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Topic: Stationkeeping

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	Orbital stationkeeping (Site not responding. Last check: 2007-10-10)
		In astrodynamics orbital stationkeeping is a term used to describe a particular set of orbital maneuvers used to keep a spacecraft in assigned orbit, either low earth orbit (LEO), or geostationary orbit (GEO).
		Stationkeeping maneuvers require inclusion of a particular delta-v in the mission's delta-v budget.
		Stationkeeping is necessary for some objects such as the International Space Station or the Mir or Salyut stations.
	www.danceage.com /biography/sdmc_Stationkeeping (444 words)

	Rocket Thrust Equation and Launch Vehicles
		In addition, solar radiation pressure caused by the transfer of momentum carried by light and infrared radiation from the sun in the form of electromagnetic waves both flattens the orbit and disturbs the orientation of the satellite.
		For an Ariane launch the separated mass in GTO is 3610 kg, the mass at BOL is 2100 kg, and the mass at EOL is 1450 kg.
		The stationkeeping propellant requirement was reduced by about 40 percent, which was critical to the selection of the Atlas IIAS launch vehicle.
	www.aticourses.com /rocket_tutorial.htm (3798 words)

	Use of Differential Drag as a Satellite Constellation Stationkeeping Strategy
		The term "stationkeeping" refers to efforts undertaken to ensure that satellites are in their proper orbits, which maximizes the usefulness of the constellation as a whole.
		Two convenient terms used in describing the stationkeeping status of satellites in a plane are "phase error" and "relative drift rate." The phase error between two satellites is defined as the actual ArgLat difference between the two minus their desired ArgLat difference.
		Imagine that we are responsible for the stationkeeping of a satellite constellation planned to consist of 6 satellites orbiting in the same plane.
	ccar.colorado.edu /asen5050/projects/projects_2003/franconeri (4729 words)

	Method and apparatus for stationkeeping a satellite offset by pitch rotation - Patent 5813633
		The method of claim 25, wherein a pair of thrusters are translationally moved along said anti-nadir face of the satellite by an amount that is dependent to the monitored amount that the satellite is rotated with respect to a pitch axis.
		This invention relates to satellite stationkeeping and, more particularly, to a method and apparatus for maintaining the satellite in a stationary orbit through the simultaneous control of tangential, radial and normal acceleration components of thrust when the satellite has been rotated about its pitch axis.
		Stationkeeping was first achieved with a spin-stabilized communication satellite launched in 1964.
	www.freepatentsonline.com /5813633.html (5011 words)

	Gemini Program (Site not responding. Last check: 2007-10-10)
		This stationkeeping exercise was cancelled early in the second revolution after depletion of 42% of the fuel, for it was determined that use of more fuel would jeopardize other mission objectives.
		Rendezvous was technically achieved and stationkeeping begun at 19:33 with the two Gemini spacecraft in zero relative motion at a distance of 110 meters.
		Its mission priorities were to demonstrate a 2-week flight, perform stationkeeping with the Gemini launch vehicle stage 2, evaluate the 'shirt sleeve' environment and the lightweight pressure suit, act as a rendezvous target for Gemini 6, and demonstrate controlled reentry close to the target landing point.
	filer.case.edu /~sjr16/advanced/20th_close_gemini.html (6831 words)

	Gemini 6
		Among the secondary objectives were stationkeeping with spacecraft No. 7, evaluating spacecraft reentry guidance capability, testing the visibility of spacecraft No. 7 as a rendezvous target, and conducting three experiments.
		Rendezvous was technically accomplished and stationkeeping began some 6 minutes later when the two spacecraft were about 120 feet apart and their relative motion had stopped.
		Stationkeeping maneuvers continued for three and a half orbits at distances from 1 to 300 feet.
	www.astronautix.com /flights/gemini6.htm (12644 words)

	Spacecraft with increased stationkeeping fuel load - Patent 5263666
		A net gain of stationkeeping time results in any of the three mixture ratio cases by comparison with loading of sufficient oxidizer for a full bipropellant burn under worst-case mixture conditions.
		Very often, the satellite manufacturer provides a further booster, such as an apogee motor, to lift the vehicle from a low intermediate orbit at which the satellite is released to the desired orbit, as, for example, the 22,400 mile geostationary orbit.
		Hence, a net gain in stationkeeping time results, since the oxidizer mass on-loaded to account for mixture ratio errors throughout non-dual mode missions is not required and an increased load of stationkeeping fuel may be substituted therefor.
	www.freepatentsonline.com /5263666.html (2833 words)

	Thermal fuel transfer and tank isolation to reduce unusable fuel - Patent 5251852
		The thrusters are operated from time to time for attitude control and/or stationkeeping, and records are kept of the cumulative fuel use.
		It should be noted that a small amount of propellant may be held in reserve for use in ejecting the spacecraft from its orbital position at the end of its useful life.
		When orbit is achieved, pressurant is released from tank 316 to pressurize the tanks, and a combination of valves 348, 358, 366 and 376 is operated to supply fuel to the thruster manifolds.
	www.freepatentsonline.com /5251852.html (4528 words)

	Gemini 7
		Among the secondary objectives were providing a rendezvous target for the Gemini VI-A spacecraft, stationkeeping with the second stage of the launch vehicle and with spacecraft No. 6, conducting 20 experiments, using lightweight pressure suits, and evaluating the spacecraft reentry guidance capability.
		It changed the amount of fuel they could spend for experiments and stationkeeping with the booster and forced modifications to turn their spacecraft into a target vehicle.
		Stationkeeping was easy, but chasing the tumbling second stage was costing more fuel than Borman liked.
	www.astronautix.com /flights/gemini7.htm (13064 words)

	Steve Tragesser
		I have been working with the AF Research Lab to assesses the frequency and average size of maneuvers necessary to stationkeep various satellite formations.
		Effects from three sources of error are considered: modeling (guidance algorithms are based on simple dynamics), knowledge (navigation errors in position and velocity) and control (execution errors in the burn).
		One potential means of reducing the stationkeeping fuel for a satellite formation is to tether the platforms together.
	www.uccs.edu /~stragess (429 words)

	About ACTS - Operations - Overview (Site not responding. Last check: 2007-10-10)
		Hydrazine fuel is consumed by the ACTS spacecraft to maintain its desired position in space (stationkeeping).
		North-south stationkeeping maneuvers used the bulk of the annual hydrazine fuel consumption of ACTS.
		Beginning in July 1998, north-south stationkeeping maneuvers were discontinued to conserve hydrazine fuel.
	acts.grc.nasa.gov /about/operations/index.shtml (914 words)

	Convoy HX 248 Page 2 - warsailors.com
		It is recommended that as far as is possible large convoys should be routed on a straight course through this area, where, at this time of year, there is over 60° of fog.
		Inevitably in a convoy of 90 ships the stationkeeping is bound to deteriorate; as the general tendency of ships in column to lag astern of station is exaggerated in columns consisting of 7 ships.
		Actual straggling was not so noticeable, though it is hard to differentiate in the early morning between straggling and bad stationkeeping, when all ships have dropped astern of their proper station during the night, the rear ship of column 7 probably being up to one mile outside his distance from leader.
	www.warsailors.com /convoys/hx248report.html (824 words)

	PERMANENT - Products and Services - Satellite Platforms
		In comparison, satellites stay up with little effort (a little stationkeeping thrust once in a while), and you can build up these transponder platforms as big as you want without losing their "flight" capabilities or operating expenses.
		The altitude is based on such factors as horizon/obstruction, number of satellites budgeted for the constellation, satellite power budget, and stationkeeping fuel.
		They either need to be resupplied with stationkeeping propellant (and probably retrofitted with a new engine to use asteroidal fuel) or picked up and scrapped.
	www.permanent.com /p-comsat.htm (7404 words)

	Indostar Attitude Control System (Site not responding. Last check: 2007-10-10)
		It has a Barnes static earth sensor for roll and pitch information and a yaw gyro that is used only during stationkeeping maneuvers.
		During stationkeeping, twelve hydrazine monopropellant thrusters are used for attitude control.
		The EHTs turne off at 550 seconds Stationkeeping is turned off and the Low Bandwidth Thruster Model (with thrusters used for nutation damping) turned on at 600 seconds.
	www.psatellite.com /products/html/indostar.php (508 words)

	The Past and Future of Rocket Engine Propulsion
		By 2001, Boeing was employing larger ion thrusters both for stationkeeping and orbit raising.
		Moreover, Hall thrusters would serve not only as an excellent thruster for orbit stationkeeping and repositioning roles, but potentially could be scaled in power and specific impulse to propel orbit transfer vehicles and future planetary probes.
		The mixture of electrons and ions in the acceleration zone means that the plasma is electrically neutral, and as such is not space-charge limited in ion current (thrust) density like ion thrusters are.
	www.fathom.com /course/21701743/session6.html (2518 words)

	Boeing: Integrated Defense Systems - Satellite Development Center - Xenon Ion Propulsion Center - XIPS: The Latest ...
		Small thrusts are required to correct for the tug of solar or lunar gravity and to reposition the satellite in its proper orbit and altitude.
		XIPS requires only one propellant, xenon, and does its stationkeeping job using a fraction of that required by a chemical propellant system.
		And, because ion thrusters operate at lower force levels, attitude disturbances during thruster operation are reduced, further simplifying the stationkeeping task.
	www.boeing.com /defense-space/space/bss/factsheets/xips/xips.html (1572 words)

	PERMANENT - Products and Services - Fuel Propellants
		These plans are going to need a lot of fuel propellant in orbit for deployment and stationkeeping of the satellites, which will number in the hundreds.
		Regarding stationkeeping, satellites are always being perturbed out of their normal orbits due to the gravitational tidal effects of the Moon and the Sun, as well as drag from Earth's atmosphere in low Earth orbits.
		Retrofitting them with a new stationkeeping thruster and moving them to a new orbit slot where they can be resold would be a profitable business.
	www.permanent.com /p-fuelp.htm (793 words)

	STS-51 - Abstract
		In past missions, the distant at which the shuttle stationkeeps from the target has been severely restricted due to communication link capabilities of the shuttle/free-flyer system.
		An additional constraint leveled on the rendezvous profile for this mission is the desire to minimize the time the payload bay is faced into the direction of the velocity vector.
		In order to accommodate this request and maintain communications with the free-flyer, the shuttle has to spend most of the stationkeeping time in front of the target (most stationkeeping is usually performed behind the target).
	www.tsgc.utexas.edu /archive/characterizations/sts_51.html (1371 words)

	The Past and Future of Rocket Engine Propulsion
		Resistojets have been used for stationkeeping communication satellites for some 20 years.
		The resistojets used on commercial spacecraft typically have specific impulses of 300 s or more (compared to CP specific impulses of 200 s for the same propellant--hydrazine), peak heater wire temperatures in excess of 2,000° C for thrust efficiencies above 50%, input power levels of 465-885 W and total impulses above 500,000 Ns (figure ET2).
		By switching from resistojets to arcjets, the Telstar 401 was able to double its propellant efficiency and thus carry a larger, more capable communications payload instead of the additional propellant normally required for its 12-year mission.
	www.fathom.com /course/21701743/session4.html (1108 words)

	PowerPedia:Spacecraft propulsion - PESWiki
		Most satellites have simple reliable chemical rockets (often monopropellant rockets) or resistojet rockets to keep their station, although some use momentum wheels for attitude control.
		Once in the desired orbit, they often need some form of attitude control so that they are correctly pointed with respect to the Earth, the Sun, and possibly some astronomical object of interest.
		They are also subject to drag from the thin atmosphere, so that to stay in orbit for a long period of time some form of propulsion is occasionally necessary to make small corrections (orbital stationkeeping).
	peswiki.com /index.php/PowerPedia:Spacecraft_propulsion (4054 words)

	OSO Daily Report
		The GOES-8 East/West stationkeeping maneuver is scheduled for October 30 at approximately 1708Z (with a backup day of November 1).
		The GOES-10 East/West stationkeeping maneuver is scheduled for November 6 at approximately 0656Z (with a backup day of November 8).
		GOES-9 will be removed from ZAP storage mode (to three-axis control) on November 13 for a two month monitoring period for orbital maintenance and to evaluate wheel and imaging performance.
	www.oso.noaa.gov /daily-news/index.asp?offset=1204 (494 words)

	Genesis : Search for Origins \| JPL \| NASA
		The flight team and spacecraft completed a sixth stationkeeping maneuver without a hitch on Sept. 25.
		Science activities are back up and running after a brief pause for the stationkeeping maneuver.
		It will be similar to the last maneuver, since in both Genesis passes close to the Sun on the way to the maneuver's starting point.
	www.genesismission.org /mission/statusupdate_qtr3.html (950 words)

	Aerospace Robotics Laboratory - Current Research (Site not responding. Last check: 2007-10-10)
		The Aerospace Robotics Laboratory conducts fundamental research in many different areas including autonomous navigation of air, land and water vehicles, underwater stationkeeping and sea floor mapping, as well as problems for robots climbing in natural terrain.
		Th is project has developed a local-area GPS-type system based on pseudolites (ground transmitters) to provide this capability in the absence of a satellite-based system.
		This project focuses on the helicopter as a system and examines ways to improve it, from the sensing onboard to the computer interface presented to the untrained user.
	sun-valley.stanford.edu /projects.html (644 words)

	NSSDC Master Catalog Display: Spacecraft
		Its mission priorities were (1) to demonstrate a 2-week flight, (2) to perform stationkeeping with the Gemini launch vehicle stage 2, (3) to evaluate the 'shirt sleeve' environment and the lightweight pressure suit, (4) to act as a rendezvous target for Gemini 6, and (5) to demonstrate controlled reentry close to the target landing point.
		Gemini 6A caught up to Gemini 7 and rendezvous was technically achieved and stationkeeping begun on 15 December at 2:33 p.m.
		EST with the two Gemini spacecraft in zero relative motion at a distance of 110 meters.
	nssdc.gsfc.nasa.gov /database/MasterCatalog?sc=1965-100A (1560 words)

	Applied Orbit Perturbation and Maintenance
		Applied Orbit Perturbation and Maintenance was written by Dr. Chia-Chun "George" Chao to summarize the perturbation theories and control (stationkeeping) algorithms needed for understanding the dynamics, stability, and maintenance of those orbits.
		The book begins with a review of two-body mechanics and the two fundamental methods of solving the equations of motion with perturbations: special and general perturbations.
		Chao, a retired Senior Engineering Specialist from The Aerospace Corporation, has more than 35 years' experience in astrodynamics, covering mission design and analysis, orbit perturbations, and stationkeeping and formationkeeping strategies for orbit determination and navigation of interplanetary missions.
	www.aero.org /publications/chao/chao_front.html (295 words)

	Elevator:2010 Forums - View Single Post - Challenge - Reality intrudes... (Site not responding. Last check: 2007-10-10)
		Stage two to lift from there i would go with http://www.tethers.com which meekg talked about in his forum.electrodynamic tethers,Good reading.
		The µPET Propulsion System is a small, low-power electrodynamic tether system designed to provide long-duration boost, deboost, inclination change, and stationkeeping propulsion for small satellites.
		Because the system uses electrodynamic interactions with the Earth's magnetic field to propel the spacecraft, it does not require consumption of propellant, and thus can provide long-duration operation and large total delta-V capability with low mass requirements.
	www.elevator2010.org /forums/showpost.php?p=134&postcount=10 (389 words)

	1
		The depth of investigation for this study was limited to that necessary to confirm, or deny, feasibility.
		There is a readily available stationkeeping system with demonstrated operation on other missions that is included in the weight budget.
		There is a readily available Stationkeeping System that can provide sufficient boost for stationkeeping, acceptable science efficiency versus boosting ratio, and adequate fuel margin for end-of-life ascent.
	www.pha.jhu.edu /groups/hst10x/0report/1summary/1summary.html (2431 words)

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