Orbital Mechanics 101, Part II

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# Orbital Mechanics 101, Part II - PowerPoint PPT Presentation

Orbital Mechanics 101, Part II. Understand basic orbital mechanics and how orbits work Understand the different types of orbits used for different purposes Understand basic principles of Interplanetary Travel mechanics. Spheres of Influence.

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Presentation Transcript
Orbital Mechanics 101, Part II
• Understand basic orbital mechanics and how orbits work
• Understand the different types of orbits used for different purposes
• Understand basic principles of Interplanetary Travel mechanics
Spheres of Influence
• A body’s sphere of influence (SOI) is the surrounding volume in which its gravity dominates a spacecraft.
• In theory, SOI is infinite.
• In practice, as a spacecraft gets farther away, another body’s gravity dominates.
• The size of a planet’s SOI depends on:
• The planet’s mass
• How close the planet is to the Sun (Sun’s gravity overpowers that of closer planets)
Types of Orbits
• Low-Earth orbit – an orbit up to about 1,240 miles above the Earth
• Medium-Earth orbit– one with an altitude of about 12,400 miles
• High-Earth orbit – an orbit at an altitude of about 22,300 miles
Maneuvering in Space
• Orbit Changes
• Moving From One Orbit to Another
• Using the Hohmann Transfer
• Rendezvous in Space
• Gravity Assist Velocity
Simple Orbit Changes:Moving from one orbit to another
• Moving from one orbit to another is a complex and orchestrated dance of speed and fuel consumption
• When we maneuver in space, we need to factor fuel into the process.
• Fuel is EVERYTHING in Space

First space rendezvous of two spacecraft (Gemini 6 and 7) in December 1965

Simple Orbit Changes:Moving from one orbit to another
• In 1925 a German engineer, Walter Hohmann, thought of a fuel-efficient way to transfer spacecraft between orbits—the Hohmann Transfer.
• The Hohmann Transfer uses an elliptical transfer orbit tangent to the initial and final orbits.
Simple Orbit Changes:Using the Hohmann Transfer
• A spacecraft changes its energy by increasing or decreasing its velocity — in essence firing rocket engines.
• Adding or subtracting velocity changes the orbit’s energy
Hohmann Transfer (Application to Rendezvous)

First space rendezvous of two spacecraft (Gemini 6 and 7) in December 1965

Interplanetary Travel
• Four bodies are involved:
• Sun
• Departure Planet
• Target Planet
• Spacecraft
• Analyzing the gravitational forces (Remember that Newton guy and his Law of Universal Gravitation) from all three central bodies on the spacecraft would amount to a “four-body” problem. Far to complicated, so….
• Simplify (A process called “Patched Conic”Approximation)
• Break into familiar, manageable pieces.
• Consider as three two-body problems.
Gravity-Assist Trajectories
• Process using a planet’s gravitational field and orbital velocity to “sling shot” a spacecraft, changing its velocity (in magnitude and direction) with respect to the Sun.
Gravity-Assist Trajectories
• As a spacecraft enters a planet’s sphere of influence (SOI), it coasts on a hyperbolic trajectory around the planet.
• Then, the planet pulls it in the direction of the planet’s motion, increasing (or decreasing) its velocity relative to the Sun.
Gravity-Assist Trajectories

Generally, gravity-assisted trajectories consist of two types:

• A gravity assist that changes the magnitude of a spacecraft’s velocity is called orbit pumping.
• Using a planet’s gravity to change the direction of travel is called orbit cranking.
Gravity-Assist Trajectories

Gravity Launch Game