Hohmann Tansfer Trajectory

Hohmann Transfer Ascent

In Hohmann transfer orbit  , the satellite and the last stage of rocket first attains a low altitude circular parking orbit,just outside the densest part of atmosphere, usually this orbit is about 200 km or more, In most launches this altitude is taken to be 185km , shortly after parking orbit injection ,the vehicle is injected into an elliptic transfer trajectory , at perijee , this transfer ellipse is tangential to the parking orbit and at apogee tangential to the required satellite orbit. This transfer orbit is proposed by W.Hohmann , therefore is called "Hohmann transfer trajectory"

Direct Ascent Trajectory

Direct Ascent

In Direct Ascent the trajectory selected such that destination point lies in the required orbit,  the satellite which in most cases is attached to the final rocket stage, approaches this destination altitude , the final stage stage motor is ignited and the satellite is accelerated to the required orbital velocity.In some cases the rocket motor required for this acceleration is not the motor of last stage, but is an integral part of satellite itself.

Ascent Trajectories

Satellites are launched from the Earth's surface by means of multi-stage rockets.After ignition of the first stage rocket Engines,these Launch vehicles first ascent vertically, A few seconds after lift-off ,the rocket is tilted and it flies a curved trajectory until the satellite reaches the predetermined position called ascend trajectory.
since its a vast topic, we discuss only the types of ascent trajectories here.

Two basic types of ascent trajectories can be distinguished for satellite launch vehicles,
1.Direct Ascent ,
2.Hohmann Transfer Ascent.


1.Direct Ascent ,

In Direct Ascent the trajectory selected such that destination point lies in the required orbit,  the satellite which in most cases is attached to the final rocket stage, approaches this destination altitude , the final stage stage motor is ignited and the satellite is accelerated to the required orbital velocity.In some cases the rocket motor required for this acceleration is not the motor of last stage, but is an integral part of satellite itself.

2.Hohmann Transfer Ascent.


In Hohmann transfer orbit  , the satellite and the last stage of rocket first attains a low altitude circular parking orbit,just outside the densest part of atmosphere, usually this orbit is about 200 km or more, In most launches this altitude is taken to be 185km , shortly after parking orbit injection ,the vehicle is injected into an elliptic transfer trajectory , at perijee , this transfer ellipse is tangential to the parking orbit and at apogee tangential to the required satellite orbit. This transfer orbit is proposed by W.Hohmann , therefore is called "Hohmann transfer trajectory"

Rocket Principle of Giant Squid in Deep seas

Certain creatures found in nature employing this rocketry principle of ejecting mass stored in their bodies to create movement, best example shall be a Giant Squid in deep seas.

The Giant Squid is a large creature about 10 to 14 m long and is found in the deep oceans.A few have been caught off the coast or have been washed ashore the New Zealand coast. 

The Giant squid moves in the deep seas by taking the water in by expanding its antle. It holds the water and pressurizes it to about 40 kpa by contracting its mantle.The pressurized water and any other matter that it has gulped, such as,fish,eggs, etc., is squeezed out through a opening ,known as the funnel that can rotate in any direction.The gradual impulse from the squirting out of the water and waste pushes it by as much as 50 m for a single squirt.It is estimated to achieve a velocity of about 7 m/s in a single push of the water and waste.A schematic diag

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.

Pseudo Force

Its a force that acts on all masses in a non inertial frame of reference, or Its a Fictitious force in a non-inertial frame of reference to correctly describe the motion of the body in the non-inertial frame of reference.
Example: passenger in any moving vehicle, The force given to the vehicle forces the objects or person inside the vehicle to move back until the interior gets balanced with the movement.

In a rotational frame of reference ,The pseudo force is a centrifugal force.

Example: when you travel faster in bike round and round around a circular place, their is a force which tries to pull you outwards.and also their is a force which balances the friction between the bike wheel and road.