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Topic: Gravity assist

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	Cassini-Huygens: Operations-Gravity Assists
		Gravity assist works because of the mutual gravitational pull between a moving planet and a spacecraft.
		One last gravity assist from Jupiter on December 30, 2000 gave Cassini-Huygens the final thrust of energy it needed to project itself all the way to Saturn.
		Gravity assist has often been called the "slingshot effect," but in reality, it is a different example altogether.
	saturn.jpl.nasa.gov /mission/gravity-assists.cfm (463 words)

	What is a gravity assist or a swingby for a spacecraft? I've heard about spacecraft gaining velocity from passing close ...
		Gravity assist is used to speed up, slow down or change the direction of a spacecraft as it approaches a planet within our solar system.
		The technique of gravity assist for a spacecraft was used as early as the Mariner 10 mission in 1973-1974 and has been used recently to create unique orbits such as with the Ulysses spacecraft.
		Gravity assist is also referred to as the swingby approach or the slingshot approach because of the way the spacecraft is swung around the planet and 'let go' like a slingshot.
	www.windows.ucar.edu /cgi-bin/tour_def/kids_space/gravity_assist.html (279 words)

	[No title] (Site not responding. Last check: 2007-10-09)
		Gravity assist dynamics involves three bodies: the primary body, the flyby body and the spacecraft.
		The gravity assist is used to increase or decrease the spacecraft's velocity (or energy) with respect to the primary body.
		With a gravity assist trajectory, the velocity "magnitude" of the spacecraft with respect to the flyby body remains essentially the same, but the gravitational attraction changes the "direction" of this relative velocity.
	quest.arc.nasa.gov /galileo/Galileo-QA/Gravity_Effect/Gravity_Assist.1 (395 words)

	PERMANENT - Transportation - Theoretical (Site not responding. Last check: 2007-10-09)
		A "gravity assist" entails using a fly-by with the Moon to divert the trajectory of a payload and to impart delta-v, saving large amounts of fuel.
		Gravity assists improve the economics of retrieving asteroid payloads, as well as outbound missions, and greatly broadens the number of attractive asteroids.
		It was to arrive in 1995 where two lunar gravity assists and a fuel thrust "capture maneuver" of 0.3 km/sec at orbit perigee would have put it into a circular orbit between the Moon and the Earth.
	www.permanent.com /t-theory.htm (3101 words)

	Stardust Equations
		The idea behind gravity assist is to use the gravitational force of a planet as a source of energy, either to change the direction of flight of a spacecraft or to increase its speed, or both.
		The most complicated gravity assist trajectory was that of Voyager 2, which swung by Jupiter, Saturn, and Uranus on its way to Neptune in August 1989, at which point it used a swing by of Neptune itself to help propel it out of the solar system and into deep space.
		Gravity assist flights depends on the fact that, in the vicinity of a planet, mathematicians can write down and solve equations that describe the path of a spacecraft that goes there, enabling them to calculate the trajectory of the craft with considerable accuracy.
	www.maa.org /devlin/devlin_2_99.html (5158 words)

	gravity-assist
		Also known as the slingshot effect, an important spaceflight technique, already used successfully on a number of interplanetary missions, including Voyager, Galileo, and Cassini, whereby the gravitational field of a planet is used to increase the speed and alter the course of a spacecraft without the need to expend fuel.
		One of the earliest, and most dramatic applications of the technique came in 1970 when the world watched as NASA used a lunar gravity-assist to rescue the Apollo 13 astronauts after an onboard explosion had severely damaged their spacecraft en route to the Moon.
		By using a relatively small amount of fuel to put the spacecraft onto a suitable trajectory, NASA engineers and the astronauts were able to use the Moon’s gravity to turn the ship around and send it back home.
	www.daviddarling.info /encyclopedia/G/gravityassist.html (285 words)

	A Gravity Assist Primer
		Here's Chapter 4, where Gravity Assist, and other trajectories are covered in a little more detail and broader perspective.
		On the other hand, using a gravity assist, a spacecraft comes up and steals some angular momentum during a single flyby of a planet in motion, removing momentum from that planet.
		Gravity assist is really much more like a baseball connecting with a fast-moving bat than it is like a slingshot.
	www2.jpl.nasa.gov /basics/grav/primer.html (1451 words)

	Howstuffworks "How does gravity assist work with interplanetary satellites?"
		The idea behind a gravity assist is to use a planet's motion to accelerate a satellite.
		From that description, it would seem like the net effect of gravity assist is zero -- the satellite gains speed as it falls toward the planet but then loses it as it heads away.
		The problem with gravity assist is that you have to wait for the planets to line up correctly for it to work.
	science.howstuffworks.com /question102.htm (262 words)

	ESA Portal - Let gravity assist you...
		Substitute a spacecraft and a planet for the car and the city, and this is called a 'gravity assist'.
		There, it used a gravity assist to throw it out of the plane of the planets into a gigantic loop that passed over the south pole of the Sun in 1994, and then the north pole 13 months later.
		It is carried on the NASA spacecraft Cassini which used four gravity assists (one with Earth, two with Venus and one with Jupiter) to accelerate it towards Saturn.
	www.esa.int /esaCP/SEMXLE0P4HD_index_0.html (684 words)

	Interplanetary Transfers Implementing Gravity Assists
		We have explored using gravity assists to further optimize the amount of time and fuel required to reach a target radius.
		A gravitational assist is an event where a spacecraft uses the gravitational influence of a planet or a moon to change its speed and direction of travel with respect to the sun (or with respect to a host planet in the case of a gravitational assist by a moon).
		This is the simplified explanation of a gravity assist that we have used in the models embedded in our software.
	ccar.colorado.edu /~parkerjs/SpaceFlight/Assists.html (1685 words)

	Gravity on mars Information (Site not responding. Last check: 2007-10-09)
		Gravity On Mars are great for when you're looking to get better at gravity on mars for selfish purposes.
		If you need help locating gravity on mars then you've come to the right place because we have all the gravity on mars you could want.
		Earth orbit the astronauts are subjected to zero gravity, whereas on the Moon they would face one-sixth Earth's gravity, and on Mars one-third.
	mars.4infochest7.info /mars-closest-to-earth/gravity-on-mars.html (246 words)

	Gravitational slingshot - TheBestLinks.com - Gravity assist, Aerospace engineering, ESA, Gravity, ...
		In orbital mechanics and aerospace engineering, a gravitational slingshot is the use of the motion of a planet to alter the path and speed of an interplanetary spacecraft.
		As the spacecraft approaches the planet, Jupiter's gravity will pull on the spacecraft, speeding it up.
		A trip using multiple gravitational assists may take longer, but will use considerably less delta V, allowing a much larger spacecraft to be sent.
	www.thebestlinks.com /Gravity_assist.html (657 words)

	IV-1 (Site not responding. Last check: 2007-10-09)
		The contours of constant delta V are marked with the delta V (in kilometers per second) and a symbol to indicate whether the departure is from the aphelion of the asteroid orbit (number within triangle) or from the perihelion (encircled numbers).
		But if the trajectory is modified by a gravity assist at a different body or by impulsive or low-thrust delta V between encounters, dramatic changes can be made.
		As mentioned in the preceding section, one method for reducing overall delta V during retrieval is to use gravity assists by Earth and Venus.
	lifesci3.arc.nasa.gov /SpaceSettlement/spaceres/IV-1.html (4488 words)

	Multiple flyby or gravity assist - It seems so easy..... - Forums powered by UBBThreads™ (Site not responding. Last check: 2007-10-09)
		This is because the probe usually has a long way to go before reaching its first gravity assist flyby -- that's plenty of time to do a trajectory correction maneuver.
		gravity assists), but because its target is a comet with a path that stretches from the Oort cloud to the inner solar system.
		The relative positions of the planets and the comet were all significant factors, because they are trying to do this with as little fuel expenditure as possible.
	uplink.space.com /showflat.php?Cat=&Board=missions&Number=35128&page=17&view=collapsed&sb=6&o=0&fpart= (1228 words)

	Cassini receives a boost from Venus en route to Saturn
		Gravity assists are well-grounded in classical newtonian physics, but they can appear paradoxical, as illustrated by this thought experiment posed by JPL's Dave Doody in the May/June 1995 issue of The Planetary Report:
		The difference between the cyclist passing through a valley on Earth and the spacecraft whizzing by Venus is this: In the example of the cyclist, the bottom of the valley is stationary with respect to the cyclist's destination (the top of the hill on the other side).
		This colorized image of Venus was recorded by the Jupiter-bound Galileo spacecraft shortly after its gravity assist flyby of Venus in February of 1990.
	science.nasa.gov /newhome/headlines/ast24jun99_1.htm (1208 words)

	Cnes - Cosmic billiards
		This gravity assist technique is used by most interplanetary missions.
		A final gravity assist from Jupiter in 2000 gave it the energy required to reach Saturn.
		The most economical way to transfer from one circular orbit to another, in the same plane and direction of travel, is to describe a half-ellipse with one end at a tangent to the initial orbit and the other to the final orbit.
	www.cnes.fr /html/_455_456_1100_1103_.php (397 words)

	MSN Encarta - Search Results - Gravity Assist (Site not responding. Last check: 2007-10-09)
		Gravity Assist, the technique of using the gravitational field and orbital motion of a planet or moon to alter the course and speed of a spacecraft,...
		All interplanetary flights by space probes now rely on the technique called gravity assist.
		It involves using the gravitational field and orbital...
	uk.encarta.msn.com /Gravity_Assist.html (114 words)

	Let gravity assist you... (Site not responding. Last check: 2007-10-09)
		'Fly-bys', or 'gravity assist' manoeuvres, are now a standard part of spaceflight and are used by almost all ESA interplanetary missions.
		The first spacecraft to experience a gravity assist was NASA's Pioneer 10.
		The ESA/NASA Ulysses mission used one of the most extraordinary gravity assists to allow it to see the polar regions of the Sun, places that are forever hidden from any observing location on Earth.
	www.brightsurf.com /news/oct_03/ESA_news_102303.php (911 words)

	Double Ball Drop
		Such maneuvers are really elastic collisions where the objects involved never hit each other but are affected by gravity as they approach.
		Galileo used a gravity-assists from Venus, two flybys of Earth, and close encounters with asteroids Gaspra and Ida on its circuitous path to Jupiter.
		The more recent Cassini spacecraft will do two gravity assist maneuvers from Venus and one from Earth before heading out to Jupiter and Saturn.
	hyperphysics.phy-astr.gsu.edu /hbase/doubal.html (463 words)

	Orbits - Gravitational Assist from Planets (Site not responding. Last check: 2007-10-09)
		The planet does not interact with the probe until it approaches close enough for the planet's gravity to be stronger than that of the Sun's.
		The Gravitational Force varies in proportion to the Mass of the attracting body and inversely with the square of the distance to the body.
		Only quite near the planets, does the planetary gravity become stronger than that of the Sun.The first reaction is to determine the point between Sun and Planet where their gravitational forces cancel out.
	www.go.ednet.ns.ca /~larry/orbits/gravasst/gravasst.html (933 words)

	MESSENGER: MErcury Surface, Space ENvironment, GEochemistry, and Ranging
		The spacecraft needs a “gravity assist” from the planet, changing its trajectory without using much fuel (again, Voyager’s flybys of the outer planets).
		A gravity assist changes a spacecraft's orbit around the Sun by having it fly by a planet.
		Using the gravity assist of inner planet flybys reduces the amount of fuel needed onboard, making the mission possible with current technology.
	messenger.jhuapl.edu /faq/faq_journey.html (1819 words)

	[No title]
		To: space-tech@cs.cmu.edu Subject: Re: gravity assist As long as this topic has come around again, if the list can hash out a description of gravity well manuevers with a reference or two, suitable for the sci.space FAQ, I'd like to add it.
		In the traditional gravity assist, the goal is the increase the velocity vector of the spacecraft relative to the Sun, and is normally done by passing close to a planet along its equatorial plane.
		Ulysses's gravity assist was the most complicated ever attemped and required very precise navigation.
	www.cs.cmu.edu /afs/cs.cmu.edu/user/mnr/st/std113 (2600 words)

	Scientific American: How does the slingshot effect (or gravity assist) work to change the orbit of a spacecraft? (Site not responding. Last check: 2007-10-09)
		The orbit of a spacecraft is primarily determined by the gravity of a single large central body like the sun, Earth, or, in the case of the Cassini spacecraft, Saturn.
		Of course, all of these changes cause an inverse change in the energy and angular momentum of the moon, but its larger mass results in changes so small that they are undetectable among all the other forces that affect the moon's orbit.
		It is interesting to note that spacecraft undergoing a gravity assist are only copying an effect that occurs on a regular basis in our solar system.
	www.sciam.com /print_version.cfm?articleID=00070374-FE82-1152-BE8283414B7F0000 (672 words)

	USS Clueless - Orbital slingshot
		While I'm pushing with my legs, the vector sum of forces points upward because my legs push harder than gravity, but after my feet leave the ground the vector sum of the forces points downward, because my legs exert no force and gravity predominates.
		Earth applies about a kilonewton of force to me via gravity, and I apply about a kilonewton to the Earth in precisely the opposite direction.
		A body in a lower orbit moves faster and has more kinetic energy, but since it's lower in the gravity well it has less potential energy, and it loses more in potential energy than it gains in kinetic energy.
	denbeste.nu /cd_log_entries/2003/09/Orbitalslingshot.shtml (2309 words)

	UCR Space Physics
		He demonstrated that careful design of the trajectory to a target planet could provide a gravity assist to move from that planet to a second planet.
		Further boosts could provide energy to visit other planets, with gains in speed that would reduce the one-way trip times to each of the planets after the first, and the only energy needed would be that to launch the spacecraft from Earth to the first planet.
		Since Jupiter is the largest planet and, consequently, has the strongest gravity field, Minovitch determined that missions to the outer planets via Jupiter would be possible.
	spacephysics.ucr.edu /index.php?content=v25/v0.html (1409 words)

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