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 InfluenceA 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 massHow 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 AnotherUsing the Hohmann Transfer

Rendezvous in SpaceGravity 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

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 TransferA 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 TrajectoriesProcess 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 TrajectoriesAs 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 TrajectoriesGravity 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