only locale in the USL where specimens can be accessed by crew members. This paper discusses the key science, engineering and operational considerations and constraints involving the LSG, such as bioisolation, accessibility, and functional versatility. Existing glovebox technology is reviewed and the potential for adding automation, robotics, and telecommunications to the LSG is discussed.

Using the microgravity environment. Space Biotechnology investigations and applications will present new opportunities for advancing earth-based biological and biomedical product development and ultimately improve man's quality of life. The potential assets and benefits of Biotechnology to NASA's Space Program are increasing daily as are the converse benefits of space to a developing biotechnology program. Through the synergy of engineering principles, biological science phenomena, and the microgravity environments of space, a number of opportunities exist to improve and develop new medical or biological products, processes, and/or services.