Rocket propulsion basics

Astronomical Unit - It is a measure of distance equals the mean distance between earth and sun (150x10^6 km)

Escape Velocity - Velocity required for a body to escape the attractive force of the planet/star. (for more details click the highlighted heading)

Frame of reference : Reference based on which the position of the body is described.

Force : Rate of change in momentum

Free fall : Body moving freely under the influence of the gravitational field , An observer in a freely falling body is in a state of weightlessness,It can be either Orbital or Sub orbital flight

Geo-Synchronous Orbit : Orbit having an angular velocity equal to the angular velocity of the planet around which orbit takes place.(for more details click the highlighted heading)

Geo-Stationary Orbit (Clarke orbit) : An orbit in the equatorial plane of the reference planet or celestial body such that the orbiting body appears to be fixed point for any observer on the reference planet or celestial body. (for more details click the highlighted heading)

Gravitational constant G : The constant in the universal law of gravitational force giving the attractive force between two masses separated by a given distance.when the mass is expressed in 'kg' and the distance in 'm' , the gravitational constant is 6.670 x 10^-11 Nm2/Kg2

Gravitational field : Force of attraction on a mass 'm' kg in a gravitational field 'g' is m x g N , Unit of gravitational field is m/s2

Impulse : change of Momentum.

Inclination : Angle between orbital plane and equatorial plane of the planet.

Inertial frame of Reference : A frame of reference that is absolutely stationary or moves at constant velocity

Kepler's Laws : laws describing the motion of planets in the solar system.
1.Law of Ellipses
2.Law of equal areas
3.Law of harmonies
(for more details click the highlighted heading)

Molniya Orbit : Highly Elliptic orbit about the earth with large eccentricity and an apogee of about 400,000 km in the northern hemisphere.

Momentum : Product of mass of a body and its velocity

Orbit : Trajectory or path of motion in space ; path in which a planet ,satellite or spaceship moves

Orbital velocity : Velocity along the path of the orbit

Polar orbit : Orbit having an inclination of 90 degrees

Pseudo-force : Fictitious force in a non-inertial frame of reference of correctly describe the motion of the body in the non-inertial frame of reference .In a rotational frame of reference ,the pseudo force is a centrifugal force

Sun Synchronous orbit : A polar orbit in which angle between the line joining sun with Earth and the orbital plane remains constant

Orbital and Sub Orbital Flight

A body in orbit is in a state of free fall i.e., the body freely moves under the influence of Gravitational field,A body when provided with an orbital velocity (Vo) tends to move along a straight line in the direction of the velocity, however ,the attractive force from the gravitational field of the planet tends to pull it towards the center. The body therefore falls towards of the planet. As the body falls,the orbit velocity Vo pushes it further away from the planet and the body always misses falling on the planet.As long as the velocity provided to a body is less than the escape velocity of gravitational attraction of the given planet will cause the body to fall towards it. when the body goes into orbit , the motion corresponds to a state of free fall.If the velocity provided is less than the orbital velocity , the body falls on the planet corresponding to a sub-orbital flight.
The motion of different planets in the solar system about the sun is also in a state of free fall.