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Porkchop plot

Chart used to plan spacecraft launches

Wikipedia contributorsAdapted for Fathomly · View authors
1 min read
Source updated April 18, 2024
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In orbital mechanics, a porkchop plot (also pork-chop plot) is a chart that shows level curves of equal characteristic energy (C3) against combinations of launch date and arrival date for a particular interplanetary flight. The chart shows the characteristic energy ranges in zones around the local minima, which resembles the shape of a porkchop slice.

By examining the results of the porkchop plot, engineers can determine when a launch opportunity exists (a 'launch window') that is compatible with the capabilities of a particular spacecraft. A given contour, called a porkchop curve, represents constant C3, and the center of the porkchop the optimal minimum C3. The orbital elements of the solution, where the fixed values are the departure date, the arrival date, and the length of the flight, were first solved mathematically in 1761 by Johann Heinrich Lambert, and the equation is generally known as Lambert's problem (or theorem).

01Math

The general form of characteristic energy can be computed as:

C_{3}=v_{\infty }^{2}\,\!

where {\textstyle v_{\infty }\, is the orbital velocity when the orbital distance tends to infinity. Note that, since the kinetic energy is {\textstyle {\frac {1}{2}}mv^{2}, C3 is in fact equal to twice the magnitude of the specific orbital energy, {\textstyle \epsilon, of the escaping object.

02Use

For the Voyager program, engineers at JPL plotted around 10,000 potential trajectories using porkchop plots, from which they selected around 100 that were optimal for the mission objectives. The plots allowed them to reduce or eliminate planetary encounters taking place over the Thanksgiving or Christmas holidays, and to plan the completion of the mission's primary goals before the end of the fiscal year 1981.

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This article is adapted from the Wikipedia article “Porkchop plot”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.

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