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Topic: Periapsis

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	The Pioneer Venus Orbiter Entry Phase
		The orbital inclination was 105.6°, and the latitude of periapsis was near 17° N. The Pioneer Venus instruments are described in IEEE Trans.
		The orbiter periapsis altitude for the entire Pioneer Venus mission is shown as a function of time in Figure 1.
		After this the periapsis altitude began to descend, and final atmospheric entry of the orbiter was expected to occur in late 1992, around orbit 5000, nearly 14 years after orbit insertion.
	www-ssc.igpp.ucla.edu /~strange/pvo_entry/pioneer.html (1778 words)

	- Cosmonautics on edge of Centuries
		The argument of periapsis (4) is the argument (angular distance) of periapsis from the ascending node.
		Time of periapsis passage (5) and the celestial longitude of the ascending node (6) are the remaining elements.
		Each periapsis pass, a swath of mapping data was taken, and the planet rotated so that swaths from consecutive orbits were adjacent to each other.
	library.thinkquest.org /C006381/PO.shtml (900 words)

	Final Gallery
		Periapsis is the point in an orbit closest to the primary.
		Periapsis and apoapsis names are modified to apply to the body being discussed such as perilune and apolune for the moon or perihelion and aphelion for the sun.
		The argument of periapsis is the angular distance between the ascending node and the point of periapsis.
	aerospacescholars.jsc.nasa.gov /has/Students/finalGall.cfm?id=132 (705 words)

	Orbit (astronomy and physics) - MSN Encarta
		The size of the orbit is given by the periapsis distance (SP) and the elongation of the orbit is given by the eccentricity (e).
		The three orbital elements that describe an orbit's orientation are the inclination (i), the longitude of the ascending node (Ω), and the argument of the periapsis (ω).
		The argument of the periapsis measures the angular displacement in the plane of the orbit between the ascending node and the line that passes through the center of the orbit (C) and the periapsis (P).
	encarta.msn.com /encyclopedia_761556131/Orbit_(astronomy_and_physics).html (928 words)

	Wikinfo \| Orbit (Site not responding. Last check: 2007-11-03)
		As an object orbits another object, periapsis is that point at which the orbiting object is closest to the object being orbited; apoapsis is that point at which the orbiting object is farthest from the object being orbited.
		The point where the orbiting body is closest to Earth is the perigee, called periapsis (less properly, "perifocus" or "pericentron") when the orbit is around a body other than Earth.
		Eventually, the periapsis of the orbit drops low enough that the body hits the surface or burns in the atmosphere.
	www.wikinfo.org /wiki.php?title=orbit (1890 words)

	AEROBRAKING ON MARS: MARS GLOBAL SURVEYOR AND FURTHER ANALYSIS OF AEROBRAKING OPTIONS
		is the density at periapsis passage, a is the semi-major axis, e is the eccentricity, and
		When periapsis is lowered to the point that the dynamic pressure values are near the limits of the mission design, the main phase begins.
		Since altitude is generally correlated to density and velocity, and the periapsis altitude is nearly constant throughout the aerobraking phase, the "density corridor" is often examined as a parameter.
	ccar.colorado.edu /asen5050/projects/projects_2000/mottinger (2710 words)

	Apsis
		In astronomy, an apsis (plural apsides) is the point of greatest or least distance of the elliptical orbit of a celestial body from a centre of attraction (the centre of mass of the system).
		According to Kepler's laws of planetary motion, as a body approaches the periapsis it will increase in velocity and as a body approaches the apoapsis it will decrease in velocity.
		This is because the segment of line running from the centre of mass to the object sweeps a fixed amount of area per unit of time; as the segment lengthens, the angular velocity diminishes and vice-versa.
	publicliterature.org /en/wikipedia/a/ap/apsis.html (301 words)

	Observation of Intense Wave Bursts at Very Low Altitudes...
		Periapsis altitude was 2 km higher for this orbit than for orbit 5055.
		We might speculate, for example, that the signal detected on orbit 5055, shown in Figure 1, turns on rapidly around 1946:10 UT and persists for at least a minute, with the slow decay being caused by attenuation of the signal by collisional damping as it propagates to higher altitudes.
		In conclusion, the intense 100 Hz wave bursts observed near periapsis during the final two periapsis passes may be the direct sub-ionospheric detection of atmospheric discharges by the Pioneer Venus Orbiter.
	www-ssc.igpp.ucla.edu /~strange/pvo_entry_vlow/wavebursts.html (2830 words)

	How Orbits Work (Site not responding. Last check: 2007-11-03)
		The periapsis altitude is raised by increasing the spacecraft's speed at apoapsis.
		Periapsis is also called ______________ at Jupiter and ______________ orbiting the sun.
		The periapsis altitude is _______________ by increasing speed at apoapsis.
	www.au.af.mil /au/awc/awcgate/jplbasic/orbits.htm (584 words)

	ch9
		At about one day before periapsis, a malfunction affected the stepping function of the telescope and a few images were partially lost before a work-around could be effected.
		There is still great activity in the cloud forms at high altitudes, but the banded structure of the tropics changes to a random pattern of cells and turbulence down to the limits of resolution.
		The colors are, however, probably less authentic than those of the images before periapsis because of an apparent change in the behavior of the instrument after passage through the intense radiation belts.
	www.hq.nasa.gov /pao/History/SP-349/ch9.htm (1960 words)

	Argument of periapsis - Wikipedia, the free encyclopedia
		The argument of periapsis (ω) is the orbital element describing the angle between an orbiting body's ascending node (the point where the body crosses the plane of reference from South to North) and its periapsis (the point of closest approach to the central body), measured in the orbital plane and in the direction of motion.
		An argument of periapsis of 0° means that the orbiting body will be at its closest approach to the central body at the same moment that it crosses the plane of reference from South to North.
		An argument of periapsis of 90° means that the orbiting body will reach periapsis at its northmost distance from the plane of reference.
	en.wikipedia.org /wiki/Argument_of_Perihelion (262 words)

	Apsis - Wikipedia, the free encyclopedia
		In astronomy, an apsis, plural apsides (IPA: /apsɪdɪːz/) is the point of greatest or least distance of the elliptical orbit of a celestial body from its center of attraction, which is generally the center of mass of the system.
		The point of closest approach is called the periapsis or pericentre and the point of farthest excursion is the apoapsis (Greek από, from, which becomes απ before a vowel, and αφ before rough breathing), apocentre or apapsis (the latter term, although etymologically more correct, is much less used).
		There are formulae used to derive apsis and periapsis:
	en.wikipedia.org /wiki/Periapsis (686 words)

	Venus and Mars
		The periapsis (the lowest altitude in the orbit) of PVO was maintained near an altitude of 150 km until 1980, when the onboard fuel supply was just about exhausted.
		Beginning around early 1992 the periapsis of PVO was again inside the ionosphere allowing direct measurements in the nightside of Venus.
		The small amount of remaining fuel was used to keep the periapsis around 140 km, but it was finally exhausted before the orbit precessed to the dayside and PVO entered the atmosphere.
	www.agu.org /revgeophys/nagy01/node2.html (1365 words)

	Global Space Initiative
		If the graph does not show the orbit as expected, or at all, this may be because the scaling of the graph axes has resulted in the orbit's being outside the display range.
		You can check the periapsis and apoapsis (if appropriate) distances (Cells A76 and A79, in Sheet1, respectively), to see what range may be desirable to display, on the graphs.
		before periapsis), to see the orbit both approaching, and receding from, periapsis (for very eccentric [flat] hyperbolic orbits, this may be too far back, so set the True Anomaly closer to zero, like maybe 315; experiment, to see what works).
	orbiter.vidmar.org /orbit-simulation.php (810 words)

	Mars '96 Mission Description
		At the periapsis of the approach hyperbola, the S/C propulsion system will be autonomously fired to place the the Orbiter into an initial orbit with a period of 43.09 ± 8.5 hr, and periapsis and apoapsis altitudes of 500 ± 200 and 52,000 km, respectively.
		Initial orbit inclination is 106.4°, and the latitude of periapsis is 26° North.
		Periapsis migrates from a sun elevation angle of -25° to +38° for the first 8 months of the mission, and then decreases for the next 16 months.
	www.msss.com /mars/mars9x/mission.html (1043 words)

	E2M
		periapsis is set at since the transx will adjust for whatever you select.
		At periapsis, fire main engines until an orbit of mars is achieved.
		On subsequent orbits at periapsis and apoapsis refine your orbit to a low mars orbit.
	www.stillmixtup.com /E2M.html (2189 words)

	Basics of Space Flight Section I. The Environment of Space
		In the third cartoon, you'll see that part of the orbit comes closer to Earth's surface that the rest of it does.
		Vanguard-1, by the way, has an orbital period of 134.2 minutes, with its periapsis altitude of 654 km, and apoapsis altitude of 3969 km.
		In practice, you can remove energy from a spacecraft's orbit at periapsis by firing the onboard rocket thrusters there and using up more propellant, or by intentionally and carefully dipping into the planet's atmosphere to use frictional drag.
	www2.jpl.nasa.gov /basics/bsf3-4.html (1216 words)

	Practical Astronautics
		periapsis - the closest point in an orbit to the primary body.
		For earth orbits periapsis is known as perigee.
		is equal to E and M at periapsis (all equal 0 degrees) and at apoapsis (all equal 180 degrees).
	www.astronautica.com /astro (1528 words)

	The Planetary Society Presents: Cassini, Day By Day (Site not responding. Last check: 2007-11-03)
		Periapsis: 15:43, 26 Jun 2005 (3.6 Rs, inc. 21.8°, phase 113°)
		Periapsis: 10:37, 8 Jun 2005 (3.6 Rs, inc. 21.9°, phase 114°)
		Periapsis: 10:21, 28 Oct 2004 (6.2 Rs, inc. 13.8°, phase 104°)
	www.planetary.org /saturn/daybyday (1040 words)

	Magellan: Mission Plan
		Magellan orbited Venus from north to south at periapsis, so "left-looking" radar was pointing east, and "right-looking" radar was pointing west.
		The incidence angle ranged from 16.5 degrees at the north pole to 45.7 degrees at periapsis.
		The final orbit had a periapsis of 180 Km from the surface, an apoapsis of 540 Km, and a period of 94 minutes.
	nssdc.gsfc.nasa.gov /planetary/mgncycles.html (636 words)

	Final Gallery
		As a satellite orbits a planet, the point in the orbit at which the satellite is closest to the planet is called the periapsis.
		The angular distance between the ascending node and the point of periapsis is known as the argument of periapsis.
		The spacecraft will accelerate to break free of the Earthâs gravity until it has reached an elliptical orbit in which the periapsis is at a point on the Earthâs orbit around the sun and the apoapsis is at a point on Marsâ orbit around the sun.
	aerospacescholars.jsc.nasa.gov /has/Students/finalGall.cfm?id=1061 (920 words)

	[No title] (Site not responding. Last check: 2007-11-03)
		This orbit will intersect the surface of the Earth if the periapsis of the orbit is less than the radius of the Earth or continue in the elliptical orbit if the radius is greater than that of the Earth.
		It is necessary to first calculate the radius at periapsis, rp, of the satellite’s orbit in order to determine if the satellite will impact the Earth.
		The argument of periapsis represents the angle between the line of nodes and the periapsis of an ellipse.
	www-personal.engin.umich.edu /~tlrichar/TR2Final3.doc (3958 words)

	Astrogator: MCS - Initial State and Update
		The angle measured in the direction of spacecraft motion, in the orbit plane, from the ascending node to the periapsis of the orbit.
		The angle from the periapsis of the orbit to the spacecraft's position vector, measured in the direction of spacecraft motion.
		Radius of Periapsis is the distance from the center of mass of the central body to the periapsis of the orbit.
	www.stk.com /resources/help/stk613/helpSystem/extfile/gator/mc-states.htm (1411 words)

	Orbital Mechanics
		The opposite of periapsis, the farthest point in an orbit, is called apoapsis.
		True anomaly, v, is the angular distance of a point in an orbit past the point of periapsis, measured in degrees.
		The launch of a satellite or space vehicle consists of a period of powered flight during which the vehicle is lifted above the Earth's atmosphere and accelerated to orbital velocity by a rocket, or launch vehicle.
	www.braeunig.us /space/orbmech.htm (6414 words)

	Gravel - Calculate elliptical orbit speed at apoapsis and periapsis (Site not responding. Last check: 2007-11-03)
		Vp is the (relative) velocity at the periapsis.
		M is the mass of the object being orbited (this is assumed to be far greater than the mass of the satellite).
		Rp is the minimum radius (periapsis) of the satellite's orbit.
	www.rclsoftware.org.uk /gravel/orbits.html (181 words)

	Definition: periapsis (Site not responding. Last check: 2007-11-03)
		periapsis: In a satellite orbit, the point that is closest to the gravitational center of the system consisting of the primary body and the satellite.
		Note: In an orbit about the Earth, periapsis is called perigee.
		In an orbit about the Moon, periapsis is called perilune, and in an orbit about the Sun, it is called perihelion.
	www.its.bldrdoc.gov /projects/devglossary/_periapsis.html (74 words)

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