Attitude control systems

Natural interventions test the robustness and reliability of infrastructure design. The cost of earthquakes averages 4.4 billion per year (FEMA, 1999). Another intervention, space weather, was the culprit in 1998. When the Galaxy 4 satellite s attitude control system failed, radio, television, pager, bank machine, and other satellite-linked services across North America were disrupted. As an example of the cost, two pager companies that did not have backup systems in place lost 5.8 million. Indirect and intangible costs included lost credit card sales, missed market trades, inability to contact doctors and emergency medical services, and many others. 

Attitude Control System. High-gain antennas must be accurately pointed toward the Earth to maintain communications with ground control. Remotesensing instruments and science packages need to be pointed at their study targets. Manned spacecraft must maintain proper attitude for safe reentry. To achieve aU of these, the altitude control system senses the orientation of the spacecraft relative to the fixed stars and reorients the spacecraft as necessary to ful-hll the mission. 

Lee, A.Y., Hanover, G., 2005. Cassini spacecraft attitude control system flight performcUice. In AIAA-2005-6269, Guidance, Navigation, and Gontrol Gonference, San Francisco, CA, August 15-18. 

This section identifies rechargeable or secondary battery requirements best suited for communications and surveillance and reconnaissance satellites. The battery power requirements are strictly dependent on several factors, including launch orbits such as LEO, elliptical, or GSO orbital height the type of stabilization technique used (i.e., mono-spin, dual-spin, or three-axis configuration) satellite operational life attitude control system and the overall DC power requirements needed to power the electronic and electrical subsystems, the electro-optical and microwave sensors, and the attitude and stabilization control mechanisms. 

Each of the potential vibration sources must be understood so that vehicle resonances are not excited and to assure that the attitude control system is able to handle any low level disturbances. 

The advantages of a monopropellant over a bipropellant combination result primarily from a substantial reduction in the number of components in the tankage and flow hardware. The attractive simplications in the propulsion system resulting from the use of monopropellants are obtained only at the expense of a reduced specific impulse. The resulting implied trade-off between simplicity and propellant performance limits the attractiveness of monopropellants to propulsion systems where a simplicity and the usually associated reliability which comes with simplicity are premium desired characteristics. Typical applications have included attitude control rockets, vernier rockets for mid-course trajectory corrections, and other low thrust propulsors, especially those having a requirement for pulsed operation or repeated restarts. Monopropellants also find application as a source of relatively low temperature working fluids, as for driving gas turbines. 

The problems may also stem from unhandled controlled-system states and environmental conditions. An F-18 was lost when a mechanical failure in the aircraft led to the inputs arriving faster than expected, which overwhelmed the software [70]. Another F-18 loss resulted from the aircraft getting into an attitude that the engineers had assumed was impossible and that the software was not programmed to handle. 

Safety Constraint on FCS that was Violated The PCS must provide the attitude control, separation, and orientation maneuvering commands to the main engines and the RCS system necessary to attain geosynchronous orbit. 

The value of continuous education on the skills of a professional is not guaranteed. A controlling system of skills and attitude can better ensure the quality of the work of the professionals. Different types of tests can give insight in the performing level of the workers. 

Some spacecraft require three-axis stability where rotation about any axis must be rigorously suj>-pressed. If the spacecraft begins to rotate in an undesired manner, onboard gyroscopes are spun up to absorb the additional rotational momentum and, by reaction, leave the spacecraft as a whole stationary. Many other spacecraft maintain stability by rotation about a fixed axis. Control of the altitude control system is the responsibility of the command and data handling system. When total rotational momentum of the spacecraft gets too large, the excess is eliminated by firing the attitude thrusters in the propulsion system. 

Propulsion System. The propulsion system performs occasional maneuvers required to keep Earthorbiting satellites on station or interplanetary probes on course. The propulsion system consists of rocket thrusters, propellant, pumps, valves, and pressure vessels. Attitude control thrusters control the rotational dynamics of the spacecraft. Course correction thrusters change the speed or direction of motion of the spacecraft. The propellant must be storable for long periods of time under the harsh conditions of space. Special pressurization techniques are necessary to move liquid propellants from tanks to thrusters in zero gravity. The spacecraft must carry enough propellant for the planned mission lifetime plus a reserve necessary for deorbit at end of life. 

The attitude determination and control system (ADCS) must maintain the proper angular orientation of the satelHte in its orbit in order to keep the antennas pointed to the Earth and the solar arrays aimed toward the sun (for example). The two prevalent stabhization methods are spin stabihzation and body stabhization. In the former, the sateUite body spins and the angular momentum maintains a gyroscopic stiffness. The latter uses momentum wheels to keep the spacecraft body orientation fixed. Components of this subsystem include the momentum wheels, torquers (which interact with the Earth s magnetic field), gyros, sun and Earth sensors, and thrusters to maintain orientation. 

Safety culture is the attitudes, beliefs and perceptions shared by natural groups as defining norms and values, which determine how they act and react in relation to risks and risk control systems. 

Installation of solar panels is required to charge the onboard batteries that are providing the electrical power to various electronics devices, stabilizing and attitude control sensors, space parameter monitoring instrument, lighting, and a host of other electrical systems that are vital in maintaining the desired performance of the satellite or spacecraft over the intended mission duration. 

Note The data presented in this table were collected in the late 1960s for a spacecraft power system. The tabulated values merely demonstrate a trend in increase in weight as a function of redundant options exercised and mission duration and must not be taken as guaranteed values for other spacecraft or communication satellite or tracking satellite. Power required for stabilization and attitude control mechanisms is significantly greater than power required for onboard electronic sensors and electrical devices. 

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