AE Review Orbital Mechanics

Orbits are described by a set of parameters called…. orbital elements or Keplerian elements

The Keplerian element set consists of 6 parameters (plus a time stamp) The Keplerian element set consists of 6 parameters (plus a time stamp). Name them. Two of these describe the size and shape of an orbit: Eccentricity (e) Semi-major axis (a) Three of these describe the orientation of the orbit in space: Inclination (i) Right ascension of the ascending node (W) Argument of perigee (w) One of these describes the location of the satellite within the orbit: True anomaly (u)

An orbit with an inclination of 0 degrees is called an equatorial orbit polar orbit

An orbit with an inclination of 90 degrees is called a equatorial orbit polar orbit

A satellite in an equatorial orbit will pass directly over the equator over the entire Earth.

A satellite in polar orbit will pass directly over the equator over the entire Earth

Which two parameters can you determine from a ground trace? Eccentricity (e) Semi-major axis (a) Inclination (i) Right ascension of the ascending node (W) Argument of perigee (w) True anomaly (u) Orbital Period Inclination (i) and Orbital Period

Eccentricity of what value means the orbit is circular? 0 (zero)

What defines the point in an orbit that is farthest from Earth Apogee

What describes the point in an orbit that is closest to Earth? Perigee

When does Apogee Altitude = Perigee Altitude? For a perfectly circular orbit

What parameter does this graphic describe? Inclination

Determining a Satellite’s Orbital Period from its Ground Trace Practice this. Orbital Mechanics Modeling Slide 25

Right Ascension of the Ascending Node (RAAN, W ) Satellites may have identical eccentricities, semi- major axes, and inclinations (e, a, and i) yet may still be oriented differently in space – they can be “rotated” or “twisted” about the Earth in various ways

Argument of Perigee (w) Argument of perigee describes the orientation of the orbit within the orbital plane

True Anomaly (u) True anomaly is 0 degrees at perigee, 180 degrees at apogee

Kepler’s Laws Know them Orbital Mechanics Modeling Slide 31

LEO (Low Earth Orbit) Many Earth-observing satellites Weather and imagery Why is this?

GEO (Geostationary) Achieved by placing the satellite in a special orbit where period exactly equals one day Altitude: roughly 36,000 km (22,200 miles) Inclination is exactly zero degrees This is NOT close enough to get good images Geostationary satellites mainly used for communications or “permanent relay station” in space

Molniya (Moly) allows for long-term communications over their northern land mass.

Other things to review A 3.2.6 Problems