What is it about?

You have a spacecraft in a high circular orbit and want to escape with the fastest speed possible for a given amount of rocket fuel. Should you use all the fuel at once in a single impulse? Hermann Oberth (in 1929), and Theodore Edelbaum (in 1959) came up with strategies that use two or three separate impulses that are superior to a single-impulse direct escape. This is due to the Oberth Effect, whereby a small impulse close to the central body can result in a large change in spacecraft energy, without violating conservation laws. We examine the final speeds and travel times to distant destinations for the three strategies, and weigh their pros and cons.

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Why is it important?

Escaping at high speed from a circular orbit is relevant to interplanetary missions, and even proposed interstellar missions or chasing after interstellar comets on their way out of the solar system. In time reverse, the maneuvers we describe allow for efficient arrival and capture into a circular orbit.

Perspectives

Even the simple case of a rocket executing impulsive maneuvers around a single central body (planet, asteroid, or Sun) can produce a rich set of connected orbital motions. Pioneers of astrodynamics worked out these orbital transfers - and sci fi author Robert Heinlein described them in his novel The Rolling Stones - all before the dawn of the Space Age in 1957. Currently, interplanetary missions use the benefit of gravity assists to boost themselves to the outer solar system. But in the near future as humanity expands outwards to Mars, the asteroids, and beyond, the Oberth and Edelbaum maneuvers may become staples of interplanetary travel, used either for escape or for capture relative to a gravitating body.

Dr. Philip Blanco
Grossmont College

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This page is a summary of: High-speed escape from a circular orbit, American Journal of Physics, January 2021, American Association of Physics Teachers (AAPT), DOI: 10.1119/10.0001956.
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