Orbit and Flight Mechanics Flashcards
What is the First Point of Aries?
The reference point used for celestial navigation, specifies the direction of the x-axis in both the equatorial and ecliptic coordinate systemes
Where is the First Point of Aries?
Point at which the sun crosses the celestial equator during the vernal equinox, meaning if a line is drawn from the center of the Earth to the sun, the First Point of Aries is exactly behind the sun at the vernal Equinox (Mar 21).
What is the ecliptic coordinate system?
XYZ, where X is in direction of the First Point of Aries at Vernal Equinox, Y in the direction of where the Earth is at Winter Solstice (Dec 21), and Z is perpendicular to both, with the Sun at point 0,0,0.
What is the Equatorial Coordinate System?
IJK, where the I is in direction of the First point of Aries, K in direction of the Celestial North Pole, and J perpendicular to both, and follows the equator. Positions for objects in the sky are defined with “right ascension” and “declination” angles (α, δ).
What is the Perifocal Coordinate System?
Coordinate system used to describe the motion of an object in motion around another object. PQW, where P and Q point to the Orbit Plane, with P pointing to the Periapsis (closest point of the orbit to the central body).
What is the difference between the two Topocentric Coordinate systems?
RSW: R and S are on the orbit plane, R being in direction of the Radius vector to the object.
NTW: N and T are on the Orbit Plane, T being in the direction of the “in flight” vector, or the velocity vector of the object.
What is the difference between a Solar and a Sidereal Day?
Solar day: Time it takes for the sun to be in the exact same position as the day before (to the highest point in the sky).
Sidereal day: Time it takes for Earth to rotate 365 degrees regardless of the position of the Sun.
A sidereal day is 23 hours 56 minutes and 4.09 seconds
What is a Julian Date?
Days elapsed since the start of the Julian Period ( 01.01 of the year 4713 BCE at noon UT).
