# So has 'swing-by' replaced flyby/fly-by? **URL:** \ **Category:** Factual Questions\ **Created:** [February 22, 2007, 5:02pm UTC](https://boards.straightdope.com/t/so-has-swing-by-replaced-flyby-fly-by/393242 "2007-02-22T17:02:24Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Earl\_Snake-Hips\_Tucker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/earl_snake-hips_tucker/32/3269_2.png) [@Earl\_Snake-Hips\_Tucker](https://boards.straightdope.com/u/Earl_Snake-Hips_Tucker)\ **Post date:** [February 22, 2007, 5:02pm UTC](https://boards.straightdope.com/t/so-has-swing-by-replaced-flyby-fly-by/393242/1 "2007-02-22T17:02:24Z")
[Link](http://www.cnn.com/2007/TECH/space/02/22/rosetta.mars.reut/index.html) First I’ve heard the term used. BTW, New Horizons, the Pluto/Kuiper Belt probe, is scheduled to make the Jupiter flyby later this month. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [February 22, 2007, 5:42pm UTC](https://boards.straightdope.com/t/so-has-swing-by-replaced-flyby-fly-by/393242/2 "2007-02-22T17:42:58Z")
Here’s the key: > [@CNN](#): > > To gather momentum while conserving as much rocket fuel as possible, controllers are using the gravitational pull of Earth and Mars to catapult the probe closer to its target. > > One such “gravity assist” maneuver – commonly known as a swing-by – was performed around Earth two years ago. The Mars maneuver is the second and most complicated of the mission, while two more Earth maneuvers are due in 2007 and 2009. I think flyby is just an ordinary pass. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [February 23, 2007, 5:18am UTC](https://boards.straightdope.com/t/so-has-swing-by-replaced-flyby-fly-by/393242/3 "2007-02-23T05:18:55Z")
“Swingby trajectory” or “gravity-assist maneuver” are the standard technical terms for a celestial mechanics maneuver that uses the gravity well of a planet to alter its velocity (either in speed or, more typically, direction). This is done to expand the science mission range of objectives and maximize the use of available impulse. I won’t go so far as to say that the terms “flyby” or “slingshot maneuver” have never been used in technical discourse (and a quick Google search shows them being used by NASA in some of their online public education materials, tsk tsk) but in literature searches going back to the days of Pioneer I haven’t seen it used by the experts. I think this is a case of media people finally getting it right after years of incorrigibly muddling the terms. Stranger ---
**Author:** ![Earl\_Snake-Hips\_Tucker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/earl_snake-hips_tucker/32/3269_2.png) [@Earl\_Snake-Hips\_Tucker](https://boards.straightdope.com/u/Earl_Snake-Hips_Tucker)\ **Post date:** [February 23, 2007, 3:22pm UTC](https://boards.straightdope.com/t/so-has-swing-by-replaced-flyby-fly-by/393242/4 "2007-02-23T15:22:06Z")
Thanks. Shoulda consulted a dictionary first. Merriam-Webster concurs. I guess all swing-bys (1965) are flybys (1953), but a swing-by is specifically the gravity-assisted trajectory maneuver. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [February 23, 2007, 4:35pm UTC](https://boards.straightdope.com/t/so-has-swing-by-replaced-flyby-fly-by/393242/5 "2007-02-23T16:35:17Z")
“Flyby” means observing a target as you fly past it, instead of slowing down and staying at that target. It may also alter your trajectory, but that’s not the main goal. For example, an interplanetary probe may do a flyby of an asteroid because there happens to be one along the way.