Spacecraft control

Space exploration application areas can be further subdivided— namely, booster propulsion, upper stage propulsion, and spacecraft control propulsion. The requirements in each of these general areas are different. 

Researchers at NASA (Rosensweig et al., 1985) experienced ferrofluids in a spacecraft control system. While ferrofluids are used often in commercial processes, for the manufacture of CDs to create sophisticated suspension systems for cars, a researcher at... 

Soft tree analysis is a tool that engineers and software progranuners can both understand. If the engineer is comfortable with fault trees, then it will not take long to feel comfortable with soft tree analysis. The logic gate symbols are the same. It can be used with any software language. NASA uses this method extensively on spacecraft control systans. 

Other work combining model checking and analysis of fault-tolerance is covered in e.g. [10,11,12]. In [10], a dual-redundant system for a spacecraft controller is verified using the model checker Spin. [11] and [12] are process algebra based modelling approaches for formalising fault-tolerant systems. 

Bus Segment - Receives electric power from the energy conversion subsystem and distributes it throughout the spacecraft. Provides the primary structural support for the space vehicle. It also contains the spacecraft control and communications subsystems. 

Mission Control will not be in direct control of each step of the startup sequence. Time delays in the communication path between Mission Control and the spacecraft preclude real time monitoring and control of plant functions. Also, continuous communication with the spacecraft is not assured during the deployment and startup phases (Level 2 Requirements are 92%). It is therefore assumed that the control architecture for the Reactor Module would be designed such that an entire series of steps or phase of the startup would be initiated by a command from Mission Control and controlled autonomously from the spacecraft. Mission Control would wait for satisfactory indications that the sequence steps had been completed before proceeding with the next phase of the sequence. How the steps in the following startup sequence would be accomplished within the respective spacecraft controllers (Reactor Module and PCAD) has not been determined. 

Rocket engines arc also used for maneuvers in space. Some operations, such as a onetime transfer of a satellite from lower to higher orbit, could be performed by a solid-propellant engine. Yet many complex maneuvers, such as rendezvous and docking with another spacecraft, require multiple engine firings and variable power impulses. Hence modern spacecraft are equipped with an assortment of attitude control engines that usually use liquid storable propellant. 

Perhaps the most striking phenomenon encountered in outer space is the wide variation in temperature that can be experienced on spacecraft surfaces and externally located equipment. Temperatures and temperature gradients not ordinarily encountered in the operation of ground or airborne structures and equipment are ambient conditions for spacecraft equipment. On such hardware, not suitably protected externally or housed deep within the space vehicle in a controlled environment, these temperature extremes can wreak destruction. Designers of earthbound... 

Now consider the hypothetical problem of trying to teach the physics of space flight during the period in time between the formulation of Kepler s laws and the publication of Newton s laws. Such a course would introduce Kepler s laws to explain why all spacecraft proceed on elliptical orbits around a nearby heavenly body with the center of mass of that heavenly body in one of the focal points. It would further introduce a second principle to describe course corrections, and define the orbital jump to go from one ellipse to another. It would present a table for each type of known spacecraft with the bum time for its rockets to go from one tabulated course to another reachable tabulated course. Students completing this course could run mission control, but they would be confused about what is going on during the orbital jump and how it follows from Kepler s laws. 

The catalysts were tested for their CO oxidation activity in an automated microreactor apparatus. The catalysts were tested at space velocities of 7,000 -60,000 hr . A small quantity of catalyst (typically 0.1 - 0.5 g.) was supported on a frit in a quartz microreactor. The composition of the gases to the inlet of the reactor was controlled by mass flow controllers and was CO = 50 ppm, CO2 = 0, or 7,000 ppm, HjO = 40% relative humidity (at 25°C), balance air. These conditions are typical of conditions found in spacecraft cabin atmospheres. The temperature of the catalyst bed was measured with a thermocouple placed half way into the catalyst bed, and controlled using a temperature controller. The inlet and outlet CO/CO2 concentrations were measured by non-dispersive infrared (NDIR) monitors. 

Aqueous, alkaline fuel cells, as used by NASA for supplemental power in spacecraft, are intolerant to C02 in the oxidant. The strongly alkaline electrolyte acts as an efficient scrubber for any C02, even down to the ppm level, but the resultant carbonate alters the performance unacceptably. This behavior was recognized as early as the mid 1960 s as a way to control space cabin C02 levels and recover and recycle the chemically bound oxygen. While these devices had been built and operated at bench scale before 1970, the first comprehensive analysis of their electrochemistry was put forth in a series of papers in 1974 [27]. The system comprises a bipolar array of fuel cells through whose cathode chamber COz-containing air is passed. The electrolyte, aqueous Cs2C03, is immobilized in a thin (0.25 0.75 mm) membrane. The electrodes are nickel-based fuel cell electrodes, designed to be hydrophobic with PTFE. 

Spacecraft need power. Rockets provide propulsion, but the equipment needed for control of the spacecraft and to provide life support for the astronauts also need a source of energy. Much of this equipment runs on electricity. One possible solution was to use batteries, but the National Aeronautics and Space Administration (NASA), the U.S. agency responsible for space exploration, rejected this idea. The problem with... 

Special applications The environmental control and life support system on a spacecraft maintains a safe and comfortable environment, in which the crew can live and work, by supplying oxygen and water and by removing carbon dioxide, water vapor, and trace contaminants from cabin air. It is apparent that the processes aimed at the recycling of air and water are vital for supporting life in the cabin. These recycling processes include separation and reduction of carbon dioxide, removal of trace gas-phase contaminants, recovery and purification of humidity condensate, purification and polishing of wastewater streams, and are performed totally or in part by adsorption equipment (Dabrowski, 2001). ... 

Units mounted on spacecraft exteriors historically have had the capability for remote commanding from the ground and downlinking mission data. Unils mounted inside reccnily have been modified to incorporate this capability. The data are displayed at NASA s Lewis ltflescicnce Support Center in Cleveland. Ohio or NASA s Marshall Payloud Operations Control Center iPOCCl in Huntsville. Ala. 

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