MIT Massachusetts Institute of Technology

Gravity Assist or Stealing a Planet's Angular Momentum and Getting Away With It

Dr. Bassem Sabra
Department of Physics & Astronomy
Faculty of Natural & Applied Sciences
Notre Dame University-Louaize

This video lesson will present Gravity Assist, or what is wrongly referred to as the gravitational slingshot. “Gravity assist” is a maneuver performed by interplanetary spacecraft to travel farther on less fuel. It is a classic exercise in Newtonian mechanics. The basics of this lesson are covered in high school physics curricula: conservation of linear momentum (to explain rocket propulsion), angular momentum, Newton's law of universal gravitation, and energy conservation. These concepts will be combined to explain orbits in the solar system. Gravity assist turns out to be carefully choreographed jumps between orbits. Only one topic reviewed in this lesson is not usually covered in high school curricula: that is distances in the solar system. A quick introduction to distances in the solar system will be enough to put the problem of fuel constraints in interplanetary travel into perspective and also to later highlight the importance of gravity assists in solving this fundamental problem. In short, “Gravity Assist” will integrate many seemingly disparate parts of high school Newtonian mechanics to present and explain a real application. Classroom activities will be group problem-solving, masses attached to strings and rotated over head, marble collisions, baseball/tennis/table tennis/badminton. Detailed directions for each of the classroom video breaks can be found in the Teachers Guide document, which can be found on this page under the menu item "For Teachers".

Bassem Sabra is an astrophysicist at Notre Dame University - Louaize where he teaches physics and astronomy courses at the graduate and undergraduate levels and pursues research on active galactic nuclei. He uses data from orbiting telescopes such as the Hubble Space Telescope (HST), the Chandra X-ray Telescope, and XMM-Newton to study the gases circulating around the supermassive blackholes in the cores or nuclei of these active galaxies. Professor Sabra received his PhD from Ohio University, USA

A collection of superb applets (I used Collisions Lab, My Solar System, and Gravity and Orbits)

Simulations of the gravity assist for the New Horizons spacecraft, and also information about the MESSENGER mission to Venus.

A gravity assist primer by NASA.

Website of the Cassini-Huygens mission. Look under “Mission Overview” for more information about the gravity assists done by this spacecraft and more information about the location and speed of the spacecraft. Please look at the Cassini Mission Overview Supplement in the “Quick Facts” page under “Mission Overview.” This file contains info about the Cassini orbiter, launch vehicle, and speeds before and after the gravity assists.

Website of the New Horizons mission to Pluto and the Kuiper Belt. I got the rockets videos and simulations from there.

The gravity assist webpage on the website of the European Space Agency (ESA).

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This Lesson is in the following clusters: Astronomy