Attitude control

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. 

Apollo command module 93 (two 6-engine sets) Attitude control... 

Radiomic a) RP-1, JP-4 JP-5 Kerosene Fractions b) IRFNA Inhibited Red Fuming Nitric Acid c) UDMH Unsym Dimethyl Hydrazine 85-100 General purpose attitude control... 

The most interesting feature of the decomposition flames is their analogy to flames of the solid monopropellants. In fact, many of these substances, which are ordinarily liquids, may support a flame directly from the liquid phase without auxiliary vaporization of the liquid. In this case, the flame supplies the necessary heat of vaporization or decomposition in exact analogy to the solid propellant flame.8 The principal usefulness of a decomposition flame is found in the simplicity of design and control of a rocket powered by such a flame, even though more powerful fuels are readily available. A recent example, which has been featured in the news, is the hydrogen peroxide attitude-control rocket used in the artificial earth satellites of the U.S.A. 

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. 

If his standard is reasonable the inventor s own attitude controls adequacy of testing (13). 

In LEO (ca. 300 km altitude), the ambient gas density and temperature are typically 10 cm and 1200 K, respectively although solar activity and diurnal phase can strongly perturb these values. With an orbital velocity of 7.5-8 km/s, the flux of neutral particles on ram surfaces is 10 m s . This corresponds to approximately ten collisions per atomic surface site per second. Atmospheric collisions lead to satellite drag and torques which hinder attitude control. Degradation of materials on ram-facing surfaces can compromise a spacecraft s flight duration as well. ... 

Methylhydrazine is burned with dinitrogen tetroxide in the attitude-control engines of the space shuttles. 

We have designed a satellite to be a pure survey instrument without pointing capability. This makes the attitude control very easy and inexpensive, because the active control can be very crude and the attitude parameters must be known to better than 1 arcmin only post factum. The rotation of the craft will be bound to the orbital motion in such a way, that the field of view never sees the Earth nor the Sun. Magnetocoils and one reaction wheel will control it. The orbital plane will rotate by 360° in one year, i.e. every source is observed every 6 months. The design life time is 1.5 years, and the expected one 3 years. 

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. 

Digital micropropulsion, consisting of an array of single-shot thrusters, has also been developed to provide short impulses for attitude control of miniature spacecraft. The approach consists of enclosing an explosive or propellant between a resistive heater and a burst diaphragm that leads to a nozzle etched in silicon. Impulse levels of 10 N/s for nun -scale thrusters have been demonstrated, with an 7sp of 11 s [9]. There is potential for finer impulse levels and better fuel utilization as the combustion process is mastered. 

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. 

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