Upload
dangmien
View
221
Download
4
Embed Size (px)
Citation preview
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
Orbital Mechanics 101, Part II
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)
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
Types of Orbits
Maneuvering in SpaceOrbit 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 SpaceFirst space rendezvous of two spacecraft
(Gemini 6 and 7) in December 1965
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:Moving from one orbit to another
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
First space rendezvous of two spacecraft
(Gemini 6 and 7) in December 1965
Hohmann Transfer (Application to Rendezvous)
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.
“Patched Conic” Approximation
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
http://www.sciencenetlinks.com/interactives/gravity.html
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
Orbital Mechanics 101, Part II